Figure 2.

Regressions of age vs EF, FS, and LVESVI in echocardiography shown by fit splines. Data from 19 golden retriever muscular dystrophy dogs in the single‐time‐point echocardiographic study demonstrate correlations between age and EF, FS, and LVESVI. Age correlated negatively with EF and FS (ρ=−0.7866 and ρ=−0.6991; P<0.001 for both), and positively with LVESVI (ρ=0.7203; P<0.001). The smoothing fit splines (λ=0.05; R ²>75%) were obtained to best fit the data points and predict the values at different ages. The splines showed a more dramatic change around the 30 to 45 month period (gray color area). The blue, red, and green color regions represent the confidence of fit. Phenotypic variation and low numbers of older dogs influenced the accuracy of splines later in the disease course. The black dash lines represent the clinical cut off values of systolic dysfunction (EF of 55% in DMD; EF of 40%, FS of 27%, and LVESVI of 55 mL/m² in canine dilated cardiomyopathy). Based on the fit splines, EF fell to 53.78% at age 34 months and to 38.82% at age 43 months. FS fell to 26.82% at 35 months. LVESVI increased to 57.29 mL/m² at 44 months. Taken together, our results indicate that systolic dysfunction occurs between 30 to 45 months of age. EF indicates ejection fraction; FS, fractional shortening; LVESVI, left ventricular end‐systolic volume index.