Figure 84-12. A: The HeartMate II LVAD (Thoratec Corporation, Pleasanton, CA) is an implantable, continuous-flow rotary left

ventricular assist device with axial design intended for long-term mechanical circulatory support for bridge to transplantation or

destination therapy. Schematic drawing showing internal rotor, stators, and bearings and external motor coils. (Drawing courtesy of

Thoratec Corporation, Pleasantan, CA.) B: Schematic representation of the HeartMate II in the preperitoneal position with

associated percutaneous lead, external controller, and power source (batteries).

The randomized, prospective, multicenter HeartMate II Pivotal Trial for DT enrolled 200 patients who

were not eligible for cardiac transplantation. They were assigned in a 2:1 ratio to receive either the

HeartMate II or HeartMate XVE and followed for at least 2 years or until death, transplantation, or

device explantation. The primary composite end-point was reached in more patients in the study group

than in the control group (46% vs. 11%; hazard ratio, 0.38; 95% CI, 0.27 to 0.54; P <0.001). The

HeartMate II population experienced higher actuarial survival rates and lower rates of pump

replacement for malfunction and thrombosis, infection, renal failure, RV failure, respiratory failure, and

arrhythmias. Both groups experienced significant improvement in functional capacity and overall

quality of life.39,50 The post–FDA-approval study supported the original pivotal clinical trial findings

regarding the efficacy and risk profile of the HeartMate II LVAD. Survival was best in patients who

were not inotrope-dependent (INTERMACS profiles 4-7).48

Jarvik 2000. The Jarvik 2000 (Jarvik Heart, Inc., New York, NY) is a continuous-flow rotary pump

with axial blood flow implanted intraventricularly79–81 (Fig. 84-13). This pump is inserted through a

sewing cuff attached to the apex of the left ventricle. The outflow orifice of the pump is attached to a

Dacron graft for anastomosis to the descending or ascending thoracic aorta. The current adult version of

the Jarvik 2000 measures 2.5 cm in diameter by 5.5 cm in length, with a weight of 85 g and a

displacement volume of 25 mL. The adult pump functions at a speed of 8,000 to 12,000 rpm, achieving

blood flows up to 8 L/min. Percutaneous power is delivered from external batteries via a controller

unit. Internal electrical wires are brought via the left pleural cavity to the apex of the chest and then

subcutaneously across the neck to the base of the skull, where a percutaneous titanium pedestal

transmits fine electrical wires through the skin of the scalp. The early clinical studies suggest that this

LVAD system can be used safely in selected patients to provide support until transplant or as DT.80–82 In

2012, the FDA approved the Jarvik 2000 to undergo clinical evaluation for DT.

2438

Figure 84-13. The Jarvik 2000 (Jarvik Heart Corporation, New York, NY) is an implantable, continuous-flow rotary left

ventricular assist device with axial design intended for long-term mechanical circulatory support for bridge to transplant or

destination therapy. Schematic representation of the placement of the Jarvik 2000 within the left ventricle.

Implantable, Continuous-Flow MCS Devices (Rotary Pumps With Centrifugal Flow Design)

Although significant improvements in pump design have occurred with continuous flow rotary pumps,

the use of a mechanical bearing support for the internal impeller, typical of most axial designs, has

potential limitations. The presence of rotor-suspending contact bearings in the blood path represents a

potential point of frictional wear that can result in device failure and subsequent need for device

exchange.76,82,83 Rotary pumps with axial design with bearing support still demonstrate the potential for

thrombus formation on the device rotor and bearing interface due to the presence of stasis and

incomplete bearing “wash” of the bearings and formation of heat from frictional at the bearing

surfaces.53,54 The presence of stators to suspend and redirect blood flow also represents an obstruction

within the blood flow path. Clinical studies have also documented reduced but persistent risk of

thromboembolic stroke as well as hemorrhagic complications owing to the required long-term

anticoagulation therapy.44,46–50,53,54 An additional potential limitation of axial designs in general is

related to their hydrodynamic performance. To observe changes in pump flow at a fixed rotor speed,

significant changes in pressure across the inlet and outlet orifices of the pump must occur.84 This

relative degree of insensitivity of the hydrodynamic performance of the pump or “steep” pressure–flow

relationship can result in left ventricular collapse and “suction” when filling pressures are abruptly

reduced as in the case of a sudden onset of a ventricular arrhythmia, or result in elevated filling

pressures with dyspnea when return to the left atrium is abruptly increased, as with exercise. Left

ventricular collapse or “suction” events can, by itself, precipitate serious ventricular arrhythmias,85

while the inability to significantly increase pump flow with exercise may limit exercise performance in

patients with axial pumps.

Implantable continuous flow rotary pumps with centrifugal flow design represent an alternative

design. These devices provide continuous flow at rotational speeds that are much slower, about 2,000 to

4,000 compared with 8,000 to 15,000 rpm observed for pumps with axial flow design. The same general

advantages and disadvantages of design features that apply to rotary pumps with axial flow design

apply to centrifugal flow design. The major feature current centrifugal designs have is the elimination

of the mechanical bearing support of the internal rotor. Current designs achieve impeller rotation and

levitation with magnetic or hydrodynamic (fluid) forces eliminating the need for bearings with

subsequent problems associated with bearing wear. These designs have a potential for very long

durability46,77,82,86,87 (Fig. 84-14). Impeller rotation to elicit blood flow is achieved through magnetic

coupling to the pump motor. Levitation systems suspend the moving impeller within the blood field

without any mechanical contact, thus eliminating frictional wear and reducing heat generation that

would normally take place at the contact surface with a contact bearing design. These levitation forces

may be achieved through magnetic or hydrodynamic bearing design. Magnetic forces may be passive

without the consumption of power (permanent magnet) or active (induction of magnetic field with

electricity) in design.46,76,82,86,87 Hydrodynamic levitation depends on fluid forces generated by the

rotating impeller to levitate the internal impeller. Pump designs can be further distinguished by the

2439

utilization of hydrodynamic levitation only, hydrodynamic levitation working in synergy with magnetic

levitation for suspension, or variations of active and/or passive magnetic levitation. Active magnetic

levitation of the impeller typically utilizes complex position sensing and control systems that increase

requirements for a larger pump size. Hydrodynamic suspension does not utilize position sensors

resulting in a less complicated electronic design and ability to miniaturize pump size. The design of any

levitation system must be adequate to control the six degrees-of-freedom of movement of the suspended

impeller.

Figure 84-14. Schematic representation of a continuous-flow rotary pump utilizing magnetic coupling of the internal impeller for

levitation and rotation that obviates the need for bearings in the blood flow path.

Centrifugal pumps typically, although not exclusively, have a more sensitive pressure–flow

relationship as compared with rotary pumps with axial design.46,76,82,86,87 This greater sensitivity of the

pressure-flow relationship in rotary pumps with centrifugal design results in greater changes in flow for

any given change in pressure across the inlet and outlet orifices of the pump. This greater pump

response to changes in flow may increase the margin of safety from creating suction events and

improves pump flow during increases in left atrial return potentially enhancing exercise

response.76,82,86,87 The improvements in design attributes of rotary pumps with centrifugal design, such

as mechanical wear, operation at low flow, and perceived improved potential for hemocompatibility,

while still maintaining a manageable size, warrant further clinical investigation. Whether these

attributes of rotary pumps with centrifugal design will result in significant improvement in clinical

outcomes over that observed with rotary pumps with axial design is not known at this time.

HVAD. The HVAD (HeartWare Corporation, Miami, FL) is a small continuous-flow rotary pump with

centrifugal and noncontact bearing design. The unique feature of the HVAD is its small design size46,88,89

(Fig. 84-15). It has a displacement volume of 45 cc and weighs 145 g with a flow capacity of up to 10

L/min. The device is small enough to place within the pericardial cavity without the need for dissection

and creation of a preperitoneal pocket. The impellor of the HVAD is suspended in place by combination

of passive magnetic and hydrodynamic (i.e., fluid) bearing systems. The impeller suspension system

uses a passive magnetic bearing for radial stiffness. Axial magnetic preload and hydrodynamic bearings

on top of each impeller blade provide axial constraint. The magnetic bearing consists of a stack of rareearth ring magnets, near the impeller’s inside diameter that repel the magnetic force of a similar stack

of magnets inside the center post. The axial alignment of the center-post magnet stack is set to provide

an axial force that pushes the impeller toward the forward housing (the assembly with the inflow

cannula). Physical contact between the housing and the impeller is prevented by a thin blood film

generated by the hydrodynamic bearings.

The HVAD is approved for use in the United States for BTT indication and is currently being evaluated

in clinical trial for DT. The ADVANCE trial was a prospective, multicenter evaluation of the HVAD for

BTT indication in the United States using a comparator group implanted contemporaneously with a

commercially available device in the INTERMACS registry.46,89 The primary outcome, success, was

defined as survival on the originally implanted device, transplantation, or explantation for ventricular

recovery at 180 days and was evaluated for both noninferiority and superiority. Secondary outcomes

included a comparison of survival between groups and functional and quality-of-life outcomes and

adverse events in the investigational device group. A total of 140 patients received the investigational

pump, and 499 patients received a commercially available pump implanted contemporaneously. Success

occurred in 90.7% of investigational pump patients and 90.1% of controls, establishing the

noninferiority of the investigational pump (P < 0.001; 15% noninferiority margin). At 6 months,

2440

median 6-minute walk distance improved by 128.5 m, and both disease-specific and global quality-oflife scores improved significantly. Kaplan–Meier survival estimates at 30, 60, 180, and 360 days were

99%, 96%, 94%, and 86%, respectively, for the investigational device group and 97%, 95%, 90%, and

85%, respectively, for the INTERMACS control group. Bleeding, infections and perioperative right-sided

heart failure were the most frequent complications. Inotropic support for greater than 14 days was

required by 16.4% of patients. Driveline exit site infections and sepsis occurred in 12.1% and 11.4% of

recipients, respectively.

Figure 84-15. A: The HVAD LVAD (HeartWare Corporation, Miami, FL) is an implantable, continuous-flow rotary pump with

centrifugal design. The device incorporates passive magnetic and hydrodynamic forces for impeller levitation and rotation. B:

Schematic representation of the HVAD with the inlet cannula inserted into the apex of the left ventricle. The outflow cannulae and

graft are anastomosed to the ascending aorta. (Photograph courtesy of HeartWare Corporation, Miami, FL.)

HeartMate III. The HeartMate III LVAD (Thoratec Corp, Pleasanton, CA) is a new compact

intrapericardial-positioned continuous flow rotary pump with centrifugal design86 (Fig. 84-16). The

unique feature of the HeartMate III is the full magnetic levitation of the internal rotor. The design

differs from currently used devices due to active control of rotation and levitation of the rotor that

permits impellor movement further away from the outer housing creating larger gaps for blood flow

within the device. The larger gaps may reduce blood component trauma and improve biocompatibility.

The HeartMate III is currently under clinical investigation in the United States.

Following the first-in-man implantation at Hannover Medical School in Germany, the device

underwent a clinical investigation in Europe and Canada through the Conformité Européene Mark

clinical trial, which enrolled 50 patients with end-stage heart failure. The 6-month follow-up is in

progress. The device is under investigation in a clinical trial in the United States, and the enrollment is

currently ongoing.

MVAD. The MVAD (HeartWare Inc., Framingham, MA) is a novel continuous axial flow pump,

approximately one-third the size of the HVAD (Fig. 84-17).90 The contactless impeller suspension

technology has a single moving part – the rotor, secured in place by a combination of passive-magnetic

and hydrodynamic forces. The device allows for two distinct flow pathways – the primary flow path is

through the impeller channels, and the secondary flow path is through the radial gap between the

impeller and inner pump housing. The MVAD is to begin clinical evaluation in 2015.

Total Artificial Hearts

Syncardia Total Artificial Heart

2441

The Syncardia TAH-t (SynCardia Systems Corporation, Tucson, AZ) is a pulsatile, volume displacement,

TAH91–93 (Fig. 84-18). The rigid polyurethane pump contains a flexible polyurethane diaphragm that

separates blood and air chambers. Two mechanical valves located at the inflow and outflow orifices

ensure unidirectional blood flow. Compressed air from the external drive console moves the diaphragm

upward, pressurizing the blood chamber and causing ejection of blood. The pump has a maximum stroke

volume of 70 mL and a maximum flow rate of 15 L/min, although the average flow rate is <8 L/min.

Pump rate, duration of systole, and driving pressure can be adjusted to achieve optimal flow conditions.

The TAH is surgically implanted in the mediastinal space after the ventricles have been excised, while

the atrial cuffs are retained. The pneumatic drivelines are externalized percutaneously and attached to

the drive console. Ambulation is facilitated by small portable drive systems and consoles. The Syncardia

TAH-t is approved by the FDA for bridge to heart transplant indication. In a recent study, Copeland and

colleagues

92 reported a survival rate of 79% to heart transplantation compared with 46% for the

observational arm. One-year posttransplant survival rate was 86%. A newer design incorporating a

smaller 50-cc ventricle to facilitate the use in smaller patients is currently in clinical evaluation.

Figure 84-16. A: The Thoratec HeartMate III (Thoratec Corp., Pleasanton, CA) is an implantable, continuous-flow rotary pump

with centrifugal design. The device incorporates complete magnetic levitation for both impeller levitation and rotation. B:

Schematic representation of the HeartMate III showing the blood path, internal rotor, and magnetic fields that achieve levitation

and rotation of the internal rotor. (From Schmitto JD, Hanke JS, Rojas SV, et al. First implantation in man of a new magnetically

levitated left ventricular assist device (HeartMate III). J Heart Lung Transplant 2015;34:858–860.)

Figure 84-17. A: The HeartWare MVAD (HeartWare Inc., Miami, FL) is an implantable, continuous-flow rotary pump with axial

2442

design. The device incorporates hydrodynamic levitation (fluid forces) for radial stability and magnetic levitation for axial stability.

B: Schematic representation of the MVAD demonstrating the blood path and internal rotor. (Photo courtesy of HeartWare, Inc.,

Miami, FL.)

Figure 84-18. A: The CardioWest total artificial heart (Syncardia Systems Corporation, Tucson, AZ) is a pneumatically driven,

pulsatile, volume displacement device. B: The device is positioned orthotopically as a complete replacement of the native heart.

The device is powered by drivelines that exit the anterior abdominal wall and connect to a pneumatic drive console. (Photos

courtesy of Syncardia, Inc., Tucson, AZ.)

FUTURE DIRECTIONS

Recent rapid technologic advancements and successful clinical applications of MCS have made the future

of this field optimistic but uncertain. Areas of continued research include the use of wireless energy

transfer to facilitate complete internalization of MCS devices, application of less invasive surgical

techniques for device implantation, application of MCS devices for the pediatric population, partial

support devices and device designs, and new materials to improve compatibility of the blood-device

interface to reduce thromboembolic complications and need for anticoagulation. It is possible that longterm MCS will provide a viable alternative to heart transplantation and medical therapy for patients

with advanced heart failure. Because of the technologic advancements, it will be difficult to predict

what devices will ultimately prove to be the most efficacious. It is likely that a variety of devices will

become available for use, depending on clinical circumstances and patient characteristics.

References

1. Rihal CS, Naidu SS, Givertz MM, et al. 2015 SCAI/ACC/HFSA/STS clinical expert consensus

statement on the use of percutaneous mechanical circulatory support devices in cardiovascular care.

J Am Coll Cardiol 2015;65(19):e7–e26.

2. Rose EC, Gelijns AC, Moskowitz AJ, et al. Long-term use of a left ventricular assist device for endstage heart failure. N Eng J Med 2001;345:1435–1443.

3. Decision memo for ventricular assist devices for bridge-to-transplant and destination therapy (CAG00432R). http://www.cms.gov/medicare-coverage-database/details/nca-decision-memo.aspx?

NCAId=268. Accessed July 3, 2015.

4. Felker GM, Rogers JG. Same bridge, new destinations—Rethinking paradigms for mechanical

cardiac support in heart failure. J Am Coll Cardiol 2006;47(5):930–932.

2443