The architecture of the ventricular mass and its functional implications for organ-preserving surgery

Abstract

It has generally been accepted that the myocardial fibres within the ventricular mass are arranged in syncytial fashion, precluding the identification of discrete and isolated muscular pathways. Recently, however, an entire hypothesis for surgical treatment has been proposed on the basis of the existence of a 'ventricular myocardial band', suggesting that this arrangement in itself points to detrimental results following partial ventriculectomy. In this review, we re-state the evidence supporting the accepted concept of the ventricular mass being made up of an undefined number of wedge-shaped functional units, each of them exerting its individually programmed contribution to the global activity of the ventricular walls. The wedge-shaped units consist of bundles of individual fibres which are arranged tangentially. An important subset of fibres intrudes into the ventricular wall, thus creating oblique pathways. Their angle of intrusion varies, and can be measured at up to 30 degrees . The steeper the angle of their intrusion, the more efficiently do the fibres counteract the systolic mural thickening. The network of supporting connective tissue, nonetheless, provides the necessary steep angulation towards the endocardium. This fibrous matrix serves as continuous chain for the transmission of forces, including that in the direction from the epicardium towards the endocardium, resulting in a dilating force. We have shown, using needle force probes, that in the hypertrophic heart the dynamic equilibrium of dilating and constricting forces acts at elevated diastolic and systolic levels, because the obliquity of the fibres increases due to the thickening of the wall, and there is a concomitant increase in connective tissue, causing an increase in the forces opposing systolic mural thickening. Then, in a vicious cycle, both populations of myocardial fibres stimulate each other to hypertrophy. Eventually, coronary perfusion becomes critically impaired, with still further deposition of connective tissue. Ultimately, the vector of the dilating force comes to dominate the constricting force, and the ventricle dilates. In this setting, partial left ventriculectomy remains a functionally sound intervention, since it is capable of improving global ventricular function by improving the geometrical state of the remaining anatomic myocardial units.