Intermittent manifestation of ventricular preexcitation with right bundle branch block induced by interpolated ventricular premature contractions: A report of 3 cases.

Electrocardiographic (ECG) analysis becomes challenging in the presence of concurrent ventricular preexcitation (WPW) and right bundle branch block (RBBB) due to their mutually interfering ECG manifestations. Interpolated ventricular premature contractions (IPVCs) can transiently alter the conduction velocity and refractory period of the WPW accessory pathway and the His-Purkinje system, thereby leading to intermittent manifestation of WPW or RBBB. In Case 1 and Case 2, IPVCs converted sinus beats from the WPW + RBBB pattern to the pure RBBB pattern; in Case 3, sinus beats after IPVCs changed from the pure WPW pattern to the WPW + RBBB pattern. Full utilization of such valuable dynamically emerging information, together with a thorough and systematic examination of the ECG including the dissection of the initial, middle, and terminal electrical forces of the QRS complex, is crucial for an accurate diagnosis.