New surgical therapies for heart failure

Left ventricular assist device placement in the setting of congenital VSD

We describe the management of a 59-year-old female with an unrepaired congenital ventricular septal defect (VSD) and end stage nonischemic cardiomyopathy necessitating placement of a left ventricular assist device (LVAD) as a destination treatment. Simultaneous repair of the VSD was performed during the LVAD implantation under a beating heart. The patient remained hemodynamically stable throughout her postoperative course, without signs of hypoxia or cyanosis. Following discharge, outpatient surveillance echocardiogram demonstrated successful VSD closure and no residual shunt.

Hemodynamic effects of support modes of LVADs on the aortic valve

As the alternative treatment for heart failure, left ventricular assist devices (LVADs) have been widely applied to clinical practice. However, the effects of the support modes of LVADs on the biomechanical states of the aortic valve are still poorly understood. Hence, the present study investigates such effects and proposes a novel fluid-structure interaction (FSI) approach that combines the lattice Boltzmann method (LBM) and finite element (FE) method. Two support modes of LVADs, namely constant speed mode and constant flow mode, which have been widely applied to clinical practice, are also designed. Results demonstrate that the support modes of LVADs could significantly affect the biomechanical states of the aortic valve and the blood flow pattern of the ascending aorta. Compared with those in the constant flow mode, the leaflets in the constant speed mode could achieve better dynamic performance and lower stress during the systolic phase. The max radial displacement of the leaflets in the constant speed mode is at 8 mm, whereas that in the constant flow mode is at 0.8 mm. Furthermore, the outflow of LVADs directly impacts the aortic surfaces of the leaflets during the diastolic phase by increasing the level of wall shear stress of the leaflets. The leaflets in the constant speed mode receive less impact than those in the constant flow mode. The condition with such minimal impact is conducive to maintaining the normal structure of leaflets and benefits the reduction of the risk of valvular diseases. In sum, the support modes of LVADs exert a crucial effect on the biomechanical environment of the aortic valve. The constant speed mode is better than the constant flow mode in terms of providing a good hemodynamic environment for the aortic valve.

The Effects of Left Ventricular Assist Device Support Level on the Biomechanical States of Aortic Valve

Background

Although aortic valve disease caused by left ventricular assist device (LVAD) support has attracted more and more attention, the precise biomechanical effects of LVAD support level on the aortic valve are still unclear.

Material/Methods

A structural finite element models study was conducted using an ideal aortic valve geometric model. Four different study conditions were designed, according to the reduction of the open duration of the aortic valve. The isotropic hyperelastic constitutive equation was chosen to reflect the mechanical property of the leaflets. The distribution of the stress, strain, and transient dynamics of the leaflet were calculated.

Results

Along with the increase of LVAD support level, the open duration of the aortic valve was also reduced by the increase of LVAD support (low support level case 0.23 seconds versus middle support level case 0.2 seconds versus high support level case 0.14 seconds). Moreover, along with the increase of support mode of LVAD, the von Mises stress in most leaflet areas was increased from the low stress level (0–0.4 MPa) to the middle region (0.4–0.8 MPa). Once the leaflets were continuously closed, the high stress level (larger than 0.8 MPa) was observed. In contrast, the support level of LVAD only had slight effects on the distribution of von Mises strain. According to the aforementioned results, maintaining the open duration of aortic valve longer than 0.2 seconds could achieve better performance of biomechanical states of leaflets.

Conclusions

This study could provide useful information on the determination of optimal LVAD support strategy.

The hemodynamic effects of the LVAD outflow cannula location on the thrombi distribution in the aorta: A primary numerical study

Although a growing number of patients undergo LVAD implantation for heart failure treatment, thrombi are still the devastating complication for patients who used LVAD. LVAD outflow cannula location and thrombi generation sources were hypothesized to affect the thrombi distribution in the aorta. To test this hypothesis, numerical studies were conducted by using computational fluid dynamic (CFD) theory. Two anastomotic configurations, in which the LVAD outflow cannula is anastomosed to the anterior and lateral ascending aortic wall (named as anterior configurations and lateral configurations, respectively), are designed. The particles, whose sized are same as those of thrombi, are released at the LVAD output cannula and the aortic valve (named as thrombiP and thrombiL, respectively) to calculate the distribution of thrombi. The simulation results demonstrate that the thrombi distribution in the aorta is significantly affected by the LVAD outflow cannula location. In anterior configuration, the thrombi probability of entering into the three branches is 23.60%, while that in lateral configuration is 36.68%. Similarly, in anterior configuration, the thrombi probabilities of entering into brachiocephalic artery, left common carotid artery and left subclavian artery, is 8.51%, 9.64%, 5.45%, respectively, while that in lateral configuration it is 11.39%, 3.09%, 22.20% respectively. Moreover, the origins of thrombi could affect their distributions in the aorta. In anterior configuration, the thrombiP has a lower probability to enter into the three branches than thrombiL (12% vs. 25%). In contrast, in lateral configuration, the thrombiP has a higher probability to enter into the three branches than thrombiL (47% vs. 35%). In brief, the LVAD outflow cannula location significantly affects the distribution of thrombi in the aorta. Thus, in the clinical practice, the selection of outflow location of LVAD and the risk of thrombi formed in the left ventricle should be paid more attention than before.

Nanoparticle drug delivery systems and their use in cardiac tissue therapy

Cardiovascular diseases make up one of the main causes of death today, with myocardial infarction and ischemic heart disease contributing a large share of the deaths reported. With mainstream clinical therapy focusing on palliative medicine following myocardial infarction, the structural changes that occur in the diseased heart will eventually lead to end-stage heart failure. Heart transplantation remains the only gold standard of cure but a shortage in donor organs pose a major problem that led to clinicians and researchers looking into alternative strategies for cardiac repair. This review will examine some alternative methods of treatment using chemokines and drugs carried by nanoparticles as drug delivering agents for the purposes of treating myocardial infarction through the promotion of revascularization. We will also provide an overview of existing studies involving such nanoparticulate drug delivery systems, their reported efficacy and the challenges facing their translation into ubiquitous clinical use.

Initial United States experience with the Paracor HeartNet⁎⁎Paracor Medical, Inc, Sunnyvale, Calif. myocardial constraint device for heart failure

OBJECTIVE

This study was undertaken to review the initial results and surgical safety data for the US Food and Drug Administration safety and feasibility trial of the Paracor HeartNet (Paracor Medical, Inc, Sunnyvale, Calif.) myocardial constraint device.

METHODS

Patients with New York Heart Association functional class II or III heart failure underwent device implantation (n = 21) through a left minithoracotomy.

RESULTS

The average age was 53 years (31-72 years). There were 18 men and 3 women, and 17 patients had nonischemic etiology of heart failure. Mean heart failure duration was 8.3 years (1.4-18.8 years). Average ejection fraction was 22% (11%-33%), with an average left ventricular end-diastolic dimension of 74 mm (55-94 mm). Previous medical therapy included angiotensin-converting enzyme inhibitors, beta-blockers, diuretics, digoxin, and aldosterone receptor blockers. At implantation, 17 patients had implantable electronic devices: 1 biventricular pacemaker, 11 biventricular pacemakers with cardioverter-defibrillators, and 5 implantable cardioverter-defibrillators. Patient comorbidities included hypertension in 10 cases, diabetes mellitus in 8, myocardial infarction in 1, and ventricular tachycardia in 8. Mean operative time was 68 minutes (42-102 minutes), and implantation time averaged 15 minutes (5-51 minutes). The average time to ambulation was 1.6 days (1-4 days). The intensive care unit stay averaged 3.3 days (1-16 days), and hospital stay averaged 6.3 days (4-16 days). Atrial fibrillation occurred in 2 patients, and there were 2 in-hospital deaths.

CONCLUSIONS

The Paracor device can be implanted in patients with heart failure and reduced left ventricular function with a high degree of success. Significant surgical complications were infrequent. The initial US experience supports the conduct of a randomized, controlled, pivotal trial.

Design and features of the Acorn CorCap Cardiac Support Device: the concept of passive mechanical diastolic support

The Laplace equation points to the importance of ventricular wall stress as a factor in heart failure development and progression. Based on animal and clinical experience with active and passive cardiomyoplasty, a synthetic passive constraint was proposed as a means of reducing excessive wall stress, and thus assuaging disease progression. The Acorn CorCap CSD Cardiac Support Device was designed to provide passive diastolic support and serve as a constraint against chronic cardiac dilation in heart failure. Basic and uncomplicated in appearance, the device nevertheless incorporates numerous sophisticated structural and functional features intended maximize therapeutic value. The device is fabricated from medical grade multifilament polyester yarn, in a specific knit construction chosen to provide structural integrity, low physical profile, pliability for intimate contact with the epicardial surface, ease of manipulation during implantation, and anisotropic compliance characteristics to encourage beneficial reverse remodeling.

Tissue-engineered myocardial patch derived from extracellular matrix provides regional mechanical function

BACKGROUND

Extracellular matrix (ECM), a tissue-engineered scaffold, recently demonstrated cardiomyocyte population after myocardial implantation. Surgical restoration of myocardium frequently uses Dacron as a myocardial patch. We hypothesized that an ECM-derived myocardial patch would provide a mechanical benefit not seen with Dacron.

METHODS AND RESULTS

Using a canine model, a full thickness defect in the right ventricle was repaired with either Dacron or ECM. A third group had no surgery and determined baseline RV function. Eight weeks later, global systolic function was assessed by the preload recruitable stroke work relationship. Regional systolic function was measured by systolic area contraction (SAC), calculated by high density mechanical mapping. Tau was used to assess global diastolic function. Recoil rate and diastolic shear were used as measures of regional diastolic function. After functional data acquisition, tissue was fixed for histological evaluation. Global systolic and diastolic functions were similar at baseline and after ECM and Dacron implantation. Regional systolic function was greater in the ECM group compared with the Dacron group (SAC: 4.1+/-0.9% versus -1.8+/-1.1, P<0.05). Regional diastolic function was also greater in the ECM group (recoil rate (degrees sec(-1)): -44+/-7 versus -17+/-2, ECM versus Dacron; P<0.05). Immunohistochemical analysis revealed cardiomyocytes in the ECM implant region, a finding not seen with Dacron.

CONCLUSIONS

At 8 weeks, an ECM-derived tissue-engineered myocardial patch provides regional mechanical function, likely related to cardiomyocyte population. These results are in sharp contrast to Dacron, a commonly used myocardial patch.

Revascularization and ventricular restoration in patients with ischemic heart failure: the STICH trial

PURPOSE OF REVIEW

As techniques for the management of patients with ischemic heart failure have evolved, controversy has arisen with respect to the roles of revascularization and ventricular restoration procedures. This review addresses current thinking on the management of these patients and describes a prospective randomized trial that will have an impact on future treatment selection.

RECENT FINDINGS

Although the basis for improved survival with coronary artery bypass grafting lies in the viability of ischemic myocardium, nuclear medicine studies and stress echocardiography have failed to adequately select for tissues that are capable of recovery. Recent studies have suggested an additional benefit to combining ventricular restoration with bypass surgery. However, the role for these techniques has not been definitively established.

SUMMARY

The currently enrolling Surgical Treatment for Ischemic Heart Failure (STICH) trial promises to address these issues and thereby improve the management of patients with this disease.