Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Role of Ventricular Assist Devices in the Management of Heart Failure

The prevalence of heart failure (HF) worldwide is estimated to be about 26 million people. In the United States alone, there are approximately 5.7 million adults with HF, and this number is projected to increase to approximately 8 million by the year 2030. Mechanical circulatory support (MCS) with a left ventricular assist device (LVAD) is now the standard management for patients with chronic refractory HF. The goals of LVAD support are twofold: (1) to decompress the failing left ventricle, thus dramatically reducing left ventricular (LV) myocardial oxygen demand (which, in certain circumstances, may promote recovery of the failing myocardium), and (2) to maintain adequate systemic perfusion to avert cardiogenic shock. The pump itself is attached to the heart and great vessels by cannulae that allow continuous collection of blood returning to the left side of the heart and ejection of that blood into the aorta.

According to the latest data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), there are currently 2000 to 3000 LVAD implantations annually at approximately 160 centers in the United States alone. Table 5.1 outlines the current indications for long-term LVAD support, as well as the current frequency and current success of each indication in the United States.

Until 2009, bridge to transplantation (BTT) was the most common indication for implantation of a durable LVAD, but the approval of the HeartMate II for destination therapy (DT) in 2010 heralded a new era of MCS because before that, a durable device that could provide years of support did not exist. Continuous-flow (CF) devices (e.g., the HeartMate II) have now been used to provide support for 100% of patients implanted for DT since 2010, as well as for more than 95% of all other LVAD indications. The first generation of pulsatile, implantable devices is essentially no longer in use.

The most common indication for LVAD implantation is now DT (see Table 5.1 ), with BTC the second most common indication and BTT (the traditional indication before 2010) now third most common. Overall, all-comer survival with a durable LVAD now approaches 80% at 1 year, and the 4-year survival rate now approaches 50%. As the survival rate has increased, the number of patients supported by LVADs requiring interventional and diagnostic procedures and noncardiac surgery (NCS) procedures has increased. The volume of NCS in LVAD-supported patients varies from institution to institution and practice to practice, but current trends indicate that the vast majority of NCS procedures performed in this population are now diagnostic and therapeutic endoscopies. Although supported patients still tend to receive their care in the academic VAD centers, there has been some expansion into the private practice settings and even some endoscopy centers.

INTERMACS

INTERMACS is a North American registry database sponsored by the National Heart, Lung and Blood Institute; the Food and Drug Administration (FDA); and the Centers for Medicare and Medicaid Services (CMS). Centered at the University of Alabama at Birmingham, INTERMACS was established in 2005 for patients receiving long-term MCS therapy with implantable, durable devices to treat advanced HF. Essentially, INTERMACS collects clinical data about VAD patients as it happens. Postimplant follow-up data are collected at 1 week, 1 month, 3 months, and 6 months and every 6 months thereafter. Major outcomes after implant (e.g., death, transplant, explant, rehospitalization, and adverse events) are entered by implanting centers as such events occur and at defined follow-up time points, along with more “complex” endpoints (e.g., the patient's level of function and quality of life), which are critical to the evaluation of current MCS therapy, for which improvements in both survival and function have been compelling. These indices are becoming increasingly important as survival improves, and new devices will be compared for outcomes beyond simple survival. A similar European-based database called EuroMACS exists in Europe, and there is also a database of pediatric MCS called PEDIMACS. A new international database maintained by the International Society for Heart and Lung Transplantation (ISHLT) called IMACS now exists, and reports of the international experience will soon provide data regarding international outcomes.

Regarding LVAD implantation by indication, the most recent INTERMACS data available at the time of this writing report that DT continues to be the most prevalent indication for LVAD implantation, having increased to 45.7% of all implants in 2014 (compared with 14.7% in 2006 and 2007, and 28.6% between 2008 and 2011). In the sixth annual report (released in 2014), BTC was the second most common modern indication for VADs, with BTT in third place, but in the seventh annual report (released in 2015), 30% of patients were already listed for transplantation at the time of implantation, with an additional 23% implanted as a BTC. “Bridge to recovery” with short-term VADs continues to constitute only a very small percentage of the usage of this technology in the most current report (0.2% in 2014). Additional data available from INTERMACS regard survival by both timing of implantation and by type of device .

The INTERMACS profile (also called the INTERMACS level) describes the clinical condition of the patient on a scale from 1 to 7, with a numerically lower profile indicating more severe illness. A level 7 patient is simply in the advanced stages of HF (e.g., New York Heart Association class III), and the clinical condition of the patient gets worse as the INTERMACS profile number gets lower. For example, a level 4 patient has symptoms at rest, a level 3 patient is essentially hemodynamically stable but inotrope dependent, a level 2 patient is deteriorating despite inotropes, and a level 1 patient is essentially in cardiogenic shock despite maximal therapy.

The experience has been that if a durable LVAD is implanted too early (at numerically higher INTERMACS levels), the risks of adverse events outweigh the benefits. Conversely, if the VAD is not implanted until the patient is already likely developing multisystem organ failure (e.g., level 1), the likelihood of ultimate rescue is low, and the survival rate is poor. Survival data suggest that implantation of durable LVADs when the patient is level 3 or 4 would be ideal to balance the risks and benefits . Large multicenter head-to-head trials conducted in the modern era with modern devices (e.g., Momentum 3, Endurance) have reported the profile of risks and benefits associated with each of the modern devices (see Suggested Reading ).

Specific Devices in Current Use

The two most commonly implanted FDA-approved durable devices in the United States are the HeartMate II (Abbott) and the HeartWare HVAD (Medtronic). The Heartmate 3 is a relatively recently introduced implantable, durable device that has received FDA approval for certain indications, although approval of other indications is still pending at the time of this writing.

HeartMate II

The HeartMate II (HM II; Fig. 5.1 ) is currently the most commonly implanted durable LVAD in the United States and in many countries around the world. The HM II is a miniaturized “second-generation” continuous axial flow pump that was FDA approved as a BTT in 2008 and as DT in 2010. According to the manufacturer, more than 16,000 patients worldwide have received the HM II, with the longest duration of support more than 8 years. Although the impeller is the only moving part, it is stabilized at both ends by bearings. Current postimplantation protocols call for warfarin anticoagulation to an international normalized ratio (INR) of 2.5 to 3.5 plus aspirin. The currently reported rate of successful BTT with the HM II is approximately 86%. Fig. 5.2 shows and discusses details regarding parameters displayed on the HM II clinical control screen.

HeartWare HVAD

The HeartWare HVAD ( Fig. 5.3 ) is a miniaturized CF centrifugal pump with a magnetically driven, hydrodynamically suspended impeller (the impeller floats in the blood without any bearings). This device is implanted within the pericardium without any significant intervening “inflow cannula”; it directly abuts the LV apex. This design provides for potential use in patients with smaller body surface areas and ostensibly results in shorter surgical implantation times. The HVAD was approved as a BTT in 2012. According to the manufacturer, more than 10,000 patients worldwide have received the HVAD, with the longest duration of support more than 7 years. Current postimplantation protocols call for warfarin anticoagulation to an INR of 2.0 to 3.0 plus aspirin. The manufacturer also recommends testing for aspirin resistance and, if detected, the adjunctive use of clopidogrel, dipyridamole, or both. The currently reported rate of successful BTT with the HVAD is 88% to 90%. The HVAD was recently approved as a DT device in the United States as a result of the ENDURANCE trial and the ENDURANCE supplemental trial. Experience with the HVAD as an implantable right ventricular assist device (RVAD) is accruing. Fig. 5.4 shows and discusses details regarding parameters displayed on the HeartWare clinical control screen.

HeartMate 3

The HeartMate 3 (HM 3, Thoratec, Pleasanton, CA; see Fig. 5.5 ) is a miniaturized CF centrifugal pump with a magnetically driven, magnetically suspended impeller. It is implanted within the pericardium and thus shares some of the potential advantages of the HVAD. Design features ostensibly improve hemocompatibility and reduce the risk of thrombus formation. Similar to the HM II and the HVAD, the HM 3 can reportedly produce 10 L/min of flow. The HM 3 was demonstrated to be noninferior to the HM II in the MOMENTUM 3 trial regarding survival free from either disabling stroke or reoperation for device malfunction at 6 months after implantation. This third-generation device was FDA approved for “short-term indications” in 2017, and its evaluation for “long-term indications” (e.g., DT) is ongoing.

Perioperative Management

The perioperative management of an LVAD-supported patient can be divided into preoperative assessment and planning for the case, intraoperative management, and postoperative considerations.