Is impedance cardiography-derived systolic time ratio a useful method to determine left ventricular systolic dysfunction in heart failure?

Abstract

s Is Impedance Cardiography-Derived Systolic Time Ratio a Useful Method to Determine Left Ventricular Systolic Dysfunction in Heart Failure? Brenda Thompson, RN, MSN, Mark H Drazner, MD, MSc, Daniel L Dries, MD, MPH and Clyde W Yancy, MD Cardiovascular Institute, University of Texas Southwestern Medical Center, Dallas, TX Introduction Ejection fraction (EF) is the most common measure of ventricular function in patients with heart failure (HF), but serial measurements of EF utilizing echocardiography or radionuclide ventriculography are not practical or cost effective for guiding frequent management decisions. This may be especially pertinent in the titration of evidence based treatment strategies for HF. Impedance cardiography (ICG) is a less expensive noninvasive method for determining hemodynamic parameters and electromechanical timing intervals. Methods To compare the relationship between EF and the ICG-derived parameter of systolic time ratio (STR) in patients with established ventricular dysfunction, retrospective chart reviews were conducted in consecutive patients enrolled in a comprehensive HF program. EF was derived from the multiple gated acquisition (MUGA) scan or echocardiogram (echo) method and STR was measured by ICG (BioZ, CardioDynamics, CA). STR was defined as pre-ejection period divided by left ventricular ejection time. Patients with EF and STR measurements within 14 days were included in the analysis. Results A total of 52 HF patients with cardiopulmonary disease were identified in consecutive manner, with 34 (65.4%) male, 34 (65.4%) white, 16 (30.8%) black, 2 (3.8%) Hispanic, age 52.4 (14.6) years, and etiology ischemic 13 (25%), viral 12%, pulmonary hypertension 7 (13%), dilated cardiomyopathy 14 (27%), diastolic dysfunction 3 (6%), idiopathic 14 (27%). NYHA Class was 2.6 (0.6) with 2 (3.8%) Class I, 17 (32.7%) Class II, 2 (3.8%) Class III, and 31 (59.6%) Class IV. MUGA EF was obtained on 23/52 (44.2%) and echo EF on 29/52 (55.8%). Mean EF was 37.6% + 20.2%, range 10 to 80%, and 39 (75%) had EF 0.50 demonstrated a sensitivity of 92%, specificity 85%, and positive and negative predictive values of 95% and 79%, respectively. Overall accuracy was 90.4%. Of the five patients in which STR did not correctly indicate EF category, two were from MUGA EF and three were from echo EF. Introduction Left ventricular ejection fraction (EF) is the most common measure of ventricular function in patients with heart failure (HF). However, serial measurements of EF utilizing echocardiography or radionuclide ventriculography are not practical or cost effective for guiding frequent management decisions. Impedance cardiography (ICG) is a noninvasive method of obtaining hemodynamics. ICG utilizes the baseline and changes in electrical impedance to calculate hemodynamic parameters, and has been shown to be valid and reproducible in studies comparing ICG with the thermodilution method using a pulmonary artery catheter. ICG also allows measurement of electromechanical timing intervals, such as the systolic time ratio (STR), defined as the ratio of the ventricular isovolumetric contraction time, measured as the pre-ejection period (PEP), divided by the left ventricular ejection time (LVET). Theoretically, a higher STR indicates poorer heart function since the isovolumetric contraction time of the ventricles takes longer in relation to the ejection time of the ventricles. As heart function deteriorates, the pre-ejection period increases and the left ventricular ejection time decreases, increasing the STR. The purpose of the study was to compare the relationship between ejection fraction (EF) and the ICG parameter STR in patients with known heart failure (HF). Conclusion In this retrospective analysis, STR demonstrated a strong relationship with EF. An STR value > 0.50 may be a valid method of determining left ventricular systolic dysfunction. Prospective validation is suggested. STR vs. LVEF STR 0.50 STR < 0.50