Left Atrial Pressure Monitoring With an Implantable Wireless Pressure Sensor After Implantation of a Left Ventricular Assist Device

Biosensors with left ventricular assist devices

Heart failure imposes a significant global health burden, standing as a primary contributor to mortality. Various indicators and physiological shifts within the body may hint at distinct cardiac conditions. Specific biosensors have the capability to identify these changes. Integrating or embedding these biosensors into mechanical circulatory support devices (MCSDs), such as left ventricular assist devices (LVADs), becomes crucial for monitoring alterations in biochemical and physiological factors subsequent to an MCSD implantation. Detecting abnormal changes early in the course of disease progression will allow for improved patient outcomes and prognosis following an MCSD implantation. The aim of this review is to explore the available biosensors that may be coupled or implanted alongside LVADs to monitor biomarkers and changes in physiological parameters. Different fabrication materials for the biosensors are discussed, including their advantages and disadvantages. This review also examines the feasibility of integrating feedback control mechanisms into LVAD systems using data from the biosensors. Challenges facing this emerging technology and future directions for research and development are outlined as well. The overarching goal is to provide an overview of how implanted biosensors may improve the performance and outcomes of LVADs through continuous monitoring and closed-loop control.

An Era of Digital Healthcare-A Comprehensive Review of Sensor Technologies and Telehealth Advancements in Chronic Heart Failure Management

Heart failure (HF) is a multi-faceted, complex clinical syndrome characterized by significant morbidity, high mortality rate, reduced quality of life, and rapidly increasing healthcare costs. A larger proportion of these costs comprise both ambulatory and emergency department visits, as well as hospital admissions. Despite the methods used by telehealth (TH) to improve self-care and quality of life, patient outcomes remain poor. HF management is associated with numerous challenges, such as conflicting evidence from clinical trials, heterogeneity of TH devices, variability in patient inclusion and exclusion criteria, and discrepancies between healthcare systems. A growing body of evidence suggests there is an unmet need for increased individualization of in-hospital management, continuous remote monitoring of patients pre and post-hospital admission, and continuation of treatment post-discharge in order to reduce re-hospitalizations and improve long-term outcomes. This review summarizes the current state-of-the-art for HF and associated novel technologies and advancements in the most frequently used types of TH (implantable sensors), categorizing devices in their preclinical and clinical stage, bench-to-bedside implementation challenges, and future perspectives on remote HF management to improve long-term outcomes of HF patients. The Review also highlights recent advancements in non-invasive remote monitoring technologies demonstrated by a few pilot observational prospective cohort studies.

Implantable Cardiovascular Devices: Current and Emerging Technologies for Remote Heart Failure Monitoring

Heart failure remains a substantial socioeconomic burden to our health care system. With the aging of the population, the incidence is expected to rise in the ensuing years. Standard heart failure management strategies have failed to reduce hospitalizations and mortality. In patients with heart failure, remote hemodynamic monitoring with implantable devices provides essential data, which can be used in unison with standard patient management to reduce heart failure hospitalizations. This review will chronicle the important clinical trials of various implantable devices and describe the emerging technologies in remote heart failure management. Cardiovascular implantable electronic devices, namely implanted cardioverter-defibrillator and cardiac resynchronization therapy devices with defibrillator, have evolved beyond sole resynchronization and currently can deliver real-time cardiac hemodynamics. Clinical data regarding hemodynamic monitoring with implanted cardioverter-defibrillator and cardiac resynchronization therapy devices with defibrillator have not consistently demonstrated a reduction in heart failure or mortality benefit. However, there is promise in the future with the application of multiparameter diagnostic algorithms with these devices. The most efficacious implantable device has been the pulmonary artery pressure sensor, CardioMEMS. This device has been proven to be safe and shown to reduce heart failure hospitalizations. Moreover, multiple newly developed devices are currently under investigation after successful first-in-man studies.

A Review of Digital Health and Biotelemetry: Modern Approaches towards Personalized Medicine and Remote Health Assessment

With the prevalence of digitalization in all aspects of modern society, health assessment is becoming digital too. Taking advantage of the most recent technological advances and approaching medicine from an interdisciplinary perspective has allowed for important progress in healthcare services. Digital health technologies and biotelemetry devices have been more extensively employed for preventing, detecting, diagnosing, monitoring, and predicting the evolution of various diseases, without requiring wires, invasive procedures, or face-to-face interaction with medical personnel. This paper aims to review the concepts correlated to digital health, classify and describe biotelemetry devices, and present the potential of digitalization for remote health assessment, the transition to personalized medicine, and the streamlining of clinical trials.

Fully implantable wireless batteryless vascular electronics with printed soft sensors for multiplex sensing of hemodynamics

The continuous monitoring of hemodynamics attainable with wireless implantable devices would improve the treatment of vascular diseases. However, demanding requirements of size, wireless operation, and compatibility with endovascular procedures have limited the development of vascular electronics. Here, we report an implantable, wireless vascular electronic system, consisting of a multimaterial inductive stent and printed soft sensors capable of real-time monitoring of arterial pressure, pulse rate, and flow without batteries or circuits. Developments in stent design achieve an enhanced wireless platform while matching conventional stent mechanics. The fully printed pressure sensors demonstrate fast response times, high durability, and sensing at small bending radii. The device is monitored via inductive coupling at communication distances notably larger than prior vascular sensors. The wireless electronic system is validated in artery models, while minimally invasive catheter implantation is demonstrated in an in vivo rabbit study. Overall, the vascular system offers an adaptable framework for comprehensive monitoring of hemodynamics.

Invasive Haemodynamic Assessment Before and After Left Ventricular Assist Device Implantation: A Guide to Current Practice

Mechanical circulatory support for the management of advanced heart failure is a rapidly evolving field. The number of durable long-term left ventricular assist device (LVAD) implantations increases each year, either as a bridge to heart transplantation or as a stand-alone ‘destination therapy’ to improve quantity and quality of life for people with end-stage heart failure. Advances in cardiac imaging and non-invasive assessment of cardiac function have resulted in a diminished role for right heart catheterisation (RHC) in general cardiology practice; however, it remains an essential tool in the evaluation of potential LVAD recipients, and in their long-term management. In this review, the authors discuss practical aspects of performing RHC and potential complications. They describe the haemodynamic markers associated with a poor prognosis in patients with left ventricular systolic dysfunction and evaluate the measures of right ventricular (RV) function that predict risk of RV failure following LVAD implantation. They also discuss the value of RHC in the perioperative period; when monitoring for longer term complications; and in the assessment of potential left ventricular recovery.

Miniaturized Fontan Circulation Assist Device: Chronic In Vivo Evaluation

We have miniaturized and optimized our implantable rotary blood pump developed to provide long-term mechanical right heart support for patients who have failing Fontan circulation. The objective of this study was to evaluate the miniaturized Fontan circulation assist device (mini-FCAD) during 30-day sheep studies (n = 5). A complete right heart bypass was performed and all return flow was supported by the pump. Postoperatively, unfractionated heparin was given to maintain thromboelastography R times of 2× normal. The first two studies were terminated on day 0 and day 4 due to complications. In the final three studies, the animals remained healthy and were electively terminated at 30 ± 2 days. Pump flow was between 5 and 7 lpm, left atrial pressure remained normal, and inlet pressures were between 3 and 18 mm Hg with no incidents of suction. There was no evidence of hemolysis, end organ or pulmonary dysfunction, thromboembolic events, nor thermal damage to the surrounding tissue. Explanted devices from two studies were free of thrombi and in the third study there were unattached thrombi on the SVC inlet of the rotor. The mini-FCAD was successfully tested in vivo as a right heart replacement device demonstrating adequate circulatory support and normal physiologic pulmonary and venous pressures.

Cardiac Output Estimation: Online Implementation for Left Ventricular Assist Device Support

OBJECTIVE

We present a novel pipeline that consists of various algorithms for the estimation of the cardiac output (CO) during ventricular assist devices (VADs) support using a single pump inlet pressure (PIP) sensor as well as pump intrinsic signals.

METHODS

A machine learning (ML) model was constructed for the prediction of the aortic valve opening status. When a closed aortic valve is detected, the estimated CO equals the estimated pump flow. Otherwise, the estimated CO equals the sum of the estimated pump flow and the aortic valve flow, estimated via a Kalman-filter approach. Both the pathophysiological conditions and the pump speed of an in-vitro test bench were adjusted in various combinations to evaluate the performance of the pipeline, as well as the individual estimators.

RESULTS

The ML model yielded a Matthews correlation coefficient of 0.771, a sensitivity of 0.913 and a specificity of 0.871. An overall CO root mean square error (RMSE) of 0.69 L/min was achieved. Replacing the pump flow and aortic pressure estimators with sensors would decrease the RMSE below 0.5 L/min.

CONCLUSION

The performance of the proposed pipeline is considered the state of the art for VADs with an integrated PIP sensor. The effect of the individual estimators on the overall performance of the pipeline was thoroughly investigated and their limitations were identified for future research.

SIGNIFICANCE

The clinical application of the proposed solution could provide the clinicians with essential information about the interaction between the patient's heart and the VAD to further improve the VAD therapy.

The left ventricular assist device as a patient monitoring system

Technological progress of left ventricular assist devices (LVADs) towards rotary blood pumps and the optimization of medical management contributed to the significant improvements in patient survival as well as LVAD support duration. Even though LVAD therapy is now well-established for end-stage heart failure patients, the long-term occurrence of adverse events (AE) such as bleeding, infection or stroke, still represent a relevant burden. An early detection of AE, before onset of major symptoms, can lead to further optimization of patient treatment and thus mitigate the burden of AE. Continuous patient monitoring facilitates identification of pathophysiological states and allows anticipation of AE to improve patient management. In this paper, methods, algorithms and possibilities for continuous patient monitoring based on LVAD data are reviewed. While experience with continuous LVAD monitoring is currently limited to a few centers worldwide, the pace of developments in this field is fast and we expect these technologies to have a global impact on the well-being of LVAD patients.

A novel wireless implant for central venous pressure measurement: First animal experience

Background/Objective

Central venous pressure (CVP) serves as a surrogate for right atrial pressure, and thus could potentially predict a wider range of heart failure conditions. The purpose of this work is to assess CVP, through an implantable sensor incorporated with a novel anchor design, in the inferior and superior vena cava of an animal model.

Methods

Two animals (Dorset sheep) were implanted with sensors at 3 different locations: inferior vena cava (IVC), superior vena cava (SVC), and pulmonary artery (PA). Two sensors with distinct anchor designs considering anatomical requirements were used. A standard PA sensor (trade name Cordella) was deployed in the PA and SVC, whereas a sensor with a modified cylindrical anchor with various struts was designed to reside in the IVC. Each implant was calibrated against a Millar catheter reference sensor. The ability of the central venous sensors to detect changes in pressure was evaluated by modifying the fluid volume of the animal.

Results

The sensors implanted in both sheep were successful, which provided an opportunity to understand the relationship between PA and CVP via simultaneous readings. The mapping and implantation in the IVC took less than 15 minutes. Multiple readings were taken at each implant location using a hand-held reader device under various conditions. CVP recorded in the IVC (6.49 mm Hg) and SVC (6.14 mm Hg) were nearly the same. PA pressure (13-14 mm Hg) measured was higher than CVP, as expected. The SVC waveforms showed clear beats and respiration. Respiration could be seen in the IVC waveforms, but not all beats were easily distinguishable. Both SVC and IVC readings showed increases in pressure (3.7 and 2.7 mm Hg for SVC and IVC, respectively) after fluid overload was induced via extra saline administration.

Conclusion

In this work, the feasibility of measuring CVP noninvasively was demonstrated. The established ability of wireless PA pressure sensors to enable prevention of decompensation events weeks ahead can now be explored using central venous versions of such sensors.

CardioMEMSTM System in the Daily Management of Heart Failure: Review of Current Data and Technique of Implantation

INTRODUCTION

Heart failure (HF) leads to significant morbidity and mortality and imposes a large economic burden. Although there have been several advances in HF monitoring and management, HF-rehospitalization remains a significant problem. Remote monitoring of HF to detect early signs of decompensation has emerged in past years as an option to prevent or reduce the incidence of HF rehospitalization. The CardioMEMS^TM HF system is a wireless pulmonary artery (PA) pressure monitoring system that detects changes in PA pressure and transmits data to the healthcare provider. Since changes in PA pressure happen early in the course of HF decompensation, the CardioMEMS^TM system allows the provider to institute timely intensification of HF therapies to alter the course. In trial and registry data, the use of the CardioMEMS^TM HF system has been associated with reduction in HF hospitalization, improvement in quality of life, symptoms, and physical activity.

AREAS COVERED

This review will focus on the available data supporting its utilization in patients with HF.

EXPERT OPINION

CardioMEMS^TM is relatively safe and cost-effective, reduces heart failure hospitalization rates, and fits into intermediate to high-value medical care.

Ultrasound-based estimation of remaining cardiac function in LVAD-supported ex vivo hearts

Left ventricular assist devices (LVAD) provide cardiac support to patients with advanced heart failure. Methods that can directly measure remaining LV function following device implantation do not currently exist. Previous studies have shown that a combination of loading (LV pressure) and deformation (strain) measurements enables quantitation of myocardial work. We investigated the use of ultrasound (US) strain imaging and pressure–strain loop analysis in LVAD‐supported hearts under different hemodynamic and pump unloading conditions, with the aim of determining LV function with and without LVAD support. Ex vivo porcine hearts (n = 4) were implanted with LVADs and attached to a mock circulatory loop. Measurements were performed at hemodynamically defined “heart conditions” as the hearts deteriorated from baseline. Hemodynamic (including LV pressure) and radio‐frequency US data were acquired during a pump‐ramp protocol at speeds from 0 (with no pump outflow) to 10 000 revolutions per minute (rpm). Regional circumferential (ε_circ) and radial (ε_rad) strains were estimated over each heart cycle. Regional ventricular dyssynchrony was quantitated through time‐to‐peak strain. Mean change in LV pulse pressure and ε_circ between 0 and 10 krpm were −21.8 mm Hg and −7.24% in the first condition; in the final condition −46.8 mm Hg and −19.2%, respectively. ε_rad was not indicative of changes in pump speed or heart condition. Pressure–strain loops showed a degradation in the LV function and an increased influence of LV unloading: loop area reduced by 90% between 0 krpm in the first heart condition and 10 krpm in the last condition. High pump speeds and degraded condition led to increased dyssynchrony between the septal and lateral LV walls. Functional measurement of the LV while undergoing LVAD support is possible by using US strain imaging and pressure–strain loops. This can provide important information about remaining pump function. Use of novel LV pressure estimation or measurement techniques would be required for any future use in LVAD patients.

Remote monitoring for better management of LVAD patients: the potential benefits of CardioMEMS

Left ventricular assist devices (LVAD) are frequently used in the treatment of end-stage heart failure (HF), and due to the shortage of heart donors and destination programs, it is likely to keep on growing. Still, LVAD therapy is not without complications and morbidity and rehospitalization rates are high. New ways to improve LVAD care both from the side of the patient and the physician are warranted. Remote monitoring could be a tool to tailor treatment in these patients, as no feedback exists at all about patient functioning on top of the static pump parameters. We aim to provide an overview and evaluation of the novel remote monitoring strategies to optimize LVAD management and elaborate on the opportunities of remote hemodynamic monitoring with CardioMEMS, at home in these patients as the next step to improve care.

A Starling-like total work controller for rotary blood pumps: An in vitro evaluation

Due to improved durability and survival rates, rotary blood pumps (RBPs) are the preferred left ventricular assist device when compared to volume displacement pumps. However, when operated at constant speed, RBPs lack a volume balancing mechanism which may result in left ventricular suction and suboptimal ventricular unloading. Starling-like controllers have previously been developed to balance circulatory volumes; however, they do not consider ventricular workload as a feedback and may have limited sensitivity to adjust RBP workload when ventricular function deteriorates or improves. To address this, we aimed to develop a Starling-like total work controller (SL-TWC) that matched the energy output of a healthy heart by adjusting RBP hydraulic work based on measured left ventricular stroke work and ventricular preload. In a mock circulatory loop, the SL-TWC was evaluated using a HeartWare HVAD in a range of simulated patient conditions. These conditions included changes in systemic hypertension and hypotension, pulmonary hypertension, blood circulatory volume, exercise, and improvement and deterioration of ventricular function by increasing and decreasing ventricular contractility. The SL-TWC was compared to constant speed control where RBP speed was set to restore cardiac output to 5.0 L/min at rest. Left ventricular suction occurred with constant speed control during pulmonary hypertension but was prevented with the SL-TWC. During simulated exercise, the SL-TWC demonstrated reduced LVSW (0.51 J) and greater RBP flow (9.2 L/min) compared to constant speed control (LVSW: 0.74 J and RBP flow: 6.4 L/min). In instances of increased ventricular contractility, the SL-TWC reduced RBP hydraulic work while maintaining cardiac output similar to the rest condition. In comparison, constant speed overworked and increased cardiac output. The SL-TWC balanced circulatory volumes by mimicking the Starling mechanism, while also considering changes in ventricular workload. Compared to constant speed control, the SL-TWC may reduce complications associated with volume imbalances, adapt to changes in ventricular function and improve patient quality of life.

The expanding role of implantable devices to monitor heart failure and pulmonary hypertension

The epidemics of heart failure and, to a lesser extent, of pulmonary arterial hypertension continue unabated worldwide and are extremely costly in terms of loss of life and earnings, as well as the burden of health-care expenditure due to repeated hospitalization. The effectiveness of newly discovered therapies for the two conditions depends on their timely application. To date, symptoms have been used to guide the application and timing of therapy. Compelling evidence now exists that symptoms are preceded by several metabolic and haemodynamic changes, particularly a rise in intravascular pressures during exercise. These observations have stimulated the development of several implantable devices for the detection of impending unstable heart failure or pulmonary arterial hypertension, necessitating admission to hospital. In this Review, we summarize the rationale for monitoring patients with heart failure or pulmonary arterial hypertension, the transition from noninvasive to implantable devices and the current and anticipated clinical uses of these devices.

Wireless Interrogation of Implantable SAW Sensors

Implantable sensors provide long-term, accurate physiological measurements after a minimally invasive procedure, particularly when designed as transponders. Wireless interrogation of deeply implanted transponders with RF remains a challenge due to the high loss at the skin-air interface and large tissue RF absorption. This paper presents a system for wirelessly interrogating surface acoustic wave (SAW) sensors implanted in the main pulmonary artery (PA), where the pressure (PAP) is a very important parameter in the management of heart failure patients. The proposed PAP monitoring system consists of an implantable SAW pressure sensor integrated with an antenna and anchor in a housing, an external antenna and an electronic interrogator. The PAP is determined by measuring the frequency of the echo signal from SAW sensor accurately. An asymmetric antenna was designed and integrated with the sensor. The combination of simulation, theoretical calculation and phantom measurement indicates that the path loss to the implant location, about 6 cm below the skin, is around 25 dB. A portable interrogator was designed based on a dual conversion receiver and single echo high frequency sampling approach to assess achievable frequency estimation accuracy predicted by Cramer-Rao Lower Bound (CRLB) analysis. The system was characterized using a high quality (Q) factor SAW sensor, fabricated at wafer level, wire-connected to the interrogator via an attenuator to simulate path loss. The signal-to-noise ratio (SNR) of captured echo signals was calculated and used in CRLB analysis. The analysis indicates that without using signal post processing, the sensor sensitivity has to be at least 440 Hz/mmHg in order to achieve a target 1 mmHg accuracy. Although the current sensor sensitivity is only 200 Hz/mmHg, the in vivo measurement showed that acceptable accuracy can be obtained by signal post processing. The results from an invasive catheter tip transducer measured simultaneously with the SAW sensor showed that the differences in pulse pressure and relative mean pressure are 0.8 mmHg and 1.4 mmHg, respectively. The accuracy could be further improved by increasing the sensor Q factor and sensitivity and reducing path loss.

An Implantable Sensorized Lead for Continuous Monitoring of Cardiac Apex Rotation

Changes in the pattern or amplitude of cardiac rotation have been associated with important cardiovascular diseases, including Heart Failure (HF) which is one of the major health problems worldwide. Recent advances in echocardiographic techniques have allowed for non-invasive quantification of cardiac rotation; however, these examinations do not address the continuous monitoring of patient status. We have presented a newly developed implantable, transvenous lead with a tri-axis (3D) MEMS gyroscope incorporated near its tip to measure cardiac apex rotation in the three-dimensional space. We have named it CardioMon for its intended use for cardiac monitoring. If compared with currently proposed implantable systems for HF monitoring based on the use of pressure sensors that can have reliability issues, an implantable motion sensor like a gyroscope holds the premise for more reliable long term monitoring. The first prototypal assembly of the CardioMon lead has been tested to assess the reliability of the 3D gyroscope readings. In vitro results showed that the novel sensorized CardioMon lead was accurate and reliable in detecting angular velocities within the range of cardiac twisting velocities. Animal experiments will be planned to further evaluate the CardioMon lead in in vivo environments and to investigate possible endocardial implantation sites.

Implantable devices to monitor patients with heart failure

Reducing heart failure hospitalizations represents a major challenge for modern clinicians. Early detection of congestion plays a key role in disease management strategy. Apart from traditional methods (patient reporting symptoms, body weight monitoring), novel home-care strategies allow guided adjustments in medical therapy through telemonitoring embedded in cardiac electronic implantable devices or through stand-alone diagnostic devices for hemodynamic monitoring. Wireless pulmonary artery pressure monitoring seems to reduce re-admission risk and is currently approved for this purpose in patients with heart failure. Multiparameter monitoring is also appealing and could be a valuable tool in managing these patients. However, invasive techniques face several safety concerns and cost-effectiveness issues. Therefore, quest for future research and emerging technologies is necessary.

Haemodynamic Monitoring Devices in Heart Failure: Maximising Benefit with Digitally Enabled Patient Centric Care

ICDs and resynchronisation devices are routinely implanted in patients with heart failure for primary prevention of sudden cardiac death or to treat the condition. The addition of device features and algorithms that directly or indirectly monitor cardiac haemodynamics to assess heart failure status can provide additional benefit by treating heart failure more continuously. Established and emerging devices and sensors aimed at treating or measuring cardiac haemodynamics represent the next era of heart failure disease management. Digitally enabled models of heart failure care, based on frequent haemodynamic measurements, will increasingly involve patients in their own disease management. Software tools and services tailored to provide patients with personalised information to guide diet, activity, medications and haemodynamic management offer an unprecedented opportunity to improve patient outcomes. This will enable physicians to care for larger populations because management will be exception based, automated and no longer depend on one-to-one patient and physician interactions.