Systematic Approach to Systematic Approach to Wide QRS TachycardiaWide QRS Tachycardia

Salah Atta, MD,

Lecturer of Cardiology

Department of Cardiology, Assiut University Hospitals

Weekly Department meeting 2004

Aberration means BBB either functional or fixed. Also non specific intraventricular Conduction delay may be 2ry to electrolyte disturbance or myocardial ischaemia.

(Pre-excited tachycardias)

Is It important to differentiate Is It important to differentiate VT from SVT with aberration?!VT from SVT with aberration?! Definitely, If you wrongly managed a patient with

VT with underlying Heart disease as having SVT with aberration and gave him Isoptin, severe haemodynamic deterioration necessitating immediate cardioversion may occur.

Furthermore, hypotension with resulting ischaemia may render the arrhythmia impossible to cardiovert.

Further long term management is different.

Assessment Of wide QRS Assessment Of wide QRS tachycardia patient:tachycardia patient:

When you are confronted with such a case:

1. Stay calm and think deeply but rapidly.

2. Rememmber that haemoynamic status is not a clue to the mechanism of arrythmia. Haemodynamic unstability means only that you must cardiover the patient immediately, not that you are dealing with a ventricular tachycardia.

When the patient is haemodynamically stable:

Evaluate systematically.

Diagnose.

Treat.

When the patient is haemodynamically unstable:

•Cardiovert.

•Stabilize.

•Evaluate systematically, assess ECG after cardioversion for existance of diagnostic changes as BBB, Pre-excitation.

•Diagnose.

Atrial activity during Atrial activity during Ventricular tachycardia: Ventricular tachycardia:

One half of all cases of ventricular have AV dissociation, a few of the remainder have some form of retrograde conduction to the atria. This may be 1:1, 2:1 or some form of retrograde wenckebach.

Recognition of AV dissociation is diagnostic of VT if P waves are less than QRS numbers.

Atrial activity during Atrial activity during Ventricular tachycardia:Ventricular tachycardia:

Detection of regular independant P waves is a very strong diagnostic sign. However, P wave identification may be difficult or impossible, therefore the evaluation of the QRS morphology and a physical examination for AV dissociation are faster and more reliable.

Narrow beats during wide Narrow beats during wide QRS TachycardiaQRS Tachycardia

These may occur during VT due to:1. A conducted sinus beat leading to capture or

fusion. Both produce a complex narrwer than the VT.

2. An echo beat: it is a form of capture or fusion beat due to downward conduction to the V of an impulse that was originally retrogradely conducted.

3. Fusion between two V ectopic foci.

ECG Differential DiagnosisECG Differential Diagnosis

QRS configuration in VT:A- If V1- positive i.e RBBB pattern :In lead V1: A monophasic or biphasic pattern,

this supports VT, where as a triphasic pattern (rSR‘) favors supraventricular tachycardia.

In lead V6, a deep S (R/S <1) or QS indicates ventricular tachycardia.

VT versus SVT in V1, V6 VT versus SVT in V1, V6 when V1 is positive i.e RBBB patternwhen V1 is positive i.e RBBB pattern

Rabbit ear signRabbit ear sign

When there are two positive peaks in lead V1, ventricular tachycardia is very likely if the left peak is taller. This is known as the rabbit ear sign, and is shown in the previous figure with dotted line. A taller right rabbit ear is of no Help in distinguishing V tach. from aberration.

If V1 is negative i.e LBBB If V1 is negative i.e LBBB patternpattern

Four signs are highly predictive of VT:

1. A broad R of 0.04 sec or more in lead V1 or V2.

2. A slurred or notched S downstroke in lead V1 or V2.

3. A distance of 0.07 sec or more from the onset of the QRS to the nadir of the QS or S in lead V1 or V2.

4. Any Q in lead V6.

VT versus SVT in V1, V6 VT versus SVT in V1, V6 when V1 is positive i.e RBBB patternwhen V1 is positive i.e RBBB pattern

V1 V6

VT

SVT

Other diagnostic cluesOther diagnostic clues

QRS width: A QRS width of 140 msec in RBBB morphology

and 160 msec in LBBB morphology favors a diagnosis of VT.

Exceptions are possible as pre-excited tachycardias which may be that wide and as ventricular tachycardia in digitalis toxicity that may have a QRS duration <0.14 sec as it originates in one of the bundle branches.

QRS Axis :QRS Axis :

An abnormal axis is a strong indicator of VT. This is specially true of an axis in the northwest quadrant (-90 degrees to –180) . Idiopathic VT however may have a normal axis.

Concordant Precordial Concordant Precordial Pattern:Pattern:

1. A totally negative precordial pattern is almostly due to a ventricuar tachycardia.

2. A positive concordance on the other hand may occur during ventricular tachycardia originating in the posterior wall of LV and also during a tachycardia using left lateral accessory pathway for AV conduction.

So collectively the morphology criteria suggestive of VT includes:

Abnormal or extreme Axis.

After Tachycardia, the 12-lead-ECG in idiopathic VT may show transient ST- T segment changes, especially in VT with a left ventricular origin i.e RBBB-shaped, as shown in the next Figure 71-3, these ST-T changes may last for several days. The duration of these changes is related to the duration and hemodynamic consequences of the VT. (Zipes et al 2000)

N.B This algorithm was found to be specially not applicable to the Idiopathic VT.

It may seem smart to It may seem smart to diagnose SVT with diagnose SVT with

aberration when the others aberration when the others suggest VT but it is wise not suggest VT but it is wise not

to do so unless sure.to do so unless sure.

Thank youThank you