68: Heart Transplantation

Published on 06/02/2015 by admin

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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

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