Group beating resulting from ventricular parasystole

D. Luke Glancy, MD

From the Section of Cardiology, Department of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana.

Supported by an unrestricted educational grant from The Medical Center of Louisiana Foundation.

Corresponding author: D. Luke Glancy, MD, Section of Cardiology, Department of Medicine, Louisiana State University Health Sciences Center, 1542 Tulane Avenue, Room 436, New Orleans, Louisiana 70112.

This electrocardiogram of a 90-year-old man shows repeating similar cycles, each consisting of 4 complexes (Figure). Every cycle begins with 2 sinus-initiated complexes followed by an early, wide QRS (ventricular premature complex) that has a right-bundle-branch-block configuration and precedes a pause that is terminated by a slightly different, wide QRS. The cycle then repeats itself. What is not readily apparent is that the interval between each ventricular premature complex and the following wide QRS (1.10 seconds) is exactly half the interval between this second wide QRS of each cycle and the ventricular premature complex of the next cycle (2.20 seconds). Furthermore, an interval of 1.10 seconds from the beginning of the last QRS of each cycle lies in the ventricular refractory period of the first sinus-initiated complex of the next cycle (vertical lines above the V₁ rhythm strip). Thus, one can make a good case for a left ventricular, parasystolic focus discharging every 1.10 seconds, with every third impulse failing to capture the ventricles because it arrives in the absolute refractory period.

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