Chapter 11. Ventricular Assist Devices and Heart Transplantation

• Adult heart surgery patients are increasingly older with varying degrees of preoperative ventricular failure. Patients routinely present with both systolic and diastolic ventricular dysfunction, ventricular remodeling, fluid retention, and pulmonary congestion. Additionally, even those patients with well-preserved ventricular function preoperatively can deteriorate intraoperatively secondary to inadequate myocardial preservation, embolism, myocardial ischemia, protamine reactions, and other "catastrophic" events (eg, anaphylaxis, aortic dissection, etc). Of course, the overwhelming majority of patients experiencing intra-operative right or left ventricular failure can be treated with a combination of inotropes and nitric oxide inhalation. However, others lack sufficient ventricular function to provide adequate delivery of oxygenated blood to the tissues. Such patients readily develop renal dysfunction, acidosis, and ultimately die from cardiogenic shock unless provided mechanical assistance to support or replace the heart's pump function. This chapter reviews the anesthetic management of patients in need of intra-aortic balloon counterpulsation, (IABP) ventricular assist devices (VADs), and heart transplantation (HT).

IABP counterpulsation is employed to assist the failing heart (Video 11–1). It is not a substitute for a beating ventricle and as such does not replace the function of the ventricle it is assisting. The patient must have some cardiac output even if not adequate. IABP is generally introduced via the femoral artery into the thoracic aorta and positioned distal to the take off of the left subclavian artery. The IABP inflates with carbon dioxide or helium during diastole and deflates during systole. Thus, it creates a counterpulsation to the pulsation generated by the heart. By inflating during diastole at the point of aortic valve closure, they augment diastolic blood pressure and thus improve coronary perfusion pressure (CPP) of the left ventricle (LV).

Recall,

CPP = Diastolic blood pressure (DBP) − Left ventricular end diastolic pressure (LVEDP)

During systole, the IABP deflates reducing the afterload against which the heart must eject, thereby potentially improving forward blood flow.

The cardiac anesthesiologist is likely to encounter the IABP in several situations:

1. Many patients presenting with myocardial ischemia refractory to medical or percutaneous interventions are provided an IABP in the cardiac catheterization laboratory to relieve ischemic chest pain. By increasing DBP and lowering LVEDP, the IABP can improve the balance of LV myocardial oxygen supply and demand. In a 1997 review of 4756 IAPB uses in a single institution over a period of 30 years, Torchiana et al suggested that preoperative placement of an IABP in those with medically refractory ischemia can improve patient outcome.1

2. In patients with cardiogenic shock, the IABP is placed to augment cardiac output in the immediate preoperative period should emergent heart surgery be warranted. Of note, the IABP is contraindicated in patients with aortic dissections, aortic aneurysms, severe aortic insufficiency, and severe atherosclerotic disease in the descending aorta.

3. IABPs are placed in the operating room in those patients whose poor ventricular function prohibits separation from cardiopulmonary bypass (CPB) in spite of maximal inotropic and vasopressor support.

4. In patients with a sudden-onset ventricular septal defect (VSD) or papillary muscle/chordal rupture secondary to acute myocardial infarction, the IABP is placed to reduce afterload, hence decrease left-to-right shunt or MR respectively.

Several parameters are important for the adequate operation of the IABP and can be set up from the IABP console. Synchronization of the IABP with the native cardiac rhythm and timing of the balloon inflation and deflation can be done using either the ECG tracing or the arterial pressure tracing. The arterial pressure rise during balloon inflation occurs with the dicrotic notch of the arterial waveform, which signifies the closure of the aortic valve and the beginning of diastole. Timing of the inflation and deflation of the IABP is critical to achieve maximal diastolic augmentation of the blood pressure and maximal afterload reduction. Another parameter that can be set up is the ratio of IABP pulsations to native ventricular pulsations. The IABP can cycle with every beat (1 to 1 assist), every other beat, or every fourth beat of the heart. In this way the degree of assist can be regulated when the patient is to be weaned from IABP support. The volume of gas used to inflate the balloon and the time required for inflation and deflation can also be setup.

Complications of IABP use include femoral artery injuries, arterial dissections, thromboembolism, and balloon rupture with gas embolism and some of these complications require exploration of the femoral artery and arterial embolectomy.

Unlike IABPs that require a working left ventricle producing some cardiac output to be effective, ventricular assist devices (VADs) can function in place of a completely dysfunctional left or right ventricle. VADs are often placed when medical therapy has been exhausted to improve cardiac function. Since deteriorations in ventricular failure can occur both acutely and chronically, VAD placement can be either elective or emergent.

The decision to place a VAD and the type of device to be employed is dependent upon both the patient's associated illnesses and the estimated time that VAD therapy will be required. VADs can be placed to provide short-term ventricular support in those cases where recovery of cardiac function or heart transplantation (HT) is expected. Both percutaneous and implantable devices have been used in this setting. At other times, recovery of the heart function is not considered likely and VADs are placed to support organ perfusion in patients awaiting heart transplantation. Still, other patients are thought not to be suitable candidates for the limited number of hearts available for transplantation and are provided a VAD as so-called "destination" therapy. In other words, it is hoped that the VAD will improve ventricular function sufficiently to provide these patients crippled by heart failure both longer and better quality lives. The decision to commit an individual to VAD support is not lightly undertaken and should be considered in situations when kidney, liver, pulmonary, and neurologic dysfunction are not so advanced that patient survival is not thought possible even with improved cardiac output. Usually, the patient's cardiologist together with a cardiothoracic surgeon will determine whether VAD as "destination" therapy or HT is warranted. Although anesthesiologists are heavily involved in the perioperative placement of these devices, they generally will not be a part of the discussion with the patient and their family regarding the decision to place the device. However, emergent VAD placement in the setting of failure to separate from cardiopulmonary bypass (CPB) should occur only after the surgeon and the anesthesiologist discuss the immediate patient management plan.

VADs are used to support the function of the left, right, or both ventricles. They can be classified according to how blood flows when they are employed. Flow through a VAD can be either continuous or pulsatile. Continuous flow VADs include devices placed percutaneously for temporary support of ventricular function (eg, Impella) and devices implanted (eg, HeartMate II). Pulsatile VADs include extracorporeal devices (eg, Abiomed BVS) for short-term support and those for support of longer duration (eg, HeartMate I).2

VADs can be placed emergently whenever ventricular function is severely compromised. Often candidates for emergent VAD placement are in cardiogenic shock requiring multiple vasoactive medications and possible IABP counterpulsation. VAD placement may prevent the development of multiorgan system failure giving time for the heart to recover function or may provide a "bridge to decision" during which the patient, his healthcare providers, and family members can discern the best course of therapy.

The type of VAD to be placed and whether one or both of the ventricles will be supported depends upon the clinical conditions. A left ventricular assist device (LVAD) is placed in the setting of cardiogenic shock and poor left ventricular systolic function (Video 11–2A and 11–2B). A right ventricular assist device (RVAD) is placed when the right heart fails such as during a right ventricular infarction or in patients with severe pulmonary artery hypertension. In this setting the LV is often underloaded as the RV does not deliver sufficient blood to the LV to eject into the systemic circulation resulting in cardiogenic shock. At times, both ventricles require mechanical support. However, LVAD placement will sometimes sufficiently unload the left ventricle such that flow through the RV improves eliminating the need for biventricular VAD (BIVAD) placement.

Emergent short-term VADs include both percutaneously and surgically placed devices. Percutaneous devices can be placed in the cardiac catheterization laboratory and thus can provide mechanical assistance without the need for surgical interventions. The TandemHeart3-5 device provides left atrial-to-femoral artery blood flow. TandemHeart is a continuous flow centrifugal device using an extracorporeal pump. The inflow cannula is inserted via the femoral vein through the intra-atrial septum into the left atrium. Oxygenated blood is then pumped from the left atrium and returned to the systemic circulation via a cannula placed in a femoral artery providing retrograde flow to most of the body. Since the lungs continue to oxygenate blood flowing into the left atrium, TandemHeart can be employed during high-risk percutaneous coronary interventions (PCIs) to provide circulatory support without requiring extra corporeal oxygenation (Figure 11–1). Although TandemHeart was capable of improving hemodynamics in a randomized trial of patients with cardiogenic shock following acute myocardial infarction compared to those treated with IABP support, the 30-day mortality was similar between the groups.4

The Impella Recover is another percutaneous device, which can be used to support left ventricular function.6 The device can be placed via the femoral artery or alternatively placed directly into the aorta intraoperatively and threaded across the aortic valve into the left ventricle. Patients with postoperative LV failure treated with an Impella Recover device were found to have a similar mortality to that of patients supported with an IABP.6 However, in the patients whose native hearts could produce 1 L/min of cardiac output the Impella device showed better long-term survival compared with an IABP. Both the Impella device and TandemHeart require anticoagulation.

In contrast to the more recent, percutaneous, non-pulsatile VADs available for short-term support, pulsatile, surgically placed devices have been employed since the 1990s. For LVAD support a drainage cannula is placed in the left atrium and blood drained into the pump to be returned to the patient through a synthetic graft attached to the aorta. Similarly, the cannulae may be placed in the right atrium and the pulmonary artery to assist right heart function (Figure 11–2).

Conditions that impede the delivery of blood to the left atrium (eg, right heart failure, clot, hypovolemia) can reduce LVAD output. Many patients with long-standing LV failure have significant pulmonary hypertension and RV failure. If RV function is inadequate, the VAD will be underfilled since blood will not be pushed across the pulmonary vasculature to return to the LA for drainage into the LVAD pump. Likewise should a patent foramen ovale (PFO) be present, systemic hypoxemia might occur as deoxygenated blood will flow across the intra-atrial septum from the right atrium into the left atrium. By draining blood from the left atrium, the VAD will lower the pressure in this chamber, therefore, deoxygenated blood will follow the pressure gradient and will enter the systemic circulation through a PFO or other septal defect leading to a right-to-left shunt. Consequently, TEE examination prior to VAD placement must rule out the presence of any septal defects.

Both pulsatile flow and axial (non-pulsatile) flow type devices have been designed to provide long-term VAD support either as a "bridge to transplantation" or as "destination" therapy. Implantable pulsatile VADs (eg, HeartMate I) have been shown to decrease the death rate in patients awaiting heart transplantation and to improve survival after these patients undergo heart transplantation7 (Figure 11–3). The initial implanted devices were somewhat large and were placed in the abdominal cavity. Blood was drained from the apex of the heart and returned to a graft in the aorta. As with short-term LVAD therapy, TEE is essential to the perioperative management of these devices. Patients with septal defects would shunt from right to left leading to hypoxemia following drainage of blood from a cannula placed in the apex of the left ventricle. Aortic insufficiency can complicate LVAD flow as well. A leaking aortic valve will merely drain blood back into the LV following delivery of the blood flow by the LVAD into the aorta. At times, surgeons will sew a closed leaky aortic valve if necessary.

Early-generation pulsatile VADs tended to be noisy and kept the patient tethered to a large console.

The REMATCH trial (randomized evaluation of mechanical assistance for the treatment of congestive heart failure) demonstrated that VADS could be employed in patients not candidates for heart transplantation with improved quality of life and survival.8

Variations in VAD design have been attempted to improve patient survival, mobility, and quality of life while reducing the incidence of complications such as bleeding, stroke, and infection. The LionHeart LVAD is entirely contained within the body eliminating the need for power or drivelines emanating from the body.9 Non-pulsatile, continuous flow assist devices are also available (VentrAssist, HeartMate II., Jarvik 2000)10 (Videos 11–3A and 11–3B). Although pulsatile devices provide excellent support, they are both noisy and subject to failure as they include a number of moving parts to displace and eject blood into the aorta. Conversely, continuous flow devices are smaller and have fewer parts permitting them to be implanted in small patients for whom pulsatile devices might be too large. The continuous flow devices require higher degrees of antithrombotic therapy compared to the implantable pulsatile devices; they too have associated risks of thrombosis, bleeding, embolism, and infection.

The anesthetic management of the patient for VAD placement is largely dependent upon the circumstances in which VAD placement is being undertaken. The patient with heart failure presenting for elective VAD placement as "bridge to transplantation" presents challenges both similar and different from the patient undergoing VAD placement for salvage following cardiac surgery.

Patients presenting for elective placement of an implantable VAD secondary to systolic heart failure are approached in a manner similar to any patient for cardiac surgery with severely compromised ventricular function. Hemodynamic collapse at the time of anesthetic induction should be anticipated irrespective of anesthetic agents employed. Inotropic agents are often necessary until CPB can be initiated. The exact choice of narcotics, inhalational agents, and muscle relaxants is less important than tailoring the anesthetic management to the goal of hemodynamic stability, preservation of blood pressure, and tissue perfusion. Patients at high risk of hemodynamic collapse can also be supported with IABP assist. Some patients may have had previous sternotomy making surgical exposure difficult. Should hemodynamic collapse ensue, the patient can be placed on femoral-femoral bypass.

Following placement of the device, the surgical team will carefully de-air the VAD prior to initiation of pumping function. Once an LVAD is placed, its loading will be dependent upon right heart function. Unfortunately, many patients with long-standing severe heart failure have developed pulmonary hypertension. Consequently, high PA pressures and RV failure may prevent maximal loading of the new LVAD leading to inadequate flow. Inhaled nitric oxide is used to decrease pulmonary arterial resistance along with agents such as epinephrine, dobutamine, or milrinone to support RV function. Should these maneuvers fail in improving RV function, mechanical support of the right ventricle will be necessary.

Patients who are already in surgery may require VAD support should separation from CPB not be possible only with inotropic and IABP support. Either a percutaneous (Impella) or surgically implanted, extra-thoracic device (Abiomed BVS) can be employed to provide short-term support of the ventricle with the hope that it will recover in the postoperative period. Anesthetic management is centered upon preservation of right ventricular function should only an LVAD be placed. Coagulopathy is corrected and intravascular volume maintained to adequately load left, right, or bi-ventricular devices. Vascular tone can be preserved with the use of norepinephrine or vasopressin infusions as would be routinely employed in any patient with vasoplegia syndrome. Pulmonary vasodilation may unload the right ventricle and can be achieved by administration of inhaled nitric oxide, hyperventilation, correction of acidosis, or administration of inodilators.

With the VAD delivering a suitable cardiac output, bleeding is controlled, the surgical procedure completed, and the patient transported to the intensive care unit. Antithrombotic medications are administered based upon the requirements of the particular device.

At times, patients recover ventricular function such that mechanical support can be discontinued. In such instances, the patient is returned to surgery, the heart is weaned from VAD support, and the device explanted.

TEE is critical in the perioperative management of the patient receiving a VAD. Prior to placement of a VAD, a comprehensive TEE examination is mandatory. TEE is essential in diagnosing: (1) intracardiac shunts such as PFO or atrial or ventricular septal defects, (2) intracavitary thrombi especially in the left atrial appendage and left ventricle apex, (3) mitral valve stenosis which may restrict flow should the LVAD inflow cannula be placed in the LV apex, (4) aortic valve insufficiency which would hinder forward flow of the LVAD outflow into the systemic circulation, (5) ascending aorta aneurysms or atheroma, and (6) right ventricle function.

After placement of the LVAD, TEE is critical to determine correct position and adequate flow through the VAD's inflow cannula.11 When continuous flow devices are employed, increasing VAD flow can compromise inflow if the ventricle walls are "sucked down" preventing adequate loading of the VAD. RV function should be reevaluated after placement of the LVAD. Drainage of the LV can alter the relationship between the right ventricle and the intraventricular septum leading to ineffective RV function. TEE is also employed perioperatively to ensure effective de-airing of the ventricle following VAD placement. Lastly, TEE is used in VAD patients along with other modalities of hemodynamic monitoring (eg, PA catheters, etc) to discern the causes of hemodynamic instability and to assess response to therapy.

The increasing number of patients with heart failure has been a major driving force behind the development of ventricular assist devices. Heart transplantation (HT) offers the heart failure patient the opportunity to live free from mechanical assistance. Unfortunately, the number of hearts available for transplantation is relatively small and as such the number of operations performed in the United States in any particular year is in the thousands. Since most of these operations are concentrated in a few heart transplant centers, the average cardiac anesthesiologist is not likely to be involved in their care. As with the VAD patients, anesthetic management is focused on maintaining hemodynamic stability in spite of greatly impaired systolic and diastolic function up until CPB can be initiated. Following placement of arterial and central venous access, anesthesia induction is undertaken using a variety of techniques (eg, high-dose narcotic) depending upon patient's comorbidities and individual preference of the anesthesiologist. Inotropes and vasoconstrictors are employed to maintain blood pressure until CPB can be initiated. Should sternotomy not be readily accomplished, femoral-femoral bypass should be considered if the patient's hemodynamics deteriorate and access to the heart and great vessels is delayed. Sterile techniques as with all cardiac surgery patients must be scrupulous. Pulmonary arterial catheters are usually not floated, as the native heart will be excised, however if desired, a PA catheter can be placed in a sterile sheath for advancement into the grafted heart to assist in separation from cardiopulmonary bypass. Close communication between the anesthesia team, the surgical team, and the organ harvest team is critical to coordinate timely delivery of the heart to be transplanted in order to minimize the ischemic time prior to implantation.

HT begins with the identification of a suitable donor. Once identified, multiple harvest teams begin the collection of various organs for transplantation. Prior to harvesting the heart, cardioplegia solution is administered and the heart removed from the chest and iced for transport. Once the harvest team is satisfied with the condition of the graft and surgeons give the "go" order, the recipient is prepared for general anesthesia. The patient's last PO intake is confirmed and the anesthetic induction managed accordingly (eg, cricoid pressure, rapid sequence induction etc). Induction and maintenance are determined by the individual preferences of the anesthesia team involved. As these patients generally have severely limited left ventricular function, the sympathectomy and reduction of vascular tone that often accompany anesthetic induction can result in profound hypotension. Vasopressin can readily restore vascular tone and support the blood pressure. Inotropes are administered to improve ventricular function. Should the heart fail and severe hemodynamic instability ensue while awaiting the graft, CPB is initiated to preserve organ perfusion.

Following surgical anastomosis of the graft, the patient is weaned from CPB in the usual manner. The surgical team will request the administration of various immunosuppressive agents (eg, methylprednisolone, cyclosporine, etc) prior to restoration of blood flow to the graft. It is important to confirm with the surgeon exactly what agents are desired and the exact timing for their delivery before the start of the case. Direct-acting inotropes are used since the grafted heart is denervated from the native sympathetic and parasympathetic nervous systems. TEE is extensively employed to assess right and left graft heart function. The right ventricle of the transplanted heart may not be accustomed to the elevated pulmonary artery pressures present in many heart failure patients. This can lead to RV failure and the need for inhaled nitric oxide administration, inotropes, and at times RVAD support. Separation from bypass is undertaken in the usual fashion; protamine administered, and blood products given as indicated.

In patients with severe pulmonary hypertension and biventricular failure combined heart lung transplants are undertaken.

Patient Failing to Wean from Cardiopulmonary Bypass

A 42-year-old man presents for coronary artery bypass surgery following anterior myocardial infarction. The estimated ejection fraction is 20% preoperatively.

Case Questions

Following completion of three bypass grafts the anesthesiologist weans the patient from CPB. BP is 60/40 mm Hg, PA pressure 60/40 mm Hg. TEE demonstrates biventricular failure. What actions might the anesthesiologist now attempt?

Anesthesiologist starts milrinone, epinephrine, and vasopressin infusions.

The BP increases to 65/45 mm Hg and the PA pressures increase to 65/46 mm Hg. The surgical team places an IABP but the patient develops ventricular fibrillation. What should be the next response of the anesthesiologist?

The bypass cannulas are still in place and the patient is returned to CPB. (No protamine had been given.) The surgeon defibrillates the patient using internal paddles. The milrinone infusion is increased and the IABP placed at one-to-one permitting the patient to be successfully separated from CPB.

Had the IABP not been effective what other options would the surgery team have?

Failure to wean from CPB could result in an intraoperative death. Additionally, after assessing left and right ventricular function a ventricular assist device could be placed. If a VAD is to be placed, a comprehensive TEE examination should evaluate for mechanical factors that might hinder adequate function of the VAD (intracardiac shunts, mitral valve stenosis, aortic valve insufficiency, etc). After placement of the VAD, TEE should evaluate proper VAD function.