68: Heart Transplantation

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CHAPTER 68 Heart Transplantation

Tamas Seres, MD, PhD

1 What are the common diagnoses indicating heart transplantation in adults?

Although historically there has been an equal split between ischemic and nonischemic cardiomyopathy as the indication for transplantation, currently the incidence of nonischemic cardiomyopathy dominates. Valvular heart diseases (2%), retransplantation (3%), adult congenital heart diseases (3%), and miscellaneous conditions (3%) are the remaining indications for heart transplantation.

2 What is the bridge-to-transplant management of patients with heart failure?

At the time of transplant, 41% of adult recipients were receiving intravenous (IV) inotropic support and 29% were on some type of mechanical support device. This is a significant increase compared to the time period of 1999 to 2001 (34% and 19%, respectively). At the same time, substantially fewer adult recipients are now hospitalized immediately before transplant (47% compared with 72% in the period from 1999 to 2001). This reflects the current practice of outpatient management of patients on inotropic therapy with left ventricular assist devices.

3 What are the criteria for the selection of transplant recipients?

Patients with cardiac conditions not responding to maximal medical therapy follow:

image Severe heart failure (Grade D) and life expectancy less than 1 year
image Ischemic heart disease with intractable angina not amenable to interventional or surgical revascularization
image Intractable ventricular tachyarrhythmia
image Hypertrophic cardiomyopathy
image Congenital diseases without irreversible pulmonary hypertension (HTN)
image Management of cardiac tumor

4 What are the priority criteria for the selection of the recipients?

To ensure equitable distribution of donor hearts, the United Network for Organ Sharing (UNOS) has created an organ allocation system. Although many patients qualify for cardiac transplantation, actual donor heart allocation is based on UNOS priority status, ABO blood group compatibility, body-size match, and distance from the donor center. This policy resulted in a major decrease in mortality of patients on the waiting list. UNOS priority status reflects the urgency of the transplantation based on the severity and treatment modalities of the heart failure:

Status 1A: Inpatient with at least one of the following:

image Assisted mechanical support for acute decompensation
image Assisted mechanical circulatory support for >30 days with significant device-related complications
image Mechanical ventilation
image Continuous infusion of a single high-dose IV inotrope or multiple inotropes
image Life expectancy without transplantation of <7 days

Status 1B: Assisted mechanical circulatory support for >30 days

image Continuous infusion of IV inotropes

Status 2: A candidate who does not meet the criteria for Status 1A or 1B

Status 7: A candidate who is considered temporarily unsuitable to receive a thoracic organ transplant.

Thoracic organs are to be allocated locally first, then within one of the five zones in the sequence described by the UNOS allocation policy.

5 What is the significance of peak VO2 measurement?

In general, the peak VO2 (maximum O2 uptake in ml/kg/min) appears to provide the most objective assessment of functional capacity in patients with heart failure (HF). Peak exercise capacity is defined as the maximum ability of the cardiovascular system to deliver O2 to exercising skeletal muscle and of the exercising muscle to extract O2 from the blood. As a result, exercise tolerance is determined by three factors: pulmonary gas exchange; cardiac performance; and skeletal muscle metabolism. Exercise capacity can be quantified clinically by measurement of O2 uptake (VO2), carbon dioxide production (VCO2), and minute ventilation. The VO2 eventually reaches a plateau despite increasing workload. At this point peak VO2 has a strong linear correlation with both cardiac output (CO) and skeletal muscle blood flow. The relationship between CO and O2 consumption also forms the basis for the Fick theorem to measure cardiac output:

image

6 What is the role of peak VO2 in the decision-making process of heart transplantation?

Patients with a profoundly reduced exercise capacity of ≤10 ml/kg/min are likely to experience the most pronounced improvement in survival with transplantation; thus this patient can step forward on the priority list. With optimal pharmacologic and device therapy, the 1-year survival rate is increasing in low exercise capacity groups. However, observations suggest that persistent peak VO2 of 10 to 12 ml/kg/min may become criteria for referral for transplantation.

7 What are the absolute contraindications for the selection of the recipients?

Malignant tumor; active infection; human immunodeficiency virus–positive serology; irreversible, severe hepatic, renal, or pulmonary disease; and alcohol or IV drug abuse are absolute contraindications for heart transplantation. High, irreversible pulmonary vascular resistance (PVR) (>6 Wood units/m2) and high transpulmonary gradient (mean pulmonary artery [PA] pressure − pulmonary capillary wedge pressure) >15 mm Hg exclude patients also from heart transplantation.

8 What are the criteria for donor selection?

Acceptance of a potential organ donor requires confirmation of brain death and organ viability. Echocardiographic evaluation of cardiac function and coronary angiography for male donors older than 45 years and female donors older than 50 years are recommended. Although cardiac transplant recipients are screened before surgery for the percentage of reactive antibodies, donors and recipients are matched only on ABO blood group and weight ratio unless the percentage of reactive antibodies is greater than 20%.

9 How is anesthesia managed for organ harvesting?

Close attention is paid to monitoring of volume status and systemic arterial and central venous pressures. An inspired O2 concentration (FiO2) of 1 is optimal for organ viability unless the lungs are to be harvested. To decrease the possibility of O2 toxicity in the case of donor lung harvest, the lowest possible FiO2 that will maintain the PaO2 greater than 100 mm Hg should be used. Although intact spinal reflexes still may result in HTN, tachycardia, and muscle movement, these signs do not indicate cerebral function or pain perception. Nondepolarizing muscle relaxants are commonly used to prevent spinal reflex-mediated muscle movement in response to noxious stimuli.

10 How is the heart harvested and preserved for transplantation?

The donor heart is excised via median sternotomy. After initial dissection the patient is fully heparinized. Perfusion-sensitive organs (kidneys and liver) are removed via laparotomy before the heart if so planned. After excision the donor heart is placed in a plastic bag containing ice-cold saline and transported in an ice-filled cooler. Optimal myocardial function after transplantation is achieved when the donor heart ischemic time is less than 4 hours.

11 In order of increasing acuity, review the physical status of patients awaiting heart transplantation

image Patients with heart failure who are taking oral medications, including angiotensin converting enzyme inhibitors, β-adrenergic blockers, diuretics, vasodilators, digoxin, and warfarin, usually have low priority on the heart transplantation list.
image Patients may be on IV inotropes with or without vasodilators. The most frequently used inotropes are dobutamine and/or milrinone with or without nitroprusside. None of these medications can be used chronically because they decrease the long-term survival. The decision should be made to use mechanical assist devices or wait for a new heart for a limited time.
image Patients may be on a mechanical assist device. Intra-aortic balloon pump or ventricular assist devices can support left ventricular (LV) or right ventricular (RV) function or both. These patients have high priority for heart transplantation.
image Patients who have a failing transplanted heart and are waiting for retransplantation.

12 What are the hemodynamic characteristics of the heart of the recipients?

Cardiac transplant recipients typically have hypokinetic, dilated, noncompliant ventricles sensitive to alterations in myocardial preload, afterload, and contractility.

13 Describe an appropriate anesthetic induction for patients with heart failure

Hemodynamic goals for anesthetic induction are to maintain heart rate (HR) and contractility, avoiding acute changes in preload and afterload. Inotropic support is often required during anesthetic induction and throughout the precardiopulmonary bypass (CPB) period. As a general rule, induction agents have negative inotropic effects on the heart. In clinical situations in which the sympathetic nervous system activated to maintain the hemodynamic stability of the patient, even etomidate or ketamine can promote cardiovascular collapse.

Rapid-sequence anesthetic induction is advisable in these cases. A full stomach and its risk for pulmonary aspiration should be considered because of short notice before the surgery. Furthermore, mask ventilation can be relatively ineffective, and the increasing CO2 level elevates PA pressure, which decreases the CO in certain cases.

Etomidate in combination with fentanyl or sufentanil can be used in these patients with small doses of midazolam, ketamine, or scopolamine to ensure amnesia. Succinylcholine is appropriate for induction because of the concern of a full stomach. Timely administration of vasoactive agents is necessary in these patients because of the prolonged onset of the effect of medications. Epinephrine, phenylephrine, atropine, or glycopyrrolate vials should be available to keep the blood pressure (BP) and HR at the appropriate level for organ perfusion.

14 How is anesthesia maintained for heart transplantation?

Patients with relatively stable hemodynamic status or on mechanical assist devices tolerate high-dose narcotics or a combination of anesthetic gases and narcotics. Patients with low CO syndrome do not tolerate anesthetic gases well. Careful titration of narcotics can be the choice in this situation. Cardiostable muscle relaxants, including vecuronium, rocuronium, or cis-atracurium, can be used safely. Because of its vagolytic and mild sympathomimetic properties, the muscle relaxant pancuronium is commonly used to counteract high-dose narcotic-induced bradycardia.

15 What monitors should be used for heart transplantation?

Noninvasive monitoring should include a standard five-lead electrocardiogram, noninvasive BP measurement, pulse oximetry, capnography, and nasopharyngeal and bladder temperature. Invasive monitoring should include systemic arterial, central venous, and PA pressure measurements. A PA catheter is helpful in the post-CPB period, permitting measuring of CO and ventricular filling pressures, and calculation of systemic and pulmonary vascular resistance. These indices are particularly useful for assessment and treatment of post-CPB pulmonary HTN and RV dysfunction. Intraoperative transesophageal echocardiography (TEE) is an important tool in evaluation of air in the transplanted heart and in monitoring LV and RV function.

16 Are there specific preparations for cardiopulmonary bypass?

Many cardiac transplant recipients will have undergone previous cardiac surgery and are at increased risk for inadvertent trauma to the great vessels, myocardium, or preexisting coronary artery bypass grafts during repeat sternotomy.

Patients undergoing repeat sternotomy should have external defibrillation pads placed, and cross matched, irradiated, packed red blood cells should be available in the operating room before anesthetic induction.

The potential for a prolonged surgical dissection time in patients undergoing repeat sternotomy often necessitates that anesthesia be induced at an earlier than usual time to coordinate with donor heart arrival.

Femoral or axillary CPB cannulation may be necessary because of the potential for increased severe bleeding and trauma to the heart and great vessels through a previous sternotomy incision.

Moderate hypothermia (28° to 30° C) is commonly used during CPB to improve myocardial protection.

Hemofiltration is common during CPB, because patients with HF often have a large intravascular blood volume and coexistent renal impairment.

High-dose IV glucocorticoids such as methylprednisolone are administered before aortic cross-clamp release to reduce the likelihood of hyperacute rejection.

17 Describe the etiology of coagulation disorders in these patients

Potential etiologies include hepatic dysfunction secondary to chronic hepatic venous congestion, preoperative anticoagulation, CPB-induced platelet dysfunction, hypothermia, and hemodilution of clotting factors. Evaluation of prothrombin time, partial thromboplastin time, platelet number and/or the parameters of the thromboelastogram (TEG) can help to assess the coagulation status and plan the administration of appropriate blood products if there is clinical need.

18 What antifibrinolytic agents can be used to decrease bleeding?

Antifibrinolytic medications such as tranexamic acid and ε-aminocaproic acid are commonly administered after anesthetic induction to prevent postoperative bleeding. Aprotinin, a polypeptide protease inhibitor with platelet-preserving properties, has been shown to decrease perioperative blood loss in patients undergoing repeat sternotomy. However, this agent was removed from the market because of adverse effects on long-term survival and renal function.

KEY POINTS: Heart Transplantation image

1. Treatment modalities of heart failure include medical therapy, ventricular assist devices, and heart transplantation.
2. More and more patients with heart failure will be on ventricular assist device before heart transplantation.
3. Anesthesia for patients with heart failure requires assessment of hemodynamic status, invasive monitoring, and careful selection and titration of anesthetic agents.
4. There is a high risk for cardiovascular collapse during induction and maintenance of anesthesia because of the negative inotropic effect of anesthetic agents.
5. Before emergence from CPB, left and RV function, cardiac rhythm, and bleeding diathesis should be assessed and treated if necessary.
6. RV function plays a central role in successful emergence from CPB after heart transplantation.

19 What preparation should be made before termination of cardiopulmonary bypass?

Before CPB termination the patient should be normothermic, and all electrolyte/acid-base abnormalities corrected. Complete de-airing of the heart before aortic cross-clamp removal is essential because intracavitary air may pass into the coronary arteries, resulting in myocardial ischemia. TEE is particularly useful for assessing the efficacy of cardiac de-airing maneuvers. Inotropic agents should be commenced before CPB termination. An HR of 100 to 120 beats/min, a mean systemic arterial BP greater than 65 mm Hg, and ventricular filling pressures of approximately 12 to 16 mm Hg (central venous pressure [CVP]) and 14 to 18 mm Hg pulmonary capillary wedge pressure (PCWP) are goals for terminating CPB.

20 What is the implication of autonomic denervation of the transplanted heart?

During orthotopic cardiac transplantation, the cardiac autonomic plexus is transected, leaving the transplanted heart without autonomic innervation. The newly denervated heart does not respond to direct autonomic nervous system stimulation or to drugs that act indirectly through the autonomic nervous system (e.g., atropine). Instead, the denervated transplanted heart only responds to direct-acting agents such as catecholamines. Because transient, slow nodal rhythms are common after aortic cross-clamp release, a direct-acting β-adrenergic receptor agonist and/or epicardial pacing is commonly begun before CPB termination to achieve a HR of 100 to 120 beats/min. Infusions of dopamine, dobutamine, milrinone, or epinephrine are effective for inotropic support.

21 What is the cause of the immediate left ventricular dysfunction after cardiopulmonary bypass?

Post-CPB LV dysfunction may be a result of a prolonged donor heart ischemic time, inadequate myocardial perfusion, intracoronary embolization of intracavitary air, or surgical manipulation. The incidence of post-CPB LV dysfunction is greater in donors requiring prolonged, high-dose inotropic support before organ harvest.

22 What is the cause of right ventricular failure after cardiopulmonary bypass?

RV failure is a significant cause of early morbidity and mortality, accounting for nearly 20% of early deaths. Therefore prevention, diagnosis, and aggressive treatment of RV dysfunction after CPB are essential. Acute RV failure after cardiac transplantation may be caused by preexistent pulmonary HTN in the recipient, transient pulmonary vasospasm, tricuspid or pulmonic valve insufficiency secondary to early postoperative RV dilation, and donor-recipient size mismatch. Additional factors that may contribute to postoperative RV dysfunction include a prolonged donor heart ischemic time, inadequate myocardial protection, and surgical manipulation of the heart.

23 How can right ventricular function be evaluated during the surgery?

RV distention and hypokinesis may be diagnosed by TEE or direct observation of the surgical field. Other findings suggesting RV failure include elevation in CVP, decreasing PA pressure, and high transpulmonary gradient (greater than 15 mm Hg). The pressure difference between CVP and mean PA pressure is a valuable parameter in evaluation of RV function. Decreasing difference or the difference <5 mm Hg may indicate failing RV.

24 What are the treatment options for right ventricular failure?

Increased FiO2, correction of acid-base abnormalities, and hyperventilation (PaCO2 of 25 to 30 mm Hg) may reduce pulmonary vascular resistance. RV function may be improved by inotropic support and pulmonary vasodilation (dobutamine, milrinone). Pharmacologic agents commonly used for pulmonary vasodilation include nitrates, prostacyclin (prostaglandin I2 [PGI2]), PGE1, phosphodiesterase III inhibitors, and inhaled nitric oxide (NO).

25 What is the advantage of nitric oxide in the management of heart transplantation?

In contrast to nonselective vasodilators such as nitroglycerin and sodium nitroprusside that typically produce systemic hypotension, inhaled NO (20 to 40 ppm) selectively reduces PVR in the ventilated area of the lung, thus improving ventilation/perfusion mismatch. NO has little systemic effect because it is inactivated by hemoglobin and has a 5- to 10-second half-life.

26 What are the side effects of administration of nitric oxide?

NO administration results in the formation of nitrogen dioxide and methemoglobin, and the levels of these toxic metabolites should be monitored. In the presence of severe LV dysfunction, selective dilation of the pulmonary vasculature by NO may lead to an increase in PCWP and pulmonary edema. Thus agents producing both pulmonary and systemic vasodilation such as IV or inhaled PGI2 may be a better choice in this setting.

27 What are the concerns in anesthetic management of post–heart transplant patients for noncardiac surgery?

Cardiac denervation is an unavoidable consequence of heart transplantation, and reinnervation is absent or incomplete. Baseline cardiac function is normal, but the response to demands for increased cardiac output is altered. HR increases only gradually with exercise, and this effect is mediated by circulating catecholamines. Increases in cardiac output in response to exercise are mostly mediated via an increase in stroke volume. Therefore maintenance of adequate preload in these patients is crucial. Lack of parasympathetic innervation is responsible for the gradual decrease in HR after exercise. Drugs that act indirectly on the heart via either the sympathetic (ephedrine) or parasympathetic (atropine, pancuronium) nervous system will generally be ineffective.

Website image

United Network for Organ Sharing

http://www.unos.org/policiesandbylaws/policies.asp

SUGGESTED READINGS

1. Quinlan J.J., Murray A.W., Casta A. Anesthesia for heart, lung and heart-lung transplantation. In: Kaplan J.A., et al, editors. Kaplan’s cardiac anesthesia. ed 5. Philadelphia: Saunders Elsevier; 2006:845-851.

2. Taylor D.O., Edwards L.B., Aurora P., et al. Registry of the International Society for Heart and Lung Transplantation: twenty-fifth official adult heart transplant report—2008. J Heart Lung Transplant. 2008;27:943-956.

3. Zacharian T., Rother A.L., Collard C.D. Anesthetic management for cardiac transplantation. In: Hensley F.A., Martin D.E., Gravlee G., editors. A practical approach to cardiac anesthesia. ed 4. Philadelphia: Lippincott Williams & Wilkins; 2008:439-463.

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