Left ventricular pressure-volume relations shift to the left after long-term loss of pericardial restraint

The short-term effect of pericardiectomy is to shift the in vivo left ventricular (LV) pressure-volume curve to the right. We studied nine weight-matched pairs of male guinea pigs 28 to 39 days (mean 35) after complete pericardiectomy or sham thoracotomy to determine the long-term effects of pericardiectomy on LV pressure-volume relations. Hemodynamic and in vitro LV pressure-volume data were collected in matched pairs on the same day, 2 to 3 hr after catheter placement and recovery from anesthesia. Cardiac output was measured by the microsphere reference sample method. Postsurgical weight gain was similar in both groups: 823 +/- 6 (mean +/- SD) to 925 +/- 6 g in the pericardiectomy group and 829 +/- 7 to 927 +/- 7 g in the sham thoracotomy group. We found no difference in LV weight: 1.555 +/- 0.145 g in the pericardiectomy group vs 1.564 +/- 0.148 g in the sham thoracotomy group, nor any difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, cardiac outputs, or stroke volumes (p = NS). LV pressure-volume relations, however, were shifted to the left in the pericardiectomy group (p less than .005). At 10 mm Hg, LV volume in the pericardiectomy group (0.85 +/- 0.22 cc) was less than that in the sham thoracotomy group (1.02 +/- 0.15 cc; p less than .025). The LV stress-elastic modulus relationship was not different between groups (p greater than .30). One month after pericardiectomy, LV pressure-volume relations in vitro were shifted to the left without a change in LV weight, LV elastic modulus, or hemodynamics. We speculate that this shift compensates for the lack of pericardial restraint and returns LV volume and hemodynamics to normal in vivo.