Valvular mitral stenosis in adult cats: knowledge gained from the clinical and pathological workup of 18 cases

INTRODUCTION/OBJECTIVES: Feline valvular mitral stenosis (VMS) is uncommonly reported. The aim of this study was to describe diagnostic and clinicopathological characteristics of VMS in adult cats. ANIMALS, MATERIALS AND METHODS: Eighteen client-owned cats were included in this study. A retrospective observational study. Clinical records were searched based on echocardiography. Data regarding clinical, laboratory, echocardiographic findings, outcome, and, in four cats, gross postmortem images of the heart were reviewed, and histological examinations performed. RESULTS: Most cats were non-pedigree (11/18), with a median age of 13.2 years. Congestive heart failure was common (15/18). Three cats had hypertrophic cardiomyopathy phenotype, including one with transient myocardial thickening. Concomitant hyperthyroidism (9/18) was frequent. In one cat, echocardiography performed one year earlier did not show any changes. Upon echocardiography, all 18 cats had characteristic hockey-stick appearance of the anterior leaflet and narrow turbulent diastolic flow across the mitral valve. Twelve cats had fused diastolic transmitral waves, with a median velocity of 0.54 m/s (0.71-3.24 m/s). The remaining six had a median peak velocity of the early and late-diastolic transmitral waves of 1.3 m/s (0.95-2.8 m/s) and 0.99 m/s (0.65-2.05 m/s), respectively. Eleven cats had died, 10 of cardiac death (median survival time: 366 days). Macroscopically, the mitral valve leaflets appeared thickened and distorted, and the surrounded ventricular endocardium thickened. Histology revealed marked endocardial fibrosis of the mitral valve and surrounding ventricular endocardium, dominated by type I collagen. CONCLUSIONS: The most striking finding is the documented acquirement of VMS in one cat, while the acquired nature of the lesion could not be confirmed in the other cases. The pathological findings are compatible with a chronic remodeling process that results in marked endocardial fibrosis in four cats.