A retrospective (2020-2025), multicenter study of myxomatous mitral valve disease in Chihuahuas from Italy, Sweden, and the United States of America.

ACVIM stage, LA enlargement, and pulmonary hypertension probability are key prognostic factors in Chihuahuas with MMVD.

This retrospective, multicenter study examined myxomatous mitral valve disease (MMVD) in 390 Chihuahuas across four cardiology centers in Italy, Sweden, and the United States (2020–2025). The cohort had a median age of 11 years, with ACVIM stage distribution of 46% B1, 22% B2, 29% C, and 3% D. Among 122 dogs with available follow-up (median 488 days), 47% progressed in ACVIM stage. Median overall survival was 783 days, with significant differences by stage: B1 (1,164 days), B2 (794 days), and combined C/D (345 days; log-rank P<0.001). Males were more represented in advanced stages (C/D), while females predominated in stage B1; however, sex did not influence survival or progression. Multivariable analysis identified ACVIM staging and pulmonary hypertension (PH) probability as independent risk factors for all-cause mortality, while left atrium-to-aorta (LA:Ao) ratio and PH probability were significant predictors of cardiac-related death. These findings highlight that left atrial enlargement, ACVIM stage, and PH probability are key prognostic indicators in this breed. Study limitations include the retrospective design, uneven center contribution, and selection bias inherent to referral populations. These results support close echocardiographic monitoring of LA size and PH assessment in Chihuahuas with MMVD to guide prognosis and clinical decision-making.

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