A storm in the desert: Ablation of a left atrial tachycardia in a heart transplant recipient

Atrial tachycardia (AT) after heart transplantation occurs in nearly 10% of orthotopic heart transplant recipients, with atrial flutter (AFL) being the most common.1Vaseghi M. Boyle N.G. Kedia R. et al.Supraventricular tachycardia after orthotopic cardiac transplantation.J Am Coll Cardiol. 2008; 51: 2241-2249Crossref PubMed Scopus (90) Google Scholar,2Joglar J. Wan E.Y. Chung M.K. et al.Management of Arrhythmias After Heart Transplant.Circ Arrhythm Electrophysiol. 2021; 14e007954https://doi.org/10.1161/CIRCEP.120.007954Crossref Scopus (12) Google Scholar However, AT may occur in the recipient as well as in the donor atria. Catheter ablation of these ATs is an effective treatment, but can result challenging because of the complexity of atrial scar and distorted atrial anatomy and substrate. A 65-year-old man was referred for catheter ablation of recurrent symptomatic atrial tachycardia. Twelve years earlier, owing to nonischemic dilated cardiomyopathy, he underwent orthotopic cardiac transplant with a standard biatrial anastomosis technique. The patient had a known right bundle-branch block intra-ventricular electrical conduction delay and no history of significant rejection, tachy-arrhythmia, sinus node dysfunction or atrioventricular block. The twelve-lead electrocardiogram (ECG) obtained during arrhythmia suggested the diagnosis of AT/AFL (Figure, panel A). Transthoracic echocardiography showed no systolic dysfunction. The coronary angiography did not reveal any sign of cardiac allograft vasculopathy and the histological analysis of multiple ventricular endomyocardial biopsies resulted normal. Owing to the recurrence of the tachyarrhythmia despite two electrical cardioversions and antiarrhythmic drug therapy with amiodarone, flecainide and beta blocker, an electrophysiological study was indicated. The pattern of atrial activation recorded with a 6 French 10-pole catheter positioned inside the coronary sinus during tachycardia suggested the presence of a septal/left-sided tachycardia circuit (Figure, Panel B), then confirmed by the electro-anatomic map of the right atrium performed with a close-spaced, multipolar steerable catheter (PentaRay NAV®, Bionsense Webester Inc, 2 mm interelectrode spacing distance, 1 mm electrode size). After left atrial (LA) access was obtained by means of intracardiac echography-guided transeptal puncture, a detailed high-density mapping of both native and donors’ LA cuffs was performed using the PentaRay catheter. The anterior wall of the donor’s atrium showed extensive low-voltage areas whereas low-amplitude complex atrial fractionated electrograms corresponding to an area of slow conduction were identified along the anastomotic suture line connecting the donor's LA with the remnants of recipient’s LA (Figure, panel C and Supplementary Figure S1) while no sign of electrical activity was detected in the massively enlarged recipient’s LA (Figure, panel D). The electrical activation map of the donor’s LA cuff was consistent with the presence of a clockwise macro-reentrant tachycardia with a protected isthmus along the LA suture lines by the roof (Supplementary Figure S2, Video). Radiofrequency ablation was then delivered using a 3.5-mm irrigated-tip catheter (ThermoCool Smart Touch® D-F, Bionsense Webester Inc, maximum power 35 Watts, Ablation Index target 500) in the donor’s LA cuff in its antero-septal superior aspect, where a linear lesion was deployed in a caudo-cranial fashion (Supplementary Figure S1, red dots) obtaining slowing of AT cycle length and eventually sinus rhythm restoration (Supplementary Figure S3). During a 1-year follow-up period the patient remained free of symptoms and maintained stable sinus rhythm as documented with periodic ECGs and 24-hour Holter monitoring, without any anti-arrhythmic medication. In heart transplant recipients atrial fibrillation is rarely seen (although associated with a poor prognosis) 3Ferretto S. Giuliani I. Sanavia T. et al.Atrial fibrillation after orthotopic heart transplantation: pathophysiology and clinical impact.IJC Heart & Vasculature. 2021; 32100710Crossref Scopus (3) Google Scholar and typical counterclockwise cavotricuspid isthmus-dependent right atrial flutter represents the most frequent atrial arrhythmia,1Vaseghi M. Boyle N.G. Kedia R. et al.Supraventricular tachycardia after orthotopic cardiac transplantation.J Am Coll Cardiol. 2008; 51: 2241-2249Crossref PubMed Scopus (90) Google Scholar,2Joglar J. Wan E.Y. Chung M.K. et al.Management of Arrhythmias After Heart Transplant.Circ Arrhythm Electrophysiol. 2021; 14e007954https://doi.org/10.1161/CIRCEP.120.007954Crossref Scopus (12) Google Scholar but more complex ATs may be encountered as well. In the latter case, a thorough understanding of the surgical anatomy with a clear illustration of the scar substrate and electrical activation patterns by 3-dimensional high-density electroanatomic mapping may allow to identify the mechanisms of these often-complex ATs and help to achieve a successful ablation outcome. In our patient a subtle form of graft dysfunction (i.e., confined only to the atrial tissue) may had underlain the development of diffuse patchy scars which acted as the pro-arrhythmic substrate. In this scenario, the proposed mechanism of arrhythmia is that the presence in the donor’s atrium of both tissue (e.g., patchy scars) and electrical (e.g., anisotropic conduction or refractory period inhomogeneity) abnormalities could have played a role in the development of the pro-arrhythmic substrate. At a macroscopic scale, the diseased tissue embedded in the donor’s atrial cuff constituted part of the AT macro-reentrant circuit, while the suture lines by the roof and the surrounding atrial tissue harbored a protected isthmus of the AT. Targeting the latter area with the ablation lesions terminated the tachycardia. Schratter et al reported the case of a patient with three different macroreentrant right atrial tachycardias running at the same time, which were mapped by means of a high-density mapping linear catheter; notably, in this patient the donor’s and recipient’s atria were electrically dissociated. 4Schratter A. Schirripa V. Kosiuk J. et al.Electroanatomical high-density mapping of different tachycardias in the right atrium after heart transplantation.Hear Case Rep. 2016; 2: 517-520Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar Shi and colleagues offered a review of the existing literature and described the case of a patient who underwent orthotopic heart transplant with biatrial anastomosis technique and developed multiple ATs: a focal one arising from donor’s right atrium, another microreentrant AT in the donor’s LA and a macroreentrant perimitral AFL. All these arrhythmias were successfully ablated after careful high-density mapping. 5Shi R. Chen Z. Mantziari L. et al.Multiple atrial tachycardias after orthotopic heart transplantation: a case report and literature review.Heart Rhythm Case Reports. 2018; 4: 538-541Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar While in the above-mentioned reports electrical dissociation between donors’ and recipient’s atria was described, strikingly in our case any electrical activity in the massively enlarged recipient’s atrial cuff was completely absent and the AT circuit was confined to the relatively small donor’s anterior atrial wall. Moreover, the patient’s complex electrical atrial activity and AT circuit would have been impossible to ascertain in detail without the use of a high-density mapping catheter: electrical signals with very small amplitude were barely detected with the Pentaray catheter even with the gain set to the highest values and would have otherwise been missed using a conventional mapping catheter (e.g., with greater interelectrode spacing distance or electrode sizing) or the ablation catheter (Supplementary Figure S1). This case report highlights the value of using a multipolar high-density mapping catheter for high-resolution mapping of extremely diseased atrial tissues, where very low-amplitude electrical signals can be missed, especially when, as in this case, large amounts of unexcitable tissue due to extensive scar are present.