Longitudinally and circumferentially directed movements of the left ventricle studied by cardiovascular magnetic resonance phase contrast velocity mapping

Abstract

Objective: Using high resolution cardiovascular magnetic resonance (CMR), we aimed to detect new details of left ventricular (LV) systolic and diastolic function, to explain the twisting and longitudinal movements of the left ventricle.

Methods: Using CMR phase contrast velocity mapping (also called Tissue Phase Mapping) regional wall motion patterns and longitudinally and circumferentially directed movements of the left ventricle were studied using a high temporal resolution technique in healthy male subjects (n = 14, age 23 +/- 3 years).

Results: Previously undescribed systolic and diastolic motion patterns were obtained for left ventricular segments (based on the AHA segmental) and for basal, mid and apical segments. The summation of segmental motion results in a complex pattern of ventricular twisting and longitudinal motion in the normal human heart which underlies systolic and diastolic function. As viewed from the apex, the entire LV initially rotates in a counter-clockwise direction at the beginning of ventricular systole, followed by opposing clockwise rotation of the base and counter-clockwise rotation at the apex, resulting in ventricular torsion. Simultaneously, as the entire LV moves in an apical direction during systole, the base and apex move towards each other, with little net apical displacement. The reverse of these motion patterns occur in diastole.

Conclusion: Left ventricular function may be a consequence of the relative orientations and moments of torque of the sub-epicardial relative to the sub-endocardial myocyte layers, with influence from tethering of the heart to adjacent structures and the directional forces associated with blood flow. Understanding the complex mechanics of the left ventricle is vital to enable these techniques to be used for the evaluation of cardiac pathology.

Figure 1

Circumferential velocity graphs for LV segments according to the AHA segment model (segments 1-6 are basal, 7-12 midventricular and 13-16 apical). The graphs represent the average values of all volunteers. Positive values show clockwise rotation as viewed from the apex, whilst negative values represent counter-clockwise rotation. Phases of the cardiac cycle: 1 - isovolumetric contraction, 2 - rapid ejection, 3 - reduced ejection, 4 - isovolumetric relaxation, 5 - rapid filling, 6 - diastasis, 7 - atrial systole, ED - end diastole, ES - end systole.

Figure 2

Average longitudinal and circumferential velocities for the left ventricular base, mid and apex. The entire LV rotates counter clockwise (as viewed from the apex), followed by a series of clockwise and counter clockwise motion patterns, leading to opposing directions of apical and basal motion during a cardiac cycle. In all slices, longitudinal motion of the heart is towards the apex during systole and towards the base during diastole.

Figure 3

Global LV torsion rate during a cardiac cycle. Ventricular torsion reflects the base to apex gradient resulting from the twisting motion of the ventricle, whilst the torsion rate reflects the speed at which this twisting motion occurs. The entire ventricle rotates counterclockwise at the beginning of systole, resulting in little gradient between the LV base and apex, with the torsion rate close to zero (a). Subsequently, as the LV base rotates in a clockwise direction, the ventricular torsion rate increases, reaching its peak value at the end of rapid ejection (b). Then, as the clockwise velocities of the ventricular base fall during the phase of reduced ejection, the ventricular torsion rate similarly declines. Repolarization was followed by a sudden onset of ventricular untwisting, reflected in a negative ventricular torsion rate (c). Subsequent smaller negative waves of the ventricular torsion rate (d, e, f) likely correspond to slightly different peaks of ventricular untwisting at the LV base and apex.

Figure 4

Longitudinal velocity graphs for LV segments according to the AHA segment model (segments 1-6 are basal, 7-12 midventricular and 13-16 apical). The graphs represent the average values of all volunteers. Positive values show downward movement along longitudinal axis (towards the ventricular apex), while negative values reflect upward displacement. Waves a to g - see text for ventricular motion description, 1 - isovolumetric contraction, 2 - rapid ejection, 3 - reduced ejection, 4 - isovolumetric relaxation, 5 - rapid filling, 6 - diastasis, 7 - atrial systole, ED - end diastole, ES - end systole.

Figure 5

LV longitudinal strain rate during a cardiac cycle. Positive strain rate values correspond to LV lenthening, where negative values indicate LV shortening. This figure demonstrates a progressive rate of longitudinal shortening with the onset of rapid ejection (phase 2), followed by a relatively constant shorthening rate throughout the rest of the rapid and reduced ejection phases. Ventricular repolarizatioin was followed by a sudden drop in longitudinal shortening with a subsequent peak of longitudinal lenthening in early diastole. a - peak systolic longitudinal strain rate, b - sudden drop in longitudinal shortening rate after repolarization, c - peak diastolic longitudinal strain rate.

Figure 6

Schematic representation of the spiraling orientation of cardiomyocytes, forming a three-dimensional mesh supported by the heart's fibrous matrix. A - cross-section, B - anterior heart surface, C - posterior heart surface, 1 - outer surface aggregates extending from the left ventricle to the anterior heart surface, 2 - outer surface aggregates limited to the LV wall, 3 - outer surface aggregates extending to the posterior heart surface, Ao - aorta, PA - pulmonary artery, LA - left atrium, RA - right atrium, LV - left ventricle, RV - right ventricle.