Ventricular arrhythmias originate from a focus of myocardial or Purkinje cells capable of automaticity, or triggered automaticity, or from reentry through areas of scar or a diseased Purkinje system. They are characterized by their electrocardiographic appearance and duration. Conduction away from the ventricular focus through the ventricular myocardium is slower than activation of the ventricles over the Purkinje system. Hence, the QRS complex during ventricular arrhythmias will be wide, typically >0.12 s.
Premature ventricular beats (also referred to as a premature ventricular contraction or PVC) are single ventricular beats that fall earlier than the next anticipated supraventricular beat (Fig. 247-1). PVCs that originate from the same focus will have the same QRS morphology and are referred to as unifocal (Fig. 247-1A). PVCs that originate from different ventricular sites have different QRS morphologies and are referred to as multifocal (Fig. 247-1B). Two consecutive ventricular beats are ventricular couplets.
A. Unifocal premature ventricular contractions (PVCs) at bigeminal frequency. Trace shows ECG lead 1 and arterial pressure (Art. Pr.). Sinus rhythm beats are followed by normal arterial waveform. The arterial pressure following premature beats is attenuated (arrows) and imperceptible to palpation. The pulse in this patient is registered at half the heart rate. B. Multifocal PVCs. The two PVCs shown have different morphologies. C. Example of accelerated idio-ventricular rhythm (see text for details).
Ventricular tachycardia (VT) is three or more consecutive beats at a rate faster than 100 beats/min. Three or more consecutive beats at slower rates are designated an idioventricular rhythm (Fig. 247-1C). VT that terminates spontaneously within 30 s is designated non-sustained (Fig. 247-2) whereas sustained VT persists >30 s or is terminated by an active intervention, such as administration of an intravenous medication, external cardioversion, or pacing or a shock from an implanted cardioverter defibrillator.
Repetitive monomorphic non-sustained ventricular tachycardia (VT) of right ventricular outflow tract origin. The VT has a left bundle branch block pattern with inferior axis with tall QRS complexes in the inferior leads.
Monomorphic VT has the same QRS complex from beat to beat, indicating that the activation sequence is the same from beat to beat, and that each beat likely originates from the same source (Fig. 247-3A). The initial site of ventricular activation largely determines the sequence of ventricular activation. Therefore, the QRS morphology of PVCs and monomorphic VT provides an indication of the site of origin within the ventricles (Fig. 247-4). The likely origin often suggests whether an arrhythmia is idiopathic or associated with structural disease. Arrhythmias that originate from the right ventricle or septum result in late activation of much of the left ventricle, thereby producing a prominent S-wave in V1 referred to as a left bundle branch ...