The mitral-to-aortic velocity-time integral ratio used to estimate regurgitant fraction in dogs with myxomatous mitral valve disease: a retrospective observational study of 1,109 echocardiographic examinations

Introduction/objectives: The mitral-to-aortic velocity-time integral ratio (MAVIR) has been proposed as a surrogate of the regurgitant fraction (RF) in humans. This study aimed to correlate MAVIR with echocardiographic and clinical variables of myxomatous mitral valve disease (MMVD) severity in dogs. Animals, materials and methods: Data from two centres were reviewed for healthy dogs and dogs with MMVD. The RF was calculated using Teichholz (RFTeichh) and Simpson (RFSMOD) methods. The correlation between MAVIR and echocardiographic indices and its difference across American College of Veterinary Internal Medicine and Mitral INsufficiency Echocardiographic (MINE) classes were assessed. A receiver operating characteristic curve analysis assessed MAVIR's ability to predict MMVD severity and RF. Results: A total of 1,109 examinations from 950 dogs were included in the present study. The MAVIR differed between healthy and MMVD at all American College of Veterinary Internal Medicine stages and MINE classes (P<0.001). It correlated with RFSMOD (Rho: 0.78, P<0.001) and RFTeichh (Rho: 0.83, P<0.001). The areas under the receiver operating characteristic curve (AUCs) for discriminating mild from moderate and moderate from severe-late stage according to the MINE score were AUCs = 0.709 (95% confidence interval [CI]: 0.673, 0.745) and 0.784 (95% CI: 0.731, 0.836), respectively; for predicting RFSMOD ≥ 50%, the AUC was 0.946 (95% CI: 0.926, 0.966), with a cutoff >1.27 (sensitivity 91.11%; specificity 84.15%). Study limitations: Retrospective study design and negative RF values are the limitations of this study. Conclusions: Although not clinically validated against a gold standard, the MAVIR is associated with MMVD severity. A MAVIR >1.27 predicts an RFSMOD ≥ 50%. Given its simplicity, MAVIR might represent a valuable tool for staging MMVD and warrants further investigation.