Current guidelines for assessing the fluid status of patients with heart failure include subjective physical findings, which often occur late in decompensation, and objective pulmonary artery catheter measurements, whose use is controversial in patients with heart failure. Impedance cardiography, which assesses cardiac function by measuring the opposition to an alternating electric current in the thorax, indicates the amount of fluid in the thorax. It is used externally by employing electrodes on the thorax but can also be used internally by electrodes within a cardiac pacemaker. Recent studies have suggested that one of its direct measurements, thoracic impedance, may identify patients at risk for decompensation of heart failure, but because these measurements inconsistently correlate with pulmonary artery catheter measurements and study sample sizes are small, further research is required before its use can be recommended.

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