Pathology in patients with ventricular assist devices

Cardiac mechanics and reverse remodelling under mechanical support from left ventricular assist devices

In recent years, development of mechanical circulatory support devices has proved to be a new treatment modality, in addition to standard pharmacological therapy, for patients with heart failure or acutely depressed cardiac function. These include left ventricular assist devices, which mechanically unload the heart when implanted. As a result, they profoundly affect the acute cardiac mechanics, which in turn, carry long-term consequences on myocardial function and structural function. Multiple studies have shown that, when implanted, mechanical circulatory assist devices lead to reverse remodelling, a process whereby the diseased myocardium reverts to a healthier-like state. Here, we start by first providing the reader with an overview of cardiac mechanics and important hemodynamic parameters. We then introduce left ventricular assist devices and describe their mode of operation as well as their impact on the hemodynamics. Changes in cardiac mechanics caused by device implantation are then extrapolated in time, and the long-term consequences on myocardial phenotype, as well as the physiological basis for these, is investigated.

Myocardial recovery following left ventricular assist device implantation

Durable left ventricular assist devices (LVADs) have consistently shown improved mortality and morbidity in patients with end-stage heart failure. Select patients with LVADs may experience significant enough myocardial recovery after device implantation to allow for explantation or decommissioning. While earlier trials suggested a high incidence of recovery, real-world clinical data have demonstrated this to be a much rarer phenomenon. Whether or not patients experience recovery, practices such as speed optimization and usage of guideline-directed medical therapy can improve patient outcomes.

Diagnostic Usefulness of Histological Examination of the Left Ventricular "Core" Excised to Insert a Left Ventricular Assist Device in Patients With Severe Heart Failure

The left ventricular assist device (LVAD) has proven to be beneficial for patients with severe heart failure poorly responsive to anti heart failure medicine. To examine both grossly and histologically the portion of left ventricular (LV) free wall excised ("the left ventricular core") to insert a LVAD in 337 patients with severe heart failure from a variety of causes. We collected together all photographs of LV "cores" and the histologic sections prepared from them and reexamined both. Despite the fact that these LV cores usually weighed >100 times the quantity of myocardium available to examine compared with that available by biotome inserted via a transvenous catheter, the number in which histologic study allowed an unequivocal diagnosis was limited. Examination of the clinical records usually was required to establish the definitive diagnosis. Although the presence of a scarred myocardial wall usually suggested ischemic cardiomyopathy (IC), the scarring may not have involved the LV apex resulting in a nonscarred portion of myocardium simulating idiopathic dilated cardiomyopathy (IDC). Moreover, about 10% of the patients with IDC have myocardial scars thus simulating IC. Involvement of the LV core by amyloid, sarcoid, myocarditis, and acute infarction, of course, allowed a specific anatomic diagnosis. Despite the presence of ample tissue to secure a definitive diagnosis, the combination of clinical input and morphologic assessment was required to arrive at a definite diagnosis in most patients.

Forensic Considerations in a Series of 14 Deaths of Patients with a Left Ventricular Assist Device

INTRODUCTION

To better understand the forensic implications of death with a left ventricular assist device (LVAD), we reviewed all deaths that were reported to a regional medical examiner jurisdiction involving patients who had an LVAD.

METHODS

Medical examiner case files between January 2012 and September 2018 were searched for "LVAD" and "left ventricular assist device" to identify deaths that were reported to the medical examiner involving a decedent who had an LVAD at the time of death.

RESULTS

During the study period, a total of 14 deaths were reported to the regional medical examiner involving decedents who had an implanted LVAD at the time of death. The average age at death was 64 years, with a range from 40 to 81 years. The underlying cardiac disease leading to LVAD implantation was ischemic heart disease (n = 9), nonischemic dilated cardiomyopathy (n = 4), and chemotherapy-related cardiotoxicity (n = 1). Of these 14 deaths, 2 deaths were due to loss of power to the LVAD, 1 death was due to traumatic subdural hemorrhage occurring in the setting of anticoagulation therapy required by LVAD implantation, and 1 death was due to femur fracture following a fall.

DISCUSSION

Medical examiners should be familiar with the potential complications of LVADs, especially those complications that may prompt consideration of non-natural manners of death. Medical examiners should also be aware of the tools and investigative strategies that may assist in the investigation of LVAD-related deaths.

Computational Analysis of Pumping Efficacy of a Left Ventricular Assist Device according to Cannulation Site in Heart Failure with Valvular Regurgitation

Mitral valve regurgitation (MR) causes blood to flow in two directions during contraction of the left ventricle (LV), that is, forward into the aorta and backward into the left atrium (LA). In aortic valve regurgitation (AR), leakage occurs from the aorta into the LV during diastole. Our objective is to analyze the contribution of a left ventricular assist device (LVAD) to MR and AR for the following two different cannulation sites: from the LA to the aorta (LAAO) and from the LV to the aorta (LVAO). Using a computational method, we simulated three ventricular conditions (normal [HF without valvular regurgitation], 5% MR, and 5% AR) in three groups (control [no LVAD], LAAO, and LVAO). The results showed that LVAD with LAAO cannulation is appropriate for recovery of the MR heart, and the LVAD with LVAO cannulation is appropriate for treating the AR heart.

Molecular basis of recovering on mechanical circulatory support

Our insights into different system levels of mechanisms by left ventricular assist device support are increasing and suggest a complex regulatory system of overlapping biological processes. To develop novel decision-making strategies and patient selection criteria, heart failure and reverse cardiac remodeling should be conceptualized and explored by a multifaceted research strategy of transcriptomics, metabolomics, proteomics, molecular biology, and bioinformatics. Knowledge of the molecular mechanisms of reverse cardiac remodeling is in its early stages, and comprehensive reconstruction of the underlying networks is necessary.

Molecular changes after left ventricular assist device support for heart failure

Heart failure is associated with remodeling that consists of adverse cellular, structural, and functional changes in the myocardium. Until recently, this was thought to be unidirectional, progressive, and irreversible. However, irreversibility has been shown to be incorrect because complete or partial reversal can occur that can be marked after myocardial unloading with a left ventricular assist device (LVAD). Patients with chronic advanced heart failure can show near-normalization of nearly all structural abnormalities of the myocardium or reverse remodeling after LVAD support. However, reverse remodeling does not always equate with clinical recovery. The molecular changes occurring after LVAD support are reviewed, both those demonstrated with LVAD unloading alone in patients bridged to transplantation and those occurring in the myocardium of patients who have recovered enough myocardial function to have the device removed. Reverse remodeling may be attributable to a reversal of the pathological mechanisms that occur in remodeling or the generation of new pathways. A reduction in cell size occurs after LVAD unloading, which does not necessarily correlate with improved cardiac function. However, some of the changes in both the cardiac myocyte and the matrix after LVAD support are specific to myocardial recovery. In the myocyte, increases in the cytoskeletal proteins and improvements in the Ca²⁺ handling pathway seem to be specifically associated with myocardial recovery. Changes in the matrix are complex, but excessive scarring appears to limit the ability for recovery, and the degree of fibrosis in the myocardium at the time of implantation may predict the ability to recover.

Disseminated malignancy after extracorporeal life support and left ventricular assist device, diagnosed by left ventricular apical core biopsy

The left ventricular apical core biopsy performed during implantation of a left ventricular assist device (VAD) is a well-known diagnostic procedure in confirming cardiomyopathies leading to end-stage heart failure. We describe a patient in whom disseminated malignancy was revealed by means of the apical core biopsy after extracorporeal life support and left ventricular assist device implantation as a bridge to transplantation. This case emphasizes the importance of thorough oncological screening before VAD implantation and the possible consequences of circulating tumour cells in this device-assisted circulation.

The future of adult cardiac assist devices: novel systems and mechanical circulatory support strategies

The recent, widespread success of mechanical circulatory support has prompted the development of numerous implantable devices to treat advanced heart failure. It is important to raise awareness of novel device systems, the mechanisms by which they function, and implications for patient management. This article discusses devices that are being developed or are in clinical trials. Devices are categorized as standard full support, less-invasive full support, partial support: rotary pumps, partial support: counterpulsation devices, right ventricular assist device, and total artificial heart. Implantation strategy, mechanism of action, durability, efficacy, hemocompatibility, and human factors are considered. The feasibility of novel strategies for unloading the failing heart is examined.

Theoretical estimation of cannulation methods for left ventricular assist device support as a bridge to recovery

Left ventricular assist device (LVAD) support under cannulation connected from the left atrium to the aorta (LA-AA) is used as a bridge to recovery in heart failure patients because it is non-invasive to ventricular muscle. However, it has serious problems, such as valve stenosis and blood thrombosis due to the low ejection fraction of the ventricle. We theoretically estimated the effect of the in-series cannulation, connected from ascending aorta to descending aorta (AA-DA), on ventricular unloading as an alternative to the LA-AA method. We developed a theoretical model of a LVAD-implanted cardiovascular system that included coronary circulation. Using this model, we compared hemodynamic responses according to various cannulation methods such as LA-AA, AA-DA, and a cannulation connected from the left ventricle to ascending aorta (LV-AA), under continuous and pulsatile LVAD supports. The AA-DA method provided 14% and 18% less left ventricular peak pressure than the LA-AA method under continuous and pulsatile LVAD conditions, respectively. The LA-AA method demonstrated higher coronary flow than AA-DA method. Therefore, the LA-AA method is more advantageous in increasing ventricular unloading whereas the AA-DA method is a better choice to increase coronary perfusion.

Incomplete recovery of myocyte contractile function despite improvement of myocardial architecture with left ventricular assist device support

BACKGROUND

Unloading a failing heart with a left ventricular assist device (LVAD) can improve ejection fraction (EF) and LV size; however, recovery with LVAD explantation is rare. We hypothesized that evaluation of myocyte contractility and biochemistry at the sarcomere level before and after LVAD may explain organ-level changes.

METHODS AND RESULTS

Paired LV tissue samples were frozen from 8 patients with nonischemic cardiomyopathy at LVAD implantation (before LVAD) and before cardiac transplantation (after LVAD). These were compared with 8 nonfailing hearts. Isolated skinned myocytes were purified and attached to a force transducer, and dimensions, maximum calcium-saturated force, calcium sensitivity, and myofilament cooperativity were assessed. Relative isoform abundance and phosphorylation levels of sarcomeric contractile proteins were measured. With LVAD support, the unloaded EF improved (10.0±1.0% to 25.6±11.0%, P=0.007), LV size decreased (LV internal dimension at end diastole, 7.6±1.2 to 4.9±1.4 cm; P<0.001), and myocyte dimensions decreased (cross-sectional area, 1247±346 to 638±254 μm(2); P=0.001). Maximum calcium-saturated force improved after LVAD (3.6±0.9 to 7.3±1.8 mN/mm(2), P<0.001) implantation but was still lower than in nonfailing hearts (7.3±1.8 versus 17.6±1.8 mN/mm(2), P<0.001). An increase in troponin I (TnI) phosphorylation after LVAD implantation was noted, but protein kinase C phosphorylation of TnI decreased. Biochemical changes of other sarcomeric proteins were not observed after LVAD.

CONCLUSIONS

There is significant improvement in LV and myocyte size with LVAD, but there is only partial recovery of EF and myocyte contractility. LVAD support was associated only with biochemical changes in TnI, suggesting that alternate mechanisms might contribute to contractile changes after LVAD and that additional interventions may be needed to alter biochemical remodeling of the sarcomere to further enhance myofilament and organ-level recovery.

Short-term in vivo preclinical biocompatibility evaluation of FW-II axial blood pump in a sheep model

We investigated the outcome of FW-II axial pump on healthy sheep (weight, 60-70 kg) for 2 weeks by perioperatively hematological and chemical tests, and circulating activated platelet and leukocyte-platelet aggregates measurements by flow cytometry assays. Complete necropsy and histopathological examinations and thorough pump inspection were performed at study termination for evidence of thrombi. In this experimental series, one sheep died of pulmonary edema, the other four sheep reached the scheduled endpoint of 14 days without device-related problems, and flow range was maintained at 2.5-4.0 L/min. The number of red blood cells and platelets decreased within first 3 days but increased gradually after the first postoperative week. In all animals, serum glutamic oxaloacetic transaminase increased significantly after surgery but gradually returned to normal limits within 2 weeks. Platelet activation, granulocyte-platelet aggregates, and monocyte-platelet aggregates reached the peak at postoperative day 2. Postexplant examinations indicated round thrombus in the hub areas of pumps. No evidence of ischemia or infarction was found in the explanted hearts, livers, spleens, kidneys, and brains of the five animals. Our results demonstrate that FW-II ventricular assist device (VAD) is a promising device for left ventricular (LV) support with moderate anticoagulation.

Aortic valve pathophysiology during left ventricular assist device support

The increased applicability and excellent results with left ventricular assist devices (LVADs) have revolutionized the available treatment options for patients with advanced heart failure. Pre-existing valve abnormalities are common in this population, and subsequent development of valve abnormalities after LVAD placement is also often noted. Although native mitral and tricuspid valve disease is more common in heart failure patients before LVAD placement, aortic valves are much more likely to generate abnormal pathophysiology in the LVAD patient during as well as after LVAD placement. The aim of this comprehensive review is to review aortic valve function in LVAD patients and highlight the consideration of pre-existing valve disease on patient treatment at the time of LVAD implant. The basis for structural changes leading to valve pathophysiology during and after LVAD placement will be described, providing a basis for improved clinical understanding and new strategies to prevent these conditions.

Histopathologic correlates of myocardial improvement in patients supported by a left ventricular assist device

BACKGROUND

Left ventricular assist devices unload the failing heart and improve hemodynamic function and tissue architecture. In some patients improvement allows for left ventricular assist device removal. We retrospectively compared histologic features in patients who were weaned off left ventricular assist device support with those who remained on support without evidence of clinical remission.

METHODS

We graded left ventricular core samples taken at implantation on a scale we designed for evaluating severity and extent of fibrosis and hypertrophy. We correlated the grades with a computerized semiquantitative analysis of picrosirius-red and Masson's trichrome-stained sections. We evaluated interstitial (10×), perivascular (20×), and replacement (4×) fibrosis. Hypertrophy was assessed by myocyte diameter, cytoplasmic area, and nuclear/cytoplasmic ratio.

RESULTS

All patients (N=17) underwent left ventricular assist device implantation for heart failure. In eight patients improvement allowed left ventricular assist device removal. The groups did not differ in age (24.1 vs. 25 years, P=.4) or mean time on left ventricular assist device support (506 vs. 414 days, P=.24). All mean measures showed significantly less hypertrophy in the left ventricular assist device-removal group than in the nonremoval group, respectively (cytoplasmic area, 58.00 vs. 77.18 μm(2), P=.021; myocyte diameter, 20.32 vs. 25.35 μm, P=.004; nuclear/cytoplasmic ratio, 11.04 vs. 8.69, P=.053). Although not statistically significant, the left ventricular assist device-removal group tended toward less overall fibrosis than the nonremoval group (11.57 vs. 13.24, P=.214).

CONCLUSIONS

Left ventricular assist device-removal patients had less hypertrophy and fibrosis overall than did nonremoval patients. These findings may help identify patients with a higher probability of left ventricular assist device removal and myocardial recovery.

Impact of left ventricular assist device (LVAD) support on the cardiac reverse remodeling process

With improved technology and expanding indications for use, left ventricular assist devices (LVADs) are assuming a greater role in the care of patients with end-stage heart failure. Following LVAD implantation with the intention of bridge to transplant, it became evident that some patients exhibit substantial recovery of ventricular function. This prompted explantation of some devices in lieu of transplantation, the so-called bridge-to-recovery (BTR) therapy. However, clinical outcomes following these experiences are not always successful. Patients treated in this fashion have often progressed rapidly back to heart failure. Special knowledge has emerged from studies of hearts supported by LVADs that provides insights into the basic mechanisms of ventricular remodeling and possible limits of ventricular recovery. In general, it was these studies that spawned the concept of reverse remodeling now recognized as an important goal of many heart failure treatments. Important examples of myocardial and/or ventricular properties that do not regress towards normal during LVAD support include abnormal extracellular matrix metabolism, increased tissue angiotensin levels, myocardial stiffening and partial recovery of gene expression involved with metabolism. Nevertheless, studies of LVAD-heart interactions have led to the understanding that although we once considered the end-stage failing heart of patients near death to be irreversibly diseased, an unprecedented degree of myocardial recovery is possible, when given sufficient mechanical unloading and restoration of more normal neurohormonal milieu. Evidence supporting and unsupporting the notion of reverse remodeling and clinical implications of this process will be reviewed.

Perioperative echocardiographic examination for ventricular assist device implantation

Ventricular assist devices (VADs) are systems for mechanical circulatory support of the patient with severe heart failure. Perioperative transesophageal echocardiography is a major component of patient management, and important for surgical and anesthetic decision making. In this review we present the rationale and available data for a comprehensive echocardiographic assessment of patients receiving a VAD. In addition to the standard examination, device-specific pre-, intra-, and postoperative considerations are essential to the echocardiographic evaluation. These include: (a) the pre-VAD insertion examination of the heart and large vessels to exclude significant aortic regurgitation, tricuspid regurgitation, mitral stenosis, patent foramen ovale, or other cardiac abnormality that could lead to right-to-left shunt after left VAD placement, intracardiac thrombi, ventricular scars, pulmonic regurgitation, pulmonary hypertension, pulmonary embolism, and atherosclerotic disease in the ascending aorta; and to assess right ventricular function; and (b) the post-VAD insertion examination of the device and reassessment of the heart and large vessels. The examination of the device aims to confirm completeness of device and heart deairing, cannulas alignment and patency, and competency of device valves using two-dimensional, and color, continuous and pulsed wave Doppler modalities. The goal for the heart examination after implantation should be to exclude aortic regurgitation, or an uncovered right-to-left shunt; and to assess right ventricular function, left ventricular unloading, and the effect of device settings on global heart function. The variety of VAD models with different basic and operation principles requires specific echocardiographic assessment targeted to the characteristics of the implanted device.

Autopsy findings in patients on postcardiotomy extracorporeal membrane oxygenation (ECMO)

OBJECTIVES

To assess the clinical sensitivity of causes of death, concomitant diseases and postoperative complications including thromboembolic events in ECMO patients.

METHODS

Between January 2000 and December 2004 154/202 patients (76.2%) died after postcardiotomy ECMO circulatory support. Autopsy was performed in 78 (50.6%) consecutive patients. Clinical and post-mortem data were prospectively recorded and compared concerning causes of death and postoperative complications including venous and arterial thromboembolisms and significant comorbidities.

RESULTS

Mean age was 62.1+/-11.3 years, ejection fraction was 43.4+/-17.3%. 39.7% were emergency operations including acute coronary syndrome in 25.6% and preoperative cardiogenic shock in 28.2%. Successful ECMO weaning rate was 43.6%. Mean postoperative survival was 11.3 days. Premortem unknown concomitant diseases were found in 63 patients (80.8%) with clinical relevance in 9 patients (11.5%). Clinically unrecognized postoperative complications were found in 59 patients (75.6%) including acute cerebral infarction (n=7), acute bowel ischemia (1), intestinal perforation (3), pneumonia (4), venous thrombus formation (25) and systemic thromboembolic events (24). Clinically based causes of death were cardiac in 62.8%, multi-organ failure in 10.3%, cerebral in 5.1%, respiratory in 10.3%, fatal pulmonary embolism in 2.6%, technical in 5.1%, and others in 3.8%. Unexpected causes of death were found by autopsy in 22 patients (28.2%) including myocardial infarction (n=5), acute heart failure (4), fatal pulmonary embolism (2), pneumonia (2), ARDS (1), lung bleeding (1), fatal cerebrovascular event (4) and multiorgan failure (3).

CONCLUSIONS

In ECMO patients major discrepancies between clinical and post-mortem examination were found. The true incidence of thromboembolic events is highly underestimated by clinical evaluation.