normal sinus rhythm debs farr 2011. course objectives to recognize the normal rhythm of the heart -...
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Normal sinus rhythm
Debs Farr 2011
Course Objectives
• To recognize the normal rhythm of the heart - “Normal Sinus Rhythm.”
• Understand normal conduction of the heart
http://caribbean.scielo.org/img/revistas/wimj/v54n3/a12fig03.jpg
R.E.Mason.,I.Likar ( 1966)
Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
The “PQRST”
• P wave - Atrial depolarization
• T wave - Ventricular repolarization
• QRS - Ventricular depolarization
The PR Interval
Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)
(delay allows time for the atria to contract before the ventricles contract)
Qt Inteval
• QT – Represents time for both ventricularDepolarisation and repolarisation.
Pacemakers of the Heart
• SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.
• AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.
• Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.
The ECG Paper
• Horizontally– One small box - 0.04 s– One large box - 0.20 s
• Vertically– One large box - 0.5 mV
The ECG Paper (cont)
• Every 3 seconds (15 large boxes) is marked by a vertical line.
• This helps when calculating the heart rate.
3 sec 3 sec
Calibration
Normal Sinus Rhythm
• “Normal sinus rhythm occurs when the impulse originates in the sino Atrial node and travels through the conduction system in a normal sequence ,at a normal and regular rate”American Heart Association,(2000).homepage:Availablehttp:/www.americanheart.org/warning.
Normal Sinus Rhythm
ECG Interpretation
• A mystery?
• An enigma?
• Confusing?
• Difficult?
Criteria - P wave
An upright rounded P-wave in leads II, III and AVF, and an inverted P-Wave in AVR which precede each QRS Complex.
• The P wave does not exceed 2.5mm in height.
• It does not exceed 3mm in width.• A biphid P wave is seen in lead V1.
Criteria - PR interval
• PR Interval
• 0.12 - 0.20seconds.
• Delay at AV node»Protect ventricles»Allow for ventricular filling
Criteria QRS complex
• Should not exceed 0.12 seconds in duration.
• Should not exceed 27mm in height.
• Sharp narrow complex
• RS in V1, QRS in V6
Criteria T wave
• The deflection produced by repolarisation of the ventricles.
• No clearly defined range
• General rule - T wave should not be more than 1/2 the height of the preceding QRS
Criteria - QT interval
• QTc Interval
• Should not exceed 0.42 seconds (QTc).
• QT interval corrected to the heart rate.
Correction Calculation
QTc = measured Qt interval
cycle length
Criteria U wave
• The origin is uncertain
• May represent repolarisation if the IVS
• May represent slow conduction of ventricular myocardium
• Prominent U waves are abnormal
• Usually most visible in V1-V4
Nomenclature - QRS
• The 1st negative deflection - Q
• The 1st positive deflection - R
• The 2nd negative deflection or If a negative follows a positive - S
Nomenclature -QRS
Nomenclature - QRS
Nomenclature - QRS
• Waves > 0.5mv (5mm) high• Capital letters e.g. QRS
• Waves < 0.5mv (5mm) high• Lower case e.g. qrs
Intervals
• P wave duration measured?
• PR interval measured?
• QRS interval measured?
• QT interval measured?
Amplitudes
• P wave height measured?
• QRS height measured?
Segments
• PR segment measured?
• ST segment measured?
Limb leads
• Measurements - lead II
• QRS Axis
• P wave Axis
Chest Leads
• Progression of R waves throughout the chest leads
• Transitional Zone
• Phases of Activation
Depolarisation Stages
1
2
3
Typical complexes in the Pre-cordial leads
V1 V2 V3 V4 V5 V6
RV RV IVS IVS LV LV
Progression of R waves throughout the chest leads
• Size of the R wave should increase from V1 to V6.
• V4 Usually at the Apex (Transitional Zone where the first negative wave appears).
R Wave Progression
Practical Challenges
Sinus Rhythms
• Sinus Bradycardia
• Sinus Tachycardia
• Sinus arrhythmia
NSR Parameters
• Rate60 - 100 bpm• Regularity regular• P waves normal• PR interval 0.12 - 0.20 s• QRS duration 0.04 - 0.12 s• QT interval not exceed 0.42
seconds. • U wave
Sinus Bradycardia
- Rate < 60 b pm
Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).
Sinus Tachycardia
- Rate > 100 bpm• Etiology: SA node is depolarizing faster than
normal, impulse is conducted normally.• Remember: sinus tachycardia is a response to
physical or psychological stress, not a primary arrhythmia.
Sinus arrythmia
• Rate – variable
Etiology: SA node is depolarizing t a variable rate , impulse is conducted normally (i.e. normal PR and QRS interval).
Normal Rhythms !!!
• *Sinus Arrest*
• Considered a ‘Sinus rhythm’ but is abnormal
Rhythm 1
130 bpm• Rate?• Regularity? regular
normal
0.08 s
• P waves?
• PR interval? 0.16 s• QRS duration?
Interpretation? Sinus Tachycardia
Rhythm 2
30 bpm• Rate?• Regularity? regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s• QRS duration?
Interpretation? Sinus Bradycardia
ECG INTERPRETATION
• If the normal ECG is known then interpretation of abnormals becomes easier
EASY ?
References/Bibliography
• www.ecglibrary.com
• www.acc.org
• www.cardionetics.com
• www.coheadquarters.com
• www.RNCEUS.com
• www.tmc.edu/thi/arrhythm.html
• ctmed