Atrial and ventricular pacing after open heart surgery

The effect of cardiac pacing, through a wide range of pacing rates, has been studied in 13 patients in stable sinus rhythm within 24 hours of operation. Using first atrial and then ventricular pacing, the cardiac rate was raised to 60% above control value. The effects of atrial and ventricular pacing were compared by observing the differences in the various parameters measured at corresponding paced heart rates. With atrial pacing there was no significant difference in the cardiac output, mean aortic pressure, mean left atrial pressure, or left ventricular work. During ventricular pacing there were significant falls in cardiac output (p<0·05), mean aortic pressure (p<0·01), and left ventricular work (p<0·01). There was a significant rise in mean left atrial pressure (p<0·01). In this study atrial pacing had no significant effect on the parameters measured, through a wide range of cardiac rates. An inotropic effect resulting from increase of rate was not seen. Reported increases in cardiac output following pacing must therefore have resulted from correction of a dysrhythmia. Ventricular pacing incurs a definite haemodynamic penalty if used in patients with an intact atrioventricular conducting pathway. If atrial pacing is not available, this penalty must be balanced against the possible haemodynamic advantage of suppressing a dysrhythmia.