A RETROSPECTIVE (2020-2025), MULTICENTER STUDY OF MYXOMATOUS MITRAL VALVE DISEASE IN CHIHUAHUAS FROM ITALY, SWEDEN AND THE UNITED STATES OF AMERICA

Introduction Chihuahuas are affected by myxomatous mitral valve disease (MMVD). Objective To investigate MMVD in Chihuahuas, specifically clinical and echocardiographic characteristics including probability of pulmonary hypertension (PH), disease progression and survival. Animals Materials and Methods Retrospective study of privately owned Chihuahuas from four cardiology centers across three countries (2020-2025). Inclusion criteria were an echocardiographic study compatible with MMVD. Differences between signalment, centers and American College of Veterinary Internal Medicine (ACVIM) stages were assessed; disease progression and survival analysis were calculated. Results Three hundred ninety Chihuahuas of both coat types, median age of 11 years, were included. One hundred-eighty-one out of 390 dogs (46%) were classified as ACVIM stage B1, 85/390 (22%) as B2, 114/390 (29%) as C and 10/390 (3%) as D. Females were more numerous in ACVIM stage B1 and males in combined stage C/D, however sex did not influence survival or disease progression. Among 122 dogs for which follow-up was available (median 488 days), 47%(57/390) progressed in stage, while 53%(65/122) remained stable. The population median survival time was 783 days; survival differed amongst ACVIM stages (survival for ACVIM stage B1 was 1164 days, ACVIM stage B2 794 days, ACVIM stage C and D 345 days, log-rank test P<0.001). Multivariable survival analysis identified ACVIM staging and PH probability as risk factors for all-cause mortality and left atrium-to-aorta ratio and PH probability for cardiac-related death. Study limitations Retrospective design, uneven center contribution Conclusions Left atrial enlargement, ACVIM staging and PH probability were prognostic factors for cardiac and non-cardiac death in Chihuahuas with MMVD.