Prevalence and characteristics of transient myocardial thickening in cats with hypertrophic cardiomyopathy phenotypes

This study aimed to propose new diagnostic criteria and provide detailed descriptions of cats diagnosed with transient myocardial thickening (TMT) using a retrospective design. HCM phenotype cases were defined as cats with echocardiographic findings of a maximum left ventricular wall thickness (LVWT) ≥6 mm on at least one presentation. TMT was defined as an increased LVWT ≥6 mm on at least two presentations, a subsequent decrease in LVWT of more than 25% within 6 months, no subsequent increase in left atrial-to-aortic root ratio (LA/Ao) ≥20% from baseline, and a fractional shortening ≤30%. A total of 145 cats had HCM phenotypes. Among cats that underwent serial echocardiography (<i>n</i> = 53), 16 were diagnosed with TMT and 34 with HCM. At presentation, the maximum LVWT was 8.3 ± 1.7 mm in cats with TMT, and decreased to 5.4 ± 0.9 mm after a median of 3.5 months [1-6 months]. Two cats initially classified as TMT were later identified as TMT on HCM based on persistent LV thickening, and all cats with TMT survived until the time of publication. The prevalence of TMT may be higher than expected when including asymptomatic TMT and TMT on HCM. Clinicians should be aware of the possibility of dynamic changes in myocardial thickness in cats.