Minute Volume Determinations in Mitral Stenosis During Auricular Fibrillation and when Restored to Normal Rhythm

Abstract

Lewis, 1 using dogs and cats, was able to demonstrate that the minute output of the heart was decreased about 20% when the auricles were caused to fibrillate by faradic stimulation. He made the observation also that the more rapid the ventricular rate, the greater the decrease in minute volume.

Eyster and Swarthout, 2 in similar experiments on dogs, were able to produce a decrease in minute volume of from 15-79% when the auricles were caused to fibrillate. The ventricular rate in their experiments was increased after fibrillation was induced so that the actual decrease in minute volume cannot be entirely attributed to the fibrillation of the auricles.

Smith, Walker and Alt 3 found that the minute volume increased approximately 30% when normal rhythm was restored by quinidine in cases of auricular fibrillation which had been previously compensated by digitalis. Realizing that in mitral stenosis auricular contraction plays an appreciable role in the filling of the left ventricle, we used only mitral stenosis cases in our series. The experiments were carried out as follows: Four cases of mitral stenosis with auricular fibrillation, some of which were decompensated, were treated with digitalis until well compensated and until the ventricular rate was between 60 and 70 per minute. These cases were kept on digitalis and this rate was maintained for some period of time before the actual measurements of minute volume were begun. These were done by the acetylene method as advocated by Grollman. 4 Decompensated cases became well compensated under the regime and in these cases, minute volume determinations were not begun until the vital capacity had reached its highest level. Then the minute volume was determined in each case and repeated until the volumes checked. Continuing the digitalis at its maintenance level, quinidinization was then begun. After regular rhythm had been established and the amount of quinidine had been reduced to a maintenance dose, several days were allowed to elapse. Minute volumes were again determined and repeated until satisfactory checks were obtained.

Using this method in 4 cases, we found that the increase in minute volume when regular rhythm was restored was from 22% to 40% with an average of 30.8%.