Page 176 - Clinical Pearls in Cardiology

164 Clinical Pearls in Cardiology

supraventricular or a ventricular origin of the arrhythmia.
This is because of the fact that some of the medications
that are given for the treatment of supraventricular
tachycardia (like intravenous verapamil) are harmful to
a patient with ventricular tachycardia.
Supraventricular rhythms usually have narrow QRS
complexes. Occasionally a supraventricular rhythm can
produce wide QRS complexes due to coexisting bundle
branch block or due to the presence of an accessory
conducting pathway, and can cause diagnostic confusion
with ventricular tachycardias. The features in favor of
ventricular tachycardia in the differential diagnosis of
broad complex tachycardias are the following:
• Evidence of A-V dissociation with P waves ‘marching
through’ the QRS complexes
• Presence of ‘capture’ or ‘fusion’ beats (Fig. 3)
• Northwest axis (i.e. axis between −90° and −180°)
• Very wide QRS complexes (>0.14s in tachycardias
with RBBB pattern and >0.16s in tachycardias with
LBBB pattern)
• Concordant pattern in precordial leads (when all the
precordial leads show either negative or positive QRS
complexes, then the pattern is called as negative or
positive concordancy respectively)
• A history of structural heart disease

Fig. 3: Fusion beat in ECG