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 diastolic time intervals. This study was designed to assess the ability of IC to accurately measure isovolumic relaxation time (IVRT) and determine relative cardiac contractility, thereby differentiating systolic from diastolic mechanisms in acute CHF.


METHODS
In an evaluation of the technique, the average differences in the diastolic time intervals measured in normal subjects by both IC tracings and phonocardiography were compared. Likewise, the average Heather index (HI) of patients with known systolic dysfunction (ejection fraction < 30% by echo-cardiography) was compared with the mean HI measured in the normal subjects. In a retrospective analysis, the clinical performance of the method was examined by extracting the values of IVRT and HI from 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 volunteers 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), contrasting to the much lower value of 2.8 (95% CI = 1.98 to 3.62) seen in eight subjects with documented systolic dysfunction. In 26 patients with decompensated 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 considerable 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 failure.


CONCLUSIONS
IC measures of contractility and diastolic time intervals are a potentially effective method for differentiating the dominant mechanisms of CHF in the emergent setting and categorizing CHF patients into different subsets.
Summers
R L
RL
Department of Emergency Medicine, University of Mississippi Medical Center, Jackson 39216, USA. rsummers@pol.net
Kolb
J C
JC
Woodward
L H
LH
Galli
R L
RL
D000208:Acute Disease; D000328:Adult; D002302:Cardiac Output / Q000502:physiology; D002307:Cardiography, Impedance; D016001:Confidence Intervals; D003971:Diastole / Q000502:physiology*; D004632:Emergency Medical Services / Q000379:methods; D005069:Evaluation Studies as Topic; D005260:Female; D006333:Heart Failure / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D017379:Hypertrophy, Left Ventricular / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D012016:Reference Values; D012189:Retrospective Studies; D013599:Systole / Q000502:physiology*; D013997:Time Factors