Assessment of regional rotation patterns improves the understanding of the systolic and diastolic left ventricular function: an echocardiographic speckle-tracking study in healthy individuals

Abstract

Aim

To elucidate the complexity of left ventricular motion throughout the cardiac cycle, we studied regional rotation in detail.

Methods and Results

Regional rotation in six subdivisions of the circumference at three levels was studied by using speckle-tracking echocardiography in 40 healthy subjects. At the basal level the inferoseptal segments rotated significantly more clockwise during systole than the opposing anterolateral segments. At the papillary level the inferoseptal segments differed significantly from the anterolateral segments, where the inferoseptal segments rotated clockwise and the anterolateral segments rotated counter-clockwise. The apical level showed significant difference in regional rotation only at aortic valve opening. In early systole, untwist before the main systolic twist was seen at the basal and apical levels; however, the duration of the basal untwist was much longer than that of the apical. The diastolic phases of rotation at the basal and apical levels matched the different filling phases.

Conclusion

Large regional differences in rotation are present at the basal and papillary levels in healthy subjects. The diastolic untwist matches the phases of both the E-wave and A-wave and seems to be related with intraventricular pressure differences, indicating that untwist plays an important role in the filling of the ventricle.

Regional rotation, Left ventricular systolic function, Left ventricular diastolic function, Speckle-tracking echocardiography, Diastolic suction, Healthy humans

Introduction

In spite of numerous studies the myocardial wall motion of the left ventricle (LV) is still not fully described and understood. The oblique subepicardial fibres and the activation sequence seem to be of special importance in induction of ventricular twist. ^1–5 The importance of this twisting ventricular motion in health and disease is not well defined.

The new echocardiographic technique, two dimensional strain (2D-strain) or ‘speckle tracking’, has enabled angle-independent measurements of regional cardiac function and has proved to be an accurate method of measuring cardiac rotation. ^6–8 However, most studies have only described the average rotation of the LV at different levels. We now present detailed analysis of regional rotation throughout the cardiac cycle in healthy subjects.

Methods

Forty healthy volunteers (18 men), mean age 60 (23–76) years, randomly selected from the local population list at the Swedish Tax Bureau were included. They were subjectively healthy without a history of hypertension or cardiac disease and were not taking any medication. The study group had normal ECG and blood pressure below 160/90 mmHg. Basic characteristics of the study population are presented in Table  1 . The study was approved by a local ethics committee.

Table 1

Basic characteristics of the study population

Variable	All subjects	Women	Men	P -value
Number	40	22	18
Age (years)	60 ± 14	60 ± 14	61 ± 14	0.770
Heart rate (bpm)	63 ± 7	63 ± 7	62 ± 7	0.622
SBP (mmHg)	136 ± 18	133 ± 31	139 ± 16	0.341
DBP (mmHg)	84 ± 10	81 ± 10	87 ± 9	0.047
LV diastole (mm)	51 ± 4	49 ± 4	53 ± 3	0.011
LV systole (mm)	33 ± 4	32 ± 4	35 ± 4	0.033
IVS diastole (mm)	10 ± 2	10 ± 2	11 ± 2	0.005
LVPW diast (mm)	8 ± 1	7 ± 1	8 ± 1	0.011
LA (mm)	38 ± 5	36 ± 4	40 ± 6	0.033
E/A ratio	1.1 ± 0.4	1.1 ± 0.3	1.1 ± 0.5	0.921
AV-disp (mm)	13 ± 1	13 ± 2	13 ± 2	0.639
Q-AVO (ms)	86 ± 9	85 ± 10	86 ± 8	0.709
Q-AVC (ms)	389 ± 21	396 ± 21	380 ± 18	0.011

Mean ± standard deviation.

SBP, systolic blood pressure; DBP, diastolic blood pressure; IVS, inter-ventricular septum; LV, left ventricle; LVPW, left ventricular posterior wall; LA, left atrium; AV-disp, mean longitudinal peak displacement of AV-plane at four sites. Q-AVO, time from the Q-wave in ECG to aortic valve opening (by Doppler); AVC, aortic valve closure; E/A, mitral early wave/mitral atrial wave from Doppler signal.

P -value denotes differences between men and women.

Standard short axis images were recorded at basal, papillary, and apical levels with a frame rate of ∼70 frames/s using an ultrasound system (Vivid 7, GE Ultrasound, Horten, Norway) with a 4S-probe in harmonic imaging at 1.7/3.4 MHz. The rotation was calculated by using an automatic frame-to-frame tracking system of grey-scale patterns (2D-Strain, EchoPac PC v.5.1.1, GE Healthcare, Horten, Norway). The software identifies acoustic markers (speckles) in the grey-scale image within the region of interest (ROI) and tracks these speckles frame by frame, thereby enabling angle-independent calculations of different variables, i.e. velocity, strain, and rotation. ⁸ The ROI was set on the luminal side of the endocardial margin to the luminal side of the epicardial margin thus delineating the whole circumference. The ROI was automatically divided into six equally large segments (anteroseptal, anterior, lateral, posterior, inferior, septal), enabling assessment of regional rotation and the tracking quality of each segment was indicated. Segments with insufficient tracking quality or incorrect tracking were excluded. The analyses were made in two parts. First one heart cycle was analysed from Q to Q in the superimposed ECG. To assess the transition from diastole to systole another analysis was made including two heart cycles. The rotation in each segment at all three levels was measured at 10 different time points in the analysis of one heart cycle; (mid-isovolumic contraction (IVC), aortic valve opening (AVO), 25% of ejection phase, 50% of ejection phase, 75% of ejection phase, aortic valve closure (AVC), mid-isovolumic relaxation (IVR), mitral valve opening (MVO), peak early filling (E-peak) and end of early filling (E-end)) and at 3 different time points in the analyses of two heart cycles (onset of atrial filling (A-onset), Q-wave and AVO of the second heart cycle (AVO2)). Time from the Q-wave to AVO, AVC, MVO, E-peak, E-end, and A-onset was measured with pulsed wave Doppler and applied to other heart cycles with similar heart rate. Early (E) and atrial (A) blood flow velocities were measured with pulsed wave Doppler. Torsion was calculated as the net difference in mean rotation between the apical and basal levels. Clockwise and counter-clockwise rotations are denoted as seen from the apex.

Statistical analysis

The data were analysed using the SPSS statistical software (SPSS v.11.5 for Windows, SPSS. Inc., Chicago, IL, USA). Means and standard deviations are used to describe central tendency and variance. Repeated measurements ANOVA and post hoc paired samples t -tests were used to compare rotational values between the levels. At each level and time, repeated measurement ANOVA and post hoc paired t -test with Bonferroni correction were used to compare segments. Paired samples t -tests were conducted comparing the time to peak rotation between the basal and the apical levels and the untwist amplitude in degrees during the E-wave between basal and apical levels. Independent samples t -tests were used to compare mean peak rotation and time to peak at basal and apical levels by gender. Correlation between E and A velocities and untwist amplitude during the E- and A-wave at basal and apical levels was analysed using Spearman's correlation test. Results of intra- and inter-observer reproducibility were analysed using the method of agreement as described by Bland and Altman and presented as the coefficient of variation (CV). ⁹P -values of 0.05 or less were considered significant.

Results

A total of 86% of the analysed segments was accepted based on the quality criteria in the system software. However, the lateral segments at the basal level had the lowest acceptance rate of 58%. Rotational data are presented in Table  2 . In order to simplify we have chosen to present differences in regional rotation only between opposite segments (anterior vs. inferior, anteroseptal vs. posterior, and septal vs. lateral). There were no significant differences between the anteroseptal and the posterior segments at any time point at each level. At the basal level the inferior segment rotated significantly more clockwise than the anterior segment during the interval between 25% of ejection to E-peak ( P < 0.016). The septal segment at the basal level rotated significantly more clockwise than the lateral segment during the interval between 25% of ejection to A-onset ( P < 0.048). At the papillary level there was a significant difference between the inferior and anterior segments during the interval between 25% ejection to E-peak ( P < 0.001) and between the septal and the lateral segments during the interval between 50% ejection to E-end ( P < 0.018). The anterolateral segments at the papillary level rotated counter-clockwise while the remaining segments rotated clockwise during the ejection phase ( Figure  1 ). At the apical level there were no significant differences between opposite segments at any time except at AVO where there was a significant difference between the anterior and the inferior segments ( P = 0.016). There was a significant difference ( P < 0.007) in mean rotation between the three levels at all time points except at 25% of the ejection and at Q (from the analysis of two heart cycles) ( Figure  2 ). Time to AVC was 389 ± 21 ms. Peak basal rotation was −6.6 ± 4.5° at 377 ± 47 ms from the Q-wave. Peak apical rotation was 12.5 ± 4.8° at 391 ± 47 ms from the Q-wave. There was no significant difference in time-to-peak rotation between basal and apical levels. Torsion at AVC was 17.6 ± 5.3°. Between men and women there was no significant difference in peak rotation or time-to-peak rotation at basal and apical levels, although men had a significantly shorter time to AVC ( P = 0.011) ( Table  1 ).

Figure 1

Mean regional rotation patterns at all three levels of the study population. Each curve represents rotation of one segment. Positive values indicate counter-clockwise rotation and negative values indicate clockwise rotation. AVO, aortic valve opening; AVC, aortic valve closure; MVO, mitral valve opening; MVC, mitral valve closure; Q, Q-wave in the ECG.

Figure 2

Mean rotation at each level and torsion as the net difference of rotation between the apical and the basal level over an entire heart cycle including the transition from diastole to systole. Positive values indicate counter-clockwise rotation and negative values indicate clockwise rotation. Q, Q-wave in the ECG; MVC, mitral valve closure; IVC, mid-isovolumetric contraction; AVO, aortic valve opening; AVC, aortic valve closure; IVR, isovolumetric relaxation; MVO, mitral valve opening; E-peak, peak of early diastolic filling; E-end, end of early diastolic filling; A-onset, onset of late diastolic filling.

Table 2

Rotational data

Event	Antsept	Ant	Lat	Post	Inf	Sept
Basal
IVC	0.3 ± 1.3	0.5 ± 1.5	1.0 ± 1.2	0.9 ± 1.1	0.5 ± 1.0	0.1 ± 1.1
AVO	0.5 ± 1.7	0.9 ± 2.2	1.2 ± 1.9	1.2 ± 2.1	0.3 ± 1.7	−0.9 ± 3.5
25% ejction	1.3 ± 2.6	2.0 ± 3.0	1.6 ± 2.5	1.0 ± 2.8	−0.4 ± 2.6	−0.7 ± 2.3
50% ejection	−1.4 ± 3.2	0.1 ± 3.3	−0.7 ± 3.4	−2.0 ± 3.1	−4.2 ± 3.0	−4.1 ± 2.9
75% ejection	−4.0 ± 4.0	−1.8 ± 3.9	−3.1 ± 3.9	−4.5 ± 3.5	−7.5 ± 3.9	−7.1 ± 3.5
AVC	−5.2 ± 4.6	−2.5 ± 4.8	−4.1 ± 4.1	−5.7 ± 4.1	−9.0 ± 4.4	−8.8 ± 3.5
IVR	−4.6 ± 4.2	−1.7 ± 4.6	−3.5 ± 3.7	−5.0 ± 3.7	−8.1 ± 3.8	−7.8 ± 3.4
MVO	−2.9 ± 4.3	−0.8 ± 4.5	−1.5 ± 3.8	−2.7 ± 3.8	−5.5 ± 3.9	−5.5 ± 3.4
E-peak	−1.3 ± 3.7	0.5 ± 3.4	1.1 ± 3.1	−0.1 ± 3.8	−2.9 ± 3.9	−3.1 ± 3.2
E-end	−1.5 ± 2.7	−1.5 ± 2.6	−0.9 ± 3.1	−1.6 ± 3.1	−2.7 ± 2.6	−2.7 ± 2.6
A-onset	−1.5 ± 2.7	−0.4 ± 3.1	0.4 ± 3.6	−0.9 ± 3.2	−2.9 ± 2.8	−2.5 ± 2.6
Q-wave	0.5 ± 3.1	1.1 ± 3.1	1.7 ± 2.6	1.5 ± 2.5	0.4 ± 2.8	0.5 ± 2.7
AVO 2	1.1 ± 3.4	1.8 ± 3.8	2.5 ± 3.4	2.7 ± 3.0	1.0 ± 3.1	0.3 ± 2.9
Papillary
IVC	−0.1 ± 1.0	0.0 ± 1.1	−0.3 ± 1.1	−0.1 ± 0.9	−0.3 ± 1.2	−0.5 ± 1.1
AVO	−0.2 ± 1.7	−0.2 ± 1.9	−0.6 ± 1.7	−0.6 ± 1.8	−0.7 ± 1.6	−0.9 ± 1.4
25% ejection	1.6 ± 2.7	1.9 ± 3.0	1.5 ± 2.7	0.5 ± 2.5	0.3 ± 2.5	0.6 ± 2.5
50% ejection	0.9 ± 2.3	1.5 ± 2.6	1.4 ± 2.8	−0.4 ± 2.3	−1.4 ± 2.4	−0.7 ± 2.3
75% ejection	0.5 ± 2.7	1.5 ± 2.9	1.6 ± 3.2	−0.9 ± 2.8	−2.4 ± 3.0	−1.5 ± 2.9
AVC	0.0 ± 2.8	1.5 ± 3.0	1.9 ± 3.2	−0.9 ± 2.9	−3.3 ± 3.0	−2.3 ± 3.0
IVR	0.1 ± 2.6	1.3 ± 2.7	1.9 ± 3.0	−0.3 ± 2.8	−2.4 ± 3.0	−1.5 ± 2.9
MVO	0.7 ± 2.7	1.4 ± 2.9	2.2 ± 2.7	0.9 ± 2.7	−1.1 ± 3.1	−0.7 ± 2.8
E-peak	0.7 ± 2.7	1.6 ± 2.9	2.3 ± 2.5	1.3 ± 2.3	−0.8 ± 2.8	−0.4 ± 2.4
E-end	−0.5 ± 1.8	−0.6 ± 2.2	0.2 ± 2.5	−0.2 ± 2.0	−1.5 ± 1.8	−0.8 ± 1.9
A-onset	−0.4 ± 2.1	0.1 ± 2.4	0.4 ± 2.6	−0.3 ± 2.9	−1.1 ± 2.5	−1.1 ± 2.1
Q-wave	0.6 ± 2.1	0.4 ± 2.3	0.4 ± 2.2	0.6 ± 2.6	0.5 ± 2.3	0.3 ± 2.2
AVO 2	0.3 ± 2.4	0.4 ± 2.8	−0.4 ± 2.6	0.1 ± 3.1	−0.3 ± 2.7	−0.6 ± 2.3
Apical
IVC	−1.3 ± 1.0	−1.2 ± 1.1	−1.1 ± 1.1	−1.1 ± 1.1	−1.3 ± 1.1	−1.3 ± 1.0
AVO	−1.5 ± 2.1	−1.8 ± 2.3	−1.8 ± 2.4	−1.5 ± 2.4	−1.3 ± 2.2	−1.3 ± 2.1
25% ejection	2.3 ± 2.8	2.0 ± 3.2	1.7 ± 3.1	2.2 ± 2.9	2.7 ± 2.7	2.7 ± 2.6
50% ejection	4.9 ± 3.3	4.9 ± 3.4	5.1 ± 3.5	5.6 ± 3.5	6.0 ± 3.1	5.5 ± 3.1
75% ejection	8.4 ± 4.0	8.8 ± 4.1	9.3 ± 4.1	9.5 ± 4.1	9.6 ± 3.8	9.0 ± 3.7
AVC	11.1 ± 4.6	11.8 ± 4.7	12.3 ± 4.7	12.1 ± 4.7	11.5 ± 4.6	11.1 ± 4.4
IVR	9.5 ± 5.5	10.0 ± 5.7	10.5 ± 5.7	10.4 ± 5.7	10.2 ± 5.5	9.7 ± 5.3
MVO	7.3 ± 6.3	7.4 ± 6.5	8.0 ± 6.5	8.2 ± 6.3	7.9 ± 6.0	7.5 ± 6.0
E-peak	5.5 ± 5.0	5.6 ± 5.2	6.0 ± 4.9	6.1 ± 4.6	6.0 ± 4.3	5.7 ± 4.6
E-end	2.1 ± 3.0	1.9 ± 3.0	1.8 ± 2.9	1.6 ± 2.7	1.7 ± 2.6	2.1 ± 2.7
A-onset	1.3 ± 3.5	1.2 ± 3.7	1.4 ± 3.6	1.2 ± 3.8	1.2 ± 3.7	1.4 ± 3.5
Q-wave	0.8 ± 3.2	0.9 ± 3.4	1.1 ± 3.4	1.0 ± 3.8	0.7 ± 3.7	0.7 ± 3.3
AVO 2	−0.9 ± 3.3	−0.9 ± 3.5	−0.6 ± 3.7	−0.6 ± 4.0	−0.8 ± 3.8	−0.9 ± 3.5

Rotational data (degrees) of each segment at all measuring points from the analyses of one and two heart cycles. Mean ± standard deviation. Positive values indicate counter-clockwise rotation and negative values indicate clockwise rotation.

IVC, mid-isovolumetric contraction; AVO, aortic valve opening; AVC, aortic valve closure; IVR, mid-isovolumetric relaxation; MVO, mitral valve opening; E-peak, peak of early diastolic filling; E-end, end of early diastolic filling; A-onset, onset of late diastolic filling (from the analyses of two heart cycles); Q-wave, Q-wave in the ECG (from two heart cycles); AVO2, aortic valve opening (from two heart cycles).

There was a significant difference in untwist between the basal and the apical levels during the E-wave as well as during the A-wave ( P < 0.001). Apical untwist was more pronounced (5.8 ± 4.9°) during the E-wave and continued until E-end, whereas the basal untwist was less pronounced (2.0 ± 2.2°) and ended already at E-peak. During the A-wave there was little untwist at the apical level (0.4 ± 1.5°), whereas untwist at the basal level was greater (1.9 ± 1.8°). The E velocity correlated significantly with untwist amplitude during the E-wave at both the basal ( r = 0.340, P = 0.032) and the apical ( r = 0,363, P = 0.021) levels. No significant correlation was seen between A velocity and untwist amplitude during the A-wave.

Reproducibility

Both inter- and intra-reproducibility tests were made for peak rotation measurements. The inter-observer reproducibility had a CV of 0.4% for measurements in five subjects. The intra-observer reproducibility tests were made several weeks after the original analysis. When re-analysing the recordings with the same ROI and measuring in 15 subjects the CV was 5.0%, describing the variation mainly because of the software. When drawing a new ROI and re-analysing six subjects the CV was 18.5% at the basal level and 13.8% at the apical level.

Discussion

There is to date no study presenting data on segmental rotation at three different levels of the LV during the entire cardiac cycle. As the importance of LV rotation for understanding normal physiology has become evident, we present pertinent data that adds to this understanding and might be used in future treatment strategies such as selecting patients for cardiac resynchronization therapy. In this study we have described in detail the normal torsional movement of the LV with a relatively new, feasible, and commercially available non-invasive technique.

The main findings of the study are the following: (i) large regional differences in rotation at basal and papillary levels, whereas small regional differences at the apical level, (ii) an early systolic counter rotation precedes the main rotation during the ejection phase at both basal and apical levels, (iii) the rotational patterns seem to correlate with myocardial fibre orientations and the activation sequence in the LV, and (iv) the diastolic untwist matches the E- and the A-wave.

Regional rotation

Studies have indicated that the subepicardial fibres are mainly responsible for the ventricular rotation. ^2–4 The large regional differences in rotation at the basal level could partially be explained by the myocardial fibre orientations in the respective segments where the anterolateral segments have more longitudinally orientated fibres than the rest of the segments. ² At the papillary level there is a heterogeneous rotation with mainly clockwise rotation of the inferoseptal segments, whereas the anterolateral segments rotate counter-clockwise ( Figure  1 ). This indicates that the transition from basal clockwise rotation to apical counter-clockwise rotation is located approximately at the mid papillary muscle level. The small regional differences in rotation at the apical level might depend on the uniform fibre structure, the short distances between the segments, and the fact that the apex is relatively free from connections to other structures.

Systole

The subendocardial fibres are orientated in a right-handed helix in contrast to the subepicardial fibres, which are orientated in a left-handed helix. ^{2 , 5 , 10} The electrical activation wave of the LV moves from apex to base, with the endocardium activated before the epicardium. ¹¹ This activation sequence of the fibres generates untwisting of the ventricle in early systole which can be seen in Figure  2 . The effect of this motion would be to stretch the fibres of the left-handed helix and thus moving further to the right on the Frank-Starling curve. The early systolic untwist at the basal and apical levels shows a temporal difference. At the basal level the untwist starts at the A-wave and ends at 25% of the ejection phase, indicating that the early part of the systolic untwist is induced by the atrial contraction, while the later part is likely due to the electrical activation and contraction of the subendocardial fibres. At the apical level the untwist starts approximately at the Q-wave and ends at AVO, and is likely to be generated primarily by the electrical activation of the endocardial fibres. A possible effect of the later activation of the basal fibres would be to keep the shape of the outflow tract unaffected until late systole, optimizing outflow conditions.

Diastole

The LV diastolic untwist is associated with reduction of LV pressure and thus creates a suction effect which contributes to diastolic filling. ^12–14 During the first part of the early filling phase, the intraventricular pressure at the apex is lower than that at the base. ^15–17 The intraventricular pressure then increases, starting at the apex and moving towards the base. ¹⁷ From the beginning of diastole until the peak of the E-wave, we found untwist of the LV at both base and apex. As the untwisting motion is related to the decrease of pressure in the ventricle this facilitates the blood to move all the way down to the apex. During the rest of the E-wave untwist was only seen at the apical level when blood continues to move to the apical half of the ventricle, but at a lower pace. ^{15 , 17} The significantly more pronounced untwist at the apical level during the E-wave indicates that mainly the apical part would actively generate suction that contributes to the early filling. During the A-wave we found untwisting only at the basal level, indicating that the late diastolic basal untwist is passive and generated by the atrial contraction.

Limitations

Obtaining high-quality images in all subjects is difficult, and 86% of the segments could be accepted. Many measurements and time events were measured in different heart cycles and a slight change in heart rate may be present. Only a small difference in delineation of an ROI affects the calculated degree of rotation with a CV of 18.5%, where 5% can be explained by the combination of the inherent CV of the software and the intra-observer variability. The analyses of two heart cycles may be more influenced by software artefacts, such as baseline drift that might explain the difference between the two analyses at Q and AVO.

Conclusion

There are large differences in regional rotation in healthy subjects. The diastolic untwist matches the filling phases of the E- and A-wave underlining the important role in the filling of the ventricle. The early diastolic untwist at the apex related to the E-wave and LV suction actively facilitates early apical filling, whereas the late diastolic untwist at the basal level seems passive and generated by the atrial contraction.

Funding

This study was supported by the Swedish Heart and Lung Foundation and the Heart Foundation of Northern Sweden.

Acknowledgements

We are indebted to Michael Haney for revision of the English text.

Conflict of interest: none declared.