Correlation between pulmonary artery pressure and thoracic impedance: Insights from daily monitoring through an implanted device in chronic heart failure

Background Thoracic impedance (TI) decrease and pulmonary artery pressure (PAP) elevation precede acute decompensation in congestive heart failure (HF). However, the relationship between TI and PAP has been studied only in the context of acute decompensation. Methods This prospective, observational study enrolled subjects with reduced ejection fraction HF, previously implanted with an ICD capable of measuring TI. Patients underwent implantation of a sensor for direct measurement of PAP (CardioMEMs™). Both TI and PAP were remotely monitored daily during follow up. Investigators were blinded to PAP values during the first three months, then PAP was used as a guide to therapy. Results Ten patients were followed up for 405 ± 141 days (3720 patient-days). During hemodynamic guided therapy, diastolic PAP (dPAP) decreased from 27.8 ± 10.2 mm Hg to 24.0 ± 8.0 mm Hg (p < 0.001); non-significant variations of TI were observed. A significant negative correlation was found between the variations of TI and PAP vs. baseline (p < 0.001). Episodes of sustained increase of PAP preceded subsequent periods of TI decrease by 5.6 ± 3.9 days, but the former were poor predictors of the latter (sensitivity 0.37). Conclusions Our study confirms the strict correlation that exists between left ventricular filling pressures and lung water content, estimated by dPAP and TI, respectively. However, dPAP acute variation analysis showed a limited value in predicting subsequent episodes of TI decrease.