The Effect of Overdrive Pacing Rate and Duration on Ventricular Escape Rhythms in Patients with Chronic Complete Atrioventricular Block

The effect of overdrive (OD) pacing rate and duration on subsidiary pacemakers was evaluated in 54 patients with third‐degree AV block. They had a permanent pacemaker implanted 61 ± 56 months earlier because of complete AV block in 38 patients and, in 16 patients because of second‐degree AV block, which in the interim advanced to complete AV block. The patients had a reliable infranodal escape rhythm, with a mean cycle length of 2,022 ± 603 msec, upon discontinuation of the ventricular OD pacing, at a rate of 40 beats/min. The escape interval and escape rhythm cycle length was evaluated after OD pacing at 40, 50, 60, 70, 80, 90, and 100 beats/ min for 30 seconds, at each rate. In 100% of the patients the subsidiary pacemaker recovered after OD pacing at 40 and 50 beats/min and the number decreased to 59% at a rate of 100 beats/min. The escape interval prolonged gradually between OD pacing at 40 and 100 beats/min, by 56%. The effect of OD pacing duration at 50 and 70 beats/min was evaluated. At an OD pacing rate of 70 beats/min there was a significant effect of the pacing duration on the escape interval. There were significant differences in the escape interval duration and escape rhythm cycle length between males and females, patients with or without coronary artery disease, and patients with narrow or wide QBS escape. However, the increase in the OD pacing rate had a similar effect on the escape interval in the above mentioned groups. There was no effect on the paced QRS duration and sinus cycle length at each OD pacing rate. In nine patients premature escape beats were present after OD pacing at 80 and 90 beats/min. In conclusion, OD pacing may suppress the infranodal subsidiary pacemakers originating at the proximal conduction system or from a ventricular site and this effect depends on the pacing rate and duration. An OD pacing at a rate of 50 beats/min or less has minimal or no effect on these inherent pacemakers. Overdrive stimulation in the form of premature escape beats is present in 17% of the patients.