Abstract
Background
Heterotopic heart transplantation (HHT) is rarely performed in contemporary practice and poses distinct electrophysiological challenges due to the coexistence of the patient's native heart and the transplanted donor organ.
Case summary
We present the case of a 56-year-old man who experienced recurrent ventricular arrhythmias 6 years post-HHT. The patient initially presented with a syncope and ventricular tachyarrhythmia originating from the donor heart while the native heart maintained sinus rhythm. The arrhythmogenic substrate was attributed to transplant vasculopathy in the donor heart. Management required implantable cardioverter-defibrillator placement and antiarrhythmic therapy.
Discussion
This case demonstrates the fundamental electrophysiological principle that simultaneous documentation of 2 different cardiac rhythms necessitates the presence of 2 independent cardiac rhythms. Although HHT is now rarely performed, this case provides insights into the cardiac electrophysiology and management of dual arrhythmogenic substrates.
Take-Home Messages
Two simultaneously detectable rhythms in the surface electrocardiogram provide compelling evidence of the presence of 2 independent cardiac excitation systems. Even a dysfunctional native heart may maintain consciousness during sustained polymorphic ventricular tachycardia of the donor heart through parallel circulation over a limited period of some hours.
Key Words: electrocardiography, heterotopic heart transplantation, transplant vasculopathy, ventricular arrhythmia
Visual Summary
Heterotopic heart transplantation (HHT) is a rare surgical approach to end-stage heart failure in which a donor heart is implanted without removing the native heart. The first successful procedure was performed by Christiaan Barnard in 1974, which involves implanting a donor heart without removing the recipient's native heart.1
Take-Home Messages
-
•
Two simultaneously detectable rhythms in the surface electrocardiogram provide compelling evidence of the presence of 2 independent cardiac excitation systems.
-
•
Even a dysfunctional native heart may maintain consciousness during sustained polymorphic ventricular tachycardia of the donor heart through parallel circulation over a limited period of some hours.
Early indications included fixed pulmonary hypertension, support during graft dysfunction or acute rejection, use of undersized donor hearts, and extended-criteria donor organs.1,2 With the introduction of combined heart-lung transplantation for irreversible pulmonary hypertension, HHT became uncommon and now accounts for <0.1% of cardiac transplant procedures worldwide.2,3
Electrophysiologically, HHT creates a unique situation in which 2 independent cardiac conduction systems coexist. Surface electrocardiography (ECG) records the vectorial sum of both hearts’ electrical activity, and identification of 2 distinct rhythms in one ECG is rare and educational.
Case Presentation
Patient history
A 56-year-old male patient underwent HHT in 1994 for end-stage ischemic cardiomyopathy with pulmonary hypertension caused by severe mitral regurgitation. Post-transplant immunosuppression included cyclosporine, azathioprine and corticosteroids. Follow-up examinations showed good donor-heart function and severe dysfunction of the native left ventricle.
Initial presentation
Six years later, the patient experienced a syncope lasting several minutes, followed by spontaneous recovery; however, the patient remained weak, confused, and disoriented for approximately 2 hours before activating emergency services. The first single-lead ECG (Figure 1) suggested ventricular fibrillation, inconsistent with preserved consciousness.
Figure 1.
Single-Lead Electrocardiogram Obtained by the Emergency Physician at the Patient’s Home
Initial interpretation as ventricular fibrillation, though the patient was fully alert and oriented.
In-hospital management
On arrival at Charité University Hospital, a 12-lead ECG demonstrated dual rhythms: the waveform observed in limb leads and leads V3-V6 was initially interpreted as atrial flutter (Visual Summary, left). In contrast, the rhythm recorded in leads V1 and V2 was diagnosed as polymorphic ventricular tachycardia (VT) at a rate of 220 beats/min. When considering HHT, it became evident that the native heart maintained a stable sinus rhythm, whereas VT originated from the donor heart, with lower-amplitude VT-related signals also detectable in the remaining leads.
Visual Summary.
Decoding Dual Rhythms in HHT: ECG Manifestation and Underlying Vector Summation
Left: At the hospital, the obtained resting ECG (recording speed = 50 mm/s) depicted polymorphic ventricular tachycardia (→) in precordial leads V1+V2 next to a stable ventricular rhythm (∗) in leads V3-V6, as well as the same arrhythmia mimicking atrial flutter in limb leads I-aVF. Right: anatomical sketch of a surgical situs after HHT, modified by Copeland’s technique where a donor heart is implanted in the right hemithorax in parallel with the native heart, both sharing systemic and pulmonary circulation via atrial and great vessel anastomoses while functioning simultaneously. Surface-ECG summation vectors (→) of each heart correspond to anatomical situs and classic position of chest wall leads, respectively. ECG = electrocardiogram; HHT = heterotopic heart transplantation.
It is likely that this rhythm was the same as that documented by the first single-lead ECG. Differences in signal amplitude were most likely related to ECG scaling and recording conditions in the prehospital setting (Figure 1).
Electrical cardioversion (360 J) restored a sinus rhythm (Figure 2).
Figure 2.
A 6-Lead Precordial Electrocardiogram Recorded After Restoration of a Sinus Rhythm
The native heart QRS complex shows a left bundle branch morphology (∗), whereas the donor heart shows a right bundle branch block morphology (→). The third and sixth beats represent fusion of native and donor QRS complexes.
Diagnostic evaluation
Coronary angiography of the donor heart revealed no epicardial stenosis. However, endomyocardial biopsy demonstrated intramyocardial arterial stenosis consistent with cardiac allograft vasculopathy. No acute rejection was detected.
Hospital course
Nosocomial pneumonia delayed implantable cardioverter-defibrillator (ICD) implantation. Twenty days later, sustained VT progressed to ventricular fibrillation in the donor heart. The patient initially remained conscious and hemodynamically compensated because the native heart maintained circulation—a situation impossible in single-heart physiology. After unsuccessful external defibrillation, urgent ICD implantation was performed. With amiodarone therapy, both hearts maintained a sinus rhythm. The patient was discharged in a stable condition under close cardiology observation and ICD monitoring. He died in 2004 from metastatic laryngeal cancer.
Discussion
To the best of our knowledge, this is the first case of a patient with HHT who has survived due to the function of their native heart only after experiencing documented VT of the donor heart.
Sustained ventricular arrhythmias occur in 15% to 20% of HHT recipients during long-term follow-up.2 Mechanisms are multifactorial: the native heart retains arrhythmogenic scar tissue, whereas the donor heart may develop allograft vasculopathy.4
Electrophysiological principles
Two simultaneous, distinct ECG rhythms demonstrate a fundamental principle: 2 distinct rhythms require 2 independent electrical sources. The surface ECG records the vectorial sum of electrical activity from both hearts simultaneously.
However, a differential diagnosis of wide complex tachycardia with a normal rhythm marching through has to consider artifacts.
Clinical management
Management requires both standard approaches and unique considerations. External cardioversion remains first-line treatment. However, efficacy may be reduced due to shielding effects from 2 hearts and extensive myocardial scarring creating high-impedance regions.
ICD therapy represents the definitive treatment for documented sustained ventricular arrhythmias.5 Antiarrhythmic therapy plays an adjunctive role, though drug interactions with immunosuppressive agents require careful monitoring.
Contemporary role of HHT: an emerging concept
Although modern mechanical circulatory support and heart-lung transplantation have reduced indications for HHT,3 interest has re-emerged, including its concept as a biological ventricular assist device and to address challenges in defining indications for clinical cardiac xenotransplantation and mitigating the risk of xenograft rejection.6,7
Conclusions
HHT provides a rare clinical model demonstrating core electrophysiological principles. The coexistence of native and donor arrhythmogenic substrates and technical challenges explains why HHT is now rarely performed.4 This case highlights the enduring relevance of fundamental electrophysiology in complex transplant cardiology.
Funding Support and Author Disclosures
The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
Acknowledgments
The authors thank Uwe Bindernagel, MD (Strausberg, Germany), for the courtesy of providing a copy of the single-lead emergency ECG, obtained at the patient’s home. They also thank Parwis Fotuhi, MD, PhD (Berlin, Germany), and Brunilda Alushi, MD, PhD (Munich, Germany), for support in writing the manuscript.
Footnotes
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the Author Center.
References
- 1.Hassoulas J., Barnard C.N. Heterotopic cardiac transplantation, a 7-year experience at Groote Schuur Hospital. S Afr Med J. 1984;65:675–682. [PubMed] [Google Scholar]
- 2.Loebe M., Hennig E., Muller J., Spiegelsberger S., Weng Y., Hetzer R. Long-term results after heart transplantation: experience with heterotopic and orthotopic methods. Thorac Cardiovasc Surg. 1995;43:247–252. [Google Scholar]
- 3.Cooper D.K., Novitzky D., Becerra E., Reichart B. Are there indications for heterotopic heart transplantation in 2004? Eur J Cardiothorac Surg. 2004;26:517–518. [Google Scholar]
- 4.Schmauss D., Weis M. Cardiac allograft vasculopathy: recent developments. Circulation. 2008;117:2131–2141. doi: 10.1161/CIRCULATIONAHA.107.711911. [DOI] [PubMed] [Google Scholar]
- 5.Könemann H., Ellermann C., Zeppenfeld K., Eckardt L. Management of ventricular arrhythmias worldwide: Comparison of the latest ESC, AHA/ACC/HRS, and CCS/CHRS Guidelines. JACC Clin Electrophysiol. 2023;9:715–728. doi: 10.1016/j.jacep.2022.12.008. [DOI] [PubMed] [Google Scholar]
- 6.Gaiotto F.A., Barbosa A.C.A.F., Tenório D.F., Steffen S.P., Jatene F.B. Heterotopic heart transplantation as a left ventricular biological assistance: a new two-stage method proposal. Braz J Cardiovasc Surg. 2020;35:986–989. doi: 10.21470/1678-9741-2020-0506. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Reichart B., Längin M., Denner J., Schwinzer R., Cowan P.J., Wolf E. Pathways to clinical cardiac xenotransplantation. Transplantation. 2021;105:1930–1943. doi: 10.1097/TP.0000000000003588. [DOI] [PubMed] [Google Scholar]