Left atrial fractional shortening in cats: a comparison between two echocardiographic views

Left atrial fractional shortening (LAFS%) is a widely used index of left atrial systolic function in cats that has been shown to predict development of hypertrophic cardiomyopathy (HCM) and cardiac mortality. It can be determined by two methods: from an M-mode right parasternal short-axis view (LAFS%^RPSA-MM) or two-dimensional right parasternal long-axis four-chamber view (LAFS%^RPLA-2D). We aimed to assess the agreement between LAFS%^RPSA-MM and LAFS%^RPLA-2D in cats and to evaluate the correlation between LAFS%^RPSA-MM and LAFS%^RPLA-2D and left ventricular systolic performance.

One hundred and seventeen cats were enrolled in the study: 40 control, 41 HCM stage B (asymptomatic), and 36 HCM stage C (symptomatic) cats. This was a retrospective case-control study. Bland-Altman analysis was used to assess agreement between LAFS%^RPSA-MM and LAFS%^RPLA-2D across the whole cohort and in cats with asymptomatic and symptomatic HCM. Correlation analysis was used to assess associations between LAFS% methods and forward aortic flow, left ventricular fractional shortening, and aortic root motion.

The LAFS% determined by LAFS%^RPSA-MM and LAFS%^RPLA-2D was similar (P=0.8), but Bland-Altman analysis showed wide limits of agreement between methods. There was a good correlation between LAFS%^RPSA-MM and LAFS%^RPLA-2D and aortic root motion (r = 0.78 and r = 0.71, respectively) and a fair correlation with left ventricular fractional shortening (r = 0.31 and r = 0.29, respectively). None of the methods showed a correlation with indices of aortic flow.

Our study suggests a poor agreement between LAFS%^RPSA-MM and LAFS%^RPLA-2D, and thus, these methods should not be used interchangeably. Both echocardiographic methods showed good correlation with aortic root motion.