Assessment of myocardial viability with dobutamine stress echocardiography in patients with ischemic left ventricular dysfunction

The noninvasive assessment of myocardial viability has proved clinically useful for distinguishing hibernating and/or stunned myocardium from irreversibly injured myocardium in patients with chronic ischemic heart disease or recent myocardial infarction, with marked regional and/or global left ventricular (LV) dysfunction. Noninvasive techniques utilized for the detection of viability in asynergic myocardial regions include positron emission tomographic imaging of residual metabolic activity, single photon emission tomography (SPECT) of radioisotope uptake with thallium-201, low-dose dobutamine echocardiography assessment of inotropic reserve and myocardial contrast echocardiography for evaluation of microvascular integrity. Of these techniques, dobutamine stress echocardiography is a safe, widely available and relatively inexpensive modality for the identification of myocardial viability for risk stratification and prognosis. Low-dose dobutamine response can accurately predict improvement of dysfunctional yet viable myocardial regions, and thus identify a subset of patients whose LV function will improve following successful coronary revascularization.     

Significance of dobutamine-induced changes in QT dispersion early after acute myocardial infarction.

This study sought to examine the effects of graded dobutamine infusion on QT dispersion early after acute myocardial infarction (AMI) and to investigate the relation of dobutamine-induced changes in QT dispersion to wall motion responses. Seventy-eight patients with a first AMI underwent dobutamine-atropine stress echocardiography 5 +/- 2 days after admission. Contractile reserve was identified in 45 patients and ischemic myocardium in 40. Sixteen patients had persistent akinesia. The best cut-off value of QT dispersion on the baseline electrocardiogram for predicting myocardial viability was 65 ms (sensitivity and specificity of 68%). Dobutamine infusion increased QT dispersion only in patients with viable myocardium (61 +/- 18 to 83 +/- 19 ms, p = 0.003) and/or ischemia (72 +/- 16 to 112 +/- 25 ms, p < 0.0001). No change was observed in patients with persistent akinesia (84 +/- 10 to 87 +/- 15 ms, p = NS). QT dispersion increased by 22 +/- 12 ms with administration of low-dose dobutamine in patients who had viable myocardium and by 47 +/- 21 ms with administration of low- to high-dose dobutamine in patients with ischemic myocardium. An increase in QT dispersion of > or = 20 ms from at rest to low-dose dobutamine infusion was associated with myocardial viability with a sensitivity of 78% and a specificity of 79%, whereas an increase in QT dispersion of > or = 10 ms from low- to high-dose dobutamine infusion predicted ischemic myocardium with a sensitivity of 85% and a specificity of 82%. In conclusion, (1) low QT dispersion on the baseline electrocardiogram is determined by the presence of viable myocardium, (2) a dobutamine-induced increase in QT dispersion is associated with viable and jeopardized myocardium, and (3) unchanged QT dispersion during dobutamine stress is a simple marker of extensive necrosis.     

Comparison of dobutamine echocardiography and positron emission tomography in patients with chronic ischemic left ventricular dysfunction

Objectives. The aim of this study was to correlate dobutamine-induced contractile reserve as detected by echocardiography with findings on positron emission tomography in patients with chronic ischemic left ventricular dysfunction.

Background. Contractile reserve induced by low dose dobutamine infusion has been proposed as a marker of myocardial viability.

Methods. Sixty patients with stable coronary artery disease and left ventricular dysfunction (mean ejection fraction [± SD] 29 ± 10%) underwent transthoracic echocardiography with dobutamine infusion (up to 10 μg/kg body weight per min) and positron emission tomography with nitrogen-13 ammonia and fluorine-18 (F-18) fluorodeoxyglucose as a perfusion and a metabolic tracer, respectively. Regional wall motion, perfusion and metabolism were analyzed semiquantitatively by using a 16-segment model. Segments with F-18 fluorodeoxyglucose uptake > 50% were considered viable on positron emission tomography.

Results. After dobutamine infusion, hemodynamic variables changed significantly, and myocardial ischemia was evident in 17 patients. All 60 patients had dysfunctional myocardium considered viable on positron emission tomography (8 ± 4 segments/patient), whereas 52 patients had dysfunctional myocardium with contractile enhancement by dobutamine echocardiography (4 ± 2 segments/patient, P = 0.01). The extent of dysfunctional myocardium with contractile reserve appeared to correlate less closely with the total extent of viable dysfunctional myocardium identified by positron emission tomography than with the number of such segments associated with a pattern of perfusion-metabolism mismatch.

Conclusions. In patients with chronic ischemic left ventricular dysfunction, echocardiography can be used to identify enhancement in the contractile function of viable dysfunctional myocardium after infusion of low dose dobutamine. In this study, the presence and extent of such enhancement were relatively less than the values obtained from positron emission tomography.     

The use of dobutamine stress echocardiography for the determination of myocardial viability

Determining the presence of viable myocardium has prognostic and therapeutic implications in the treatment of ischemic heart disease. Dobutamine stress echocardiography (DSE) is one possible technique to help identify both hibernating and stunned but viable myocardium. Low-dose dobutamine infusion has an increased inotropic effect, while higher doses cause both inotropic and chronotropic effects. Thus, at lower doses cardiac augmentation occurs, and at higher doses regions of ischemia may be produced in the presence of significant coronary artery disease. This is manifested echocardiographically as changes in segmental wall motion. in theory, therefore, areas of viable myocardium should show improved wall motion at low doses, and areas of irreversible myocardial damage will remain akinetic. Five studies have investigated DSE for determining viability in the setting of acute myocardial infarction, thus looking for stunned but viable myocardium. DSE was shown to compare favorably with positron emission tomography and was highly sensitive and specific for predicting functional myocardial recovery. Five additional studies examined DSE for determining the presence of hibernating myocardium. The sensitivity and specificity of DSE were found to range from 71 to 92% and from 73 to 93%, respectively. The benefits of DSE include lower cost, convenience to both patient and physician, additional ancillary information, and determination of the possible need for urgent revascularization. Limitations of DSE include occasional technical difficulty in obtaining and interpreting studies and the need for larger volumes of viable myocardium to detect changes predictive of functional recovery. Larger trials are currently underway to confirm DSE as a reliable technique for determining myocardial viability.     

Low-dose dobutamine radionuclide ventriculography for prediction of myocardial viability: quantitative analysis of regional left ventricular function

BACKGROUND: It is important to distinguish viable myocardium from necrotic tissue in order to decide upon therapy in patients with ischemic heart disease. HYPOTHESIS: We verified the hypothesis that quantitative analysis of regional left ventricular function using low-dose dobutamine radionuclide ventriculography (RNV) can sensitively predict myocardial viability and compared its usefulness with thallium-201 (201Tl) single-photon emission computed tomography (201Tl-SPECT). METHODS: Radionuclide ventriculography at rest and during low-dose dobutamine infusion (5 micrograms/kg/min), 201Tl-SPECT, and coronary angiography were performed in 51 subjects with severe ischemia-related stenosis of coronary arteries and 3 subjects without coronary artery disease. 201Tl uptake was assessed as normal (control), low perfusion (LP), or defect. We compared the response of regional function to dobutamine with the regional 201Tl uptake. The accuracy of both methods for identifying viable myocardium was investigated in 17 patients who underwent successful coronary revascularization, with a resulting improvement in wall motion. RESULTS: The increase in regional ejection fraction (delta r-EF) in response to dobutamine was significantly greater in the control (12 +/- 6%) and LP (16 +/- 11%) regions than in the defect (5 +/- 10%) regions. The increase in one-third regional ejection fraction (delta r-1/3EF) was also significantly higher in the control (14 +/- 7%) and LP (10 +/- 8%) regions than in the defect regions (5 +/- 6%). We defined myocardial viability as a delta r-EF > 5% or a delta r-1/3EF > 2%. The sensitivity and specificity of the delta r-EF for identification of myocardial viability were 91.4 and 55.5%, respectively. The sensitivity and specificity of the delta r-1/3EF were 91.4 and 66.6%, respectively; the corresponding values for 201Tl SPECT were 74.2 and 77.8%. CONCLUSION: Low-dose dobutamine RNV with quantitative analysis of regional left ventricular function was more sensitive for identification of viable myocardium than 201Tl-SPECT.     

Pulsed-wave tissue Doppler quantification of systolic and diastolic function of viable and nonviable myocardium in patients with ischemic cardiomyopathy

Background

Detection of myocardial viability is crucial for clinical treatment of patients with ischemic cardiomyopathy. Currently, quantitative information for the evaluation of systolic and diastolic function of viable tissue is limited. Our aim was to compare quantitatively systolic and diastolic function in viable and nonviable dysfunctional myocardium in patients with ischemic cardiomyopathy.

Methods

A total of 93 patients (mean age, 62 ± 10 years) underwent dobutamine stress echocardiography to assess myocardial viability. Pulsed-wave tissue Doppler imaging (TDI) was used to assess systolic ejection velocity (V_S) and early (V_E) and late (V_A) diastolic velocities at rest and at low-dose dobutamine infusion (10 μg/kg per minute) in viable and nonviable dysfunctional regions. Analysis was repeated after dividing study population in patients ≥65 years old (n = 40) and <65 years old (n = 53).

Results

Pulsed-wave TDI demonstrated that V_S was comparable in dysfunctional viable and nonviable regions at rest (V_S, 6.3 ± 1.9 cm/s vs 6.3 ± 2.0 cm/s, respectively, P = .93). However, at low-dose dobutamine challenge, V_S was significantly higher in viable regions (8.5 ± 2.7 cm/s vs 7.8 ± 2.4 cm/s, P = .002). Viable regions had higher V_E at rest compared with nonviable regions (8.4 ± 2.5 cm/s vs 7.5 ± 2.8 cm/s, P = .003). Myocardial velocities were significantly higher in patients ≥65 years old, both in viable and nonviable regions.

Conclusions

Quantification of myocardial motion by pulsed-wave TDI demonstrates that at low-dose dobutamine stress, systolic velocity is markedly improved in viable myocardium, indicating the presence of contractile reserve in viable regions. A superior early diastolic filling at rest can also differentiate viable from nonviable myocardium.     

Comparison of dobutamine stress echocardiography with dipyridamole stress echocardiography for detection of viable myocardium after myocardial infarction treated with thrombolysis.

OBJECTIVE: To compare the ability of dobutamine and dipyridamole stress echocardiography to detect functional recovery of stunned but viable myocardial regions early after acute myocardial infarction, and to predict late functional recovery of the reperfusion salvaged myocardium within the infarct area. METHODS: Within 10 d of acute myocardial infarction, 51 patients--30 anterior and 21 inferior, 44 Q wave and seven non-Q-wave infarction--were submitted to a dobutamine echocardiography test at low dose (5-10 micrograms/kg/min over 5 min) and high dose (20-40 micrograms/kg/min over 3 min) and to dipyridamole echocardiography test (0.56 mg/kg over 4 min + 0.28 mg/kg over 2 min) on different days and in random order, after interruption of any vasoactive drug. Resting echocardiography was repeated at two months in 41 of 51 patients (80%). Regional wall motion of the left ventricle was analysed in a semiquantitative manner on a 14-segment model. Viability was defined as improvement of one grade or more of at least two basally asynergic segments in the infarcted area. RESULTS: Regional functional recovery was detected by low dose dobutamine in 38/51 patients (75%) and in 147/308 (48%) of basally asynergic segments, compared to 25/51 patients (49%; P < 0.001) and 78/308 segments (25%; P < 0.001) only identified by dipyridamole. Late spontaneous functional recovery was detected in 24/41 patients (59%) and in 78/254 basally asynergic segments (31%). The sensitivity of dobutamine and dipyridamole echocardiography for predicting spontaneous functional recovery was 72% and 51% respectively (P < 0.001), specificity 68% and 82% (P < 0.001), positive predictive value 50% and 56%, and negative predictive value 85% and 79%. CONCLUSIONS: In comparison with dipyridamole in patients with thrombolysed myocardial infarction, dobutamine induces regional functional recovery. This suggests that dobutamine is more sensitive in showing the presence of viable myocardium within the infarct zone, though it has a lower specificity in predicting delayed spontaneous functional recovery of non-contractile but still viable areas.     

Assessment of myocardial viability: comparison of echocardiography versus cardiac magnetic resonance imaging in the current era

Detecting viable myocardium, whether hibernating or stunned, is of clinical significance in patients with coronary artery disease and left ventricular dysfunction. Echocardiographic assessments of myocardial thickening and endocardial excursion during dobutamine infusion provide a highly specific marker for myocardial viability, but with relatively less sensitivity. The additional modalities of myocardial contrast echocardiography and tissue Doppler have recently been proposed to provide further, quantitative measures of myocardial viability assessment. Cardiac magnetic resonance (CMR) has become popular for the assessment of myocardial viability as it can assess cardiac function, volumes, myocardial scar, and perfusion with high-spatial resolution. Both 'delayed enhancement' CMR and dobutamine stress CMR have important roles in the assessment of patients with ischaemic cardiomyopathy. This article reviews the recent advances in both echocardiography and CMR for the clinical assessment of myocardial viability. It attempts to provide a pragmatic approach toward the patient-specific assessment of this important clinical problem.     

Noninvasive characterization of stunned, hibernating, remodeled and nonviable myocardium in ischemic cardiomyopathy

OBJECTIVES: We evaluated a novel protocol of dual-isotope, gated single-photon emission computed tomographic (SPECT) imaging combined with low and high dose dobutamine as a single test for the characterization of various types of altered myocardial dysfunction. BACKGROUND: Myocardial perfusion tomography and echocardiography have been used separately for the assessment of myocardial viability. However, it is possible to assess perfusion, function and contractile reserve using gated SPECT imaging. METHODS: We studied 54 patients with ischemic cardiomyopathy using rest and 4 h redistribution thallium-201 imaging and dobutamine technetium-99m sestamibi SPECT imaging. The sestamibi images were acquired 1 h after infusion of the maximal tolerated dose of dobutamine and again during infusion of dobutamine at a low dose to estimate contractile reserve. Myocardial segments were defined as hibernating, stunned, remodeled or scarred. RESULTS: Severe regional dysfunction was present in 584 (54%) of 1,080 segments. Based on the combination of function and perfusion characteristics in these 584 segments, 24% (n = 140) were labeled as hibernating; 23% (n = 136) as stunned; 30% (n = 177) as remodeled; and 22% (n = 131) as scarred. Contractile reserve, represented by improvement in wall motion/thickening by low dose dobutamine, was observed in 83% of stunned, 59% of hibernating, 35% of remodeled and 13% of scarred myocardial segments (p<0.05). CONCLUSIONS: It is possible with this new imaging technique to characterize dysfunctional myocardium as stunned, hibernating, remodeled and nonviable. These subtypes often coexist in the same patient.     

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.     

Significance of low-dose dobutamine stress echocardiography for the prediction of the long-term prognosis for patients with acute myocardial infarction

OBJECTIVES: Detection of stunned myocardium using low-dose dobutamine stress echocardiography is a good predictor of improvement of cardiac function in patients with acute myocardial infarction during short hospital stays. The present study evaluated the detection of stunned myocardium as a predictor of the long-term prognosis for patients with acute myocardial infarction. METHODS: One hundred and two patients (83 males, 19 females, mean age 61.5 years) with initial myocardial infarction underwent successful reperfusion therapy (direct percutaneous transluminal coronary angioplasty or stent) in the acute stage. Within 7 days, low-dose dobutamine was administered by intravenous drip and improvement of wall motion of the infarct area was evaluated by echocardiography. The patients were divided into two groups, the viable group that showed one grade or more improvement (61 patients), and the non-viable group that showed no improvement (41 patients). These groups were compared to determine the differences in clinical findings such as remodeling of the left ventricle measured by two-dimensional echocardiography, physical work capacity during serial multi-step exercise testing, and the prognosis. RESULTS: The viable group showed greater improvement in hemodynamics and wall motion of the infarct areas than the non-viable group. After discharge, the physical work capacity was significantly increased and there was no recognizable enlargement of the left ventricle in the viable group. No sudden cardiac death or heart failure occurred in the viable group, in contrast to incidences of 6% and 9%, respectively, in the non-viable group. Unstable angina and nonfatal re-infarction occurred more frequently in the viable group. CONCLUSIONS: The presence of stunned myocardium is a predictor of the prognosis for patients with acute myocardial infarction.     

Clinical relevance of hibernating myocardium in ischemic left ventricular dysfunction

Patients with chronic ischemic left ventricular dysfunction may have a substantial amount of viable, hibernating myocardium, which is a state of chronic contractile dysfunction with reduced blood flow at rest. Coronary revascularization in these patients may result in improvement of left ventricular function; in the absence of viability, left ventricular function will not improve postrevascularization. Various noninvasive imaging techniques are available for detection of viable myocardium, including magnetic resonance imaging, dobutamine stress echocardiography, and nuclear imaging with single photon emission computed tomography or positron emission tomography. Because these techniques probe different characteristics of viable myocardium, the sensitivities and specificities of the techniques are not precisely identical; in general, dobutamine stress echocardiography has the highest specificity, whereas the nuclear techniques have the highest sensitivity. The presence of myocardial viability also is related to prognosis: patients with viable myocardium who undergo revascularization have a good prognosis, whereas patients with viable myocardium who are treated medically have poor outcome. Accordingly, assessment of viability is important in the therapeutic decision-making process of patients with chronic ischemic left ventricular dysfunction.     

Experimental validation of circumferential, longitudinal, and radial 2-dimensional strain during dobutamine stress echocardiography in ischemic conditions.

OBJECTIVES: The aim of this study was to assess and validate 2-dimensional (2D) strain for the detection of ischemia during dobutamine stress echocardiography (DSE). BACKGROUND: Evaluation of abnormalities of left ventricular (LV) function from wall thickening during DSE is unsatisfactory and requires a high level of expertise. METHODS: In 10 open-chest anesthetized pigs, myocardial deformation was studied before and during dobutamine infusion, under control and ischemic conditions produced by various degrees of coronary artery constriction: 2 of nonflow-limiting stenoses (NFLS) of increasing severity reducing left anterior descending artery hyperemic flow by 40% and 70% and 2 flow-limiting stenoses (FLS) reducing resting coronary flow by 25% and 50%. Agreement between 2D strain echocardiography and sonomicrometry (reference method) was evaluated by linear regression and Bland-Altman analysis. RESULTS: Good correlation and agreement were observed between 2-dimensional strain and sonomicrometry at rest and during dobutamine infusion; longitudinal strain: r = 0.77, p < 0.001 and r = 0.80, p < 0.001; radial strain: r = 0.57, p < 0.05 and r = 0.63, p < 0.05; and circumferential strain: r = 0.74, p < 0.001 and r = 0.58, p < 0.001. Circumferential and longitudinal strains in the risk area were significantly decreased at rest in the presence of FLS and during dobutamine infusion in the presence of NFLS. By contrast, radial strain was significantly decreased in the presence of severe FLS only during dobutamine infusion. CONCLUSIONS: The 2D strain provides accurate assessment of LV regional function. Evaluation of circumferential and longitudinal strains during DSE has real potential for quantitative evaluation of LV deformation in the routine assessment of ischemia.     

Assessment of viable myocardium by dobutamine transesophageal echocardiography and comparison with fluorine-18 fluorodeoxyglucose positron emission tomography

Objectives. The aim of this study was to assess whether dobutamine transesophageal echocardiography can identify viable myocardium in patients with chronic myocardial infarction.Background. Experimental and clinical studies have shown that dobutamine can recruit a contraction reserve in postischemic viable but akinetic segments, indicating that dobutamine-induced functional recovery is a potential ultrasound marker of myocardial viability.Methods. Forty patients underwent rest and dobutamine transesophageal echocardiography (dobutamine 5, 10 and 20 μg/kg body weight per min) and fluorine-18 (F-18) fluorodeoxyglucose positron emission tomography at rest. Three representative shortaxis tomograms and a transverse four-chamber-view were used for wall motion and F-18 fluorodeoxyglucose-uptake analysis in corresponding myocardial regions. A basally asynergic segment was considered viable by transesophageal echocardiography if dobutamine-induced systolic wall motion could be observed. Viability by positron emission tomography was defined as F-18 fluorodeoxyglucose uptake ≥50% of the maximal uptake in a region with normal wall motion by left ventriculography.Results. Functional recovery within the infarct region was found in 21 (53%) of 40 patients during dobutamine infusion. Infarct region-related viability by F-18 fluorodeoxyglucose uptake was diagnosed in 25 (63%) of 40 patients, yielding a diagnostic agreement between both techniques in 90% of patients. In 210 (89%) of 235 akinetic segments at rest, data on myocardial viability were concordant by the two techniques. The positive and negative predictive accuracy of dobutamine transesophageal echocardiography for viability defined by F-18 fluorodeoxyglucose uptake was 81% and 97%, respectively. Such uptake was significantly different (p < 0.001) between segments remaining akinetic (mean ± SD 45 ± 9%) during dobutamine infusion and segments with a dobutamine-induced contraction reserve (68 ± 11%).Conclusions. Dobutamine transesophageal echocardiography provides a promising low cost and widely available approach to unmask myocardial viability in patients with chronic myocardial infarction, and results compare favorably with those of F-18 fluorodeoxyglucose positron emission tomography.     

Identification of viable myocardium by echocardiography during dobutamine infusion in patients with myocardial infarction after thrombolytic therapy: comparison with positron emission tomography

To assess the presence of viable myocardium salvaged by coronary artery reperfusion, 17 patients with acute anterior myocardial infarction were studied. Each received intravenous thrombolysis within the first 3 h of symptoms and underwent two-dimensional echocardiography before and during dobutamine infusion (10 micrograms/kg per min) 7 +/- 4 days after admission and positron emission tomography 9 +/- 5 days after admission. Echocardiography and positron emission tomography were again performed 9 +/- 7 months later. Six comparable segments specific for the territory of the left anterior descending artery were selected for comparison of the two techniques. Wall thickening was evaluated by using an echocardiographic score index. Segmental perfusion and glucose uptake were measured and normalized to the peak activity. A ratio of glucose uptake to perfusion was calculated for each segment. Concordant interpretation of the two techniques was found in 79% of affected segments for both acute and follow-up studies. Positron emission tomography revealed the presence of viable myocardium in 11 patients (group 1); perfusion was within normal limits in 5 of these (group 1A). Myocardial thickening improved with dobutamine infusion in these five patients, the echocardiographic score index decreasing from 12 +/- 2 at rest to 7.8 +/- 1.3 during dobutamine infusion (p = 0.003). Functional recovery was demonstrated in all five patients (follow-up score index 7.4 +/- 1.7). Six patients exhibited decreased perfusion but an abnormally high glucose to perfusion ratio (group 1B); their score index improved with dobutamine from 14.8 +/- 2.2 to 12 +/- 2.1 (p = 0.05), but late functional recovery was found in only one of the six patients (mean follow-up score index in group 1B 16 +/- 1.7). In the six remaining patients in whom no viable myocardium was detected with positron emission tomography (group 2), the echocardiographic score index did not change with dobutamine (15 +/- 0.9 to 14.7 +/- 0.8, p = NS) and there was no functional recovery (follow-up score index 15.5 +/- 1.0). Echocardiography during dobutamine infusion is a promising method to unmask viable myocardium in acute myocardial infarction. Early recovery of perfusion in the area at risk is associated with a good functional outcome, whereas a high glucose to perfusion ratio indicates jeopardized myocardium that frequently loses viability.     

Effect of dobutamine on regional left ventricular function measured by tagged magnetic resonance imaging in normal subjects

The effect of inotropic stimulation on the pattern and magnitude of regional left ventricular contraction was studied using tagged magnetic resonance imaging to assess whether dobutamine exacerbates variation in regional contraction at rest. Dobutamine stress testing defines a normal response as a homogeneous increase in regional wall motion. In 8 normal subjects, 4 equally spaced left ventricular short-axis levels were imaged through systole using tagged magnetic resonance imaging. The baseline imaging sequence was repeated with 5-, 10-, 15-, and 20-microg/kg/min dobutamine infusion. Regional myocardial displacement, radial thickening, and circumferential shortening were measured. The left ventricle was analyzed by level (base to apex) and wall (septum, inferior, lateral, anterior). Dobutamine did not alter baseline regional functional heterogeneity. Dobutamine infusion resulted in a uniform increase in displacement, radial thickening, and circumferential shortening from baseline to 10-microg/kg/min infusion without additional increases at higher doses.     

Cine MR imaging after myocardial infarction – Assessment and follow-up of regional and global left ventricular function

Myocardial infarction often leads to regional wall motion defects and in case of large defects to remodeling of the left ventricle. With this study, changes in regional and global myocardial function of 12 patients 3 weeks after myocardial infarction and after revascularization therapy were determined using MRI. Cine MRI was performed at study entry at rest and during low-dose dobutamine stimulation. All patients were re-examined at rest 3 and 6 months after the revascularization, including analysis of wall thickening and of left ventricular end-diastolic volume index (LVEDVI), end-systolic volume index (LVESVI), ejection fraction (LVEF), and mass index. After revascularization, 6 patients with stress-induced improvement of regional wall thickening recovered, 4 patients without improvement did not, but 2 patients without stress-induced improvement of wall thickening also recovered. Concerning global cardiac function, patients with mainly improved regional wall motion also showed a lower LVESVI and a higher LVEF than patients without improvement of regional contractility 6 months after revascularization in comparison to study entry. In conclusion, improvement of global myocardial function after revascularization is higher in patients with improved contractility in the infarcted region. The extent of the response of regions with wall motion defects to dobutamine stress correlates with the actual improvement after revascularization, and, therefore, dobutamine stress MRI may be helpful in selecting patients that will have a higher benefit from a revascularization therapy.     

Detection of viable myocardium by dobutamine stress tagging magnetic resonance imaging with three-dimensional analysis by automatic trace method

The present study attempted to detect the viability of myocardium by quantitative automatic 3-dimensional analysis of the improvement of regional wall motion using an magnetic resonance imaging (MRI) tagging method. Twenty-two subjects with ischemic heart disease who had abnormal wall motion on echocardiography at rest were enrolled. All patients underwent dobutamine stress echocardiography (DSE), coronary arteriography and left ventriculography. The results were compared with those of 7 normal volunteers. MRI studies were done with myocardial tagging using the spatial modulation of magnetization technique. Automatic tracing with an original program was performed, and wall motion was compared before and during dobutamine infusion. The evaluation of myocardial viability with MRI and echocardiography had similar results in 19 (86.4%) of the 22 patients; 20 were studied by positron emission tomography or thallium-201 single photon emission computed tomography for myocardial viability, or studied for improvement of wall motion following coronary intervention. The sensitivity of dobutamine stress MRI (DSMRI) with tagging was 75.9% whereas that of DSE was 65.5%. The specificity of DSMRI was 85.7% (6/7) and that of DSE was 100% (7/7). The accuracy of DSMRI was 77.8% (28/36) and that of DSE 72.2% (26/36). DSMRI was shown to be superior to DSE in terms of evaluation of myocardial viability.     

Reversible myocardial dysfunction: basics and evaluation

Large areas of non-functional but viable myocardium with reversible dysfunction are commonly seen in patients with acute myocardial infarction. Both reperfusion of acutely ischemic myocardium and chronic myocardial ischemia may produce a reversible forms of ventricular dysfunction. The two main conditions that lead to reversible myocardial dysfunction are stunned myocardium and hibernating myocardium. Myocardial stunning represents post-ischemic myocardial dysfunction that persists despite restoration of normal flow, with gradual return of contractile function. Hibernating myocardium is a state of persistently impaired myocardial function at rest due to reduced coronary blood flow owing to residual stenosis that can be restored toward normal by revascularization. The success of the revascularization procedures depends on the presence of amount of dysfunctional but viable myocardium. The basics and evaluation of reversible myocardial dysfunction are reviewed.     

The effect of inotropic dose of dobutamine during reperfusion on myocardial infarct size

We examined whether dobutamine infusion during reperfusion modifies myocardial infarct size in a rabbit ischemia-reperfusion model. Prior to the infarct size study, the hemodynamic response to dobutamine 5, 10, and 15 micrograms/kg/min i.v. was evaluated in the rabbit model. Ten micrograms/kg/min of dobutamine increased the left ventricular dp/dt max by 34.0 +/- 4.9% (n = 7) and the myocardial blood flow from 0.86 +/- 0.16 to 2.19 +/- 0.57 ml/min/g without change in the collateral blood flow (n = 4). The heart rate, systolic and diastolic blood pressures were elevated by only 4.7 +/- 1.0%, 9.4 +/- 3.0%, and 8.0 +/- 3.7%, respectively (n = 7). In the infarct size study, a coronary branch was occluded for 30 min and then reperfused. Seventy-two hours after reperfusion, the myocardium supplied by the occluded artery (area at risk, AAR) and the infarcted area were determined by fluorescent particles and histology (hematoxylin-eosin and modified Mallory's staining), respectively. In the dobutamine treated group (DB group), 10 micrograms/kg/min of dobutamine were infused for 30 min starting immediately after reperfusion, and a comparable volume of saline was infused in the control group. Hemodynamic parameters and the size of AAR were comparable in the control and DB groups. Myocardial infarct size, expressed as the percentage of AAR, was 45.1 +/- 3.9% in the control (n = 11) and 40.2 +/- 2.4% in the DB group (n = 10), which was not significantly different. These findings indicated that the inotropic dose of dobutamine administered during reperfusion did not cause myocardial necrosis by disturbing the recovery process of the myocardium from ischemic injury.