Myocardial Function, Blood Flow, and Metabolism with Different Forms of Myocardial Protection

Summary

The protective myocardial effect of 3 different cardioplegic solutions - Bretschneider (HTP), St. Thomas' Hospital Solution (THOM), Eppendorf solution (EPP) - was investigated in 15 dogs put on extracorporeal circulation (2 hours of cardiac ischemia, 37 ml/kg cardioplegic solution every 30 minutes at 4 °C). After the onset of cardioplegic perfusion, electric cardiac activity was significantly prolonged in the EPP group (3 minutes) as compared with the HTP and THOM groups (1.5 minutes). A myocardial temperature of 15 °C was reached after 5 minutes in EPP as opposed to 3 minutes in HTP and THOM. This can be related to a low perfusion rate in EPP (130 ml/minutes vs 286 ml/minutes in HTP and /THOM) due to the high viscosity of the EPP solution (9.56 centistokes (cst) vs 1.79 cst in HTP and 1.62 cst in THOM at 4 °C.

After 2 hours of ischemia, there was marked hyperemia, low myocardial O₂-consumption (MVO₂) but no lactate production. After 30 minutes of blood reperfusion, MVO₂ reached the normal values of the empty beating heart in HTP and THOM whereas MVO₂ in EPP stayed low at 1.79 ml/100 g/minute.

In all groups, there was a comparable derangement in the autoregulation of myocardial blood flow (MBF) after ischemia; the initially close correlation between left ventricular (LV) function and MBF was no longer present.

In all groups, postischemic developed peak LV pressure as well as dp/dtmax were diminished by about 40% at an enddiastolic volume of 30ml,

In conclusion: In contrast to results obtained on isolated hearts, a moderate functional metabolic impairment is observed irrespective of the cardioplegic solution used when the study is performed under surgical conditions with extracorporeal bypass.

Key words

Cardioplegic arrest - Extracorporeal circulation - Myocardial function - Myocardial - Metabolism