Changes in atrial biopsies in chronic rheumatic heart disease. II: Muscle fibre reaction

Wavelength and conduction inhomogeneity in each atrium in patients with isolated mitral valve disease and atrial fibrillation

INTRODUCTION

Patients with mitral valve disease frequently have atrial fibrillation (AF), and the left atrium is presumed to be the primary atrium that develops AF. However, it is still not clear whether the electrophysiologic abnormalities responsible for AF are confined to the left atrium in this subset of patients.

METHODS AND RESULTS

To examine the AF vulnerability of each atrium, we measured the wavelength and inhomogeneity of the conduction at the lateral right atrium, lateral left atrium, and Bachmann's bundle after defibrillation of AF in seven patients undergoing the maze procedure and mitral valve surgery for AF and isolated mitral valve disease, respectively (AF group). The data were compared with five coronary surgery patients in sinus rhythm (SR group). The wavelength in the AF group was significantly shorter (P < 0.05) than in the SR group not only at the lateral left atrium (225 +/- 62 vs 285 +/- 36 mm) but also at the lateral right atrium (214 +/- 54 vs 254 +/- 34 mm). The variation coefficient of the local maximum activation phase difference in the AF group (1.9 +/- 0.8 at the right atrium, 2.1 +/- 0.8 at the lateral left atrium, and 2.0 +/- 0.6 at Bachmann's bundle) was significantly greater (P < 0.05) than in the SR group at all atrial regions.

CONCLUSION

AF vulnerability was not confined to the left atrium immediately after defibrillation in AF patients with isolated mitral valve disease. Electrical remodeling resulting from perpetuation of AF, pathological changes extending to the right atrium, geometric changes caused by the atrial interactions occurring across the interatrial septum, or a combination of these may explain the results.

Fine structure of A: autonomic nerve fibers and terminals in human myocardium; and B: myocardial changes in congenital heart disease

In a histological and fine structural study of right atrial biopsy specimens from 31 patients with rheumatic heart disease (RHD), aged 7 to 46 years, and 11 patients with congenital heart disease (CHD), aged 3 to 36 years, nerve fibers or endings were seen by electron microscopy in 11 specimens. There was concurrence of ordinary axons along with terminals bearing pale cholinergic or dark adrenergic synaptic vesicles. Smaller and denser cholinergic vesicles suggested proliferation followed by exhaustion of such nerve endings. The closest proximity of nerve terminal to muscle fiber was about 100 nm. In one RHD specimen a "specific terminal cell" was present between a nerve ending and muscle fiber; in another a possible neuromuscular contact was developing at the surface of a regenerating small muscle fiber with a few myofilaments. Unmyelinated axons amidst increased subendocardial and subepicardial collagen, with prominent fibroblasts and depleted muscle fibers, were seen more frequently in specimens of CHD. Loss of myofibrils and accumulation of mitochondria, with infrequent formation of lipofuscin bodies, characterized degenerating muscle fibers in CHD also, although to a lesser degree than in RHD (reported earlier, 1985). The myocardial blood vessels in CHD tended to have pale swollen endothelial cells and narrowed lumen. The most severely affected cases of CHD were those with (1) a very wide atrial septal defect (ASD), (2) ventricular septal defect (VSD) with vegetations near the defect, (3) infundibular pulmonary stenosis, and (4) Fallot's tetralogy.