Chronobiology of Cardiac Ventricular Fibrillation Development in Experimental Acute Coronary Failure

Numerous experiments on simulation of acute coronary failure in initially intact rabbits showed that under the same experimental conditions irreversible ventricular fibrillation developed in some animals and did not develop anothers. We hypothesize that the probability of fibrillation development was determined by the time of the day, during which acute coronary failure developed. The study was carried out on 2 groups of rabbits in winter in Moscow. In group 1, the failure was induced by ligation of the left descending coronary artery at the interface between its middle and lower thirds at 11.00-18.00 with 30-min intervals. In group 2, the microcirculatory status of the left-ventricular myocardium was studied by light microscopy and morphometry at 12.00 and 18.00. Induction of coronary failure during the period from 15.30 to 18.00 led to irreversible ventricular fibrillation and death in 100% cases. Modeling of the condition from 11.00 to 15.00 caused no ventricular fibrillation in 89% cases, and the animals survived. The area of left-ventricular myocardial capillaries at 12.00 virtually 2-fold surpassed that at 18.00. Presumably, the electrolyte balance and metabolic characteristics of the myocardium switch over to the nocturnal mode of functioning at 15.30 due to changes in blood filling of the myocardium. The appearance of an ischemic focus in the myocardium during this period inevitably leads to the development of irreversible ventricular fibrillation.