Impact of administering cardiac medication to small-breed dogs with preclinical myxomatous mitral valve disease on survival after congestive heart failure onset

Myxomatous mitral valve disease (MMVD) is the most common cardiovascular disease in small-breed dogs, and some affected dogs develop congestive heart failure (CHF). Although pimobendan is recommended to delay the onset of CHF, its effect on survival following CHF onset development remains unclear. This retrospective study evaluated the survival prognosis of 143 small-breed dogs diagnosed with first-time CHF due to MMVD, comparing pretreated (<i>n</i> = 54) and untreated (<i>n</i> = 89) groups. Pretreated dogs received cardiac medications including pimobendan for at least five weeks before CHF onset. Pretreated dogs had a significantly larger normalized left ventricular internal diameter (LVIDDN; <i>p</i> = 0.002) and higher left atrium-to-aortic root ratio (LA/Ao; <i>p</i> = 0.044) at CHF onset than untreated dogs. The median survival time after CHF onset was significantly longer in untreated dogs (481 days, 95% confidence interval (CI) 393-569 days) than in pretreated dogs (212 days, 95% CI 73-351 days; <i>p</i> = 0.028). Univariable Cox proportional hazards analysis identified pretreatment (<i>p</i> = 0.031), chordae tendineae rupture (<i>p</i> = 0.011), and the LA/Ao (<i>p</i> < 0.001) as significant predictors of survival. Our findings suggest that the administration of cardiac medications, including pimobendan, prior to the onset of CHF was not independently associated with improved survival following CHF.