EXPLANATION


Dysrhythmia following orthotopic heart transplantation (OHT) occurs in approximately 40% of pediatric recipients. Factors predisposing to dysrhythmia are multifactorial. One contributing factor relates to unopposed sympathetic tone secondary to donor heart denervation. Denervation leads to a lack of response to the modulating influence of the vagus nerve and to the higher baseline heart rate. Surgical techniques employed for orthotopic heart transplantation have also been implicated in the development of dysrhythmia. The biatrial technique preserves part of the recipient’s right and left atrial tissue to facilitate the incorporation of the cardiac graft. The bicaval technique incorporates a cuff of the recipient’s left atrial tissue. Scarring of the atria creates a predisposition to atrial flutter. In the biatrial method, P waves may be generated from both the cardiac graft and native atrial tissue which mimics atrial flutter. Additionally, sinus node activity from native atrial tissue may be conducted intermittently and thus manifest as ectopic atrial beats. As cuffs of atrial tissue are preserved in both techniques, all patients are expected to develop some degree of increased atrial size after OHT. Other factors which contribute to the risk of dysrhythmia after OHT include prolonged graft ischemic time, donor-recipient size mismatching (which contributes to atrial enlargement), acute and chronic rejection, and cardiac allograft vasculopathy.


Atrial fibrillation and atrial flutter have been reported in 10% to 25% of patients after OHT with the majority of cases occurring in the first few weeks after transplantation and with eventual resolution in the majority of patients. Bradydysrhythmias occurring after OHT (which also frequently resolve spontaneously) include atrioventricular block and sinus bradycardia. Common causes include sinus node injury or ischemia, sympathetic denervation, and medication side effects.


Temporary pacing for bradydysrhythmia is often utilized following OHT while the cardiac conduction system recovers from injury. Rarely, when normal cardiac conduction does not return, consideration of permanent pacemaker implantation is necessary. The 2021 PACES expert consensus on pediatric cardiovascular implantable electronic devices recommends waiting at least one week for spontaneous recovery of sinus node function.


A systematic review of 11 studies by Mylonas et al. which included a total of 7,198 pediatric patients who underwent heart transplantation demonstrated that 1.9% of patients received a permanent pacemaker. However, although overall sinus node dysfunction was the most frequent indication for pacemaker placement (54.4% versus 45.6% for complete atrioventricular block), in almost half of the cases there was no indication reported. The need for pacemaker placement occurred earlier in the postoperative course in patients with complete atrioventricular block. The median time interval between OHT and permanent pacemaker implantation ranged from 17 days to 6.5 years in patients with complete heart block while it was 2.7 months to 12.5 years for sinus node dysfunction. The biatrial technique was utilized in 62.2% of patients and the bicaval technique in the remaining 37.8%.


In a single-center study by Mahmood et al., of 314 pediatric transplant recipients, 16 (5.1%) patients required permanent pacemaker placement. Indications for pacemaker placement were complete heart block in 75% of patients and sinus node dysfunction in 25% of patients. In 9 of 12 (75%) patients with complete heart block, the pacemaker was implanted within 21 days of the transplant. Three out of the four patients with sinus node dysfunction had pacemaker implantation at 61 days or longer after transplant.


The patient described in the question stem has undergone OHT two weeks prior without restoration of normal sinus rhythm and is most likely to have persistent complete atrioventricular block given the described time frame. Although symptomatic sinus bradycardia and second degree Mobitz Type II heart block can occur, they either resolve or persist to meet the indication for permanent pacemaker implantation at a later timepoint as compared to complete heartblock. At this early stage after OHT, close evaluation is important to rule out reversible causes of bradydysrhythmia such as acute rejection or antiarrhythmic medication side effects.


REFERENCES


Navas-Blanco JR, Modak RK. Perioperative care of heart transplant recipients undergoing non-cardiac surgery. Ann Card Anaesth. 2021;24(2):141-148 doi: 10.4103/aca.ACA_130_19.


Joglar JA, Wan EY, Chung MK, et al. Management of arrhythmias after heart transplant: current state and considerations for future research. Circ Arrhythm Electrophysiol .2021;14(3):e007954. doi: 10.1161/CIRCEP.120.007954.


Shah MJ, Silka MJ, Silva JNA, et al. 2021 PACES expert consensus statement on the indications and management of cardiovascular implantable electronic devices in pediatric patients. Cardiol Young. 2021;31(11):1738-1769. doi:10.1017/S1047951121003413


Mylonas KS, Repanas T, Athanasiadis DI, et al. Permanent pacemaker implantation in pediatric heart transplant recipients: A systematic review and evidence quality assessment. Pediatr Transplant. 2020;24(3):e13698. doi: 10.1111/petr.13698.


Mahmood A, Andrews R, Fenton M et al. Permanent pacemaker implantation after pediatric heart transplantation: Risk factors, indications, and outcomes. Clin Transplant .2019;33(4) e13503. doi: 10.1111/ctr.13503.


Herrmann FEM, Wellmann P, Hagl C, Juchem G. Pediatric heart transplantation-What are the risk factors for pacemaker implantation and how much pacing is required? Pacing Clin Electrophysiol. 2018;41(3):267-276. doi: 10.1111/pace.13276.