Database development and survival analysis in a clinical and historical cohort of dogs affected by myxomatous mitral valve disease treated or not with pimobendan using causal inference techniques

The aim of this work was to retrospectively evaluate the influence of pimobendan on the survival time (ST) of dogs with myxomatous mitral valve disease at different stages using an Inverse Probability Weighting (IPW) analysis. An IPW method was used to minimize confounding and IPW weighted time-repeated logistic model was used to approximate survival curves (SCs) and calculate survival differences. Subjects were allocated into exposed (E) and unexposed (U). Dogs in the American College of Veterinary Internal Medicine (ACVIM) B2 class treated with pimobendan (± ACE-inhibitors) were selected for the E group, as well as symptomatic patients (ACVIM class C) treated with triple (furosemide, ACE-inhibitor, pimobendan) or quadruple (furosemide, ACE-inhibitor, pimobendan and spironolactone) therapy. The U group included ACVIM class B2 dogs not treated with any medication and ACVIM C dogs treated with a combination of furosemide and ACE-inhibitor/spironolactone without pimobendan. The survival curve (SC) of the E group crossed the U group at 1634 days. The difference between the two SCs at the time of maximum survival difference in favor of the U group was 11.3% (CI 1.7%-20.9%) (significant), in favor of the E group was 3.9% (CI -8.6%-16.4%) (not significant) and at the mean ST was 3.6% (CI -8.5%-15.7%) (not significant) in favor of the E group. For times greater than 1634 days the survival was in favor of the E group, but there were no statistically significant differences in survival in favor of the E group in this clinical population.