Implant experience with an implantable hemodynamic monitor for the management of symptomatic heart failure

Implementation of an epicardial implantable MEMS sensor for continuous and real-time postoperative assessment of left ventricular activity in adult minipigs over a short- and long-term period

The sensing of left ventricular (LV) activity is fundamental in the diagnosis and monitoring of cardiovascular health in high-risk patients after cardiac surgery to achieve better short- and long-term outcome. Conventional approaches rely on noninvasive measurements even if, in the latest years, invasive microelectromechanical systems (MEMS) sensors have emerged as a valuable approach for precise and continuous monitoring of cardiac activity. The main challenges in designing cardiac MEMS sensors are represented by miniaturization, biocompatibility, and long-term stability. Here, we present a MEMS piezoresistive cardiac sensor capable of continuous monitoring of LV activity over time following epicardial implantation with a pericardial patch graft in adult minipigs. In acute and chronic scenarios, the sensor was able to compute heart rate with a root mean square error lower than 2 BPM. Early after up to 1 month of implantation, the device was able to record the heart activity during the most important phases of the cardiac cycle (systole and diastole peaks). The sensor signal waveform, in addition, closely reflected the typical waveforms of pressure signal obtained via intraventricular catheters, offering a safer alternative to heart catheterization. Furthermore, histological analysis of the LV implantation site following sensor retrieval revealed no evidence of myocardial fibrosis. Our results suggest that the epicardial LV implantation of an MEMS sensor is a suitable and reliable approach for direct continuous monitoring of cardiac activity. This work envisions the use of this sensor as a cardiac sensing device in closed-loop applications for patients undergoing heart surgery.

MEMS Technology in Cardiology: Advancements and Applications in Heart Failure Management Focusing on the CardioMEMS Device

Heart failure (HF) is a complex clinical syndrome associated with significant morbidity, mortality, and healthcare costs. It is characterized by various structural and/or functional abnormalities of the heart, resulting in elevated intracardiac pressure and/or inadequate cardiac output at rest and/or during exercise. These dysfunctions can originate from a variety of conditions, including coronary artery disease, hypertension, cardiomyopathies, heart valve disorders, arrhythmias, and other lifestyle or systemic factors. Identifying the underlying cause is crucial for detecting reversible or treatable forms of HF. Recent epidemiological studies indicate that there has not been an increase in the incidence of the disease. Instead, patients seem to experience a chronic trajectory marked by frequent hospitalizations and stagnant mortality rates. Managing these patients requires a multidisciplinary approach that focuses on preventing disease progression, controlling symptoms, and preventing acute decompensations. In the outpatient setting, patient self-care plays a vital role in achieving these goals. This involves implementing necessary lifestyle changes and promptly recognizing symptoms/signs such as dyspnea, lower limb edema, or unexpected weight gain over a few days, to alert the healthcare team for evaluation of medication adjustments. Traditional methods of HF monitoring, such as symptom assessment and periodic clinic visits, may not capture subtle changes in hemodynamics. Sensor-based technologies offer a promising solution for remote monitoring of HF patients, enabling early detection of fluid overload and optimization of medical therapy. In this review, we provide an overview of the CardioMEMS device, a novel sensor-based system for pulmonary artery pressure monitoring in HF patients. We discuss the technical aspects, clinical evidence, and future directions of CardioMEMS in HF management.

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Hemodynamic monitoring in heart failure and pulmonary hypertension: From analog tracings to the digital age

Hemodynamic monitoring has long formed the cornerstone of heart failure (HF) and pulmonary hypertension diagnosis and management. We review the long history of invasive hemodynamic monitors initially using pulmonary artery (PA) pressure catheters in the hospital setting, to evaluating the utility of a number of implantable devices that can allow for ambulatory determination of intracardiac pressures. Although the use of indwelling PA catheters has fallen out of favor in a number of settings, implantable devices have afforded clinicians an opportunity for objective determination of a patient’s volume status and pulmonary pressures. Some devices, such as the CardioMEMS and thoracic impedance monitors present as part of implantable cardiac defibrillators, are supported by a body of evidence which show the potential to reduce HF related morbidity and have received regulatory approval, whereas other devices have failed to show benefit and, in some cases, harm. Clearly these devices can convey a considerable amount of information and clinicians should start to familiarize themselves with their use and expect further development and refinement in the future.

[Implantable hemodynamic monitoring devices]

Heart failure is one of the most frequent diagnoses in hospital admissions in Germany. In the majority of these admissions acute decompensation of an already existing chronic heart failure is responsible. New mostly wireless and remote strategies for monitoring, titration, adaptation and optimization are the focus for improvement of the treatment of heart failure patients and the poor prognosis. The implantation of hemodynamic monitoring devices follows the hypothesis that significant changes in hemodynamic parameters occur before the occurrence of acute decompensation requiring readmission. Three different hemodynamic monitoring devices have so far been investigated in clinical trials employing right ventricular pressure, left atrial pressure and pulmonary artery pressure monitoring. Only one of these systems, the CardioMENS™ HF monitoring system, demonstrated a significant reduction of hospitalization due to heart failure over 6 months in the CHAMPION trial. The systematic adaptation of medication in the CHAMPION trial significantly differed from the usual care of the control arm over 6 months. This direct day to day management of diuretics is currently under intensive investigation; however, further studies demonstrating a positive effect on mortality are needed before translation of this approach into guidelines. Without this evidence a further implementation of pressure monitoring into currently used devices and justification of the substantial technical and personnel demands are not warranted.

Microelectromechanical systems and nephrology: the next frontier in renal replacement technology

Microelectromechanical systems (MEMS) are playing a prominent role in the development of many new and innovative biomedical devices, but they remain a relatively underused technology in nephrology. The future landscape of clinical medicine and research will only see further expansion of MEMS-based technologies in device designs and applications. This enthusiasm stems from the ability to create small-scale device features with high precision in a cost-effective manner. MEMS also offers the possibility to integrate multiple components into a single device. The adoption of MEMS has the potential to revolutionize how nephrologists manage kidney disease by improving the delivery of renal replacement therapies and enhancing the monitoring of physiologic parameters. To introduce nephrologists to MEMS, this review will first define relevant terms and describe the basic processes used to fabricate devices. Next, a survey of MEMS devices being developed for various biomedical applications will be illustrated with current examples. Finally, MEMS technology specific to nephrology will be highlighted and future applications will be examined. The adoption of MEMS offers novel avenues to improve the care of kidney disease patients and assist nephrologists in clinical practice. This review will serve as an introduction for nephrologists to the exciting world of MEMS.

New diagnostic devices in heart failure

PURPOSE OF REVIEW

Heart failure is among the leading causes of morbidity and mortality in the United States. In recent years, implantable devices have been developed that aim to predict impending heart failure events in time to prevent clinical decompensation. This review focuses on these emerging technologies and the implications they hold for the future of heart failure management.

RECENT FINDINGS

Many devices have recently been studied in patients with heart failure. These devices either evaluate hemodynamic values, including pulmonary and left atrial pressures, or intrathoracic impedance, which is related to pulmonary congestion. In small trials, device-acquired parameters like these have correlated well with data obtained during pulmonary artery catheterization. At least one trial has suggested a possible reduction in clinical heart failure events in patients with a device measuring pulmonary pressures. Other trials, recently completed or ongoing, are expected to shed more light on the role of diagnostic devices in improving heart failure outcomes.

SUMMARY

Incorporation of diagnostic devices into the management of heart failure patients may prove instrumental in reducing the burden of this disease on patients and healthcare systems.

Implantable hemodynamic monitors

The evaluation and management of volume status in patients with heart failure is a challenge for most clinicians. In addition, such an evaluation is possible only during a personal clinician-patient interface. The ability to acquire hemodynamic data continuously with the help of implanted devices with remote monitoring capability can provide early warning of heart failure decompensation and thus may aid in preventing hospitalizations for heart failure. The data obtained also may improve the understanding of the disease process. It is important for the clinician treating patients who have heart failure to become acquainted with this type of technology and learn to interpret and use these data appropriately. This article reviews the implantable hemodynamics monitors currently available.

Estimation of cardiac output in patients with congestive heart failure by analysis of right ventricular pressure waveforms

Background

Cardiac output (CO) is an important determinant of the hemodynamic state in patients with congestive heart failure (CHF). We tested the hypothesis that CO can be estimated from the right ventricular (RV) pressure waveform in CHF patients using a pulse contour cardiac output algorithm that considers constant but patient specific RV outflow tract characteristic impedance.

Method

In 12 patients with CHF, breath-by-breath Fick CO and RV pressure waveforms were recorded utilizing an implantable hemodynamic monitor during a bicycle exercise protocol. These data were analyzed retrospectively to assess changes in characteristic impedance of the RV outflow tract during exercise. Four patients that were implanted with an implantable cardiac defibrillator (ICD) implementing the algorithm were studied prospectively. During a two staged sub-maximal bicycle exercise test conducted at 4 and 16 weeks of implant, COs measured by direct Fick technique and estimated by the ICD were recorded and compared.

Results

At rest the total pulmonary arterial resistance and the characteristic impedance were 675 ± 345 and 48 ± 18 dyn.s.cm^-5, respectively. During sub-maximal exercise, the total pulmonary arterial resistance decreased (Δ 91 ± 159 dyn.s.cm^-5, p < 0.05) but the characteristic impedance was unaffected (Δ 3 ± 9 dyn.s.cm^-5, NS). The algorithm derived cardiac output estimates correlated with Fick CO (7.6 ± 2.5 L/min, R² = 0.92) with a limit of agreement of 1.7 L/min and tracked changes in Fick CO (R² = 0.73).

Conclusions

The analysis of right ventricular pressure waveforms continuously recorded by an implantable hemodynamic monitor provides an estimate of CO and may prove useful in guiding treatment in patients with CHF.

Implantable hemodynamic monitors: Can be conductance catheter system successfully implemented?

Successful management of cardiac heart failure requires a multifactorial approaching. It has been suggested that implantable hemodynamic long-term monitoring can improve patient care. This paper presents an analysis of the hemodynamic parameters commonly recorded, the most used implantable devices and their associated clinical trials. Newly implantable miniaturized sensors and devices are revisited. Finally, a newly implantable conductance-catheter based system is presented. The feasibility to realise volume and pressure measurements in the human left ventricular cavity using an implantable conductance-catheter based system is evaluated. It has the advantage to obtain LV signals continuously. In addition, it allows to realise maneuvers such as calibration and LV function by telemetry being avoiding patient hospitalizations. The rapid advances in device monitoring capabilities could change the new paradigm of the heart disease management.

Safety and accuracy of a wireless pulmonary artery pressure monitoring system in patients with heart failure

BACKGROUND

Implantable hemodynamic monitoring to guide heart failure (HF) therapy is a promising area of active research. The goal of this investigation was to evaluate the safety and technical performance of a novel wireless pulmonary artery pressure monitoring system in 17 patients with symptomatic HF.

METHODS

The monitoring system consists of a sensor, delivery catheter, interrogator, and home monitoring device. The HF sensor was implanted into a distal branch of the pulmonary artery. Pulmonary artery pressures were monitored using the external device, which powers the HF sensor and transmits the hemodynamic data from the patient's home to a secure Internet database. The accuracy of the system was assessed by comparison with standard right heart catheterization (RHC).

RESULTS

The HF sensor was safely and successfully implanted in all patients. Agreement between the HF sensor and RHC for systolic, diastolic, and mean pulmonary artery pressures was excellent, with correlation coefficients of 0.94, 0.85, and 0.95, respectively (all P < .0001). Using Bland-Altman plots, the average differences for systolic, diastolic, and mean pulmonary artery pressures for the HF sensor vs RHC were -4.4 ± 0.3, 2.5 ± 1.0, and -0.8 ± 1.3 mm Hg, respectively. There were no serious device-related adverse events. A postmortem analysis of the HF sensor in a patient who died 12 months after implant demonstrated complete endothelialization and no evidence of thrombosis.

CONCLUSIONS

This trial supports the safety and accuracy of this pulmonary artery pressure monitoring system in patients with HF and the conduct of randomized trials of implantable hemodynamic monitoring in HF, using this system.

Implantable hemodynamic monitors

The evaluation and management of volume status in patients with heart failure is a challenge for most clinicians. In addition, such an evaluation is possible only during a personal clinician-patient interface. The ability to acquire hemodynamic data continuously with the help of implanted devices with remote monitoring capability can provide early warning of heart failure decompensation and thus may aid in preventing hospitalizations for heart failure. The data obtained also may improve the understanding of the disease process. It is important for the clinician treating patients who have heart failure to become acquainted with this type of technology and learn to interpret and use these data appropriately. This article reviews the implantable hemodynamics monitors currently available.

Long term, implantable blood pressure monitoring systems

An overview of implantable measurement systems suitable for the long-term, continuous monitoring of blood pressure is presented in this paper. The challenges, design considerations and tradeoffs inherent in these systems are overviewed and implantable sensors from both industrial and research environments are reviewed. The paper is concluded with an outlook of future directions for implantable blood pressure monitoring systems.

Left ventricular endocardial pacing: a transarterial approach

INTRODUCTION

We tested the feasibility of a new technique of direct left ventricular endocardial lead placement across the aortic valve in a chronic (six month) pig model. The potential for aortic valve damage, systemic embolization, and pacing lead maturation and function within the left ventricle are unknown.

METHODS

Ten minipigs were successfully implanted with a transaortic left ventricular lead (Medtronic CapSureFix, Minneapolis, MN, USA) placed in the left ventricular apex via the carotid artery. Each pig received either a polyurethane (n = 5) or silicone (n = 5) lead. Post implant each pig received clopidogrel and aspirin for seven days. After six months all surviving pigs underwent thorough necropsy.

RESULTS

Each pig had adequate sensing (12.1 +/- 4 mV) and pacing thresholds (0.79 +/- 0.2 @ 0.5 V) at implant. Postoperatively two pigs died of a respiratory illness. One pig died postoperatively due to sepsis. At the six-month follow-up, all surviving pigs (n = 7) were in a healthy state. Of the pigs without dislodgement (n = 5) there was adequate sensing, but a rise in pacing thresholds. Echocardiography revealed a normal ejection fraction and only trace to mild aortic insufficiency in all pigs. Of the seven surviving pigs there were no thromboembolic events noted. One silicone lead was noted to have thrombosis along the lead screw and shaft.

CONCLUSION

Direct transaortic placement of a left ventricular lead is feasible. After six months, there was no significant aortic regurgitation and no evidence of thromboembolism despite no anticoagulation. Lead function was acceptable and only one silicone lead (and no polyurethane lead) was noted to have significant thrombosis.

Direct Left Atrial Pressure Monitoring in Ambulatory Heart Failure Patients

Background— We describe the first human experience with a permanently implantable, direct left atrial pressure (LAP) monitoring system in ambulatory patients with chronic heart failure.

Methods and Results— Eight patients with established heart failure and at least 1 heart failure hospitalization or unplanned visit for parenteral therapy in the last year underwent device implantation under fluoroscopic guidance. All subjects received aspirin 150 mg and clopidogrel 75 mg daily. Subjects measured LAP twice daily and attended a clinic regularly for data upload and device calibration. Right heart catheterization was performed at the time of device implantation and at 12 weeks. The device was implanted in all subjects with no procedural complications. At the 12-week follow-up, 87% of device LAP measurements were within ±5 mm Hg of simultaneous pulmonary capillary wedge pressure readings over a wide range of pressures (1.6 to 71 mm Hg). Net drift corrected by calibration was −0.2±1.9 mm Hg/mo. During short-term follow-up, there were no device-related complications or systemic emboli. There were no deaths, no unplanned heart failure clinic visits, and no admissions for heart failure.

Conclusions— Ambulatory monitoring of direct LAP with a new implantable device was well tolerated, feasible, and accurate at a short-term follow-up. Further follow-up and investigation are warranted to evaluate the clinical utility of LAP monitoring in patients with heart failure.

A radio frequency identification implanted in a tooth can communicate with the outside world

A radio frequency identification (RFID) transponder covering the 13.56 MHz band was adapted to minimize its volume so that it could be placed in the pulp chamber of an endodontically treated human tooth. The minimized transponder had a maximum communication distance of 30 mm. In an animal experiment, the transponder was fixed in the cavity of a mandibular canine of a dog. An RFID reader positioned close to the dog's face could communicate with the transponder in the dog's tooth. In certain cases, the system is applicable for the personal identification procedures for hospitalized patients instead of an identification wristband.

Who should pay for home monitoring of heart failure?

Despite the recent advancement in medical therapy for heart failure, morbidity associated with heart failure continues to be excessive, with rising hospitalization rates and costs. Disease management models have been instituted successfully for several chronic disease states, and observational trials have shown different models to be beneficial. A multidisciplinary approach to management of heart failure improves outcomes. Multiple recent trials involving various models of integrated and comprehensive disease management have demonstrated promising results, such as reduction in mortality and hospitalizations. Future models for disease monitoring may include implantable devices that directly monitor hemodynamics combined with multidisciplinary care.

Cardiac rhythm management: the shape of things to come

PURPOSE OF REVIEW

The aim of this article is to forecast a major imminent change in the clinical practice of cardiac rhythm management, which is argued to be remote patient monitoring, its potential benefits to clinical practitioners and its barriers to widespread diffusion.

RECENT FINDINGS

All four major manufacturers of cardiac rhythm management devices have recently introduced varying types of systems that allow remote patient monitoring. These remote patient monitoring systems promise more efficient patient management in today's clinical setting of rapidly growing numbers of patients with increasingly heterogeneous etiology, varying indications and comorbidities. The major differences between current systems are related to the degree of patient involvement in remote patient monitoring and limits on patient mobility. Other important factors that influence the value of remote patient monitoring are the degree to which remote follow-up would completely fulfill the requirements of an in-office follow-up and the inclusion of sensors that enable the prediction of major clinical events such as heart failure decompensation with a high degree of accuracy.

SUMMARY

Even if the different remote patient monitoring systems currently available offer several clinical benefits such as early detection of cardiac events and complications, reduced follow-up costs and increased safety, the full potential of such systems requires the possibility to easily transfer relevant patient data to common patient databases that are linked to hospital information systems or electronic patient records. Only then will it be possible to gain a complete picture of patient conditions. This will require the development of common protocols for data communication and may involve issues of patient data ownership and integrity.