Arrhythmias that originate in the ventricular myocardium or His-Purkinje system include premature ventricular beats, ventricular tachycardias that can be sustained or nonsustained, and ventricular fibrillation. Arrhythmia may emerge 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. Ventricular arrhythmias are often associated with structural heart disease and are an important cause of sudden death (Chap. 35). They also occur in some structurally normal hearts, in which case they are usually benign. Evaluation and management are guided by the risk of arrhythmic death, which is assessed based on symptoms, type of arrhythmia, and associated underlying heart disease.
Ventricular arrhythmias 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 premature ventricular contractions [PVCs]) are single ventricular beats that fall earlier than the next anticipated supraventricular beat (Fig. 18-1). PVCs that originate from the same focus will have the same QRS morphology and are referred to as unifocal (Fig. 18-1A). PVCs that originate from different ventricular sites have different QRS morphologies and are referred to as multifocal (Fig. 18-1B). Two consecutive ventricular beats are ventricular couplets.
A. Unifocal PVCs follow every sinus beat in a bigeminal frequency. Trace shows electrocardiogram 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 idioventricular rhythm. The second QRS is a normally conducted beat. All other QRS complexes on this rhythm strip are ventricular due to accelerated idioventricular rhythm.
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. 18-1C). VT that terminates spontaneously within 30 s is designated nonsustained (Fig. 18-2), whereas sustained VT persists longer than 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 nonsustained 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.
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