Bioimpedance-derived Differences in Cardiac Physiology during Exercise Stress Testing in Low-risk Chest Pain Patients

Non-invasive measurement of cardiac output by whole-body bio-impedance during dobutamine stress echocardiography: Clinical implications in patients with left ventricular dysfunction and ischaemia

OBJECTIVES

To compare non-invasive determination of cardiac index (CI) by whole body electrical bioimpedance using the NICaS apparatus and Doppler echocardiography, and the role of cardiac power index (Cpi) and total peripheral resistance index (TPRi) calculation during dobutamine stress echocardiography (DSE).

SUBJECTS AND METHODS

We enrolled 60 consecutive patients undergoing DSE. Patients were prospectively divided into 3 groups: Group 1 (n = 20): normal DSE (control). Group 2 (n = 20): EF<40% without significant ischaemia. Group 3 (n = 20): patients with significant ischaemia on DSE. Measurements of CI were performed at the end of each stage of DSE by both echocardiographic left ventricular outflow track flow and the NICaS apparatus, using whole-body bio-impedance. MAP was measured simultaneously and TPRi and Cpi were calculated.

RESULTS

The correlation between non-invasive CI as determined by NICaS and echocardiography was 0.81, although Echocardiographic readings of CI were higher during administration of higher doses of dobutamine. Lower EF correlated with lower Cpi, especially stress induced Cpi. Hence, patients with reduced EF (group 2) had a blunted increase in Cpi during stress. Patients with ischaemia (group 3) had a blunted increase in Cpi as well as a decrease in Cpi and increase in TPRi during the last stages of DSE.

CONCLUSION

Measurement of CI by NICaS correlated well with Doppler derived CI. The calculation of Cpi and TPRi changes during dobutamine stress may provide important clinical information.

[Thoracic electrical bioimpedance in the follow-up of patients with cardiovascular disorders]

Thoracic electrical bioimpedance is a new non-invasive technique for obtaining haemodynamic parameters. The method involves the passing of low amperage, high frequency current through the thorax. The current induces a change of resistance within the thorax, which is registered by electrodes. The overall impedance of the thorax is a measure of the electrical resistance of the thorax to this high frequency, low amplitude current. In clinical practice, thoracic electrical bioimpedance has been applied in diagnostic, therapeutic, and prognostic use in patients with heart failure and hypertension, patients with pacemakers, within the scope of early diagnosis of implant rejection following heart transplantation, as well as in patients with kidney disorders, before and after dialysis. However, one of its most important applications is in the determination of antihypertensive therapy, because it provides the parameters that reflect the genesis of arterial blood pressure. In assessing these parameters, optimal therapy adjusted to the haemodynamic status of each patient can be prescribed.

Transthoracic electrical bioimpedance: a means of filling the void?

OBJECTIVES

To examine the published evidence regarding the use of transthoracic electric bioimpedance (TEB) for the non-invasive monitoring of cardiac output in the ED.

METHOD

Databases of the medical literature, relevant textbooks and the Internet were searched for articles regarding TEB. Criteria for inclusion were drawn up prior to examination of the articles and included adherence to guidelines for comparing methods of clinical measurement.

RESULTS

Results are discussed under the following headings: technological capability, diagnostic accuracy, limitations, range of possible uses, therapeutic impact, impact on health care providers, patient outcome and future directions.

CONCLUSION

TEB is a technique for the non-invasive monitoring of cardiac output whose ease of use, continuous data acquisition and versatility suggest it may have a role to play in the care of patients in our EDs.