Relationship between bioimpedance, thermodilution, and ventriculographic measurements in experimental congestive heart failure

Abstract

PURPOSE OF INVESTIGATION - Bioimpedance cardiography has been suggested as a non-invasive means to monitor cardiac function but has not been tested in cases of severe ventricular dysfunction. This study compared thermodilution stroke volume, ventriculographic left ventricular ejection fraction, bioimpedance stroke volume, and the maximum first derivative of the bioimpedance signal dZ/dtmax, during the development of experimental congestive heart failure. DESIGN - Simultaneous thermodilution stroke volume, ventriculography, and bioimpedance measurements were serially measured in pigs following acute pacing, and after 1, 2, and 3 weeks of tachycardia. Thermodilution stroke volume measurements were obtained by positioning a thermistor tipped catheter into the pulmonary artery and integrating the thermodilution curve with respect to heart rate. Left ventricular stroke volume and ejection fractions were measured from single plane ventriculograms using the area-length method. Using a series of electrodes positioned on the thoracic segment and a low level current (2.5 ma), the bioimpedance waveform was recorded and stroke volume and dZ/dtmax computed. SUBJECTS - The subjects were eight pigs (23-30 kg) with developing ventricular dysfunction due to chronic rapid atrial pacing (240 beats.min-1) and four controls. MEASUREMENTS AND MAIN RESULTS - Left ventricular ejection fraction decreased significantly from acutely paced values following 7 d tachycardia [60(SEM 1)% v 41(3)% respectively, p less than 0.01] and continued to decline with longer durations of tachycardia. A significant correlation was observed between ejection fraction and dZ/dtmax (r = 0.74, n = 32). Thermodilution and bioimpedance stroke volumes fell significantly from acutely paced values after week 2 of tachycardia [thermodilution: 13.8(0.9) v 8.5(1.4) ml; bioimpedance: 13.6(1.1) v 11.2(1.5) ml respectively, p less than 0.05] and were highly correlated throughout the study period (r = 0.90, n = 32). However, bioimpedance overestimated thermodilution values at week 2 (p less than 0.05) and at week 3 of tachycardia [thermodilution: 8.4(0.8) ml v bioimpedance: 9.6(1.0) ml, NS]. CONCLUSION - In a tachycardia induced model of heart failure, bioimpedance was significantly correlated with thermodilution stroke volume. The peak first derivative of the bioimpedance signal dZ/dtmax may provide a non-invasive index of ventricular pump performance. While these results are promising, further studies are required to evaluate the diagnostic value of bioimpedance cardiography in the clinical setting.

Feasibility of Using an Implantable System to Measure Thoracic Congestion in an Ambulatory Chronic Heart Failure Canine Model

“…Externally measured transthoracic electrical impedance techniques have been shown to reflect alterations in intrathoracic fluid and pulmonary edema in both acute animal and human studies 7–9 . Specifically, when using high‐rate pacing in a swine model to develop and establish heart failure, thoracic impedance decreased significantly over a 3‐week period 10 …”

Estimation of left ventricular stroke volume by impedance cardiography: its relation to the aortic reservoir

“…Although stroke volume measurements with ICG have been impressively accurate in many circumstances (Teo et al 1985; Spinale et al 1988, 1990; Spinale, 1995; Pianosi, 1997; Van De Water et al 2003), no one has offered an explanatory mechanism. Based on the present study, in which we used our recently proposed reservoir–wave approach, we suggest that the rate of change of aortic reservoir volume precisely predicts the aortic flow waveform that, when integrated, yields stroke volume (see Fig.…”

“…Those advantages led to extensive laboratory and clinical studies designed to establish its reliability and validity. The ICG‐derived SV has been compared with SV measured by established techniques, including thermodilution (Spinale, 1995), direct and indirect Fick methods (Teo et al 1985; Pianosi, 1997), ventriculography (Spinale et al 1990; Schwaab et al 1999) and echocardiography (Sodolski & Kutarski, 2007) in subjects ranging in age from children (Pianosi, 1997) to the elderly (Spinale et al 1988; Kamath et al 2009), both healthy and critically ill (Teo et al 1985; Spinale et al 1988; Pianosi, 1997; Kamath et al 2009). However, the theoretical basis of ICG remains controversial, and the parameters generated by the ICG have not been related satisfactorily to the haemodynamic events upon which they must be based.…”

Utility of Impedance Cardiography for the Identification of Short-Term Risk of Clinical Decompensation in Stable Patients With Chronic Heart Failure

“…The flow of blood within the thorax can produce striking but transient changes in electrical impedance, which may be detected by ICG (6,7). By assessing the change in impedance of an alternating current applied across the chest, this technique can measure the baseline impedance as well as the magnitude and duration of the change in impedance during systole (Fig.…”

“…Noninvasive impedance cardiography (ICG) uses changes in thoracic electrical impedance to measure thoracic fluid content, changes in the duration of cardiac ejection, and the velocity of blood flow within the aorta (6,7). Impedance cardiography has been used to estimate cardiac output and cardiac filling pressure in patients with and without HF (6 -11), but little is known about its ability to predict episodes of clinical decompensation.…”