Beat‐to‐beat variability of echocardiographic measurements of left ventricular end diastolic diameter and performance

Echocardiographic measurements of left ventricular dimensions and performance correlate well with similar data from other sources. However, little attention has been paid to the beat‐to‐beat variations in these parameters in individual subjects. Considerable variability in measurements of left ventricular end diastolic diameter (EDD), R‐R interval, mean circumferential fiber shortening velocity (V cf ), and ejection fraction (EF) has been demonstrated in subjects in both sinus rhythm and atrial fibrillation. The coefficients of variation have varied from 2.5 to 9 percent, 2.1 to 11.2 percent, 4.4 to 11.0 percent, and 3.4 to 7.8 percent, respectively, in different individuals in sinus rhythm and from 2.0 to 7.9 percent, 2.1 to 20.7 percent, 4.9 to 30.0 percent, and 1.9 to 90.0 percent, respectively, in different patients in atrial fibrillation. Recent ultrasound studies of the interrelationships among preload, afterload, cycle length, and indices of left ventricular performance have yielded variable results. In this study the relationships between both EDD and R‐R interval and echocardiographic measurements of left ventricular function were analyzed in individual subjects in both sinus rhythm and atrial fibrillation. Changes in EDD and, to a lesser extent, cycle length were shown to be accompanied by predictable changes in indices of left ventricular function. EDD correlated better than did R‐R interval with V cf and EF in 8 of 10 and 10 of 10 normal subjects, respectively, and in 9 of 11 and 7 of 11 patients in atrial fibrillation, respectively. The data suggest that preload has a more important effect than cycle length on left ventricular performance.