Reproducibility of clinical and hemodynamic parameters during pacing stress testing in patients with angina pectoris.

The reproducibility of clinical and hemodynamic events during two successive pacing periods separated by a 20-minute interval was evaluated in 33 patients with stable angina pectoris. Continuous pacing with stepwise increase in pacing rate was assessed in 19 patients and discontinuous pacing in which pacing was temporarily interrupted at each rate was evaluated in the other 14 patients. During continuous pacing, the group values for pacing rates that induced angina, the pacing time to angina, ST-segment depression, rate-pressure product, cardiac output and left ventricular end-diastolic pressure (LVEDP) were similar during the two pacing periods, but postpacing LVEDP was lower after the second pacing period (p < 0.05). During the second pacing period, angina could not be reproduced at the same pacing rates in four patients and postpacing LVEDP varied by 5 mm Hg or more in 10 of the 19 patients. During discontinuous pacing, the group mean values for pacing rates that induced angina and the pacing time to angina were higher (p < 0.05), and cardiac output lower (p < 0.05) during the second pacing period, while rate-pressure product, ST-segment depression, and LVEDP were similar during the two pacing periods. During the second pacing study, angina could not be induced at the same pacing rates in six patients and the postpacing LVEDP varied by 5 mm Hg or more in three of the 14 patients. The results show that continuous pacing is preferable to discontinuous pacing. With continuous pacing, the group values for the clinical and many of the hemodynamic parameters were reproducible. We recommend the demonstration of the reproducibility of events during pacing in studies in which the effects of therapeutic interventions are being assessed, especially in a small number of patients.