Dobutamine stress echocardiography at 7.5 mg/kg/min using color tissue Doppler imaging M-mode safely predicts reversible dysfunction early after reperfusion in patients with acute myocardial infarction

Relationship between post-systolic motion during dobutamine stress echocardiography and functional recovery of myocardium after successful percutaneous coronary intervention

BACKGROUND AND OBJECTIVES

Doppler myocardial imaging (DMI) has been suggested as a method of quantifying inducible ischemia during dobutamine stress echocardiography (DSE). Post-systolic motion (PSM) detected by DMI is related to peri-infarct ischemia during DSE. We hypothesized that PSM during DSE would predict recovery of dysfunctional myocardium after successful percutaneous coronary intervention (PCI).

SUBJECTS AND METHODS

Thirty patients with dysfunctional myocardium in the left anterior descending coronary artery (LAD) territory were divided into two groups according to improvement of wall motion score index (WMSI) in the LAD territory at 6 months after successful PCI of the LAD. DMI was evaluated in the LAD territory during DSE. Fifteen patients showed improved WMSI (1.42+/-0.39) while the other 15 had unchanged WMSI (1.75+/-0.46) 1 month after PCI. Myocardial velocity was measured in the mid-septal, apico-septal, and basal anterior segments of the LAD artery territory. PSM was defined as a positive wave appearing after the curve of systolic ejection had reached the zero line.

RESULTS

Although there was no difference between resting PSMs in both groups, PSM during DSE was significantly higher in the improved WMSI group than in the WMSI group where it was unchanged.

CONCLUSION

PSM during DSE predicts recovery of dysfunctional myocardium after successful PCI.

Recent advances in dobutamine stress echocardiography

Dobutamine stress echocardiography (DSE) is a reliable cardiac risk stratifier that has widespread applicability because of its clinical accuracy and cost effectiveness. Dobutamine has positive inotropic and chronotropic effects and is commonly used in patients who cannot exercise or achieve an adequate heart rate response with exercise. Recently available long-term results from several independent clinical trials, combined with enhancements in image quality, have improved the ability to detect significant coronary artery disease and determine myocardial viability. Dobutamine stress echocardiography has an excellent safety profile with clinical results superior to regular exercise electrocardiography and comparable with exercise echocardiography and radionucleotide perfusion stress imaging. Low-dose dobutamine response can accurately predict dysfunctional yet viable myocardial regions that may improve with revascularization. Clinical studies are now available refining the common use of DSE preoperatively in female patients with valvular disease, as well as in the emergency department. Dobutamine stress echocardiography does have some limitations in discriminating particular regions of ischemia when multiple ventricular segments are involved and when the imaging is suboptimal. It can be applied using minimal additional resources in an otherwise functioning echocardiography laboratory and, with appropriate training, can result in clinical results comparable with those of large-scale multicenter trials. Ongoing improvements in technology and the development of new reagents such as myocardial contrast agents hold promise for further advancement in the near future.

Power motion imaging can improve image quality in stress conditions with tachycardia

BACKGROUND

Stress echocardiographic studies are useful, but the evaluation of wall motion is sometimes suboptimal. The recently developed technique of power motion imaging can enhance mobile tissue definition.

HYPOTHESIS

The study was undertaken to determine whether power motion imaging improves endocardial definition during tachycardia compared with conventional two-dimensional (2-D) imaging.

METHODS

Twenty pigs were studied during pacing rates of 100, 120, and 150 beats/min. We compared power motion imaging with standard 2-D imaging using systolic thickening visualization (STV) scores (3 = excellent definition of systolic thickening approximately 0 = total lack of visualization of systolic thickening) at each heart rate. We calculated the sum of the scores of 22 left ventricular segments as the overall STV score, and also calculated the sum of the scores in 10 parasternal segments and 12 apical segments separately.

RESULTS

The overall STV scores in both imaging methods were similar at 100 beats/min, but scores for power motion imaging were significantly higher than those of usual 2-D imaging at 120 and 150 beats/min. Using power motion imaging, the overall STV scores were similar as heart rate was increased; however, while using standard 2-D imaging, STV scores were significantly decreased as heart rate was increased. Findings were analyzed separately by parasternal and apical images. Especially in the parasternal images, the scores were significantly increased as heart rate was increased using power motion imaging.

CONCLUSIONS

We conclude that power motion imaging improves the detection of endocardial border in stress condition with tachycardia, and thus this modality is useful for stress echocardiography.

Tissue Doppler and innovative myocardial-deformation imaging techniques for assessment of myocardial viability

PURPOSE OF REVIEW

Visual analysis of stress echocardiography allows evaluation of myocardial viability in acutely and chronically impaired left-ventricular function. Tissue Doppler and derived echocardiographic imaging techniques provide a tool for quantification of regional left-ventricular function which overcomes the limitations of subjective, experience-dependent reading of stress echocardiography.

RECENT FINDINGS

Regional systolic and diastolic myocardial velocities as well as the derived myocardial-deformation parameters strain and strain rate are impaired in patients with left-ventricular dysfunction. Increase of myocardial velocities, strain and strain rate during stress stimulation are indicators of functional reserve in viable segments, while failure to increase indicates nonviability. Previous studies with very precise determination of regional myocardial deformation have shown that even analysis of resting function without evaluation of the functional reserve during stimulation allows assessment of myocardial viability. New two-dimensional echocardiography-based tissue-tracking techniques yield an angle-independent imaging modality that is likely to further improve the clinical applicability of echocardiographic imaging techniques to define regional myocardial viability.

SUMMARY

This review attempts to define the role of tissue Doppler and new innovative myocardial-deformation imaging techniques for identification of myocardial viability in patients with impaired left-ventricular function.

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.

Sensitive method of detecting myocardial ischemia during dobutamine stress echocardiography

To test the hypothesis that dobutamine-induced myocardial ischemia causes early-systolic asynchrony predominantly in the regional left ventricular wall, color kinesis (CK) images during dobutamine stress echocardiography (DSE) were recorded in 13 patients with coronary artery disease and in 10 patients without, all of whom showed normal wall motion at rest. Based on the visual interpretation of DSE and the angiographic findings, 21 segments in the short-axis images at the papillary muscle level were defined as ischemic, and 60 segments of the patients without coronary artery disease were defined as normal. The incremental fractional segmental area change (IFAC) was calculated at 33-ms intervals from the CK images. At the peak dose, IFACs during the first 33 and 33-67 ms were significantly lower in the ischemic segments than in the normal ones, and IFACs during 133-167, 200-233 and 233-267 ms were significantly higher in the ischemic segments. The ratio (peak/low dose) of the cumulative fractional area change at 100 ms gave the best sensitivity (= specificity) for differentiating the 2 groups (86%). Dobutamine-induced ischemia is characterized by an early-systolic asynchrony rather than a change in overall wall excursion and CK can provide an objective assessment of ischemia developing during DSE.

Usefulness of quantitative echocardiographic techniques to predict recovery of regional and global left ventricular function after acute myocardial infarction

The left ventricular response to dobutamine may be quantified using tissue Doppler measurement of myocardial velocity or displacement or 3-dimensional echocardiography to measure ventricular volume and ejection fraction. This study sought to explore the accuracy of these methods for predicting segmental and global responses to therapy. Standard dobutamine and 3-dimensional echocardiography were performed in 92 consecutive patients with abnormal left ventricular function at rest. Recovery of function was defined by comparison with follow-up echocardiography at rest 5 months later. Segments that showed improved regional function at follow-up showed a higher increment in peak tissue Doppler velocity with dobutamine therapy than in nonviable segments (1.2 +/- 0.4 vs 0.3 +/- 0.2 cm/s, p = 0.001). Similarly, patients who showed a >5% improvement of ejection fraction at follow-up showed a greater displacement response to dobutamine (6.9 +/- 3.2 vs 2.1 +/- 2.3 mm, p = 0.001), as well as a higher rate of ejection fraction response to dobutamine (9 +/- 3% vs 2 +/- 2%, p = 0.001). The optimal cutoff values for predicting subsequent recovery of function at rest were an increment of peak velocity >1 cm/s, >5 mm of displacement, and a >5% improvement of ejection fraction with low-dose dobutamine.

Pulsed Doppler tissue imaging for the assessment of myocardial viability: comparison with 99mTc sestamibi perfusion imaging

The aim of the present study was to examine whether Doppler tissue imaging demonstrated comparable diagnostic performance for the detection of viable myocardium compared to myocardial perfusion imaging with Tc hexakis-2-methoxyisobutylisonitrile (MIBI). We studied 30 patients with old myocardial infarction who underwent percutaneous transluminal coronary angioplasty (PTCA). Myocardial single photon emission computed tomography (SPECT) with Tc-MIBI and two-dimensional echocardiography were carried out within 7 days before PTCA. We measured regional Tc-MIBI uptake for each myocardial segment from SPECT and peak systolic velocity and a ratio of regional pre-ejection period to regional ejection time (PEP/ET) from pulsed Doppler tissue imaging. Biplane left ventriculography was performed before interventional procedures and repeated 3 months after PTCA. Myocardial viability was determined when wall motion was improved at least one grade after PTCA. The peak systolic velocity was positively correlated with regional Tc-MIBI uptake (R =0.59, P<0.01). The PEP/ET demonstrated inverse correlation with Tc-MIBI uptake ( R=-0.59, P<0.01). Peak systolic velocity of viable segments was higher than that of non-viable segments ( P<0.05). The PEP/ET was lower in viable segments than in non-viable segments ( P<0.05). Peak systolic velocity and PEP/ET demonstrated high diagnostic accuracy for detecting viable myocardium compared with Tc-MIBI perfusion imaging (80% and 79% vs 90%). These data indicate that measurements of regional peak systolic velocity and PEP/ET by Doppler tissue imaging are useful for evaluating myocardial viability quantitatively and provide helpful information for a clinical judgment in an interventional strategy.

Use of pharmaceuticals in noninvasive cardiovascular diagnosis

A number of pharmaceuticals are employed as diagnostic agents for cardiovascular diseases. Four groups of agents are reviewed here: 1) vasoactive substances employed as adjuncts to physical maneuvers in diagnosis of structural heart disease; 2) vasodilators used to produce heterogeneity of coronary flow; 3) sympathomimetic agents simulating the effects of exercise on the heart for the purpose of detection of coronary artery stenosis; and 4) ultrasonic contrast agents used to enhance myocardial imaging for the assessment of segmental wall motion. In the first group are amyl nitrate, a vasodilator, and methoxamine and phenylephrine, both vasopressors. The vasodilators of the second group are dipyridamole and adenosine. When combined with scintigraphic perfusion imaging or with echocardiographic assessment of segmental wall motion, these agents can detect single- or multiple-vessel coronary artery disease with sensitivity and specificity comparable to submaximal exercise. They are especially useful for preoperative risk assessment before noncardiac surgery. The sympathomimetic agents of the third group, dobutamine and arbutamine, increase myocardial contractility and heart rate, and dilate the peripheral vasculature. As with the vasodilators, when combined with nuclear or echocardiographic techniques they are equivalent to exercise in detection of coronary disease. They are especially useful in patients with bronchospastic disease and for assessment of myocardial viability. Agents from groups 2 and 3 have acceptable side-effect and safety profiles. The last group reviewed includes echocardiographic contrast agents that, in this investigative setting, are employed to enhance detection of segmental wall motion when used with agents from groups 2 and 3.

Early systolic mitral annular motion velocities responses to dobutamine infusion predict myocardial viability in patients with previous myocardial infarction

OBJECTIVE

This study was undertaken for the determination of the correlation between myocardial viability and regional systolic mitral annular motion velocity (MAV) response to dobutamine stress in patients with previous myocardial infarction (MI) with pulsed tissue Doppler scan imaging.

METHODS

The study included 45 patients (mean age, 65 +/- 12 years) with previous MI with 1 major coronary lesion and 30 healthy individuals (mean age, 61 +/- 14 years). 99mTc-methoxyisobutylisonitrile scintigraphy was performed to divide the patients into 2 groups: the viability (+) group (n = 25) and the viability (-) group (n = 20). Dobutamine was infused (at 2, 5, 10, and 20 microg/kg/min), and the peak first and second systolic MAVs (Sw1 and Sw2, respectively) were measured at the level of the mitral annulus corresponding to the infarct regions in the MI group and to the 6 mitral annular sites in the control group. In addition, the left ventricular wall motion score index (WMSI) was determined with 2-dimensional echocardiography.

RESULTS

At baseline, the WMSI was significantly greater and the mean Sw1 and Sw2 were significantly lower in both the viability (+) and (-) groups than in the control group, but there were no significant differences between the viability (+) and (-) groups. After dobutamine infusion, the WMSI improved only in the viability (+) group. The mean Sw1 and Sw2 increased significantly with 2 microg/kg/min and 5 microg/kg/min of dobutamine, respectively, in the viability (+) group. With an increase in Sw1 of 2.0 cm/s or more with 5 microg/kg/min of dobutamine, viable myocardium was detected, with a sensitivity of 92% and a specificity of 90%. There were no significant increases in Sw1 or Sw2 in the viability (-) group with dobutamine infusion.

CONCLUSION

Viable left ventricular myocardium is identified with peak early systolic MAV during dobutamine infusion.

Strain rate measurement by doppler echocardiography allows improved assessment of myocardial viability inpatients with depressed left ventricular function

OBJECTIVES

This study sought to evaluate whether objective assessment of the myocardial functional reserve, using strain rate imaging (SRI), allows accurate detection of viable myocardium.

BACKGROUND

Strain rate imaging is a new echocardiographic modality that allows quantitative assessment of segmental myocardial contractility.

METHODS

In 37 patients (age 58 +/- 9 years) with ischemic left ventricular dysfunction, myocardial viability was assessed using low-dose (10 microg/kg body weight per min) two-dimensional dobutamine stress echocardiography (DSE), tissue Doppler imaging, SRI and (18)F-fluorodeoxyglucose ((18)FDG) positron emission tomography (PET). The peak systolic tissue Doppler velocity and peak systolic myocardial strain rate were determined at baseline and during low-dose dobutamine stress from the apical views.

RESULTS

A total of 192 segments with dyssynergy at rest were classified by (18)FDG PET as viable in 94 and nonviable in 98. An increase of peak systolic strain rate from rest to dobutamine stimulation by more than -0.23 1/s allowed accurate discrimination of viable from nonviable myocardium, as determined by (18)FDG PET with a sensitivity of 83% and a specificity of 84%. Receiver operating characteristic (ROC) curve analysis showed an area under the curve for prediction of nonviable myocardium, as determined by (18)FDG PET using SRI, of 0.89 (95% confidence interval [CI] 0.88 to 0.90), whereas the area under the ROC curve using tissue Doppler imaging was 0.63 (95% CI 0.61 to 0.65).

CONCLUSIONS

The increase in the peak systolic strain rate during low-dose dobutamine stimulation allows accurate discrimination between different myocardial viability states. Strain rate imaging is superior to two-dimensional DSE and tissue Doppler imaging for the assessment of myocardial viability.

Overview of stress echocardiography: uses, advantages, and limitations

Responses of the heart to changes in our environment are probably even more important than how the heart functions at rest. Accordingly, stress testing with noninvasive imaging has become important for diagnosis, prognosis, and monitoring the effects of therapy. Echocardiography at rest and with stress permits characterization of global and segmental left ventricular function as well as valvular structure and function. Moreover, echocardiography can be performed during or after a number of different physical or even mental stressors. Advantages of stress echocardiography include its ready availability, relatively low capital cost, and incremental value in that it allows characterization of cardiac anatomy as well as the myocardial response to a potentially ischemic stimulus. Moreover, echocardiography has the potential to image myocardial perfusion along with wall motion and wall thickening. Substantial literature has now been accumulated on the value of stress echocardiography for the diagnosis of ischemic disease, preoperative risk assessment, and assessment of myocardial viability. Echocardiography has compared generally well with nuclear imaging techniques for the detection of angiographic coronary artery disease. Overall sensitivity, however, has been slightly less, particularly for the detection of single-vessel coronary disease, although specificity has been on average somewhat higher than nuclear cardiology techniques. Because of the potential for variability in study acquisition as well as interpretation, careful safeguards need to be employed. Specifically, meticulous technique needs to be applied to obtain high-quality images and to assure that those images are obtained promptly after treadmill exercise stress. Only readers with specific interest and expertise should interpret stress echocardiography studies. Continuing efforts need to be made to assess and minimize variability and to assure continuing quality improvement. Advances in instrumentation, including evolving technology for real-time 3-dimensional imaging, and echocardiography contrast assessment of myocardial perfusion will likely improve the sensitivity of echocardiography and further extend its usefulness.

Tissue Doppler echocardiography

Tissue Doppler echocardiography (TDE) is a relatively recent addition to the diagnostic ultrasonographic examination. This is similar to routine Doppler ultrasonography to assess blood flow, but technologic features focus on lower velocity frequency shifts. Two techniques are used to assess myocardial function: pulsed TDE and color-coded TDE. A great deal of data has been generated on TDE over the last 5 years, and this review allows for only a small portion of these emerging data to be discussed. One clinical application is to assess peak systolic mitral annular velocity from the apical windows as an index of global ventricular function. The six-site average for peak systolic mitral annular velocity by the color-coded TDE method of greater than 5.4 cm/sec is predictive of an ejection fraction greater than 50% with an 88% sensitivity and a 97% specificity. An emerging application is to use pulsed-TDE to assess ventricular filling pressures. The mitral annular to inflow ratio (E/Ea) greater than 10 is predictive of a mean pulmonary capillary wedge pressure greater than 15 mm Hg with a 92% sensitivity and 80% specificity. Another application is to use peak early diastolic velocity to help differentiate constrictive pericarditis from restrictive cardiomyopathy. Peak early diastolic velocity is blunted with restrictive cardiomyopathy and preserved with constrictive pericarditis. These are just a few of the many evolving clinical applications of this new quantitative diagnostic ultrasonographic method.

Prediction of viability by pulsed-wave Doppler tissue sampling of asynergic myocardium during low-dose dobutamine challenge

Dobutamine stress echocardiography is widely used to predict reversible left ventricular dysfunction, but evaluation with this method is subjective. Pulsed-wave tissue Doppler imaging is a new technique that allows to obtain quantitative data on wall motion velocities of different myocardial segments through sample-volume placement. Therefore, this tool in combination with DSE may be suitable for identifying viability in asynergic myocardium. To evaluate this, in 40 patients (mean age 57+/-9) with resting dyssynergy (akinesis in 52, hypokinesis in 30) baseline wall motion scores and tissue Doppler variables were collected before and after 5 min infusion of 10 microg/kg per min dobutamine. Forty-six of 82 segments were classified as viable (a reduction in segmental score of at least one grade) according to follow-up echocardiography that was performed 4 weeks after revascularization. While myocardial S velocity percent increase in viable segments was 45+/-10, the increase was 25+/-12 in necrotic segments (n=36) during 10 microg dobutamine infusion (P=0.0001). Assuming 35% as a cut-off for viability the increase in S velocities by DSE yielded an 89% sensitivity and 86% specificity for predicting post-revascularization functional recovery. In conclusion, pulsed-wave tissue Doppler imaging of asynergic myocardium during dobutamine stress echocardiography can identify the viability quantitatively.

Dobutamine stress echocardiography for the diagnosis of myocardial viability: assessment of left ventricular systolic velocities in longitudinal axis by pulsed Doppler tissue imaging

Dobutamine (DOB) stress two-dimensional echocardiography is an established method for the detection of viable myocardium, but conventional assessment of wall motion is subjective. We measured quantitatively the left ventricular systolic velocities along the longitudinal axis by pulsed Doppler tissue imaging (DTI). In 30 patients with previous myocardial infarction, pulsed DTI focused on the infarct area was performed from an apical two- or four-chamber view before and during DOB (10 microg/kg/min) stress one day before coronary angioplasty. We calculated peak systolic velocity (S), regional pre-ejection period (PEP, the time interval from the onset of QRS to the onset of systolic wave) and regional ejection time (ET). Left ventriculography was obtained before and 3 months after coronary angioplasty to assess regional wall motion. Improvement of abnormal wall motion was observed in 19 patients (group P) but not in 11 (group N). Group P had significantly larger S and smaller PEP/ET than group N during DOB stress, although there were no significant differences in these indices between the groups at baseline. As a consequence, group P had a significantly larger percent change in S and a smaller percent change in PEP/ET than group N (164+/-39 vs 117+/-20% and 88+/-17 vs 116+/-29%, respectively, p < 0.01). It is suggested that the quantitative measurement of longitudinal systolic velocities during DOB stress by DTI is useful for the precise assessment of myocardial viability.