Acute effects of external and internal pacing on ejection fraction in patients with severe cardiac failure.

The present study aims at evaluating the acute hemodynamic effects of external and internal (3 and 15 mA) pacing on 30 patients with severe cardiac failure. The global and regional ejection fraction were calculated by repeated radionuclide ventriculography at rest (control) and during increasing pacing rates. Blood pressure was measured at the end of each scintigraphy data acquisition period. The pacing rate was increased by 10 beats/min in every step and varied between +10 to +60 beats/min above the resting heart rate. The ejection fraction during pacing was lower than the resting ejection fraction in every pacing mode (resting ejection fraction = 23.30 +/- 7.67%, external pacing = 19.36 +/- 9.30%, p < 0.05, internal pacing 3 mA = 22.15 +/- 7.00%, p = N.S., internal pacing 15 mA = 19.92 +/- 6.95%, p < 0.05). The resting ejection fraction was higher than the ejection fraction in every pacing rate. In 4 out of 30 patients the ejection fraction was higher in every pacing mode and rate than the resting ejection fraction. The regional ejection fraction of the interventricular septum during internal pacing was lower (p < 0.001) than resting and/or external pacing. In conclusion, pacing in patients with severe cardiac failure reduces the control ejection fraction. This reduction increases as the pacing rate increases. The reduction is greater with internal pacing of 15 mA while the hemodynamic effect in external pacing did not differ significantly from internal pacing. Overall, the resting ejection fraction was higher than the paced ejection fraction, although in some patients pacing improved their resting ejection fraction.