Dissecting the Cardiac Conduction System: Is It Worthwhile?

Abstract

Background Pathologic examination of conduction system (CS) is not routinely performed, and histologic changes are mostly reported in forensic practice. Methods We studied the value of dissecting the CS in a cohort of pediatric patients with unexplained sudden death or severe, inexplicable arrhythmias. Histopathologic changes present in CS components were recorded and correlated with findings noted in other cardiac structures. Results Twenty-one subjects (11 unexplained sudden deaths and 10 life-threatening arrhythmias) were identified; 18 (86%) had CS pathologic abnormalities. In 13 patients (62%), the CS findings mirrored those found in other cardiac sections (inflammation, allograft vasculopathy, vascular fibromuscular dysplasia, cardiomyopathy-related changes, and tumor/tumor-like conditions). Five cases (24%) had abnormalities restricted to CS (bundle of His [BH] with fibrotic scar and patch material following ventricular septal defect repair, inflammation, BH with fibrosis and calcifications, and intimal fibroplasia of sinoatrial node artery). Conclusions Pathologic changes within the CS are present in a high number of pediatric patients presenting with unexplained sudden death or life-threatening arrhythmias. Frequently, the findings mirror those observed in other cardiac structures. However, in a significant number of cases (24%), the changes are restricted to CS and likely explain the patients’ symptoms or cause of death, suggesting that systematic dissection of CS unveils valuable information.

Lesions of the Cardiac Conduction System and Sudden Death

“…As mentioned in section 4, Burke et al 20 reported a patient who had a cardiac hemangioma that replaced the AV node. An 8-month-old infant with extensive histiocytoid cardiomyopathy had her AV node replaced by the lesion and presented with Wolff-Parkinson-White syndrome 37 …”

“…Duchenne and Becker muscular dystrophy are characterized by mutations in the dystrophin gene on the X chromosome. Dystrophin is located in the Purkinje cells and its absence causes abnormal conduction and replacement of the Purkinje cells by fat or fibrous tissue 37,51,66 …”

“…Postsurgical heart block can occur from fibrotic scarring associated with patch material after ventricular septal defect repair 37 . Other causes of iatrogenic heart block include aortic valve surgery, septal alcohol ablation, percutaneous coronary artery procedures, or electrophysiological ablation of the region of the AV node may cause CHB 66 …”

“…Song et al 63 reported that half of their series of 150 autopsied cases had calcification of the central fibrous body, the membranous septum, and summit of the muscular interventricular septum, with 7 patients having calcific compression of the AV node, His bundle, or bundle branches. Congenital AV block due to maternal lupus has associated calcification of the AV node and His bundle 37,54,57 . Lev disease can initiate AV block by calcification of the proximal portion of the bundle branches 67…”

“…Numerous miscellaneous causes of AV block have been reported and are too numerous for a detailed discussion. These include but are not limited to infectious (myocarditis, protozoal infections, Rickettsia, bacterial, including Lyme disease, Trypanosomal infection [Chaga disease], viral myocarditis), posttransplant vasculopathy, and histiocytoid cardiomyopathy with involvement of the conduction system 37,66 . Other causes include radiation, 68,69 immune checkpoint inhibitors, for example, nivolumab, 70 and endocardial fibroelastosis 37 .…”