pacing manual

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Lancashire & South CumbriaCardiac Network

PACING MANUAL

Cardiac Physiologist Training Manual

D:\PACING MANUAL.doc04/01/2005 Created by ButlerL


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THE PACEMAKER SYSTEM AN OVERVIEW

Normal Conduction

Abnormal Conduction and the indications for pacing

Pacemakers and the modes of pacing

Ventricular pacing systems

Atrial Pacing systems

Dual chamber Pacing systems

Implantation techniques and measurements

End of Life Details



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Normal Conduction

AV ring

SA Node

AV Node

Left Bundle

Branch

Right Bundle Branch

The impulse that is responsible for depolarisation of the heart is initiated bythe Sino-Atrial Node (SA Node), which is positioned in the top corner of theright atrium, close to the SVC and atrial myocardial junction.The impulse travels across the atria to form the P wave of the ECG. It isthought that distinct muscle fibres assist in the spread of atrial depolarisationacross the atria.The impulse reaches the Atrio-Ventricular Node (AV Node) at the junction of

the atria and ventricles within the atrial/ventricular septum. The onlypassageway for the impulse in the normal heart is through the AV Node andBundle of His. This is due to the presence of the electrically isolated AV ring.

At the AV node there is a delay, which allows time for ventricular filling andprotects the ventricles from fast conducting atrial arrhythmias.The impulse then travels down the left and right bundle branches. Furtherdivisions eventually form the purkinje fibres. These form an intricate networkof specialised conducting cells which spread throughout the myocardium. Theimpulse initiates ventricular depolarisation (QRS complex). Repolarisation ofthe ventricles then takes place (T wave).



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Abnormal Conduction and Indications for pacing

Abnormal conduction overview

The SA Node has the ability to discharge an impulse with no externalstimulation. It usually does so at a rate of approximately 80 beats per minute(bpm), unless acted upon by the sympathetic / parasympathetic nervoussystem or chemical substances e.g. adrenalin, nor adrenalin.If the SA node fails, the AV node may be able to take over this function andthe intrinsic discharge rate is approximately 60 bpm. The Bundle of His has anintrinsic discharge rate of 50 bpm and bundle branches of 40 bpm. Thepurkinje fibres will discharge at 20 bpm.If there are any abnormalities of the SA node or further down the conductingsystem the rate may fall and pacing becomes necessary.

Indications for pacing

Group 1

Implantation is considered acceptable and necessary, provided that theconditions are chronic or recurrent and not due to a transient cause.

1. Sinus Node Dysfunction

2. Congenital Complete Heart Block

3. Acquired Complete Heart Block4. Symptomatic Mobitz type II, second degree heart block

5. Symptomatic Mobitz type I, second degree heart block

6. Symptomatic sinus bradycardia



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Group 2

Implantation is considered acceptable and necessary, provided the medicalhistory and prognosis of the patient can be documented and there is evidencethat pacemaker implantation will assist in the overall management of the

patient

1. Bifascicular/trifascicular block accompanied by syncope

2. Asymptomatic Mobitz type I, second degree heart block

3. Symptomatic sinus bradycardia that is a consequence of long-termdrug treatment for which there is no acceptable alternative.

4. Patients with recurrent and refractory ventricular tachycardia

5. Atrial/ventricular arrhythmias

6. Heart failure

Group 3

Conditions listed below should be an indication in support to those given ingroups 1 and 2.

1. Syncope of undetermined cause

2. Sinus bradycardia without significant symptoms

3. Sino-Atrial block without significant symptoms4. 1 st degree AV block, atrial fibrillation or other causes of transient

pauses

5. Bradycardia during sleep

6. Right Bundle Branch Block with LAD



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Pacemakers And Modes Of Pacing

A pacemaker system consists of a pulse generator and lead. The pulsegenerator has contained in its housing a power source and electronic circuitrywhich enables proper pacemaker function. The lead is made up of aconductor covered by insulation. At the proximal end is a terminal pin whichfits into the pulse generator snugly and makes the connection between leadand generator. At the distal end is the electrode which makes contact with theheart muscle. In unipolar systems, the pulse generator is the positive anodeand the electrode tip in the heart is the negative cathode.

Pacing The USCI code

The USCI code is the standard code for labelling the mode of pacing.

1ST letter chamber(s) paced

2nd letter chamber(s) sensed

3 rd letter Mode of action

Either the atria or ventricles can be paced and hence either pure atrial, pureventricular or both atrial and ventricular pacing can be employed. Thereforemodes of AAI, VVI, VVT, VAT, DDI, DDD and others may be chosen. Themode of action is either inhibited (I), where the pacemaker will suppress itsoutput if an intrinsic beat is seen or triggered (T), where the output of a

pacemaker is triggered to a sensed event.The triggered mode is used in normal DDD function or to prevent undesirableinhibition e.g. oversensing of skeletal muscle activity.



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Ventricular Pacing Systems

VOO Ventricular Asynchronous

In this mode the pacemaker stimulates at a fixed rate and voltage. There is nosensing and hence the pacemaker will continue to pace irrespective of theunderlying rhythm. The pacemaker will capture the heart if the impulsedelivered falls outside the refractory period of the intrinsic beat.This mode can also be seen with application of magnet on most pacemakermodels.

VVI Ventricular Inhibited

This is by far the most common of ventricular only pacing modes.Spontaneous impulses are sensed and the subsequent output is stopped. Ifno spontaneous impulses occur the pacemaker will pace at the regular rate atwhich the pacemaker is set.



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VVT- Ventricular Triggered

In this mode when a spontaneous ventricular intrinsic beat is seen the outputof the pacemaker is delivered. It must be noted that the beat will not be fullycaptured by the pacemaker as the output delivered will fall in the refractoryperiod of the intrinsic beat and make no contribution to the depolarisation ofthe heart (this is called a pseudo-fusion beat).



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Atrial Pacing Systems

AOO Atrial Asynchronous

This mode is rarely used. As in VOO, the pacemaker stimulates at a fixed rateirrespective of the underlying rhythm.This mode can also be seen on application of a magnet on most pacemakermodels.

AAI Atrial Inhibited

This mode is the same as the VVI mode except the lead is positioned next toatrial myocardium and therefore the pacemaker will inhibit when an intrinsicatrial beat is seen.



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AAT Atrial Triggered

In this mode when a spontaneous atrial intrinsic beat is seen the output of thepacemaker is delivered. It must be noted that the beat will not be fullycaptured by the pacemaker as the output delivered will fall in the refractoryperiod of the intrinsic beat and make no contribution to the depolarisation ofthe heart (this is called a pseudo-fusion beat).



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Dual Chamber Pacing Systems

DOO AV Synchronous

The D in the USCI code stands for dual, meaning atria and ventricle. In thisinstance, both chambers are paced at a fixed rate with no sensing,irrespective of the underlying rhythm. This mode is rarely used and can beseen with application of a magnet on most DDD pacemaker models.

Atrial Synchronous (VAT)

This mode occurs when the atrial intrinsic rate is sensed and the ventricularchamber is paced. The pacemaker output is triggered to a sensed event, thatevent being a sinus P wave. In this way AV synchrony is maintained and theresponse will be physiological because it will follow the intrinsic rate of the

sinus node.



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Fully Automatic

The pacemaker has the ability to:

1. Sense and pace the atrium2. Sense and pace the ventricle3. Inhibit atrial and ventricular intrinsic beats4. Trigger a paced event to a sensed event (VAT)

In this mode there will always be AV Synchrony, whether sinus, Atrial pacing,VAT pacing or AV pacing occurs.

With sinus and VAT pacing there will also be a physiological response toexercise due to the increase in sinus rate of the patient.

Chronotropic competence the sinus rate will increase in response toexercise, emotion etc.

Chronotropic incompetence the sinus rate will not increase in response toexercise, emotion etc.

For the dual chamber DDD mode to be effective chronotropic competencemust be present.



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Implantation Techniques and Measurements

Implantation Techniques

The routine placement of pacemaker leads involves placing the atrial lead(electrode) in the right atrial appendage and the ventricular lead in the rightventricular apex.

The route used is the subclavian or cephalic vein. Either the stab technique(inserting a needle until the subclavian vein is found) or a cut down technique(separating superficial tissues until cephalic vein is found) is employed.

A stylet is introduced into the lead to give stiffness to the electrode. The leadis then passed down the vein into the desired position.

The atrial appendage is in a posterior and superior position and the atrial Jshaped lead is hooked up into this region.

The right ventricle has undulations or trabeculae, its surface being roughrather than a smooth wall lining. The tip of the electrode has small plasticattachments called fins or tines. Their presence assists in the electrodeattaching to the trabeculae, aiding its fixture to the endocardial wall.Fibrous tissue will eventually integrate itself into and around the tip of theelectrode, providing firm attachment of the lead.

Measurements can be carried out to confirm a good position of the lead, afterwhich the electrode can be firmly sutured into the vein to prevent movementof the electrode. The pulse generator can then be attached to the lead. Theterminal pin of the lead is pushed into the connector head of the pulsegenerator and to ensure electrical contact the connector head screw is

tightened. A pocket is made in the pectoral muscle sheath to allow placement of thepulse generator. The wound can then be closed and the area cleaned.

Measurements Taken At Implant.



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Measurements are taken after lead positioning. This confirms an adequateposition and checks the stability of the lead.

1. Voltage ThresholdThe least amount of energy required to depolarise themyocardium.

2. Current flow3. Lead impedance4. Amplitude of intrinsic P/R wave

Asking the patient to cough, sniff and breathe deeply whilst pacing andscreening the heart tests the stability of the lead.

If all these measurements are satisfactory it indicates good placement of thelead and good contact between electrode tip and myocardial interface.

End Of Life Details

The end of life or recommended replacement time of a pacemaker isestablished by numerous methods. These include:

1. Magnet test2. Battery status3. Battery voltage measurement4. Battery impedance measurement

Each model and manufacturer type of pacemaker has different EOL or RRT

characteristics. These can be established from the pacemaker manuals.

LJR.TPS.001.01



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ECG INTERPRETATION

Normal methods of ECG interpretation cannot be applied to the ECGrecorded during pacing.

AAI PACING

The impulse is seen on the ECG as a spike (pacing artefact) followed by atrialdepolarisation a paced p wave.

The paced P will be abnormal in shape to that of a sinus p wave due to theatria being depolarised from a different stimulus.

Paced PacedP wave P wave

With AAI pacing it is important to have an intact conducting system from the AV node onwards.

In this way AAI pacing gives synchronisation between atria and ventricles AV synchrony.

Intermittent SA arrest AAI pacing.

Chronic SA arrest AAIR pacing.

SA arrest + sinus bradycardia AAIR pacing.



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I.e. if chronotropic response is missing from the SA node then rate responsepacing is needed to give an increase in rate to exercise.

AAI SENSING

AAI pacing allows inhibition (mode of action) of any sensed intrinsic beatsarising from the atria.

Sensed intrinsicP wave

After sensing an intrinsic P wave the pacemaker resets and waits the

programmed interval before emitting a further stimulus.



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VVI PACING

The impulse is seen on the ECG as a spike (pacing artefact) followed byventricular depolarisation a paced QRS complex.

The paced QRS is (1) abnormal in shape (bizarre)(2) broad(3) abnormal T wave

Paced Paced PacedQRS QRS QRS

There is no synchronisation between the atria and ventricles and the sinus pwaves show no correlation to the QRS on the ECG.

QRS QRS QRS

P P P P P P



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VVI SENSING

VVI pacing mode allows inhibition of any sensed intrinsic beats.Mode of action inhibited

After sensing an intrinsic QRS the pacemaker resets and waits theprogrammed interval before emitting a further stimulus.



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DDD

Chambers paced Dual (ATRIA AND VENTRICLES)

Chambers sensed Dual (ATRIA AND VENTRICLES)

Mode of action Dual (INHIBITED AND TRIGGERED)

Sensed P wave - INHIBIT

Sensed QRS complex - INHIBIT

Paced P wave

Sensed QRS complex - INHIBIT

Sensed P wave - INHIBIT

Paced QRS complex - TRIGGERED

Paced P wave

Paced QRS complex

(AV sequential pacing)



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FAILURE TO CAPTURE

Not enough energy is being delivered to cause depolarisation of themyocardium (all or nothing phenomena).

E.g. VVI Failure to capture

Intermittent failure to capture

FAILURE TO SENSE

No intrinsic cardiac activity is seen by the pacemaker and therefore continuesto output at the programmed interval.

E.g. VVI failure to sense (UNDERSENSING)

LJR..PI001.



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TECHNICAL MEASUREMENTS AT IMPLANT

ECG MONITORING

The lead usually chosen for pacemaker implants is limb lead II, however if alllimb leads are available, as many as possible should be used to monitor thepatient during the procedure. This holds the advantage of being able to seeclear pacing spikes, followed by depolarization of either atria or ventricularmyocardium. Particularly useful when looking for atrial capture.

Ventricular Axis

If the ventricular pacing electrode is positioned in the right ventricular apex, aleft Bundle Branch Block pattern is seen with a Left Axis Deviation or Superior

Axis. This is because depolarization begins at the site of activation, the apexof the Right Ventricle. In LBBB, the spread of activation is first seen in the RVand then spreads to the LV.

If the ventricular pacing electrode is positioned at the Right VentricularOutflow Tract (RVOT), a LBBB pattern is seen but this time with an inferioraxis or Right Axis Deviation.

If a right bundle branch pattern is seen, this may imply electrode position inthe LV, possibly through an existing VSD or even through a septal rupture.

Atrial Axis

The P wave Axis in normal sinus rhythm is the same as the QRS axis(between -30 & +90). Right Atrial Appendage (RAA) pacing will also give anormal P wave axis. Septal pacing (usually posteroseptal) will give a superioraxis and would lead to inverted P waves in the inferior leads.



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EQUIPMENT REQUIREMENTS

(A) NEW SYSTEM

A Pacing Systems Analyser (PSA) is used to provide pacing at varyingoutputs and pulse durations for the purpose of taking electrode/pacing leadmeasurements.

Lead connectors connect from the PSA to the pacing electrode(s)positioned in the heart.The positive (red) (anode) lead is the indifferent electrode and in a unipolarsystem can be electrically connected to the body tissues by a spatula/spadepositioned in the pacemaker pocket.The negative (black) (cathode) is the active lead and is connected to the leadtip via the proximal end of the electrode.In a bipolar system, the Positive (red) lead is connected to the Ring electroderepresented at the proximal end of the electrode. The negative (black) lead isconnected to the proximal end of the electrode itself and like the unipolarsystem takes measurements from the tip of the lead.

Introducers, pacing electrodes and pacemaker.Ensure compatibility with introducer and lead diameter (French) size.Ensure compatibility with pacing electrode and pacemaker connection size.



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(B) PACEMAKER REPLACEMENT

Underlying rhythm should be assessed prior to the procedure and temporarypacing cover provided if necessary.

Once the pacemaker is exposed a screwdriver is needed to release theelectrode from the pacemaker.

The lead is checked in the normal manner. For leads in situ long term, higherthresholds (up to 2.0v) may be accepted provided it is consistent with recentpacemaker checks. The new pacemaker can then be connected in the normalmanner.

If the new pacemaker has an incompatible connector size to the lead in situthen the old lead may need to be adapted. Pacemaker lead adaption shouldbe avoided by the correct choice of pacemaker size. The risks of adapting apacemaker lead include electrode damage and loose connection.

Method of Adaption

The electrode is cut using wire cutters and the insulation cut back slightly toexpose the wire.The bare wire is placed into the adaptor and according to design is crimped orscrewed into place using crimpers or small screwdriver.The insulation of the adaptor is moved over the bare wire and measurementsof the lead rechecked.Particular attention should be paid to check lead impedances and for pectoralmuscle stimulation that would indicate a gap in insulation between lead andadaptor.



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ELECTRODE MEASUREMENTS

Once the electrode has been positioned various electricalmeasurements are taken to check electrode placement and stability.

These measurements are:

(a) Stimulation voltage threshold(b) Current(c) Impedance(d) Sensing Threshold, P/R wave amplitude(e) Slew Rate(f) Intracardiac ECG

PULSE DURATION the actual duration (time) of the pacemaker stimulusmeasured in milliseconds (ms). The pulse duration is usually set to 0.5ms andthe stimulation, voltage threshold is measured at this setting.

Voltage(V)

PulseDuration

(ms)



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STIMULATION THRESHOLD

This is the minimum output required to stimulate the heart. The pulseduration of the pacemaker stimulus should be set to 0.5ms. The voltageoutput is decreased until it fails to capture the heart. i.e. fails to provideenough energy to cause contraction of the atria or ventricles. The stimulationthreshold is 0.1V above the point at which loss of capture is seen.

The output/stimulation threshold is measured in volts (V).

LOC LOC

LOC loss of capture

The stimulation threshold should be below 1 volt to ensure satisfactoryplacement of the electrode.

CURRENT

The delivered current at voltage threshold is then measured. This figure isderived from the threshold voltage and the measured impedance (V=IxR). Thevoltage and current have an exponential relationship.The current is measured in milliamps (ma).



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IMPEDANCE

The impedance is a measure of resistance to current flow down the electrode.It is a result of the sum of the electrical resistance of the wire, the electrodetip/myocardial interface and the impedance of the return circuit to thepacemaker (the body and blood pool). The impedance should be measured atstimulation threshold and is used to check for lead or insulation break.

A normal impedance is usually between 400 1000 Ohms ( )

A low impedance < 400 Ohms may indicate current leakage caused by abreak in insulation.

A high impedance > 1000 Ohms may indicate a resistance to current flow andmay be due to a fracture of the electrode or poor electrode/pacemakerconnection.

Stability of this measurement is important and the lead impedances todayappear to be higher than previous. If all other measurements are satisfactoryborderline impedance measurements can be accepted. Available are highimpedance electrodes which will produce high impedance measurements upto 2500 Ohms. High Impedance electrodes aim to reduce current flow andlead to increased longevity.

Impedance is measured in Ohms ( ).

SENSING THRESHOLD / INTRINSIC AMPLITUDE

The amplitude of the P or R wave must be measured to ensure the

pacemaker will adequately sense the intrinsic rhythm if present from both theatrial and ventricular chambers independently.

The P wave amplitude should be > 3mvThe R wave amplitude should be > 5mv

Any measured P/R waves smaller than these values may lead toundersensing.

Intrinsic amplitudes are measured in Millivolts (mv)



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SLEW RATE

This is the measure of the slope of the upstroke (dV/dt) of the sensed P/Rwaves. A large slew rate helps the pacemaker to correctly identify sensedevents and so appropriately ignore other sensed events (T waves and muscleactivity).

The slew rate should be above the following;

P wave Acute 0.6 to 1.7 v/sChronic 0.5 to 1.5 v/s

R wave Acute 0.8 to 2.0 v/sChronic 0.6 to 1.5 v/s

Slew rates below these values can lead to far field sensing or failure to senseintrinsic activity. As the lead matures the slew rate will decrease byapproximately 40 % and therefore the intrinsic deflection may not be enoughto trigger the pacemaker once the lead enters the chronic phase.

The slew rate is measured in Volts/second (V/s).



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INTRACARDIAC ECG

The intracardiac ECG recorded from the tip of the implanted electrode (knownas the ID intrinsic deflection) can be used for the following:

(a) To check for capture(b) To establish large amplitude of intrinsic waves (correlate to

measured P and R waves)(c) To check current of injury(d) To check for the presence or absence of retrograde P waves.

This can exclude the likely event of PMT in a DDD system(e) The intrinsic deflection in the acute lead is usually

(i) bi-phasic (58 %)(ii) monophasic positive (30 %)(iii) monophasic negative (12 %)

ACUTE VENTRICULAR EGM

Current of injury is seen asST segment elevation. Theintrinsic deflection (largerapid bi-phasic signal)should coincide with thesurface QRS.

CHRONIC VENTRICULAR EGM

The Current of injuryshould decrease leaving aniso-electric ST segment inthe chronic lead.

The atrial EGM is quite similar to but smaller than the ventricular Electrogram.Ideal ventricular electrode EGM measurements include:

(i) R wave of at least 4mv(ii) Slew rate of at least 1.5mv/s(iii) Current of injury of at least 2mv



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FIXATION TESTS

Once the measurements are completed, it is advisable to check a stable leadposition. This is particularly important with passive fixation leads, although

displacement should not be ruled out with active fixation leads and therefore,fixation tests should be performed with these leads also.The output of the PSA is set to twice threshold or a 1volt minimum value.Pacing with capture should be observed. The patient is asked to perform anyor all of the following:

(i) deep breathing(ii) coughing(iii) sniffing

X-Ray Screening is advised to observe for excessive lead movement andpacing and capture observed throughout. If excessive movement or failure tocapture is seen, the lead should be repositioned.

DIAPHRAGMATIC TWITCHING

A final stimulation test should be performed to check that diaphragmaticstimulation does not occur. This may be caused by inappropriate stimulationof the phrenic nerve that innervates the diaphragm or direct stimulationthrough a thin walled right ventricle or RV puncture.

A high output establishing pacing and capture should be performed.Observation of the diaphragm with X-Ray screening and palpation of thediaphragm area performed.If twitching does occur then the electrode should be repositioned.If the threshold is low, then reprogramming the pacemaker to a slightly loweroutput may be considered and eradicate the twitching. However, reducing theoutput is not an ideal solution initially as the stimulation threshold may riseover the first twelve weeks, possibly leading to failure to capture.

LJB.MAI.001.02



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PACING MODES

1ST LETTER CHAMBER PACED

2ND LETTER CHAMBER SENSED

3RD LETTER MODE OF ACTION

4TH LETTER ( R ) RATE MODULATION

5TH LETTER ANTITACHYCARDIA CAPABILITIES(PACING, SHOCKING, DUAL)



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AAI(R)

Chamber paced atrium

Chamber sensed atrium

Mode of action - inhibited

AAI

Indications

Sinus node dysfunction, with an intact AV node AAI pacing gives a physiological response i.e. AV synchrony

Contra-indications

Presence of AV blockPresence of atrial tachyarrhythmias (AF/AFL)

AAIR

Indications

Are the same as for AAI but with the absence of chronotropic response

Contra-indications

Are the same as for AAI or patients who are unable to tolerate high rates



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VVI(R)

Chamber paced ventricle

Chamber sensed ventricle

Mode of action inhibited

VVI

Indications

Sinus node dysfunctions AV blockIdeally VVI mode should be used for AV block with the presence of chronicatrial tachyarrhythmias

Contra-indications

In the presence of pacemaker syndrome

VVIR Indications

Are the same as for VVI but where there is an indication for rate response

Contra-indications

Are the same as for VVI or patients who are unable to tolerate high ratesDDD(R)



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Chamber paced Dualatrium and ventricle

Chamber sensed Dualatrium and ventricle

Mode of action DualInhibited and Triggered

DDD

Indications

AV block in the presence of normal sinus node function

Contra-indications

Chronic / intermittent atrial tachyarrhythmias (see mode switch)

DDDR

Indications

AV block in the presence of sinus node dysfunction

Contra indications

Are the same as for DDD or patients who are unable to tolerate high rates



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SSIR

S single

Either AAIR or VVIR

Chamber paced atrium or ventricle

Chamber sensed atrium or ventricle

Mode of action inhibited

Extra R RATE RESPONSE

SENSORS

(1) activity

(2) minute volume

(3) QT interval measurements

(4) temperature

ACTIVITY is the most successful and therefore the most common.

There are two types of activity sensor

(1) piezo crystal(2) accelerometer



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Physiological response

AV synchrony

Chronotropic response

AAI pacing AV synchrony is presentChronotropic response is dependent upon the type of SA nodaldisease

AAIR pacing AV synchrony is presentChronotropic response is present

VVI pacing No AV synchrony presentNo chronotropic response present

VVIR pacing No AV synchrony presentChronotropic response is present

DDD pacing AV synchrony is presentChronotropic response is present, assuming normal SA nodalfunction

DDDR pacing AV synchrony is presentChronotropic response is present



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WHICH MODE FOR WHICH PATIENT

Consider

(1) ECG indications

(2) mobility

(3) age

ECG INDICATIONS

(1) Check for sinus node disease

(2) Check for AV nodal disease

MOBILITY

The more mobile a patient, the more physiological mode should be chosen.

AGE

Younger patients should be given a physiological mode

The choice of pacemaker should be dominated by the ECG indications andalways be discussed with the Physician prior to implantation.

Age and mobility should be considered but not have a strong influence overthe decision.

LJR..PM001.



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TECHNICAL ASPECTS OF FOLLOW UP

When following up a patient with a pacemaker implanted there arevarious technical aspects, which need to be observed.

1) battery assessment

2) electrode assessment

3) parameter settings

4) telemetry

5) Special Features

To perform all these tests the patient must be made comfortable andan ECG monitored throughout. A three lead ECG is preferable with the abilityto perform full 12 lead ECGs should be available. A pacing analyser must bemade available which has the facility to measure the pacing rate, pacinginterval and pulse duration of the pacing stimulus. Pacemaker programmerssuited to individual pacemaker models must be available. Resuscitationequipment should be close by.

As well as the technical aspects of follow up, the medical aspects are alsoimportant and need to be considered.



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BATTERY ASSESSMENT

Once the pacemaker is implanted it must be checked regularly for batterydepletion.

(1) magnet measurements each pacemaker has a fixed VOO rate, usuallyhigher than the programmed base rate, which occurs with application of amagnet over the pacemaker site.

Magnet applied

If the patients intrinsic rhythm is faster than the magnetic rate then it may bedifficult to ensure capture, however the measurements of the pacemakerstimulus can still be taken by the analyser to check for battery depletion.



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The analyser measures the pacing rate (pulses per minute, ppm), pacinginterval (ms) and pulse duration of the pacing stimulus (ms). As the batterydepletes, the magnetic rate will gradually decreases until a certain rate is

reached. At this pacing rate the battery has reached the RecommendedReplacement Time (RRT) and further drop in magnet rate will give End Of Life(EOL) indicators.

Each pacemaker type has different magnet rates at the Beginning Of Life(BOL), RRT and EOL.

With some pacemakers, application of a magnet over the pacemaker will notgive a magnet response. This is due to in-built safety features, which can beoverridden with external programming. In this instance the magnet functionmay have to be programmed ON before any response to magnet is seen.



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(2) Real-time telemetry (see later) - will also give readings of the batteryvoltage, impedance and estimated longevity in most modern pacemakers.

As the battery depletes the voltage reduces and the impedance increases.Most pacemaker battery voltages begin at 2.8v and will reach End of Lifeat 2.4v.



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ELECTRODE ASSESSMENT

(1) Stimulation threshold - is performed at each visit after implant. This is to

ensure electrode stability, to check for any acute rise in threshold due to thescarring/oedematous process (during the first 6 weeks) and to further checkthe lead integrity and function throughout the life of the pacing system.

Threshold is performed in the same way as at implant, reducing the outputvoltage until loss of capture is seen. Some pacemakers only offer eithervoltage or pulse-width thresholds as an automatic feature. If a more accuratethreshold is required a pulse duration threshold can also be measured at thevoltage threshold setting. This is called a strength duration thresholdmeasurement.

Some pacemaker types operate a vario threshold test, which usually has tobe programmed ON. With application of a magnet in this vario mode thevario threshold is performed at a higher rate than the programmed base rate.With each stimulus the output is automatically decreased until after 16 pulses



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the output has reached zero. Once loss of capture is seen, removal of themagnet restores standard or programmed settings.

Most programmers offer an automatic threshold function, gradually reducingthe output until the test is terminated. The method of termination will vary

between programmers.The results may be printed out and often a recommended output setting issuggested.

Autocapture

Some pacemakers offer the option to perform an internal threshold looking forventricular depolarisation through the lead following an output at differentvoltage settings. Reduction of the voltage setting is then automaticallyadjusted in an out of hospital setting.



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(2) Electrode sensing function - should be established. A measurement of P orR wave can assess satisfactory intrinsic activity, which can allow fine-tuning of

the sensitivity settings to be programmed. Some pacemakers allow anautomatic sensing threshold to be performed. The sensitivity is automaticallyreduced and the test ended when failure to sense occurs.

(3) Lead Impedance should always be checked. This may indicate fracture(high

impedance) or insulation break (low impedance). Many models now offer acontinuous monitoring of lead impedance. Care should be taken toincorporate slight changes from acute to chronic lead status.



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PARAMETER REPROGRAMMING

(1) Output Voltage Opinions vary as to when output reprogramming to a

lower value should take place. The oedematous reaction usually occurs withinthe first six weeks after implant and therefore no further increase in thresholdshould occur. Occasionally, late increases in threshold can occur although theuse of steroid-eluting electrodes has reduced the incidence of this. After the1 st year of implant the lead should be stable and securely fixed to themyocardial tissue. If the stimulation threshold has been low and stable for allprevious pacemaker checks then reprogramming the output to a lower valuecan be done at this time.Reprogramming the output to a lower level increases the longevity (life span)of the pacemaker battery. It is usual to reprogram the output voltage to twicethe threshold voltage to retain a safety element in case a sudden increase instimulation threshold occurs.

Longevity(yrs)

15

10

5

00.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5

Pulse Width

It can be seen from the longevity table that a halving of output voltageincreases the longevity of battery by almost twice the number of years.Changing the pulse width (duration) also has an effect although the battery lifesaved is more significant with a decrease in output voltage than in pulseduration.

If the stimulation threshold rises at any time then the output voltage setting willneed to be revised. Thought must be given as to the reason for the highthreshold with a view to further action being taken.

(2) Base Rate reduction of base rate and hysteresis reprogramming canroutinely be programmed to facilitate intrinsic rhythm.



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High base rates may need to be programmed, to suppress any arrhythmias inthose patients more at risk.

(3) AV Delay can be lengthened to facilitate intrinsic AV conduction.It can be shortened to enhance pre-exitation of ventricular depolarisation in

patients with Hypertrophic CardioMyopathy (HOCM).

(4) Activity Sensor If the histograms and/or patient symptoms suggest thatthe activity sensor in a rate responsive unit is under active giving little or norate response (see below) then the activity threshold or rate response slopecan be reprogrammed.

If the histograms and/or patient symptoms suggest an over-active sensor(see below) then the activity threshold or rate response slope can bereprogrammed.

Ventricular RateHistogram



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(5) Sensitivity If under or over sensing is seen at any time, the sensitivity of

the pacemaker must be reprogrammed to an optimal setting. Ideally thesensitivity should be set to allow a 3 x safety margin for sensing intrinsicactivity.

(6) Polarity If using Bipolar pacing leads, reprogramming the polarity eitherto Bipolar sense and Unipolar pace can be considered. Whether thepreference is towards unipolar or bipolar pacing, the sensing function shouldalways be bipolar if possible. This will reduce inappropriate inhibition due toextra-cardiac/corporeal interference.

(7) Maximum tracking/Maximum sensor (in rate responsive models) rate should be programmed appropriately for the age and activity level for eachindividual patient.

(8) Mode switching in the DDD models should be programmed ON.Especially important for those patients with previous atrial arrhythmias.



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TELEMETRY

(1) measured data - most pacemakers have telemetry functions either storedor real-time, which allow detailed measurements of battery, lead status and/ordetailed histograms showing pacemaker activity, pacemaker sensor activity,intrinsic cardiac activity, distribution of heart rates (paced and intrinsic), andintrinsic P and R wave measurements.

Battery status:Longevity (years and months)Battery impedance (k )Battery voltage (volts,v)

These measurements allow close monitoring of battery levels, with the batteryvoltage reducing and the battery impedance increasing over time.

Lead status: Lead impedance (ohms, )

Automatic threshold resultP/R wave measurements (millivolts, mv)

The lead impedance can be monitored regularly to check for lead fracture(high impedance) or insulation break (low impedance).



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(2) Histograms Event, heart rate, frequency of mode switch and sensorhistograms all give useful and sometimes vital information that can aidreprogramming and allow improved troubleshooting of pacemaker problems.

Event histogram

Shows amount of time or number of beats that have been sensed or paced bythe pacemaker.



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Rate Histogram

Shows the distribution of heart rates, either sensed or paced.The heart rate histograms can indicate presence of high atrial or ventricularrates.



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Atrial Rate Histogram showing Atrial Arrhythmias



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P/R wave amplitude histogram

Shows the distribution of measured intrinsic P or R waves.



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The example below shows Normal P wave amplitude distribution.

The example below shows a variable P wave amplitude histogram, usuallyseen in AF.



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SPECIAL FEATURES

Many models now have special features incorporated. Mode switch hasbecome common place but other features are unique to individual models.Rate drop response algorithms, atrial pacing therapies, high atrial and/or

ventricular rate counters and the storage of Intracardiac Electrograms (IEGM)at the onset, during or at termination of these events is also available.

The stored IEGMs which can establish the type of arrhythmia andappropriateness of pacemaker modalities is crucial.



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A special Ratedrop therapy has been given and information regarding thisis shown in this histogram below.



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MEDICAL ASPECTS

Once technical measurements have been taken, routine checks do notusually need medical input, although it should be available if needed.

Special medical consideration should be given at the first pacemaker clinicvisit (between three and six weeks), although other medical problems at anystage, should never be disregarded.

The 4 week check:

establishes all technical aspects are satisfactory and medically a thoroughwound check is essential to check for infection at this time.

re-enforcement of the positive aspects of pacing and the discussion of anyconcerns may be included at this visit.

investigation of symptoms, not established and/or solved at technical check.

Any cardiovascular disease present must always be considered in the re-programming of the pacing system and any further treatments.



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PROGRAMMABLE PARAMETERS

BASIC RATE

The basic rate is the lowest rate at which the pacemaker will output, and therange varies between pacemakers.

When the pacemaker is programmed to a dual chamber mode, the highestbasic rate allowed is determined by the selected AV delay.

Often when the replacement time of the generator is reached, the base rateinterval will increase by a certain number of milliseconds (ms).

Clinical Advantages Of Reprogramming

1. Favour sinus rhythm

2. Improve cardiac output

3. Overdrive atrial and ventricular arrhythmias

4. Stand-by function

5. Diagnostic purposes

HYSTERESIS

The escape interval after a sensed intrinsic beat is greater than the escapeinterval after a paced beat.

Clinical Advantage Of Reprogramming

To facilitate intrinsic rhythm, particularly useful if the intrinsic rate is similar tothe programmed base rate.



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MAXIMUM TRACKING RATE (MTR)

Use of this parameter is limited to the DDD and DDDR pacing modes.Regardless of the patients atrial rate, the ventricular pacing rate will neverexceed the programmed maximum tracking rate, if the pulse generator istracking the patients intrinsic atrial activity.

The pacing rate can exceed the programmed MTR during activity-responsivepacing if the maximum sensor rate is programmed higher than the maximumtracking rate (DDDR).

In the event that the patient develops an atrial rhythm faster than the selectedMTR, the pacemaker circuit may exhibit a Wenckebach effect a progressivelengthening of the P to V interval or even a 2:1 block.When a P wave occurs within the atrial refractory period, the atrial event willnot be sensed, resulting in a dropped synchronous beat.Therefore in the presence of atrial activity above the maximum tracking rate,the P to V interval will progressively increase, eventually resulting in adropped ventricular beat when the P wave falls within the refractory period,similar to the physiological Wenckebach effect.The maximum tracking rate is limited by the programmed AV interval as wellas the programmed atrial refractory period.


1. Allow high rates and maintain AV synchrony during vigorous exercise

2. Limit high rates due to tracking of atrial arrhythmias



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PULSE AMPLITUDE AND DURATION

Pulse amplitude and duration are independently programmable and both have

an effect on energy of the pulse delivered.The pulse amplitude mostly varies from 0v to 7.5 or 10v, the pulse durationbetween 0ms and 1.0ms.

duration

amplitude

With new lead implants, outputs should be kept high to prevent loss of capturedue to early threshold rises.Once the lead position has stabilised (usually one to three months) increasesin pulse generator longevity can be can be obtained by reducing the pulseamplitude and duration.Capture threshold therefore gives an indication as to the setting of these twoparameters.


1. Adjust output to suit individual capture thresholds, allowing a safety margin

2. Avoid muscle/nerve stimulation

3. Save energy and therefore extend longevity

amplitude

duration



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REFRACTORY PERIOD

Immediately following a sensed or paced event, the pacemaker ceases torespond to any signals occurring within the refractory period.This prevents the pacemaker responding to a detected depolarisation signal(terminal QRS) or repolarisation signals (T waves), which may result in timingerrors resulting in lower than programmed base rates.

The ventricular refractory period is always initiated by a sensed/pacedventricular event.

The atrial refractory period is split into two segments.1. The first segment starts with a sensed/paced atrial event and continues

until a sensed / paced ventricular event.2. The second segment starts with a sensed / paced ventricular event and

continues for a programmed interval. This portion of atrial refractory periodis called the post ventricular atrial refractory period (PVARP) .

Atrial refractory period ranges from approx. 200-500ms.Ventricular from 200-500ms in non-tracking modes [DDI(R) and VVI(R)modes] and is limited to 325ms in tracking modes [DDD(R) modes].


1. Prevent oversensing

2. Ensure arrhythmia sensing (AF/AFL) in mode switching devices



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SENSITIVITY

If a cardiac signal of sufficient amplitude and frequency occurs during thepacemakers alert period, pacemaker output will be inhibited or triggeredaccording to the mode selected.Sensing circuits are designed to specifically reject extraneous signals whilesensing P or R waves.

If intrinsic signals are low amplitude, the sensitivity should be reprogrammedto a more sensitive level (lower value).Conversely, if the pacemaker is responding to other extraneous signals,reprogramming to a less sensitive setting may be employed (higher value).

A

B

C

D

A NO SENSINGB INTERMITTENT SENSING muscleC STABLE SENSINGD SENSING OF MUSCLE NOISE cardiac

It is generally recommended that a sensing margin of 2-4 times the amplitudeof intrinsic cardiac signals be chosen, although in practice this is often difficult.

Atrial sensitivity usually varies between 0.5 and 5 mv.

Ventricular sensitivity between 1 and 10mv.


Adapt the sensitivity to the prevailing intrinsic cardiac signals.



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AV DELAY

The AV delay defines the time interval between an atrial impulse and aventricular impulse.The time interval between a sensed atrial and a paced ventricular event ( PVdelay ) should always be approx 25ms less than a paced atrial and pacedventricular event ( AV delay ).This difference between the PV and AV intervals is to compensate for the timelag taken between the atrial impulse and atrial contraction.This is to enable a consistent interval between atrial and ventricularcontraction, regardless of the mode of action (VAT or AV pacing).

PV delay

AV delay

The AV delay usually varies from 30ms to 300ms.


1. The PV delay should be 25ms less than the AV delay to maintain AVsynchronous contraction.

2. The AV/PV delay should be extended to facilitate intrinsic rhythm.

3. In HOCM patients the AV/PV delay should be shortened to maintainventricular pre- excitation due to ventricular pacing.



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RATE RESPONSIVE AV DELAY

When RR AV delay is enabled, the PV interval during atrial tracking willgradually shorten as the detected intrinsic atrial rate increases.

The time interval between a sensed atrial event and the ventricular impulse(PV delay) will always be at least 25ms shorter than the programmed AVdelay, even when RR AV delay is disabled.When RR AV delay is enabled, the PV interval will shorten further as thesensed atrial rate increases.

If the device is programmed to DDDR with the RR AV delay enabled, the AV

delay will shorten as the pacing rate increases in response to patient activity.This feature is intended to optimise cardiac output by mimicking thedecreasing PR interval which occurs in the normal heart as the atrial rateincreases.



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BLANKING PERIOD

The blanking period is a short interval after each pulse output where thepacemakers sensing circuits are completely blind, and NO sensing occurs.

Ventricular Blanking

A blanking period will momentarily occur in the ventricular sensing circuit,coincident with any atrial output.This feature is employed to prevent detection of an atrial output by theventricular sensing circuit which would result in ventricular output inhibitionand a reset of pulse generator timing.

This is known as CROSSTALK.

The range will usually vary between 13 and 50ms.

Atrial Blanking

A blanking period will momentarily occur in the atrial sensing circuit,coincident with any ventricular output.This feature is employed to prevent detection of a ventricular output by theatrial sensing circuit which would result in attempts at inappropriate trackingand would cause havoc in a mode switching device.

The range will usually vary between 50 and 150ms.


A short atrial blanking is useful to assist in the detection of atrial arrhythmias

in mode switching devices.



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PMT OPTIONS

The PMT (Pacemaker Mediated Tachycardia) options are designed toterminate PMTs if and when they occur in the DDD mode.

If consistent tracking at the maximum tracking rate occurs for a select numberof cycles, an attempt is made to break the PMT cycle by purposefully failing totrack a sensed retrograde P wave.The detection criteria will vary between manufacturers and with recenttechnology even consistent VA measurements can now be made to confirmthe presence of a PMT.

This option is not always programmable and this feature is often an integralpart of some pacemaker models.



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POLARITY

Pulse polarity and sensing polarity is often independently programmable forboth atrial and ventricular chambers.

PULSE POLARITY CONFIGURATION

If unipolar configuration is selected, the distal tip electrode of the lead willserve as the pacing cathode (-) with the uncoated portion of the pacemakerstitanium case serving as the anode (+).If a bipolar configuration is selected, the distal electrode will continue to serve

as the pacing cathode (-) with the leads proximal ring electrode serving as thepacing anode (+).During bipolar pacing the generators titanium case is electrically isolated fromthe pacing circuit.


1. Advantage of bipolar pacing is to eliminate the potential of pocketstimulation.

2. The advantage of unipolar pacing is to produce a large stimulation artefact

which can be easily visualised on the surface ECG, promoting easyinterpretation.

SENSING POLARITY CONFIGURATION

If unipolar sensing is selected, the voltage difference between the pacingleads distal electrode and the exposed area of the generators titanium casewill be sensed.If bipolar is selected, the pacemaker will sense in a bipolar manner betweenthe leads distal and proximal electrodes.


Bipolar sensing reduces susceptibility to detection of myopotentials andexternal electromagnetic interference.



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SENSOR

Most sensor-driven generators incorporate an activity piesoelectric sensorbonded to the inside of the generator case.The sensor generates a signal in response to vibrations which result fromambulation or repetitive upper body movements.When the sensor is programmed ON, the sensor signal is processed toallow an increase in pacing rate in response to activity.

MAXIMUM SENSOR RATE

The maximum rate allowed by the generator in response to activity.The maximum sensor rate chosen is usually similar to the maximum trackingrate.


Sensor rates higher than maximum tracking rates may be chosen in thepresence of paroxysmal atrial arrhythmias.

SLOPE

The programmed slope value determines the increase in pacing rate whichoccurs at various levels of activity.

In general a low slope, low sensor level corresponds to a low level of patientactivity whereas a maximum slope, high sensor level corresponds to a highlevel of patient activity.

Higher slopes will result in a greater increase in pacing rate than a low slopefor any level of activity.



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THRESHOLD

The activity threshold is the minimum level the sensor signal has to reachbefore allowing a pacing rate increase in response to activity.

At low activity threshold settings a pacing rate increase can be observed inresponse to minimum activity.

At high activity threshold settings a much higher level of activity is required tocause any pacing rate increase.

REACTION TIME (ACCELERATION TIME)

The value selected for the reaction time determines the minimum time allowedfor the sensor-driven rate to increase from base to maximum.

The programmed reaction time only applies to increases in sensor-drivenrates, not during atrial tracking.

A short reaction time will allow the pacing rate to increase rapidly in responseto patient activity.

A long reaction time will force a slow increase in pacing rate.

The range will usually vary between 0.5 to 2.5 minutes, although somemodels have pre-determined times giving a range from very low to very high.

RECOVERY TIME (DECELERATION TIME)

The value selected for recovery time determines the minimum time required

for a decrease in pacing rate from the maximum sensor-driven rate to thebase rate.

This feature is intended to prevent an abrupt decrease in pacing rateconcurrent with the conclusion of patient activity.

A long recovery time will result in a slow decrease in pacing rate when thepatients activity level decreases.

A short recovery time will allow the pacing rate to decrease more rapidly.

The range will usually vary between 2.5-5 minutes.



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MODE SWITCH

Modern technological advances allow this feature as routine on mostcommercially available DDD pacemakers.

In the presence of an atrial arrhythmia, the generator switches from a trackingmode (DDD) to a non-tracking mode (DDI).To prevent the rate suddenly dropping from a tracking mode (VAT pacing) tobase rate, it is recommended that sensor-driven modes are present during thetime of mode switch.

In this way the mode will switch from a tracking mode (DDD) to a sensor-driven non-tracking mode (DDIR).

Detection criteria of atrial arrhythmias will vary between manufacturers.

Reprogramming of some basic parameters will often assist in the true sensingand therefore the true detection of atrial arrhythmias as soon as possible.

1. Atrial sensing to bipolar

2. Shorten atrial blanking

3. Increase atrial sensitivity (lower value)

LJR..PP001.00



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COMPLICATIONS OF FOLLOW UP

FAILURE TO CAPTURE

Failure to capture occurs when more energy is required to stimulate the heart.

VVI

LOC (V)

AAI

LOC (A)

DDD

LOC (V)

DDD

LOC (A)



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UNDERSENSING FAILURE TO SENSE

VVI

Failure toSense (V)

AAI

Failure toSense (A)

Failure to sense occurs when the pacemaker fails to see intracardiac signalsthat are the result of an intrinsic beat.

In this case the sensitivity of the pacemaker is inadequate, this is calledUNDERSENSING .



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OVERSENSING

(A) FAR FIELD SENSING

Inappropriate inhibition due to inappropriate sensing of a cardiac source.

The pacemaker is OVERSENSING .

P waves - sensed by a ventricular system (VVI)

QRS waves sensed by an atrial system (AAI)

T waves usually in ventricular systems.

(B) EMG (electromyographic) INHIBITION (oversensing)

Inappropriate inhibition due to the pacemaker sensing myopotentials fromskeletal muscle. (Usually pectoral muscle stimulation).

Seen in unipolar systems.

Muscle Tremor



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(C) CROSS TALK (oversensing)

Inappropriate inhibition due to one electrode sensing the output from the otherelectrode. Occurs in DDD mode only.

(D) EXTRA-CORPOREAL SOURCE (oversensing)

ElectromagneticElectrical



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EXTRA-CARDIAC STIMULATION

(A) SKELETAL MUSCLE STIMULATION

Pectoral muscle/rectus sheath muscle sti mulation

Skeletal muscle stimulation occurs with current from the pacing systemdirectly stimulating nearby tissue.The indifferent plate of the pulse generator (in a unipolar system) must bepositioned away from muscle tissue.

A break in lead insulation close to the generator site may allow currentleakage to directly stimulate nearby muscle.Incomplete lead connection with pacemaker.

(B) DIAPHRAGMATIC STIMULATION

Direct Ventricular lead apical position may directly stimulate the diaphragm.This may occur with thin walled ventricles or myocardial tissue perforation.

Indirect Atrial appendage lead position may indirectly stimulate thediaphragm via stimulation of the phrenic nerve.



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PACEMAKER MEDIATED TACHYCARDIA

A tachycardia due to the tracking of retrograde P waves in the DDD mode,usually initiated by atrial or ventricular ectopics.

Many pacemakers have PMT protection algorithms that extend the atrialrefractory period if maximum tracking occurs for an extended period of time.This will encourage the retrograde P wave to fall within the refractory periodand failure to track this P wave will break tachycardia.Permanent programming of the atrial refractory period may be needed and toallow high maximum tracking rates to be programmed, the AV delay mayneed to be shortened.

PACEMAKER SYNDROME

Some patients experience dizziness or lethargy after implantation of a VVIpacing system.

The loss of AV synchrony may lead to a reduced cardiac output.

Retrograde conduction of a P wave can cause contraction of the atria againsta closed AV valve.

VVI pacing alone with a normal sinus P wave or normally conducting atria cancause a reduced cardiac output leading to the symptoms above.

WOUND INFECTION

If the pacemaker site becomes infected early Antibiotic treatment isnecessary.Failure to treat infection may lead to the removal of pacemaker and leads.This is an attempt to prevent the spread of infection to the myocardium and soprevent Endo/Myocarditis.



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pacing manual

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