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+/-331 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.