Effect of atenolol on heart rate, arrhythmias, blood pressure, and dynamic left ventricular outflow tract obstruction in cats with subclinical hypertrophic cardiomyopathy.

Abstract

OBJECTIVE: To investigate the negative chronotropic, antiarrhythmic, and obstruction-relieving effects of atenolol in cats with subclinical hypertrophic cardiomyopathy (HCM). ANIMALS: Seventeen cats with HCM. METHODS: Results for echocardiography, electrocardiography, Doppler blood pressure, and 24 h Holter monitoring were compared in cats before and 2-4 weeks after atenolol therapy (6.25-12.5 mg PO q 12 h). RESULTS: The left ventricular outflow tract maximum velocity (LVOT Vmax) decreased after atenolol administration (mean Vmax pre-treatment 3.3 m/s &#xb1; 1.8 m/s; post-treatment 1.6 m/s &#xb1; 1.0 m/s, p < 0.0001). Heart rate (HR) decreased after atenolol for all HR modalities. The total number of ventricular origin complexes (TotVent) and ventricular premature complexes (VPCs) decreased after atenolol. The VPCs decreased from a geometric mean of 61 complexes/24 h (range, 11-620 complexes/24 h) to 15 complexes/24 h (range, 1-1625 complexes/24 h) (p < 0.0001). Murmur grade decreased after atenolol from a median grade of 3/6 to 2/6 (p < 0.0001). The systolic blood pressure did not change (mean pre-treatment 130 mmHg &#xb1; 16 mmHg, mean post-treatment 123 mmHg &#xb1; 20 mmHg, p = 0.2). CONCLUSION: Atenolol decreases HR, murmur grade, and LVOT obstruction, and to a lesser degree, frequency of ventricular ectopy, in cats with subclinical HCM. Further studies are needed to determine if sudden cardiac death or long-term outcome is influenced by atenolol administration.