Intrathoracic impedance monitoring to detect chronic heart failure deterioration: Relationship to changes in NT proBNP

Background: An alert algorithm, based on intrathoracic impedance monitoring, has been incorporated into a cardiac resynchronisation device (CRT) to detect pulmonary fluid accumulation, and to audibly alert patients to decompensating chronic heart failure (CHF). Aims: To evaluate this algorithm, alert events were correlated with changes in NT-proBNP concentration and CHF status. Methods and results: In a prospective observational study of 62 patients (89% male, aged 67 +/- 1 year), NT proBNP plasma concentrations, clinical CHF status, and device data were collected at enrolment, during regular follow-up and at device alerts. Over a mean follow-up of 27 +/- 2 weeks, pooled data indicated a weak, but significant inverse relationship between relative changes in intrathoracic impedance and NT proBNP (r=-0.3; p < 0.001). In 52 device alerts from 35 patients, NT proBNP increased by 66 +/- 19% from 2039 +/- 1331 pg/ml (p < 0.001). The increase in NT proBNP was higher in alerts with clinical signs of CHF deterioration (n = 30, 89 +/- 25%;p < 0.001) than in alert events without clinical signs (n = 22, 25 +/- 15%; p = n.s.). Conclusion: Intrathoracic impedance based alert events are associated with a significant increase in NT-proBNP concentration. These data indicate that intrathoracic impedance monitoring might facilitate the outpatient management of CHF patients with implanted CRT devices. 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.