Myocardial Electrophysiological Response to Ischemia and Reperfusion Depends on the Age of Rats

Age is a major driver of the risk of acute myocardial infarction and malignant ventricular arrhythmias. However, age-related changes in the ischemic myocardium remain largely unclear. The present study aimed to evaluate electrophysiological responses of myocardium to experimental ischemia-reperfusion conditions in rats aged 3, 12, and 24 months. Epicardial mapping (64 leads) was performed in a total of 34 anesthetized animals. In each lead, activation time (AT), end of repolarization time (RT), and activation-repolarization interval (ARI), were measured as dV/dt min during QRS, dV/dt max during T-wave, and RT – AT difference, respectively. Dispersion of repolarization (DOR) was determined as the RTmax – RTmin difference throughout all leads. Ischemia was induced by a 5-min ligation of the left anterior descending coronary artery. It was found that the 24-month-old rats had shorter baseline ATs and ARIs (p < 0.05), greater AT prolongation and less ARI shortening at ischemia (p < 0.05) and more complete recovery of the ARI at reperfusion (p < 0.001; all comparisons vs 3-month-old animals). At reperfusion, the absolute values of AT and DOR were lower in the old and middle-aged animals as compared to the young rats (p < 0.05); however, the absolute values of ARI durations did not differ between the groups. The data obtained suggest existence of age-related differences in the sensitivity of myocardium to ischemia-reperfusion conditions and that old animals are more susceptible to adverse changes regarding activation spread and more resilient regarding repolarization characteristics as compared to young adult animals.