Background: Studies describing the clinical progression of animals with reverse patent ductus arteriosus (PDA) are lacking. Objectives: To describe the signalment, presenting signs, echocardiographic features, and survival in a group of dogs and cats with bidirectional and continuous right-to-left PDA. Animals: Forty-six client-owned animals included, comprising 43 dogs and 3 cats with bidirectional or continuous right-to-left PDA. Methods: Retrospective multicenter study. Medical records and echocardiographic findings reviewed from animals diagnosed with bidirectional or continuous right-toleft PDA. Impact of ductal morphology, spectral Doppler flow profile, PCV, sildenafil treatment at presentation, sildenafil dose, severity of pulmonary hypertension, general anesthesia with or without surgery and the presence of right-sided congestive heart failure (R-CHF) on crude mortality rate were evaluated via Mantel-Cox log rank comparison of Kaplan-Meier survival curves. Univariable and multivariable Cox proportional hazards analysis was performed, and hazard ratio (HR) (95% confidence intervals [CI]) was presented. Results: Hindlimb collapse was the most common presenting sign in dogs (n = 16). Clinical signs in cats were variable. Median survival time was 626 days in dogs (range 1-3628 days). Dogs with R-CHF had a shorter median survival time (58 days vs 1839 days, P = .03). Dogs treated with sildenafil at initial presentation survived longer (1839 days vs 302 days, P = .03), which was the only independent predictor of survival (HR 0.35, CI 0.15-0.86, P = 0.021).

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