Noninvasive devices, such as scales, blood pressure monitors, ECG devices, and wearables, have demonstrated benefits in multiparametric data transmission, ease of use, integrative monitoring of comorbidities (eg, diabetes), and cost-effectiveness.

Evidence for the efficacy of noninvasive cardiovascular telemonitoring first emerged in the mid-2000s, leading to a differentiation between trials based on invasive or noninvasive sensor technology. Three major landmark trials—INH (Interdisciplinary Network for Heart Failure), TIM-HF (Telemedical Interventional Monitoring in Heart Failure Study), and TIM-HF2 (Telemedical Interventional Management in Heart Failure II)—were conducted in Germany and received public funding from the German Ministry of Education and Research, as well as the Federal Ministry for Economic Affairs and Climate Protection.

The randomized, controlled, multicenter INH (Interdisciplinary Network for Heart Failure) study program (ISRCTN23325295) investigated the effects of regular telephone-based monitoring and education provided by HF nurses as part of an intensified care approach by a specialized HF center. The remote patient management strategy emphasized patient self-monitoring of vital parameters and HF symptoms. The first phase of the trial assessed the 6-month risk of mortality and morbidity in 715 patients with an LVEF of ≤40%, all of whom had been hospitalized for acute decompensated HF.

The composite primary outcome for time to all-cause death or rehospitalization was neutral between the telemonitoring group (n=352) and the usual care control group (n=363). This observation was influenced by a significant reduction in all-cause mortality to 38% in the remote patient management group, which was associated with a trending increase in hospitalization rates in the intervention arm. Additionally, patients in the telemonitoring group demonstrated improvements in quality of life, functional class, and adherence to medical therapy.

A long-term evaluation of the INH trial (the “E-INH study”) in a larger population (n=1022) demonstrated that telephone-based monitoring over an 18-month period led to a significant reduction in all-cause and cardiovascular mortality after 120 months in the group of survivors who had received remote patient management (33% vs 40%; P=.04). Additionally, HF-related and cardiovascular hospitalizations were significantly reduced at 18, 36, and 60 months by –25%, –29%, and –30%, respectively. As previously noted, the telemonitoring procedures did not include automated transmission of patient-recorded vital signs. Instead, they relied on postdischarge telephone monitoring, where specialized nurses reviewed patients’ self-monitored results. These nurses also provided information, education, and guidance on optimal medical therapies; advised on appropriate actions in case of suspected HF decompensation; supported self-adjustment of diuretic agents; and coordinated specialist care as needed.

Overall, the INH study program suggests that telephone-based monitoring and education alone can improve short-term quality of life and mortality, with a sustained long-term impact demonstrated by reduced all-cause and cardiovascular mortality, fewer hospitalizations, and improved quality of life [6,7].

The TIM-HF study (NCT00543881) and the TIM-HF2 study (NCT01878630) were large, randomized, controlled, open, parallel telemedical trials that investigated the efficacy of noninvasive, multiparameter telemonitoring in a population with moderate to severe HF (New York Heart Association [NYHA] class II or III).

Both studies were fully publicly funded. The core element of this telemedical care model was a telemedical center staffed with experienced HF specialists and nurses, offering regular and emergency telemedical services 24 hours a day, 7 days a week, functioning as a “virtual emergency department” [8].

The TIM-HF trial was a telemedical randomized controlled trial conducted between 2008 and 2010 across 4 German federal states: Berlin, Brandenburg, Saxony-Anhalt, and Baden-Württemberg. The main inclusion criteria were an LVEF below 35% and a history of HF hospitalization within 24 months before randomization. The primary endpoint was all-cause mortality. The study concluded on a predetermined date (April 30, 2010), resulting in varying follow-up periods for each patient, with a minimum of 12 months and a maximum of 28 months (mean follow-up 21.5 months, SD 7.2 months). The results for the primary endpoint were neutral [9]. However, a post hoc analysis identified a subset of patients who may benefit most from telemonitoring [10].

TIM-HF2 was a nationwide telemedical randomized controlled trial conducted between 2013 and 2018 across 13 German federal states. The main inclusion criteria were informed by the post hoc analysis of the TIM-HF study. Patients were enrolled regardless of their LVEF status if they had experienced an HF-related hospitalization within 12 months before randomization. A total of 1538 patients were randomized equally into either a telemedical intervention arm or a control arm. The study follow-up period was 1 year. The primary endpoint was defined as “days lost due to unplanned cardiovascular hospitalization or death within 1 year.” The secondary endpoint was total mortality. Telemedical intervention showed a significant benefit in the primary endpoint, with 17.8 days lost in the telemedical group compared with 24.2 days in the control group (P=.046). Additionally, there was a nearly 30% reduction in 1-year mortality in the telemedical group, with a mortality rate of 7.9% per 100 patient-years (95% CI 6.14-10.10) compared with 11.3% per 100 patient-years in the control group (95% CI 9.21-13.95). This corresponded to a hazard ratio of 0.70 (95% CI 0.50-0.96; P=.028) [11].

The 2 subsequent TIM-HF studies offered robust evidence supporting the efficacy of noninvasive telemonitoring in a specific subgroup of patients with HF.

Active implants, also known as cardiac implantable electronic devices (CIEDs), not only serve their primary function of treating cardiac arrhythmias through defibrillators or cardiac resynchronization therapy, but also provide an option for telemonitoring. In the context of telemonitoring, these devices periodically transmit data on physical activity, submit ECG readings, and may detect changes in pulmonary impedance. However, this active home monitoring application is limited to a specific subgroup of patients with HF who meet the eligibility criteria for CIED therapy.

The IN-TIME (Influence of Home Monitoring on Mortality and Morbidity in Heart Failure Patients with Impaired Left Ventricular Function) landmark trial marked the beginning of an era characterized by technology-based, industry-funded study designs, moving away from reliance on governmental funding. This shift has paved the way for the generation of fundamental evidence and has further shaped the research landscape in telemedicine. As a result, companies providing device therapy have become involved as principal investigating parties in telemedical research.

The IN-TIME trial (NCT00538356) is currently the only study that has investigated device-based multiparameter telemonitoring using active CIEDs and has reported a positive primary endpoint for a composite score that includes all-cause mortality.

This international multicenter randomized trial was conducted at 36 centers across Israel (2 sites), Australia (1 site), and Europe (33 sites), including 26 sites in Germany, and was funded by BIOTRONIK SE & Co. KG. A total of 664 patients with congestive heart failure classified as NYHA class II-III, with an LVEF of less than 35%, who had undergone implantation of a dual-chamber CIED, either an implantable cardiac defibrillator (ICD) or a cardiac resynchronization therapy with a defibrillator (CRT-D), were randomized in a 1:1 ratio to either the standard care control arm or the device-based telemonitoring in addition to standard care arm.

The telemonitoring software installed in the CIEDs transmitted daily tracked data to the manufacturer’s online platform. These data included not only arrhythmic events but also parameters related to the device’s functionality. For the intervention group, any subsequent abnormalities were further forwarded to the study centers, where HF nurses conducted structured interviews to assess typical HF symptoms and discussed potential interventions with physicians.

With the primary endpoint defined as a “modified Packer score,” which includes the incidence rate of all-cause mortality, HF-related hospitalizations, changes in NYHA class, and quality of life assessments, the intervention group receiving telemonitoring demonstrated a significantly lower occurrence rate of the composite clinical endpoint compared with the control arm (18.9% vs 27.2%, respectively; P=.013). Importantly, total mortality was significantly lower in the telemonitoring arm compared with the control arm (3.0% vs 8.2%; hazard ratio 0.36; P=.004). However, the rates of hospital admissions for worsening HF did not differ significantly between the 2 groups. In a post hoc analysis, no interactions were found between the effect of telemonitoring and device type (ICD or CRT-D), NYHA class at enrollment, or age (≤67 or >67 years), indicating a consistently significant impact of telemonitoring across all subgroups.

Thus, the IN-TIME trial demonstrated the beneficial impact of device-based telemonitoring in patients with HF through daily data transmission. Consequently, these results may not be directly transferable to remote monitoring platforms that utilize less frequent data transmissions [12].

In the invasive telemonitoring OptiLink-HF study (Optimization of Heart Failure Management using Medtronic OptiVol Fluid Status Monitoring and CareLink Network; NCT00769457), a total of 1002 patients were enrolled following implantation of an ICD or CRT-ICD [13]. These CIEDs also included the capability to measure intrathoracic impedance. In the event of a significant decrease in thoracic impedance, indicative of pulmonary fluid overload, the devices transmitted fluid threshold crossing alerts.

Patient enrollment occurred across 65 centers in Germany from October 2008 to April 2013. The mandatory inclusion criteria for participants included CHF classified as NYHA class II or III, an LVEF of less than 35%, and at least one of the following: an HF hospitalization within the past 12 months, the use of intravenous diuretic medication for outpatient treatment, or an increase in natriuretic peptide levels within the preceding 30 days.

Patients were randomized in a 1:1 ratio, with the telemedicine function either turned on or off. Physicians were required to respond within 2 working days using a prespecified intervention algorithm [14]. During these phone contacts, discussions included changes in body weight, medication adjustments, and symptoms of decongestion. The initiation of therapeutic measures was at the discretion of the physicians, allowing for a range of responses from no action to reprogramming the fluid threshold crossing alert threshold. If fluid threshold crossing alerts continued for more than 12 days, patients were prompted to attend an in-office or in-hospital visit for further evaluation.

The follow-up period for all study participants was set at 18 months, with an option for reinformed consent to extend follow-up until the last patient completed their study visit. This led to a mean follow-up duration of 22.9 months for the participants.

The primary endpoint of the study was the rate of death from any cause and the rate of cardiovascular hospitalizations. Notably, the primary composite endpoint and its individual components were not achieved. Major limitations of the study included technical issues, with 24% of the impedance alarms failing to transmit to the treating physicians. Additionally, inappropriate responses to the alerts were observed in 40% of cases, which included instances of no patient contact at all (12.4%); patient contact exceeding the 2-working-day threshold (10.8%), particularly during weekends and public holidays (4.0%); and a lack of appropriate medical intervention (32.8%).

Interestingly, a post hoc analysis of the OptiLink-HF trial suggested that impedance-based telemonitoring could have significant prognostic effects when alert transmissions were managed appropriately [15]. Additionally, the intervention was found to significantly decrease the primary endpoint in patients with preserved renal function, while it did not demonstrate the same benefit in those with chronic kidney disease [16]. This highlights the critical importance of timely and effective management of alert transmissions, especially in these vulnerable patients [17].

The alterations in intracardiac filling pressures, which serve as the ideal surrogate for incipient congestion, are not well reflected by changes in body weight. Invasive hemodynamic telemonitoring provides the advantage of earlier detection of impending cardiac decompensation events [18]. However, regardless of the underlying technical devices used, reliable and prompt integration into the workflows of telemedical centers is considered crucial for achieving therapeutic effectiveness.

Intracardiac filling pressures can be monitored by tracking the pulmonary artery pressure (PAP), right ventricle, or left atrium. These implants enable the transmission of tracked values in a “passive” manner upon query with a wireless external readout device.

The electrode- and battery-free PAP sensor CardioMEMS (Abbott Laboratories) is implanted in a proximal branch of the pulmonary artery and calibrated to the individual patient. Changes in pulsatile flow are converted into a pressure derivative and wirelessly transmitted to a remote dashboard, such as that at a telemedical center. Daily measurements must be initiated actively by the patient, and specialized staff regularly interrogate the PAP trends accumulating over time to determine whether and which actions need to be taken. In the Abbott-funded CHAMPION trial (NCT00531661) [19], conducted in the United States and Canada, 550 patients in NYHA functional class III, regardless of LVEF, had PAP sensors implanted. The CHAMPION trial reported a 39% risk reduction in HF-related hospitalizations after 6 months in patients who received physician-led interventions based on the assessed PAP values compared with the control group [19]. These effects were sustained after 12 months and remained consistent in the nonrandomized 3-year extended follow-up period [20]. The prospective MEMS-HF registry (CardioMEMS European Monitoring Study for Heart Failure) had an observational design and yielded comparable effects when utilized within the European health care system [21].

These findings were corroborated by the pre–COVID-19 impact analysis of the GUIDE-HF trial (NCT03387813), which studied 1000 patients in NYHA class II or III from the United States [22], and the recent MONITOR-HF trial (NTR7673), conducted in 348 NYHA class III patients in the Netherlands [23]. Both trials indicated a sizeable benefit of PAP-guided management on HF hospitalization rates compared with the control group.

As aforementioned, the G-BA evaluates medical innovations for inclusion in the medical services covered by health insurance. Given the major differences in health care systems between the United States and Germany, the G-BA made a novel decision to directly fund a telemedicine randomized controlled trial across 50 study centers. The still ongoing PASSPORT-HF trial (Pulmonary Artery Sensor System Pressure Monitoring to Improve Heart Failure Outcomes; NCT04398654) aims to recruit 554 patients in NYHA class III who have experienced an HF hospitalization within the last 12 months.

PASSPORT-HF is investigating whether PAP-guided care, supported by HF nurses and utilizing daily monitoring of PAP values with the CardioMEMS system (Abbott), reduces the number of unplanned HF-related hospitalizations or all-cause mortality after 12 months.

In the PASSPORT-HF trial, patients with CHF are being randomized in a 1:1 ratio to either device implantation or, in contrast to the CHAMPION trial, no device implantation in the control arm. Both groups will receive structured telephone support from HF nurses in addition to guideline-compliant pharmacotherapy, which exceeds standard practice in Germany. Therefore, PASSPORT-HF aims to evaluate whether the previously reported benefits of PAP-guided hemodynamic monitoring as a novel HF management tool in routine outpatient telemedical care can be replicated in the German health care setting. Initial study results are expected in 2026 [24].

The Cordella HF Management System (Cordella, Endotronix Inc.) comprises an implantable, battery-free PAP sensor and an external handheld patient reader. This system was evaluated in the SIRONA study program (NCT03375710).

The Cordella HF Management System is the first to facilitate the simultaneous recording of both invasive PAP data and externally measured parameters, such as blood pressure, heart rate, body weight, and oxygen saturation. This capability offers a more comprehensive overview of a patient’s compensation status to the HF care team. Additionally, the system enables patients to access their trending data through an easy-to-use handheld device for PAP measurement. Unlike the CardioMEMS HF system, the Cordella HF Management System allows for PAP measurements to be taken in various body positions and under stress conditions. This flexibility is particularly important, as patients have expressed a clear preference for measurements conducted while seated [25].

The Cordella system was initially evaluated in a first-in-human study involving 15 patients, where the PAP difference measured 90 days after implantation showed no significant difference between the values obtained from the Cordella sensor and those from right heart catheterization. Notably, patient compliance with daily remote monitoring exceeded 98% [26]. Following this, the SIRONA-2 multicenter, single-arm, open-label study (NCT03375710) included 70 patients with HF in NYHA class III across 4 sites in Ireland and Belgium, as well as 3 centers in Germany.

The primary efficacy endpoint that compared the Cordella PAP sensor measurements with established catheter-derived reference pressure at 90 days was met (mean PAP difference 0.0-2.9 mmHg, P=.003), remaining in good agreement for up to 12 months of observation. There were no reports of sensor failures or deaths within the 90-day period [25], and improvements in NYHA class and 6-minute walk distance were observed [27]. Hence, the Cordella management system appears feasible and safe and is currently under investigation in the PROACTIVE-HF single-arm study (NCT04089059), which has prespecified safety and effectiveness endpoints to provide objective evidence of a similar risk-benefit profile to the CardioMEMS system in 450 patients in NYHA class III (Figure 2).

Telemonitoring is an effective technology regarding availability, accessibility, and affordability. However, improvements in outcomes for patients with CHF through telemedicine have not been universally demonstrated across all available technologies and devices. Refining the current evidence remains challenging due to unresolved questions about the most appropriate monitoring technology for individual patients, the optimal time to initiate telemonitoring, and, most importantly, the duration of monitoring following cardiac decompensation [51].

Furthermore, there is a need to incorporate current evidence for special patient populations, such as patients with HF with preserved ejection fraction [52], into the catalog of services provided by statutory health insurance without requiring a complete restart of the authorization process.

In contrast to the introduction of a new drug therapy, transferring a digital therapy from a controlled study setup to routine health care is significantly more complex. To facilitate the introduction of noninvasive telemedicine in HF, the publicly funded prospective phase IV registry study, “TIM-HF4” (Telemedical Interventional Management in Heart Failure 4), will commence in 2025. This study aims to investigate patient acceptance and the effectiveness of noninvasive telemonitoring in HF under real-life conditions, focusing on outcomes such as repeated hospitalizations due to HF, death from any cause, and health economic criteria.

The transferability of telemonitoring to other cardiological indications has not been sufficiently explored in scientific trials to date. However, telemonitoring could be beneficial in clinical settings by improving discharge processes, such as accelerating patient discharge following rhythmological interventions and enhancing aftercare. Notably, telemedical supervision may facilitate faster and more reliable uptitration of guideline-directed medical therapy, taking into account patients’ clinical tolerability and vital signs. The STRONG-HF trial highlighted this potential, demonstrating a significantly reduced risk of HF readmission, and alleviated symptoms when guideline-directed medical therapy was uptitrated within 2 weeks of discharge, alongside monitoring of the clinical status and evaluation of laboratory values [53].

In the context of a prehospital setting, the ongoing randomized controlled study, ResKriVer-TAVI, funded by the Federal Ministry for Economic Affairs and Climate Action (German Clinical Trials Register DRKS00027842), is investigating whether telemedical interventional management enhances clinical outcomes, specifically cardiovascular hospitalization and death from any cause, in patients with aortic stenosis awaiting transcatheter aortic valve implantation [54].

While feasibility studies demonstrate the proof of concept for the latest technologies, there is a critical need for randomized trials to evaluate the clinical efficacy of cutting-edge telemonitoring devices and their eventual integration into routine practice. As it stands, it remains unclear whether noninvasive measurements obtained through wearable devices are equally effective compared with implanted cardiac devices. Additionally, the potential advantages of combining methods that integrate multiple sensors have yet to be tested against a single-sensor approach for superiority.

As the number of patients eligible for telemedical care continues to grow, machine learning tools hold significant promise for addressing the challenges of numerical scaling and the preprocessing of complex health data from diverse sources. Currently, triaging vital parameters is an established practice. In the future, advancements in pattern recognition are expected to enhance prioritization and improve the prediction of individual decompensation thresholds.

Nevertheless, AI applications are currently not eligible for standard cardiovascular telemedicine care. With the implementation of the European AI Act in March 2024 [55], clear transparency requirements and specific obligations for higher-risk AI applications will create a wide range of opportunities for research into their applications in telemonitoring patient care.

AI is also a promising tool for identifying novel HF parameters: AI applications could integrate smartwatch-based data with established intracardiac and extracardiac device monitoring data. A real-time analysis of wearable-derived intrinsic hemodynamic changes (such as heart rhythm, heart rate, level of activity, pedometer data, and oxygen saturation) could further enhance patient-related outcomes by providing instant alerts to the telemedical center.

The telemedical sensor system will likely be complemented by automated speech analysis to detect pulmonary congestion, as promising data showed a prediction of HF events up to 3 weeks in advance [56]. The “Cordio HearO” smartphone app was introduced in a pilot study including 40 patients with acute cardiac decompensation [57]. This innovative strategy is currently investigated as part of the “Telemed5000-Stimme” observational study (DRKS00020763) in patients on regular hemodialysis [58] in Germany, as well as the “VAMP-HF” study (AI-Based Voice Analysis for Monitoring Patients Hospitalized With Acute Decompensated Heart Failure) in patients with acute decompensated HF at the Deutsches Herzzentrum der Charité and the US Mayo Clinic [59].

Besides their promising transformative potential, the implementation of AI tools in cardiovascular telemonitoring remains a challenge in terms of ethical scenarios and data protection.