BACKGROUND:In patients with cardiac resynchronization therapy defibrillators (CRT-Ds), intracardiac impedance measured by dedicated CRT-D software may be used to monitor hemodynamic changes. We investigated the relationship of hemodynamic parameters assessed by intracardiac impedance and by echocardiography in a controlled clinical setting. METHODS:The study enrolled 68 patients (mean age, 66 ± 9 years; 74% males) at 12 investigational sites. The patients had an indication for CRT-D implantation, New York Heart Association class II/III symptoms, left ventricular ejection fraction 15%-35%, and a QRS duration ≥150 ms. Two months after a CRT-D implantation, hemodynamic changes were provoked by overdrive pacing. Intracardiac impedance was recorded at rest and at four pacing rates ranging from 10 to 40 beats/min above the resting rate. In parallel, echocardiography measurements were performed. We hypothesized that a mean intra-individual correlation coefficient (rmean) between stroke impedance (difference between end-systolic and end-diastolic intracardiac impedance) measured by CRT-D and the aortic velocity time integral (i.e., stroke volume) determined by echocardiography would be significantly larger than 0.65. RESULTS:The hypothesis was evaluated in 40 patients with complete data sets. The rmean was 0.797, with a lower confidence interval bound of 0.709. The study hypothesis was met (p = 0.007). A stepwise reduction of stroke impedance and stroke volume was observed with increasing heart rate. CONCLUSIONS:Intracardiac impedance measured by implanted CRT-Ds correlated well with the aortic velocity time integral (stroke volume) determined by echocardiography. The impedance measurements bear potential and are readily available technically, not requiring implantation of additional material beyond standard CRT-D system.

Aims: Remote monitoring by implantable devices substantially improves management of heart failure (HF) patients by providing diagnostic day-to-day data. The use of thoracic impedance (TI) as a surrogate measure of fluid accumulation is still strongly debated. The multicenter HomeCARE-II study evaluated clinically apparent HF events in the context of remote device diagnostics, focusing on the controversial role of TI. Methods and results: We followed 497 patients (66.6 +/- 10.1 years, 77% male, QRS 139.8 +/- 36.0 ms, ejection fraction 26.8 +/- 7.0%) implanted with a CRT-D (67%) or an ICD (33%) for 21.4 +/- 8.1 months. An independent event committee confirmed 171 HF events of which 82 were used to develop a TI-based algorithm for the prediction of imminent cardiac decompensation. Highly inter-individual variations in patterns of TI trends were observed. The algorithm resulted in a sensitivity of 41.5% (50.0%) with 0.95 (1.34) false alerts per patient year, and a positive predictive value of 7.9% overall and 27.9% in the HF event group of patients. Averaged ratio statistics showed a significant pre-hospital decrease and a highly significant in-hospital increase in TI after intensified diuresis. Recurrent decompensations turned out to be preceded by a significantly stronger decrease of TI compared to first events with a higher chance for detection (63.6% sensitivity, p < 0.05). Conclusions: Overall performance in predicting imminent decompensation by monitoring TI alone is limited due to its high inter-patient variability. TI stand-alone applications should be redirected towards a target population with more advanced symptoms where post-hospital observation aimed to maintain the patient's discharge status might be the most valuable approach. (C) 2019 Elsevier Inc All rights reserved.

AIMS Heart failure patients are often equipped with implanted devices and are frequently hospitalized due to volume overload. Reliable prediction of imminent fluid congestion has the potential to provide early detection of cardiac decompensation and therefore might be capable of enhancing therapy management. We investigated whether implant-based impedance (Z) measurement is closely correlated with directly assessed extravascular lung water and might thus be useful for patient monitoring. METHODS AND RESULTS In sheep, pulmonary fluid congestion was induced. Continuous haemodynamic monitoring was performed and extravascular lung water index (EVLWI) assessed. An implanted device with a right ventricular lead measured Z using different electrode configurations. All animals developed gradual pulmonary fluid accumulation leading to inclining lung oedema: EVLWI did increase from 9.5 +/- 1 to 21.1 +/- 5.1 mL/kg (+127%). A concomitant decrease of Z by up to 23%, depending on the electrode configuration, was observed and regression analysis between Z and EVLWI yielded a significant inverse correlation. CONCLUSION Changes of Z show a strong inverse correlation with changes of directly measured EVLWI. This allows the application of Z as a measure of intrathoracic fluid status and has the potential to optimize patient care, especially in the context of evolving telemedicine concepts.

Background: Implantable device diagnostics may play an essential role in simplifying the care of heart failure patients by providing fundamental insights into their complex clinical patterns. Early recognition of heart failure progression by a continuous hemodynamic monitoring would allow for timely therapeutic interventions to prevent decompensation and hospitalization. In this study, the feasibility of assessing ventricular volume changes by implant‐based measurements of intracardiac impedance was tested in a heart failure animal model. Methods: Heart failure was induced in five minipigs by high‐rate pacing over 3 weeks. During a final open‐chest examination a graded dobutamine stress test was performed. Stroke volume (SV) was measured by an ultrasonic flow probe at the ascending aorta. End diastolic pressure (EDP) and maximum pressure slope (dP/dtmax) were calculated from a left ventricular microtip catheter signal. Impedance was measured by an implanted pacemaker between biventricular leads. Stroke impedance (SZ) was calculated as the difference between end‐systolic and end‐diastolic impedance (EDZ). Results: Administration of dobutamine led to an increase in SV (55 ± 16%), dP/dtmax (107 ± 89%), and SZ (56 ± 30%). EDP changed by 37 ± 21% whereas EDZ changed by 7.4 ± 4%. Significant correlations were found between SZ and SV (r = 0.88), and between EDZ and EDP (r =−0.82). Conclusion: The strong correlation with SV allows the application of intracardiac impedance measurements for an implant‐based continuous monitoring of cardiac function. Impedance may also be used for hemodynamic optimization of cardiac resynchronization therapy.

Introduction: Recently, it was shown that continuous implant-based measurements of intrathoracic impedance (Z) as a surrogate measure of intrathoracic fluid status allows detection of cardiac decom...

Introduction : Heart failure (HF) is often associated with hospitalizations due to pulmonary congestion resulting in cardiogenic lung edema (LE). Implant-based monitoring of intrathoracic impedance as a surrogate measure of thoracic fluid status provides the chance to detect early stages of cardiac decompensation. Previously pulmonary fluid congestion has been related to clinical or preload parameters. In this study we tested for the first time the correlation between changes in intrathoracic impedance (Z) and directly measured intrathoracic fluids during LE induction as well as LE recovery. Methods : 20 anesthetized sheep were studied, 3 served as controls, in 17 acute pulmonary fluid overload was induced by hypervolemia in combination with gradually increasing peripheral arterial resistance, in 5 sheep restitution of pulmonary fluid overload was attempted. Hemodynamics were continuously monitored including LVEDP. A transpulmonary thermodilution system was used to determine intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). Z was measured between the coil of a right ventricular ICD lead and an implanted device case. Results : All variables remained stable for the control group, whereas pulmonary fluid accumulation was observed in the LE group, confirmed by mean increases of LVEDP (4 to 28 mmHg), ITBV (1464 to 2273 ml) and EVLW (954 to 1267 ml). There was a concomitant decrease in intrathoracic impedance Z (−15%). Regarding LE recovery, intensified diuresis resulted in restitution of pulmonary fluid overload and a decrease in ITBV (−22%) paralleled by an increase of Z (+6%). Significant inverse correlations between Z and LVEDP (r=−0.84), ITBV (r=−0.85) and EVLW (r=−0.77) were calculated. Conclusions : Here we show for the first time that changes of intrathoracic impedance show a strong inverse correlation with changes in directly assessed intrathoracic fluids and preload parameters during formation of and recovery from lung edema. Therefore, implants capable of long term monitoring of intrathoracic impedance will have the potential to enhance therapy management in HF patients. A combination of these device-based features with existing telemedicine concepts has a tremendous potential to improve outpatient HF management.