ARRHYTHMIAS AND DEATH AFTER CORONARY-ARTERY OCCLUSION IN THE RAT - CONTINUOUS TELEMETRIC ECG MONITORING IN CONSCIOUS, UNTETHERED RATS

Background The onset of acute myocardial infarction (MI) is accompanie d by a rapid increase in electrical instability and often fatal ventri cular arrhythmias. The aim of this study was to assess the continuous arrhythmia profile during the initial 48 hours after coronary artery l igation in the rat in relation to time course, mortality, and infarct size. Methods and Results Continuous ECG recordings were obtained in 2 6 conscious, untethered rats for 24 hours before and 48 hours after co ronary ligation by use of an implantable telemetry system. All episode s of ventricular tachycardia and fibrillation were counted and their d urations summed. Infarct size was measured at 48 hours after MI or aft er spontaneous death. After ligation, two distinctly active arrhythmog enic periods developed (A1, 0 to 0.5 hours; A2, 1.5 to 9 hours), each followed by a quiescent phase of low ectopy (Q1, 0.5 to 1.5 hours; Q2, 10 to 48 hours). The total mortality rate of 65% was found within the two active periods, with 13 of 15 deaths occurring in A2. Rats with l arger infarcts (greater than or equal to 50%) and nonsurvivors tended to have increased arrhythmia frequency and duration compared with both animals with smaller MIs (<50%) and survivors. Conclusions Two distin ct arrhythmogenic periods occur in rats with acute MI that may be caus ed by different mechanisms and correspond to the bimodal arrhythmia ti me course seen in dogs and humans after acute MI. Telemetric monitorin g of the ECG in the conscious rat after infarction will be useful in a ssessment of the differential effects of therapeutic interventions on these two arrhythmogenic periods and in the study of potential mechani sms for the spontaneous resolution of ventricular ectopy and risk of s udden death.