Monitoring of Changes in Intrathoracic Impedance Is Useful for Predicting Decompensated Heart Failure

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Backgrounds: It has been recently shown that the monitoring of changes in Fluid Index (FI) calculated by intrathoracic impedance with cardiac resynchronization therapy (CRT) may be useful for early detection of decompensated heart failure (DHF). However, the relation of changing pattern in FI and DHF remains uncertain, because several factors other than pulmonary congestion may affect on intrathoracic impedance. Therefore, we investigated this issue in order to predict the manifestation of DHF correctly. Methods and Results: We studied 26 chronic heart failure patients (19 males, mean age 66±11 years) who had implanted CRT-defibrillator with impedance monitoring. In the observation term (10.9±4.2 months), 20 patients experienced 48 episodes of FI over 60ω-days. These episodes were divided into two groups whether medical treatment for DHF was required (group A, n=21) or not (group B, n=27). Based on daily FI, we determined linear approximate equation (Y=aX, Y: daily FI, a: the slope of increasing FI, X: the days from the beginning of increasing FI to crossing 60ω-days). We next compared the slope of increasing FI between two groups. The slope of increasing FI was significantly steeper in group A than in group B (3.68±0.88 vs. 2.84±0.96, P<0.01). Conclusions: These results suggest that the monitoring of the slope of increasing FI was helpful for predicting patients with DHF.