Episode 952: Heart Transplants

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Apr 14, 2025

Delve into the fascinating world of heart transplants where unique physiological changes like the absence of vagal tone lead to an increased heart rate. Discover how transplant patients face atypical symptoms during rejection, such as fatigue instead of chest pain. Immunosuppressants raise infection risks, adding complexity to patient care. Plus, a surprising study reveals that radiographic cardiomegaly doesn't necessarily indicate heart failure, challenging conventional wisdom.

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INSIGHT

Denervated Heart

Transplanted hearts lack vagal tone due to the severed vagus nerve.
This results in a faster resting heart rate and unresponsiveness to atropine.

ADVICE

Treating Arrhythmias

While atropine is ineffective, adenosine can treat transplant bradyarrhythmia.
For tachycardia caused by rejection, consult transplant surgery; 500mg methylprednisolone may help.

INSIGHT

Rejection Symptoms

Rejection mimics heart failure with elevated troponin and BNP, causing pulmonary edema.
Due to denervation, patients experience weakness and fatigue instead of chest pain.

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Contributor: Travis Barlock, MD

Educational Pearls:

Key clinical considerations when managing heart transplant patients due to their unique pathophysiology
1. Arrhythmias

A transplanted heart is denervated, meaning it lacks autonomic nervous system innervation

The lack of vagal tone results in an increased resting heart rate
Adenosine can be used since it primarily slows conduction through the AV node
Atropine is ineffective in treating transplant bradyarrhythmia because its mechanism is to inhibit the vagus nerve - but the heart lacks vagal tone

Allograft rejection can also cause tachycardia

Consult transplant surgery - treatment is usually 500 mg methylprednisolone

2. Rejection

Transplant patients are administered immunosuppressants
Clinical presentation of acute rejection looks similar to heart failure with increased BNP, increased troponin, and pulmonary edema
Cardiac allograft vasculopathy is a form of chronic rejection
Patients will not report chest pain due to denervated heart

Symptoms are usually weakness and fatigue

3. High risk of infection due to immunosuppression

Increased risk of infections which includes CMV, legionella, tuberculosis, etc
Immunosuppressants have side effects such as acute kidney injury or pancytopenia

4. Radiographic Cardiomegaly

A study found that radiographic cardiomegaly does not connote heart failure
They hypothesized it is instead the result of a mismatch between the size of the transplanted heart and the space in the thoracic cavity

References

Murphy JD, Mergo PJ, Taylor HM, Fields R, Mills RM Jr. Significance of radiographic cardiomegaly in orthotopic heart transplant recipients. AJR Am J Roentgenol. 1998 Aug;171(2):371-4. doi: 10.2214/ajr.171.2.9694454. PMID: 9694454.
Park MH, Starling RC, Ratliff NB, McCarthy PM, Smedira NS, Pelegrin D, Young JB. Oral steroid pulse without taper for the treatment of asymptomatic moderate cardiac allograft rejection. J Heart Lung Transplant. 1999 Dec;18(12):1224-7. doi: 10.1016/s1053-2498(99)00098-4. PMID: 10612382.
Pethig K, Heublein B, Wahlers T, Dannenberg O, Oppelt P, Haverich A. Mycophenolate mofetil for secondary prevention of cardiac allograft vasculopathy: influence on inflammation and progression of intimal hyperplasia. J Heart Lung Transplant. 2004 Jan;23(1):61-6. doi: 10.1016/s1053-2498(03)00097-4. PMID: 14734128.

Summarized by Meg Joyce, MS1 | Edited by Meg Joyce & Jorge Chalit, OMS3

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