1

What is a ventricular assist device?

Ventricular assist devices (VADs) are pumps implanted to assist the failing ventricle and maintain systemic perfusion. Various VADs are approved for use in the United States, and an even larger variety are used worldwide. Some VADs are intended for short-term use after an acute cardiac event as a “bridge-to-recovery,” and some devices are intended for intermediate-term or long-term use as a “bridge-to-transplantation.” In patients who are not eligible for transplantation, some devices have been approved as “destination therapy” as a final, permanent management strategy for end-stage heart failure. In many instances, a period of VAD support can improve multiorgan failure and improve a patient’s status to become eligible for transplantation; in such instances, VADs are used as a “bridge-to-improved-candidacy.” Devices also are available that can provide circulatory support as a “bridge-to-immediate-survival” (e.g., from acute cardiogenic shock) and as a “bridge-to-next-decision” (e.g., in a patient with uncertain neurologic or multiorgan status after a cardiac arrest).

VADs function by collecting blood from the failing ventricle and pumping it downstream into the systemic circulation. An LVAD provides support for the left ventricle by draining blood most commonly from the apex of the left ventricle and returning it by pump to the ascending aorta. A right ventricular (RV) assist device provides support for the right ventricle by draining blood from the right atrium and returning it by pump to the main pulmonary artery. Some VADs are implanted within the body, and some remain paracorporeal during support, connected to long cannulas implanted in the heart and great vessels.

First-generation LVADs (approved in the mid-1990s) were pulsatile devices that were intended to capture the entire potential output of the failed ventricle and eject a physiologic stroke volume. Their output was pulsatile, although the “pulse” rarely coincided with the underlying cardiac rhythm because the devices were generally set to eject only when they were full. Outputs were generally about 5 to 8 L per minute as long as intravascular volume status and RV function were adequate. Filling relied on gravity drainage augmented by residual ventricular contractions. Ejection was accomplished by either pneumatic or electrically controlled mechanical compression of the blood chamber within the device. First-generation pulsatile VADs have essentially been supplanted worldwide by the second generation of VADs and are now rarely used.

Second-generation VADs (currently being implanted) provide nonpulsatile circulatory support with miniaturized impellers. The design of the impeller varies but can essentially be “axial” (similar to an Archimedean screw) or centrifugal. Although some devices use bearings and impellers with fixed attachment, the impellers can also be magnetically levitated, and some are hydrodynamically suspended by the patient’s flowing blood (so-called third-generation devices).

The next generation devices generally are much smaller than the first-generation devices, which has increased not only the ease of implantation but also the relative percentage of patients who can receive one. Further miniaturized devices are available for pediatric patients. Several advantages have been demonstrated for continuous flow compared with pulsatile flow, including potentially less hemolysis, lower incidence of thromboembolic complications, reduced stroke rate, silent operation, and decreased incidence of RV failure during LVAD support. Continuous flow devices do not seek to decompress the left ventricle completely (which alters the geometry of the right ventricle in an unfavorable way) but instead provide true left ventricular “assistance.”

As of this writing, in the United States, it is most likely that a patient with an LVAD presenting for a noncardiac surgery has a HeartMate II LVAD (Thoratec Corporation, Pleasanton, CA) ( Figure 9-1 ). The HeartMate II is a miniaturized axial flow pump with an internal volume of 63 mL and a potential maximum output of 10 L per minute against a mean arterial pressure (MAP) of 100 mm Hg. The U.S. Food and Drug Administration approved the HeartMate II as a bridge-to-transplantation in 2008 and for destination therapy in 2010.

Schematic of implanted HeartMate II.

(Reprinted with the permission of Thoratec Corporation, Pleasanton, CA.)

More widespread acceptance of VADs has occurred as a result of a demonstrated decreased incidence of complications associated with the HeartMate II compared with previous LVADs, new understandings of risk factors that may result in complications, increased patient management experience over the years, significant improvement in multiorgan function in patients with VADs, and very favorable published data from clinical trials of new continuous flow devices. The increasing use of VADs and enhanced survival of patients with VADs mean that more and more patients with devices are presenting for elective noncardiac procedures. Anesthesiologists should become familiar with VADs and related physiology.

2

What are important preanesthetic considerations for patients with a left ventricular assist device?

The preoperative clinical status of a patient with an LVAD is the result of multiple factors, including end-organ damage sustained during low cardiac output states before VAD implantation, complications following implantation, current surgical problems, and preexisting comorbidities. Some patients with an LVAD are ambulatory and appear to be uncompromised. Others have varying degrees of renal, hepatic, pulmonary, or central nervous system insufficiency. A thorough preoperative evaluation of all major organ systems is essential even for minor procedures. Another consideration is that further deterioration in the perioperative period may preclude full recovery or disqualify a patient from later heart transplantation. Preoperative discussions with knowledgeable colleagues, the surgeon, and the physician managing the VAD are strongly encouraged. Issues to be considered include the following:

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  Perioperative fluid management

  
  
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  Perioperative anticoagulation

  
  
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  Perioperative antibiotic prophylaxis

  
  
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  Perioperative management of pacemakers and implantable cardioverter-defibrillators (ICDs)

  
  
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  Appropriate location for postoperative recovery (i.e., postanesthesia care unit [PACU] vs. intensive care unit [ICU])

  
  
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  Postoperative pain management

3

What anesthetic agents and techniques are appropriate for a patient with a left ventricular assist device?

No specific anesthetic agents are contraindicated in the presence of a VAD. The selection of anesthetic agents and the dosages used should be appropriate for the procedure and should take into account the potentially dysfunctional unsupported right ventricle in a patient with an LVAD as well as any other existing comorbidities as in any other patient. Most patients with a VAD receive a general anesthetic because of the requisite anticoagulation associated with extracorporeal support through the VAD. However, in select cases, superficial regional blocks placed with ultrasound guidance or a regional intravenous technique (e.g., a Bier block) may be appropriate. Major conduction anesthetics (e.g., spinals, epidurals) are generally contraindicated. Intubation and extubation criteria are the same as for any patient. First-generation VADs were large and were implanted in a preperitoneal pocket, requiring “full stomach” precautions (e.g., consideration of rapid sequence induction, etc). The current generation of VADs has been miniaturized, and patients are no longer necessarily relegated to “full stomach” status. Whenever possible, early (if not immediately postoperative) extubation is desirable because prolonged intubation predisposes to pulmonary infections and requires prolonged sedation. There is no reason for patients to remain intubated just because they have a VAD.