Physiological range of mechanical synchronicity of the human heart: comparison between different echocardiographic assessment modalities

Assessment of intraventricular time differences in healthy children using two-dimensional speckle-tracking echocardiography

BACKGROUND

Parameters describing intraventricular time differences are increasingly assessed in both adults and children. However, to appreciate the implications of these parameters in children, knowledge of the applicability of adult techniques in children is essential. Hence, the aim of this study was to assess the applicability of speckle-tracking strain-derived parameters in children, paying special attention to age and heart rate dependency.

METHODS

One hundred eighty-three healthy subjects (aged 0-19 years) were included. Left ventricular global peak strain, time to global peak strain, and parameters describing intraventricular time differences were assessed using speckle-tracking strain imaging in the apical two-chamber, three-chamber, and four-chamber views (longitudinal strain) and the parasternal short-axis view (radial and circumferential strain). Parameters describing intraventricular time differences included the standard deviation of time to peak strain and differences in time to peak strain between two specified segments. Age and heart rate dependency were evaluated using regression analysis, and intraobserver and interobserver variability were tested.

RESULTS

Acquisition and analysis of longitudinal six-segment time-strain curves was successful in 94.8% of subjects and radial and circumferential time-strain curves in 89.5%. No clinically significant linear relation was observed between age or heart rate and parameters describing intraventricular time differences. The coefficient of variation of time to global peak strain parameters was <10, while it was >10 for parameters describing intraventricular time differences.

CONCLUSIONS

The feasibility of speckle-tracking strain analysis in children is relatively good. Furthermore, no linear relation was observed between age or heart rate and parameters describing intraventricular time differences. However, the limited reproducibility of some parameters describing intraventricular time differences will confine their applicability in clinical practice.

Distribution of dyssynchrony in subjects with no known cardiac disease and comparison of velocity vector imaging to color-coded tissue Doppler imaging

Data on the distribution of dyssynchrony in subjects with normal ejection fraction (EF) and normal QRS are scarce. We studied 100 subjects with no known cardiac disease (52% male, mean age 60 ± 17 years) using velocity vector imaging (VVI). Seventeen percent had septal to lateral (S-L) wall longitudinal delay >75 msec, 63% of subjects had S-L wall radial delay >75 msec, and 25% had a circumferential opposing wall delay >100 msec. Those with circumferential opposing wall delay of >100 msec had a lower EF (57 ± 5% vs. 62 ± 5%, P < 0.05). In an additional group of 33 patients, we compared the longitudinal dyssynchrony parameters as assessed by VVI and tissue Doppler imaging (TDI) and found them to be comparable. In conclusion, we find significant variation in time to peak velocities in subjects with no known cardiac disease, who had a normal left ventricular ejection fraction and QRS duration. VVI is comparable to TDI.

Measures of dyssynchrony in the left ventricle of healthy children and young patients with dilated cardiomyopathy

BACKGROUND

Doppler tissue imaging may help identify children with dyssynchrony who could benefit from resynchronization therapy. However, few studies have quantified dyssynchrony measures in children; no study has investigated the relationship among age, heart rate, and dyssynchrony measures in children; and no study has quantified cross-correlation delay in children. The aim of this study was to test the hypotheses that measures of left ventricular dyssynchrony would correlate with age, primarily because of the correlation between heart rate and age, and that children with cardiomyopathy would have left ventricular dyssynchrony.

METHODS

Sixty healthy children and 11 children with dilated cardiomyopathy were prospectively enrolled. Seven dyssynchrony measures were quantified: septal-to-lateral delay, peak velocity difference, the standard deviations of times to peak in 12 segments in systole and diastole, and cross-correlation delay in systole, diastole, and the whole cycle.

RESULTS

The seven dyssynchrony measures were either not correlated with age or only weakly correlated with age after correcting for heart rate using Bazett's formula. Septal-to-lateral delay, peak velocity difference, and the standard deviation of times to peak in 12 segments in systole showed dyssynchrony in 57% to 85% of normal controls, compared with 20% for cross-correlation delay in the whole cycle and 3% for the standard deviation of times to peak in 12 segments in diastole. Cross-correlation delay in systole, cross-correlation delay in diastole, cross-correlation delay in the whole cycle, and the standard deviation of times to peak in 12 segments in diastole were elevated in children with dilated cardiomyopathy compared with controls.

CONCLUSIONS

Echocardiographic dyssynchrony measures should be corrected for heart rate using Bazett's formula in children. Time-to-peak Doppler tissue imaging dyssynchrony measures classify many healthy children as having abnormalities with the timing of left ventricular contraction, which suggests that the methodology is not accurate in children. In preliminary studies, cross-correlation dyssynchrony measures show elevated systolic and diastolic measures of dyssynchrony in children with dilated cardiomyopathy compared with controls, which deserves further investigation to help identify children who may benefit from resynchronization therapy.

Synchronicity of systolic deformation in healthy pediatric and young adult subjects: a two-dimensional strain echocardiography study

Two-dimensional speckle tracking echocardiography (2DSTE) offers valuable information in the echocardiographic assessment of ventricular myocardial function. It enables the quantification and timing of systolic ventricular myocardial deformation. In addition, 2DSTE can be used to identify mechanical dyssynchrony, which is an important parameter in predicting the response to cardiac resynchronization therapy for heart failure. Detailed knowledge of normal timing of systolic deformation and its degree of synchronicity in children is lacking. We aimed to establish the normal timing of left ventricular myocardial systolic deformation using 2DSTE in a large cohort of healthy children and young adults. Transthoracic echocardiograms were acquired in 195 healthy subjects (139 children and 56 young adult <40 yr of age) and were retrospectively analyzed. Time to peak systolic longitudinal, circumferential, and radial strain was determined by means of speckle tracking. Strong, statistically significant relations between age as well as various anthropometric variables (e.g., heart rate) and timing of systolic deformation ( P < 0.0001) were present. The extent of dyssynchronous deformation increased with age. This is the first report that establishes reference values per cardiac segment for time to peak systolic myocardial strain values in all three directions assessed with 2DSTE in a large pediatric and young adult cohort. We emphasize the need for using age-specific reference values as well as heart rate correction for the adequate interpretation of 2DSTE measurements.

Myocardial first-pass perfusion: influence of spatial resolution and heart rate on the dark rim artifact

Myocardial perfusion images can be affected by the dark rim artifact. This study aimed to evaluate the effects of the spatial resolution and heart rate on the transmural extent of the artifact. Six pigs under anesthesia were scanned at 1.5T using an echo-planar imaging/fast gradient echo sequence with a nonselective saturation preparation pulse. Three short-axis slices were acquired every heart beat during the first pass of a contrast agent bolus. Two different in-plane spatial resolutions (2.65 and 3.75 mm) and two different heart rates (normal and tachycardia) were used, generating a set of four perfusion scans. The percentage drop of signal in the subendocardium compared to the epicardium and the transmural extent of the artifact were extracted. Additionally, the signal-to-noise and the contrast-to-noise ratios were evaluated. The signal drop as well as the width of the dark rim artifact increased with decreased spatial resolution and with increased heart rates. No significant slice-to-slice variability was detected for signal drop and width of the rim within the four considered groups. signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) ratios decreased with increasing spatial resolution. In conclusion, low spatial and temporal resolution could be correlated with increased extent of the dark-rim artifact and with lower SNR and CNR.

Ventricular asynchrony of time-to-peak systolic velocity in structurally normal heart by tissue Doppler imaging

BACKGROUND

Echocardiographic measurements of time-to-peak systolic velocities (Ts) are helpful for assessing the degree of cardiac asynchrony. We assessed the degree of ventricular asynchrony in structurally normal heart according to Ts by tissue Doppler imaging.

METHODS

We performed conventional echocardiography and tissue velocity imaging for 65 healthy adult volunteers to measure the Ts of 12 left ventricular segments in the mid and basal levels delay of Ts and standard deviation (SD) of Ts in all and basal segments. Six frequently used markers of dyssynchrony were measured and were also compared between men and women. Data are presented as median (25th and 75th percentile).

RESULTS

Septal-lateral and anteroseptal-posterior delays were 50 (20, 90) and 20 (0, 55) ms. The delay between the longest and the shortest Ts in basal and all segments were 100 (80, 120) and 110 (83, 128) ms, respectively. SD of Ts was 39 (24, 52) ms for basal and 41 (28, 51) ms for all segments. Overall, 76.9% of cases had at least one marker of dyssynchrony. Frequencies of dyssynchrony markers were almost significantly higher in women compared to men. The most frequently observed dyssynchrony marker was SD of Ts of all segments (70.8%) and the lowest was anteroseptal-posterior delay (21.5%).

CONCLUSIONS

Normal population almost had dyssynchrony by previously described markers and many of these markers were more frequent in women. Conducting more studies on normal population by other tissue Doppler modalities may give better description of cardiac synchronicity.

Comparison of left ventricular dyssynchrony by two-dimensional speckle tracking versus tissue Doppler imaging in patients with non-ST-elevation myocardial infarction and preserved left ventricular systolic function

Assessment of left ventricular (LV) dyssynchrony after myocardial infarction has prognostic value. There were no reference ranges for 2-dimensional (2D) speckle tracking synchrony, and it was unclear whether color tissue Doppler imaging and 2D speckle tracking synchrony indexes were comparable. One hundred twenty-two healthy volunteers and 40 patients with non-ST-elevation myocardial infarction (NSTEMI) had LV systolic and diastolic synchrony, defined as the SD of time to peak systolic (2D-SDTs) and early diastolic (2D-SDTe) velocities in the 12 basal and mid segments using 2D speckle tracking, respectively. Mean 2D-SDTs and 2D-SDTe were 29.4 +/- 16.1 and 14.2 +/- 6.1 ms in healthy subjects, respectively. Gender and mean 2D systolic velocity independently predicted 2D-SDTs, and mean 2D early diastolic velocity independently predicted 2D-SDTe. Bland-Altman analysis showed suboptimal agreement between 2D speckle tracking and tissue Doppler imaging dyssynchrony indexes. 2D speckle tracking showed lower coefficients of variation for time to peak systolic and early diastolic velocities than tissue Doppler imaging. There were no significant differences in coefficients of variation for 2D speckle tracking systolic and diastolic synchrony for high versus low frame rates. Patients with NSTEMI had significantly lower ejection fraction, but higher LV mass and wall stress than healthy subjects. Only 2D-SDTs was significantly higher in patients with NSTEMI compared with healthy subjects (37.1 +/- 22.5 vs 29.4 +/- 16.1 ms; p = 0.02). In conclusion, 2D-SDTs was gender specific and influenced by global systolic function, and 2D-SDTe was influenced by global diastolic function. 2D speckle tracking and tissue Doppler imaging dyssynchrony indexes were not comparable. 2D speckle tracking may be a more sensitive discriminator of LV systolic dyssynchrony than tissue Doppler imaging.

Assessment of Longitudinal and Radial Ventricular Dyssynchrony in Ischemic and Nonischemic Chronic Systolic Heart Failure: A Two-Dimensional Echocardiographic Speckle-Tracking Strain Study

BACKGROUND

Current guidelines recommend a QRS greater than or equal to 120 milliseconds to select candidates for cardiac resynchronization therapy. However, ischemic and nonischemic cardiomyopathies are two different entities and they might be selected following different approaches. We sought, thus, after a validation the new 2-dimensional (2D) speckle-tracking strain (STS) against color Doppler tissue imaging (DTI)-strain (S) to compare the different correlation between electrical and mechanical dyssynchrony (DYS) in ischemic and nonischemic cardiomyopathies.

METHODS

We measured: (1) QRS duration; (2) mechanical interventricular DYS (the difference between preaortic and prepulmonary ejection times); (3) left intraventricular DYS (the SD of time-to-peak of longitudinal DTI-S); and (4) longitudinal and radial 2D-STS in the basal and middle segments of lateral and septal left ventricular walls in 95 patients with chronic heart failure caused by ischemic (n = 49) or nonischemic (n = 46) heart disease. Twelve healthy control subjects were also explored.

RESULTS

Mechanical interventricular DYS was correlated (DTI-S: P < .001) with QRS-duration, but not in ischemic heart disease. DTI-S and 2D-STS measurements were correlated (R = 0.6, P < .001) in the overall population. Longitudinal 2D-S DYS was correlated with QRS duration in patients with nonischemic, (P = .003) but not with ischemic heart disease, whereas radial 2D-S DYS was correlated with QRS width in both subgroups (r = 0.48, P = .003, and r = 0.43, P = .003, respectively).

CONCLUSIONS

The profile of DYS is influenced by the underlying cause of heart failure. The 2D-STS is a new tool for cardiac DYS assessment. Its ability to measure both longitudinal and radial intraventricular DYS is noteworthy.

Cross-correlation Quantification of Dyssynchrony: A New Method for Quantifying the Synchrony of Contraction and Relaxation in the Heart

BACKGROUND

Quantification of left ventricular dyssynchrony using Doppler tissue imaging may improve selection of patients who will benefit from cardiac resynchronization therapy. Most methods used to quantify dyssynchrony use a time-to-peak analysis, which is quantitatively simplistic and requires manual identification of systole and selection of peak velocities.

METHODS

We developed and tested a new, highly automatable dyssynchrony parameter, cross-correlation delay (XCD), that does not require identification of systole or manual selection of peak systolic velocities. XCD uses all velocity data points from 3 consecutive beats (approximately 420 points). We tested XCD on 11 members of a positive control group (responders to cardiac resynchronization therapy with a >or=15% reduction in left ventricular end-systolic volume) and 12 members of a negative control group (normal 12-lead electrocardiogram and 2-dimensional echocardiogram findings). We compared XCD to septal-to-lateral delay in time-to-peak (SLD), maximum difference in the basal 2- or 4-chamber times to peak (MaxDiff), and SD of the 12 basal and midwall times-to-peak (Ts-SD).

RESULTS

XCD and Ts-SD were significantly different between the positive and negative control groups (both P <or= .0001). SLD and MaxDiff demonstrated no difference between the positive and negative control groups. XCD and Ts-SD were superior to SLD and MaxDiff in discriminating between positive and negative control groups (both P < .01 by receiver operating characteristic comparison). XCD, SLD, MaxDiff, and Ts-SD demonstrated dyssynchrony in 0%, 50%, 58%, and 50% of the negative control group, respectively. XCD was the only parameter that decreased after resynchronization in the positive control group (from 160 +/- 88-69 +/- 61 milliseconds, P = .003).

CONCLUSION

XCD is superior to existing parameters at discriminating patients with left ventricular dyssynchrony from those with normal function.

Concordance Between Mechanical and Electrical Dyssynchrony in Heart Failure Patients: A Function of the Underlying Cardiomyopathy?

BACKGROUND

Cardiac resynchronization therapy (CRT) improves heart failure (HF) symptoms through a reduction of cardiac mechanical dyssynchrony. Mechanical dyssynchrony is currently estimated by electrical dyssynchrony (QRS duration). It is known that electrical and mechanical dyssynchrony are not well correlated in HF patients. However, there is limited information about whether this relationship might be influenced by the underlying cardiomyopathy.

METHODS

Doppler echocardiography was performed in 88 patients presenting with heart failure due to ischemic (n = 42) or nonischemic (n = 46) heart disease, left ventricular ejection fraction <40%, New York Heart Association class II-IV, regardless of their QRS duration. Interventricular dyssynchrony was assessed by the time interval between preaortic and prepulmonary ejection times. Intraventricular dyssynchrony was ascertained by (1) the delay between the earliest and the latest peak negative longitudinal strain recorded in the basal and mid-segments of the lateral and septal walls (TMinMax) and (2) the standard deviation of time-to-peak in the same segments (SDdys).

RESULTS

The correlation coefficient between QRS duration and mechanical interventricular dyssynchrony was r = 0.47 (P < 0.001) in patients with nonischemic disease and nonsignificant in patients with ischemic disease. Similarly, the correlation coefficient between QRS duration and mechanical intraventricular dyssynchrony was significant in patients with nonischemic disease (r = 0.37, P = 0.01 for TMinMax; r = 0.42, P = 0.003 for SDdys) and nonsignificant in patients with ischemic disease.

CONCLUSION

The concordance between electrical dyssynchrony assessed by QRS duration and mechanical dyssynchrony assessed by myocardial strain is dependent upon the underlying cardiomyopathy. This observation may improve our understanding of the various responses observed in CRT patients.