Interdigitating Myocardial Tongues in Pediatric Cardiac Fibromas:: Plausible Substrate for Ventricular Tachycardia and Cardiac Arrest

Abstract Objectives This study sought to evaluate for the presence of and characterize the interdigitating and entrapped myocardium within cardiac fibromas (CF) and correlate tissue findings with symptoms and surgical outcomes. Background The mechanism of ventricular tachycardia (VT) in CF is unclear. The authors hypothesized that CF harbor tongues of interdigitating myocardium, which could be a substrate for episodes of arrhythmia analogous to peri-infarct zones. Methods A total of 29 patients (14 boys) with CF were identified; all subjects had undergone at least partial tumor resection. A semiquantitative grading system was used to assess the degree of myocardial interdigitation and entrapment, myocyte morphology (hematoxylin and eosin stain and immunohistochemical stain for desmin), tumor collagen density, and cellularity (trichrome stain). The subjects’ ages at presentation, types of arrhythmia, and responses to surgery were correlated with histology. Results CF consistently demonstrated interdigitating and entrapped myocardium, and the extent correlated negatively with age at surgery, as did cellularity, whereas collagen increased with age. Median age at arrhythmia recognition was 8 months. Sustained VT was present in 18 of 29 patients (62%), and 5 of 6 patients with prenatally diagnosed conditions developed VT before 8 months. All 8 patients who experienced cardiac arrest had clinically significant arrhythmia events. Sustained arrhythmia episodes correlated with more diffuse myocyte interdigitation. Ten patients had abnormal karyotype: chromosomes 9 (n = 3) and 3 (n = 1) deletions; isolated translocations: t(4;13), t(5;11) and t(1;9); and undefined aberrations (n = 3). All patients who underwent complete resection were cured of arrhythmias, whereas 2 of 14 patients who had subtotal resections had recurrence, with resolution following re-resection in 1 patient. Conclusions Interdigitating myocardium represents a potential histopathologic substrate for VT and cardiac arrest in CF, which may also explain the occasional recurrence of arrhythmia following incomplete resection.