Effect of a Flexible Ventricular Restraint Device on Cardiac Remodeling after Acute Myocardial Infarction

Next-Generation Cardiac Interfacing Technologies Using Nanomaterial-Based Soft Bioelectronics

Cardiac interfacing devices are essential components for the management of cardiovascular diseases, particularly in terms of electrophysiological monitoring and implementation of therapies. However, conventional cardiac devices are typically composed of rigid and bulky materials and thus pose significant challenges for effective long-term interfacing with the curvilinear surface of a dynamically beating heart. In this regard, the recent development of intrinsically soft bioelectronic devices using nanocomposites, which are fabricated by blending conductive nanofillers in polymeric and elastomeric matrices, has shown great promise. The intrinsically soft bioelectronics not only endure the dynamic beating motion of the heart and maintain stable performance but also enable conformal, reliable, and large-area interfacing with the target cardiac tissue, allowing for high-quality electrophysiological mapping, feedback electrical stimulations, and even mechanical assistance. Here, we explore next-generation cardiac interfacing strategies based on soft bioelectronic devices that utilize elastic conductive nanocomposites. We first discuss the conventional cardiac devices used to manage cardiovascular diseases and explain their undesired limitations. Then, we introduce intrinsically soft polymeric materials and mechanical restraint devices utilizing soft polymeric materials. After the discussion of the fabrication and functionalization of conductive nanomaterials, the introduction of intrinsically soft bioelectronics using nanocomposites and their application to cardiac monitoring and feedback therapy follow. Finally, comments on the future prospects of soft bioelectronics for cardiac interfacing technologies are discussed.

Cardioprotective effect of silicon-built restraint device (ASD), for left ventricular remodeling in rat heart failure model

This study aims to evaluate the feasibility and cardio-protective effects of biocompatible silicon-built restraint device (ASD) in the rat's heart failure (HF) model. The performance and compliance characteristics of the ASD device were assessed in vitro by adopting a pneumatic drive and ball burst test. Sprague-Dawley (SD) rats were divided into four groups (n = 6); control, HF, HF + CSD, and HF + ASD groups, respectively. Heart failure was developed by left anterior descending (LAD) coronary artery ligation in all groups except the control group. The ASD and CSD devices were implanted in the heart of HF + ASD and HF + CSD groups, respectively. The ASD's functional and expansion ability was found to be safe and suitable for attenuating ventricular remodeling. ASD-treated rats showed normal heart rhythm, demonstrated by smooth -ST and asymmetrical T-wave. At the same time, hemodynamic parameters of the HF + ASD group improved systolic and diastolic functions, reducing ventricular wall stress, which indicated reverse remodeling. The BNP values were reduced in the HF + ASD group, which confirmed ASD feasibility and reversed remodeling at a molecular level. Furthermore, the HF + ASD group with no fibrosis suggests that ASD has significant curative effects on the heart muscles. In conclusion, ASD was found to be a promising restraint therapy than the previously standard restraint therapies. Stepwise ASD fabrication process (a) 3D computer model of ASD was generated by using Rhinoceros 5.0 software (b) 3D blue wax model of ASD (c) Silicon was prepared by mixing the solutions (as per manufacturer instruction) (d) Blue wax model of ASD was immersed into liquid Silicon (e) ASD model was put into the oven for 3 hours at 50 °C. (f) Blue wax started melting from the ASD model (g) ASD model was built from pure silicon (h) Two access lines were linked to the ASD device, which was connected with an implantable catheter (Port-a-cath), scale bar 100 µm. (Nikon Ldx 2.0).

Optimizing Epicardial Restraint and Reinforcement Following Myocardial Infarction: Moving Towards Localized, Biomimetic, and Multitherapeutic Options

The mechanical reinforcement of the ventricular wall after a myocardial infarction has been shown to modulate and attenuate negative remodeling that can lead to heart failure. Strategies include wraps, meshes, cardiac patches, or fluid-filled bladders. Here, we review the literature describing these strategies in the two broad categories of global restraint and local reinforcement. We further subdivide the global restraint category into biventricular and univentricular support. We discuss efforts to optimize devices in each of these categories, particularly in the last five years. These include adding functionality, biomimicry, and adjustability. We also discuss computational models of these strategies, and how they can be used to predict the reduction of stresses in the heart muscle wall. We discuss the range of timing of intervention that has been reported. Finally, we give a perspective on how novel fabrication technologies, imaging techniques, and computational models could potentially enhance these therapeutic strategies.

Cardio-supportive devices (VRD & DCC device) and patches for advanced heart failure: A review, summary of state of the art and future directions

Congestive heart failure (CHF) is a complicated pathophysiological syndrome, leading cause of hospitalization as well as mortalities in developed countries wherein an irregular function of the heart leads to the insufficient blood supply to the body organs. It is an accumulative slackening of various complications including myocardial infarction (MI), coronary heart disease (CAD), hypertension, valvular heart disease (VHD) and cardiomyopathy; its hallmarks include hypertrophy, increased interstitial fibrosis and loss of myocytes. The etiology of CHF is very complex and despite the rapid advancement in pharmacological and device-based interventional therapies still, a single therapy may not be sufficient to meet the demand for coping with the diseases. Total artificial hearts (TAH) and ventricular assist devices (VADs) have been widely used clinically to assist patients with severe HF. Unfortunately, direct contact between the patient's blood and device leads to thromboembolic events, and then coagulatory factors, as well as, infection contribute significantly to complicate the situation. There is no effective treatment of HF except cardiac transplantation, however, genetic variations, tissue mismatch; differences in certain immune response and socioeconomic crisis are an important concern with cardiac transplantation suggesting an alternate bridge to transplant (BTT) or destination therapies (DT). For these reasons, researchers have turned to mechanically driven compression devices, ventricular restraint devices (VRD) and heart patches. The ASD is a combination of all operational patches and cardiac support devices (CSD) by delivering biological agents and can restrain or compress the heart. Present study summarizes the accessible peer-reviewed literature focusing on the mechanism of Direct Cardiac Compression (DCC) devices, VRD and patches and their acquaintance to optimize the therapeutic efficacy in a synergistic way.

The promising future of ventricular restraint therapy for the management of end-stage heart failure

Complicated pathophysiological syndrome associated with irregular functioning of the heart leading to insufficient blood supply to the organs is linked to congestive heart failure (CHF) which is the leading cause of death in developed countries. Numerous factors can add to heart failure (HF) pathogenesis, including myocardial infarction (MI), genetic factors, coronary artery disease (CAD), ischemia or hypertension. Presently, most of the therapies against CHF cause modest symptom relief but incapable of giving significant recovery for long-term survival outcomes. Unfortunately, there is no effective treatment of HF except cardiac transplantation but genetic variations, tissue mismatch, differences in certain immune response and socioeconomic crisis are some major concern with cardiac transplantation, suggested an alternate bridge to transplant (BTT) or destination therapies (DT). Ventricular restraint therapy (VRT) is a promising, non-transplant surgical treatment wherein the overall goal is to wrap the dilated heart with prosthetic material to mechanically restrain the heart at end-diastole, stop extra remodeling, and thereby ultimately improve patient symptoms, ventricular function and survival. Ventricular restraint devices (VRDs) are developed to treat end-stage HF and BTT, including the CorCap cardiac support device (CSD) (CSD; Acorn Cardiovascular Inc, St Paul, Minn), Paracor HeartNet (Paracor Medical, Sunnyvale, Calif), QVR (Polyzen Inc, Apex, NC) and ASD (ASD, X. Zhou). An overview of 4 restraint devices, with their precise advantages and disadvantages, will be presented. The accessible peer-reviewed literature summarized with an important considerations on the mechanism of restraint therapy and how this acquaintance can be accustomed to optimize and improve its effectiveness.

Exo-organoplasty interventions: A brief review of past, present and future directions for advance heart failure management

Heart failure (HF) is a debilitating disease in which abnormal function of the heart leads to imbalance of blood demand to tissues and organs. The pathogenesis of HF is very complex and various factors can contribute including myocardial infarction, ischemia, hypertension and genetic cardiomyopathies. HF is the leading cause of death and its prevalence is expected to increase in parallel with the population age. Different kind of therapeutic approaches including lifestyle modification, medication and pacemakers are used for HF patients in NYHA I-III functional class. However, for advance stage HF patient's (NYHA IV), ventricle assist devices are clinically use and stem cells are under active investigation. Most of these therapies leads to modest symptoms relief and have no significant role in long-term survival rate. Currently there is no effective treatment for advance HF except heart transplantation, which is still remain clinically insignificant because of donor pool limitation. As HF is a result of multiple etiologies therefore multi-functional therapeutic platform is needed. Exo-organoplasty interventions are studied from almost one century. The major goals of these interventions are to treat various kind of heart disease from outside the heart muscle without having direct contact with blood. Various kind of interventions (devices and techniques) are developed in this arena with the passage of time. The purpose of this review is to describe the theory behind intervention devices, the devices themselves, their clinical results, advantages and limitations. Furthermore, to present a future multi-functional therapeutic platform (ASD) for advance stage HF management.

Physiological Implications of Myocardial Scar Structure

Once myocardium dies during a heart attack, it is replaced by scar tissue over the course of several weeks. The size, location, composition, structure, and mechanical properties of the healing scar are all critical determinants of the fate of patients who survive the initial infarction. While the central importance of scar structure in determining pump function and remodeling has long been recognized, it has proven remarkably difficult to design therapies that improve heart function or limit remodeling by modifying scar structure. Many exciting new therapies are under development, but predicting their long-term effects requires a detailed understanding of how infarct scar forms, how its properties impact left ventricular function and remodeling, and how changes in scar structure and properties feed back to affect not only heart mechanics but also electrical conduction, reflex hemodynamic compensations, and the ongoing process of scar formation itself. In this article, we outline the scar formation process following a myocardial infarction, discuss interpretation of standard measures of heart function in the setting of a healing infarct, then present implications of infarct scar geometry and structure for both mechanical and electrical function of the heart and summarize experiences to date with therapeutic interventions that aim to modify scar geometry and structure. One important conclusion that emerges from the studies reviewed here is that computational modeling is an essential tool for integrating the wealth of information required to understand this complex system and predict the impact of novel therapies on scar healing, heart function, and remodeling following myocardial infarction.

Injectable microsphere gel progressively improves global ventricular function, regional contractile strain, and mitral regurgitation after myocardial infarction

BACKGROUND

There is continued need for therapies which reverse or abate the remodeling process after myocardial infarction (MI). In this study, we evaluate the longitudinal effects of calcium hydroxyapatite microsphere gel on regional strain, global ventricular function, and mitral regurgitation (MR) in a porcine MI model.

METHODS

Twenty-five Yorkshire swine were enrolled. Five were dedicated weight-matched controls. Twenty underwent posterolateral infarction by direct ligation of the circumflex artery and its branches. Infarcted animals were randomly divided into the following 4 groups: 1-week treatment; 1-week control; 4-week treatment; and 4-week control. After infarction, animals received either twenty 150 μL calcium hydroxyapatite gel or saline injections within the infarct. At their respective time points, echocardiograms, cardiac magnetic resonance imaging, and tissue were collected for evaluation of MR, regional and global left ventricular function, wall thickness, and collagen content.

RESULTS

Global and regional left ventricular functions were depressed in all infarcted subjects at 1 week compared with healthy controls. By 4-weeks post-infarction, global function had significantly improved in the calcium hydroxyapatite group compared with infarcted controls (ejection fraction 0.485 ± 0.019 vs 0.38 ± 0.017, p < 0.01). Similarly, regional borderzone radial contractile strain (16.3% ± 1.5% vs 11.2% ± 1.5%, p = 0.04), MR grade (0.4 ± 0.2 vs 1.2 ± 0.2, p = 0.04), and infarct thickness (7.8 ± 0.5 mm vs 4.5 ± 0.2 mm, p < 0.01) were improved at this time point in the treatment group compared with infarct controls.

CONCLUSIONS

Calcium hydroxyapatite injection after MI progressively improves global left ventricular function, borderzone function, and mitral regurgitation. Using novel biomaterials to augment infarct material properties is a viable alternative in the current management of heart failure.

Engineering the heart: evaluation of conductive nanomaterials for improving implant integration and cardiac function

Recently, carbon nanotubes together with other types of conductive materials have been used to enhance the viability and function of cardiomyocytes in vitro. Here we demonstrated a paradigm to construct ECTs for cardiac repair using conductive nanomaterials. Single walled carbon nanotubes (SWNTs) were incorporated into gelatin hydrogel scaffolds to construct three-dimensional ECTs. We found that SWNTs could provide cellular microenvironment in vitro favorable for cardiac contraction and the expression of electrochemical associated proteins. Upon implantation into the infarct hearts in rats, ECTs structurally integrated with the host myocardium, with different types of cells observed to mutually invade into implants and host tissues. The functional measurements showed that SWNTs were essential to improve the performance of ECTs in inhibiting pathological deterioration of myocardium. This work suggested that conductive nanomaterials hold therapeutic potential in engineering cardiac tissues to repair myocardial infarction.

Diastolic ventricular support with cardiac support devices: an alternative approach to prevent adverse ventricular remodeling

Heart failure is a global epidemic with limited therapy. Abnormal left ventricular wall stress in the diseased myocardium results in a biochemical positive feedback loop that results in global ventricular remodeling and further deterioration of myocardial function. Mechanical myocardial restraints such as the Acorn CorCap and Paracor HeartNet ventricular restraints have attempted to minimize diastolic ventricular wall stress and limit adverse ventricular remodeling. Unfortunately, these therapies have not yielded viable clinical therapies for heart failure. Cellular and novel biopolymer-based therapies aimed at stabilizing pathologic myocardium hold promise for translation to clinical therapy in the future.

Biomaterials for the treatment of myocardial infarction: a 5-year update

The first review on biomaterials for the treatment of myocardial infarction (MI) was written in 2006. In the last 5 years, the general approaches for biomaterial treatment of MI and subsequent left ventricular remodeling remain the same, namely, left ventricular restraints, epicardial patches, and injectable therapies. Nonetheless, there have been significant developments in this field, including advancement of biomaterial therapies to large animal pre-clinical studies and, more recently, to clinical trials. This review focuses on the progress made in the field of cardiac biomaterial treatments for MI over the last 5 years.

Hemodynamics and myocardial blood flow patterns after placement of a cardiac passive restraint device in a model of dilated cardiomyopathy

BACKGROUND

The present study examined a cardiac passive restraint device which applies epicardial pressure (HeartNet Implant; Paracor Medical, Inc, Sunnyvale, Calif) in a clinically relevant model of dilated cardiomyopathy to determine effects on hemodynamic and myocardial blood flow patterns.

METHODS

Dilated cardiomyopatht was established in 10 pigs (3 weeks of atrial pacing, 240 beats/min). Hemodynamic parameters and regional left ventricular blood flow were measured under baseline conditions and after acute placement of the HeartNet Implant. Measurements were repeated after adenosine infusion, allowing maximal coronary vasodilation and coronary flow reserve to be determined.

RESULTS

Left ventricular dilation and systolic dysfunction occurred relative to baseline as measured by echocardiography. Left ventricular end-diastolic dimension increased and left ventricular fractional shortening decreased (3.8 ± 0.1 vs 6.1 ± 0.2 cm and 31.6% ± 0.5% vs 16.2% ± 2.1%, both P < .05, respectively), consistent with the dilated cardiomyopathy phenotype. The HeartNet Implant was successfully deployed without arrhythmias and a computed median mid-left ventricular epicardial pressure of 1.4 mm Hg was applied by the HeartNet Implant throughout the cardiac cycle. Acute HeartNet placement did not adversely affect steady state hemodynamics. With the HeartNet Implant in place, coronary reserve was significantly blunted.

CONCLUSIONS

In a large animal model of dilated cardiomyopathy, the cardiac passive restraint device did not appear to adversely affect basal resting myocardial blood flow. However, after acute HeartNet Implant placement, left ventricular maximal coronary reserve was blunted. These unique results suggest that cardiac passive restraint devices that apply epicardial transmural pressure can alter myocardial blood flow patterns in a model of dilated cardiomyopathy. Whether this blunting of coronary reserve holds clinical relevance with chronic passive restraint device placement remains unestablished.

Pathophysiology of myocardial injury and remodeling: implications for molecular imaging

Despite advances in reperfusion therapy, acute coronary syndromes can still result in myocardial injury and subsequent myocardial infarction (MI). Molecular, cellular, and interstitial events antecedent to the acute MI culminate in deleterious changes in the size, shape, and function of the left ventricle (LV), collectively termed LV remodeling. Three distinct anatomic and physiologic LV regions can be described after MI: the infarct, border zone, and remote regions. Given the complexity of post-MI remodeling, imaging modalities must be equally diverse to elucidate this process. The focus of this review will first be on cardiovascular MRI of the anatomic and pathophysiologic LV regions of greatest interest with regard to the natural history of the post-MI remodeling process. This review will then examine imaging modalities that provide translational and molecular insight into burgeoning treatment fields for the attenuation of post-MI remodeling, such as cardiac restraint devices and stem cell therapy.