Intracardiac measurement of pre-ejection myocardial velocities estimates the transmural extent of viable myocardium early after reperfusion in acute myocardial infarction

Wave propagation of myocardial stretch: correlation with myocardial stiffness

The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart walls. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in 16 pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (E VP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end-diastolic stress-strain relation (E SS). Myocardial distensibility and α- and β-coefficients of stress-strain relations were calculated. Vp was higher at reperfusion compared to baseline (2.6 ± 1.3 vs. 1.3 ± 0.4 m/s; p = 0.005) and best correlated with E SS (r2 = 0.80, p < 0.0001), β-coefficient (r2 = 0.78, p < 0.0001), distensibility (r2 = 0.47, p = 0.005), and wall thickness/diameter ratio (r2 = 0.42, p = 0.009). Elastic moduli (E VP and E SS) were strongly correlated (r2 = 0.83, p < 0.0001). Increasing preload increased Vp and E VP and decreased distensibility. At multivariate analysis, E SS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2 model = 0.83, p < 0.0001). In conclusion, the main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography.

Viscoelastic properties of normal and infarcted myocardium measured by a multifrequency shear wave method: comparison with pressure-segment length method

Our aims were (i) to compare in vivo measurements of myocardial elasticity by shear wave dispersion ultrasound vibrometry (SDUV) with those by the conventional pressure-segment length method, and (ii) to quantify changes in myocardial viscoelasticity during systole and diastole after reperfused acute myocardial infarction. The shear elastic modulus (μ1) and viscous coefficient (μ2) of left ventricular myocardium were measured by SDUV in 10 pigs. Young's elastic modulus was independently measured by the pressure-segment length method. Measurements made with the SDUV and pressure-segment length methods were strongly correlated. At reperfusion, μ1 and μ2 in end-diastole were increased. Less consistent changes were found during systole. In all animals, μ1 increased linearly with left ventricular pressure developed during systole. Preliminary results suggest that μ1 is preload dependent. This is the first study to validate in vivo measurements of myocardial elasticity by a shear wave method. In this animal model, the alterations in myocardial viscoelasticity after a myocardial infarction were most consistently detected during diastole.

Ultra-high frame rate tissue Doppler imaging

We describe a new tissue Doppler imaging (TDI) method, ultra-high frame rate tissue Doppler imaging (UFR-TDI). With two broad transmit beams covering only the ventricular walls, we achieve 1200 frames/s in a four-chamber apical view. We examined 10 healthy volunteers to study the feasibility of this method. Ultra-high-frame-rate TDI provided peak annular velocities and time to peak S' intervals in good agreement with those measured with conventional TDI. Moreover, UFR-TDI provided additional information in early and late systole: In all subjects, the method was able to separate the timing of electrical activation, start of mechanical contraction, mitral valve closure and start of ejection. The earliest mechanical activation was seen before mitral valve closure. The method was also able to measure the propagation speed of the mechanical wave created by aortic valve closure.

Segmental color Doppler myocardial imaging derived pre-ejection velocities are not clinically useful in the assessment of post-infarction scar transmurality

INTRODUCTION

The presence of a velocity in isovolumic contraction phase (Vivc) evaluated using tissue Pulse wave Doppler myocardial imaging (PWDMI) correlates with a transmural extent of scar after myocardial infarction. The possible clinical usefulness of Vivc evaluated using color Doppler myocardial imaging (CDMI) in detection of a scar after myocardial infarction extent in patients with coronary heart disease (CHD) and low LV systolic function remains to be clarified.

PATIENTS AND METHODS

57 patients with CHD (average LVEF 33.5±5%), examined echocardiographicaly (17-segment LV model, 689 segments evaluated) and by cardiac magnetic resonance. All segments were scanned for Vivc presence using CDMI. Vivc presence/absence was correlated with signs of a scar after MI in all segments and in akinetic segments separately.

RESULTS

We found significantly larger values of wall thickness (8.2±2,2 vs. 7.1±1.9, p<0.0001), significantly lower values of average late enhancement (LE) extent (1.32±1.78 vs. 1.66±1.98, p=0.041) and LE/wall thickness ratio (20.1±29.8 vs. 29.6±36.7, p=0.008) in segments with present Vivc. Vivc presence in a segment with an abnormal wall motion had a sensitivity of 72.9% and a specificity of 35.7% in recognizing a segment without a transmural scar (LE/ wall thickness ratio ≤75%). Vivc absence in a segment with an abnormal wall motion had a sensitivity of 72.7% and a specificity of 41.2% in recognizing a segment with a transmural scar (LE/wall thickness ratio ≥75%).

CONCLUSIONS

Isovolumic velocities evaluation assessed using color Doppler myocardial imaging is not applicable in a real-world clinical setting. The presence or absence of a velocity pattern during LV isovolumic contraction is not useful in in the assessment of a post-infarction scar transmurality.

Feasibility of prediction of myocardial viability with Doppler tissue imaging following percutaneous coronary intervention for ST elevation anterior myocardial infarction

BACKGROUND

In patients with acute ST elevation myocardial infarction (STEMI), it is clinically important to determine the viability of akinetic segments soon after acute reperfusion therapy. The purpose of this study was to determine whether Doppler tissue imaging can predict myocardial viability in this clinical setting.

METHODS

Twenty-four consecutive patients with the first acute anterior STEMI with akinetic apical segments were enrolled. Color-coded Doppler tissue imaging was performed. Myocardial velocity and strain values were determined from the septal and lateral walls at the normal basal and akinetic apical levels of the left ventricle on day 1 after percutaneous coronary intervention. The presence of isovolumic contraction of tissue velocity (TVivc) and strain rate (SRivc) were also determined.

RESULTS

Twenty patients (mean age 62 +/- 15 years; 11 men) returned for follow-up echocardiography to assess wall motion recovery and viability. Ten patients who had recovery of akinetic segments showed lower baseline E/e' ratios than those without recovery (13.4 +/- 5.9 vs 19.1 +/- 5.7; P = .04). There was no difference between 19 recovered and 21 nonrecovered apical segments in all TV, SR, and strain values except early diastolic SR (SRe; 0.64 +/- 0.35 vs 0.43 +/- 0.25 s(-1); P = .04) at day 1. With a cutoff value of 0.32 s(-1) for SRe, the receiver operating characteristic curve for the prediction of recovery showed the highest sensitivity of 84%. The presence of TVivc had sensitivity and specificity of 79% and 33%, respectively, and for SRivc, sensitivity and specificity were 84% and 63%, respectively. With the combination of SRe and SRivc, specificity was increased to 78%.

CONCLUSION

Patients with functional recovery from anterior STEMI showed better diastolic function, better SRe, and more isovolumic contraction. These parameters appear to be promising predictors for myocardial viability, and SR imaging was found to be a better method than TV imaging for the identification of viable myocardium in patients with STEMIs who underwent percutaneous coronary intervention.

Atrium-driven Mitral Annulus Motion Velocity Reflects Global Left Ventricular Function and Pulmonary Congestion During Acute Biventricular Pacing

BACKGROUND

The short-term effect of acute biventricular pacing on cardiac function in patients with chronic heart failure undergoing heart surgery is widely unknown. The present study was designed to determine whether mitral annular tissue Doppler imaging (TDI) is useful to predict acute changes in global systolic function determined by the continuous cardiac output method that was measured postoperatively during various pacing configurations in patients with depressed left ventricular (LV) function.

METHODS

TDI peak velocities of systolic (Sm), early diastolic (Em), and late diastolic (Am) mitral annular motion waves were measured in 17 patients (age 67 +/- 8 years, 10 male) with depressed LV systolic function (LV ejection fraction < or = 35%) and QRS duration > 120 ms undergoing temporary epicardial biventricular pacing after aortocoronary bypass and valve surgery. TDI velocities, QRS duration on surface electrocardiogram, cardiac index (CI), right atrial pressure, pulmonary artery pressure, and pulmonary capillary wedge (PCW) pressure were measured simultaneously during various pacing configurations (right atrial-biventricular, right atrial-LV, right atrial-right ventricular, atrial inhibited, and no pacing).

RESULTS

Univariate linear regression analysis showed a good correlation between Am and CI (r = 0.53, P = .0001) determined in all pacing modes, a weak correlation between Sm and CI (r = 0.31, P = .017), and no correlation between Em and CI (r = 0.21, P = .074). Am > 6 cm/s predicted a CI of 2.5 L/min/m(2) or more with a sensitivity of 95% and a specificity of 30%. All TDI values correlated negatively with PCW (r = -0.53, P = .0001 for Sm; r = -0.34, P = .01 for Em; r = -0.50, P = .0001 for Am). Am greater than 6 cm/s predicted a PCW of 16 mm Hg or less with a specificity of 100% and a sensitivity of 34%. Mean values of TDI velocities and hemodynamic parameters were not significantly different between each pacing configuration.

CONCLUSIONS

Peak Am mitral annular velocity correlates well with CI and PCW, respectively, thus providing an easy means to assess LV systolic function and pulmonary congestion during cardiac pacing in chronic heart failure.

Clinical validity of longitudinal pre-ejectional myocardial velocity for identifying the transmural extent of viable myocardium: early after reperfusion of an infarct-related coronary artery

BACKGROUND

Positive longitudinal pre-ejectional velocity (+PEVL) was recently reported to be a reliable index of myocardial recovery early after successful revascularization in myocardial infarction (MI); that is, it recognizes the transmural extent of viable myocardium. The applicability of PEVL in the real-world clinical setting for identifying the transmural extent of viable myocardium in reperfused recent MI was assessed.

METHODS AND RESULTS

Using tissue Doppler imaging, the resting basal and mid myocardial PEVLs were determined within 3 days after revascularization in 41 consecutive patients with recent MI. Infarct thickness was semi-quantified using delayed gadolinium-enhanced magnetic resonance imaging (MRI) at baseline and at 6-month follow up to differentiate transmural from nontransmural MI. The proportion of segments showing the presence of +PEVL was not significantly changed as infarct thickness increased (p=0.2), with 66.2% having +PEVL even in segments involving >75% transmural infarction. Moreover, +PEVL was found in a large fraction of segments with akinesia (70.4%). Specificity and negative predictive value of +PEVL for assessing infarct nontransmurality were disappointingly low (32.0% and 26.9%, respectively). All of these results were not altered when the 6-month follow-up MRI was done.

CONCLUSIONS

+PEVL cannot be regarded as a reliable marker for predicting the transmural extent of viable myocardium in recent MI.

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.

Renewed Interest in Preejectional Isovolumic Phase: New Applications of Tissue Doppler Indexes: Implications to Ventricular Dyssynchrony

There is renewed interest in isovolumic contraction (IC) in tissue Doppler echocardiography of the myocardial walls, which is revisited in this editorial with new regional velocity data. The aims are to recall traditional background information and to emphasize the need to master the rapidly evolving tissue Doppler procedures for the accurate display of brief IC. IC, a preejectional component of great physiologic interest, is very demanding in terms of ultrasound technology. The onset and end of its motion velocities should be unambiguously defined versus the QRS complex and ejection wall motion. This is a prerequisite for exploiting the new information as guidance toward new therapeutic strategies from a practical viewpoint. However, IC preload dependence should be kept in mind, because of its limited potential for contractility studies. Finally, when only duration measurements are made in the assessment of ventricular dyssynchrony, regional preejectional duration is the pertinent tool to single out the onset of ejection local wall motion.

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.

Tissue Doppler echocardiographic quantification. Comparison to coronary angiography results in Acute Coronary Syndrome patients

Background

Multiples indices have been described using tissue Doppler imaging (DTI) capabilities. The aim of this study was to assess the capability of one or several regional DTI parameters in separating control from ischemic myocardium.

Methods

Twenty-eight patients with acute myocardial infarction were imaged within 24-hour following an emergent coronary angioplasty. Seventeen controls without any coronary artery or myocardial disease were also explored. Global and regional left ventricular functions were assessed. High frame rate color DTI cineloop recordings were made in apical 4 and 2-chamber for subsequent analysis. Peak velocity during isovolumic contraction time (IVC), ejection time, isovolumic relaxation (IVR) and filling time were measured at the mitral annulus and the basal, mid and apical segments of each of the walls studied as well as peak systolic displacement and peak of strain.

Results

DTI-analysis enabled us to discriminate between the 3 populations (controls, inferior and anterior AMI). Even in non-ischemic segments, velocities and displacements were reduced in the 2 AMI populations. Peak systolic displacement was the best parameter to discriminate controls from AMI groups (wall by wall, p was systematically < 0.01). The combination IVC + and IVR< 1 discriminated ischemic from non-ischemic segments with 82% sensitivity and 85% specificity.

Conclusion

DTI-analysis appears to be valuable in ischemic heart disease assessment. Its clinical impact remains to be established. However this simple index might really help in intensive care unit routine practice.

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.

A new Doppler tissue ratio to revisit systole: The pre-ejectional isovolumic to ejectional velocity ratio–application to aging

Most diagnostic applications of Doppler tissue echocardiography rely on peak (Pk) velocity (V) values of single variables or myocardial V gradient. Whereas age-related changes in diastolic V are well-known, previous Doppler tissue echocardiography studies of systolic function showed no age effect for pre-ejectional (Ej) isovolumic (PEI) and Ej inward wall motion Pk V. In addition to myocardial V gradient, ratios were calculated between PEI and Ej Pk V, and mean V averaged over systole (PEI/Ej V ratios) at each layer of the posterior wall using M-mode color on two control groups: A (27 +/- 5 years) and B (54 +/- 10 years). The only changes were for PEI/Ej V ratios (mean V endocardial 21 +/- 7% vs 34 +/- 20%, P = .01; mean V epicardial 27 +/- 8% vs 40 +/- 18%, P = .006; Pk epicardial V 21 +/- 10% vs 30 +/- 16%, P = .04 for groups A and B, respectively). Correlation versus age were r = 0.52 and P = .005 (mean V endocardial), r = 0.50 and P = .007 (mean V epicardial), and r = 0.32 and P = .03 (Pk epicardial V). PEI/Ej V ratios and mean V studied in separate layers showed that the new systolic approach had advantages over single variable or Pk V to study age-related changes.

Distinctive changes in end-diastolic wall thickness and postsystolic thickening in viable and infarcted myocardium

OBJECTIVES

In this study, we sought to compare the magnitude of changes in end-diastolic wall thickness (WT(ed)) and postsystolic thickening (PST) in a swine model of stunning and reperfused acute myocardial infarction, and to explore the relationship between WT(ed) and PST.

METHODS

Twenty-six pigs were subjected to left anterior descending coronary artery occlusion followed by reperfusion to induce stunning (n = 6), nontransmural (n = 8), or transmural (n = 12) myocardial infarction. Myocardial wall thickness was measured using intracardiac echocardiography. Transmural extent of necrosis (TEN) was quantified by triphenyltetrazolium chloride technique.

RESULTS

During the first minutes of reperfusion, a marked increase in WT(ed) occurred in the myocardial walls with nontransmural and transmural infarct (42% and 102%, respectively) but less in those with stunning (19%). PST persisted at reperfusion in walls with stunning and nontransmural infarct (23% and 26%, respectively). In transmurally infarcted walls, PST progressively decreased either during occlusion (5/12 pigs) or shortly after reperfusion (7/12 pigs). PST at reperfusion was virtually absent when TEN was >70%. Both PST and the increase in WT(ed) at reperfusion correlated well with TEN (P <.0001 for both). Changes in PST at reperfusion were weakly correlated with changes in WT(ed).

CONCLUSIONS

A marked increase in WT(ed) after reperfusion and absence of PST indicate transmural myocardial infarction. Presence of PST at reperfusion indicates viable tissue in more than 30% of wall thickness. The results suggest that amplitude of PST is modulated predominantely by factors related to the severity of ischemia and, to a smaller extent, by changes in wall thickness.

Tissue doppler imaging predicts recovery of left ventricular function after recanalization of an occluded coronary artery

OBJECTIVES

We tested the hypothesis that the tissue Doppler imaging (TDI)-derived positive preejection velocity (+VIC) can predict the recovery of contractile function after revascularization in patients with a recent myocardial infarction.

BACKGROUND

In experimental studies, the presence and extent of TDI-derived +VIC correlated with the extent of viable myocardium.

METHODS

Forty-three patients with a large myocardial infarction and an occluded left anterior descending (n = 38) or dominant right coronary (n = 5) artery were selected. The median duration of occlusion was 24 h. Longitudinal myocardial velocities were recorded at rest by pulsed-wave TDI echocardiography 6 +/- 2 h after revascularization. Functional recovery was defined as an increase in segmental chordal shortening > or =10% at three-month follow-up left ventricular angiogram as compared with baseline.

RESULTS

A good quality TDI signal was obtained in 309 of 324 analyzed segments (95.4%). Severe dysfunction was present in 198 segments of which 126 (64%) showed recovery at three-month follow-up. Sampling of all dysfunctional segments lasted 11 +/- 4 min per patient. Sensitivity, specificity, and accuracy of the +VIC to predict segmental recovery were 91%, 71%, and 84%, respectively. The percentage of segments that were dysfunctional at angiography but showed a +VIC correlated with improvement of both global left ventricular ejection fraction (r = 0.60, p = 0.001) and wall motion score index (r = -0.78, p < 0.0001) at follow-up.

CONCLUSIONS

Assessment of +VIC by pulsed-wave TDI is a simple and accurate method that predicts recovery of contractile function after revascularization in patients with a recent myocardial infarction.

Noninvasive Imaging of Myocardial Viability

Complete knowledge of myocardial structure, metabolism, and function is crucial to understanding the response of the heart to injury such as ischemia. Increasingly, this type of knowledge is required at multiple levels, from that of the isolated myocyte to the functioning organism, to provide basic scientists and clinical investigators a common framework for translation of findings and information feedback. This article focuses on the utilization of imaging methods to assess myocardial viability in vivo. It discusses the advantages and pitfalls of different imaging techniques, with particular emphasis on available data in humans and large animal models. Because of their novelty and potential for accurate phenotyping of human pathophysiology, magnetic resonance modalities will be highlighted.

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.