Bridge to transplantation with the MicroMed DeBakey ventricular assist device axial pump: a single centre report

Update on ventricular assist devices

PURPOSE OF REVIEW

Over the past two decades, medicine has seen a robust increase in the use of ventricular assist devices. The purpose of this review is to update the information concerning these devices, their advantages and disadvantages as well as their complications. This is essential, as the demand for these devices is increasing due to the increasing number of patients with end-stage heart failure and limited number of donor hearts available for transplantation.

RECENT FINDINGS

First-generation devices consisted of large, cumbersome consoles requiring patient immobilization and often times hospitalization in an ICU setting. Second-generation models focused on patient mobility and discharge from hospital with an improvement in infection rates as well as 1 and 2-year survival rates. Designs for newer devices are focusing on full implantation without percutaneous lines, axial flow mechanisms and patient comfort. Additionally, total artificial hearts are being designed for the treatment of biventricular failure. The indications for ventricular assist devices are also being expanded to include destination therapy and alternatives to cardiac transplantation, as the supply of organs continues to be limiting.

SUMMARY

This paper reviews the characteristics, outcomes and design of ventricular assist devices.

Initial clinical experience with the VentrAssist left ventricular assist device: the pilot trial

BACKGROUND

The VentrAssist (VA) is a novel, continuous flow left ventricular assist device (LVAD). The purpose of this trial was to investigate the safety and efficacy of the VA in elderly patients with end-stage heart failure.

METHODS

In this prospective trial, patients requiring circulatory support either as destination therapy (DT) or as a bridge to transplant (BTT) were implanted with a VA device.

RESULTS

Between June 2003 and August 2006, 9 elderly patients (mean age 65 years) were implanted. The median support time was 454 (range 73 to 977) days for the DT and 35 (range 26 to 508) days for the BTT cohort. All patients survived implantation; 30-day mortality was 22% (n = 2). The adverse event profile was encouraging, with no embolic neurologic events and minimal sepsis. Cumulative trial support time was 7.3 patient-years.

CONCLUSIONS

The VentrAssist shows promise as a safe and reliable "third-generation" VAD. Having demonstrated potential as a DT and prolonged BTT device, extended clinical trials are warranted.

Destination therapy: does progress depend on left ventricular assist device development?

The role of therapy using mechanical circulatory support devices has evolved rapidly over the last two decades. New developments in the field achieved smaller adverse events, but, currently, only minor improvements in survival were observed in published observational data. The authors discuss the development of mechanical circulatory support devices as a "destination therapy" option for patients who have end-stage heart failure and are ineligible for heart transplantation as it relates to left ventricular assist device development.

Choroidal Microcirculation in Patients With Rotary Cardiac Assist Device

BACKGROUND

In recent years, fully implanted rotary blood pumps have been used for long-term cardiac assist in patients with end-stage heart failure. With these pumps, the pulsatility of arterial blood flow and arterial pressure pulse is considerably reduced. Effects on end-organ perfusion, particularly microcirculation, have been assessed.

METHODS

The ocular choroid offers a unique opportunity to study the pulsatile component of blood flow by measurement of fundus pulsation amplitude (FPA) as well as the microcirculation by laser Doppler flowmetry. Both techniques were applied in three male patients with rotary pumps (MicroMed DeBakey VAD), in whom pump velocity was adjusted to four levels of flow between individual minimal need and maximal support. In addition, blood flow velocities in the ophthalmic artery (peak, end-diastolic and mean flow velocity--PSV, EDV and MFV, respectively) were measured using color Doppler imaging.

RESULTS

Systolic blood pressure increased by 6 to 22 mm Hg with increasing support. At maximal support FPA was reduced by -60% to -52% as compared with minimal pump support. Blood flow in the choroidal microvasculature, however, did not show relevant changes. A reduction in PSV (-31%, range -47% to -21%) and a pronounced rise in EDV (+93%, range +28% to +147%) was observed, whereas MFV was independent of pump flow.

CONCLUSIONS

Our data indicate that mean choroidal blood flow is maintained when pump support is varied within therapeutic values, whereas the ratio of pulsatile to non-pulsatile choroidal flow changes. This study shows that, in patients with ventricular assist devices, a normal perfusion rate in the ocular microcirculation is maintained over a wide range of support conditions.

Development of the functionally total artificial heart using an artery pump

Based on the assumption that only the pump function of the diseased heart should be assisted or replaced by device while resecting the native heart is unnecessary, the concept of a "functionally total artificial heart (FTAH)" was explored. An artery pump (AP) was designed for the FTAH. The fabricated pattern of the AP, having an outer diameter of 28 mm and a length of 42 mm, was implanted in the position of ascending aorta or pulmonary trunk, joining in series to the chambers of the left ventricle or the right ventricle. The total weight of the AP pattern is 74 g, and it displaces 29 mL of volume and can achieve 5 L/min against 100 mm Hg pressure with a speed lower than 10,000 rpm. In mock circulation, two APs were connected in series with each other, and their flow rates could automatically balance each other. Simulative cardiac output and atria pressures can be maintained within a suitable range by properly adjusting the rotational speeds of each pump. Because the response of the APs to the pressure alterations at their inlets and outlets are similar to that of native heart, no intricate regulating mechanism would be necessary. This preliminary study shows that the concept of the FTAH is feasible if two APs are simultaneously implanted to replace native heart function.