Standardized Comparison of Cardioplegic Methods in the lsolated Paracorporeal Dog Heart

Summary

The protective properties of St. Thomas' Hospital cardioplegic solution (ST-CP) and Bretschneider's histidine buffer cardioplegic solution (B-CP) were compared in an isoiated paracorporeal dog heart model. Two groups of 6 hearts each were subjected to 120 min of cardioplegic arrest at 20 °C, induced by 1000 ml of ST-CP and 3000 ml of B-CP.

Postischemic left ventricular function was significantly different in the 2 groups. After 20 min reperfusion and at 20 mmHg enddiastolic pressure, developed left ventricular pressure recovered 98.8% of preischemic control values in the B-CP group as compared to 66.4 % in the ST-CP group and peak left ventricular dp/dt recovered 95.5% and 68.6% of control, respectively. Diastolic left ventricular wall stiffness showed a more pronounced postischemic rise in the ST-CP group, measured as an 18% increase in diastolic pressure/volume ratio at 20 mmHg diastolic pressure, this increase being 6 % in the B-CP group.

Neither lactate metabolism nor myocardial enzyme release differed significantly between the groups.

The critical importance of cardioplegic washout was illustrated in a third group of 6 hearts, subjected to transaortic perfusion with cold (20 °C) arterial blood at a rate of 0.4 ml/100 g min over a 100 min period during 2 hours of cardioplegic arrest by St. Thomas' solution. Left ventricular function was preserved significantly better in this group than in the ST-CP hearts without washout. Left ventricular developed pressure and peak dp/dt recovered 84.8% and 87.8%, respectively, of preischemic control values.

It is concluded, that myocardial protection by B-CP is superior to that by ST-CP in dog hearts under standardized experimental conditions. Noncoronary collateral blood flow producing cardioplegic washout in studies with the heart in situ may conceal different protective properties of cardioplegic methods.

Key words

Cardioplegic arrest - Postischemic left ventricular funetion - Extracoronary collateral myocardial blood flow