Hemodynamic monitoring by intracardiac impedance measured by cardiac resynchronization defibrillators: Evaluation in a controlled clinical setting (BIO.Detect HF II study).

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.

Evaluation of thoracic impedance trends for implant-based remote monitoring in heart failure patients - Results from the (J-)HomeCARE-II Study.

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 ±â€¯10.1 years, 77% male, QRS 139.8 ±â€¯36.0 ms, ejection fraction 26.8 ±â€¯7.0%) implanted with a CRT-D (67%) or an ICD (33%) for 21.4 ±â€¯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. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT00711360 (HomeCARE-II) and NCT01221649 (J-HomeCARE-II).

Device-based impedance measurement is a useful and accurate tool for direct assessment of intrathoracic fluid accumulation in heart failure.

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.

Assessing acute ventricular volume changes by intracardiac impedance in a chronic heart failure animal model.

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.

Intracardiac impedance monitors hemodynamic deterioration in a chronic heart failure pig model.

INTRODUCTION: A large number of heart failure (HF) patients benefit from cardiac resynchronization therapy. Measurements of intrathoracic impedance (ITZ) by implantable devices correlate with intrathoracic fluid content and are used for monitoring lung edema formation in HF patients. However, intrathoracic fluid is only an indirect parameter of cardiac function. We hypothesized that changes in intracardiac impedance correlate with left ventricular (LV) volume changes. Therefore, measurements of intracardiac impedance between a right ventricular lead and a LV lead may be used to monitor long-term changes of LV function. METHODS AND RESULTS: HF was successfully induced in nine mini-pigs by continuous high-rate pacing. Hemodynamic parameters as well as intracardiac impedance and ITZ were measured before HF induction and after 20 +/- 5 days of high-rate pacing. After the pacing period, we found a significant deterioration of hemodynamics, reflected by a reduction of ejection fraction from 71+/-11% to 48+/-7% and an increase of LV end diastolic pressure (EDP) from 12 +/- 4 mmHg to 26 +/- 8 mmHg. Worsening of cardiac function correlated with a significant >30% decrease of end diastolic intracardiac impedance, in accordance with a >20% increase of end diastolic volume (EDV). ITZ decreased by more than 8%. We observed a significant inverse correlation between end diastolic intracardiac impedance and EDP (r =-0.81, P < 0.001). CONCLUSIONS: In this animal model, changes of intracardiac impedance revealed hemodynamic deterioration as reflected by EDV and EDP pressure. Thus, intracardiac impedance is a promising new application to monitor heart failure status within implantable devices.