Effect of increasing heart rate in patients with aortic regurgitation. Effect of incremental atrial pacing on scintigraphic, hemodynamic and thermodilution measurements.

This study was performed to assess the effect of pacing-induced tachycardia in patients with aortic regurgitation. In 12 patients (5 men and 7 women with a mean age of 53 years) with aortic regurgitation, left ventricular end-diastolic and end-systolic volume indexes were measured with multigated equilibrium blood pool imaging, and forward cardiac index was determined with thermodilution, both at rest (mean heart rate +/- standard deviation 72 +/- 8 beats/min) and during atrial pacing at 100 and 120 beats/min. Pacing caused a decremental reduction in left ventricular end-diastolic and end-systolic volume indexes and radionuclide-determined stroke volume index but no change in radionuclide-determined cardiac index or left ventricular ejection fraction. Forward cardiac index increased incrementally from the baseline value at rest to that at 120 beats/min despite a decremental reduction in stroke volume index. There was a stepwise decrease in regurgitant volume/stroke (46 +/- 20 ml/m2 at baseline, 27 +/- 15 at 120 beats/min; p less than 0.05) but no change in regurgitant volume/min (3.38 +/- 1.80 liters/min per m2 at baseline, 3.22 +/- 1.78 at 120 beats/min; difference not significant [NS]) or regurgitant fraction (0.54 +/- 0.13 at baseline, 0.49 +/- 0.13 at 120 beats/min; NS). Mean femoral arterial, pulmonary arterial and pulmonary capillary wedge pressures did not change with pacing.