Conduction block and thin and hypokinetic myocardial segments in feline hypertrophic cardiomyopathy

A 12-year-old castrated male domestic shorthair cat was referred for respiratory distress. Physical examination revealed a systolic heart murmur at the left apex and crackles in all lung fields. Thoracic radiography showed Valentine-shaped cardiomegaly, pulmonary oedema, and pleural effusion. Echocardiography revealed focal thickening of the interventricular septum [11.01 mm; reference interval (RI) = 3.00-5.20 mm] and left ventricular posterior wall (7.41 mm; RI = 3.00-5.10 mm) during diastole. In the apex region, the free wall was focally thinned to approximately 1.6 mm with hypokinetic myocardial movement, indicating thin and hypokinetic myocardial segments. Additionally, decreased left atrial fractional shortening (12.5%; RI = 23.9-34.9%) and an increased left atrial-to-aortic ratio (2.87; RI = 0.88-1.43) were observed, along with spontaneous echocardiographic contrast in the left atrium, indicating increased thrombotic risk. The electrocardiogram showed a left axis deviation with small R waves and deep S waves in lead II, which is consistent with a left anterior fascicular block caused by delayed conduction in the left anterior fascicle. This case report describes the coexistence of a left anterior fascicular block and thin, hypokinetic myocardial segments in feline hypertrophic cardiomyopathy, suggesting a possible pathophysiological link.