Acute hypercalcemia and increased work load in canine transplanted heart. Coronary blood flow adjustments

Coronary vasodilator adjustments following cardiac transplantation might be adversely affected during severe rejection. We studied the coronary blood flow response following intravenous bolus administration of calcium (0.04-0.05 mEq/kg) in canine cardiac transplants. Fifteen dogs were submitted to orthotopic heart transplantation and equipped with electronic implants for monitoring of hemodynamic parameters. Of these animals, 9 were not immunosuppressed, while 6 were treated with ciclosporin, azathioprine, and prednisone. The effects of calcium administration upon cardiac function were evaluated during the postoperative period, at recovery (2-3 days after transplantation) and during severe rejection (7-10 days after transplantation), and also in immunosuppressed animals. Rapid calcium administration elicits brief increases in arterial pressure, cardiac index, stroke work, and coronary blood flow. There were significant differences in these effects, depending on the hemodynamic status of these animals. Coronary blood flow was significantly increased in all experiments, except when severe rejection was evidenced. These results indicate that changes in myocardial metabolic demand (work load) are not adequately matched with coronary blood flow adjustments in the presence of severe rejection.