Cardiac Helical Function. Fulcrum and Torsion

Background: The aim of this study was to investigate a) the starts and ends of the continuous myocardium; b) the slippage between the myocardial segments, when performing both torsion and ventricular detorsion, implies that there should be an antifriction mechanism that avoids dissipating the energy; c) the electrical activation of the endocardial and epicardial myocardium and secondarily understand ventricular twist and the mechanism of active suction during the diastolic isovolumic phase.
Methods: Twenty-four hearts were used: a) Fitteen two-year-old bovine hearts weighing 800-1000 g; b) nine human hearts (two 16- and 23- week gestation embryos, one from a 10-year-old child weighing 250 g and six from adults, with an average weight of 300 g); b) five patients with no structural cardiac abnormalities and normal QRS complexes underwent three-dimensional endoepicardial electroanatomic mapping.
Results: We have found in all the bovine and human hearts studied a nucleus (fulcrum) underlying the right trigone, whose osseus, chondroid or tendinous histological structure depends on the specimen analyzed. All the hearts studied presented myocardial attachment to the rigid structure of the fulcrum. Hyaluronic acid was found in the cleavage planes between the myocardial bundles. Endo-epicardial mapping demonstrates an electrical activation sequence in the area of the apex loop in agreement with the synchronic contraction of the descending and ascending band segments, consistent with the mechanism of ventricular twist. The late activation of the ascending segment is consistent with its persistent contraction during the initial period of the isovolumic diastolic phase (the basis of the suction mechanism).
Conclusions: The finding of the fulcrum gives support to the spiral myocardial band being the point of fixation that allows the helical torsion. The hyaluronic acid would act as a lubricant and provide great resistance to mechanical pressures. This study explains the ventricular twist and the active suction mechanism during the isovolumic diastolic and early ventricular filling phases.

Keywords:Cardiac anatomy; Ventricular band; Fulcrum; Friction; Hyaluronic Acid; Heart/physiology; Cardiac Electrophysiology

Abbreviations:TEM: Three-dimensional Electroanatomical Mapping; MS: Milliseconds; LVEF: Left Ventricular Eyection Fraction; LV: Left Ventricle