Delay of onset of second degree pacemaker block by beta-blockade in patients with P-synchronous pacemakers

Second degree pacemaker block is a safety mechanism of the synchronous pacer at atrial rates above 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 y.) were submitted to graded, submaximal exercise on a bicycle ergometer without drug and after 0.8 mg pindolol i.v. (6 pats.) or alprenolol orally (1 pat.). Pacemaker block developed at much higher total work after beta-blockade in 3 patients (5800 vs. 1900 kpm. p less than 0.0005), while 4 patients had to stop work due to exhaustion before pacemaker block occurred. Total work increased significantly after beta-blockade (p less than 0.005). Lack of a stable i.v. atrial electrode has delayed the extensive use of the synchronous pacemaker. The design of the generator, however, is not optimal 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. It is suggested that 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.