Susceptibility to Atrial Fibrillation:

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Abstract
Propensity for Extrastimulus to Induce AF. 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 pacing‐induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters. Methods and Results: Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF thresbold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6‐week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA FRP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology. Conclusion: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure.