State of the art of mechanical circulatory support

In vivo Hemodynamic Evaluation of an Implantable Left Ventricular Assist Device in a Long-term Anti-coagulation Regimen

Left ventricular assist devices (LVADs) are used to treat patients with severe (New York Heart Association class IV) heart failure. Thrombosis and bleeding are severe LVAD-related complications; thus, an effective anticoagulation regimen is crucial for successful postoperative management. The CH-VAD™ (CH Biomedical, Inc.) is a small, implantable, full-support (>5 L/min) LVAD with a centrifugal flow pump that has a fully magnetically levitated rotor, which confers superior hemocompatibility. In this study, the CH-VAD™ was implanted in two calves to evaluate its hemocompatibility and to establish an anticoagulation regimen for future GLP (good laboratory practice) studies. Heparin infusion was used during the surgery, and during postoperative management, the proper dosage of warfarin was given orally to maintain an international normalized ratio (INR) between 2.0 and 3.0. Pump performance, animal condition, and hematology results were recorded throughout the study (approximately 60 days). The results show that under the established anticoagulation regimen, the CH-VAD™ was well tolerated in the bovine model, with no significant thrombus or thromboembolic lesion formation in distal end organs. Low plasma free hemoglobin levels suggest that the device did not cause hemolysis. These results and the experience gained pave the way for future GLP studies.

Numerical and Experimental Approach to Characterize a BLDC Motor with Different Radial-gap to Improve Hemocompatibility Performance

Left ventricular assist devices (LVADs) have increasingly been used clinically to treat heart failure patients. However, hemolysis, pump thrombosis, infection and bleeding still persist as major limitations of LVAD technology. Assessing LVAD hemocompatibility using a blood shear stress device (BSSD) has clear advantages, as the BSSD could provide a better experimental platform to develop reliable, quantifiable blood trauma assays to perform iterative testing of LVAD designs. In this study, a BSSD was proposed with short blood exposure time and no seals or contact bearings to reduce blood trauma caused by the test platform. Enlarged air-gap drive motor in BSSD is essential to avoid high shear stress; however, it would significantly reduce the motor torque, which may result in inadequate force to drive the entire system. In order to evaluate and optimize the drive motor air-gap to ensure adequate motor torque as well as acceptable range for blood exposure time and shear stress, a numerical brushless DC (BLDC) motor model was established using finite element method (FEM) in numerical simulation software COMSOL. The model was first validated by the experimental results. Then numerical model with different air-gap was evaluated on the torque and speed constant changes. In the end, two equations were generated based on the curves derived from the torque and speed constant calculations. Determining these relationships between motor performance and motor air-gap will facilitate the development of an appropriate BLDC motor size for the BSSD, considering the design limitations in our future work.

Pulsatile arterial blood pressure mimicking aortic valve opening during continuous-flow LVAD support: a case report

BACKGROUND

Left ventricular assist devices (LVAD) have become a common treatment option in advanced heart failure. Lack of aortic valve opening during left ventricular unloading is a common complication and associated with a worse outcome. Maintaining a minimum pulse pressure is an important goal during the early postoperative period after LVAD implantation since it is commonly seen as secure sign of aortic valve opening.

AIMS/OBJECTIVE

We report a case of an LVAD-supported patient with early permanent closure of the aortic valve despite a pulse pressure > 15 mmHg at all times following LVAD implantation. We demonstrate how careful assessment of the invasive arterial blood pressure curve can indicate aortic valve closure irrespective of pulsatile blood flow.

METHOD

A 69-year old male patient with terminal ischemic cardiomyopathy was referred for long-term mechanical circulatory support. Due to mild aortic regurgitation both an aortic bioprosthesis and a continuous-flow left ventricular assist device were implanted. Postoperative echocardiography documented a patent aortic bioprosthesis and an acceptable residual systolic left ventricular contractility. During invasive arterial blood pressure monitoring repetitive transient slight blood pressure decreases followed by slight blood pressure increases coincided with programmed LVAD flushing cycles. Permanent pulsatile flow with a pulse pressure of ≥15 mmHg conveyed systolic opening of the aortic valve. Echocardiography, however, proved early permanent aortic valve closure. In retrospect, transformation of the automated LVAD flushing cycles into visible changes of the arterial blood pressure curve during invasive blood pressure monitoring is indicative of ejection of the complete cardiac output through LVAD itself, and therefore an early clinical sign of aortic valve closure.

DISCUSSION/CONCLUSION

We present this interesting didactic case to highlight caveats during the early postoperative period after LVAD implantation. Moreover, this case demonstrates that careful and differentiated observation of the arterial blood pressure waveform provides crucial information in this unique and growing patient population of continuous-flow LVAD support.

Clinical implications of LDH isoenzymes in hemolysis and continuous-flow left ventricular assist device-induced thrombosis

Pump-induced thrombosis continues to be a major complication of continuous-flow left ventricular assist devices (CF-LVADs), which increases the risks of thromboembolic stroke, peripheral thromboembolism, reduced pump flow, pump failure, cardiogenic shock, and death. This is confounded by the fact that there is currently no direct measure for a proper diagnosis during pump support. Given the severity of this complication and its required treatment, the ability to accurately differentiate CF-LVAD pump thrombosis from other complications is vital. Hemolysis measured by elevated lactate dehydrogenase (LDH) enzyme levels, when there is clinical suspicion of pump-induced thrombosis, is currently accepted as an important metric used by clinicians for diagnosis; however, LDH is a relatively nonspecific finding. LDH exists as five isoenzymes in the body, each with a unique tissue distribution. CF-LVAD pump thrombosis has been associated with elevated serum LDH-1 and LDH-2, as well as decreased LDH-4 and LDH-5. Herein, we review the various isoenzymes of LDH and their utility in differentiating hemolysis seen in CF-LVAD pump thrombosis from other physiologic and pathologic conditions as reported in the literature.

In Vivo Feasibility Study of an Intra-Atrial Blood Pump for Partial Support of the Left Ventricle

We are designing an intra-atrial pump (IAP) that will be affixed to the atrial septum and support the compromised left ventricle (LV) in patients with early-stage heart failure without harming the ventricular tissue. It will operate in parallel with the LV, drawing blood from the left atrium and unloading the LV. In previous hydraulic and hemodynamic studies, different blade geometries were tested for the IAP, and the hemodynamic results obtained using a mock circulatory loop showed that the IAP can successfully reduce end-diastolic volume and increase the total systemic flow rate. In the current study, we used a bovine model to validate the in vitro hemodynamic results and better understand how the IAP interacts with the cardiovascular system in vivo. Because this was the first study assessing the complete device in a living system, it was also necessary to determine the best manufacturing techniques and ideal sensor placements. In the bovine model, we were able to successfully implant the IAP across the atrial septum with the outflow graft connected to a peripheral artery. The implanted IAP was capable of providing partial support (1-3 L/min) in vivo. These results indicate that atrial cannulation is feasible and creates a beneficial hemodynamic environment.

In Vivo Hemodynamic Evaluation of CH-VAD in a Bovine Model for 14 Days

The CH-VAD is a centrifugal-flow magnetically levitated (maglev) left ventricular assist device (LVAD) used to treat end-stage heart failure. It is implanted in the chest cavity; the inflow cannula is inserted into the apex of the left ventricle, and the outflow graft is anastomosed to the aorta. Among several key VAD system improvements, the CH-VAD has a smaller body size than other LVADs and its maglev system offers a large-gap design that makes it superior in terms of hemocompatibility. In this study, we implanted the CH-VAD in a calf and evaluated the hemodynamic and hemocompatibility characteristics over a 14-day period. The hemodynamic parameters, the pump data, and blood test results were recorded throughout the study. The results showed that the CH-VAD provided hemodynamic stability. Hemocompatibility testing indicated negligible hemolysis throughout the study, and no signs of infection were seen. On necropsy, the results showed only expected focal mild-to-moderate adhesions between the pericardial sac (along the pump) and the adjacent rib cage, and between the pericardial sac and the heart. Gross examination of internal organs was unremarkable. Examination of the CH-VAD after explantation revealed no evidence of thrombus formation internally or around the inflow or outflow cannulas.

Design Method Using Statistical Models for Miniature Left Ventricular Assist Device Hydraulics

Left ventricular assist devices (LVADs) are increasingly used to treat heart failure patients. These devices' impeller blades and diffuser vanes must be designed for hydraulic performance and hemocompatibility. The traditional design method, applying mean-line theory, is not applicable to the design of small-scale pumps such as miniature LVADs. Furthermore, iterative experimental testing to determine how each geometric variable affects hydraulic performance is time and labor intensive. In this study, we tested a design method wherein empirical hydraulic results are used to establish a statistical model to predict pump hydraulic performance. This method was used to design an intra-atrial blood pump. Five geometric variables were chosen, and each was assigned two values to define the variable space. The experimental results were then analyzed with both correlation analysis and linear regression modeling. To validate the linear regression models, 2 test pumps were designed: mean value of each geometric variable within the boundaries, and random value of each geometric variable within the boundaries. The statistical model accurately predicted the hydraulic performance of both pump designs within the boundary space. This method could be expanded to include more geometric variables and broader boundary conditions, thus accelerating the design process for miniature LVADs.

Rotary mechanical circulatory support systems

A detailed survey of the current trends and recent advances in rotary mechanical circulatory support systems is presented in this paper. Rather than clinical reports, the focus is on technological aspects of these rehabilitating devices as a reference for engineers and biomedical researchers. Existing trends in flow regimes, flow control, and bearing mechanisms are summarized. System specifications and applications of the most prominent continuous-flow ventricular assistive devices are provided. Based on the flow regime, pumps are categorized as axial flow, centrifugal flow, and mixed flow. Unique characteristics of each system are unveiled through an examination of the structure, bearing mechanism, impeller design, flow rate, and biocompatibility. A discussion on the current limitations is provided to invite more studies and further improvements.

The future of mechanical circulatory support for advanced heart failure

PURPOSE OF REVIEW

Mechanical circulatory support (MCS) has become the main focus of heart replacement therapy for end stage heart failure patients. Advances in technology are moving towards miniaturization, biventricular support devices, complete internalization, improved hemocompatibility profiles, and responsiveness to cardiac loading conditions. This review will discuss the recent advances and investigational devices in MCS for advanced heart failure.

RECENT FINDINGS

The demand for both short-term and long-term durable devices for advanced heart failure is increasing. The current devices are still fraught with an unacceptably high incidence of gastrointestinal bleeding and thromboembolic and infectious complications. New devices are on the horizon focusing on miniaturization, versatility for biventricular support, improved hemocompatibility, use of alternate energy sources, and incorporation of continuous hemodynamic monitoring.

SUMMARY

The role for MCS in advanced heart replacement therapy is steadily increasing. With the advent of newer generation devices on the horizon, the potential exists for MCS to surpass heart transplantation as the primary therapy for advanced heart failure.

Osteopathic treatment in a patient with left-ventricular assist device with left brachialgia: a case report

This study deals with an osteopathic approach used for a patient with left-ventricular assist device (L-VAD) affected by left brachialgia. Clinical examination revealed the presence of thoracic outlet syndrome and pectoralis minor syndrome, with compression of the left proximal ulnar nerve, related to the surgical sternotomy performed. The osteopathic techniques used can be classified as indirect and direct, addressed to the pectoralis minor and the first left rib, respectively. To our knowledge, this is the first text in literature with an osteopathic treatment in a patient with L-VAD.

Surgical implant techniques of left ventricular assist devices: an overview of acute and durable devices

Left ventricular support for the failing heart has evolved to include short-term and long-term devices. These devices are implanted percutaneously and surgically. This manuscript provides a general overview of the contemporary, typically practiced, implant techniques with additional insight on minimally invasive approaches.

The Jarvik-2000 ventricular assist device implantation: how we do it

The Jarvik-2000 is a non-pulsatile axial-flow left ventricular assist device (LVAD) that is largely used in patients who present in end-stage heart failure, as a bridge to transplant support or destination therapy. From its first utilization, several implantation techniques have been elaborated, starting from a median sternotomy with cardiopulmonary bypass (CPB) support and moving towards a minimally invasive access with an off-pump strategy. Here we present the favored surgical technique used in our department to implant the Jarvik-2000, in a step-by-step fashion.