Daily Shock Impedance Measured by Implantable Cardioverter Defibrillator is Useful in the Management of Congestive Heart Failure

Background Clinical data suggest that changes in intrathoracic impedance and fluid accumulation in the lung are inversely related. Methods and Results Daily shock impedance (S-IMP) was evaluated in 29 patients in whom a Ventak Prizm 2 was implanted (61±14 years old). The mean follow-up period was 45±18 weeks, during which 6 patients had episodes of decompensated heart failure (DHF group) and the others did not (NHF group). There was no significant difference between the DHF group and NHF group in the mean value of the S-IMP (46.4±3.3 vs 45.4±5.4 Ω). The range of S-IMP in individual patients in the DHF group was significantly greater than that in the NHF group (13.8±0.38 vs 7.0±3.1 Ω, p<0.0001). Mean weekly change of S-IMP in individual patients in the DHF group was significantly greater than that in the NHF group (1.583±0.630 vs 1.092±0.361 Ω, p<0.0176). When the cut-off value was set at >1.242Ω, sensitivity was 100% and specificity was 69.6% for a diagnosis of DHF. There was a significant negative correlation between the percent increases in brain natriuretic peptide (BNP) and S-IMP (correlation coefficient: -0.775 p<0.0001) in the DHF group. There was an inverse relation between BNP and S-IMP. Conclusions Measurement of shock impedance may be useful in the management of congestive heart failure.