Human subpulmonary infundibulum has an endocardial network of specialized conducting cardiomyocytes

BACKGROUND The right ventricular outflow tract is the most common source of ventricular arrhythmias in nonstructural heart disease. Most of these arrhythmias are of endocardial origin, but their morphologic substrate is mostly unknown. OBJECTIVE The purpose of this study was to identify potential morphologic substrates for such arrhythmias originating within the right ventricular outflow tract. METHODS Three adult human hearts that had been fixed in 4% formaldehyde were examined. In 2 of the hearts, which were obtained subsequent to necropsies, the base of the anterior papillary muscle of the tricuspid valve was removed at the site of its fusion with the moderator band. The block of removed myocardium was submitted to routine histologic processing and sectioned at 5-mu m thickness. The free-standing subpulmonary infundibulum also was removed as a series of macroscopic preparations, which were sectioned in their short axis at 5-mu m thickness. The third heart was assessed using microcomputed tomography after it had been stained with 7.5% I2KI contrast agent for 14 days, with the contrast agent refreshed on the seventh day. RESULTS Specialized conducting cardiomyocytes from the base of the anterior papillary muscle to the supraventricular crest and subpulmonary infundibulum were identified and tracked using histology in 2 hearts and microcomputed tomography in the other. Transitional cells were also found at these sites. CONCLUSION The existence of such specialized cardiomyocytes within the infundibulum is of clinical significance because they could be the morphologic substrate for arrhythmias known to originate from these sites.