Differentiating systolic from diastolic heart failure using impedance cardiography

Objective: Differentiating systolic from diastolic congestive heart failure (CHF) is often difficult in the ED. Impedance cardiography (IC) allows for the noninvasive evaluation of systolic function and measurement of diastol ic time intervals. This study was designed to assess the ability of IC to a ccurately measure isovolumic relaxation time (IVRT) and determine relative cardiac contractility, thereby differentiating systolic from diastolic mech anisms in acute CHF. Methods: In an evaluation of the tec`hnique, the avera ge differences in the diastolic time intervals measured in normal subjects by both IC tracings and phonocardiography were compared. Likewise, the aver age Heather index (HI) of patients with known systolic dysfunction (ejectio n fraction < 30% by echo-cardiography) was compared with the mean HI measur ed in the normal subjects. In a retrospective analysis, the clinical perfor mance of the method was examined by extracting the values of IVRT and HI fr om IC tracings of patients presenting with CHF. The determined IVRT and HI values were then correlated to clinical markers for diastolic and systolic dysfunction. Results: Analysis of 280 IC tracings in eight healthy voluntee rs revealed an average difference of 0.0075 seconds (95% CI = -0.0067 to 0. 0217) when IVRT intervals measured by phonocardiography and IC are compared . The HI in this normal group averaged 14.2 (95% CI = 9.4 to 19.0), contras ting to the much lower value of 2.8 (95% CI = 1.98 to 3.62) seen in eight s ubjects with documented systolic dysfunction. In 26 patients with decompens ated CHF, there was a close correlation (r = 0.81) of the measured IVRT to left ventricular hypertrophy by voltage criteria and while a fall in the HI was correlated with intravascular volume expansion. Though there was consi derable overlap (46%) in mechanisms of CHF, 35% of the patients were found to have only systolic dysfunction (HI < 5 and IVRT < 0.125), while 19% had a predominantly diastolic etiology (IVRT > 0.125 and HI > 5) for their fail ure. Conclusion: IC measures of contractility and diastolic time intervals are a potentially effective method for differentiating the dominant mechani sms of CHF in the emergent setting and categorizing CHF patients into diffe rent subsets.