Atrial Pressure and Experimental Atrial Fibrillation

Abstract

A possible profibrillatory effect on the atria of an elevated atrial pressure and the site of atrial stimulation was examined. In 15 anesthetized dogs, right or left atrial or biatrial pacing was applied at a high rate (300-600/min) for 5 seconds at double threshold intensity under a wide range of atrial pressures achieved by venous or arterial transfusion or bleeding. Induction of atrial fibrillation in 236 of 1,971 pacing runs was associated with a significantly higher (P < 0.001) atrial pressure (21.6 +/- 12.2 mmHg, mean +/- SD) than maintenance of sinus rhythm (16.8 +/- 11.1 mmHg in 1,735 of 1,971 pacing runs). Stimulation of the right atrium resulted in atrial fibrillation more frequently than left atrial or biatrial stimulation, with biatrial stimulation less frequent than right or left atrial stimulation. The induction of atrial fibrillation was related to the atrial pressure and to the site of stimulation but not to the pacing rate or the prepacing heart rate. The prepacing heart rate, associated with failure to induce sustained atrial fibrillation, was higher than that associated with atrial fibrillation in 12 of 15 experiments (significantly in 6) and not significantly lower in 3 of 15. Atrial fibrillation lasting 1 minute or more was more frequently associated with simultaneous stimulation of both atria than of either atrium alone. Thus, an elevated atrial pressure may facilitate the induction of atrial fibrillation. The site of stimulation also plays an important role for both the induction and maintenance of atrial fibrillation in this model.

Left Atrial Volume Predicts the Risk of Atrial Fibrillation After Cardiac Surgery

“…The thinned areas of atrial myocardium are vulnerable to stretch caused by increased filling pressures (30). Myocyte stretch increases the atrial effective refractory period dispersion through mechano-electrical feedback and, amplified by collagen deposition, lowers the arrhythmogenic threshold (31,32). These observations have been confirmed in community-based cohorts using diastolic dysfunction as a surrogate for elevated filling pressures to predict nonsurgery-related AF (33).…”

Electrical Remodeling of the Atria Following Loss of Atrioventricular Synchrony

“…Atrial dilatation caused by volume loading and AV interval manipulation in dogs is associated with heterogenous increases in atrial ERPs, interatrial conduction delays, and a propensity to AF. 5,18,19 A nonsignificant prolongation of atrial refractoriness has also been demonstrated after short-term volume loading in goats. 26 In contrast, short-term increases in atrial pressure in an isolated rabbit model resulted in susceptibility to AF and shortening of atrial ERPs.…”

Histologic Assessment of Right Atrial Appendage Myocardium in Patients with Atrial Fibrillation after Coronary Artery Bypass Graft Surgery

“…These investigators showed that less fibrosis was found in the group pretreated with candesartan than those in the control group. In animal studies, it has been reported that high atrial pressure directly reduced atrial refractoriness and increased refractoriness dispersion, resulting in increased vulnerability to AF [23,24,25]. It has been demonstrated that ACE and extracellular signal-regulated kinase (Erk)1/Erk2levels were increased in patients with AF [26], and that an angiotensin II type 1 receptor antagonist decreases atrial pressure.…”