Effect of repeated episodes of drug-induced ventricular dyskinesia on subsequent regional function in the dog: Comparison with myocardial stunning produced by repeated coronary occlusions

Stunned myocardium can be produced by repeated short episodes of ischemia. Histochemical and ultrastructural abnormalities such as sarcomere lengthening and myofiber thinning have been noted in myocardium soon after the onset of ischemia and have been attributed to the mechanical stretching that occurs during ventricular systole. To test whether mechanical forces alone could produce the residual dysfunction seen in stunned myocardium, regional dyskinesia was produced in open chest dogs by six repeated intracoronary infusions of either potassium chloride, 0.2 mEq/min for 2.5 minutes, or lidocaine, a 10 mg bolus followed by 1 to 3 mg/min for 5 minutes. These dogs were matched with dogs that had six repeated coronary occlusions of 2.5 and 5 minutes' duration, respectively. Regional function was analyzed using fractional systolic shortening and the load-independent end-systolic pressure-length relation. Both potassium chloride and lidocaine produced regional dyskinesia that was similar to the dyskinesia produced by coronary occlusion. Although regional ventricular function after repeated coronary occlusions remained significantly reduced, function returned completely to normal within 5 minutes after the last druginduced dyskinesia. In conclusion, regional dysfunction produced by potassium chloride and lidocaine does not produce residual dysfunction despite mechanical forces during systole similar to those seen during coronary occlusion.