Rate-corrected mean velocity of fiber shortening-stress at peak systole as a load-independent measure of contractility

The relation of mean velocity of fiber shortening-stress at end-systole is a good load-independent index of left ventricular contractility, but involves simultaneous M-mode echocardiography, carotid tracing and blood pressure determination, which may be impractical in children. As stress at peak systole and end-systole are closely related, this study examined whether the relation of mean velocity of fiber shortening-stress at peak systole could be used as a simpler method of assessing left ventricular contractility in a normal population of children. In addition, the cross-sectional normal range for a pediatric population was obtained. In 25 normal children aged 4 to 17 years (mean age 11), rate-corrected mean velocity of fiber shortening (MVCF_c), stress at peak systole (σPS), and end-systolic stress (σES) were determined using echocardiography, carotid pulse tracing and blood pressure measurement. Six patients with cardiomyopathy (mean age 8 years) were also studied. The relation of stress at peak systole and end-systolic stress was σPS = 1.004 σES + 12.0 (r = 0.91, SEE = 4.98; p < 0.001) for the normal group, and σPS = 1.083 σES + 7.7 (r = 0.99, SEE = 4.07; p < .001) for the cardiomyopathic group. This slope of the regression line was slightly higher and the difference was statistically significant. The slope of MVCF_c = 0.0066 σPS + 1.55 (SEE = 0.131, r = -0.52) was nearly identical to that of MVCF_c = 0.0065 σES + 1.46, (SEE = 0.135, r = -0.46), with no difference in the regression coefficients. Individual measurements for the cardiomyopathic group fell on similar parts of the graph whether stress at peak systole or end-systole was used for the ordinate of the plot with MVCF_c. Thus, in the absence of outflow obstruction, the relation of MVCF_c-stress at peak systole correlates well with the relation using stress at end-systole and can be used to assess left ventricular contractility.