Objective: During cardiovascular surgery, lidocaine is administered to the cardioplegic system to stabilize cell membranes and prevent arrhythmia. Lidocaine is also commonly used in hypothermia. Both lidocaine and hypothermia are myocardially protective. Under normothermia, lidocaine displays its full pharmacological effects, which are apt, however, to be suppressed under hypothermia. We conducted experiments to determine the optimal temperature for myocardial protection in continuous lidocaine cardioplegia.
Methods: In Langendorff mode, rat hearts were continuously perfused with 1 mMol/l of lidocaine solution at 36 +/- 0.5 degrees C (Group A), 24 +/- 0.5 degrees C (Group B), or 7 +/- 0.5 degrees C (Group C) during preservation. Cardiac function and intracellular calcium concentration were measured during both preservation and reperfusion. Heat shock protein 70 (HSP70) was subsequently analyzed by Western blotting.
Results: Rapid cardiac arrest was obtained in Groups A and C. Heart rate recovery was good and ultimately the best in Group B, but worst in Group A. During lidocaine perfusion, the volume of coronary perfusion flow decreased gradually in all groups. After reperfusion, Group A showed only a slight increase in coronary perfusion, While Groups B and C showed a marked increase. Left ventricular contractility showed good recovery in all groups. The calcium concentration increased slightly in Group A, but decreased in Groups B and C. No calcium overload was evident in Group A. The same HSP70 level was detected in all groups.
Conclusion: Lidocaine used in normothermia does not decrease cardiac metabolism or oxygen consumption, and displays full pharmacological effectiveness in preventing ischemic injury. We found 36 degrees C to be the optimal temperature for heart preservation by coronary perfusion with lidocaine cardioplegia.