An improved isolated heart preparation for external assessment of myocardial metabolism

To facilitate characterization of myocardial metabolism with the use of positron-emitting tracers, we developed an isolated heart preparation designed to simulate physiological levels of flow and substrate extraction. Isovolumically beating hearts were perfused retrograde at 60 mmHg with modified non-recirculating Krebs-Henseleit (KH) solution with or without washed sheep red blood cells at a hematocrit of 25 or 40 (KH-RBC25, KH-RBC40). Left ventricular (LV) systolic pressure averaged 63 mmHg with KH alone, 78 with KH-RBC25, and 98 with KH-RBC40. LV dP/dt, pressure-time index, and oxygen consumption increased in an analogous fashion. Fatty acid extraction increased from 1.5% with KH to 11.8% in hearts perfused with KH-RBC40, although net uptake was not increased markedly because of the associated differences in flow (4.6 ml.g-1.min-1 with KH and 1.5 with KH-RBC40). Hearts perfused with erythrocyte-rich media exhibited functional and metabolic stability and less edema. The preparation avoids intrinsic limitations encountered with buffer-perfused hearts and should prove useful for characterization of cardiac metabolism with radiolabeled tracers relevant to positron emission transaxial tomography.