Myocardial strain imaging: review of general principles, validation, and sources of discrepancies.

Myocardial tissue tracking imaging techniques have been developed for a more accurate evaluation of myocardial deformation (i.e. strain), with the potential to overcome the limitations of ejection fraction (EF) and to contribute, incremental to EF, to the diagnosis and prognosis in cardiac diseases. While most of the deformation imaging techniques are based on the similar principles of detecting and tracking specific patterns within an image, there are intra- and inter-imaging modality inconsistencies limiting the wide clinical applicability of strain. In this review, we aimed to describe the particularities of the echocardiographic and cardiac magnetic resonance deformation techniques, in order to understand the discrepancies in strain measurement, focusing on the potential sources of variation: related to the software used to analyse the data, to the different physics of image acquisition and the different principles of 2D vs. 3D approaches. As strain measurements are not interchangeable, it is highly desirable to work with validated strain assessment tools, in order to derive information from evidence-based data. There is, however, a lack of solid validation of the current tissue tracking techniques, as only a few of the commercial deformation imaging softwares have been properly investigated. We have, therefore, addressed in this review the neglected issue of suboptimal validation of tissue tracking techniques, in order to advocate for this matter.

Assessment of left ventricular mass and volumes by three-dimensional echocardiography in patients with or without wall motion abnormalities: comparison against cine magnetic resonance imaging.

AIM: To evaluate if three-dimensional echocardiography (3-DE) is as accurate and reproducible as cine magnetic resonance imaging (cMR) in estimating left ventricular (LV) parameters in patients with and without wall motion abnormalities (WMA). METHODS: 83 patients (33 with WMA) underwent 3-DE and cMR. 3-DE datasets were analysed using a semi-automatic contour detection algorithm. The accuracy of 3-DE was tested against cMR in the two groups of patients. All measurements were made twice by two different observers. RESULTS: LV mass by 3-DE was similar to that obtained by cMR (149 (SD 42) g vs 148 (45) g, p = 0.67), with small bias (1 (28) g) and excellent interobserver agreement (-2 (31) g vs 4 (26) g). The two measurements were also highly correlated (r = 0.94), irrespective of WMA. End-diastolic and end-systolic LV volumes and ejection fraction by 3-DE and cMR were highly correlated (r = 0.97, 0.98, 0.94, respectively). Yet, 3-DE underestimated cMR end-diastolic volumes (167 (68) ml vs 187 (70) ml, p<0.001) and end-systolic volumes (88 (56) ml vs 101 (65) ml, p<0.001), but yielded similar ejection fractions (50% (14%) vs 50% (16%), p = 0.23). CONCLUSION: 3-DE permits accurate determination of LV mass and volumes irrespective of the presence or absence of WMA. LV parameters obtained by 3-DE are also as reproducible as those obtained by cMR. This suggests that 3-DE can be used to follow up patients with LV hypertrophy and/or remodelling.

Exaggerated chronotropic and energetic response to dobutamine after orthotopic cardiac transplantation.

BACKGROUND: After heart transplantation, the transplanted denervated heart displays both an exaggerated chronotropic and an exaggerated inotropic response to circulating catecholamines. This study assessed whether denervated transplanted hearts also display an exaggerated energetic response when challenged with dobutamine. METHODS AND RESULTS: A total of 18 heart transplant recipients and 14 normal volunteers underwent measurements of myocardial oxygen consumption (MVO2), external work (EW), and pressure-volume area (PVA), at rest and during infusion of dobutamine. At rest, calculated myocardial (PVA/MVO2) and mechanical (EW/MVO2) efficiencies were similar among transplant recipients and normal volunteers. During low-dose dobutamine infusion (8 microg/kg/min), transplant recipients exhibited a larger increase in heart rate (to 126 +/- 14 vs 87 +/- 26 beats/min, p < 0.001) and MVO2 (to 269 +/- 43 vs 233 +/- 19 J/min/100g, p < 0.05) and a smaller increase in EW (64 +/- 18 vs 72 +/- 13 J/min/100g, p < 0.05) and PVA (70 +/- 16 vs 81 +/- 13 J/min/100g, p < 0.05) than did normal volunteers. As a result, both myocardial (26 +/- 4 vs 35 +/- 4%, p < 0.05) and mechanical (23 +/- 4 vs 30 +/- 4%, p < 0.001) efficiencies were lower during dobutamine infusion in transplant recipients than in normal volunteers. During the infusion of a higher dose of dobutamine (19 microg/kg/min), the chronotropic and inotropic responses of heart transplant recipients were even more exaggerated. The fall in myocardial efficiency induced by dobutamine correlated with the increase in heart rate (r = -0.58) and could be reproduced in normal volunteers by coadministration of atropine. CONCLUSIONS: Transplant recipients exhibit a larger fall in contractile efficiency and a larger oxygen-wasting effect during dobutamine infusion than do normal volunteers. Because normal volunteers pre-medicated with atropine presented with a similar increase in heart rate and a similar fall in efficiency, the exaggerated energetic response of transplanted hearts to dobutamine likely resulted from the same mechanisms as their chronotropic supersensitivity, i.e., the loss of inhibitory parasympathetic innervation.

Positron emission tomography using(18)F-fluoro-deoxyglucose and euglycaemic hyperinsulinaemic glucose clamp: optimal criteria for the prediction of recovery of post-ischaemic left ventricular dysfunction. Results from the European Community Concerted Action Multicenter study on use of(18)F-fluoro-deoxyglucose Positron Emission Tomography for the Detection of Myocardial Viability.

AIMS: To assess the accuracy of positron emission tomography to predict recovery of global cardiac function after revascularization in patients with coronary artery disease. METHODS AND RESULTS: One hundred and seventy-eight patients (157 male, 58+/-10 years) with coronary artery disease and left ventricular dysfunction (mean ejection fraction 39+/-14%) were enrolled in six European centres. They underwent a common protocol for the assessment of viability using(18)F-fluoro-2-deoxyglucose (FDG) positron emission tomography during a standardized euglycaemic hyperinsulinaemic glucose clamp before revascularization by either surgery (n=140) or angioplasty (n=38). Seven patients were excluded because of incomplete revascularization of a dysfunctional region. Based on the recovery of global ejection fraction 2-6 months after revascularization, patients were classified into two groups: 82 patients who had a >5% improvement in ejection fraction postoperatively, and 89 patients without postoperative ejection fraction improvement. Optimal cut-off points for postoperative improvement of global cardiac function were computed, using receiver operating curve analysis. The highest sensitivity (79%) and specificity (55%) for predicting postoperative ejection fraction improvement by positron emission tomography was found when three or more dysfunctional segments had a relative FDG uptake >45% of normal remote myocardium (overall accuracy 67%). CONCLUSIONS: In a large cohort of coronary patients with impaired ejection fraction, FDG positron emission tomography demonstrated high sensitivity and moderate specificity to predict improvement of cardiac function after coronary revascularization.

Relation between Gd-DTPA contrast enhancement and regional inotropic response in the periphery and center of myocardial infarction.

BACKGROUND: Gd-DTPA contrast-enhanced (CE) MRI identifies patterns of early hypoenhancement and delayed hyperenhancement in acute myocardial infarction, but their clinical significance for the prediction of myocardial viability remains controversial. Therefore, we closely examined the relationship between these CE patterns and regional inotropic response to low-dose dobutamine infusion at a regional level. METHODS AND RESULTS: Thirteen dogs underwent CE and tagged MRI at rest and during 5 microg. kg(-1). min(-1) dobutamine 48 hours after MI. CE patterns and 3D regional strains were measured in 96 segments per animal. Segments were categorized as being normofunctional (n=828) if resting circumferential shortening was within the range of remote myocardium, or dysfunctional (n=420) if not. Inotropic response in resting dysfunctional segments was assessed according to CE patterns. Significant improvement of radial thickening (from +12+/-1% [mean+/-SEM] to +22+/-2%, P<0.05) and circumferential shortening (from +1+/-1% to -5+/-1%, P<0.05) strains occurred in dysfunctional myocardium with normal CE pattern but not in myocardium with early hypoenhancement. Delayed hyperenhanced myocardium displayed a more complex behavior. Circumferential stretching improved in the peripheral regions (from +4+/-1% to -2+/-2%, P<0.05), where the infarct was nontransmural (38+/-3% transmurality), but not in centrally hyperenhanced regions (from +4+/-1% to +1+/-1% P=NS), where the infarct was 66+/-3% transmural. CONCLUSIONS: Inotropic reserve was confined to dysfunctional myocardium with normal contrast enhancement but not to myocardium with early hypoenhancement. Inotropic response in delayed hyperenhanced myocardium is influenced by transmurality of necrosis. These observations support the use of CE MRI for the clinical detection of myocardial viability.

Microvascular obstruction and left ventricular remodeling early after acute myocardial infarction.

BACKGROUND: The presence of microvascular obstruction (MO) within infarcted regions may adversely influence left ventricular (LV) remodeling after acute myocardial infarction. This study examined whether the extent of MO directly alters the mechanical properties of the infarcted myocardium. METHODS AND RESULTS: Seventeen dogs underwent 90 minutes of balloon occlusion of the left anterior descending coronary artery, followed by reperfusion. Gadolinium-enhanced perfusion MRI and 3D-tagging were performed 4 to 6 and 48 hours (8 animals) and 10 days (9 animals) after reperfusion. Early increase in LV end-diastolic volume (from 42+/-9 to 54+/-14 mL, P<0.05) between 4 to 6 and 48 hours after reperfusion was predicted by both extent of MO (r=0.89, P<0.01) and infarct size (r=0.83, P<0.01), defined as MRI hypoenhanced and hyperenhanced regions, respectively. Multivariate analysis demonstrated that extent of MO had better and independent value to predict LV volume than overall infarct size. A strong inverse relationship existed between magnitude of first principal strain (r=-0.80, P<0.001) and relative extent of MO within infarcted myocardium. Also, infarcted myocardium involved by extensive areas of MO demonstrated reductions of circumferential (r=-0.61, P<0.01) and longitudinal (r=-0.53, P<0. 05) stretching. Furthermore, significant reductions of radial thickening (9+/-6% versus 14+/-3%, P<0.01) occurred in noninfarcted regions adjacent to infarcts that had increased (>35%) amounts of MO. CONCLUSIONS: In the early healing phase of acute myocardial infarction, the extent of MO in infarcted tissue relates to reduced local myocardial deformation and dysfunction of noninfarcted adjacent myocardium. Such strain alterations might explain the increased remodeling observed in patients with large regions of MO.

Time course of functional recovery after coronary artery bypass graft surgery in patients with chronic left ventricular ischemic dysfunction.

Chronic left ventricular (LV) ischemic dysfunction, a condition often referred to as myocardial hibernation, is associated in humans with ultrastructural alterations of the myocytes, including the loss of myofilaments and the accumulation of glycogen. Given the severity of these structural changes, contractile function is unlikely to resume immediately upon revascularization. Therefore, the aim of the present study was to assess the time course of functional improvement after successful revascularization as well as its potential structural correlates. We studied 32 patients with coronary disease and chronic LV ischemic dysfunction who underwent bypass surgery. Dynamic positron emission tomography with N-13 ammonia and F-18 deoxyglucose to assess myocardial perfusion and glucose metabolism was performed in 29 patients. In all patients, a transmural biopsy was harvested from the center of the dysfunctional area, to quantify the increase in extracellular matrix and the presence of structurally altered cardiomyocytes. LV function was serially measured by digitized 2-dimensional echocardiography before and at 10 days, 2 months, and 6 months after revascularization. The time course of recovery of regional function was estimated from the monoexponential decrease in dysfunctional wall motion score. At follow-up, 19 patients had improved LV function, whereas 13 patients showed persistent dysfunction. Before revascularization, reversibly dysfunctional segments had higher myocardial blood flow (82 +/- 29 vs 53 +/- 21 ml. (min. 100 g)(-1), p = 0.044), higher glucose uptake (40 +/- 16 vs 21 +/- 9 micromol. (min. 100 g)(-1), p = 0.001), and less increase in extracellular matrix (25 +/- 15% vs 46 +/- 17%, p = 0.0008) than segments with persistent dysfunction. The extent to which function recovered was positively correlated with myocardial blood flow and negatively correlated with the increase in the extracellular matrix. In patients with reversible dysfunction, the return of segmental function was progressive and followed a monoexponential time course with a median time constant of 23 days (range 6 to 78). The rate of recovery correlated best with the proportion of altered cardiomyocytes in the biopsy. The present study thus indicates that the recovery of regional and global LV function after successful revascularization is progressive and follows a monoexponential time course that is influenced by the extent of the structural changes affecting cardiomyocytes.

Magnetic resonance imaging of myocardial infarct.

Magnetic resonance imaging offers the unique opportunity to directly visualize the size and location of myocardial infarcts (MIs) with excellent spatial resolution. Because infarct size is the most important determinant of postinfarct outcome, precise determination of infarct size may be valuable to risk stratify patients after acute MI. In addition, infarct imaging may provide direct information on the amount of irreversibly injured myocardium and thus can be used to identify myocardial viability in dysfunctional regions. Acute infarcts can be recognized as hyperintense signal on T2-weighted spin-echo images. This technique, however, does not identify chronic infarcts and may overestimate infarct size by including area at risk. Also, T2-weighted images often have a low signal-to-noise ratio. Contrast-enhanced perfusion imaging provides better-quality images. Extravascular contrast agents such as (Gd-DTPA) gadolinium diethyletriamine-pentaacetic acid identify infarcts as hyperenhanced regions on images acquired late after contrast injection. In addition, these tracers can examine the integrity and permeability of infarct microvasculature on first-pass perfusion images. Necrosis avid tracers and 23Na imaging are other new exciting approaches to identify infarcted myocardium acutely after MI. These techniques, are still investigational, and their value for clinical imaging remains to be established.

Myocardial perfusion and oxygen consumption in reperfused noninfarcted dysfunctional myocardium after unstable angina: direct evidence for myocardial stunning in humans.

OBJECTIVES: To positively establish the diagnosis of myocardial stunning in patients with unstable angina and persistent wall motion abnormalities after reperfusion by coronary angioplasty. BACKGROUND: Although myocardial stunning is thought to occur in several clinical conditions, definite proof of its existence in humans is still lacking, owing to the difficulty of measuring myocardial blood flow (MBF) in absolute terms. METHODS: We studied 14 patients with unstable angina due to proximal left anterior descending coronary artery disease who presented persistent anterior wall motion abnormalities despite revascularization of the culprit lesion by percutaneous coronary angioplasty (PTCA) and who did not have clinical evidence of necrosis. Dynamic positron emission tomography (PET) with [13N]-ammonia and [11C]-acetate was performed 48 h after PTCA to determine absolute MBF and oxygen consumption (MVO2). Regional wall thickening and regional cardiac work were determined using two-dimensional echocardiography. Improvement of segmental wall motion abnormalities was followed for a median of 4 months (1.5 to 14 months). RESULTS: As judged from the changes in segmental wall motion score, regional dysfunction was spontaneously reversible in 12/14 patients and improved from 2.2 +/- 0.3 to 1.2 +/- 0.3 at late follow-up (p < 0.001). With PET, [13N]-ammonia MBF was similar among dysfunctional and remote normally contracting segments (85 +/- 29 vs. 99 +/- 20 ml x min (-1) x 100g(-1), p = not significant [n.s.]), thus demonstrating a perfusion-contraction mismatch. Despite the reduced contractile function, dysfunctional myocardium presented near normal levels of MVO2 (6.5 +/- 4.2 vs. 8.0 +/- 1.9 ml x min (-1)x 100g(-1), p = n.s.). Consequently, the regional myocardial efficiency (regional work divided by MVO2) of the dysfunctional myocardium was found to be markedly decreased as compared with normally contracting myocardium (6 +/- 6% vs. 26 +/- 6%, p < 0.001). CONCLUSIONS: This study demonstrates that human dysfunctional myocardium capable of spontaneously recovering contractile function after unstable angina endures a state of perfusion-contraction mismatch. These data for the first time provide unequivocal direct evidence for the existence of acute myocardial stunning in humans.

Nitrogen-13-ammonia and oxygen-15-water estimates of absolute myocardial perfusion in left ventricular ischemic dysfunction.

UNLABELLED: Measurements of resting myocardial blood flow (MBF) in patients with chronic left ventricular ischemic dysfunction by 15O-water with 13N-ammonia and PET have yielded conflicting results. The aim of this study was to perform a head-to-head comparison of both tracers in the same patient population and to answer the question of whether distinctive tracer properties account for differences in estimates of MBF in chronically dysfunctional myocardium by both tracers. METHODS: A total of 30 patients with chronic dysfunction of the anterior myocardial wall due to significant left anterior descending coronary artery disease underwent PET measurements of absolute MBF in the anterior wall by use of 15O-water and 13N-ammonia before coronary revascularization by either coronary artery bypass graft (n = 24) or percutaneous transluminal coronary angioplasty (n = 6). Improvement of regional contractile function was assessed by two-dimensional echocardiography at a mean of 7.5 +/- 2.1 mo after revascularization. As judged from the changes in anterior myocardial wall motion after revascularization, patients were considered to have either reversibly (n = 16) or persistently (n = 14) dysfunctional myocardium. Estimates of MBF by 15O-water and 13N-ammonia, obtained in every patient before revascularization, were compared among the two patient groups by use of previously validated methods. RESULTS: With 13N-ammonia, resting regional MBF was significantly higher in reversibly as opposed to persistently dysfunctional segments [84 +/- 8 versus 48 +/- 6 ml (min x 100 g)(-1), mean +/- s.e.m., p < 0.01]. By contrast, no such difference was found when using 15O-water to measure MBF [74 +/- 6 versus 86 +/- 9 ml (min x 100 g)(-1), p = ns]. This was mainly due to the fact that the perfusable tissue fraction (PTF), a fitted parameter of the 15O-water model, was significantly higher in reversibly as opposed to persistently dysfunctional segments (0.63 +/- 0.03 versus 0.50 +/- 0.03, p < 0.05). As a consequence, the 15O-water perfusable tissue index (PTI), which is the ratio of the PTF to the anatomical tissue fraction, was greater in reversibly dysfunctional as opposed to persistently dysfunctional segments (1.07 +/- 0.07 versus 0.79 +/- 0.05, p < 0.01). CONCLUSION: This study demonstrates significant differences in MBF estimates between 15O-water and 13N-ammonia in chronically dysfunctional ischemic myocardium. Our results indicate that the 15O-water method yields higher absolute MBF values than the 13N-ammonia approach. Our results also support the use of PTI as a marker of myocardial tissue viability.

Head-to-head comparison of exercise-redistribution-reinjection thallium single-photon emission computed tomography and low dose dobutamine echocardiography for prediction of reversibility of chronic left ventricular ischemic dysfunction.

OBJECTIVES: We sought to directly compare the diagnostic value of exercise-redistribution-reinjection thallium single-photon emission computed tomography (SPECT) and low dose dobutamine echocardiography for prediction of contractile recovery after revascularization. BACKGROUND: Both thallium SPECT and dobutamine echocardiography have been proposed to predict the reversibility of left ventricular dysfunction after revascularization. Although both techniques permit differentiation of viable from nonviable myocardium, few studies have directly compared their accuracy in the same patients. METHODS: Seventy-three consecutive patients (mean [+/- SD] age 59 +/- 9 years) with coronary disease and regional left ventricular dysfunction underwent exercise-redistribution-reinjection thallium SPECT and dobutamine echocardiography before revascularization. Recovery of function was evaluated with echocardiography 5.5 +/- 2.5 months after revascularization. For analysis, the left ventricle was divided into 16 segments, in which percent thallium uptake was quantitated using circumferential profiles, and regional wall motion was graded semiquantitatively (normal = 1; akinetic = 3). RESULTS: The diagnostic performance of the two tests was investigated both for individual patients and for individual segments. Individual patient analysis showed that left ventricular ejection fraction improved > 5% after revascularization in 43 patients, whereas 30 showed no change. Receiver operating characteristic curves were used to select optimal criteria for prediction of functional recovery after revascularization. According to a mean thallium uptake > 54% at reinjection, SPECT had a sensitivity of 72%, a specificity of 73% and an overall accuracy of 73%. Similarly, according to an improvement in wall motion score > 3.5 grades during doubutamine echocardiography, echocardiography had a sensitivity of 88%, a specificity of 77% and an overall accuracy of 84% (p = NS vs. thallium). Segmental analysis showed that SPECT and dobutamine echocardiography had similar sensitivity (77% and 75%, respectively), but SPECT had lower specificity (56% vs. 86%, p < 0.01). CONCLUSIONS: Quantitative exercise-redistribution-reinjection thallium SPECT and dobutamine echocardiography have comparable accuracy for prediction of reversibility of global left ventricular dysfunction after revascularization. However, dobutamine echocardiography has greater specificity than thallium imaging for prediction of functional recovery on a segmental basis.

Myocardial blood flow, glucose uptake, and recruitment of inotropic reserve in chronic left ventricular ischemic dysfunction. Implications for the pathophysiology of chronic myocardial hibernation.

BACKGROUND: Previous work has documented that dysfunctional noninfarcted collateral-dependent myocardium, a condition typical of myocardial hibernation, exhibited almost normal resting perfusion. The present study was designed to test whether these observations could be extended to unselected patients with chronic dysfunction and a previous infarction. METHODS AND RESULTS: Dynamic positron emission tomographic imaging with [13N]ammonia and [18F]fluorodeoxyglucose (FDG) to assess myocardial perfusion and glucose uptake was performed in 39 patients with chronic anterior wall dysfunction undergoing coronary revascularization. Left ventricular function was evaluated by echocardiography before (at rest and during low-dose dobutamine infusion) and 5 months after revascularization. At follow-up, wall motion was improved in 24 patients and unchanged in 15 patients. Before revascularization, absolute myocardial blood flow was higher (84 +/- 27 versus 60 +/- 26 mL.min-1 x 100 g-1, P = .007) in reversibly compared with persistently dysfunctional segments. In segments with reversible dysfunction, values of myocardial blood flow were similar to those in the remote segments of the same patients or in anterior segments of normal volunteers. During glucose clamp, FDG uptake was higher (69 +/- 17% versus 49 +/- 18%, P < .01) but myocardial glucose uptake was not different (38 +/- 20 versus 29 +/- 19 mumol.min-1.100 g-1, P = NS) in reversibly compared with persistently dysfunctional segments. A flow-metabolism mismatch was present in 18 of 24 reversibly injured but absent in 10 of 15 persistently dysfunctional segments. With dobutamine, wall motion improved in 17 of 24 reversibly dysfunctional segments and did not change in 13 of 15 segments with persistent dysfunction. CONCLUSIONS: This study indicates that chronic but reversible ischemic dysfunction is associated with almost normal resting myocardial perfusion, with maintained FDG uptake, and with recruitable inotropic reserve. These data support the contention that chronic hibernation is not the consequence of a permanent reduction of transmural myocardial perfusion at rest.

Preoperative selection of patients with severely impaired left ventricular function for coronary revascularization. Role of low-dose dobutamine echocardiography and exercise-redistribution-reinjection thallium SPECT.

BACKGROUND: Both thallium imaging and low-dose dobutamine echocardiography have been proposed to predict the reversibility of left ventricular (LV) dysfunction in patients with coronary disease. The present study was designed to evaluate whether the use of these techniques during the preoperative assessment of coronary patients with depressed LV function can improve our ability to identify those likely to have improved LV function after surgery. METHODS AND RESULTS: Forty consecutive patients (age, 60 +/- 10 years) with coronary disease and an ejection fraction < or = 35% underwent dobutamine echocardiography (10 micrograms/kg per minute) and exercise-redistribution-reinjection thallium single photon emission computed tomography (SPECT) before coronary revascularization by bypass surgery (n = 33) or angioplasty (n = 7). Recovery of LV function was evaluated by echocardiography 5.3 +/- 2.4 months after revascularization. According to the changes in end-systolic volume and ejection fraction after revascularization, the patients were categorized into groups with (n = 19) and without (n = 21) postoperative functional improvement, defined as a > 5% increase in ejection fraction and > 10 mL decrease in end-systolic volume. Before revascularization, patients with improved postoperative function had smaller end-diastolic volume and less wall motion abnormalities than those with persistent dysfunction. They also showed greater improvement of wall motion score with dobutamine (6.1 +/- 2.4 versus 1.8 +/- 4.2 grades, P < .001) and smaller thallium defect score after exercise (38 +/- 12 versus 47 +/- 14 grades, P = .04). Discriminant analysis selected the improvement in wall motion score with dobutamine and baseline end-diastolic volume as independent predictors of postoperative recovery. Consideration of both parameters allowed prediction of functional outcome in 84% of the patients with and 81% of those without postoperative improvement. CONCLUSIONS: Among the parameters commonly available before surgery in coronary patients with depressed LV function, the maintenance of significant inotropic reserve, the severity of LV remodeling, and the magnitude of the perfusion defect after exercise can predict the reversal of LV dysfunction after revascularization.