Fluid Index Threshold Research Articles

Abstract 13998: Predicting Atrial and Ventricular Tachyarrhythmias by Monitoring Intra-Thoracic Impedance, an Updated Meta-Analysis

Background: Many cardiac implantable devices have the capability of monitoring the volume status in patients with heart failure by tracking the intra-thoracic impedance changes over time measured by OptiVol fluid index. Objective: The aim of this study is to evaluate the association between the intra-thoracic impedance measured by OptiVol fluid index and the onset of tachyarrhythmias. Methods: We searched Medline and EMBASE databases through January 2021 looking for studies evaluating intra-thoracic impedance measured by OptiVol with either ventricular tachycardia/ventricular fibrillation (VT/VF) or atrial tachycardia/atrial fibrillation (AT/AF). After extracting the data from each study, we calculated the odds ratio with 95% confidence intervals using RevMan 5 software. Results: Ten studies met our inclusion criteria with a total of 118,504 patients were included in our analysis. Seven studies measured VT/VF included 94,816 patients and 5 studies measured AT/AF included 23,688 patients. Two studies measured both AT/AF and VT/VF. The odds ratio for developing VT/VF with OptiVol fluid index crossing a threshold of 60 Ω-days was 1.55 (95% CI 1.35, 1.78) (P<0.00001) and for developing AT/AF was 1.79 (95% CI 1.43, 2.24) (P<0.00001) {Figure1} Conclusion: The decrease in intra-thoracic impedance measured by OptiVol fluid index threshold crossing of 60 Ω-days is associated with higher risk for developing new onset AT/AF and VT/VF. Key Words: intra-thoracic impedance; OptiVol; tachyarrhythmia Figure1: Forest Plot for risk of developing VT/VF Figure: Forest Plot for risk of developing AT/AF

Differences in management of telemedicine alerts on weekdays and public holidays: Results from the OptiLink heart failure trial

Background In the OptiLink heart failure study, timely and appropriate reactions to telemedicine alerts improved clinical outcomes in heart failure patients. This analysis investigates the relation between the weekday of alert transmission and the subsequent patient contact. Methods In patients enrolled in the intervention arm of the OptiLink heart failure study (n = 505, age 66.1 ± 10.1, 77.2% male, left-ventricular ejection fraction 26.7% ± 6.1%), fluid index threshold crossing alerts were analysed according to the weekday of the transmission. Transmissions on Mondays–Thursdays were categorized as TD1, Fridays–Sundays as well as public holidays as TD2. Results Of 1365 transmitted alerts, 867 (63.5%) were categorized as TD1 and 498 (36.5%) as TD2. Same day telephone contacts were more frequent in TD1 (46.2%) than in TD2 (18.3%; p < 0.001). Accordingly, the median time to contact was significantly longer in TD2 compared with TD1 (2(1–3) vs 0(0–1) days; p < 0.001). Rates of no telephone contact were no different between the groups (12.1% vs 12.4%; p = 0.866). Although signs of worsening heart failure were prevalent in 32.4% in TD1 versus 32.1% in TD2 (p = 0.996), initiation of a pharmacological intervention occurred more likely in TD1 compared with TD2 (27.9% vs 22.9%; p = 0.041). No differences existed concerning hospitalization for heart failure within 30 days after alert transmission (3.9% vs 3.4%; p = 0.636). Conclusion Alert transmissions during weekends and public holidays were less likely associated with timely patient contacts and initiation of pharmacological interventions than during the week. Telemedical centres providing 24/7 remote monitoring service and specific education programmes for physicians might help to optimize patient care.

Remote Monitoring With Appropriate Reaction to Alerts Was Associated With Improved Outcomes in Chronic Heart Failure: Results From the OptiLink HF Study.

Impedance-based remote monitoring (RM) failed to reduce clinical events in the OptiLink heart failure (HF) trial. However, rates of alert-driven interventions triggered by intrathoracic fluid index threshold crossings (FTC) were low indicating physicians' inappropriate reactions to alerts. We separated appropriate from inappropriate contacts to FTC transmissions in the OptiLink HF trial (Optimization of Heart Failure Management Using OptiVol™ Fluid Status Monitoring and CareLink™). Appropriate contacts had to meet the following criteria: (1) initial telephone contact within 2 working days after FTC transmission, (2) follow-up contacts according to study protocol, and (3) medical intervention initiated after FTC due to cardiac decompensation. We compared time to cardiovascular death or HF hospitalization between RM patients contacted appropriately or inappropriately and patients with usual care. In the RM group, at least one FTC alert was transmitted in 356 patients (70.5%; n=505). Of note, only 55.5% (n=758) of all transmitted FTCs (n=1365) were followed by an appropriate contact. While 113 patients (31.7%; n=356) have been contacted appropriately after every FTC, in 243 patients (68.3%; n=356) at least one FTC was not responded by an appropriate contact. Compared with usual care, RM with appropriate contacts to FTC alerts independently reduced the risk of the primary end point (hazard ratio, 0.61 [95% CI, 0.39-0.95]; P=0.027). RM appropriate reactions to FTC alerts are associated with significantly improved clinical outcomes in patients with advanced HF and implantable cardioverter-defibrillators.

Handling of remote monitoring alerts according to the weekday of transmission: results from the OptiLink HF study

Abstract Background Remote monitoring of patients suffering from heart failure (HF) did not result in improved clinical outcomes in the OptiLink-HF trial. However, initiation of medical intervention after transmission of telemedicine alerts triggered by fluid index threshold crossings (FTCs) was low. The relation between weekday of transmission of FTC and subsequent patient contact is unknown. Methods Patients enrolled in the intervention arm of the OptiLink HF trial (n=505, age 66.1±10.1, male 77.2, EF 26.7±6.1%) were analyzed according to the weekday of transmission of FTC. Transmissions of FTC on Mondays to Thursdays were categorized as TD1, Fridays to Sundays as well as bank holidays as TD2. Primary endpoint was time between transmission and telephone contact; secondary endpoints were subsequent medical intervention and hospitalizations. Results During a follow-up of 18 months, 1364 FTC (866 (63.5%) categorized to TD1, 498 (36.5%) to TD2) alerts occurred in 356 patients. In 46.2% of FTC same day telephone contact was performed in group TD1 compared to 18.3% in group TD2 (p&amp;lt;0.001). Accordingly, the median time to contact was significantly longer in TD2 compared to TD1 (2 (1–3) vs. 0 (0–1); p&amp;lt;0.001). Rates of no telephone contact were not different between the groups (12.1% vs. 12.4%; p=0.866). Although, signs of worsening HF were prevalent in 32.4% in TD1 vs. 32.1% in TD2 (p=0.996), initiation of a pharmacological intervention was more likely in TD1 compared to TD2 (27.9% vs. 22.9%; p=0.041). No differences existed concerning hospitalization for HF within 30 days after FTC (3.9% vs. 3.4%; p=0.636). Conclusion Transmission of FTC alerts during weekends and on bank holidays were less likely associated with timely patient contacts and initiation of pharmacological intervention than during the week. Telemedical centers providing 24/7 remote monitoring service might help to optimize patient care. Funding Acknowledgement Type of funding source: None

Adequate contacts after remote monitoring alerts were associated with improved outcomes in chronic heart failure: results from the OptiLink HF study

Abstract Aims To investigate the effects of adequate reactions to telemedicine alerts triggered by fluid index threshold crossings (FTC) on clinical outcomes in the OptiLink HF trial. Methods We separated adequate from inadequate reactions to FTC transmissions in patients with remote impedance-based monitoring (RM) of fluid status in the OptiLink HF trial. Adequate contacts had to meet the following criteria: i) initial telephone contact within 2 working days after FTC transmission, ii) follow-up contacts according to study protocol, and iii) medical intervention initiated after FTC due to true fluid overload. We compared time to cardiovascular (CV) death or heart failure (HF) hospitalization and all CV- and HF-hospitalizations at follow-up between RM patients contacted adequately or inadequately and patients with usual care (UC). Results In the RM group, transmission of at least one FTC alert occurred in 356 patients (70.5%; n=505). While 113 patients (31.7%; n=356) have been contacted adequately after every FTC, in 243 patients (68.3%; n=356) at least one FTC was not responded by an adequate contact. Adequate responses to RM significantly reduced risk of the primary endpoint (hazard ratio (HR), 0.68; 95% confidence interval (CI) 0.48–0.95; p=0.025, figure 1), and led to a significantly lower number of CV (52.1±7.5 vs. 99.9±19.8; p=0.007) and HF hospitalizations per 100 patient years when compared with UC (26.1±4.4 vs. 67±15.2; p=0.007). Conclusion RM with adequate reactions to FTC alerts significantly reduced total number of both CV and HF hospitalizations and improved clinical outcomes in patients with advanced HF and implantable cardioverter defibrillator (ICD). Funding Acknowledgement Type of funding source: None

Intra-thoracic Impedance and the Onset of Atrial and Ventricular Tachyarrhythmias: A Meta-analysis

Background and purposeAdvances of implantable cardioverter–defibrillator (ICD) devices allow correlating changes in the intra-thoracic impedance (TI), an indicator of fluid overload, with the onset of arrhythmic events. In an attempt to attain a better understanding of this relationship, we conducted a meta-analysis of studies that investigated the association between TI changes and the onset of AT/AF and/or VT/VF in patients with ICD devices. MethodsWe performed a meta-analysis of studies published through January 2017 that reported an association between a decrease in the TI measured by the OptiVol fluid index (OI) and occurrence of AT/AF and VT/VF. We searched four databases: PubMed, Embase, CINAHL and Cochrane. Effect estimates were extracted from each study in the form of odds ratio (OR) and 95% confidence intervals. ResultsWe identified 8 articles with results of the original research, allowing us to extract data for the OR calculation. Our pooled sample included 94,666 patients from 4 studies for AT/AF and 23,601 patients from 6 studies for VT/VF. Two studies were included in both analyses. The pooled OR for fluid index threshold crossing of 60Ω-days was 1.56 (95% CI 1.35, 1.81) for VT/VF and 1.8 (95% CI 1.43, 2.27) for AT/AF. ConclusionThe findings of our meta-analysis based on the large pooled population of >110,000 patients, reveal that decreased TI (measured by OI threshold crossing of 60Ω-days) is a significant risk factor for the onset of AT/AF and VT/VF.

Intracardiac impedance after cardiac resynchronization therapy is a novel predictor for worsening of heart failure.

Intrathoracic impedance measured by cardiac resynchronization therapy (CRT) varies because several factors other than pulmonary congestion may affect this parameter. Therefore, we hypothesized that changes in intracardiac impedance between the right and left ventricular leads would be more accurate to identify worsening heart failure in patients with CRT. The study enrolled21 patients with CRT defibrillator (15 males, 70 ± 12years). During the follow-up period (12 ± 7months), the subjects experienced 37 fluid index threshold (60 ohm-days) crossing events. These events were divided into two groups whether hospitalization due to worsening heart failure was required (group-H, n = 14) or not (group-NH, n = 23). Based on the intracardiac impedance at the beginning of increasing fluid index (BI) and the crossing of 60ohm-days (CI), the rate of impedance change (BI-CI/BI) was estimated. Then, the time elapsed from BI to CI (T) was evaluated. We calculated the rate of intracardiac impedance change per day (BI-CI/BI × T) in each group. The rate of intrathoracic impedance change per day was also determined using the same method. The median rate of intracardiac impedance change per day was 0.27 (IQR 0.22-0.54) %/day in group-H, and 0 (IQR 0-0.08) %/day in group-NH with a significant difference (P < 0.0001), whereas the rate of intrathoracic impedance change per day was similar between the two groups. By receiver operating characteristic curve for identification of hospitalization due to worsening heart failure, the best cutoff value of the rate of intracardiac impedance change per day was 0.20%/day (sensitivity 92%, specificity 88%, and AUC 0.98). In contrast, the best cutoff value of the rate of intrathoracic impedance change per day was 0.19%/day (sensitivity 86%, specificity 43%, and AUC 0.68). These results suggest thatincreased rate of change of decreasing intracardiac impedance measured by CRT is a novel useful predictor for worsening heart failure.

Worsening thoracic impedance as a ventricular tachyarrhythmia risk.

The use of heart failure classification to identify patients with systolic dysfunction who are at risk for ventricular tachyarrhythmias (VAs), sudden cardiac death, and shocks from implantable cardioverter defibrillators (ICDs) is limited by its subjectivity. Measurement of thoracic impedance offers a more objective tool for assessing worsening of heart failure. We sought to look at the correlation between ventricular arrhythmia and heart failure as assessed objectively by thoracic impedance. We reviewed device interrogation data on thoracic impedance from ICD with Medtronic's OptiVol® feature (Medtronic Inc., Minneapolis, MN) at two medical centers. Data from the last two interrogations of the same device separated by at least 2 months were included. An OptiVol fluid index threshold of 60 represented early heart failure prior to appearance of symptoms. VAs included were ventricular fibrillation and/or ventricular tachycardia lasting more than 16 beats. Chi square distribution test was used in statistical data analysis. There were 24 VAs identified among the 322 interrogations reviewed (7.5%). Elevated OptiVol fluid index was seen in 71% (17/24), whereas normal OptiVol index was seen in the remaining 29% (7/24) of these interrogations with VA (P < .05). Our review shows that heart failure patients who have VA are approximately 2.5 times as likely to have worsening thoracic impedance as assessed objectively by the OptiVol fluid index. Careful monitoring of the OptiVol fluid index may identify a population at high risk of VA that merits more intense attention.

Predictive impact of the decreasing rate of intrathoracic impedance in worsening chronic heart failure

Intrathoracic impedance monitoring is useful for heart failure (HF) management in patients with cardiac resynchronization therapy (CRT). However, more accurate identification of worsening chronic HF (CHF) is required in the clinical setting. We investigated this issue by estimating changes in impedance. We studied 38 CHF patients (29 males, mean age 67 years) with CRT-defibrillator capable of impedance monitoring. During the follow-up period (20.7 ± 7.8 months), the subjects experienced a total of 129 fluid index threshold (60 ohm·days) crossing events. These events were divided into two groups: HF events (n = 70) and no HF events (n = 59). Based on the impedance at the beginning of increasing fluid index (S) and at the crossing of 60 ohm·days (E), the rate of impedance change (S - E / S) was estimated. In addition, the elapsed time from S to E (T) was evaluated. Then, we calculated the rate of impedance change per day (S - E / S × T) in each group. The rate of impedance change per day was significantly higher in HF events than in no HF events (0.86 ± 0.48 vs. 0.37 ± 0.22%/day, P < 0.01). By receiver operating characteristic curve for identification of HF events, the best cutoff value of the rate of impedance change was 0.48%/day (sensitivity 80%, specificity 81%, and area under the curve 0.85). These results suggest that a faster drop in intrathoracic impedance reflected worsening CHF in patients with CRT-defibrillator. Thus, intrathoracic impedance monitoring based on the rate of impedance change may provide a more accurate identification of worsening CHF.

Efficacy of Intrathoracic Impedance and Remote Monitoring in Patients With an Implantable Device After the 2011 Great East Japan Earthquake

Several studies have revealed that stress after catastrophic disasters can trigger cardiovascular events, however, little is known about its association with the occurrence of heart failure in past earthquakes. The objective of the present study was to determine whether the Great East Japan Earthquake on March 11, 2011, increased the incidence of worsening heart failure in chronic heart failure (CHF) patients with implantable devices. Furthermore, we examined whether intrathoracic impedance using remote monitoring was effective for the management of CHF.We enrolled 44 CHF patients (32 males, mean age 63 ± 12 years) with implantable devices that can check intrathoracic impedance using remote monitoring. We defined the worsening heart failure as accumulated impedance under reference impedance exceeding 60 ohms-days (fluid index threshold), and compared the incidence of worsening heart failure and arrhythmic events 30 days before and after March 11.Within the 30 days after March 11, 10 patients exceeded the threshold compared with only 2 patients in the preceding 30 days (P < 0.05). Although 9 patients using remote monitoring among the 10 patients with threshold crossings were not hospitalized, one patient without the system was hospitalized due to acute decompensated heart failure. On the contrary, arrhythmic events did not change between before and after March 11.Our results suggest that earthquake-induced stress causes an increased risk of worsening heart failure without changes in arrhythmia. Furthermore, intrathoracic impedance using remote monitoring may be a useful tool for the management of CHF in catastrophic disasters.

Atrial Tachyarrhythmias Temporally Precede Fluid Accumulation in Implantable Device Patients

The complex relationship between heart failure and atrial tachyarrhythmias (AT/atrial fibrillation [AF]) is not well understood. We examined the temporal association between changes in intrathoracic impedance, suggesting thoracic fluid accumulation, and AT/AF occurrence in cardiac resynchronization therapy-defibrillator and implantable cardioverter defibrillator (ICD) patients. A retrospective analysis was conducted on stored implantable device data to identify patients with automatic monitoring of daily AT/AF burden and intrathoracic impedance. Daily population trends in AT/AF burden before and after a fluid index threshold crossing (FIC) were determined. A total of 73,018 patients (68 ± 12 years, 51% ICD, 75% male) were evaluated over 18.6 ± 11.5 months. Kaplan-Meier analysis indicated a significantly higher probability of FIC events in the first month following the onset of persistent AT/AF when compared to a matched group without persistent AT/AF (hazard ratio [HR] 1.65, 95% confidence interval [CI] [1.58, 1.72], P < 0.001). Conversely, patients were significantly more likely to experience an episode of persistent AF in the first month after the FIC event (HR 1.32, 95% CI [1.08, 1.63], P = 0.008). The probability of a fluid index crossing within 30 days of the onset of persistent AT/AF was significantly lower in a subgroup of patients with adequate rate control (35.8% [34.3-37.4%] vs 42.0% [39.6-44.6%]; HR 1.24 [1.13-1.36]). Thoracic fluid accumulation, as indicated by decreasing intrathoracic impedance, was more likely to occur immediately after the onset of persistent AT/AF, especially in the presence of inadequate rate control. Likewise, the onset of persistent AT/AF was more likely following a decrease in intrathoracic impedance.

Uncovering Interim Clinical Events at the Time of Clinical Encounter by Reviewing Intrathoracic Impedance Threshold Crossings

Background Acute decreases in intrathoracic impedance monitored by implanted devices have been shown to precede heart failure exacerbations, although there is still debate regarding its clinical utility in predicting and preventing future events. However, the usefulness of such information to direct patient encounter and enhance patient recall of relevant preceding clinical events at the point of care has not been carefully examined. Methods and Results In this multicenter study, we interviewed 326 patients with heart failure who received an implanted device with intrathoracic impedance–monitoring capabilities both before and after device information was reviewed. We compared the self-reported clinically relevant events (including heart failure hospitalizations, signs and symptoms of worsening heart failure, changes in diuretic therapy, or other fluid-related events) obtained before and after device interrogation, and then examined the relationship between such events with impedance trends documented by the devices. Over 333 ± 96 days of device monitoring, 215 of 326 patients experienced 590 intrathoracic impedance fluid index threshold–crossing events at the nominal threshold value (60 Ω-d). Review of device-derived information led to the discovery of 221 (37%) previously unreported clinically relevant events in 138 subjects. This included 60 subjects not previously identified as having had clinically relevant events (or 35% of the 171 subjects who did not report events). Conclusions Our data demonstrated that reviewing device-derived intrathoracic impedance trends at the time of clinical encounter may help uncover self-reporting of potential clinically relevant events.

ICD and CRT-D Heart Failure Patients with an Intrathoracic Impedance Fluid Index Threshold Crossing Have Significantly Increased Risk of Ventricular Tachyarrhythmias

The association between intrathoracic impendence (IP) and nonsustained (NSVT) and sustained (VT/F) ventricular arrhythmia occurrence in heart failure (HF) patients is not fully understood. We investigated the relationship between VT/VF and threshold crossings of an intrathoracic impedance-derived fluid index (FTC) in HF patients with ICD/CRT-D devices.

A Critical Link Between Heart Failure Self-care and Intrathoracic Impedance

Effective self-care is regarded as essential to the management of heart failure (HF). The influence of self-care on HF decompensation, however, is not well understood. Accordingly, we examined the relationship between self-care and fluid accumulation accompanying worsening HF as indexed by decreasing intrathoracic impedance (Z). Z data were collected from 58 HF patients with OptiVol enabled devices (Medtronic Inc, Minneapolis, Minnesota). Heart failure self-care was measured with the European Heart Failure Self-care Behaviour Scale. Regression modeling was used to describe the influence of HF self-care on the likelihood of a fluid index (FI) threshold crossing, the number of threshold crossings, and number of days spent above threshold. Patients were elderly (74.98 [SD, 8.12] years), with a mean left ventricular ejection fraction of 26.21% (SD, 9.77%), and 63.7% had class New York Heart Association III HF. Patients were followed up for 317 (SD, 96) days; 65.5% had FI threshold crossings (mean 1.45 [SD, 1.56] crossings), spending an average of 33.8 (SD, 42.4) days above FI threshold. Controlling for age, sex, left ventricular ejection fraction, functional class, and duration of follow-up, each additional point on the European Heart Failure Self-care Behaviour Scale was associated with an increase in the odds of having had an FI threshold crossing (adjusted odds ratio, 1.201; 95% confidence interval, 1.013-1.424; P<.05) and more days spent above FI threshold (incidence rate ratio, 1.051; 95% confidence interval, 1.002-1.102; P<.05). Intrathoracic impedance measurements obtained from implantable devices provide important information regarding the influence of self-care on fluid accumulation in patients with HF.

Improved Algorithm to Detect Fluid Accumulation via Intrathoracic Impedance Monitoring in Heart Failure Patients With Implantable Devices

Background Intrathoracic impedance fluid monitoring has been shown to predict worsening congestive heart failure (CHF) in patients with implantable devices. We developed and externally validated a modified algorithm to identify worsening heart failure (HF) by using intrathoracic impedance. Methods and Results The modified algorithm was developed by using published data from 81 CHF subjects averaging 259 days of follow-up. Device-measured daily impedance was input to both the existing and the modified intrathoracic impedance fluid monitoring algorithms to determine a reference impedance and a fluid index (FI). Separate validation sets included 326 cardiac resynchronization therapy device (CRT-D) patients with an average 333 days of follow-up (group 1) and 104 CRT-D/implantable cardioverter/defibrillator (ICD) patients followed for an average of 520 days (group 2). Clinicians and patients in group 2 were blinded to impedance and FI data. HF events included adjudicated HF hospitalizations or emergency room visits. Sensitivity was defined as the percentage of HF events preceded by FI exceeding the predefined threshold (60 Ω-d) within the last 2 weeks. Unexplained detections were FI threshold crossing events not followed by a HF event within 2 weeks. The modified algorithm significantly decreased unexplained detections by 30% ( P = .01; GEE) in the development set, 30% ( P < .001) in the group 1 validation set, and 43% ( P < .001) in group 2. Sensitivity did not change significantly in any group. Simulated monthly review of FI threshold crossings identified subjects at significantly greater risk of worsening HF within the next 30 days. Conclusions A modified intrathoracic impedance based fluid detection algorithm lowered the number of unexplained FI threshold crossings and identified patients at significantly increased immediate risk of worsening HF.

Significant Increase in the Incidence of Ventricular Arrhythmic Events After an Intrathoracic Impedance Change Measured With a Cardiac Resynchronization Therapy Defibrillator

Cardiac resynchronization therapy defibrillator (CRT-D) devices are now capable of monitoring changes in intrathoracic impedance. Intrathoracic impedance monitoring resulting in a fluid index threshold crossing has been proven to predict heart failure (HF) exacerbations. We retrospectively investigated the relationship between changes in intrathoracic impedance and the occurrence of arrhythmic events. From 282 patients with New York Heart Association class III or IV HF who were implanted with a CRT-D device with a fluid index feature based on intrathoracic impedance monitoring capabilities, arrhythmic events were retrospectively analyzed in terms of the threshold crossings. The patients were divided into 2 groups: those with fluid index threshold crossings and those without threshold crossings. A total of 4,725 tachyarrhythmic events were reported in 129 patients (46%), and there were 221 fluid index crossing events in 145 patients (51%) during 10.0 ± 3.2 months. Tachyarrhythmic events were more frequently recorded in patients with threshold crossing events than in those who did not experience a threshold crossing (3,241 vs. 1,484 events, P<0.0001). Ventricular tachyarrhythmic events mainly occurred within the first 30 days after the threshold crossing event; however, a similar trend was not observed for the atrial tachyarrhythmic events. Intrathoracic impedance monitoring may predict arrhythmic events, especially ventricular arrhythmias, in patients with HF and provides an additional management tool.

Insights From Internet‐Based Remote Intrathoracic Impedance Monitoring as Part of a Heart Failure Disease Management Program

Changes in intrathoracic impedance (Z) leading to crossing of a derived fluid index (FI) threshold has been associated with heart failure (HF) hospitalization. The authors developed a remote monitoring program as part of HF disease management and prospectively examined the feasibility and resource utilization of monitoring individuals with an implanted device capable of measuring Z. An HF nurse analyzed all transmitted data daily, as they were routinely uploaded as part of quarterly remote device monitoring, and called the patient if the FI crossed the threshold (arbitrarily defined at 60 Omega) to identify clinically relevant events (CREs) that occurred during this period (eg, worsening dyspnea or increase in edema or weight). A total of 400 uploads were completed during the 4-month study period. During this period, 34 patients (18%) had an FI threshold crossing, averaging 0.52 FI threshold crossings per patient-year. Thirty-two of 34 patients contacted by telephone (94%) with FI threshold crossing had evidence of CREs during this period. However, only 6 (18%) had HF hospitalizations, 19 (56%) had reported changes in HF therapy, and 13 (38%) reported drug and/or dietary plan nonadherence. The average data analysis time required was 30 min daily when focusing on those with FI threshold crossing, averaging 8 uploads for review per working day and 5 telephone follow-ups per week. Our pilot observations suggested that Internet-based remote monitoring of Z trends from existing device interrogation uploads is feasible as part of a daily routine of HF disease management.

Changes in Intrathoracic Impedance are Associated With Subsequent Risk of Hospitalizations for Acute Decompensated Heart Failure: Clinical Utility of Implanted Device Monitoring Without a Patient Alert

Background Acute decreases in intrathoracic impedance monitoring have been shown to precede heart failure hospitalization in a limited population of heart failure patients. We evaluated the relationship between changes in intrathoracic impedance with hospitalizations associated with acute decompensated heart failure (ADHF) in patients with cardiac resynchronization therapy plus defibrillator (CRT-D) devices. Methods and Results The study enrolled 326 heart failure patients who had received CRT-D with impedance-monitoring capabilities (InSync Sentry, Medtronic). The date and duration of ADHF hospitalizations were retrospectively identified before device interrogation to obtain device diagnostic information. During 333 ± 96 days of device monitoring, 228 patients experienced 540 intrathoracic impedance fluid index threshold crossings events (TCE) at the nominal threshold value (60 Ω. days). During the initial 4-month evaluation period, 17 subjects experienced 22 ADHF hospitalizations. In the subsequent monitoring period (206 ± 95 days), 18 patients experienced 24 hospitalizations. The occurrence of TCEs during the monitoring period was independently correlated with the subsequent rate of ADHF hospitalization such that each TCE event during the risk stratification period was associated with a 35% increased risk for ADHF hospitalization in the remaining study period ( P = .001). Poisson regression indicated that the subgroup of patients with an annual average rate of more than 3 threshold crossings per year during the monitoring period were significantly more likely to be hospitalized for ADHF than those patients with no TCE during the monitoring period (0.76 [0.20–1.325] vs. 0.14 [0.05–0.23] hospitalizations/subject/y [95%CI]; P = .02). Likewise, Kaplan-Meier analysis revealed that subsets of patients with more than 3 TCEs per year or with more than 30 days per year above threshold during the risk stratification period had significantly higher rates of ADHF hospitalization during the post risk stratification period than subjects with no TCE events, respectively. Conclusions In this multicenter retrospective cohort study, serial decreases in intrathoracic impedance sufficient to generate a fluid index threshold crossing as well as the net duration that the index remained above threshold during a 4-month monitoring period were associated with subsequent risk of ADHF hospitalization.

Implantable CRT device diagnostics identify patients with increased risk for heart failure hospitalization

To determine the association between device-determined diagnostic indices, including intrathoracic impedance, and heart failure (HF) hospitalization. Clinical and device diagnostic data of 558 HF patients indicated for CRT-D therapy (In Sync Sentry, Medtronic Inc.) were prospectively collected from 34 centers. Device-recorded intrathoracic impedance fluid index threshold crossing event (TCE), mean activity counts, tachyarrhythmia events, night heart rate (NHR) and heart rate variability (HRV) were compared within patients with vs. without documented HF hospitalization. Mean follow-up was 326 +/- 216 days. Patients hospitalized for HF had significantly higher rates of TCE, a higher percentage of days with the thoracic impedance fluid index above the programmed threshold, a higher percentage of days with low activity, with low HRV or with high NHR. Multivariate analysis showed that TCE resulted in a 36% increased probability of HF hospitalization. Both TCE duration and patient activity were also significantly associated with hospitalization. Kaplan Meier analysis indicated that patients with more TCE events were significantly more likely to be hospitalized (log rank test, p = 0.005). Decreased intrathoracic impedance, low patient activity and low HRV were all independently associated with increased risk for HF hospitalization in HF patients treated with resynchronization therapy. Device-derived diagnostic data may provide valuable and reliable indices for the prognostic stratification of HF patients.

Changes in Intrathoracic Impedance Identify ICD Patients at Increased Risk of Heart Failure Hospitalizations

Background: Heart failure (HF) programs have been shown to decrease hospital readmissions for worsening HF. However, identification of patients most likely to benefit from such programs has not been studied. Recently, implantable devices have been shown to predict worsening HF and hospitalizations by determining a fluid index based upon decreasing intrathoracic impedance. We examined the relationship between ejection fraction and fluid index threshold crossing events (TCE) in HF patients with ICDs that were or were not followed in the HF clinic.