Ventricular bigeminy

Ventricular bigeminy

Ventricular premature complexes are seen alternating with normal sinus complexes in ventricular bigeminy. VPCs are identified as bizarre QRS complexes not preceded by P waves and occurring before the expected P wave in a premature fashion. In this tracing the normal P waves originating from the sinus node are seen as small humps in the ST segments of the VPC.

Clinical findings in ventricular bigeminy

In this case, as P waves during the VPC are occurring when the atrioventricular valves are closed due to ventricular systole of the VPC, they will produce regular cannon waves in the jugular venous pulse at a rate half that of the ventricular rate. The pulse will be showing a patterned irregularity in the form of pulsus bigeminus. The premature pulse will have a lower volume compared to the sinus beat because of reduced time for ventricular filling. Sometimes the pulse may not be felt during the VPC so that it may appear as a bradycardia. This can occur if the beat is so premature that the ventricular contraction is not forceful enough to open the aortic valve. In that situation the first heart sound is not followed by a second heart sound as the aortic valve remains closed through out that cardiac cycle. Ventricular premature beats are the commonest cause of cannon waves as they are much more frequent in incidence than complete heart block which is the more well known cause for cannon waves in the jugular venous pulse.