M-Mode Echocardiographic Ratio Indices in Normal Dogs, Cats, and Horses: A Novel Quantitative Method

Abstract

A novel method for quantitative echocardiographic interpretations is introduced based on the calculation of ratio indices in which each raw M-mode measurement is divided by the aortic root dimension (Ao). "Aorta-based" indices were calculated with the animal's measured aortic root dimension (Ao(m)) as the length standard. Conversely, "weight-based" indices employed an idealized estimate of aortic dimension (Ao(w)) with a weighted least squares linear regression against the cube root of body weight (Ao(w) = kW(1/3)). Use of these indices circumvented undesirable statistical characteristics inherent in linear regression of echocardiographic dimensions against body weight and, to a lesser extent, body surface area. Compared with the regressions, ratio indices resulted in substantial refinement of the predictive range for each M-mode measurement in dogs, particularly with decreasing body size. Weight-based indices outperformed aorta-based indices in this regard. To refine the predictive range, neither type of index was clearly advantageous in cats compared with the simple average method typically employed for that species. Several of the raw M-mode measurements, however, were correlated with body weight in cats and horses, indicating the need for an appropriate correction for body size in these species. The ratio index method was suitable for this purpose. Summary statistics derived from normal dogs (n = 53), cats (n = 32), and horses (n = 17) are presented for each index, including novel clinical indices calculated from area ratios. The latter were designed to represent body size-adjusted lett ventricular stroke area (ie, volume overload) and myocardial wall area (ie, hypertrophy).

Methods and reliability of echocardiographic assessment of left atrial size and mechanical function in horses

“…Therefore, correction to body weight (or body weight raised to the nth power) may be preferable because indexing to a constant would not affect reliability of the variable. 23,41,49 The area-and volume-based 2-dimensional indices of LA reservoir function and LA pump function performed similarly in regards to reliability of measurements, while all components of the LA fractional shortening were highly variable. Following our recommendations for assessment of LA size, we suggest using the area-based variables for assessment of LA reservoir function and LA pump function in horses.…”

“…The LA linear dimensions, area, and volume, respectively, were measured or calculated during maximal atrial filling, immediately prior to mitral valve opening, and indexed to the size of the aorta. 3,15,16,23 For this purpose, the aortic annulus diameter was determined from a right parasternal long-axis view by measuring the inner distance between the opened aortic valve leaflets during peak systole. Left atrial passive and active emptying were characterized by use of calculated ejection-phase indices, including passive, active, and total LA fractional shortening, fractional area change, and emptying fraction.…”

Assessment of Left Atrial Deformation and Function by 2‐Dimensional Speckle Tracking Echocardiography in Healthy Dogs and Dogs With Myxomatous Mitral Valve Disease

“…Wall thickness and chamber diameter of the LV were obtained from 2D guided M‐mode images acquired from a right parasternal short‐axis view at the level of the papillary muscles. In particular, LV end‐diastolic and end‐systolic dimensions were normalized to the aortic root (Ao) diameter and compared with previously published reference intervals, in order to identify the presence of LV dilatation 32. Left atrial diameter, Ao diameter, and Ao area were measured on 2D images obtained from a right parasternal short‐axis view at the basilar level,5 and a LA/Ao ratio <1.5 was considered normal 33.…”

“…According to the guidelines for the diagnosis and treatment of MMVD,34 dogs were divided into different groups as follows: control, healthy dogs with normal LV and LA dimensions (group A); dogs having MMVD with normal LV and LA dimensions (group B1); dogs having MMVD with LV, LA, or both dimensions above the reference limits32, 33 but without confirmed radiographic evidence of CHF (group B2); dogs with symptomatic MMVD and radiographic evidence of pulmonary edema/pleural effusion; or dogs with at least 1 confirmed episode of CHF in the past (group C + D).…”

Post-operative echocardiographic evaluation of bioprosthetic mitral valve implantation in sheep

“…Body surface area was calculated using the formula generally accepted for animals: body surface area ¼ 0.101 Â 0.67 body weight. 8 Right parasternal long axis with left ventricular outflow view. In this view (Figure 4), the size of the aortic annulus ( Figure 4b) was measured to evaluate cardiac output and cardiac index.…”