The axial flow pumps are typically regarded as second-generation VADs, as compared to the first generation of volume displacement pumps. Such pumps incorporate both continuous flow and rotary pump technologies as the foundation of their design and construction. They have an impeller inside the pump that can generate high-speed rotations in a blood system (Fig. 39.4). Depending on the motor capacity and rotational speed, an axial flow pump can function either as a partial-flow or full-flow support VAD. The speed of a rotor can reach an RPM of 9000, and it can generate up to 10 L/min of flow with a mean pressure of 100 mmHg.

Initially, serious doubts about the utility of such pumps were raised due to the concerns of red blood cell destruction and heat generated by the high-speed motor inside the blood system. But (starting with conjunction) such theoretical concerns were discarded when a Hemopump was successfully used in a clinical setting without significant hemolysis [17]. The Hemopump thus set the stage for evaluation of other types of axial flow pumps that could be used to pump blood in the human body [6, 7, 9–11].

The common features of axial flow pumps include the following: (1) the simpler design of continuous flow rotary pump technology promises increased long-term mechanical reliability; (2) they do not require valves to create a unidirectional flow nor do they require an external vent or a compliance chamber, thus making them more likely to be used as the platform for future development of a totally implantable VAD; (3) the inflow cannulas are inserted into the left ventricular apexes or totally inside the left ventricle, and the outflow grafts can be connected to either the ascending or descending thoracic aorta (i.e., which is important if abnormalities in the ascending aorta exist); (4) the size of such pumps is relatively small, one-fifth to one-seventh the size of the volume displacement pumps, thereby extending therapy to underserved patient populations including women and even some children; and/or (5) these pumps are associated with minimal noise generation and overall greater patient comfort [6, 7, 9–11, 14, 15].

The HeartMate II LVAD (Thoratec Corp.), the DeBakey MicroMed LVAD (MicroMed Cardiovascular, Inc., Houston, TX, USA), and Jarvik 2000 (Jarvik Heart, Inc., Manhattan, NY, USA) are currently available representatives of this group of VADs. Among them the HeartMate II and the DeBakey MicroMed LVAD have many similarities: (1) they are about the same size, (2) both devices consist of an internal blood pump with a percutaneous lead that connects the pump to an external system driver and power source, and (3) both pumps can generate up to 10 L/min of flow. The initial results appeared to be encouraging, with data supporting effective circulatory support and durability [6, 7, 9–11, 14, 15]. Of particular interest is that the diminished pulse pressures that are associated with utilizing an axial flow pump seemed to be tolerated well in patients, at least for the short term. Importantly, the long-term consequences of using axial flow pumps have yet to be evaluated. Additionally, hemolysis associated with the use of axial flow pumps has been detectable, yet the level has been considered clinically insignificant. Nevertheless, these pumps seem to activate platelets because of the physical strain on blood cells; such activation could be an important source of intravascular thrombosis and/or embolic complications. It should be noted that the incidence of thromboembolism seems to be particularly high for the MicroMed LVAD. Therefore, intense anticoagulation regimens targeting platelet activation and clotting cascade have been employed to deal with these potential problems. A combination of coumadin and Plavix has been recommended for patients who have been provided with a MicroMed LVAD.

The HeartMate II LVAD has shown improved clinical outcomes both as bridge to transplant and destination therapy, with markedly better functional status and quality of life. An actuarial survival of 89 % at 1 month and 75 % at 6 months was reported [14]. The HeartMate II LVAD has proven to be safe and effective as bridge to transplantation. Furthermore, compared to HeartMate XVE, the HeartMate II significantly reduced the device- and surgery-related complications. It is considered that the lower incidence of postoperative bleeding and device-related infection may be due to its smaller size and the lack of need for a large pocket to house its pump and smaller driveline. The absence of a large preperitoneal pocket (which was required with the larger pulsatile devices) has reduced: (1) the need for extensive dissection, (2) postoperative bleeding, and (3) LVAD pocket hematomas and the development of pocket infection. Based on multiple clinical trial outcomes [14, 15, 18], the FDA approved the HeartMate II LVAD to be used as bridge to transplant as well as destination therapy for end-stage CHF patients in 2008 and 2010, respectively. To date, the clinical use of the HeartMate II LVAD has increased rapidly since FDA approval, and thus far over 17,000 patients have received implantation of the HeartMate II LVAD worldwide.