Changes in sinus function at rest and during physical exertion after permanent atrial electrostimulation in patients with sick sinus syndrome

: We studied the unnatural history of sinus node function in severe sick sinus syndrome treated with AAI or DDD pacemakers. In 19 patients (10 m; 9 f; mean age +/- 1 SD 69 +/- 7 years) we executed serial bicycle exercise tests and electrophysiological studies before, 7 days and 3 months after pacemaker implant. Sinus heart rate at maximum effort was: 118 +/- 23 beats/min and 117 +/- 23 beats/min (two different evaluations) before pacemaker implant, 125 +/- 21 beats/min after 7 days (p less than 0.05) and 133 +/- 20 beats/min after 3 months (p less than 0.001) with an average increment of 12.7%. A positive correlation (y = 50.4 + 0.7 X beats/min; p less than 0.001) between the first basal test and the third month one was found. In analogy exercise test lasted 8.7 +/- 3, 8.6 +/- 2.8, 9.5 +/- 2.5, 9.7 +/- 2.5 minutes respectively, with an average increment of 11.5% between the first basal test and the third month one. Sinus heart rate at maximum effort in 14 age matched normal subjects was 138 +/- 15 beats/min. The difference with sick sinus syndrome patients was statistical (p less than 0.05) when compared with the basal test but not with 3rd month test. Parameters determined during electrophysiological studies were: spontaneous heart rate, corrected sinus node recovery time, sino-atrial conduction time evaluated before and after autonomic blockade (propranolol 0.2 mg/kg i.v. plus atropine 0.04 mg/kg i.v.). All these parameters, excepting basal corrected sinus node recovery time, improved significantly after pacemaker implant.(ABSTRACT TRUNCATED AT 250 WORDS)