Bioimpedance Spectroscopy for the Evaluation of Heart Failure

The technique involves attaching electrodes to the patient's forearm and ipsilateral ankle, with the patient in a supine position. The BCM® measures the body resistance and reactance to electrical currents of 50 discrete frequencies, ranging between 5 and 1000 kHz. Based on a fluid model using these resistances, the extracellular water (ECW), the intracellular water (ICW) and the total body water (TBW) are calculated. All calculations are automatically performed by the software of the BCM® device. Absolute fluid overload (AFO) is is defined as the difference between the expected patient's ECW under normal physiological conditions and the actual ECW, whereas the relative fluid overload (RFO) is defined as the absolute fluid overload AFO to ECW ratio.

Examinations will be performed in the supine position. Scanning of the anterior and lateral chest will be performed on both sides of the chest, from the second to the fourth (on the right side to the fifth) intercostal spaces, at parasternal to mid-axillary lines. B-lines will be recorded in each intercostal space and were defined as a hyperechoic, coherent US bundle at narrow basis going from the transducer to the limit of the screen. B-lines starting from the pleural line can be either localized or scattered to the whole lung and be present as isolated or multiple artifacts (with a distance 7 mm between 2 artifacts). The sum of B-lines produces a score reflecting the extent of lung water accumulation (0 being no detectable B-line).

All echocardiographic measurements will be carried out according to the recommendations of the American Society of Echocardiography by an observer unaware of the lung ultrasound and bioimpedance results. Echocardiographic evaluation will provide information about cardiac anatomy (e.g. volumes, geometry, mass) and function (e.g. left ventricular function and wall motion, valvular function, right ventricular function, pulmonary artery pressure, pericardium).