The Correlation between Enzyme Release and Myocardial Ultrastructure in Two Different Types of Myocardial Protection during Cardiopulmonary Bypass

Summary

This study investigates the effects of ischemic arrest on enzymatic release (CPK, CPK-MB, LDH and SGOT in the theater and during the postoperative hours, and correlates these with ultrastructural findings. Thirty-five patients undergoing routine valve replacement surgery were divided into 2 groups (Gl, GII) and treated with 2 different types of myocardial protection (MP) methods: deep hypothermia 25 ± 3°C with topical cooling, and deep hypothermia 24 ± 1 °C with cardioplegia (St. Thomas'). The samples were taken before, during and after CPB and then every 2 hours for a further 46 hours. Two myocardial biopsies were taken before aortic cross-clamping and 10 minutes after aortic cross-clamp release. Our results show that not all the serum enzymes are capable of reflecting the differences expected. Total CPK, LDH and SGOT for example, are very insensitive, while CPK-MB is more specific. However, comparing the 2 groups, global significant differences could be obtained, p = 0.05 for CPK and p < 0.001 for CPK-MB. The enzymatic activity increased until the second hour postoperatively in both groups and then a decline occurred. But, in GII a second phase of enzyme release appeared at the 28th hour postoperatively. This phenomenon can probably be related to cardioplegia. In comparing the groups, the Statistical analysis with Student's T-test showed many significantly different levels from the 32nd until the 46th postoperative hour. These levels of significance tended to increase with time (p = 0.025 to p < 0.001). On the other hand, the ultrastructural investigations showed good MP during ischemic arrest in all groups with only slight signs of ischemic injuries. The enzymatic activity tended to increase and to maintain a high level in GII while it normalized in GI. In conclusion, the enzymatic activity can be very closely related to the kinds of MP methods. The slight myocardial injuries observed in GII can become irreversible, expiaining the prolonged and delayed enzyme release. However, the possibility of late toxic effects of cardioplegia were not studied. In this study, CPK-MB appears to be a better parameter for differentiating the groups than CPK, LDH and SGOT.

Key words

Cardiopulmonary bypass - Myocardial protection - Creatine Phosphokinase - Lactic dehydrogenase - Serum glutamic oxalo-acetic transaminase