Vectorcardiographic analysis of ventricular tachycardia.

From a study of 69 patients with ventricular tachycardia using digitised vectorcardiograms, it is suggested that the following features are evidence of a ventricular origin. 1. Anterior QRS predominantly in the left anterior quadrant. 2. Slow initial tangential QRS velocity greater than or equal to 20 ms in the presence of an anterior QRS monophasic loop. 3. QRS totally in the right posterior quadrant. 4. In the presence of a QRS in the left posterior quadrant slow anterior QRS initial forces lasting greater than or equal 20 ms in the horizontal plane. The following features are suggestive of a ventricular origin. 1. Slow initial tangential QRS velocity greater than or equal to 20 ms in the presence of an anterior QRS loop resembling right bundle branch block (RBBB). 2. Anterior monophasic QRS loop with counterclockwise rotation. 3. Slow initial QRS forces posteriorly (TV of first 40 ms less than 10 mV . s-1) in the presence of a QRS loop in the left posterior quadrant. 4. A vertical right QRS axis greater than or equal to +60 degrees in the presence of a left bundle branch block (LBBB) loop in the horizontal plane and any axis greater than or equal to +90 degrees less than or equal to -160 degrees. The importance of three simultaneous perpendicular leads for recording or arrhythmias is stressed. In addition vectorcardiograms have clearly separated multifocal ventricular tachycardia from multiformity, fusion beats with and without aberration, and bundle branch ventricular tachycardia. It is suggested that further study of the QRS waveform at the initiation and termination of ventricular tachycardia will elucidate the mechanisms and types of tachycardias.