To analyze the prognosis of the sick sinus syndrome (SSS), we compared the clinical aspects among unpaced, ventricular paced, and physiologically paced patients who were followed over a long period. Unpaced intrinsic SSS was not always progressive and patients did not necessarily require permanent pacing. The incidence of concomitant AV conduction disturbance was 65.6% before pharmacologic autonomic block, (PAB), but this was significantly reduced to 31.7% after PAB. Follow-up study of the physiologically paced groups revealed no development of either new or more than second degree AVB. The VVI group had significantly more complications (68%) than the physiologically paced groups, mainly chronic atrial fibrillation (36%) and thromboembolism (20%). In addition, cardiothoracic ratio (CTR) in the VVI group was significantly greater compared with that in the physiologic groups. Nine deaths occurred during the follow-up period in the pacing groups, including six with VVI and three with physiologic pacing. In the VVI pacing group, heart failure and thromboembolism were most commonly the causes of death, while in the physiologic pacing groups, the causes of death were noncardiac. Although the survival rate in the ventricular paced group was not significantly different from that in the physiologic pacing groups, cardiac deaths were fewer in the latter group. Considering our clinical data, the decision to use ventricular pacing needs to be carefully weighed in patients with sick sinus syndrome, and physiologic pacing is more highly recommended.
Abstract-The effects of a large amount of adenosine and ATP (100 to 3000 ug) were investigated on sinus rate and developed tension, using the isolated dog atrium which was perfused with arterial blood from a heparinized donor dog. Each of the substances used for study was administered into the cannulated sinus node artery of the isolated atrium. Adenosine caused monophasic negative chronotropic and inotropic effects in a dose related manner. However, ATP induced two-peaked positive chronotropic phases during a long-lasting negative chronotropic phase, i.e., initially, brief positive (t-1) effects and secondarily, relatively longer positive chronotropic (t-2) effects. These responses were repetitively induced during the experiment. The t-1 and t-2 were not influenced by treatment with propranolol which significantly blocked the positive chronotropic effect of norepinephrine. Aminophylline treatment significantly suppressed t-2 but not t-1. Quinidine (100-1000 ug) did not affect either the t-1 or t-2. It is suggested that ATP induced tachycardia in the dog is partially due to activation of the P1-purinoceptors named by Burnstock.
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