Nonviable Myocardium In Patients Research Articles

ACCURACY OF PATHOLOGIC Q WAVE ON ELECTROCARDIOGRAPHY TO PREDICT NON-VIABLE MYOCARDIUM

A prospective study was conducted to determine the diagnostic accuracy of Q wave on ECG in predicting the non-viable myocardium in patients with myocardial infarction, considering SPECT as the gold standard in the Department of Nuclear Cardiology, Ch. Pervaiz Elahi Institute of Cardiology (CPEIC), Multan, from June 2022 to June 2023. A total of 414 patients with myocardial infarction were included in the study. Demographic and clinical data such as age, gender, smoking history, diabetes, and hypertension were collected. Before the SPECT scan, 12 lead ECG was done in all patients to determine the pathologic Q wave. Pathologic Q-wave on ECG was found in 252 (60.87%) and not in 162 (39.13%) patients. Non-viable myocardium on SPECT was found in 231 (55.80%) and not in 183 (44.20%) patients. Pathologic Q-wave was 68.80% sensitive and 49.20% specific, with 63.10% PPV and 55.60% NPV compared to SPECT. This difference was statistically significant (P<0.001). Development of pathologic Q wave on ECG was significantly associated with male gender (P =0.006), hypertension (P=0.008), and smoking (P=0.002). In conclusion, pathologic Q wave on ECG is a reliable tool for predicting non-viable myocardium in CAD patients.

Value of 12-lead electrocardiogram to predict myocardial scar on FDG PET in heart failure patients

PurposeA surface 12-lead electrocardiogram (ECG) is widely available, fast, inexpensive, and safe. However, its value to predict a true myocardial scar in patients with ischemic cardiomyopathy (ICM) has not been studied extensively yet. This study was conducted to assess whether Q waves on resting surface 12-lead ECG are predictive of non-viable myocardium in patients with ICM. MethodsWe analyzed resting ECGs of 149 patients with ICM undergoing cardiac positron emission tomography (PET) with 13N-ammonia (NH3) and 18F-fluorodeoxyglucose (FDG) at our institution. Pathological Q waves and QS complexes were assigned to one of three coronary artery territories and compared to the PET findings. Myocardial scar was defined as 2 or more contiguous myocardial segments with an average (matched) reduction of NH3 and FDG uptake <50% of the maximum value. ResultsPathological Q waves had a sensitivity and specificity of 70% and 40%, respectively, and a PPV and NPV of 37% and 73%, respectively, to detect myocardial scar on FDG PET. For QS complexes, sensitivity and specificity were 46% and 59%, respectively, and PPV and NPV were 36% and 68%, respectively. Sensitivity was lower, but specificity was significantly higher in both the LCX and RCA compared to the LAD territory (p<0.001), particularly for QS complexes. ConclusionPathological Q waves on resting 12-lead ECG have poor or at best moderate sensitivity and specificity to detect myocardial scar on FDG PET. These findings support the use of more advanced imaging techniques to assess myocardial viability in ICM.

Invited Commentary

The inability to predict the response of the left ventricle to myocardial revascularization and mitral valve repair in ischemic mitral regurgitation (MR) patients remains problematic. Morgan and colleagues [1Morgan A.E. Zhang Y. Tartibi M. et al.Ischemic mitral regurgitation: abnormal strain overestimates nonviable myocardium.Ann Thorac Surg. 2018; 105: 1754-1762Abstract Full Text Full Text PDF Scopus (10) Google Scholar] compared the ability of tagged cardiac magnetic resonance imaging (MRI) and late gadolinium-enhanced (LGE) MRI to determine the amount of nonviable myocardium in patients with ischemic MR. Their hypothesis was that strain measurements using tagged cardiac MRI overestimate the amount of nonviable myocardium in ischemic MR when compared with LGE MRI, suggesting that much of the myocardium deemed nonviable by strain measurements is actually viable but nonfunctional (ie, stunned or hibernating). This is a critical issue because it is believed that the degree of stunned myocardium in patients with ischemic MR correlates not only with functional myocardial recovery due to revascularization but also with the degree of ventricular remodeling and, thus, the success or failure of mitral valve surgery in these patients. Although LGE MRI is helpful in identifying nonviable myocardium, it is not necessarily as helpful in determining the response of viable myocardium to surgery for ischemic MR. Gadolinium chelate distributes in the extracellular space but does not cross the intact cell membrane. Through a combination of increased extracellular volume and slower washout kinetics, there is a relative accumulation of gadolinium in areas of necrosis, fibrosis, and inflammation in the late washout phase. LGE MRI depends on this relative accumulation of gadolinium in areas of damaged myocardium, but it may miss areas of diffuse fibrosis and underestimate the true extent of nonviable muscle. Grapsa and colleagues [2Grapsa J. Zimbarra Cabrita I. Jakaj G. et al.Strain balance of papillary muscles as a prerequisite for successful mitral valve repair in patients with mitral valve prolapse due to fibroelastic deficiency.Eur Heart J Cardiovasc Imaging. 2015; 16: 53-61Crossref PubMed Scopus (3) Google Scholar], using 3-D echo speckle-tracking, showed that a disproportionate increase in the deformation of the papillary muscles is a predictor of recurrent MR following mitral valve annuloplasty and that global longitudinal deformation depends on the degree of mitral regurgitation. The amount of deformation of the mitral apparatus in patients with only minor degrees of MR was zero. It would be instructive to include tagged cardiac MRI and LGE MRI in a group of patients with ischemia and no MR to compare with patients with ischemic MR. Pasque and associates used MRI-based multiparametric strain data calculated from 15,300 grid points per patient in normal volunteers and in ischemic patients with and without MR [3Lancaster T.S. Kar J. Cupps B.P. et al.Topographic mapping of left ventricular regional contractile injury in ischemic mitral regurgitation.J Thorac Cardiovasc Surg. 2017; 154: 149-158.e1Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar]. They showed that ischemic MR is caused by dysfunction of the subpapillary ventricular wall and that the free ventricular wall segments outside the subpapillary regions showed the same strain patterns in ischemic MR patients and in ischemic patients without MR. The relationships between nonviability, functional recovery, and response to surgical intervention for ischemic MR are not yet clear. What is needed now are studies comparing these types of preoperative measurements in patients with ischemic MR with similar postoperative measurements on the same patients that might clarify the preoperative parameters that are truly capable of predicting postoperative outcomes. Perhaps we would then have a better understanding of precisely how to treat ischemic MR in individual patients. Ischemic Mitral Regurgitation: Abnormal Strain Overestimates Nonviable MyocardiumThe Annals of Thoracic SurgeryVol. 105Issue 6PreviewTherapy for moderate ischemic mitral regurgitation remains unclear. Determination of myocardial viability, a necessary prerequisite for an improvement in regional contractility, is a likely key factor in determining response to revascularization alone. Myocardial strain has been proposed as a viability measure but has not been compared with late gadolinium enhancement (LGE) cardiac magnetic resonance imaging. We hypothesized that abnormal strain overestimates nonviable left ventricular (LV) segments measured with LGE and that ischemia and mechanical tethering by adjacent transmural myocardial infarction (TMI) also decreases strain in viable segments. Full-Text PDF

Blood flow, flow reserve, and glucose utilization in viable and nonviable myocardium in patients with ischemic cardiomyopathy

The aim of the study was to determine whether glucose uptake in viable myocardium of ischemic cardiomyopathy patients depends on rest myocardial blood flow (MBF) and the residual myocardial flow reserve (MFR). Thirty-six patients with ischemic cardiomyopathy (left ventricular ejection fraction 25 ± 10%) were studied with (13)N-ammonia and (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Twenty age-matched normals served as controls. Regional MBF was determined at rest and during dipyridamole hyperemia and regional FDG extraction was estimated from regional FDG to (13)N-ammonia activity ratios. Rest MBF was reduced in viable (0.42 ± 0.18ml/min per g) and nonviable regions (0.32 ± 0.09ml/min per g) relative to remote regions (0.68 ± 0.23ml/min per g, p < 0.001) and to normals (0.63 ± 0.13ml/min per g). Dipyridamole raised MBFs in controls, remote, viable, and nonviable regions. MBFs at rest (p < 0.05) and stress (p < 0.05) in viable regions were significantly higher than that in nonviable regions, while MFRs did not differ significantly (p > 0.05). Compared to MFR in remote myocardium, MFRs in viable regions were similar (1.39 ± 0.56 vs 1.70 ± 0.45, p > 0.05) but were significantly lower in nonviable regions (1.23 ± 0.43, p < 0.001). Moreover, the FDG and thus glucose extraction was higher in viable than in remote (1.40 ± 0.14 vs 0.90 ± 0.20, p < 0.001) and in nonviable regions (1.13 ± 0.21, p < 0.001). The extraction of FDG in viable regions was independent of rest MBF but correlated inversely with MFRs (r =-0.424, p < 0.05). No correlation between the FDG extraction and MFR was observed in nonviable regions. As in the animal model, decreasing MFRs in viable myocardium are associated with increasing glucose extraction that likely reflects a metabolic adaptation of remodeling hibernating myocytes.

Comparison of multidetector CT with F-18-FDG-PET and SPECT in the assessment of myocardial viability in patients with myocardial infarction: A preliminary study

Objective To evaluate the ability of MDCT to detect a nonviable myocardium in patients with myocardial infarction (MI). Methods and material This study included 17 patients with MI in the acute ( n = 13) or chronic stage ( n = 4). MDCT, SPECT, and F-18-FDG-PET were performed in 10 patients during the acute stage and in 2 during the chronic stage of MI. MDCT and SPECT were performed in 13 patients with acute stage and in 4 with chronic stage of MI. Sixteen-slice MDCT was performed 10 min after injection of 120 mL of nonionic contrast media. MDCT, SPECT and PET images were analyzed using a 17-segment model. The depth of hyperenhancement >2/3 was defined as nonviable at MDCT. Results MDCT and SPECT were concordant in localizing the MI in 84.2% (272/323 segments) and were discordant in 15.8% (51/323). MDCT and PET were concordant in localizing MI in 89.2% (182/204) and discordant in 10.8% (22/204). The sensitivity, specificity and diagnostic accuracy of MDCT in determining the nonviable segments were 70.4%, 85.3%, 81.4% as compared with PET, respectively, and 69.4%, 81.8%, 79.9% compared with SPECT, respectively, and 73.5%, 79.4%, 78.4% compared with combined PET and SPECT, respectively. MDCT findings suggested nonviability in additional 16 segments (5.0%) and 7 segments (3.4%) where MI was not detected on SPECT and FDG-PET, respectively. Conclusion MDCT is useful for determining myocardial viability in patients with myocardial infarction and more sensitive than SPECT and FDG-PET in detecting a nonviable myocardium.

Energetic differences between viable and non-viable myocardium in patients with recent myocardial infarction are not an effect of differences in wall thinning— a multivoxel 31P-MR-spectroscopy and MRI study

To evaluate multivoxel (31)P-MR spectroscopy (MRS) for assessment of energy metabolism in patients with myocardial infarction (MI) in correlation to left ventricular (LV) wall thickness and the outcome of revascularization. Thirty patients with subacute anterior myocardial infarction and planned revascularization were enrolled. 3D-chemical shift imaging was applied to determine PCr/ATP ratios in two areas: infarcted/anterior and noninfarcted/septal myocardium. MRI was used to evaluate LV function and wall thickness, and was repeated 6 months after revascularization to assess myocardial viability. Fifteen volunteers were controls. Fifteen patients showed normalization of wall motion abnormalities after revascularization (Group 1; viable), 15 not (Group 2; non-viable). Regarding infarcted/anterior myocardium, Group 2 had lower PCr/ATP ratios (0.81 +/- 0.60 vs 1.17 +/- 0.25), and PCr/ATP ratios were reduced in both groups compared to controls (1.45 +/- 0.29). Regarding noninfarcted/septal myocardium, again Group 2 had lower ratios (0.93 +/- 0.53 vs 1.31 +/- 0.38); however, compared to controls (1.51 +/- 0.32) a reduction of PCr/ATP ratios was only found in Group 2. For both myocardial regions, no correlations between PCr/ATP ratios and LV wall thickness were detected. The more severe energetic alteration in irreversibly damaged myocardium is not an effect of differences of wall thinning. Additional alterations of noninfarcted, adjacent myocardium can be detected.

Low-Dose Dobutamine Tissue-Tagged Magnetic Resonance Imaging With 3-Dimensional Strain Analysis Allows Assessment of Myocardial Viability in Patients With Ischemic Cardiomyopathy

Tissue-tagged magnetic resonance imaging (MRI) with 3-dimensional (3D) myocardial strain analysis allows quantitative assessment of myocardial contractility. We assessed the hypothesis that 3D strain determination at rest and with low-dose dobutamine would discriminate between viable and nonviable myocardium in patients with ischemic cardiomyopathy (ICM). MRI with radiofrequency tissue-tagging at rest and with low-dose dobutamine was performed in 16 normal volunteers and 14 patients with ICM. Three-dimensional global and regional circumferential strains (Ecc) were computed for all subjects at rest and with dobutamine. Results were compared with clinically indicated conventional viability studies. Compared with normal volunteers, global left ventricular Ecc was significantly decreased in patients with ICM at rest (-0.15+/-0.06 versus -0.27+/-0.03; P<0.001) and with dobutamine (-0.17+/-0.08 versus -0.37+/-0.10; P<0.001). Ecc was significantly decreased in nonviable regions compared with viable segments at rest (-0.08+/-0.06 versus -0.17+/-0.10; P<0.001) and with dobutamine (-0.07+/-0.06 versus -0.21+/-0.11; P<0.001). Ecc in viable segments increased significantly in response to dobutamine (P=0.04), whereas Ecc did not change in nonviable segments (P=0.50). Normal controls (96 segments) had increased Ecc at rest (-0.27+/-0.07) and with dobutamine (-0.37+/-0.15) compared with both viable and nonviable regions in ICM patients (P<0.001). Noninvasive dobutamine tissue-tagged MRI with calculation of 3D strain allows the identification, quantification and display of regionally varying ventricular function. The response of systolic strain to low-dose dobutamine has significant promise in discriminating between viable and nonviable myocardium.

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.

1037-142 Postsystolic shortening is consistently prevalent in nonviable myocardium in patients with acute myocardial infarction: Comparison with contrast-enhanced magnetic resonance imaging

1037-142 Postsystolic shortening is consistently prevalent in nonviable myocardium in patients with acute myocardial infarction: Comparison with contrast-enhanced magnetic resonance imaging

Recent advances in cardiac positron emission tomography in the clinical management of the cardiac patient.

Despite being primarily a research tool, positron emission tomography (PET) has seen slow but steady growth in the clinical management of the cardiac patient. The two major clinical applications of cardiac PET are regional myocardial perfusion imaging to determine the presence and severity of coronary artery disease and metabolic imaging to differentiate viable from nonviable myocardium in patients with ischemic left ventricular dysfunction. Indeed, PET with either nitrogen 13 ammonia or rubidium 82 may offer advantages over current single photon emission computed tomography approaches to assess myocardial perfusion. PET with fluorine 18 fluorodeoxyglucose is considered the current gold standard for identifying viable myocardium. Finally, the use of PET to quantify myocardial perfusion, metabolism, and innervation has led to key insights into the role of altered microvascular function, substrate metabolism, and neuronal function in a variety of cardiac disease processes.

Myocardial Viability: Comparison of Free-Breathing Navigator-echo-gated Three-Dimensional Inversion-Recovery Gradient-Echo MR and Standard Multiple Breath-Hold Two-Dimensional Inversion-Recovery Gradient-Echo MR

Purpose: To compare a free-breathing, navigator-echo-gated, three-dimensional, inversion-recovery, gradientecho, MR pulse sequence (3D-MRI) with standard, multiple breath-hold, two-dimensional, inversion-recovery, gradient-echo MR (2D-MRI) for the evaluation of delayed hyperenhancement of nonviable myocardium in patients with chronic ischemic heart disease. Materials and Methods: Ten patients with chronic ischemic heart disease were enrolled in this study. MRI was performed on a 1.5-T system. 3D-MRI was obtained in the short axis plane at 10 minutes after the administration of Gd-DTPA (0.2 mmol/kg, 4 cc/sec). Prospective gating of the acquisition based on the navigator echo was applied. 2D-MRI was performed immediately after finishing 3D-MRI. The area of total and hyperenhanced myocardium measured on both image sets was compared with paired Student t-test and Bland-Altman method. By using a 60-segment model, the transmural extent and segmental width of the hyperenhanced area were recorded by 3-scale grading method. The agreement between the two sequences was evaluated with kappa statistics. We also evaluated the agreement of hyperenhancement among the three portions (apical, middle and basal portion) of the left ventricle with kappa statistics. Results: The two sequences showed good agreement for the measured area of total and hyperenhanced myocardium on paired t-test (p=0.11 and p=0.34, respectively). No systematic bias was shown on Bland-Altman analysis. Good agreement was found for the segmental width (ĸ=0.674) and transmural extent (ĸ=0.615) of hyperenhancement on the segmented analysis. However, the agreement of the transmural extent of hyperenhancement in the apical segments was relatively poor compared with that in the middle or basal portions. Conclusion: This study showed good agreement between 3D-MRI and 2D-MRI in evaluation of non-viable myocardium. Therefore, 3D-MRI may be useful in the assessment of myocardial viability in patients with dyspnea and children because it allows free-breathing during the examination.

Present assessment of myocardial viability by nuclear imaging

Prospective delineation of viable from nonviable myocardium in patients with coronary artery disease in an important factor in deciding whether a patient should be revascularized or treated medically. Two common techniques--single-photon emission computed tomography (SPECT) and positron-emission computed tomography (PET)--are used in nuclear medicine using various radiopharmaceuticals for the detection of myocardial viability in patients. Thallium-201 (201Tl) and technetium-99m (99mTc)-sestamibi are the common radiopharmaceuticals used in different protocols using SPECT, whereas fluoride-18 (18F)-fluorodeoxyglucose (FDG) and rubidium-82 (82Rb) are most widely used in PET. The SPECT protocols involve stress/redistribution, stress/redistribution/reinjection, and rest/redistribution imaging techniques. Many studies have compared the results of 201Tl and (99mTc)-sestamibi SPECT with those of FDG PET; in some studies, concordant results have been found between delayed thallium and FDG results, indicating that 201Tl, although considered a perfusion agent, shows myocardial viability. Discordant results in a number of studies have been found between sestamibi and FDG, suggesting that the efficacy of sestamibi as a viability marker has yet to be established. Radiolabeled fatty acids such as iodine-123 (123I)-para-iodophenylpentadecanoic acid and carbon-11 (11C)-palmitic acid have been used for the assessment of myocardial viability with limited success. 11C-labeled acetate is a good marker of oxidative metabolism in the heart and has been used to predict the reversibility of wall motion abnormalities. (18F)-FDG is considered the marker of choice for myocardial viability, although variable results are obtained under different physiological conditions. Detection of myocardial viability can be greatly improved by developing new equipment and radiopharmaceuticals of better quality.

Positron emission tomographic measurements of absolute regional myocardial blood flow permits identification of nonviable myocardium in patients with chronic myocardial infarction

Objectives. This study tested the hypothesis that nonviable myocardium can be identified by quantitative measurements of regional myocardial blood flow obtained using positron emission tomography in conjunction with a mathematical model of nitrogen-13 (N-13) ammonia tracer kinetics.Background. Under steady state basal conditions there is a minimal level of blood flow required to sustain myocardial viability. Therefore, the hypothesis predicts that regions with flow below a certain threshold are likely to be composed primarily of scar.Methods. Studies were conducted in 26 patients with chronic myocardial infarction. Positron emission tomographic measurements of basal regional myocardial blood flow (N-13 ammonia) and fluorine-18 (F-18) fluorodeoxyglucose uptake were made and correlated with information about coronary anatomy and regional wall motion to assess myocardial viability.Results. In patients with chronic myocardial infarction, normal zone blood flow (0.81 ± 0.32 ml/min per g [mean ± SD]) was greater (p < 0.02) than that of border zones (0.59 ± 0.29 ml/min per g), which in turn exceeded (p < 0.001) that of infarct zone flow (0.27 ± 0.17 ml/min per g). Good correlation was noted between relative F-18 fluorodeoxyglucose uptake and relative regional myocardial blood flow in all zones (r = 0.63, p < 0.001). Mismatch between blood flow and F-18 fluorodeoxyglucose uptake, with a single exception, was not observed in any segment with blood flow < 0.25 ml/min per g. All dyskinetic segments (n = 5) also had blood flow < 0.25 ml/min per g. In contrast, 43 of 45 myocardial segments (23 patients) with normal contraction or only mild hypokinesia had flow ≥ 0.39 ml/min per g (average flow 0.78 ± 0.35 ml/min per g).Conclusions. In patients with chronic myocardial infarction, myocardial viability is unlikely when basal regional myocardial blood flow is < 0.25 ml/min per g. Average basal flow in segments with normal or nearly normal wall motion is 0.78 ± 0.35 ml/min per g. Thus, positron emission tomographic measurement of regional myocardial blood flow is helpful in identifying nonviable myocardium in these patients.

Metabolic evidence of viable myocardium in regions with reduced wall thickness and absent wall thickening in patients with chronic ischemic left ventricular dysfunction

Reduced end-diastolic wall thickness with absent systolic wall thickening has been reported to represent nonviable myocardium in patients with chronic coronary artery disease. To assess whether reduced regional end-diastolic wall thickness and absent wall thickening accurately identify nonviable myocardium, 25 patients with ischemic left ventricular dysfunction (ejection fraction at rest 27 ± 10%) underwent positron emission tomography with oxygen-15-labeled water and 18fluorodeoxyglucose to assess metabolic activity and spin-echo gated nuclear magnetic resonance imaging to measure regional end-diastolic wall thickness and wall thickening. The presence of metabolic activity was defined as 18fluorodeoxyglucose uptake (corrected for partial volume) >50% of that in normal regions.Of 355 myocardial regions evaluated, 266 were hypokinetic or normokinetic at rest and 89 were akinetic (that is, absent wall thickening). 18Fluorodeoxglucose uptake was observed in 97% of the hypokinetic and normokinetic regions and in 74% of the akinetic regions. End-diastolic wall thickness was greater in akinetic regions with than in those without 18fluorodeoxyglucose uptake (11 ± 4 vs. 7 ± 3 nun, p < 0.01). The highest values for sensitivity and specificity of end-diastolic wall thickness in predicting the absence of metabolic activity in akinetic regions were 74% and 79%, respectively, and corresponded to an end-diastolic threshold of 8 mm. However, the positive predictive accuracy was only 55% and did not improve for other end-diastolic wall thickness values. In all myocardial regions, there was only a weak correlation between 18fluorodeoxyglucose activity and either end-diastolic wall thickness (r = 0.17) or wall thickening (r = 0.32).Thus, metabolic activity is present in many regions with reduced end-diastolic wall thickness and absent wall thickening. These data indicate that assessment of regional anatomy and function may be inaccurate in distinguishing asynergic but viable myocardium from nonviable myocardium.