Estudio experimental de la llamada fase de relajación isovolumétrica del ventrículo izquierdo

Anatomical Correlation of the Helical Structure of the Ventricular Myocardium Through Echocardiography

INTRODUCTION AND OBJECTIVES

The helical structure of the ventricular myocardium provides a simple view of cardiac anatomy, based on physiological evidence that has been broadly demonstrated in experimental and imaging studies, and helps to explain the electromechanical contraction of the myocardium during the cardiac cycle. The aim of this study was to standardize and provide a detailed description of the technique for preparing and manually dissecting the myocardium proposed empirically by Torrent-Guasp. A further aim was to anatomically and topographically correlate the helical band with echocardiographic long-axis, short-axis, and 4-chamber projections.

METHODS

We dissected 42 hearts-20 bovine, 20 porcine and 2 human hearts-to standardize the myocardial dissection technique. Subsequently, the distinct segments were color coded to correlate the anatomical specimens with echocardiographic projections.

RESULTS

Loss of 38% of the myocardial mass after boiling was sufficient to standardize myocardial dissection and allowed an efficient technique. No morphological differences were found between the bands of the hearts studied. The 4 myocardial segments could be identified in the echocardiographic projections.

CONCLUSIONS

Standardization of the technique is useful to dissect any type of heart. Echocardiography is useful to assess the distinct segments that compose the myocardium. More research is needed to generate practical applications of this knowledge to echocardiography and other fields.

Myocardial Contraction during the Diastolic Isovolumetric Period: Analysis of Longitudinal Strain by Means of Speckle Tracking Echocardiography

BACKGROUND

According to the ventricular myocardial band model, the diastolic isovolumetric period is a contraction phenomenon. Our objective was to employ speckle-tracking echocardiography (STE) to analyze myocardial deformation of the left ventricle (LV) and to confirm if it supports the myocardial band model.

METHODS

This was a prospective observational study in which 90 healthy volunteers were recruited. We evaluated different types of postsystolic shortening (PSS) from an LV longitudinal strain study. Duration of latest deformation (LD) was calculated as the time from the start of the QRS complex of the ECG to the latest longitudinal deformation peak in the 18 segments of the LV.

RESULTS

The mean age of our subjects was 50.3 ± 11.1 years. PSS was observed in 48.4% of the 1620 LV segments studied (19.8%, 13.5%, and 15.1% in the basal, medial, and apical regions, respectively). PSS was more frequent in the basal, medial septal, and apical anteroseptal segments (>50%). LD peaked in the interventricular septum and in the basal segments of the LV.

CONCLUSIONS

The pattern of PSS and LD revealed by STE suggests there is contraction in the postsystolic phase of the cardiac cycle. The anatomical location of the segments in which this contraction is most frequently observed corresponds to the main path of the ascending component of the myocardial band. This contraction can be attributed to the protodiastolic untwisting of the LV.

Helical structure of the cardiac ventricular anatomy assessed by diffusion tensor magnetic resonance imaging with multiresolution tractography

INTRODUCTION AND OBJECTIVES

Deeper understanding of the myocardial structure linking the morphology and function of the heart would unravel crucial knowledge for medical and surgical clinical procedures and studies. Several conceptual models of myocardial fiber organization have been proposed but the lack of an automatic and objective methodology prevented an agreement. We sought to deepen this knowledge through advanced computer graphical representations of the myocardial fiber architecture by diffusion tensor magnetic resonance imaging.

METHODS

We performed automatic tractography reconstruction of unsegmented diffusion tensor magnetic resonance imaging datasets of canine heart from the public database of the Johns Hopkins University. Full-scale tractographies have been built with 200 seeds and are composed by streamlines computed on the vector field of primary eigenvectors at the diffusion tensor volumes. We also introduced a novel multiscale visualization technique in order to obtain a simplified tractography. This methodology retains the main geometric features of the fiber tracts, making it easier to decipher the main properties of the architectural organization of the heart.

RESULTS

Output analysis of our tractographic representations showed exact correlation with low-level details of myocardial architecture, but also with the more abstract conceptualization of a continuous helical ventricular myocardial fiber array.

CONCLUSIONS

Objective analysis of myocardial architecture by an automated method, including the entire myocardium and using several 3-dimensional levels of complexity, reveals a continuous helical myocardial fiber arrangement of both right and left ventricles, supporting the anatomical model of the helical ventricular myocardial band described by F. Torrent-Guasp.