Understanding Transient Myocardial Thickening in Cats

Presentation Description / Summary: This session will review the literature on transient myocardial thickening (TMT), discuss our current understanding of the condition, and present new findings in cats. TMT is a transient myocardial disease that mimics hypertrophic cardiomyopathy (HCM). It is relatively uncommon, mostly affecting young cats, often following an antecedent event (e.g., general anesthesia), and is associated with an excellent long-term prognosis. Cats typically present in acute congestive heart failure with an HCM phenotype on echocardiography, but their hearts undergo rapid reverse remodeling, with normalization of wall thickness and atrial size within weeks to months. Once the heart returns to normal, cardiac medications can usually be discontinued without relapse of clinical signs. The pathophysiology of TMT remains unclear. The observed rapid reverse remodeling suggests that myocardial edema may play a role. Similar conditions mimicking HCM have been reported in people with acute myocarditis and stress-induced (Takotsubo) cardiomyopathy. Myocarditis is poorly described in small animals, but myocardial thickening has been reported in some cases. Alternatively, the myocardial changes in TMT could result from a catecholamine surge triggered by stress related to antecedent events. Support for this hypothesis comes from cats with thermal burn injuries from wildfires, which have been shown to develop TMT. TMT is associated with a significantly better prognosis than HCM, making it critical for clinicians to recognize and differentiate the condition. Given the excellent long-term prognosis, aggressive efforts to treat cats with CHF and potential TMT are worthwhile.