Tachycardias with Broad Ventricular Complexes



Though bundle branch block can sometimes occur during supraventricular tachycardias and therefore lead to broad ventricular complexes, most broad complex tachycardias are ventricular in origin.

    Pointers towards ventricular tachycardia as opposed to supraventricular tachycardia with bundle branch block include the presence of myocardial damage, direct or indirect evidence of independent atrial activity, QRS duration greater than 0.14 s, a concordant pattern in the chest leads, and marked axis deviation. Neither minor irregularities during tachycardia nor the haemodynamic effect of the arrhythmia are useful in ascertaining its origin.

    When supraventricular tachycardias are associated with bundle branch block the morphology of the ventricular complexes is usually that of typical left or right bundle branch block. Never use verapamil for a diagnostic test. Wherever possible, record a 12-lead ECG during tachycardia for diagnostic purposes.




Tachycardias of supraventricular origin sometimes result in broad ventricular complexes. Thus they may mimic ventricular tachycardia. Now that this is widely appreciated, the tendency is to misinterpret ventricular tachycardia as supraventricular, rather than the reverse.


Causes of a broad complex tachycardia


Tachycardias with broad ventricular complexes may be due to:



1. ventricular tachycardia;

2. supraventricular tachycardia when bundle branch block has already been present during sinus rhythm;

3. supraventricular tachycardia with rate-related bundle branch block (i.e. bundle branch block develops during tachycardia);

4. Wolff–Parkinson–White syndrome: if atrial impulses during atrial flutter or fibrillation are conducted to the ventricles by the accessory AV pathway, or in the uncommon ‘antidromic’ form of AV re-entrant tachycardia, when AV conduction is via the accessory pathway.

A number of guides are used to distinguish a supraventricular tachycardia with broad ventricular complexes from ventricular tachycardia.


Useless guidelines


It is often said that whereas ventricular tachycardia leads to major haemodynamic disturbance, supraventricular tachycardia does not. This is wrong. Sometimes ventricular tachycardia causes few or even no symptoms, whereas supraventricular tachycardia, if very fast or in the presence of underlying heart disease, can cause shock or heart failure (Figure 14.1).


Another widely quoted but incorrect rule is that whereas supraventricular tachycardia is regular, ventricular tachycardia is slightly irregular.


Verapamil may terminate supraventricular tachycardia or slow the ventricular response to atrial fibrillation or flutter. It has been used as a ‘therapeutic’ test of the origin of tachycardia. However, dangerous hypotension may result when the drug is given during ventricular tachycardia. Never use verapamil to establish the origin of a broad complex tachycardia.



Figure 14.1 Dramatic drop in arterial pressure with onset of AV re-entrant tachycardia.

image

Useful guidelines


Independent atrial activity


If there is direct or indirect (Figures 12.2, 12.4, 12.10, 14.2, 14.3

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  4. Polymorphic Ventricular Tachycardia and Ventricular Fibrillation

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Jun 4, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Tachycardias with Broad Ventricular Complexes

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