R-on-T Phenomenon

A PVC that occurs early, appearing on top of the T wave, creates an R-on-T phenomenon. This phenomenon can induce ventricular tachycardia or ventricular fibrillation. R-on-T is common in patients with an ischemic myocardium.

ECG Representing R-on-T Phenomenon ⁵⁵

Interpolated Premature Ventricular Contractions

An interpolated PVC occurs when the premature beat does not interfere with the subsequent normal beat or when there is no postextrasystolic pause. This type of PVC has no clinical significance.

Fusion Beat

A fusion beat occurs when the ventricles are simultaneously activated by the PVC and the supraventricular impulses. The QRS morphology is a combination of a supraventricular QRS complex and a ventricular QRS complex. This type of beat is produced during the phase 4 PVCs. It is also a sign of impending ventricular tachycardia, also known as Dressler beats, in parasystole and in accelerated idioventricular rhythm.

Concealed Bigeminy

Concealed bigeminy occurs when an odd number of supraventricular beats occur between the PVCs. When the bigeminy is concealed, it has no clinical implications on the hemodynamics of the patient. Concealed bigeminy is often seen in patients being pharmacologically treated for bigeminy.