Efficacy of a mitral regurgitation severity index to predict long‐term outcome in dogs with myxomatous mitral valve disease

Abstract Background Predicting progression of myxomatous mitral valve disease (MMVD) in dogs can be challenging. Hypothesis/Objectives The mitral regurgitation severity index (MRSI) will predict time to congestive heart failure (CHF) and all‐cause death in dogs with MMVD. Animals Eight hundred sixty‐nine client‐owned dogs. Methods Retrospective study pooling data from 4 previous samples including dogs with MMVD stage B2 or C. MRSI was calculated as: (heart rate [HR]/120) × left atrium‐to‐aorta ratio (LA:Ao) × (age in years/10) × 100. Alternative MRSI formulas substituting radiographic measures of left atrial size were also calculated. Cox proportional hazard modeling and time‐dependent receiver‐operator characteristic curves quantified prognostic performance. Results For Stage B2 pooled samples, MRSI > 156 was predictive of time to CHF (median 407 vs 1404 days; area under the curve [AUC] 0.68; hazard ratio 3.02 [95% CI 1.9‐4.9]; P 173 was predictive of all‐cause death (median survival 868 vs 1843 days; AUC 0.64; hazard ratio 4.26 [95% CI 2.4‐7.5]; P