Clinical utility of left atrial diameter normalized for body weight in healthy and cardiomyopathic cats

Introduction/Objectives: Left atrial dimensions correlate with body weight (BW) in cats. Atrial dimensions can be obtained from both right parasternal long-axis (RPLAx) and right parasternal short-axis images. However, reference ranges for RPLAx-derived left atrial diameter (LAD) obtained from a large sample of healthy cats are needed. This study measured LAD from the RPLAx view and calculated a normalized value to BW (LADn) and left atrial diameter-to-aortic annulus ratio (LAD:Ao). Study aims included developing prediction intervals for LADn, defining reference intervals for LAD:Ao, and investigating useful cutoffs for these variables for detection of congestive heart failure (CHF) in cats with cardiomyopathy. Animals, Materials and Methods: Healthy cats (n = 303) and cats with different types of cardiomyopathy (198 preclinical; 71 with CHF). From RPLAx images, the LAD was measured from the interatrial septum to the free wall at end-systole and aortic diameter was measured at the annulus to calculate the LAD:Ao. Linear regression analysis was used to investigate the effect of BW on the LAD. Cutoffs of LADn and LAD:Ao that identified cats with CHF were generated. Results: The LAD correlated to BW (r = 0.52, P<0.001). The formula to calculate LADn was LAD (mm)/BW (kg)0.19, while median RPLAx LAD:Ao was 2.0 (95% reference interval: 1.55–2.47). Values of LADn >12.7 and LAD:Ao >2.5 had a sensitivity of 92.8% and 88.7% and a specificity of 91.5% and 93.6%, respectively, in detecting CHF. Study Limitations: Due to the retrospective design of the study and lack of longitudinal follow-up, the inclusion of cats with occult CM in the healthy group cannot be entirely ruled out. Conclusions: The LAD correlates with BW in cats. In the evaluation of LA dimension, LADn and LAD:Ao might be preferable to unadjusted LAD, especially in smaller and larger breeds of cats.