VPC in trigeminy
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The lower lead II rhythm strip shows wide QRS complexes for every third beat, without a preceding P wave and followed by a compensatory pause, characteristic of ventricular premature complexes (VPC). The ST depression and T wave inversion are repolarization abnormalities secondary to the abnormal sequence of activation of the VPC. The QRS is wide and bizarre because of the slow and abnormal sequence of depolarization which is occuring throught the ventricular myocardium rather than the fast conducting system of the heart. The QRS complexes of the VPC have a left bundle branch block pattern suggesting a right ventricular origin. The VPCs are positive in inferior leads, indicating origin from the right ventricular tract, the common site of origin of most benign VPCs. The pulse in this case will be in groups of three and called pulsus trigeminus. The third pulse in the group will have a lower volume while the pulse after the pause will have a higher volume to due to long period of diastolic ventricular filling. Sometimes the premature beat may not have a pulse if it is too premature because the ventricular contraction may not be forceful enough to open the aortic valve. In such a situation, the aortic component of second heart sound will be absent. If both semilunar valves fail to open, the second heart sound will be absent during that cycle.