ECG Quiz 18: Interpolated ventricular ectopic beats

ECG Quiz 18: Interpolated ventricular ectopic beats

Interpolated ventricular ectopic beats are recognized as wide bizarre QRS complexes, not preceded by a P wave. These are called interpolated ectopic beats because they are not disturbing the basic sinus rhythm. This usually occurs when the sinus rhythm is slower as in this case where the basic rate is around 60 per minute. Interpolation also implies that the ventricular ectopic beat is not getting conducted up to the sinus node to reset it; nor is it blocking the antegrade conduction of the subsequent sinus beat at the AV node.

If it does so, varying degrees of AV block can occur for the subsequent sinus beat. Sometimes it will manifest just as prolongation of PR interval, while at the other extreme it might totally be non conducted. In that case the ectopic beat will no longer be ‘interpolated’ and there will be a compensatory pause visible. In interpolated ectopic beats, there is no pause at all.