Assessment of the Helical Ventricular Myocardial Band Using Standard Echocardiography

Abstract

n the discussion of their recent article, Hayabuchi and his colleagues[1] acknowledge that the “helical myocardial band” remains controversial. In the accompanying editorial, Buckberg harbored no such doubts.[2] Are the limited echocardiographic findings illustrated truly sufficient for Hayabuchi and his colleagues to conclude that there is a “helical ventricular myocardial band”?[1] They refer to a model that Torrent-Guasp had carved out of the ventricular muscular mass by disrupting myriads of myocardial branches, suggesting moreover that this band is freely moveable on itself. The histological studies produced by Hort[3] and Feneis,[4] however, provided evidence that the ventricular cone does not have discrete origins and insertions of the cardiomyocytes as found in skeletal muscle. Pettigrew had demonstrated more than a century ago[5] the multiple interleaving sheets of cardiomyocytes to be found within the cone. Lev and Simkins,[6] cited by Buckberg, also had emphasized that the cone can be dissected at the whim of the prosector, as achieved by Torrent-Guasp when subjectively producing the preparations now modeled by Buckberg.[7] Our investigations, cited by Hayabuchi and colleagues,[1] endorse the works of Feneis[3] and Hort.[4] The histological findings show no obvious anatomical substrate, other than the obvious change in alignment of the aggregated chains of cardiomyocytes, to explain the echocardiographic feature emphasized by the Japanese workers. They certainly provide none that represent a substantial proportion of the width of the septum, as the echocardiograms seem to suggest. The echogenic band is seen in the equatorial and basal regions of each of the walls of the left ventricle when viewed from the apex. No such band is seen when the ventricular mass is viewed using the parasternal window. We suggest that the echogenic band represents an area of distinct myocyte orientation within the continuous mesh of the septum, where the reflected ultrasound is perpendicular to the dominant orientation of the cardiomyocytes, thus giving maximum intensity compared with the surrounding tissue. The echogenic band, when viewed from the apex, therefore, is likely to represent no more than the chains of cardiomyocytes located within the mid-wall of the ventricular cone which are aligned circumferentially. The concept of the helical ventricular myocardial band does not model the circumferential orientation in this region.

There are further problems, however, with the concepts advanced by Buckberg,[2] His inferences are based on imaging systems that measure only strain, as opposed to assessing the local development of force. The onset of shortening is not identical with the onset of contraction, so it is his mistake to interpret late shortening as delayed contraction. We have shown that within the ventricular cone, there are extended zones in which the myocardium contracts auxotonically, that is, the force increases during systole.[8] The features of such auxotonic contraction are delayed onset, restricted shortening, and delayed termination.