Echocardiographic Ratio Indices in Overtly Healthy Boxer Dogs Screened for Heart Disease

Abstract

Background Boxer dogs are routinely screened by echocardiography to exclude congenital and acquired heart disease. Individuals of a given breed may span a large range of body sizes, potentially invalidating linear regression of M-mode measurements against body weight. Echocardiographic ratio indices (ERIs) provide a novel method of characterizing echocardiographic differences between Boxers and other dog breeds. Hypothesis ERIs obtained from overtly healthy Boxer dogs presented for cardiac screening will be different from ERIs established for normal non-Boxer dogs, and those differences will be unrelated to aortic velocity or systolic blood pressure. Animals Eighty-one Boxers with no outward clinical signs of heart disease were studied. Methods All dogs were examined by 2-dimensional, M-mode, and Doppler echocardiography. M-mode measurements were used to perform ERI calculations, and the indices in Boxers were compared between Boxers with varying severity of arrhythmia and those of normal non-Boxer dogs. Results Differences in weight-based ERIs, which reflect increased thickness of the left ventricular free wall (LVW) and interventricular septum (IVS) and smaller aortic size, were found in overtly healthy Boxer dogs compared with normal non-Boxer dogs. ERIs of left atrial and LV cavity size in overtly healthy Boxers were not significantly different from those of non-Boxer dogs. Conclusions and Clinical Importance Boxer dogs may have an increased relative thickness of the LVW and IVS that is independent of aortic size, aortic velocity, or arterial blood pressure, and this morphology should be taken into consideration when screening Boxers by echocardiography.

Simpson's Method of Discs for Measurement of Echocardiographic End‐Diastolic and End‐Systolic Left Ventricular Volumes: Breed‐Specific Reference Ranges in Boxer Dogs

“…A characteristic of the Boxer breed, which could theoretically affect afterload and thus ESVI, is the smaller diameter of the aortic annulus compared with other breeds 5, 6. Although Boxers were found to have increased indices of LV wall thickness compared with healthy non‐Boxer dogs, this was independent of LV cavity size,5 and thus unlikely to substantially affect ESVI in this study.…”

“…To provide breeders and owners with optimal screening programs, development of breed‐specific reference values is important. Indeed, previous studies have shown a smaller left ventricular (LV) outflow tract, higher aortic blood flow velocities, and increased LV wall thickness in Boxers compared with non‐Boxer dogs 5, 6…”

Normal Echocardiographic Values

“…Indeed, in this breed the septum and left ventricular free wall tend to be thicker than in other breeds [13]. This trait seems independent of the size of the aorta, velocity of aortic blood flow, and systemic arterial pressure.…”

Association of Dilated Cardiomyopathy with the Striatin Mutation Genotype in Boxer Dogs

“…The DCM phenotype was defined as left ventricular fractional shortening (FS%) <21%, left ventricular internal diastolic dimension (LVIDD) >4.8 centimeters (cm), and left ventricular systolic internal dimension (LVIDS) >3.3 cm. These values were chosen based on being outside of (either above for LVIDD and LVIDS, or below for FS%) the reference range as defined for normal adult Boxer dogs . M‐mode echocardiographic measurements were recorded from 2‐dimensional guided right parasternal short axis views obtained with either a 3.5 or 5‐MHz transducer with the dog positioned in right lateral recumbency.…”