Introduction

Mitral regurgitation (MR) is the most common cardiovascular disease found in geriatric small-breed dogs. Currently, no medical treatment has been successfully demonstrated to slow the disease progression. Sildenafil is a selective phosphodiesterase-5 inhibitor that has been proved to reduce left ventricular remodeling and improve cardiac function in rat with chronic MR. Heart rate variability (HRV) has been shown to detect early improvement of cardiac autonomic regulation.

Objectives

This study aimed to assess effects of long-term treatment with sildenafil on spectral analysis of heart rate variability in dogs with asymptomatic MR.

Methods

Thirty-one dogs were used in this study: 13 age-matched healthy dogs without heart disease and 18 client-owned asymptomatic MR dogs. The continuous, at least 1-hour ECG, was performed during resting period by using Holter recording at day 0 and 90 days after given sildenafil 2–3 mg/kg, BID (n = 9/18). ECG was analyzed by SCM510 software to calculate spectral analysis of HRV.

Results

In dogs with asymptomatic MR, the low frequency (LF), high frequency (HF) and total power (TP) were significantly lower than those of healthy dogs (p < 0.05); and LF/HF ratio was significantly higher (p < 0.01) when compared to healthy dogs. In asymptomatic MR dogs, oral sildenafil for 90 days tended to improve all of the frequency domain parameters when compared to baseline.

Conclusions

This data suggested that long-term treatment with sildenafil could improve the sympathovagal imbalance in dogs with asymptomatic MR; however, the number of enrolled animals should be increased to warrant the significance of the result.