Comparison of changes in ejection fraction to changes in impedance cardiography cardiac index and systolic time ratio.

Ejection fraction (EF) is the most common measure of left ventricular function in patients with heart failure. However, serial measurements of EF are costly and not practical for guiding frequent management decisions. Impedance cardiography (ICG) provides noninvasive hemodynamic measures with proven validity. The purpose of this study was to assess how changes in ICG parameters compared with changes in EF in heart failure subjects enrolled in a comprehensive outpatient management program. Retrospective chart review identified 13 subjects with two sets of paired echocardiography and ICG measurements (before and after treatment in an outpatient heart failure clinic setting). Mean age was 69+/-11 years, etiology was 54% ischemic heart disease, and mean New York Heart Association class was 2.5+/-0.5. The mean time between pre- and posttreatment EF measurements was 198+/-161 days. Changes in cardiac index and systolic time ratio by ICG were compared with changes in EF by echocardiography. From entry to final measurement, mean EF improved 9%+/-13%. Seven (54%) subjects had >5% improvement in EF, three (23%) had >5% decrease, and three had <5% change. Changes in ICG cardiac index and systolic time ratio were highly correlated with changes in EF (0.85, -0.73). ICG may be a practical, reliable, and cost-effective method of monitoring left ventricular function and guiding management decisions.