SUSCEPTIBILITY TO ATRIAL-FIBRILLATION - A STUDY IN AN OVINE MODEL OF PACING-INDUCED EARLY HEART-FAILURE

Introduction: The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of paci ng-induced stable early heart failure to describe, quantify, and relat e the level of susceptibility to AF to changes in structural and elect rophysiologic parameters. Methods and Results: Epicardial electrodes w ere implanted on the atria and right ventricles of nine sheep. The AF threshold, atrial vulnerability period, atrial effective refractory pe riod (ERP), and interatrial conduction time were examined during contr ol and over a 6-week period of ventricular pacing at 190 beats/min. Le ft atrial (LA) area and left ventricular (LV) fractional shortening we re monitored using echocardiography, There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA ERP400 (P < 0.0002), Rate of increase in LA area was related positivel y to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.00 2), LV fractional shortening decreased to approximately 50% of control value (P < 0.00001), No changes were observed in right atrial electro physiology, Conclusion: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predet ermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysi ology and structure.