Morphological structure of the right ventricular outflow tract (RVOT) muscle including anatomical variations - clinical implications for electrocardiological procedures using autopsy material
Authors: Jakiel M , Holda M K , Jakiel R , Batko J , Dyngosz E , Kurek M , Gutkowska K , Bolechala F 
Published: November 2023

Abstract

Background/Introduction
The therapeutic effect of the electrocardiological procedure results not only from the correct supply of rhythm or conduction disturbances, but also from the avoidance of complications. The optimisation of the procedure is furthermore related to the efficient reaching of the target site and avoiding blockage of the used equipment by myocardial bridges or trabeculations.

Purpose
The purpose of our study was to evaluate in detail the right ventricular outflow tract (RVOT) muscle and to determine the types and extent of variation in this area.

Methods
We analysed 220 hearts (82 female, 37.2%) obtained during forensic medicine section from adult donors without structural heart disease. Collected hearts were fixed in 10% formaldehyde solution. The RVOT was opened by dissecting the muscle along its right periphery. The researchers assessed the presence and position of myocardial bridges, myocardial recesses and trabeculations. In addition, wall thickness and the presence of epicardial fat were assessed at 3 levels along the long axis of the RVOT at 4 points at each level. Linear dimensions were recorded using a precision electronic calliper by 2 different investigators. Statistical analyses were performed using STATISTICA 13.1.

Results
The presence of myocardial trabeculations covering the entire RVOT free wall was found in 72 hearts (35.5%), with 12 (5.90%) having a completely smooth wall. In the remaining 119 (58.6%), myocardial trabeculations covering the free wall partially were found. In the transition of the free wall to the posterior wall, trabeculations were found on the right and left periphery in 44 (21.6%) and 72 (35.6%) cases, respectively. At the same time, trabeculations were found in the middle part of the posterior wall in only 2 cases (1%). The RVOT recesses were found in 190 cases (92.2%), their number ranging from 1 and 6, with 3 being the most frequently found (26.7%). They were most frequently described on the left and right periphery (in 62.4%, 59.9% of hearts, respectively). Muscle bridges, running through the RVOT lumen, were localised within the left periphery in 109 cases (40.1%). RVOT muscle thickness ranged from 10.5 mm [5.24 mm] (median [IQR]) on the posterior wall, in the middle level, to 4.00 mm [1.36 mm] (mean [SD]), proximally, on the left periphery of the RVOT. The occurrence of epicardial adipose tissue ranged from 196 (96.1%) on the right periphery, in the middle part of the RVOT, to 102 [54.5%] proximally, on the anterior periphery.

Conclusions
The presence of myocardial bridges and RVOT recesses, while varying in their location and size, are factors that make full access difficult. The small thickness of the RVOT free wall in different regions suggests to consider wall perforation as a probable complication of the procedure, and the concomitant epicardial adipose tissue may be a factor explaining the subacute course of complications, including cardiac tamponade.