Fifty years ago, the first ventricular assist device (VAD) was implanted by DeBakey, with the aim of acting as a bridge to recovery. VADs are mechanical circulatory pumps which partially or completely take over ventricular function in order to assist systemic circulation and improve end-organ perfusion. A VAD may be used as a left ventricular (LVAD), right ventricular (RVAD), or as a biventricular assist device (BiVAD).

Initially introduced in the 1980s, the first generation LVADs were large paracorporeal devices such as the Thoratec PVAD and Abiomed BVS 5000 (and subsequently the AB 5000). Intracorporeal devices included the HeartMate I IP/VE (Thoratec Inc., Pleasanton, California, USA) (Fig. 2.1) and the Novacor N100 (WorldHeart Inc., Salt Lake City, Utah, USA). All of these functioned on the basis of pulsatile systemic perfusion, otherwise known as “pulsatile-flow” devices. However, their bulkiness, lack of durability, and proclivity to malfunction and complications meant that patients were often bedridden and had less than optimal outcomes, including high stroke rates [4]. Subsequent miniaturization of the control and power-supply components resulted in smaller versions of these first-generation pulsatile VADs that could be implanted intra-abdominally [5, 6]. While these enabled patients to mobilize, devices still remained restricted to patients with a large body surface area; device failure rates remained high, infections continued to be problematic, and durability remained poor [7].

The second generation of LVADs consist of smaller continuous axial flow pump systems that allow considerably less extensive surgery (thus reducing the risk of complications, see Fig. 2.2), and confer improved durability, ability to use in a wider range of patients due to smaller size, and reduced thrombogenicity. The increase in durability arises in part from the fact that there is only one moving part. The prototypic device of this class is the HeartMate II (HM II; Thoratec Inc., Pleasanton, California, USA) (Fig. 2.1), which is the most commonly used LVAD with over 20,000 implants worldwide. Introduction of these devices has proved successful, with demonstrated superior survival and less organ failure in patients on continuous-flow VADs compared to patients on pulsatile VADs. 1-year survival for these more modern devices has been reported at 81% for bridge-to-transplantation and 73% for destination therapy [8, 9], which while not as impressive as the 90% seen in heart transplantation, is certainly much improved from the first-generation of LVADs. Furthermore, in continuous flow devices, quality of life, general well-being and ability to perform self-care are significantly improved post-LVAD implantation [9, 10]. This improvement means that LVAD patients are now able to engage in daily life as outpatients relatively unperturbed.

The subsequent third-generation LVADs have sought to further refine the continuous-flow concept, minimizing contact between the pump and the axial rotor by using magnetic levitation technology, thus reducing friction and mechanical wear of the device. Given the small size, the pumps can be implanted within the pericardium, thus further reducing postoperative complications. Examples of third-generation LVADs include the DuraHeart (Terumo Heart Inc., Ann Arbor, Michigan, USA), VentrAssist LVAD (Ventracor Ltd., Chatswood, New South Wales, Australia), Incor (Berlin Heart Inc., Berlin, Germany), and the HeartWare HVAD centrifugal pump (HeartWare International Inc., Framingham, Massachusetts, USA) (Fig. 2.1).

The ADVANCE (Evaluation of the HeartWare Ventricular Assist Device for the Treatment of Advanced Heart Failure) Trial (and continued access enrollment) included 332 pts. implanted with the HeartWare HVAD with 91% survival at 180 days and 84% at 1 year [11]. Currently, over 5000 HeartWare HVADs have been implanted worldwide and has CE approval in Europe. In the U.S. along with the HM II LVAD, it is the only FDA approved LVAD for bridge-to-transplant candidates. With respect to destination therapy (see below), the HM II LVAD is the only FDA approved device at the current time. However, the ENDURANCE (Clinical Trial to Evaluate the HeartWare® Ventricular Assist System) Trial for destination therapy comparing the HVAD to HM II is ongoing [12]. Another multicenter trial of the VentrAssist LVAD in 33 patients demonstrated a favorable efficacy and safety profile for the use of this device as bridge-to-transplant [13], with 82% of the patients surviving at 5 months post-implant. However, this device is no longer available. The DuraHeart, a LVAD used primarily in Europe, has also shown comparable survival as bridge-to-transplant, with 77% at 1 year and 61% at 2 years [14]. However, longer follow-up and data is required before firm conclusions can be drawn.

An emerging alternative to VADs in patients with biventricular failure, TAHs will be covered in more detail in Chap. 17.

Ventricular assist devices are typically used in one of 3 ways: to stabilize the waitlist patient until a donor heart becomes available, otherwise known as bridge-to-transplant; to stabilize the patient with an anticipated possibility of future listing for transplant, known as bridge-to-candidacy; and as “destination” therapy, which means that the patient is not a transplant candidate and thus the VAD is the terminal treatment. In patients who eventually end up with VAD as destination therapy, LVADs are often implanted with the intention of bridging to transplant (with the exception of those contraindicated to transplant). However, in recent years destination therapy survival has improved [15]; furthermore, as the waiting list for a heart becomes longer, the duration of MCS becomes longer, and some patients may remove themselves from the waiting list.

In rare cases (<5% of implants), LVADs have acted as a bridge to recovery, the theory being that unloading of the ventricle leads to reverse ventricular remodeling and subsequent functional improvement [16]; while this appears more likely to occur in myocarditis and other recoverable etiologies of heart failure, there are no reliable parameters to predict which patients will demonstrate this.

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) represents the largest registry of MCS device utilization in the world, with 166 participating hospitals across the US and Canada. Its purpose is to collect MCS-related data and assess trends in survival, device strategy and risk factors for poor outcomes. The most recent seventh INTERMACS annual report presents MCS data from 23 June 2006 to 31 December 2014. Of the 15,745 patients who received an MCS device, 13,286 received an LVAD. Not surprisingly, given the survival benefits, over 90% (12030) of these patients received a continuous flow LVAD, with 955 receiving a pulsatile device and a further 301 receiving a TAH. Survival for continuous-flow devices implanted since 2008 remains at 80%, with 2-year survival at 70% [15]. Freedom from device exchange or death related to device malfunction has been demonstrated to be similar for pulsatile and continuous flow devices for the first 8 months (96%). However, there is a significant linear decrease in the freedom from device malfunction in the pulsatile device from 8 months until 24 months post-implant (40% at 24 months), compared to the relatively steady freedom from malfunction at 24 months in the continuous flow LVAD (94% at 24 months) [10].