EXPRESS: Efficacy of High-Dose Carvedilol Treatment for Cats with Stage B1 Obstructive Hypertrophic Cardiomyopathy.

Objectives The aim of the study was to investigate the effects of high-dose (HD) carvedilol treatment in client-owned cats with stage B1 obstructive hypertrophic cardiomyopathy (oHCM) where a standard dose (SD) had failed to adequately alleviate left ventricular outflow tract (LVOT) obstruction. Methods A prospective, interventional study was conducted in which cats underwent echocardiography, including evaluation of myocardial strain using speckle-tracking echocardiography. Myocardial injury was quantified using a cardiac troponin I (cTnI) assay. Echocardiographic variables and the cTnI level were compared before treatment and after SD and HD carvedilol treatment. Results LVOT velocity (LVOTV) decreased after SD compared with before treatment in all cats, but remained above 2.5 m/s after SD (before treatment 4.9 m/s [interquartile range [IQR] 4.3–5.0]; SD 4.3 m/s [IQR 3.9–4.7]), whereas HD decreased LVOTV to below 2.5 m/s in 10/11 cats (1.6 m/s [IQR 1.5–2.0]). Longitudinal strain was improved after SD and HD compared with before treatment (endocardial layer: before treatment 12.1% [IQR 9.6–15.8]; SD 20.0% [IQR 15.9–21.7]; HD 18.9% [IQR 12.9–22.8]; P = 0.003 and P = 0.006, respectively; epicardial layer: before treatment 9.4% [IQR 7.0–10.7]; SD 11.6% [IQR 10.0–12.7]; HD 12.5% [IQR 10.0–13.3]; P = 0.013 and P = 0.001, respectively). Circumferential strain demonstrated no changes. The cTnI level decreased after SD and HD compared with before treatment, and after HD compared with SD (before treatment 0.334 ng/ml [IQR 0.117–0.931]; SD 0.192 ng/ml [IQR 0.111–0.377]; HD 0.018 ng/ml [IQR 0.009–0.161]; P = 0.043, P = 0.043 and P = 0.043, respectively). No cats experienced adverse effects such as bradycardia or hypotension. Conclusions and relevance HD improved LVOTV, myocardial function and cTnI level without adverse effects in cats with stage B1 oHCM.