Effect of Ischemic Preconditioning on Myocardial Protection: A Comparative Study between Normothermic and Moderate Hypothermic Ischemic Hearts Induced by Cardioplegia in Rats

Cho, Seong Joon; Hwang, Jae Joon; Kim, Hark Jei

Abstract

BACKGROUND: Most of the studies conducted have investigated the beneficial effects of ischemic preconditioning on normothermic myocardial ischemia. However, the effect of preconditioning could be attenuated through the use of multidose cold cardioplegia as practiced in contemporary clinical heart surgical procedures. The purpose of this study was to investigate whether preconditioning improves postischemic cardiac function in a model of 25 degrees C moderate hypothermic ischemic heart induced by cold cardioplegia in isolated rat hearts. MATERIAL AND METHOD: The isolated Sprague-Dawley rat hearts were randomly assigned to four groups. All hearts were perfused at 37 degrees C for 20 minutes with Krebs-Henseleit solution before the baseline hemodynamic data were obtained. Group 1 consisted of preconditioned hearts that received 3 minutes of global ischemic preconditioning at 37 degrees C, followed by 5 minutes of reperfusion before 120 minutes of cardioplegic arrest (n=6). Cold (4 degrees C) St. Thomas Hospital cardioplegia solution was infused to induce cardioplegic arrest. Maintaining the heart at 25 degrees C, infusion of the cardioplegia solution was repeated every 20 minutes throughout the 120 minutes of ischemic period. Group 2 consisted of control hearts that underwent no manipulations between the periods of equilibrium and 120 minutes of cardioplegic arrest (n=6). After 2 hours of cardioplegic arrest, Krebs solution was infused and hemodynamic data were obtained for 30 minutes (group 1, 2: cold cardioplegia group). Group 3 received two episodes of ischemic preconditioning before 30 min of 37 degrees C normothermic ischemia and 30 minutes of reperfusion (n=6). Group 4 served as ischemic controls for group 3 (group 3, 4: warm ischemia group). RESULT: Preconditioning did not influence parameters such as left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), rate-pressure product (RPP) and left ventricular dp/dt (LV dp/dt) in the cold cardioplegia group. (p=NS) However, preconditioning before warm ischemia attenuated the ischemia induced cardiac dysfunction, improving the LVSP, LVEDP, RPP, and LVdp/dt. Less leakage of CPK and LDH were observed in the ischemic preconditioning group compared to the control group (p<0.05).
CONCLUSION
Ischemic preconditioning improved postischemic cardiac function after warm ischemia, but did not protect cold cardioplegic hearts.