C02 - Repeatability of Early versus Late Diastolic Left Atrium/Aorta in Cats with Hypertrophic Cardiomyopathy

Abstract: Background: Short-axis left atrial diameter indexed to the aorta (LA/Ao), usually measured at end-systole (LA/Aomax), might be easier to measure at end-diastole (LA/Aomin) without sacrificing prognostic value.

Hypothesis: LA/Aomin would be more repeatable than LA/Aomax and be an independent predictor of survival in cats with hypertrophic cardiomyopathy (HCM).

Animals: 247 client-owned cats (81 healthy cats, 118 HCM stage B cats and 48 HCM stage C cats).

Methods: Patient records were retrospectively reviewed and LA/Aomax and LA/Aomin measured by two investigators. Data presented as mean (95%CI).

Results: LA/Aomin reference interval for healthy cats was 0.84 (90%CI 0.80-0.87) to 1.28 (90%CI 1.25-1.32). Compared to LA/Aomax, LA/Aomin showed a higher inter-operator ICC (0.99 [0.98–1.00] versus 0.91 [0.80–0.97]), lower inter-operator CV (6.6% versus 10.6%) and less bias (-0.01 [-0.18–0.16] versus -0.13 [-0.43–0.18]). The aortic valve was visible 64% less frequently for LA/Aomax than LA/Aomin (chi-squared=14.9, p< 0.001). In receiver operating characteristics curve analysis LA/Aomin differentiated stage C from stage B cats with an area under the curve (AUC) of 0.95 (0.92 – 0.98), similar to LA/Aomax (AUC 0.94 [0.90–0.98]). Kaplan-Meier analysis showed an LA/Aomin >1.9 (upper quartile) was associated with increased all-cause mortality (p< 0.001), with no difference between other quartiles (p>0.4). The univariable Cox’s proportional hazard ratio for LA/Aomin >1.9 was 7.5 (3.76–16.3). Multivariable analysis identified LA/Aomin >1.9, symptomatic status and left ventricular systolic function as independent predictors of survival.

Conclusions and clinical importance: LA/Aomin demonstrated higher repeatability compared to LA/Aomax and was an independent predictor of survival in cats with HCM.