Real-time strain rate echocardiographic imaging: temporal and spatial analysis of postsystolic compression in acutely ischemic myocardium

Appropriate Window Function and Window Length in Multifrequency Velocity Estimator for Rapid Motion and Locality of Layered Myocardium

The heart wall has a multilayered structure and moves rapidly during ejection and rapid filling periods. Local strain rate (SR) measurements of each myocardial layer can contribute to accurate and sensitive evaluations of myocardial function. However, ultrasound-based velocity estimators using a single-frequency phase difference cannot realize these measurements owing to insufficient maximum detectable velocity, which is limited by a quadrature frequency. We previously proposed a velocity estimator using multifrequency phase differences to improve the maximum detectable velocity. However, the improvement is affected by a spatial discrete Fourier transform (DFT) window length that represents the locality of the velocity estimation. In this article, we theoretically describe that shortening the window increases the interference between different frequency components and decreases the maximum detectable velocity. The tradeoff between the maximum detectable velocity and the window length was confirmed through simulations and a water-tank experiment. Under the tradeoff, the Hanning window, which was used in previous studies, is not always appropriate for the local measurement of the velocity, which sometimes exceeds 100 mm [Formula: see text] depending on the subject, direction of the ultrasound beam to the heart wall, and cardiac periods. In the in vivo measurement with the short window, the Tukey window with a large flat part that has a high-frequency resolution and ameliorates the discontinuity at both edges of the windowed signal was appropriate to measure the maximum velocity. This study offers the potential for local measurements of each myocardial layer using the multifrequency velocity estimator with the appropriate window function and window length.

Segmental Tissue Speckle Tracking Predicts the Stenosis Severity in Patients With Coronary Artery Disease

Objective

Two-dimensional speckle tracking echocardiography (2D-STE) has been used as a diagnostic tool for coronary artery disease (CAD). However, whether vessel supplied myocardial strain and strain rate (SR) predict the severity of coronary artery stenosis in patients with CAD is unknown. This study aimed to investigate correlation of cardiac mechanical parameters in tissue speckle tracking measurements with coronary artery stenosis diagnosed by cardiac catheterization in patients with clinically diagnosed CAD.

Methods and Results

Among 59 patients analyzed, 170 vessels were evaluated by coronary angiography and the corresponding echocardiography to quantify left ventricular myocardial strain and SR. The average longitudinal strain and SR of the segmental myocardium supplied by each coronary artery were calculated to achieve vessel myocardium strain (VMS) and strain rate (VMSR). The VMS and VMSR at each of four severity levels of stenosis showed significant differences among groups (p = 0.016, and p < 0.001, respectively). The strain and SR in vessels with very severe stenosis (≥75%, group IV; n = 29), 13.9 ± 4.3, and 0.9 ± 0.3, respectively, were significantly smaller than those of vessels with mild stenosis ≤ 25%, group I; n = 88, 16.9 ± 4.9, p = 0.023, and 1.2 ± 0.3, p = 0.001, respectively. The SR in vessels with moderate stenosis (26–49%, group II; n = 37), 1.0 ± 0.2, was significantly smaller than that in vessels with mild stenosis vessels (p = 0.021). The lower VMS and VMSR, the higher possibility of severe coronary stenosis is. The VMS and VMSR lower than 13.9 ± 4.3 and 0.9 ± 0.3, respectively predicted the severe coronary stenosis. The VMS and VMSR higher than 16.9 ± 4.9 and 1.2 ± 0.3, respectively predicted mild or no coronary artery stenosis.

Conclusions

The actual stenosis rate in catheterization demonstrates that this technique was able to assess coronary artery condition. Thus, the application of a non-invasive method of 2D-STE to evaluate and simplify diagnosis of CAD is feasible.

Myocardial Postsystolic Shortening and Early Systolic Lengthening: Current Status and Future Directions

The concept of paradoxical myocardial deformation, commonly referred to as postsystolic shortening and early systolic lengthening, was originally described in the 1970s when assessed by invasive cardiac methods, such as ventriculograms, in patients with ischemia and animal experimental models. Today, novel tissue-based imaging technology has revealed that these phenomena occur far more frequently than first described. This article defines these deformational patterns, summarizes current knowledge about their existence and highlights the clinical potential associated with their understanding.

Post-systolic shortening: normal values and association with validated echocardiographic and invasive measures of cardiac function

Post-systolic shortening (PSS) does not contribute to the ejection of blood and may inhibit diastolic filling. We determined normal values of PSS in healthy subjects and investigated associations with echocardiographic and invasive measures of systolic and diastolic function. We prospectively analyzed participants from the general population (n = 620, mean age 47 ± 14 years) with no cardiovascular disease. Participants underwent echocardiography, including speckle tracking assessment of the post-systolic index (PSI), strain and time. We defined the PSI as: 100 × [(peak global longitudinal strain - peak systolic longitudinal strain)/(peak global longitudinal strain)]. We also included stable patients (n = 44) referred for left ventricle (LV) catheterization and echocardiography. Normal values: median PSI 2.0% (IQR 0.7, 4.8), post-systolic strain 0.4% (IQR 0.2, 0.8) and post-systolic time 22.6 ms (IQR 10.7, 40.8). Sex modified the relationship between PSI and age (P interaction = 0.037), such that PSI increased with age in women but not in men. PSI was associated with diastolic function (e', E/e' and E/A) (P < 0.05 for all), but not with LV ejection fraction (P = 0.08). PSI was associated with invasively measured LV pressure decline in early diastole, dP/dt min ([Formula: see text] = 0.12, P = 0.010), but not with LV pressure rise in early systole, dP/dt max ([Formula: see text]= - 0.05, P = 0.30). A PSI > 5% had 82% specificity and 99% sensitivity for identifying impaired LV systolic and/or diastolic function. Normal values of PSS are modified by sex. The PSI is associated with most validated echocardiographic and invasive measures of cardiac systolic and diastolic function.

Segmental early relaxation phenomenon as determined by tissue Doppler imaging

BACKGROUND

The early diastolic peak velocity of left ventricular (LV) wall segment has always been thought to appear in the rapid filling phase. However, we find a segmental early relaxation phenomenon (SERP), characterized by an early diastolic peak velocity lying in the isovolumic relaxation (IVR) period. The present study aimed to investigate the characteristics of SERP segments with tissue Doppler imaging (TDI) echocardiography.

METHODS

TDI was performed in 119 patients with known or suspected coronary heart disease (CHD) and 60 normal subjects. The segmental early diastolic velocity pattern was classified as normal pattern (NP), postsystolic shortening (PSS) and SERP.

RESULTS

Segmental early diastolic velocity pattern was significantly associated with actual coronary diameter stenosis, relative coronary stenosis, wall motion score, and segmental location in LV wall. Compared with other segments, SERP segments had a higher IVR velocity and lower early diastolic peak velocity.

CONCLUSION

SERP most frequently occurs in the distribution of artery with the relatively mildest stenosis, and is more likely accompanied by simultaneous PSS elsewhere in LV wall, which occurs most frequently in the distribution of artery with the relatively most severe stenosis. A decreased early diastolic peak velocity of SERP segment dose not necessarily mean impaired myocardial relaxation.

Mechanisms of postsystolic thickening in ischemic myocardium: mathematical modelling and comparison with experimental ischemic substrates

In the setting of regional ischemia, the "at-risk" myocardium exhibits a flow-related reduction in systolic thickening with a concomitant development of abnormal thickening after aortic valve closure (postsystolic thickening [PST]). With the introduction of high time-resolution ultrasonic-based strain/strain-rate imaging, this short lived phenomenon can be measured accurately in the clinical setting. The mechanisms underlying this ischemia-related PST are poorly understood and both active and passive etiologies have been proposed. This study aims at elucidating the potential mechanisms behind PST in the intact heart. A theoretical model, describing active force development, elasticity and segment interaction has been developed to simulate radial deformation during systole and iso-volumetric relaxation. Simulation results have been compared with experimental deformation curves obtained from postero-basal segments of a pig model undergoing varying controlled ischemic challenges. Three forms of regional ischemia could be simulated by varying the model parameters of the ischemic segments: (i) chronic regional hypo-perfusion (reduced and prolonged active force development; preserved elasticity); (ii) acute short-lived ischemia-temporary vessel occlusion (no active force development; preserved elasticity); and (iii) chronic myocardial infarction (no active force development; decreased elasticity). For all ischemic substrates, the simulated curves closely correlate to the deformation measured in the corresponding porcine models without the need for active force development during the occurrence of PST. This suggests that segment interaction is the key determinant in the development of PST. Thus, in all instances, at the time of its manifestation, ischemia-related PST could be explained in a unified way as a passive phenomenon that was the result of elastic segment interaction. Its occurrence originates from the end-systolic inhomogeneous state where neighboring segments have a different wall thickness. The occurrence of these differences at end-systole depends on the presence of regional differences within the ventricle in the magnitude and duration of the developed contraction force during the first part of systole, the elasticity of the ischemic segment and the left-ventricular pressure.

Early diastolic peak velocity of left ventricular wall segment lying in isovolumic relaxation period as determined by tissue Doppler imaging

BACKGROUND

The early diastolic peak velocity of left ventricular (LV) wall segment has always been regarded as appearing in the rapid filling phase. However, we find some segments of which early diastolic peak velocities appear in the isovolumic relaxation period (PVIVR segments). The present study aimed to investigate the characteristics of PVIVR segments.

METHODS

Tissue Doppler imaging was performed in each of the 16 segments of LV wall in 99 patients with known or suspected coronary heart disease and 50 normal subjects. Early diastolic velocity pattern was classified as PVIVR, post-systolic shortening (PSS) and normal pattern.

RESULTS

The multivariate logistic regression analyses showed that the significant echocardiographic predictors of the presence of PVIVR in a patient were transmitral E/A ratio and isovolumic relaxation time. Segmental early diastolic velocity pattern was significantly associated with actual coronary stenosis, relative coronary stenosis and wall motion score. PVIVR segments had a lower early diastolic peak velocity than other segments.

CONCLUSION

PVIVR segments more frequently appear in the territory with the relatively mildest coronary stenosis, whereas PSS segments more frequently appear in the territory with the relatively most severe coronary stenosis. Patients with PVIVR have lower global LV diastolic function. A decreased early diastolic peak velocity of PVIVR segments does not necessarily mean impaired myocardial relaxation.

Effect of medical therapy for heart failure on segmental myocardial function in patients with ischemic cardiomyopathy

The adjustment of medications and dosages to the needs of individual patients with heart failure is mostly intuitive, but even when their effect on global myocardial function is measured by classic indexes, their effect on segmental function is overlooked. This study was conducted to assess the feasibility of using echocardiographic myocardial strain imaging to evaluate the effect of medication on global and segmental function in 21 ambulatory patients with heart failure (mean age 65+/-11 years) who had echocardiographic studies performed before and 2 hours after ingesting their regular morning medications. The ejection fraction, global and regional strain, and time to regional peak strain were compared between the 2 examinations. Medication induced no significant changes in mean ejection fraction (28.6+/-7.8% to 27.5+/-9.9%) and mean global strain (-9.5+/-3.6% to -9.8+/-3.2%). Changes in segmental strain depended on baseline function: normal segments (peak strain more negative than -12%) deteriorated (-15.5+/-2.7% to -13.7+/-4.6%, p<0.0001), but dysfunctional segments (peak strain less negative than -8%) improved (-5.3+/-2.0% to -7.4+/-4.3%, p<0.0001). Medication also improved segmental synchronization: average time to peak strain of segments in which peak strain was attained before aortic valve closure increased (325+/-69 to 375+/-100 ms, p<0.0001), but that of segments with postsystolic shortening at baseline decreased (451+/-93 to 435+/-93 ms, p<0.006). Thus, the time interval between time to peak strain of segments with systolic and post-systolic shortening at baseline was halved after medication. In conclusion, medications for heart failure induced an increase in the echocardiographically determined peak strain of myocardial segments with impaired function at baseline but decreased the peak strain of normally contracting segments. Medications also improved the synchronization of myocardial contraction. Neither the global ejection fraction nor global strain reflected these changes. Thus, medication tended to improve the homogeneity of left ventricular contraction.

Detection of significant stenotic lesions in the left anterior descending coronary artery using adenosine triphosphate stress strain imaging: comparison with coronary flow velocity reserve measurement using transthoracic Doppler echocardiography

To evaluate the usefulness of adenosine triphosphate stress strain imaging for detecting significant coronary artery disease in the left anterior descending coronary artery (LAD), 34 patients underwent coronary flow velocity reserve measurement in the distal LAD and adenosine triphosphate stress strain imaging simultaneously. Time to peak strain (TPS) was measured in the apical septal segment. TPS ratio was obtained as the ratio between TPS at adenosine triphosphate stress and at baseline. TPS ratio in 11 patients with LAD lesions was significantly greater than that in 23 patients without LAD lesions (1.24 +/- 0.17 vs 0.92 +/- 0.12, respectively, P < .0001). With a cut-off value greater than or equal to 1.1 for the TPS ratio and less than 2.0 for the coronary flow velocity reserve, diagnostic accuracy for the presence of significant LAD lesions were 88% and 82%, respectively. In conclusion, strain imaging can differentiate ischemic and nonischemic myocardium accurately comparable with coronary flow velocity reserve measurement.

Analysis of Postsystolic Myocardial Thickening Work in Selective Myocardial Layers During Progressive Myocardial Ischemia

BACKGROUND

Myocardial function is transmurally heterogeneous. Postsystolic work may functionally reflect ischemic but viable myocardium. We calculated systolic and postsystolic regional myocardial work index (RMWi) in subendocardial and subepicardial layers of myocardium supplied by a slowly occluding coronary artery.

METHODS

Progressive stenosis of the left anterior descending coronary artery lasting 11 +/- 5 days (end point) was induced in 10 dogs, and pressure-strain loops were obtained from subendocardial and subepicardial layers of apical and middle anterior segments by intracardiac ultrasound.

RESULTS

At baseline, the RMWi was significantly higher (P < .05) in the subendocardial layer. At the end point, there was no significant change in the RMWi in ischemic myocardium; however, the postsystolic RMWi was higher (P < .05) in the subendocardial layer and accompanied a decrease in subendocardial myocardial blood flow, although viability was largely maintained.

CONCLUSION

A significant subendocardial postsystolic RMWi at rest suggests an impending ischemic injury in coronary artery disease when segmental function is still preserved.

Identification of stimulation site of pacemaker lead using tissue tracking method

PURPOSE

We aimed to identify the electrical stimulation sites of pacemaker leads using a tissue tracking method of tissue Doppler imaging.

METHODS

The study group consisted of 30 patients who had undergone permanent pacemaker implantation. During tissue Doppler imaging, the initial contraction site was seen as a red area stimulated by the pacemaker lead. This red area was analyzed precisely using time-distance curves generated by tissue tracking.

RESULTS

The initial contraction site of the myocardium was located in the interventricular septum in seven patients and in the apical portion of the right ventricle in 11 patients. Furthermore, analysis of time-distance curves demonstrated that one point within the red area started to move earlier than the others.

CONCLUSION

The site of electrical stimulation within the myocardium can be determined from the time-distance curves generated by the tissue tracking method.

Which Doppler Parameters Are Load Independent? A Study in Normal Volunteers After Blood Donation

OBJECTIVES

We sought to assess the effects of blood donation on different echocardiographic parameters in healthy volunteers.

METHODS

A total of 101 healthy male volunteers were evaluated by echocardiography before and immediately after a 500-mL blood donation. In addition to traditional Doppler indices of left ventricular filling, Doppler tissue, color flow propagation, strain (epsilon), and epsilon rate were measured.

RESULTS

There was a statistically significant decrease in mitral peak E and A values after blood donation (E wave 0.85 +/- 0.12 vs 0.79 +/- 0.14 cm/s, P = .01; A wave 0.65 +/- 0.10 vs 0.60 +/- 0.12 cm/s, P = .05). Mitral color flow propagation velocity was not affected (560 +/- 123 vs 571 +/- 132 mm/s, P = not significant). There were no significant differences in the Doppler tissue parameters of peak systolic, and early and late diastolic velocities after blood donation (Sm 13.5 +/- 4.6 vs 13.3 +/- 4.9 cm/s, P = not significant; Em 15.5 +/- 4.9 vs 15.9 +/- 5.1 cm/s, P = not significant; and Am 14.1 +/- 3.9 vs 14.1 +/- 3.5 cm/s, P = not significant, respectively). The peak systolic decreased significantly (-28 +/- 8% vs -21 +/- 4%, P = .03) whereas the peak systolic rate was not affected (1.5 +/- 0.35 vs 1.4 +/- 0.40 s(-1), P = not significant).

CONCLUSION

In healthy male volunteers, preload reduction induced by a 500-mL blood donation does not affect the color propagation velocity, rate, and Doppler tissue velocities.

Apex-to-base dispersion in regional timing of left ventricular shortening and lengthening

OBJECTIVES

We investigated whether the onset and progression of regional left ventricular (LV) shortening and lengthening parallel the apex-to-base differences in depolarization and repolarization.

BACKGROUND

Limited information exists regarding apex-to-base differences in longitudinal and circumferential deformation sequence of the LV.

METHODS

The apex-to-base differences in electric activation and the progression of longitudinal and circumferential shortening and lengthening sequences were determined in 8 porcine beating hearts in situ by implanting bipolar electrodes and an array of 14 sonomicrometry crystals in the LV free wall.

RESULTS

Electric activation started at the apical subendocardium and showed significant delay in reaching the LV base. The onsets of mechanical activation and subsequent 20%, 40%, and 80% peak longitudinal shortenings required longer time to occur at base compared to the apex. The repolarization sequence propagated in reverse, with the base repolarizing before the apex. Subendocardial longitudinal shortening at base and subepicardial circumferential shortening at apex continued beyond the period of LV ejection, resulting in an apex-to-base gradient in the onset of lengthening. This gradient correlated with the duration of isovolumic relaxation (r = 0.85, p = 0.004) and the time required for reaching the lowest LV diastolic pressure (r = 0.70, p = 0.04).

CONCLUSIONS

Apex-to-base delay in mechanical shortening of LV parallels the apex-to-base direction of the electric activation sequence. Basal subendocardial and apical subepicardial regions deform through a characteristic phase of postsystolic shortening. Short-lived apex-to-base and subendocardial-to-subepicardial relaxation gradients at the onset of diastole may have a physiologic significance in facilitating active restoration of the LV cavity in diastole.

Noninvasive Quantification of Regional Ventricular Function in Rats: Assessment of Serial Change and Spatial Distribution Using Ultrasound Strain Analysis

BACKGROUND

The optimal method for quantitative assessment of regional ventricular function in rats remains unclear. The goal of this study was to investigate the use of ultrasonic strain rate (SR) and strain analysis in evaluating the serial change and spatial distribution of regional contractile function in rats.

METHODS

In all, 22 anesthetized rats underwent incremental dobutamine infusion (protocol 1) for assessment of serial change or underwent coronary ligation (protocol 2) for assessment of spatial distribution. For protocol 1, the serial change of systolic SR and strain during dobutamine was measured in the posterior myocardium on the short-axis view, and the systolic strain was compared with the percent change in wall thickening. For protocol 2, the spatial distribution of strain profile was analyzed in normal, peripheral ischemic, and central ischemic regions that were identified by myocardial contrast echocardiography.

RESULTS

In protocol 1, the incremental dobutamine infusion resulted in a gradual increase in peak systolic SR. In contrast, peak systolic strain increased with low-dose dobutamine but tended to decrease for higher doses of dobutamine. Further, the serial change of peak systolic strain corresponded to changes in percent change in wall thickening, but the strain values were always lower than percent change in wall thickening. In protocol 2, the strain profile indicated postsystolic thickening in the peripheral ischemic region and indicated systolic wall thinning in the central ischemic region.

CONCLUSIONS

Ultrasonic determination of SR and strain is an accurate and noninvasive method of quantitation of the serial change and spatial distribution of regional contractile function in rats.

Biphasic tissue Doppler waveforms during isovolumic phases are associated with asynchronous deformation of subendocardial and subepicardial layers

Subendocardial and subepicardial layers of the left ventricle (LV) are characterized with right- and left-handed helical orientations of myocardial fibers. We investigated the origin of biphasic deformations of the LV wall during isovolumic contraction (IVC) and relaxation (IVR). In eight open-chest adult pigs, strain rates were measured along the right- and left-handed helical directions in the LV anterior wall by implanting 16 sonomicrometry crystals. Sonomicrometry strain rates were compared with the longitudinal subendocardial strain rates obtained by tissue Doppler imaging. During ejection and diastolic filling, shortening and lengthening occurred synchronously along the right- and left-handed helical directions. However, during IVC and IVR, the deformations were dissimilar in the two directions. Transmural shortening during IVC occurred along the right-handed helical direction and was accompanied with transient lengthening in the left-handed helical direction. Conversely, during IVR, the LV lengthened along the left-handed helical direction and shortened in the right-handed helical direction. Peak subendocardial strain rates obtained by tissue Doppler imaging during IVC and IVR correlated with corresponding sonomicrometry strain rate values obtained along the right- and left-handed helical directions ( r = 0.81, P < 0.001 and r = 0.70, P = 0.001, respectively). Our data suggest that brief counterdirectional movements occur within the LV wall during IVC and IVR. Shortening along the right-handed helical direction is accompanied with reciprocal lengthening in the left-handed helical direction during IVC and vice versa during IVR. The results support an association between asynchronous deformation of subendocardial and subepicardial muscle fibers and the biphasic isovolumic movements observed with high-resolution tissue Doppler imaging.

Delayed Onset of Subendocardial Diastolic Thinning at Rest Identifies Hypoperfused Myocardium

Background— Onset of myocardial relaxation is highly energy dependent. Perfusion and therefore energy substrate delivery are predominantly reduced in the subendocardial myocardium in the early stages of progressive ischemia. We hypothesized that delayed onset of subendocardial diastolic thinning will functionally identify regionally hypoperfused resting myocardium.

Methods and Results— Progressive left anterior descending coronary artery stenosis was induced by an ameroid occluder and maintained for 1 or 2 weeks (end point) in 12 dogs. M-mode tissue Doppler images of the anterior apical and middle segments (testing region) and middle inferior segment (control region) were acquired selectively in the subendocardium and subepicardium. The time to the onset of thinning was measured with the use of tissue Doppler velocity (TOTv) and a thickness function (TOTt). At the end point in the testing region, myocardial flow was significantly lower in the subendocardial layer ( P <0.05) in all animals, whereas viability staining showed preserved transmural viability in 10 dogs and thin subendocardial necrosis in 2 dogs. Both TOTv and TOTt were significantly ( P <0.01) prolonged in the testing region. The mean difference between subendocardial and subepicardial TOTv values versus that in the control region identified the ischemic region, even when only dogs with hypoperfused but transmurally viable myocardium were considered ( P <0.05). Systolic and diastolic myocardial velocities did not identify subendocardial hypoperfusion.

Conclusions— In resting myocardium subtended to progressive coronary stenosis, a delayed onset of subendocardial thinning suggests an early stage of hypoperfusion, before the development of local wall motion abnormalities.

Two-dimensional strain-a novel software for real-time quantitative echocardiographic assessment of myocardial function

OBJECTIVES

We sought to assess the feasibility of 2-dimensional strain, a novel software for real-time quantitative echocardiographic assessment of myocardial function.

METHODS

Conventional and a novel non-Doppler-based echocardiography technique for advanced wall-motion analysis were performed in 20 patients with myocardial infarction and 10 healthy volunteers from the apical views. Two-dimensional strain is on the basis of the estimation that a discrete set of tissue velocities are present per each of many small elements on the ultrasound image. This software permits real-time assessment of myocardial velocities, strain, and strain rate. These parameters were also compared with Doppler tissue imaging measurements in 10 additional patients.

RESULTS

In all, 80.3% of infarct and 97.8% of normal segments could be adequately tracked by the software. Peak systolic strain, strain rate, and peak systolic myocardial velocities, calculated from the software, were significantly higher in the normal than in the infarct segments. In the 10 additional patients, velocities, strain, and strain rate obtained with the novel software were not significantly different from those obtained with Doppler tissue imaging.

CONCLUSION

Two-dimensional strain can accomplish real-time wall-motion analysis, and has the potential to become a standard for real-time automatic echocardiographic assessment of cardiac function.

Strain rate and strain: a step-by-step approach to image and data acquisition

The advent of strain and strain rate imaging in clinical echocardiography prompted an examination of proper techniques for image acquisition and analysis. For this promising and relatively new method of assessing myocardial performance to be successful in diagnostic echocardiography, close adherence to a standardized method is imperative. This article provides the echocardiographer with a step-by-step approach.

Improved recognition of dysfunctioning myocardial segments by longitudinal strain rate versus velocity in patients with myocardial infarction

Doppler tissue imaging (DTI) can measure myocardial velocities but velocities alone cannot distinguish active from passive wall motion, whereas this is possible by strain rate (SR) imaging (SRI). We evaluated the accuracy of SRI for recognition of abnormal regional systolic function compared with DTI, B-mode echocardiography, and anatomic M-mode in 24 patients with myocardial infarction who underwent gated stress Tc 99m sestamibi scan. Sensitivity and specificity for recognition of infarct segments were 91% and 84% for visual SRI, 63% and 73% for visual DTI, 78% and 71% for B-mode echocardiography, and 87% and 77% for anatomic M-mode, respectively. Peak SRs correlated with wall-motion assessment by B-mode echocardiography better than peak velocities (P =.66 vs.10), with less overlap between groups. Therefore, SRI improves evaluation of regional wall motion compared with DTI and conventional ultrasound techniques in patients with myocardial infarction, mainly because it identifies segments that are moving passively but not shortening normally.

Tissue Doppler, strain, and strain rate echocardiography for the assessment of left and right systolic ventricular function

Tissue Doppler (TDE), strain, and strain rate echocardiography are emerging real time ultrasound techniques that provide a measure of wall motion. They offer an objective means to quantify global and regional left and right ventricular function and to improve the accuracy and reproducibility of conventional echocardiography studies. Radial and longitudinal ventricular function can be assessed by the analysis of myocardial wall velocity and displacement indices, or by the analysis of wall deformation using the rate of deformation of a myocardial segment (strain rate) and its deformation over time (strain). A quick and easy assessment of left ventricular ejection fraction is obtained by mitral annular velocity measurement during a routine study, especially in patients with poor endocardial definition or abnormal septal motion. Strain rate and strain are less affected by passive myocardial motion and tend to be uniform throughout the left ventricle in normal subjects. This paper reviews the underlying principles of TDE, strain, and strain rate echocardiography and discusses currently available quantification tools and clinical applications.

Clinical applications of strain rate imaging

Myocardial strain (epsilon) is a dimensionless index of change in myocardial length in response to an applied force. epsilon Rate (SR) is the rate of change of length and is usually obtained as the time derivative of the epsilon signal. In echocardiography, SR is calculated as the difference between 2 velocities normalized to the distance between the 2 velocities. SR imaging (SRI) has a theoretic advantage over Doppler tissue imaging in that SRI is relatively immune to cardiac translational motion and tethering. Therefore, SRI may be superior to Doppler tissue imaging in quantitative assessment of regional myocardial function and may find clinical application in the interrogation of coronary artery disease. The high frame rates of SRI have also renewed interest in timings of global and regional mechanical events, and their potential clinical applications. The high temporal resolution allows SRI to depict regional systolic and diastolic asynchrony. Ongoing clinical trials will determine the sensitivity, specificity, and accuracy of SRI parameters for a variety of clinical conditions. Potential clinical applications include investigation of ischemia (at rest and with stress), myocardial viability, and altered global and regional systolic and diastolic function in cardiomyopathies. Suboptimal signal quality remains a major limitation of strain imaging, and advances in data acquisition and postprocessing capabilities will help determine its future incorporation into standard regional myocardial assessment.

Strain rate acceleration yields a better index for evaluating left ventricular contractile function as compared with tissue velocity acceleration during isovolumic contraction time: an in vivo study

OBJECTIVE

Our study aimed to investigate whether strain rate acceleration (SRA) during isovolumic contraction time (IVCT) could serve as a sensitive indicator of myocardial function.

METHODS

A total of 8 sheep underwent occlusion of left anterior descending coronary artery or diagonal branches and 2 sheep underwent left circumflex coronary artery occlusion to create septal, apical, or basal segment myocardial ischemia 19 to 27 weeks before the study. Baseline, volume-loading, dobutamine, and metoprolol infusion were used to produce 4 hemodynamic stages for each sheep. Doppler tissue imaging was acquired using a 5-MHz probe (GE/VingMed Vivid Five, GE Medical Systems, Milwaukee, Wis) on open-chest animals using the liver as a standoff at the apex. Using software (EchoPac, GE Medical Systems), SRA during IVCT was calculated and compared with tissue velocity acceleration (TVA) during IVCT from areas located in the normal and ischemic zones. Also, invasively monitored left ventricle dP/dt was measured as reference contractile function.

RESULTS

Both TVA and SRA during IVCT showed higher values for normal tissue than for ischemic area (P <.0001). SRA for normal wall segments changed significantly during the 4 stages (P =.01) with corresponding changes on high-fidelity left ventricular pressure catheters (r = 0.92). TVA over normal segments showed no significant change (P =.29) in the 4 hemodynamic stages. Both TVA and SRA of the ischemic segments showed no significant change with pharmacologic maneuvers or loading conditions.

CONCLUSIONS

SRA and TVA during IVCT are both useful indicators for detecting abnormal heart wall motion. However, SRA tends to be more sensitive than TVA for differentiating the response to stress conditions.

Strain during gastric contractions can be measured using Doppler ultrasonography

This study was undertaken to explore if strain of the muscle layers within the gastric wall could be measured by transabdominal strain rate imaging (SRI), a novel Doppler ultrasound (US) method. A total of 9 healthy fasting subjects (8 women, 1 man; ages 22 to 55 years) were studied and both grey-scale and Doppler US data were acquired with a 5- to 8-MHz linear transducer in cineloops of 97 to 256 frames. Rapid stepwise inflation (5 to 60 mL) of an intragastric bag was carried out and bag pressure and SRI were measured simultaneously. SRI enabled detailed studies of layers within the gastric wall in all subjects. Great variations in strain distribution of the muscle layers were found. Radial strain was much higher in the circular than in the longitudinal muscle layer. Strains derived from SRI correlated well with strains obtained with B-mode measurements (r = 0.98, p < 0.05). During balloon distension, we found an inverse correlation between pressure and radial strain (r = -0.87, p < 0.05). Intraobserver correlation of strain estimation was r = 0.98 (p < 0.05) and intraobserver agreement was 0.2% +/- 18.6% (mean difference +/- 2SD, % strain). Interobserver correlation was r = 0.84 (p < 0.05) and interobserver agreement was 6.9% +/- 56.8%. SRI enables detailed mapping of radial strain distribution of the gastric wall and correlates well with B-mode measurements and pressure increments.

Strain and strain rate echocardiography

Strain and strain rate echocardiography is an emerging technique for assessing myocardial systolic and diastolic function. It is envisioned that this modality could change the quantitative assessment of regional wall motion and improve the accuracy and reproducibility of test readings. Myocardial strain and strain rate can detect inducible ischemia and at earlier stages than visual estimation of wall motion or wall thickening parameters. Changes in systolic strain rate and strain have potential to discriminate between different myocardial viability states. Measurement of diastolic rate of deformation can differentiate physiologic from pathologic hypertrophy, and restrictive from constrictive cardiomyopathy. This article reviews basic principles and current experimental and clinical applications of strain and strain rate echocardiography.

Time to onset of regional relaxation: feasibility, variability and utility of a novel index of regional myocardial function by strain rate imaging

OBJECTIVES

Time to onset of regional relaxation (T(R)) has been proposed as a novel index of regional myocardial function. This study sought to prospectively establish the feasibility and variability of T(R) in healthy volunteers (CONTROL) and to examine its utility in patients with inducible ischemia (PATIENT).

BACKGROUND

Strain rate imaging (SRI) depicts myocardial deformation and enables quantitation of regional myocardial function with high temporal and spatial resolution. Thus, regional mechanical events can be accurately timed with SRI. The time point of regional transition from contraction to relaxation is altered in pathologic states.

METHODS

Resting mean segmental T(R) was determined in 60 subjects: 20 in the CONTROL group and 40 in the PATIENT group. T(R) was also measured at peak dobutamine stress in the PATIENT group. An automated image analysis program determined the time point of transition from regional contraction to relaxation activity, and calculated T(R), defined as the time, in milliseconds, from the electrocardiogram R-wave to this transition point.

RESULTS

Automated T(R) measurements were feasible in more than 90% of the segments in CONTROL and PATIENT groups. Mean T(R) was 353 +/- 24 ms and was shorter in the mid segments compared to apical and basal segments. Intra- and interobserver variability were low (6% and 9%, respectively). In the PATIENT group, the percent decrease in T(R) during dobutamine stress was significantly higher in normal compared to ischemic segments (30% vs. 19%, respectively, p = 0.01). A percent change >20% in T(R) identified patients with an ischemic response during dobutamine infusion (sensitivity 92%, specificity 75%).

CONCLUSIONS

T(R), a novel quantitative index of regional myocardial function, can be determined with low variability and satisfactory feasibility in routine clinical settings. Percent change in T(R) identifies ischemic segments during dobutamine stress echocardiography (DSE) and may allow quantitative assessment of DSE.

Diastolic function in hypertension

Diastolic dysfunction in patients with hypertension may present as asymptomatic findings on noninvasive testing, or as fulminant pulmonary edema, despite normal left ventricular systolic function. Up to 40% of hypertensive patients presenting with clinical signs of congestive heart failure have normal systolic left ventricular function. In this article we review the pathophysiologic factors affecting diastolic function in individuals with diastolic function, current and emerging tools for measuring diastolic function, and current concepts regarding the treatment of patients with diastolic congestive heart failure.