Circulatory Consequences of Changes in Cardiac Rhythm Produced in Patients by Transthoracic Direct-Current Shock*

Most arrhythmias have long been regarded as undesirable.The salutary clinical consequences of abolishing ventricular and atrial tachycardias are often immediately apparent, and, in general, the circulatory disadvantages of an inappropriately rapid ventricular rate in man would seem well accepted.The effect on the circulation of atrial arrhyth- mias without tachycardia, particularly atrial fibrillation, however, is not clear.Lower cardiac outputs have been reported in groups of patients with rheumatic heart disease and atrial fibrillation than in those with sinus rhythm (1, 2).Studies of the same patients first with atrial fibrillation and later in sinus rhythm after quinidine con- version have been reported by several investiga- tors (3-7).Of the 35 patients in two of these studies in which only mean data are presented (4, 7), the majority of patients had increased outputs after conversion.Of the 27 patients in the other three studies (3, 5, 6), the output was increased at rest after conversion in eighteen and was unchanged or less in nine.In the two studies in which heart rates were available (4, 5), no rates of over 100 in atrial fibrillation were found.In published data, therefore, it is evident that restoration of sinus rhythm with quinidine does not regularly result in an increased cardiac output when measurements are made days to weeks after conversion.