The Changes in Cardiac Output with Reversion of Atrial Fibrillation to Sinus Rhythm.

ONE of the aims in reverting atrial fibril-lation to sinus rhythm is to improve cardiac function. Previous studies comparing the cardiac output during atrial fibrillation and following the restoration of sinus rhythm have demonstrated no change to as much as 140 per cent increase.1-3 Because of the experimental design of these studies, the validity of the observation that an increase in cardiac output was due to change in rhythm alone is questionable. It therefore seemed timely to restudy the changes in cardiac output with the change from atrial fibrillation to sinus rhythm under resting and exercise conditions. By use of the technic of car-dioversion and with modification of the experimental design some of the objections of former studies can be overcome, and the observation can be more readily attributed to changes in rhythm alone. Method Twelve patients were included in this study. The clinical information pertinent to the group is shown in table 1. The age of the patients ranged from 19 to 66 years. Six had rheumatic heart disease , five ischemic heart disease, and one post-operative congenital heart disease. The duration of the episode of atrial fibrillation treated in this study varied from 4 months to 17 years. All were on steady daily doses of various digitalis preparations and had adequate control of the ventricular rate. The functional classifications (New York Heart Association) were as follows: two patients class I, six patients class II, and four patients class III. The patients were observed in the hospital several days after attaining a stable weight and being edema-free. All were free from clinical evidence of congestive heart failure at rest during this period. Hyperthyroidism was excluded in each patient by suitable laboratory tests. Cardioversion, as described by Lown and as-sociates14 was used to revert atrial fibrillation to sinus rhythm. Quinidine therapy for maintenance of normal sinus rhythm was not instituted before or after reversion to sinus rhythm until the completion of our observations. Cardioversion was accomplished with a commercially available direct current defibrillator.* The procedure was carried out under light thiobarbiturate anesthesia (sodium thiamylal); the dosage varied from 160 to 300 mg. In eight patients succinyl choline was also used in doses from 60 to 160 mg. The time of anesthesia, from induction to full recovery, varied from 12 to 30 minutes, the average time being 20.5 minutes. Nothing by mouth was allowed for 7 hours prior to the study. …