Improving the physiological realism of experimental models.
Effects of crystalloid buffer and blood-buffer perfusates on cardiac electrophysiological parameters were compared in four groups of isolated, working rabbit hearts. Hearts were perfused with Krebs-Henseleit buffer or blood plus Krebs-Henseleit buffer (10% hematocrit) over a range of left ventricular afterload (30-100 cmH2O) and cardiac outputs (30-180 ml/min). Left ventricular monophasic action potential duration (APD) was significantly shorter at low afterload and high cardiac output in buffer-perfused (114 +/- 35 ms) compared with blood-perfused hearts (177 +/- 23 ms, P < 0.001). APD shortened in blood-perfused hearts after an increase in afterload to 100 cmH2O (P < 0.05), and APD was similar in blood-perfused (151 +/- 19 ms) compared with buffer-perfused hearts (142 +/- 24 ms, P = NS). Ventricular effective refractory period (VERP) was significantly shorter at low afterload in buffer-perfused (154 +/- 32 ms) compared with blood-perfused hearts (227 +/- 17 ms, P < 0.001). VERP shortened in blood-perfused hearts after an increase in afterload to 100 cmH2O (P < 0.05) and was similar in blood-perfused (166 +/- 26 ms) compared with buffer-perfused hearts (151 +/- 37 ms, P = NS). Determination of VERP was associated with induction of ventricular fibrillation in 10 of 15 buffer-perfused hearts, whereas ventricular fibrillation was not observed in blood-perfused hearts (P < 0.001). Thus significant differences in ventricular repolarization and cardiac hemodynamics are observed in working rabbit hearts perfused with a blood-buffer perfusate compared with a crystalloid buffer. Blood-perfused working hearts are electrophysiologically more stable.