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Mitral valve hemorrhage and mitral annulus shrinkage in rabbits with transient ventricular bigeminies induced by vagal stimulation.

BACKGROUND AND AIM OF THE STUDY
Cervical vagal stimulation in rabbits frequently induces transient ventricular bigeminies, followed by mitral regurgitation lasting a few days, and development of peculiar lesions of the mitral complex. The present study investigated early lesions of the mitral valve and subsequent deformation of the mitral annulus associated with ventricular bigeminies in this animal model


METHODS
A 1-min period of right cervical vagal electrical stimulation was repeated in anesthetized rabbits under ECG monitoring. Animals were sacrificed at 1 h after stimulation to investigate early mitral valve lesions (n = 71; group A), or after one week for measurement of mitral annulus area, using photographic planimetry (n = 56; group B).


RESULTS
Ventricular bigeminies were recorded during vagal stimulation in 72% of group A (n = 51), and 73% of group B (n = 41). The most prominent early mitral valve lesion comprised widespread punctate hemorrhages over the chordae and leaflets, which developed in most animals with ventricular bigeminies (88%), but rarely in those without ventricular bigeminies (5%). This inter-group difference was highly significant (p <0.001). Gross examinations performed at one week after vagal stimulation revealed a deformed mitral annulus resulting from stiff, edematous periannular myocardial tissues. Animals with ventricular bigeminies displayed a significantly smaller mitral annulus area than those without ventricular bigeminies (26.8 +/- 1.0 versus 31.7 +/- 1.2 mm2; p <0.01).


CONCLUSION
Early mitral valve hemorrhage and later mitral annulus shrinkage occur following vagus-induced transient ventricular bigeminies. This may result from unusual mechanical stress on the mitral complex secondary to distorted ventricular contraction in the context of ventricular bigeminies.