Heart transplantation overview

# Overview
Heart transplantation or cardiac transplantation, is a surgical transplant procedure performed on patients with end-stage heart failure or severe coronary artery disease when medical and device therapy have failed.  The most common procedure is to take a working heart from a recently deceased organ donor (allograft) and implant it into the patient. The patient's own heart may either be removed (orthotopic procedure) or, less commonly, left in to support the donor heart (heterotopic procedure).
Cardiac transplantation is reserved for patients with end-stage congestive heart failure despite all interventions. 1 year survival is 80%, and 5 year survival is 60%. Lifelong immunosuppressive therapy is used to prevent (or postpone) rejection, but increases the risk for opportunistic infections and malignancies.
The indications for heart transplantation include severe hemodynamic compromise due to heart failure which equires IV inotropic support to maintain adequate organ perfusion; a peak Vo2 <10 ml/kg/min; NYHA Class IV symptoms not amenable to any other intervention; or recurrence of symptomatic ventricular arrhythmias refractory to all therapeutic intervention.

# Historical perspective
The first heart transplant into a human occurred in 1964. The first human-to-human heart transplant was performed by Dr. Christian Barnard in 1967.  Norman Shumway performed the first adult human to human heart transplant in the United States. Further developments in the field saw the emergence of standardization of recipient selection criteria, introduction of surveillance endocardial biopsy, distant donor heart procurement, and introduction of Cyclosporine A as an immunosuppressive regimen.

# Classification
Cardiac Transplantation may be classified according to the surgical procedure performed into Orthotopic procedure and Heterotropic procedure.

# Pathophysiology
The pathogenesis leading to a cardiac transplant involves the mechanisms leading up to heart failure. Heart failure leads to an inadequate output of the heart to meet the metabolic demands of the body. Features of chronic heart failure like biventricular hypertrophy, four-chamber dilatation, fibrotic scars, myofibrillar loss, sarcoplasmic vacuolation, interstitial fibrosis may be seen in the diseased heart. Post-transplantation changes indicating acute or chronic rejection may be seen. Non-rejection changes include coronary artery disease (eccentric), Quilty effect, interstitial fibrosis, nodular lymphocytic endomyocardial infiltrates, and posttransplant lymphoproliferative disorder in the transplanted heart.

# Causes
The need for cardiac transplantation may result from advanced, irreversible heart failure with a severely limited life expectancy.
Common causes include- Systolic Heart Failure with a Left Ventricular Ejection Fraction less than 35%, Ischemic Coronary Artery Disease with Refractory Angina, Intractable life-threatening Arrhythmias, Cardiomyopathies, and congenital Heart Disease.

# Epidemiology and demographics
About 4,000 heart transplants occur annually and about 2,200 per year in the United States. The leading indications for transplant in adult recipients is
non-ischemic dilated cardiomyopathy. The median recipient age is 55 years. Death due to acute graft rejection is highest in the first 30 days and infectious complications are the leading cause in the first year. Post-transplant survival has improved over time.

# Prognosis and Complications
The prognosis of the patient depends on a number of donor and recipient factors. If left untreated, patients develop acute graft rejection. Common complications of cardiac transplant include acute graft rejection, graft failure, infections, Cardiac allograft vasculopathy (CAV), malignancies, and late graft rejection.

# Diagnosis
There is no single diagnostic study of choice. A thorough evaluation should be done- including a physical examination and appropriate imaging to select the patients for a heart transplant. The indications and criteria should be fulfilled; the contraindications should be looked out for.

## Indications
Patients requiring a cardiac transplant are generally with advanced, irreversible heart failure with a severely limited life expectancy. These patients would have failed medical and device therapy. Common indications include causes that led to this like- systolic heart failure with a left ventricular ejection fraction less than 35%, ischemic coronary artery disease with refractory angina, intractable life-threatening arrhythmias, cardiomyopathies, and congenital heart disease.

## Contraindications
Contraindications to cardiac transplantation include any multisystem/systemic or life-shortening disease with a life expectancy of less than years, despite a heart transplant. Other factors that may be potential contraindications to be considered are- age, obesity, cancer, diabetes, renal dysfunction, peripheral vascular disease, infections, and substance abuse.

## Criteria for cardiac transplantation
Criteria that should be met by the recipient to make cardiac transplantation suitable include evaluation with cardiopulmonary stress testing (peak oxygen consumption), heart failure prognosis scores- Seattle Heart Failure Model (SHFM), Heart Failure Survival Score (HFSS) and Index for Mortality Prediction After Cardiac Transplantation (IMPACT) score and diagnostic right heart catheterization.

# Treatment

## Medical therapy
Post cardiac transplantation, medical therapy with immunosuppressive drugs is essential to prevent both acute and chronic rejection. Immunosuppressive therapy is given in two phases- Induction therapy and Maintenance therapy. The drugs used include different combinations of drugs like IL-2 Receptor antagonists, Anti-thymocyte antibodies, calcineurin inhibitor, anti-metabolite, glucocorticoids, mammalian target of rapamycin  inhibitors, proliferation signal inhibitors and monoclonal Antibody OKT3.

## Surgery
Surgery is usually reserved for patients with advanced, irreversible heart failure with a severely limited life expectancy. Surgery is not the first-line treatment option for patients with heart failure. The mainstay of treatment for heart failure is medical/device therapy. The two types of operative procedures that can be performed are- orthotopic procedure and heterotropic procedure.

# Follow-up

## Heart transplantation associated arrhythmias
Many patients suffer from heart transplantation associated arrhythmias. These can be either tachyarrhythmias or bradyarrhythmias. These may arise due to presence of suture lines, graft manipulation, inflammatory changes, denervation, and rejection changes.

## EKG Findings
EKG shows accessory atrial activity due to some of the original sinus node still remains in addition to the donor sinus node after a cardiac transplant. For information on 2012 ACCF/AHA/HRS Focused Update of the 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities, click here.