Systolic ventricular filling

Abstract

The evidence of the ventricular myocardial band (VMB) has revealed unavoidable coherence and mutual coupling of form and function in the ventricular myocardium, making it possible to understand the principles governing electrical, mechanical and energetical events within the human heart. From the earliest Erasistratus' observations, principal mechanisms responsible for the ventricular filling have still remained obscured. Contemporary experimental and clinical investigations unequivocally support the attitude that only powerful suction force, developed by the normal ventricles, would be able to produce an efficient filling of the ventricular cavities. The true origin and the precise time frame for generating such force are still controversial. Elastic recoil and muscular contraction were the most commonly mentioned, but yet, still not clearly explained mechanisms involved in the ventricular suction. Classical concepts about timing of successive mechanical events during the cardiac cycle, also do not offer understandable insight into the mechanism of the ventricular filling. The net result is the current state of insufficient knowledge of systolic and particularly diastolic function of normal and diseased heart. Here we summarize experimental evidence and theoretical backgrounds, which could be useful in understanding the phenomenon of the ventricular filling. Anatomy of the VMB, and recent proofs for its segmental electrical and mechanical activation, undoubtedly indicates that ventricular filling is the consequence of an active muscular contraction. Contraction of the ascendent segment of the VMB, with simultaneous shortening and rectifying of its fibers, produces the paradoxical increase of the ventricular volume and lengthening of its long axis. Specific spatial arrangement of the ascendent segment fibers, their interaction with adjacent descendent segment fibers, elastic elements and intra-cavitary blood volume (hemoskeleton), explain the physical principles involved in this action. This contraction occurs during the last part of classical systole and the first part of diastole. Therefore, the most important part of ventricular diastole (i.e. the rapid filling phase), in which it receives >70% of the stroke volume, belongs to the active muscular contraction of the ascendent segment. We hope that these facts will give rise to new understanding of the principal mechanisms involved in normal and abnormal diastolic heart function.

Left Ventricular Form and Function

“…Large animal model studies should be designed that demonstrate how multiple site pacing can modify electrical and mechanical activation sequences in the failing myocardium, reduce chamber dilatation and regional wall stress, and identify the cellular and extracellular mechanisms for these effects, including potential changes in interstitial proteins. Models such as that of Torrent-Guasp et al, 6 which proposes conduction along fiber orientation in a single muscular band and defies conventional concepts of activation, should be investigated.…”

Three-Dimensional Speckle-Tracking Imaging for Left Ventricular Rotation Measurement

“…1 Left ventricular twist may be related to the helical fiber orientation of the LV, which results in opposing rotational directions of the apex and the base and which determines the magnitude of this torsional deformation. 2,3 It has been proposed that LV twist is a sensitive marker of changes in both regional and global LV function. [4][5][6] Recently, efforts have focused on 2D speckle-tracking imaging (STI) to assess LVrot.…”

Right Ventricular Pacing and Mechanical Dyssynchrony

“…When viewed from the apex, fibers are arranged in a counter clockwise direction in the epicardium and a clockwise direction in the endocardium (Ashikaga et al 2004;Buckberg 2002;Torrent-Guasp et al 2004). The orientation of the myocardial fibers results in intricate three-dimensional motion during contraction and relaxation.…”

“…It is estimated that, as a result of these mechanics, the heart can generate an ejection fraction (EF) of 50% or more with a fiber shortening of only 15% (Buckberg 2002;Torrent-Guasp et al 2004). Maintaining this efficient pumping mechanism may be critical to ensuring proper cardiac function.…”

“…The helical structure of the fibers, and the twisting motion generated by the contraction of these fibers was described as early as the 1600's by Leonardo DaVinci (Geleijnse and van Dalen 2009). The more recent work of Torrent-Guasp and others has led to renewed appreciation for the relationship between cardiac structure and function, and the importance of LV rotational motion on systolic and diastolic performance (Torrent-Guasp et al 2004). …”