Predictive impact of the decreasing rate of intrathoracic impedance in worsening chronic heart failure.

PURPOSE: Intrathoracic impedance monitoring is useful for heart failure (HF) management in patients with cardiac resynchronization therapy (CRT). However, more accurate identification of worsening chronic HF (CHF) is required in the clinical setting. We investigated this issue by estimating changes in impedance.
METHODS: We studied 38 CHF patients (29 males, mean age 67 years) with CRT-defibrillator capable of impedance monitoring. During the follow-up period (20.7 ± 7.8 months), the subjects experienced a total of 129 fluid index threshold (60 ohm·days) crossing events. These events were divided into two groups: HF events (n = 70) and no HF events (n = 59). Based on the impedance at the beginning of increasing fluid index (S) and at the crossing of 60 ohm·days (E), the rate of impedance change (S - E / S) was estimated. In addition, the elapsed time from S to E (T) was evaluated. Then, we calculated the rate of impedance change per day (S - E / S × T) in each group.
RESULTS: The rate of impedance change per day was significantly higher in HF events than in no HF events (0.86 ± 0.48 vs. 0.37 ± 0.22%/day, P < 0.01). By receiver operating characteristic curve for identification of HF events, the best cutoff value of the rate of impedance change was 0.48%/day (sensitivity 80%, specificity 81%, and area under the curve 0.85).
CONCLUSIONS: These results suggest that a faster drop in intrathoracic impedance reflected worsening CHF in patients with CRT-defibrillator. Thus, intrathoracic impedance monitoring based on the rate of impedance change may provide a more accurate identification of worsening CHF.