Direct left atrial pressure monitoring in severe heart failure: long-term sensor performance

Soft Bioelectronics for Heart Monitoring

Cardiovascular diseases (CVDs) are a predominant global health concern, accounting for over 17.9 million deaths in 2019, representing approximately 32% of all global fatalities. In North America and Europe, over a million adults undergo cardiac surgeries annually. Despite the benefits, such surgeries pose risks and require precise postsurgery monitoring. However, during the postdischarge period, where monitoring infrastructures are limited, continuous monitoring of vital signals is hindered. In this area, the introduction of implantable electronics is altering medical practices by enabling real-time and out-of-hospital monitoring of physiological signals and biological information postsurgery. The multimodal implantable bioelectronic platforms have the capability of continuous heart sensing and stimulation, in both postsurgery and out-of-hospital settings. Furthermore, with the emergence of machine learning algorithms into healthcare devices, next-generation implantables will benefit artificial intelligence (AI) and connectivity with skin-interfaced electronics to provide more precise and user-specific results. This Review outlines recent advancements in implantable bioelectronics and their utilization in cardiovascular health monitoring, highlighting their transformative deployment in sensing and stimulation to the heart toward reaching truly personalized healthcare platforms compatible with the Sustainable Development Goal 3.4 of the WHO 2030 observatory roadmap. This Review also discusses the challenges and future prospects of these devices.

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.

Evaluating Research Grade Bioimpedance Hardware Using Textile Electrodes for Long-Term Fluid Status Monitoring

Fluid overload is a chronic medical condition that affects over six million Americans with conditions such as congestive heart failure, end-stage renal disease, and lymphedema. Remote management of fluid overload continues to be a leading clinical challenge. Bioimpedance is one technique that can be used to estimate the hydration of tissue and track it over time. However, commercially available bioimpedance measurement systems are bulky, expensive, and rely on Ag/AgCl electrodes that dry out and can irritate the skin. The use of bioimpedance today is therefore limited to clinical and research settings, with measurements performed at daily intervals or over short periods of time rather than continuously and long-term. This paper proposes using wearable calf bioimpedance measurements integrated into a compression sock for long-term fluid overload management. A PCB was developed using standard measurement techniques that measures the calf bioimpedance using a custom analog front-end built around an AD8302 gain-phase detection chip. Data is transmitted wirelessly via Bluetooth Low Energy to an iOS device using a custom iOS app. Bioimpedance data were collected both from the wearable system and a commercial measurement system (ImpediMed SFB7) using RRC networks, Ag/AgCl electrodes, and the textile compression sock. Bioimpedance data collected from the wearable system showed close agreement with data from the SFB7 when using RRC networks and in five healthy human subjects with Ag/AgCl electrodes. However, when using the textile compression sock the wearable system had worse precision than the SFB7 (4% run to run compared to <1% run to run) and there were larger differences between the two systems than when using the RRC networks and the Ag/AgCl electrodes. Wearable system precision and agreement with the SFB7 was improved by pressure or light wetting of the current electrodes on the sock. Future research should focus on reliable elimination of low-frequency artifacts in research grade hardware to enable long-term calf bioimpedance measurements for fluid overload management.

The V-LAP System for Remote Left Atrial Pressure Monitoring of Patients with Heart Failure: Remote Left Atrial Pressure Monitoring

OBJECTIVE

Patients with heart failure (HF) are at an increased risk of hospital admissions. The aim of this report is to describe the feasibility, safety and accuracy of a novel wireless left atrial pressure (LAP) monitoring system in HF patients.

METHODS

The V-LAP Left Atrium Monitoring systEm for Patients With Chronic sysTOlic & Diastolic Congestive heart Failure (VECTOR-HF) study is a prospective, multicenter, single-arm, open-label, first-in human clinical trial to assess the safety, performance and usability of the V-LAP system (Vectorious Medical Technologies, Ltd) in NYHA Class III HF patients. The device was implanted in the inter-atrial septum via a percutaneous, trans-septal approach, guided by fluoroscopy and echocardiography. Primary endpoints included the successful deployment of the implant, ability to perform initial pressure measurements and safety outcomes.

RESULTS

To date, 24 patients were implanted with the LAP monitoring device. No device-related complications have occurred. LAP was reported accurately, agreeing well with wedge pressure at 3 months (Lin's CCC=0.850). After 6 months, NYHA class improved in 40% of the patients (95% CI =16.4%-63.5%), while 6-minute walk test distance had not changed significantly (313.9 ± 144.9 vs. 232.5 ± 129.9 meters, p=0.076).

CONCLUSION

The V-LAP left atrium monitoring system appears to be safe and accurate.

Implantable devices for heart failure monitoring

Heart failure (HF) is associated with considerable morbidity and mortality. The increasing prevalence of HF and inpatient HF hospitalization has a considerable burden on healthcare cost and utilization. The recognition that hemodynamic changes in pulmonary artery pressure (PAP) and left atrial pressure precede the signs and symptoms of HF has led to interest in hemodynamic guided HF therapy as an approach to allow earlier intervention during a heart failure decompensation. Remote patient monitoring (RPM) utilizing telecommunication, cardiac implantable electronic device parameters and implantable hemodynamic monitors (IHM) have largely failed to demonstrate favorable outcomes in multicenter trials. However, one positive randomized clinical trial testing the CardioMEMS device (followed by Food and Drug Administration approval) has generated renewed interest in PAP monitoring in the HF population to decrease hospitalization and improve quality of life. The COVID-19 pandemic has also stirred a resurgence in the utilization of telehealth to which RPM using IHM may be complementary. The cost effectiveness of these monitors continues to be a matter of debate. Future iterations of devices aim to be smaller, less burdensome for the patient, less dependent on patient compliance, and less cumbersome for health care providers with the integration of artificial intelligence coupled with sophisticated data management and interpretation tools. Currently, use of IHM may be considered in advanced heart failure patients with the support of structured programs.

A Sensorless Control System for an Implantable Heart Pump Using a Real-Time Deep Convolutional Neural Network

Left ventricular assist devices (LVADs) are mechanical pumps, which can be used to support heart failure (HF) patients as bridge to transplant and destination therapy. To automatically adjust the LVAD speed, a physiological control system needs to be designed to respond to variations of patient hemodynamics across a variety of clinical scenarios. These control systems require pressure feedback signals from the cardiovascular system. However, there are no suitable long-term implantable sensors available. In this study, a novel real-time deep convolutional neural network (CNN) for estimation of preload based on the LVAD flow was proposed. A new sensorless adaptive physiological control system for an LVAD pump was developed using the full dynamic form of model free adaptive control (FFDL-MFAC) and the proposed preload estimator to maintain the patient conditions in safe physiological ranges. The CNN model for preload estimation was trained and evaluated through 10-fold cross validation on 100 different patient conditions and the proposed sensorless control system was assessed on a new testing set of 30 different patient conditions across six different patient scenarios. The proposed preload estimator was extremely accurate with a correlation coefficient of 0.97, root mean squared error of 0.84 mmHg, reproducibility coefficient of 1.56 mmHg, coefficient of variation of 14.44%, and bias of 0.29 mmHg for the testing dataset. The results also indicate that the proposed sensorless physiological controller works similarly to the preload-based physiological control system for LVAD using measured preload to prevent ventricular suction and pulmonary congestion. This study shows that the LVADs can respond appropriately to changing patient states and physiological demands without the need for additional pressure or flow measurements.

Implantable devices for heart failure monitoring and therapy

Heart failure (HF), the cardiovascular epidemic of the twenty-first century, is associated with significant comorbidities and high mortality. The prevalence of HF is estimated around 6.5 million people and is expected to increase to 8 million by the year 2030. The associated costs to care for these patients continue to increase. Despite the advancement of pharmacologic therapy with significant improvement in morbidity and mortality, the 5-year survival for heart failure still stands at 61%. The challenges faced by HF patients include difficulty with lifestyle modifications, nonadherence to complex medical regimens, financial limitations, lack of access to medical care, and unfavorable side effects. The sickest HF patients, who are ACC/AHA stage D, have advanced therapeutic options such as left ventricular assist devices and orthotopic heart transplant; however, the majority of patients are ACC/AHA stage C and/or not candidates for such advanced care. With constraints placed on hospitals by Medicare on HF readmissions as well as the multiple comorbidities imposed by this disease, intense interest is focused on the development of implantable devices as add-on therapy. This review discusses the innovative devices under varying stages of investigation or approved for monitoring and treatment of HF.

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.

Interventional Heart Failure and Hemodynamic Monitoring

Convergence of the fields of heart failure (HF) and interventional cardiology has led to the formation of a discipline referred to as interventional HF. Although the term may be applied to essentially any invasive procedure performed in patients with HF (eg, coronary angiography, percutaneous coronary intervention, invasive assessment of hemodynamics), it is more commonly reserved for the application of invasive diagnostic or therapeutic procedures to improve the clinical decision-making, functional status, and outcomes of HF patients. This article reviews developing modalities.

A Multiphysics Biventricular Cardiac Model: Simulations With a Left-Ventricular Assist Device

Computational models have become essential in predicting medical device efficacy prior to clinical studies. To investigate the performance of a left-ventricular assist device (LVAD), a fully-coupled cardiac fluid-electromechanics finite element model was developed, incorporating electrical activation, passive and active myocardial mechanics, as well as blood hemodynamics solved simultaneously in an idealized biventricular geometry. Electrical activation was initiated using a simplified Purkinje network with one-way coupling to the surrounding myocardium. Phenomenological action potential and excitation-contraction equations were adapted to trigger myocardial contraction. Action potential propagation was formulated within a material frame to emulate gap junction-controlled propagation, such that the activation sequence was independent of myocardial deformation. Passive cardiac mechanics were governed by a transverse isotropic hyperelastic constitutive formulation. Blood velocity and pressure were determined by the incompressible Navier-Stokes formulations with a closed-loop Windkessel circuit governing the circulatory load. To investigate heart-LVAD interaction, we reduced the left ventricular (LV) contraction stress to mimic a failing heart, and inserted a LVAD cannula at the LV apex with continuous flow governing the outflow rate. A proportional controller was implemented to determine the pump motor voltage whilst maintaining pump motor speed. Following LVAD insertion, the model revealed a change in the LV pressure-volume loop shape from rectangular to triangular. At higher pump speeds, aortic ejection ceased and the LV decompressed to smaller end diastolic volumes. After multiple cycles, the LV cavity gradually collapsed along with a drop in pump motor current. The model was therefore able to predict ventricular collapse, indicating its utility for future development of control algorithms and pre-clinical testing of LVADs to avoid LV collapse in recipients.

Chronic heart failure management and remote haemodynamic monitoring

Heart failure (HF) has a large societal and economic burden and is expected to increase in magnitude and complexity over the ensuing years. A number of telemonitoring strategies exploring remote monitoring and management of clinical signs and symptoms of congestion in HF have had equivocal results. Early studies of remote haemodynamic monitoring showed promise, but issues with device integrity and implantation-associated adverse events hindered progress. Nonetheless, these early studies established that haemodynamic congestion precedes clinical congestion by several weeks and that remote monitoring of intracardiac pressures may be a viable and practical management strategy. Recently, the safety and efficacy of remote pulmonary artery pressure-guided HF management was established in a prospective, single-blind trial where randomisation to active pressure-guided HF management reduced future HF hospitalisations. Subsequent commercial use studies reinforced the utility of this technology and post hoc analyses suggest that tight haemodynamic management of patients with HF may be an additional pillar of therapy alongside established guideline-directed medical and device therapy. Currently, there is active exploration into utilisation of this technology and management paradigm for the timing of implantation of durable left ventricular assist devices (LVAD) and even optimisation of LVAD therapy. Several ongoing clinical trials will help clarify the extent and utility of this strategy along the spectrum of patient with HF from individuals with chronic, stable HF to those with more advanced disease requiring heart replacement therapy.

Implantable Sensors for Regenerative Medicine

The translation of many tissue engineering/regenerative medicine (TE/RM) therapies that demonstrate promise in vitro are delayed or abandoned due to reduced and inconsistent efficacy when implemented in more complex and clinically relevant preclinical in vivo models. Determining mechanistic reasons for impaired treatment efficacy is challenging after a regenerative therapy is implanted due to technical limitations in longitudinally measuring the progression of key environmental cues in vivo. The ability to acquire real-time measurements of environmental parameters of interest including strain, pressure, pH, temperature, oxygen tension, and specific biomarkers within the regenerative niche in situ would significantly enhance the information available to tissue engineers to monitor and evaluate mechanisms of functional healing or lack thereof. Continued advancements in material and fabrication technologies utilized by microelectromechanical systems (MEMSs) and the unique physical characteristics of passive magnetoelastic sensor platforms have created an opportunity to implant small, flexible, low-power sensors into preclinical in vivo models, and quantitatively measure environmental cues throughout healing. In this perspective article, we discuss the need for longitudinal measurements in TE/RM research, technical progress in MEMS and magnetoelastic approaches to implantable sensors, the potential application of implantable sensors to benefit preclinical TE/RM research, and the future directions of collaborative efforts at the intersection of these two important fields.

Implantable Hemodynamic Monitoring for Heart Failure Patients

Rates of heart failure hospitalization remain unacceptably high. Such hospitalizations are associated with substantial patient, caregiver, and economic costs. Randomized controlled trials of noninvasive telemedical systems have failed to demonstrate reduced rates of hospitalization. The failure of these technologies may be due to the limitations of the signals measured. Intracardiac and pulmonary artery pressure-guided management has become a focus of hospitalization reduction in heart failure. Early studies using implantable hemodynamic monitors demonstrated the potential of pressure-based heart failure management, whereas subsequent studies confirmed the clinical utility of this approach. One large pivotal trial proved the safety and efficacy of pulmonary artery pressure-guided heart failure management, showing a marked reduction in heart failure hospitalizations in patients randomized to active pressure-guided management. "Next-generation" implantable hemodynamic monitors are in development, and novel approaches for the use of this data promise to expand the use of pressure-guided heart failure management.

The Role of Implantable Hemodynamic Monitors to Manage Heart Failure

Heart failure is associated with high rates of hospitalization and rehospitalization, resulting in substantial clinical and economic burden. Current approaches to monitoring patients with heart failure have done little to reduce these high rates of heart failure hospitalization. Implantable hemodynamic monitors have been developed to remotely provide direct measurement of intracardiac and pulmonary artery pressures in ambulatory patients with heart failure. These devices have the potential to direct day-to-day management of patients with heart failure to reduce hospitalization rates. The use of a pulmonary artery pressure measurement system has been shown to reduce the risk of heart failure hospitalization in patients with systolic and diastolic heart failure.

Intracardiac Pressures Measured Using an Implantable Hemodynamic Monitor: Relationship to Mortality in Patients With Chronic Heart Failure

BACKGROUND

The purpose of this analysis was to examine whether implantable hemodynamic monitor-derived baseline estimated pulmonary artery diastolic pressure (ePAD) and change from baseline ePAD were independent predictors of all-cause mortality in patients with chronic heart failure.

METHODS AND RESULTS

Retrospective analysis used data from 3 studies (n=790 patients; 216 deaths). Baseline ePAD was related to mortality using a multivariable model including baseline and demographic data. Changes in ePAD defined as change from baseline to 6 months and from baseline to 14 days before death or exit from study were related to subsequent mortality, and analysis was adjusted for baseline ePAD. Area under the pressure versus time curve during 180 days before death or exit from study was related to mortality. Baseline ePAD, independent of other covariates, was a significant predictor of mortality (hazard ratio=1.07; 95% confidence interval=1.05-1.09; P<0.0001). Change in ePAD was an independent predictor of mortality (hazard ratio=1.07; 95% confidence interval=1.05-1.100; P=0.0008). Increased ePAD of 3, 4, or 5 mm Hg from baseline to 6 months was associated with increased mortality risk of 23.8%, 32.9%, or 42.8%. Change in ePAD from baseline to 14 days before death or exit from study was higher in patients who died (3.0±8 versus 1.7±10 mm Hg; P=0.003). Area under the pressure versus time curve in the final 180 days before death or exit from study was higher in patients who died versus those alive at end of study (185±668 versus 17±482 mm Hg.days; P=0.006).

CONCLUSIONS

Implantable hemodynamic monitor-derived baseline ePAD and change from baseline ePAD were independent predictors of mortality in chronic heart failure patients.

[Implantable sensors for outpatient assessment of ventricular filling pressure in advanced heart failure : Which telemonitoring design is optimal?]

INTRODUCTION

Patients with advanced heart failure suffer from frequent hospitalizations. Non-invasive hemodynamic telemonitoring for assessment of ventricular filling pressure has been shown to reduce hospitalizations. We report on the right ventricular (RVP), the pulmonary artery (PAP) and the left atrial pressure (LAP) sensor for non-invasive assessment of the ventricular filling pressure.

METHODS

A literature search concerning the available implantable pressure sensors for noninvasive haemodynamic telemonitoring in patients with advanced heart failure was performed.

RESULTS

Until now, only implantation of the PAP-sensor was able to reduce hospitalizations for cardiac decompensation and to improve quality of life. The right ventricular pressure sensor missed the primary endpoint of a significant reduction of hospitalizations, clinical data using the left atrial pressure sensor are still pending.

CONCLUSION

The implantation of a pressure sensor for assessment of pulmonary artery filling pressure is suitable for reducing hospitalizations for heart failure and for improving quality of life in patients with advanced heart failure.

Digital monitoring and care: Virtual medicine

Remote digital health monitoring technologies can be synergistically organized to create a virtual medical system providing more continuous care centered on the patient rather than the bricks and mortar medical complex. Utilization of the digitalized patient health monitoring can facilitate diagnosis, treatment plans, physician-patient interaction, and accelerate the progress of medical research, education, and training. The field of cardiac electrophysiology has been an early adopter of this shift in care and serves as a paradigm applicable to all areas of medicine. The overall impact of this remote virtual care model on the quality of medical care and patient experience requires greater study, as well as vigilance as to the differences between technology and care in order to preserve the intangible and immeasurable factors that bring humanity to the art and science of medicine.

A Novel Combined-Catheter to Monitor Left and Right Atrial Pressures: A Simple and Reliable Method for Pediatric Cardiac Surgery

OBJECTIVE

To introduce a novel combined-catheter to monitor left and right atrial pressures.

DESIGN

Prospective observational study.

SETTING

Fuwai Hospital, China.

PATIENTS

A total of 113 pediatric patients (77 men), median age 10.3 months, admitted between July 10, 2014, and February 5, 2015, were divided into two groups: the novel-catheter group and the traditional-method group.

INTERVENTIONS

All patients received routine anesthesia and surgery. Left atrial pressure and central venous pressure (an estimate of right atrial pressure), measured through a catheter needle during surgery, were identified as the "gold standard." A novel combined-catheter, composed of a reformed triple-lumen catheter with a microtube inserted within its central cavity, was used in the novel-catheter group. A traditional triple-lumen catheter to monitor central venous pressure plus another single-lumen catheter to monitor left atrial pressure were used in the traditional-method group.

MEASUREMENTS AND MAIN RESULTS

The novel combined-catheter could accurately monitor left atrial pressure and central venous pressure. Pressure values measured by the novel catheter correlated well with the gold standard (left atrial pressure, R = 0.98; central venous pressure, R = 0.99). Bland-Altman analyses revealed good agreement between pressures measured by the novel catheter and the gold standard. The absolute value of maximum difference was 0.67 mm Hg for left atrial pressure and 0.33 mm Hg for central venous pressure, which are acceptable in clinical practice. Left atrial pressure-monitoring catheter displaced into the right atrium occurred significantly less frequently in the novel-catheter group when compared with the traditional-method group (5 and 12 cases, respectively).

CONCLUSIONS

This novel combined-catheter was safe and reliable at monitoring left and right atrial pressures, and infusion involved only one catheter without the disadvantages of the traditional method. This new novel method may be particularly useful in pediatric open-heart surgery.

Evaluation of Physiological Control Systems for Rotary Left Ventricular Assist Devices: An In-Vitro Study

Rotary left ventricular assist devices (LVADs) show weaker response to preload and greater response to afterload than the native heart. This may lead to ventricular suction or pulmonary congestion, which can be deleterious to the patient's recovery. A physiological control system which optimizes responsiveness of LVADs may reduce adverse events. This study compared eight physiological control systems for LVAD support against constant speed mode. Pulmonary (PVR) and systemic (SVR) vascular resistance changes, a passive postural change and exercise were simulated in a mock circulation loop to evaluate the controller's ability to prevent suction and congestion and to increase exercise capacity. Three active and one passive control systems prevented ventricular suction at high PVR (500 dyne s cm(-5)) and low SVR (600 dyne s cm(-5)) by decreasing LVAD speed (by 200-515 rpm) and by increasing LVAD inflow cannula resistance (up to 1000 dyne s cm(-5)) respectively. These controllers increased LVAD preload sensitivity (to 0.196-2.415 L min(-1) mmHg(-1)) compared to the other control systems and constant speed mode (0.039-0.069 L min(-1) mmHg(-1)). The same three active controllers increased pump speed (600-800 rpm) and thus LVAD flow by 4.5 L min(-1) during exercise which increased exercise capacity. Physiological control systems that prevent adverse events and/or increase exercise capacity may help improve LVAD patient conditions.

Remote hemodynamic monitoring for ambulatory left ventricular assist device patients

Left ventricular assist devices (LVADs) have been shown to markedly improve survival and quality of life in patients with end-stage heart failure. However, despite ongoing improvements in survival and quality of life, significant challenges still exist in the management of these patients, including a high rate of recurrent heart failure and rehospitalizations. Similar challenges exist in the non-LVAD heart failure population as well, and recent efforts to utilize remote hemodynamic monitoring techniques to improve outcomes have shown promise. No data currently exist demonstrating extension of this benefit into the LVAD population, although a theoretical benefit can be extrapolated. Herein we review current remote hemodynamic methods and potential applications towards LVAD patients.

Health care sensor--based systems for point of care monitoring and diagnostic applications: a brief survey

Continuous, real-time remote monitoring through medical point--of--care (POC) systems appears to draw the interest of the scientific community for healthcare monitoring and diagnostic applications the last decades. Towards this direction a significant merit has been due to the advancements in several scientific fields. Portable, wearable and implantable apparatus may contribute to the betterment of today's healthcare system which suffers from fundamental hindrances. The number and heterogeneity of such devices and systems regarding both software and hardware components, i.e sensors, antennas, acquisition circuits, as well as the medical applications that are designed for, is impressive. Objective of the current study is to present the major technological advancements that are considered to be the driving forces in the design of such systems, to briefly state the new aspects they can deliver in healthcare and finally, the identification, categorization and a first level evaluation of them.

[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.

Evolution from electrophysiologic to hemodynamic monitoring: the story of left atrial and pulmonary artery pressure monitors

Heart failure (HF) is a costly, challenging and highly prevalent medical condition. Hospitalization for acute decompensation is associated with high morbidity and mortality. Despite application of evidence-based medical therapies and technologies, HF remains a formidable challenge for virtually all healthcare systems. Repeat hospitalizations for acute decompensated HF (ADHF) can have major financial impact on institutions and resources. Early and accurate identification of impending ADHF is of paramount importance yet there is limited high quality evidence or infrastructure to guide management in the outpatient setting. Historically, ADHF was identified by physical exam findings or invasive hemodynamic monitoring during a hospital admission; however, advances in medical microelectronics and the advent of device-based diagnostics have enabled long-term ambulatory monitoring of HF patients in the outpatient setting. These monitors have evolved from piggybacking on cardiac implantable electrophysiologic devices to standalone implantable hemodynamic monitors that transduce left atrial or pulmonary artery pressures as surrogate measures of left ventricular filling pressure. As technology evolves, devices will likely continue to miniaturize while their capabilities grow. An important, persistent challenge that remains is developing systems to translate the large volumes of real-time data, particularly data trends, into actionable information that leads to appropriate, safe and timely interventions without overwhelming outpatient cardiology and general medical practices. Future directions for implantable hemodynamic monitors beyond their utility in heart failure may include management of other major chronic diseases such as pulmonary hypertension, end stage renal disease and portal hypertension.

In Vitro Comparison of Active and Passive Physiological Control Systems for Biventricular Assist Devices

The low preload and high afterload sensitivities of rotary ventricular assist devices (VADs) may cause ventricular suction events or venous congestion. This is particularly problematic with rotary biventricular support (BiVAD), where the Starling response is diminished in both ventricles. Therefore, VADs may benefit from physiological control systems to prevent adverse events. This study compares active, passive and combined physiological controllers for rotary BiVAD support with constant speed mode. Systemic (SVR) and pulmonary (PVR) vascular resistance changes and exercise were simulated in a mock circulation loop to evaluate the capacity of each controller to prevent suction and congestion and increase exercise capacity. All controllers prevented suction and congestion at high levels of PVR (900 dynes s cm(-5)) and SVR (3000 dynes s cm(-5)), however these events occurred in constant speed mode. The controllers increased preload sensitivity (0.198-0.34 L min(-1) mmHg(-1)) and reduced afterload sensitivity (0.0001-0.008 L min(-1) mmHg(-1)) of the VADs when compared to constant speed mode (0.091 and 0.072 L min(-1) mmHg(-1) respectively). The active controller increased pump speeds (400-800 rpm) and pump flow by 2.8 L min(-1) during exercise, thus increasing exercise capacity. By reducing suction and congestion and by increasing exercise capacity, the control systems presented in this study may help increase quality of life of VAD patients.

Anatomy and Physiology of Left Ventricular Suction Induced by Rotary Blood Pumps

This study in five large greyhound dogs implanted with a VentrAssist left ventricular assist device focused on identification of the precise site and physiological changes induced by or underlying the complication of left ventricular suction. Pressure sensors were placed in left and right atria, proximal and distal left ventricle, and proximal aorta while dual perivascular and tubing ultrasonic flow meters measured blood flow in the aortic root and pump outlet cannula. When suction occurred, end-systolic pressure gradients between proximal and distal regions of the left ventricle on the order of 40-160 mm Hg indicated an occlusive process of variable intensity in the distal ventricle. A variable negative flow difference between end systole and end diastole (0.5-3.4 L/min) was observed. This was presumably mediated by variable apposition of the free and septal walls of the ventricle at the pump inlet cannula orifice which lasted approximately 100 ms. This apposition, by inducing an end-systolic flow deficit, terminated the suction process by relieving the imbalance between pump requirement and delivery from the right ventricle. Immediately preceding this event, however, unnaturally low end-systolic pressures occurred in the left atrium and proximal left ventricle which in four dogs lasted for 80-120 ms. In one dog, however, this collapse progressed to a new level and remained at approximately -5 mm Hg across four heart beats at which point suction was relieved by manual reduction in pump speed. Because these pressures were associated with a pulmonary capillary wedge pressure of -5 mm Hg as well, they indicate total collapse of the entire pulmonary venous system, left atrium, and left ventricle which persisted until pump flow requirement was relieved by reducing pump speed. We suggest that this collapse caused the whole vascular region from pulmonary capillaries to distal left ventricle to behave as a Starling resistance which further reduced right ventricular output thus contributing to a major reduction in pump flow. We contend that similar complications of manual speed control also occur in the human subject and remain a major unsolved problem in the clinical management of patients implanted with rotary blood pumps.

Experimental feasibility study of estimation of the normalized central blood pressure waveform from radial photoplethysmogram

The feasibility of a novel system to reliably estimate the normalized central blood pressure (CBPN) from the radial photoplethysmogram (PPG) is investigated. Right-wrist radial blood pressure and left-wrist PPG were simultaneously recorded in five different days. An industry-standard applanation tonometer was employed for recording radial blood pressure. The CBP waveform was amplitude-normalized to determine CBPN. A total of fifteen second-order autoregressive models with exogenous input were investigated using system identification techniques. Among these 15 models, the model producing the lowest coefficient of variation (CV) of the fitness during the five days was selected as the reference model. Results show that the proposed model is able to faithfully reproduce CBPN (mean fitness = 85.2% ± 2.5%) from the radial PPG for all 15 segments during the five recording days. The low CV value of 3.35% suggests a stable model valid for different recording days.

Rationale and Design of the Left Atrial Pressure Monitoring to Optimize Heart Failure Therapy Study (LAPTOP-HF)

BACKGROUND

Daily measurements of left atrial pressure (LAP) may be useful for guiding adjustments in medical therapy that prevent clinical decompensation in patients with severe heart failure (HF).

STUDY DESIGN

LAPTOP-HF is a prospective, multicenter, randomized, controlled clinical trial in ambulatory patients with advanced heart failure in which the safety and clinical effectiveness of a physician-directed patient self-management therapeutic strategy based on LAP measured twice daily by means of an implantable sensor will be compared with a control group receiving optimal medical therapy. The trial will enroll up to 730 patients with New York Heart Association functional class III symptoms and either a hospitalization for HF during the previous 12 months or an elevated B-type natriuretic peptide level, regardless of ejection fraction, at up to 75 investigational centers. Randomization to the treatment group or control group will be at a 1:1 ratio in 3 strata based on the ejection fraction (EF > or ≤35%) and the presence of a de novo CRT device indication.

SUMMARY

LAPTOP-HF will provide essential information about the role of implantable LAP monitoring in conjunction with a new HF treatment paradigm across the spectrum of HF patients.

Preload-based starling-like control for rotary blood pumps: numerical comparison with pulsatility control and constant speed operation

In this study, we evaluate a preload-based Starling-like controller for implantable rotary blood pumps (IRBPs) using left ventricular end-diastolic pressure (PLVED) as the feedback variable. Simulations are conducted using a validated mathematical model. The controller emulates the response of the natural left ventricle (LV) to changes in PLVED. We report the performance of the preload-based Starling-like controller in comparison with our recently designed pulsatility controller and constant speed operation. In handling the transition from a baseline state to test states, which include vigorous exercise, blood loss and a major reduction in the LV contractility (LVC), the preload controller outperformed pulsatility control and constant speed operation in all three test scenarios. In exercise, preload-control achieved an increase of 54% in mean pump flow ([Formula: see text]) with minimum loading on the LV, while pulsatility control achieved only a 5% increase in flow and a decrease in mean pump speed. In a hemorrhage scenario, the preload control maintained the greatest safety margin against LV suction. PLVED for the preload controller was 4.9 mmHg, compared with 0.4 mmHg for the pulsatility controller and 0.2 mmHg for the constant speed mode. This was associated with an adequate mean arterial pressure (MAP) of 84 mmHg. In transition to low LVC, [Formula: see text] for preload control remained constant at 5.22 L/min with a PLVED of 8.0 mmHg. With regards to pulsatility control, [Formula: see text] fell to the nonviable level of 2.4 L/min with an associated PLVED of 16 mmHg and a MAP of 55 mmHg. Consequently, pulsatility control was deemed inferior to constant speed mode with a PLVED of 11 mmHg and a [Formula: see text] of 5.13 L/min in low LVC scenario. We conclude that pulsatility control imposes a danger to the patient in the severely reduced LVC scenario, which can be overcome by using a preload-based Starling-like control approach.

Heart failure with preserved ejection fraction: mechanisms, clinical features, and therapies

The clinical syndrome comprising heart failure (HF) symptoms but with a left ventricular ejection fraction (EF) that is not diminished, eg, HF with preserved EF, is increasingly the predominant form of HF in the developed world, and soon to reach epidemic proportions. It remains among the most challenging of clinical syndromes for the practicing clinician and scientist alike, with a multitude of proposed mechanisms involving the heart and other organs and complex interplay with common comorbidities. Importantly, its morbidity and mortality are on par with HF with reduced EF, and as the list of failed treatments continues to grow, HF with preserved EF clearly represents a major unmet medical need. The field is greatly in need of a more unified approach to its definition and view of the syndrome that engages integrative and reserve pathophysiology beyond that related to the heart alone. We need to reflect on prior treatment failures and the message this is providing, and redirect our approaches likely with a paradigm shift in how the disease is viewed. Success will require interactions between clinicians, translational researchers, and basic physiologists. Here, we review recent translational and clinical research into HF with preserved EF and give perspectives on its evolving demographics and epidemiology, the role of multiorgan deficiencies, potential mechanisms that involve the heart and other organs, clinical trials, and future directions.

Physiological control of dual rotary pumps as a biventricular assist device using a master/slave approach

Dual rotary left ventricular assist devices (LVADs) can provide biventricular mechanical support during heart failure. Coordination of left and right pump speeds is critical not only to avoid ventricular suction and to match cardiac output with demand, but also to ensure balanced systemic and pulmonary circulatory volumes. Physiological control systems for dual LVADs must meet these objectives across a variety of clinical scenarios by automatically adjusting left and right pump speeds to avoid catastrophic physiological consequences. In this study we evaluate a novel master/slave physiological control system for dual LVADs. The master controller is a Starling-like controller, which sets flow rate as a function of end-diastolic ventricular pressure (EDP). The slave controller then maintains a linear relationship between right and left EDPs. Both left/right and right/left master/slave combinations were evaluated by subjecting them to four clinical scenarios (rest, postural change, Valsalva maneuver, and exercise) simulated in a mock circulation loop. The controller's performance was compared to constant-rotational-speed control and two other dual LVAD control systems: dual constant inlet pressure and dual Frank-Starling control. The results showed that the master/slave physiological control system produced fewer suction events than constant-speed control (6 vs. 62 over a 7-min period). Left/right master/slave control had lower risk of pulmonary congestion than the other control systems, as indicated by lower maximum EDPs (15.1 vs. 25.2-28.4 mm Hg). During exercise, master/slave control increased total flow from 5.2 to 10.1 L/min, primarily due to an increase of left and right pump speed. Use of the left pump as the master resulted in fewer suction events and lower EDPs than when the right pump was master. Based on these results, master/slave control using the left pump as the master automatically adjusts pump speed to avoid suction and increases pump flow during exercise without causing pulmonary venous congestion.

Effects of AV delay and VV delay on left atrial pressure and waveform in ambulant heart failure patients: insights into CRT optimization

BACKGROUND

We hypothesized that left atrial pressure (LAP) obtained by a permanent implantable sensor is sensitive to changes in cardiac resynchronization therapy (CRT) settings and could guide CRT optimization to improve the response rate. We investigated the effect of CRT optimization on LAP and its waveform parameters in ambulant heart failure (HF) patients.

METHODS

CRT optimization was performed in eight ambulant HF patients, using echocardiography as reference. LAP waveform was acquired at each of eight atrioventricular (AV) intervals and five inter-ventricular (VV) intervals. Selected waveform parameters were also evaluated for their sensitivity to CRT changes and agreement with echocardiography-guided optimal settings.

RESULTS

Optimal AV and VV intervals varied considerably between patients. All patients exhibited significant changes in waveform morphology with AV optimization. Optimal AV delay determined from echocardiography ranged between 140 ms and 225 ms. Mean LAP tended to be lower at optimal setting 14 ± 3 mmHg compared to shorter (<100 ms) or longer (>160 ms) AV settings (P = 0.16). There were clear trends to smaller peak a-wave (P = 0.11) and gentler positive a-slope (P = 0.15) and positive v-slope (P = 0.09) with longer AV delays. Mean LAP and negative v-wave slope correlated well with echo-guided optimal setting, r = 0.91 (P = 0.001) and 0.79 (P = 0.03), respectively. No significant effects on LAP or waveform were seen during VV optimization.

CONCLUSIONS

LAP and its waveform changes considerably with AV optimization. There is good agreement between echo-guided optimal setting and LAP. LAP could provide an objective guide to CRT optimization. (Clinical Trial Registry information: URL: http://www.clinicaltrials.gov. Unique Identifier: NCT00632372).

Wireless blood pressure monitoring with a novel implantable device: long-term in vivo results

PURPOSE

Devices constantly tracking the blood pressure (BP) of hypertensive patients are highly desired to facilitate effective patient management and to reduce hospitalization. We report on experiences gathered in a pilot study that was designed to evaluate the prototype of a newly developed, minimally invasive implantable sensor system for long-term BP monitoring.

METHODS

The device was implanted in the femoral artery (FA) of 12 sheep via standard FA catheterization under fluoroscopic control. Accuracy of the recorded blood pressure was determined by comparison with a reference catheter, which was positioned in the contralateral FA immediately after implantation. Regular follow-up included angiography, computed tomography (CT), and control of functionality and position of the BP sensor. Animals were euthanized after 6 months. FA segments with in situ pressure sensor underwent macroscopic and histopathologic examinations.

RESULTS

All implantations of the novel sensor device in the FA were successful and uneventful. High-quality BP recordings were documented. Bland-Altman plots indicate very good agreement. Comparison with measurements taken from the reference sensor revealed mean differences and standard deviations of -0.56 ± 0.85, 0.29 ± 1.44, and 0.85 ± 2.27 mmHg (diastolic, systolic, and pulse pressure, respectively) after exclusion of one outlier. CT uncovered deficiencies in cable stability that were addressed in a redesign. No thrombus formation, necrosis, or apoptosis were detected.

CONCLUSIONS

The pilot study proved the technical feasibility of wireless BP measurement in the FA via a novel miniature sensor device.

Disease management: remote monitoring in heart failure patients with implantable defibrillators, resynchronization devices, and haemodynamic monitors

Heart failure represents a major public health concern, associated with high rates of morbidity and mortality. A particular focus of contemporary heart failure management is reduction of hospital admission and readmission rates. While optimal medical therapy favourably impacts the natural history of the disease, devices such as cardiac resynchronization therapy devices and implantable cardioverter defibrillators have added incremental value in improving heart failure outcomes. These devices also enable remote patient monitoring via device-based diagnostics. Device-based measurement of physiological parameters, such as intrathoracic impedance and heart rate variability, provide a means to assess risk of worsening heart failure and the possibility of future hospitalization. Beyond this capability, implantable haemodynamic monitors have the potential to direct day-to-day management of heart failure patients to significantly reduce hospitalization rates. The use of a pulmonary artery pressure measurement system has been shown to significantly reduce the risk of heart failure hospitalization in a large randomized controlled study, the CardioMEMS Heart Sensor Allows Monitoring of Pressure to Improve Outcomes in NYHA Class III Heart Failure Patients (CHAMPION) trial. Observations from a pilot study also support the potential use of a left atrial pressure monitoring system and physician-directed patient self-management paradigm; these observations are under further investigation in the ongoing LAPTOP-HF trial. All these devices depend upon high-intensity remote monitoring for successful detection of parameter deviations and for directing and following therapy.

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.

An implantable left atrial pressure sensor lead designed for percutaneous extraction using standard techniques

Background

An implantable left atrial pressure (LAP) monitoring system for guiding the management of patients with advanced heart failure has the potential to require extraction, particularly in the setting of infection. The LAP sensor lead was designed to be suitable for ease of percutaneous extraction using standard techniques for extracting pacemaker and defibrillator leads. The clinical experience, to date, with percutaneous extraction of the LAP sensor lead is presented.

Methods

A total of 82 patients underwent successful implantation of the LAP sensor lead using transseptal catheterization. Five patients of the 82 patients during a cumulative follow-up period of 267 patient-years (median of 2.9 years/patient) underwent percutaneous extraction using manual traction with a locking stylet and/or an excimer laser sheath to bore through adhesions. The distal fixation anchors of the LAP sensor lead are designed to fold forward during extraction so that the sensor module can easily separate from the interatrial septum.

Results

Percutaneous extraction of the LAP sensor lead was accomplished successfully in all five patients with no embolic events, vascular tears, perforations, or other complications requiring surgical intervention. Manual traction alone was sufficient to detach the LAP sensor lead from the interatrial septum in all cases. Use of the excimer laser sheath was needed in selected cases to bore through scar tissue within the venous insertion site, but not within the heart.

Conclusions

The extraction of the LAP sensor lead was accomplished safely using standard techniques and equipment for percutaneously extracting pacemaker and defibrillator leads.

Implantable cardiovascular sensors and computers: interventional heart failure strategies

Despite evidence-based medical and pharmacologic advances the management of heart failure remains challenging, whether in the ambulatory setting where daily weight monitoring has failed, or in the inpatient setting where readmission rates and morbidity remains high. There is an urgent need to develop strategies to reduce hospitalizations and readmission rates for heart failure in general. There may be a shift in the paradigm with respect to the treatment of heart failure, which may usher in an era of invasive heart failure therapies and specialists. Experimental invasive devices and monitors have the potential to be game-changing therapies, and cardiac resynchronization therapy has evolved beyond just resynchronization and has the potential to provide important real-time hemodynamic feedback.