Delay of Onset of Second Degree Pacemaker Block by Beta‐Blockade in Patients with P‐Synchronous Pacemakers

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Abstract
Second degree pacemaker block is a safety mechanism of the synchronous pacer at atrial rates > 120-130. The aim of the present study was to determine the work level at which pacemaker block occurred before and after .beta.-blockade. Seven patients (mean age 53 yr) were submitted to graded, submaximal exercise on a bicycle ergometer without drug and after 0.8 mg pindolol i.v. (6 patients) or alprenolol orally (1 patient). Pacemaker block developed at much higher total work after .beta.-blockade in 3 patients (5800 vs. 1900 kpm [kilopound meter], P < 0.0005), while 4 patients had to stop work due to exhaustion before pacemaker block occurred. Total work increased significantly after .beta.-blockade (P < 0.0005). Lack of a stable i.v. atrial electrode has delayed the extensive use of the synchronous pacemaker. The design of the generator is not optimal as the upper escape rate at which pacemaker block occurs is too low for a number of patients. .beta.-Blockade effectively delays the occurrence of pacemaker block and can be of therapeutic value. The P-synchronous pacer should be redesigned with a programmable basic rate (50-70 beats/min) and a programmable upper rate (130-180 beats/min) to ensure that the obvious physiologic advantages of the atrial triggered pacemaker can be maintained both at rest and during physical exercise.