Prevalence and Prognosis of Atenolol-Responsive Systolic Anterior Motion of the Septal Mitral Valve Leaflet in Young Cats with Severe Dynamic Left Ventricular Outflow Tract Obstruction

SIMPLE SUMMARY: The most common heart disease in adult cats is hypertrophic cardiomyopathy (HCM), which is a slowly progressive, uncurable disease. Most cats with HCM live several years without obvious problems. However, several cats eventually develop life-threatening clinical signs or die suddenly. Hypertrophic cardiomyopathy is difficult to diagnose in clinically healthy cats because of the absence of any abnormalities on physical examination. However, several cats with HCM develop a heart murmur, which veterinarians can pick up at routine health checks. The reason for the murmur in many cats is an abnormal movement of a valve, which causes a leak and an obstruction. These findings can be visualized with cardiac ultrasonography. Noteworthy, the same ultrasonographic findings can be encountered in cats that do not have HCM but have an abnormality developed valve instead. An important difference between these two conditions is that some of the latter cases might be cured with life-long administration of a beta-blocker. The present study showed that the number of cats that benefited from atenolol therapy was disappointingly low. The reason why we examined only young cats with a heart murmur was that HCM occurs more frequently in elderly cats, whereas the potentially curable congenital disorder is present from birth. ABSTRACT: Background: Severe dynamic left ventricular outflow tract obstruction (DLVOTO) secondary to the systolic anterior motion of the septal mitral valve leaflet (SAM) can result either from congenital mitral valve disorders or left ventricular concentric hypertrophy of any cause, in cats commonly hypertrophic cardiomyopathy (HCM). Though HCM cannot be reversed, the question remains whether atenolol can cure cats with severe DLVOTO resulting from a presumed mitral valve dysplasia. Methods: In this retrospective case series, client-owned asymptomatic cats younger than 1.5 years with echocardiographic evidence of SAM and severe DLVOTO were included. Oral atenolol therapy and recheck echocardiography after 2–3 months were recommended. The owners and referring veterinarians were called for long-term follow-up information. Results: Of the 28 included cats, 23 were treated with atenolol. Recheck echocardiography performed in 17 cats showed a resolution of SAM in 47%. In the long term, SAM remained absent in only 9% of the treated cats. Cardiac-related death occurred in 26% of the atenolol-treated cats. Conclusions: The long term benefit of twice-daily atenolol therapy was documented in 9% of cats. Whether the cats where atenolol failed to resolve DLVOTO on long-term had HCM, or a therapy-resistant congenital primary mitral valve disorder remains unclear.