Study Participants

The study population consisted of 142 healthy volunteers. All provided informed consent, as established by the Research Ethics Board at the University of Alberta. Inclusion criteria were age range between 3 and 40 years, normal blood pressure, normal electrocardiographic and transthoracic echocardiographic results, and ability to cooperate for the study. Subjects were divided into 5 subgroups by age: group 1, 3 to 9 years; group 2, 10 to 16 years; group 3, 17 to 24 years; group 4, 25 to 32 years; and group 5, 33 to 40 years ( Table 1 ).

Echocardiography

Two LV short-axis planes obtained at the basal and the apical levels were acquired using a Vivid 7 machine (GE Healthcare, Milwaukee, WI) with an M5 or M4S probe at 75 to 125 frames/s. At each plane, 3 consecutive cardiac cycles were acquired during a breath hold at end-expiration. In younger children, 3 cardiac cycles at end-expiration on the respiratory trace were selected.

Terminology

Rotation is clockwise or counterclockwise movement around the long axis of the heart. Counterclockwise rotation is displayed as positive when viewed from the apex. Torsion or twist is the net difference between apical and basal rotation (apex − base). Recoil is the opposite movement to rotation at the apical and basal slice. Untwisting (negative torsion) is the opposite direction to torsion.

LV Rotation and Rotational Rate

The onset of the Q wave on the electrocardiogram and aortic valve closure and mitral valve opening (MVO) were measured using M-mode echocardiography with a simultaneous cursor through each valve at end0expiration. From the basal and apical short-axis data, one cardiac cycle at a time was selected for subsequent analysis. Using EchoPAC version 4.03 (GE Healthcare), the endocardial border of each short axis in the end-systolic frame was manually traced. A region of interest was then drawn to include the whole myocardium. The software automatically segmented the LV short axis into 6 segments and selected suitable speckles for tracking. Individual regional tracking was scored with a value of 1 (excellent), 2 (acceptable), or 3 (poor). The assessment of LV rotation was regarded as feasible when all or >5 segments were “passed” with a score of 1. Finally, software defined the ventricular centroid for the midmyocardial line on each frame and calculated the time domain LV rotation and LV rotational rate profiles for each segment in both short-axis planes. Averaged LV rotation and rotational rate profiles from 6 segments were used for the calculation of LV torsion.

Measurements

Raw speckle locations were read into a custom software package (MATLAB; The MathWorks, Inc, Natick, MA) to allow consistent calculation of all parameters and normalization of the time course for all subjects to the duration of systole (ie, at the onset of the QRS wave [ t = 0%] and at end-systole [ t = 100%]). End-systole and MVO were determined from the M-mode images as described above.

The centroid of each short-axis set of speckles was calculated for each time frame and used for all subsequent rotation measurements for that slice. Rotation was calculated for each speckle location and averaged for all circumferential positions to calculate the mean rotation. The rotation curves from 3 cardiac cycles were averaged to arrive at a final mean rotation time course for both apical and basal slices. To account for variations in heart rate, the shortest of the combined cardiac cycles was used to determine the final cardiac cycle duration.

Parameters Reflecting Predominantly Systolic Events

A total of 3 parameters were measured (numbers in parentheses refer to curves in the corresponding figures): peak basal rotation in early systole (1), peak negative basal rotation (2), and peak apical rotation (3) ( Figure 1 ). Following this, peak torsion (4) was measured. Maximal (5) and minimal (6) peak rotation rates were measured at the basal level ( Figure 2 ). At the apical slice, the peak systolic rotation rate was measured (7). The peak torsion rate (8) was also measured. Torsion was normalized for end-diastolic length, the latter measurement being obtained from an apical 4-chamber view. The measurement was made from the center of a horizontal line connecting the hinge points of the mitral valve and the apex.

LV torsion (LVTor) and rotation (LVrot) profile curves. The blue line indicates LV torsion. The red and green lines indicate apical and basal level rotation. Arrows indicate peak values. 1 = basal rotation at early systole, 2 = basal rotation, 3 = apical rotation, 4 = torsion. AoVC , Aortic valve closure; AoVO , aortic valve opening.

LV torsion (LVTor) rate and rotation (LVrot) rate profile curves. The blue line indicates LV torsion rate. The red and green lines indicate apical and basal level rotation rate. Arrows indicate peak values. 5 = basal rotation rate at early systole, 6 = basal rotation rate, 7 = peak apical systolic rotation rate, 8 = peak torsion rate, 9 = maximal basal recoil rate, 10 = minimal basal recoil rate, 11 = peak untwisting rate. AoVC , Aortic valve closure; AoVO , aortic valve opening.

Parameters Reflecting Predominantly Diastolic Events

During early diastole, maximal basal (9) and minimal apical recoil rate (10) were measured ( Figure 2 ), as was peak untwisting rate (11). The degree of untwisting (negative torsion) at MVO and 120% of systole were chosen because these would account for the major components of early diastole.

Pulsed-Wave Doppler

The mitral inflow E wave, A wave, E/A ratio, and isovolumic relaxation time were calculated.

Statistical Analysis

Data are expressed as mean ± SD. All group differences were assessed using one-factor analysis of variance with post hoc comparison. The correlation between age and each value was evaluated by both linear and nonlinear regression. Interobserver and intraobserver measurement variability was determined by measuring LV torsion, LV torsion rate, and percentage untwisting at early diastole in 10 randomly selected volunteers >1 month apart.

Feasibility

Five volunteers did not meet inclusion criteria and were excluded, as were 26 with inadequate data at both basal and apical slices. Of the remaining 111, 91 had adequate data for both apical and basal slices, 16 for only the basal slice, and 4 for only the apical slice. All data with >5 passed segments at each slice had an excellent tracking score of 1.0.

LV Systolic Events

LV Torsion and Rotation Pattern

Peak torsion increased with advancing age because of the augmentation of the apical LV rotation but disappeared when normalized by length ( Table 2 , Figure 3 A ). Basal negative LV rotation was not correlated with increasing age unless normalized by LV length when it decreased, with a minimal value at approximately 25 years of age. The LV basal slice demonstrated a unique counterclockwise rotation at early systole, which decreased with advancing age and was enhanced when normalized by the LV length.

Table 2

Systolic profile

	Group 1 (3-9 y)	Group 2 (10-16 y)	Group 3 (17-24 y)	Group 4 (25-32 y)	Group 5 (33-40 y)
Variable	(n = 29)	(n = 24)	(n = 15)	(n = 20)	(n = 20)	P
Peak torsion (°)	10.0 ± 3.3	12.2 ± 4.3	11.7 ± 4.3	13.2 ± 13.9	14.2 ± 3.1	<.05
Normalized peak torsion (°/cm)	1.67 ± 0.51	1.63 ± 0.32	1.45 ± 0.27	1.61 ± 0.50	1.81 ± 0.38	NS
Peak torsion rate (°/s)	84.5 ± 24.1	88.8 ± 31.2	72.1 ± 29.5	62.5 ± 17.4	73.9 ± 24.6	NS
Normalized torsion rate (°/cm/s)	14.2 ± 18.5	12.1 ± 4.7	8.9 ± 3.2	7.7 ± 2.4	9.4 ± 3.2	<.001
Apical rotation (°)	6.5 ± 2.3	8.5 ± 3.1	8.5 ± 3.3	8.9 ± 3.5	10.1 ± 1.9	<.05
Normalized apical rotation (°/cm)	1.1 ± 0.3	1.2 ± 0.4	1.1 ± 0.4	1.1 ± 0.4	1.2 ± 0.2	NS
Apical rotation rate (°/s)	68.1 ± 28.4	65.4 ± 26.8	57.8 ± 17.5	49.4 ± 20.6	61.6 ± 25.3	NS
Normalized apical rotation rate (°/cm/s)	11.5 ± 4.2	9.1 ± 4.1	7.2 ± 2.2	6.2 ± 3.3	7.8 ± 3.3	<.001
Basal rotation at early systole (°)	4.3 ± 1.9	4.7 ± 1.5	4.0 ± 2.0	3.4 ± 1.6	2.9 ± 1.9	<.01
Normalized basal rotation at early systole (°/cm)	0.7 ± 0.3	0.7 ± 0.2	0.5 ± 0.3	0.4 ± 0.2	0.4 ± 0.3	<.001
Basal rotation (°)	−5.0 ± 2.0	−4.6 ± 2.4	−4.0 ± 2.2	4.8 ± 2.5	4.9 ± 2.0	NS
Normalized basal rotation (°/cm)	−0.9 ± 0.4	−0.6 ± 0.3	−0.5 ± 0.3	−0.6 ± 0.3	−0.7 ± 0.3	<.005
Basal rotation rate at early systole (°/s)	60.3 ± 28.4	58.4 ± 20.0	43.7 ± 15.7	32.2 ± 13.7	29.4 ± 15.6	<.001
Normalized basal rotation rate at early systole (°/cm/s)	10.4 ± 5.4	7.8 ± 2.7	5.4 ± 2.0	4.1 ± 2.3	3.9 ± 2.1	<.001
Basal rotation rate (°/s)	−70.1 ± 21.1	−60.6 ± 19.6	−51.6 ± 16.8	−44.5 ± 13.2	−44.2 ± 17.8	<.001
Normalized basal rotation rate (°/cm/s)	−12.3 ± 4.2	−8.2 ± 2.7	−6.3 ± 1.8	−5.5 ± 2.2	−5.9 ± 2.4	<.001

(A) Regression plots between peak torsion, normalized (N) peak torsion, peak apical rotation, normalized peak apical rotation, peak basal rotation, normalized peak basal rotation. (B) Age-related alterations in normalized peak torsion rate, normalized peak apical rotation rate and normalized peak basal rotation rate. CI , Confidence interval; PI , prediction interval.

LV Diastolic Events

Apical and basal LV recoil rates decreased throughout the whole age range ( Table 3 , Figure 4 ), with a minimal value at around 30 years, after which there was an increase. Peak LV untwisting rate was constant during childhood and decreased during adulthood. When normalized by LV length, peak LV untwisting rate decreased throughout the whole age range ( Figure 4 ).

Table 3

Diastolic profile

	Group 1 (3-9 y)	Group 2 (10-16 y)	Group 3 (17-24 y)	Group 4 (25-32 y)	Group 5 (33-40 y)
Variable	(n = 29)	(n = 24)	(n = 15)	(n = 20)	(n = 20)	P
Untwisting rate (°/s)	−104.9 ± 40.8	−103.8 ± 31.2	−98.6 ± 33.5	−82.3 ± 32.8	−77.7 ± 22.8	<.05
Normalized untwisting rate (degree/cm)/s	−17.3 ± 5.3	−14.0 ± 4.6	−12.4 ± 4.7	−10.2 ± 4.5	−9.9 ± 2.7	<.001
% of untwisting at MVO	30.7 ± 22.4	16.4 ± 18.7	14.6 ± 13.3	−0.0 ± 9.1	4.2 ± 14.38	<.001
% of untwisting at 120% of systole	38.0 ± 22.3	30.8 ± 18.8	33.1 ± 17.6	7.8 ± 15.4	7.2 ± 14.2	<.001
Apical recoil rate (°/s)	−83.6 ± 29.8	−77.9 ± 22.9	−67.1 ± 23.4	−54.3 ± 18.9	−60.0 ± 16.0	<.001
Normalized apical recoil rate (°/cm)/s	−14.3 ± 5.2	−10.8 ± 3.7	−8.5 ± 3.2	−6.6 ± 2.5	−7.3 ± 1.9	<.001
Basal recoil rate (°/s)	58.1 ± 18.6	50.5 ± 19.6	41.7 ± 15.3	42.4 ± 21.9	35.9 ± 13.7	<.001
Normalized basal recoil rate (°/cm/s)	10.1 ± 3.6	6.8 ± 2.7	5.2 ± 2.1	5.3 ± 3.4	4.8 ± 2.0	<.001

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