The effects on atrial electrophysiology and structure of surgically induced right atrial enlargement in dogs.

Abstract

We evaluated the relationship between susceptibility to arrhythmias caused by right atrial (RA) enlargement and alterations in transmembrane potentials and ultrastructure. RA enlargement was produced in eight dogs (TI) by excising the septal cusp of the tricuspid valve through a right atriotomy and constricting the pulmonary artery. This procedure resulted in RA dilation and hypertrophy. Four sham-operated dogs (S) also were studied. Neither TI nor S dogs developed spontaneous atrial arrhythmias. Atrial overdrive (OD) and premature stimulation (PS) were used to initiate and terminate arrhythmias. At 2 weeks and for 20 to 30 weeks after surgical preparation, TI dogs were more susceptible to arrhythmias than S dogs. The duration of arrhythmias exceeded 10 minutes more often in TI dogs than in S dogs. Sixty-one percent of all arrhythmias in the TI dogs had rates of 320-450 impulses/min, and electrogram and ECG characteristics of atrial flutter (type II rhythm), whereas no S dogs developed rhythms with these slower rates. The type II rhythms were persistent, 30% lasting longer than 30 minutes, while 22% lasted more than 60 minutes. Transmembrane potentials recorded in vitro from the RA free wall of TI dogs, and responses to norepinephrine and acetylcholine were not different from control. Histological and ultrastructural studies on TI atria showed hypertrophy of fibers and some increase in connective tissue between cells. These results suggests that altered susceptibility to long-lasting arrhythmias need not be associated with significant abnormalities of cellular electrophysiology.

Value of the P-wave signal-averaged ECG for predicting atrial fibrillation after cardiac surgery.

“…Experimental data suggest that atrial enlargement and hypertrophy create the requisite milieu for AF. 16 The use of P-wave SAECG in this population will need to be confirmed in other populations before these results can be extrapolated. Other high-risk populations, such as patients with valvular heart disease, hypertension, or coronary heart disease, may be suitable candidates.…”

Development of a Substrate of Atrial Fibrillation During Chronic Atrioventricular Block in the Goat

“…The first animal studies were performed in the early 1980s by Boyden and Hoffman. 16 In 8 dogs with tricuspid regurgitation and stenosis of the pulmonary artery, RA volume increased by 40%. Spontaneous atrial arrhythmias did not occur, but the inducibility and duration of atrial tachyarrhythmias were higher.…”

Effects of Experimental Heart Failure on Atrial Cellular and Ionic Electrophysiology

“…Alterations in atrial cellular electrophysiology have been reported in patients [2][3][4][5][6] and experimental animals 7,[15][16][17] with atrial disease and/or dilation. Similar to our observations at slower rates, APD was not substantially altered in dogs with tricuspid insufficiency 15 and chronic mitral regurgitation. 16 Cats with endogenous cardiomyopathy had APDs that were either unchanged or (in more severe cases) increased in the left atrium.…”