Ventricular premature beats and recognition of fusion beats
THE CONTEXT
Ventricular premature beats (VPBs)* occur in healthy people and in patients with heart disease. Their significance depends on whether underlying heart disease is present.
Occurrence and symptoms
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VPBs are frequent in healthy people, and prevalence increases with age. In otherwise normal hearts, ectopic beats are more prominent at rest and disappear with exercise.
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VPBs may indicate subclinical coronary artery disease or cardiomyopathy, or occur in established heart disease after myocardial infarction.
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Most patients are asymptomatic. Symptoms can include irregular or missed beats, fatigue and light-headedness.
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An abnormally strong beat results from increased cardiac output of the post-ectopic sinus beat.
Pulse and ECG findings
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The pulse may be irregular with weak or missed beats. Premature left ventricular contraction occurs before filling is complete, reducing stroke volume.
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Sequential rather than simultaneous ventricular activation produces broad, bizarre QRS complexes.
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Unifocal beats have identical morphology and arise from one ectopic focus; multifocal beats have varying morphology and arise from multiple foci.
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A couplet consists of two successive ectopic beats, and a triplet consists of three. Ventricular bigeminy is an alternating sequence of sinus and ventricular ectopic beats.
Capture and fusion beats in ventricular tachycardia
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Ventricular tachycardia has independent atrial and ventricular activity. An occasional atrial impulse conducted through the atrioventricular node may produce a normal sinus beat within the tachycardia, called a capture beat.
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More commonly, the conducted impulse combines with an impulse from the tachycardia to produce a fusion beat. Fusion requires atrioventricular dissociation and is diagnostic of ventricular tachycardia.