ALTERATIONS IN LEFT-VENTRICULAR RELAXATION DURING ATRIOVENTRICULAR PACING IN HUMANS

To determine whether the asynchronous left ventricular contraction-relaxation sequence that exists during right ventricular pacing alters left ventricular relaxation, measurements of both the maximal rate of decline of left ventricular pressure (peak negative dP/dt) and the time constant of left ventricular relaxation were obtained during atrial and atrioventricular (AV) pacing in 25 patients referred for diagnostic cardiac catheterization. Heart rate was maintained at 10 to 15 beats/min above the sinus rate at rest, and relaxation was assessed during atrial pacing, AV pacing and repeat atrial pacing. The patients were classified into two groups. Group 1 included 10 patients with normal left ventricular systolic function at rest (ejection fraction >0.55) and without evidence of prior myocardial infarction. Group 2 included 15 patients with a depressed left ventricular ejection fraction or akinesia of one or more left ventricular segments on the contrast ventriculogram, or both. Heart rate, peak left ventricular systolic pressure, end-systolic pressure and end-diastolic pressure remained constant during atrial, AV pacing and repeat atrial pacing in all patients. In group 1 patients, the decrease in peak negative dP/dt (1,507 ± 200 versus 1,424 ± 187 mm Hg/s) and the increase in the time constant of left ventricular relaxation (48 ± 11 versus 51 ± 11 ms) during AV pacing was not significantly different when compared with values during atrial pacing. In group 2 patients, peak negative dP/dt decreased from 1,358 ± 333 during atrial pacing to 1,222 ± 240 mm Hg/s (p < 0.0005) during AV pacing, and the time constant of left ventricular relaxation increased from 59 ± 8 to 71 ± 15 ms (p < 0.0001). Maximal rate of rise of left ventricular pressure (peak positive dP/dt) also decreased during AV pacing in patients in group 1 (1,499 ± 310 to 1,381 ± 261 mm Hg/s; p < 0.0005) and group 2 (1,385 ± 271 to 1,233 ± 231 mm Hg/s; p < 0.0005). These results suggest that the asynchronous contraction-relaxation sequence that occurs during right ventricular pacing alters left ventricular relaxation in patients with abnormal left ventricular systolic function. © 1990.