Ventricular Premature Complexes (VPC), also know as ventricular ectopic beats are recognized in the ECG as bizarre QRS complexes not preceded by a P wave and followed by a compensatory pause. The interval between the previous QRS and and ectopic beat is known as the coupling interval. Usually the coupling interval is constant if the ectopic beats are arising from a single focus. These unifocal ectopic beats are also monomorphic, meaning that they have same morphology in a given lead. Monomorphic ventricular ectopic beats can have varying coupling intervals if they are arising from a parasystolic focus. The compensatory pause after the ventricular ectopic beat is said to be fully compensated, meaning that the sum of the coupling interval and the compensatory pause will be equal to twice the previous RR interval. This is because the sinus cycle is not reset by the retrograde conduction of the ectopic beat. It the sinus cycle is reset by the retrograde conduction, as in atrial ectopic beats, the compensatory pause will be less than fully compensated. If the ventricular ectopic beat occurs between two consecutively conducted sinus beats, it is known as an interpolated ventricular ectopic beat.
Isolated monomorphic ventricular ectopic beats are quite common and most often benign. They usually decrease in frequency and disappear with exercise and reappear during recovery at a critical heart rate. When ventricular ectopy is associated with structural heart disease and ventricular dysfunction, they may be the forerunners of ventricular tachycardia. If three or more ventricular ectopic beats occur in a sequence at a rate above 100 per minute, it is known as non-sustained ventricular tachycardia. A sequence of three ventricular ectopics in a row is also known as a salvo.
Very frequent ventricular ectopics, ectopics occurring in couplets and salvos and very premature ectopics leading on to R-on-T phenomenon are likely to proceed on to ventricular tachycardia / fibrillation and hence considered potentially malignant. Multiform ventricular ectopy indicating several irritable foci are also likely to be dangerous.
Frequent ventricular ectopy can lead to left ventricular dysfunction and tachycardiomyopathy due to dyssynchrony during the abnormal activation sequence, in rare cases. Hence there is a view that very frequent ventricular ectopy need electrophysiologic mapping and radiofrequency catheter ablation.