Regional left ventricular wall thickening. Relation to regional uptake of 18fluorodeoxyglucose and 201Tl in patients with chronic coronary artery disease and left ventricular dysfunction

Incremental value of myocardial wall motion and thickening to perfusion alone by gated SPECT myocardial perfusion imaging for viability assessment in patients with ischemic heart failure

PURPOSE

The objective of this study was to assess the incremental value of myocardial wall motion and thickening compared with perfusion alone obtained from gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) in diagnosing myocardial viability in patients with ischemic heart failure.

METHODS

Eighty-three consecutive patients with ischemic heart failure who underwent both 99mTc-MIBI gated SPECT MPI and 18F-FDG positron emission tomography (PET) myocardial metabolic imaging were retrospectively enrolled. SPECT/PET myocardial viability was defined as the reference standard. Segmental myocardial perfusion, wall motion, and thickening were measured by an automated algorithm from gated SPECT MPI. Univariate and stepwise multivariate analysis were conducted to establish an optimal multivariate model for predicting hibernating myocardium and scar.

RESULTS

Among the 1411 segments evaluated, 774 segments had normal perfusion and 637 segments had decreased perfusion. The latter were classified by 18F-FDG PET into 338 hibernating segments and 299 scarred segments. The multivariate regression analysis showed that the model that combined myocardial perfusion uptake with wall motion and thickening scores had the optimal predictive efficiency to distinguish hibernating myocardium from scar in the segments with decreased perfusion. The model had the largest C-statistic (0.753 vs 0.666, P < 0.0001), and the global chi-square was increased from 53.281 to 111.234 when compared with perfusion alone (P < 0.001).

CONCLUSIONS

Assessment of myocardial wall motion and thickening in addition to conventional perfusion uptake in the segments with decreased perfusion enables better differentiation of hibernating myocardium from scar in patients with ischemic heart failure. Considering wide availability and high cost-effectiveness, regional myocardial function integrated with perfusion on gated SPECT MPI has great promise to become a clinical tool in the assessment of myocardial viability.

Usefulness of cardiac MRI in the prognosis and follow-up of ischemic heart disease

Cardiac magnetic resonance imaging (MRI) is an important tool that makes it possible to evaluate patients with cardiovascular disease; in addition to infarction and alterations in myocardial perfusion, cardiac MRI is useful for evaluating other phenomena such as microvascular obstruction and ischemia. The main prognostic factors in cardiac MRI are ventricular dysfunction, necrosis in late enhancement sequences, and ischemia in stress sequences. In acute myocardial infarction, cardiac MRI can evaluate the peri-infarct zone and quantify the size of the infarct. Furthermore, cardiac MRI's ability to detect and evaluate microvascular obstruction makes it a fundamental tool for establishing the prognosis of ischemic heart disease. In patients with chronic ischemic heart disease, cardiac MRI can detect ischemia induced by pharmacological stress and can diagnose infarcts that can be missed on other techniques.

Myocardial reverse remodeling

Despite an extensive literature defining the mechanisms and significance of pathological myocardial remodeling, there has been no comprehensive review of the inverse process, often labeled reverse remodeling. Accordingly, the goal of this review is to overview the varied settings in which clinically significant reverse remodeling has been well documented. When available, we reviewed relevant randomized, controlled clinical trials, and meta-analyses with sufficient cardiac imaging data to permit conclusions about reverse remodeling. When these types of studies were not available, relevant case-control studies and case series that employed appropriate methodology were reviewed. Regression of pathological myocardial hypertrophy, chamber shape distortions, and dysfunction occurs in a wide variety of settings. Although reverse remodeling occurs spontaneously in some etiologies of myocardial dysfunction and failure, remodeling is more commonly observed in response to medical, device-based, or surgical therapies, including β-blockers, revascularization, cardiac resynchronization therapy, and valve surgery. Indeed, reverse remodeling following pathophysiologically targeted interventions helps validate that the targeted mechanisms are propelling and/or sustaining pathological remodeling. The diverse clinical settings in which reverse remodeling has been observed demonstrates that myocardial remodeling is bidirectional and occurs across the full spectrum of myocardial disease severity, duration, and etiology. Observations in several settings suggest that recovered hearts are not truly normal despite parallel improvements at organ, tissue, and cellular level. Nevertheless, the link between reverse remodeling and improved outcomes should inspire further research to better understand the mechanisms responsible for both reverse remodeling and persistent deviations from normalcy.

Systolic 3D first-pass myocardial perfusion MRI: Comparison with diastolic imaging in healthy subjects

Three-dimensional (3D) first-pass myocardial perfusion imaging (MPI) is a promising alternative to conventional two-dimensional multislice MPI due to its contiguous spatial coverage that is beneficial for estimating the size of perfusion defects. Data acquisition at mid-diastole is a typical choice for 3D MPI yet is sensitive to arrhythmia and variations in R-R interval that are common in cardiac patients. End systole is the second longest quiescent cardiac phase and is known to be less sensitive to the R-R variability. Therefore, 3D MPI with systolic acquisition may be advantageous in patients with severe arrhythmia once it is proven to be comparable to diastolic MPI in subjects with negligible R-R variation. In this work, we demonstrate the feasibility of 3D MPI with systolic data acquisition in five healthy subjects. We performed 3D MPI experiments in which 3D perfusion data were acquired at both end-systole and mid-diastole of every R-R interval and analyzed the similarity between resulting time intensity curves (TIC) from the two data sets. The correlation between systolic and diastolic TICs was extremely high (mean = 0.9841; standard deviation = 0.0166), and there was a significant linear correlation between the two time intensity curve upslopes and peak enhancements (P < 0.001).

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.

The assessment of myocardial viability and hibernation using resting thallium imaging

Rest-redistribution thallium-201 imaging is widely used to assess recovery of regional systolic dysfunction in patients with chronic coronary artery disease. In several studies, this technique has demonstrated very high sensitivity but reduced specificity, as reported in general for radionuclide imaging. In clinical terms, this implicates that many dysfunctional territories will not recover after revascularization despite a substantial amount of tracer uptake. Yet, the amount of tracer uptake in a given myocardial segment, although not perfect, remains the best indicator for predicting reversible dysfunction. In fact, the occurrence of redistribution after rest injection is not very common and it does not substantially contribute to the accuracy of the test. However, it is still undetermined whether the presence of redistribution is relevant for prognostic implications.

Prediction of functional recovery after revascularization in patients with coronary artery disease and left ventricular dysfunction by gated FDG-PET

BACKGROUND

Traditionally, cardiac fluorodeoxyglucose (FDG) uptake is combined with regional perfusion for optimal evaluation of viability. Gated FDG-positron emission tomography (PET) may be an alternative technique for detection of viability because it permits combined assessment of glucose metabolism uptake and wall thickening (WT). In this study the value of FDG uptake and WT (analyzed from a stand-alone gated FDG-PET study) for the prediction of recovery of regional and global left ventricular (LV) function in patients with coronary artery disease undergoing revascularization is studied.

METHODS AND RESULTS

Thirty-eight patients with chronic coronary artery disease and LV dysfunction were included. Patients underwent gated FDG-PET to assess viability. Magnetic resonance imaging was performed before and 6 months after revascularization to assess regional and global LV function and LV volumes. Of the 213 revascularized dysfunctional segments, 133 (62%) exhibited functional recovery on follow-up magnetic resonance imaging. Receiver operating characteristic curve analysis indicated that a cutoff level for FDG uptake of 50% or greater yielded a sensitivity and specificity of 93% and 85%, respectively, on gated FDG-PET for prediction of improvement in regional function. Similarly, a cutoff level of 10% or greater for WT was optimal with a sensitivity and specificity of 89% and 78%, respectively. Improvement in LV ejection fraction was best predicted by the number of viable segments. Reverse LV remodeling could be predicted with a sensitivity and specificity of 89% and 65%, respectively, by use of FDG uptake of 50% or greater and 78% and 70%, respectively, by use of WT of 10% or greater.

CONCLUSION

Accurate prediction of outcome after revascularization (including improvement in regional and global LV function and reverse remodeling) is possible with gated FDG-PET by use of a threshold of 50% or greater for FDG uptake or a threshold of 10% or greater for WT.

MRI Assessment of Myocardial Viability

In the presence of coronary artery disease, global left ventricular (LV) systolic function is a critical prognostic indicator. Because of enhanced therapy for myocardial infarction, more patients survive but are left with residual myocardial damage that predisposes them to developing CHF in the future. Although treatments for CHF are evolving, preventing and minimizing further deteriorations in LV function are paramount in this population. Distinguishing severe LV dysfunction caused by thinned, infarcted myocardium with fibrosis and scarring from that due to viable but dysfunctional myocardium from chronic hypoperfusion has significant implications for clinical management. In patients in whom noninvasive testing identifies viability, undergoing revascularization improves outcomes. Noninvasive imaging techniques used to assess viable myocardium are based on demonstrating the presence of one or more of the following features: (1) contractile reserve; (2) sufficient perfusion for the delivery of substrates and removal of metabolic byproducts; (3) intact myocyte membranes to maintain ionic/electrochemical gradients; and (4) preserved metabolism with generation of high-energy phosphates. While nuclear and dobutamine echocardiography have been widely used for viability assessment, cardiac magnetic resonance imaging (CMR) is increasingly becoming an accepted clinical tool, particularly in light of its high spatial resolution, intrinsic ability to image 3-dimensionally, and greater soft tissue differentiation. Moreover, the versatility of the technique potentially allows for the simultaneous assessment of regional wall motion, perfusion, and metabolism. An overview of the CMR techniques is presented.

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.

Assessment of Global and Regional Left Ventricular Function by Electrocardiographic Gated N-13 Ammonia Positron Emission Tomography in Patients With Coronary Artery Disease

BACKGROUND

Electrocardiographic gated 13N-ammonia positron emission tomography (PET) enables simultaneous assessment of myocardial blood flow and left ventricular (LV) function. The aim of this study was to assess the accuracy of gated 13N-ammonia PET for evaluating global and regional LV function in patients with coronary artery disease (CAD) in comparison with conventional left ventriculography (LVG).

METHODS AND RESULTS

Fifty-four patients with CAD underwent gated 13N-ammonia PET and LVG. The LV end-diastolic and end-systolic volumes (LVEDV, LVESV) and ejection fraction (LVEF) by gated 13N-ammonia PET were calculated using Cedars-Sinai automated quantitative gated single photon emission computed tomography (QGS) and compared with those obtained by LVG. The regional wall motion (RWM) was visually scored, and compared with that on LVG. There were good correlations between the 2 methods for LVEF, LVEDV and LVESV (R=0.828, R=0.821 and R=0.874 respectively). The RWM assessed by gated 13N-ammonia PET also agreed well with that by LVG (complete agreement was 70.4%, kappa=0.58).

CONCLUSIONS

Gated 13N-ammonia PET combined with QGS works reasonably well for the assessment of both global and regional LV function in CAD patients, although additional calibration may be necessary.

201Tl gated single photon emission computed tomographic myocardial perfusion imaging in the assessment of global and regional left ventricular function. Would it be favoured over equilibrium radionuclide angiography?

BACKGROUND

This study investigates the clinical performance of routine 201Tl gated single photon emission computed tomographic (201Tl GSPECT) myocardial perfusion imaging. Equilibrium radionuclide angiography (ERNA) was used as the standard for comparison.

METHODS AND RESULTS

One hundred and seventy-two consecutive patients were submitted to both myocardial 201Tl GSPECT imaging, at stress and in redistribution, and ERNA. Left ventricular ejection fractions (LVEF) and regional wall motion were assessed from both stress and redistribution 201Tl GSPECT datasets, and from ERNA. Linear regression analysis showed a good correlation between LVEF calculated by ERNA and 201Tl GSPECT (r=0.73 at stress, r=0.75 in redistribution, P<0.0001). However, the 95% prediction intervals of 201Tl GSPECT LVEF from ERNA LVEF were wide (minimum 35.4% at stress and 33.2% in redistribution). Moreover, a difference in LVEF > or =10% between ERNA and 201Tl GSPECT was found in 26.4% of cases at stress and 28.6% of cases in redistribution. A fair agreement between ERNA and 201Tl GSPECT was found in regional wall motion assessment in segments with normal or mildly reduced tracer uptake (kappa=0.32 at stress and kappa=0.33 in redistribution). In segments with moderately to severely reduced tracer uptake, a moderate agreement was found in regional wall motion assessment between ERNA and 201Tl GSPECT (kappa=0.44 at stress and kappa=0.42 in redistribution).

CONCLUSIONS

Left ventricular function may be misinterpreted in a significant proportion of patients if the calculation of LVEF is based on 201Tl GSPECT. Moreover, the evaluation of regional wall motion by 201Tl GSPECT appears unsatisfactory.

Contribution of myocardium hydraulic skeleton to left ventricular wall interaction and synergy in dogs

The most premature motion change after coronary occlusion is early diastolic thinning of the ischemic left ventricular (LV) wall, with concomitant thickening of the normoperfused wall. We aimed 1). to demonstrate that these early changes are the result of the absence of fluid within the ischemic myocardium (hydraulic skeleton) rather than to cell anoxia and 2). to quantitate the contribution of the lack of hydraulic skeleton to left ventricular asynergy of contraction in seven anesthetized dogs submitted to acute, short-lasting circumflex artery (Cx) occlusion (ischemia) and to perfusion of the Cx with an oxygen-free solution (anoxia). We analyzed the time course of regional work index (WI, area of the LV pressure-wall thickness loop) and regional efficiency (defined as the ratio of WI to the maximum possible work). Interwall asynergy was defined as the difference between the regional efficiency of the anterior and posterior walls. After 9-10 s, posterior wall efficiency decreased 37 +/- 6% with anoxia and 72 +/- 3% with ischemia (P < 0.025), and interwall asynergy was 0 +/- 6% with anoxia and 32 +/- 5% with ischemia (P < 0.05). The contribution of absent hydraulic skeleton to interwall asynergy (calculated as the difference between %asynergy in anoxia and %asynergy in ischemia) was 30 +/- 8% (P < 0.05). In conclusion, the earliest wall motion change observed after acute coronary occlusion, namely ischemic wall thinning concomitant with normoperfused wall thickening during isovolumic relaxation, is the result of the absence of intracoronary fluid. The lack of hydraulic skeleton within the myocardium contributes approximately 30% to interwall asynergy.

Ischemic cardiomyopathy: value of different MRI techniques for prediction of functional recovery after revascularization

OBJECTIVE

The purpose of this study was to compare the value of different MRI techniques for the assessment of myocardial viability. SUBJECTS AND METHODS. Eighteen infarct patients (mean age +/- SD, 62 +/- 8 years) with myocardial ischemia were examined using MRI before and after revascularization. The MRI study before treatment consisted of an evaluation of first-pass perfusion, contractile function at rest and during dobutamine stress, and delayed hyperenhancement. Findings were correlated with segmental and global cardiac function after revascularization.

RESULTS

In initially dysfunctional segments, the likelihood of functional recovery after revascularization was 91% for segments without delayed hyperenhancement, 43% for segments with delayed hyperenhancement with transmural extent of 75% or less, and 8% for segments with delayed hyperenhancement with transmural extent of more than 75% (p < 0.05). Improved function at dobutamine stress MRI indicated functional recovery in 87%, whereas functional recovery was observed in only 30% of segments not responding at dobutamine stress MRI (p < 0.05). No significant correlation was found between the results of first-pass perfusion MRI and functional recovery. The ejection fraction after revascularization was best predicted by the MRI-derived infarct volume (p < 0.001, R(2) = 0.63).

CONCLUSION

A simple protocol consisting of baseline contractility and delayed enhancement MRI studies is adequate to differentiate dysfunctional but viable from nonviable myocardium. Dobutamine stress and perfusion MRI studies offer little or no additional information.

Quantitative gated myocardial perfusion single photon emission computed tomography improves the prediction of regional functional recovery in akinetic areas after coronary bypass surgery: useful tool for evaluation of myocardial viability

OBJECTIVE

Assessment of myocardial viability in akinetic areas is essential in surgery for ischemic heart disease, including coronary artery bypass grafting and left ventriculoplasty. The aim of this study is to evaluate the utility of quantitative indices of perfusion uptake, wall motion, and wall thickening of each region calculated by quantitative electrocardiogram-gated single photon emission computed tomography (SPECT) for prediction of functional recovery after coronary artery bypass grafting.

METHODS

Forty patients scheduled for coronary artery bypass grafting were prospectively included. Electrocardiogram-gated SPECT was performed before and 1 week and 3 months after operation, and coronary angiography was performed before and after operation. The myocardium was divided into 9 segments and myocardial viability, assessed by improvement of the wall motion score using a cine mode display, and evaluated by radionuclide criteria (perfusion uptake, wall motion, wall thickening). Twenty-four segments with moderate hypokinesis and 14 segments with akinesis with patent grafts were assessed.

RESULTS

All segments with moderate hypokinesis except 1 (96%) had improved wall motion scores postoperatively, whereas of 14 segments with akinesis only 7 segments (50%) had improved wall motion scores. The preoperative perfusion uptake in the improved segments was significantly higher than in the nonimproved segments (62.7% +/- 15.6% vs 46.4% +/- 24.5%, P =.01). There was a significant difference in wall motion between the improved and nonimproved segments (3.8 +/- 2.2 mm vs 1.4 +/- 1.4 mm, P =.001), and the preoperative wall thickening of the improved segments was significantly higher than in the nonimproved segments (27.2% +/- 14.1% vs 8.2% +/- 10.3%, P <.0001). The optimal cutoff level of perfusion uptake was 50%, with the highest accuracy of 72%, and the optimal cutoff levels of wall thickening and wall motion were 10% and 1.5 mm, with the highest accuracies of 76% and 85%, respectively.

CONCLUSION

The regional functional index calculated by electrocardiogram-gated SPECT indicated that wall thickening was well correlated with functional recovery compared with wall motion or perfusion uptake. This suggests that the wall thickening calculated by electrocardiogram-gated SPECT may be more useful to predict functional recovery than regional myocardial perfusion. Or, it could suggest that in addition to perfusion uptake, wall thickening could enhance the objective assessment of myocardial viability.

Detection of scarred and viable myocardium using a new magnetic resonance imaging technique: blood oxygen level dependent (BOLD) MRI

BACKGROUND

The identification of viable myocardium in patients with impaired left ventricular contraction secondary to coronary heart disease is important clinically as such myocardium is likely to benefit from revascularisation. Blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) relies on changes in deoxyhaemoglobin concentration under stress for signal generation and could be used for the differentiation between scarred and viable myocardium.

AIM

To assess the signal change on BOLD MRI in viable and scarred myocardium as identified by positron emission tomography (PET).

METHOD

19 patients with impaired left ventricular contraction and at least one akinetic area were enrolled. They underwent rest and dipyridamole stress MRI, using a double breath hold T2* weighted, ECG gated sequence to produce BOLD contrast images, and cine-MRI for wall thickening assessment. Dynamic perfusion and metabolic PET images followed the MRI. Signal change on BOLD MRI and the wall thickening were compared between rest and stress images in hibernating and scarred segments identified by PET on two short axis slices of mid ventricle, with eight segments each.

RESULTS

Using PET, 68 segments were identified as hibernating and 42 as scarred. The hibernating segments were found on BOLD MRI to have an average signal change between rest and stress of -9.53%, compared with -2.15% in the scarred segments (p = 0.008). The average wall thickening was 8.7 mm in the hibernating segments compared with 5.9 mm in the scarred segments (p < 0.0001).

CONCLUSIONS

BOLD MRI with wall thickening may differentiate scarred and viable myocardium and help identify suitable patients for revascularisation. Further larger studies are needed to establish a threshold for detection, sensitivity, and specificity.

Prediction of functional recovery after coronary bypass surgery using quantitative gated myocardial perfusion SPECT

Previous studies have demonstrated that myocardial perfusion imaging using 99mTc-tetrofosmin at rest allows viability assessment similar to that obtained with 201Tl imaging and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET). The simultaneous assessment of perfusion and regional function is now available by quantitative gated myocardial perfusion single-photon emission computed tomography (SPECT). This study was designed to evaluate the utility of quantitative values of wall motion and wall thickening, calculated by quantitative gated myocardial perfusion SPECT, for the prediction of functional recovery after coronary bypass grafting (CABG). Fifty-six patients with coronary artery disease scheduled for CABG were included prospectively. All patients underwent 99mTc-tetrofosmin gated SPECT imaging at rest preoperatively and 3 months after CABG. The myocardium was divided into nine segments and the average quantitative values of regional perfusion (percentage uptake) (%), wall motion (mm) and wall thickening (%) were determined automatically using quantitative gated SPECT (QGS) software. The wall motion score was defined visually using a four-point scale (0, normal; 3, akinesis), and segments with severe asynergy (score of 2 or 3) with patent grafts were assessed. Of 77 segments with severe asynergy, 56 segments showed improved wall motion and 21 segments did not improve after CABG. The area under the receiver operating characteristic curve of wall thickening for the prediction of functional recovery was significantly higher (0.92) than that of the percentage uptake (0.77, P<0.017) or wall motion (0.60, P<0.0001). When each analysis used the optimal threshold, the wall thickening analysis (>or=10%) had a sensitivity of 95% and a specificity of 81%. These values tended to be higher than those of the percentage uptake (sensitivity, 86%; specificity, 67%). The wall motion analysis (>or=1.5 mm) had a significantly lower sensitivity of 75% and specificity of 43% than the wall thickening analysis (P=0.0038 and P=0.011, respectively). The results indicate that wall thickening, calculated by QGS software, may be more useful than regional perfusion or wall motion analysis for the prediction of functional recovery after CABG. The areas of asynergy with relatively preserved wall thickening may have the potential for improved function despite severely decreased perfusion.

ECG-gated 18F-FDG positron emission tomography

AIM

18F-fluorodeoxyglucose (18F-FDG)-positron emission tomography (PET) provides information about myocardial glucose metabolism to diagnose myocardial viability. Additional information about the functional status is necessary. Comparison of tomographic metabolic PET with data from other imaging techniques is always hampered by some transfer uncertainty and scatter. We wanted to evaluate a new Fourier-based ECG-gated PET technique using a high resolution scanner providing both metabolic and functional data with respect to feasibility in patients with diseased left ventricles.

METHODS

Forty-five patients with coronary artery disease and at least one left ventricular segment with severe hypokinesis or akinesis at biplane cineventriculography were included. A new Fourier-based ECG-gated metabolic 18F-FDG-PET was performed in these patients. Function at rest and 18F-FDG uptake were examined in the PET study using a 36-segment model.

RESULTS

Segmental comparison with ventriculography revealed a high reliability in identifying dysfunctional segments (> 96%). 18F-FDG uptake of normokinetic/hypokinetic/akinetic segments was 75.4 +/- 7.5, 65.3 +/- 10.5, and 35.9 +/- 15.2% (p < 0.001). In segments > or = 70% 18F-FDG uptake no akinesia was observed. No residual function was found below 40% 18F-FDG uptake. An additional dobutamine test was performed and revealed inotropic reserve (viability) in 42 akinetic segments and 45 hypokinetic segments.

CONCLUSION

ECG-gated metabolic PET with pixel-based Fourier smoothing provides reliable data on regional function. Assessment of metabolism and function makes complete judgement of segmental status feasible within a single study without any transfer artefacts or test-to-test variability. The results indicate the presence of considerable amounts of viable myocardium in regions with an uptake of 40-50% 18F-FDG.

Assessment of myocardial viability by positron emission tomography

Accurate assessment of myocardial viability is critical for identifying patients likely to benefit from coronary revascularization. Positron emission tomography (PET) has several advantages over single photon emission computed tomography (SPECT), including higher sensitivity and specificity, as well as the ability to measure myocardial blood flow and myocardial metabolism in absolute terms, which is important in understanding the pathophysiology of ischemic cardiomyopathy. The most commonly used PET tracer is [18F]2-fluoro-2deoxy-D-glucose (FDG). The dependence of ischemic myocardium on glucose metabolism makes FDG an ideal tracer in this setting. Studies have shown positive and negative predictive values for the detection of viable myocardium in the range of 48-94%, and 73-96%, respectively. FDG is superior to SPECT using thallium or technetium myocardial perfusion agents, as well as echocardiography with dobutamine infusion. FDG PET also provides important prognostic information. Patients with evidence of myocardial viability by FDG PET have fewer cardiac events and survive longer if revascularized compared to patients who are treated medically. This article will review myocardial metabolism, PET procedures and interpretive criteria, as well as problems and limitations. Data from the literature regarding diagnostic and prognostic information will also be summarized.

Myocardial viability assessment with gated SPECT Tc-99m tetrofosmin % wall thickening: comparison with F-18 FDG-PET

OBJECT

This study was designed to assess the value of gated SPECT Tc-99m-tetrofosmin (TF) wall thickening (WT) in addition to TF exercise (Ex)/rest myocardial SPECT, in comparison with F-18 fluorodeoxyglucose (FDG)-PET.

METHODS

The study population consisted of 33 patients with old myocardial infarction (27 men and 6 women; mean age, 62 +/- 8 years old). All patients underwent Ex/rest TF SPECT and glucose loading FDG-PET. Polar map images of Ex/rest TF were generated and divided into 24 segments for further analysis. We classified LV segments according to the exercise-rest perfusion scintigraphy. LV segments with less than 70% of the maximum TF activity on the exercise image were defined as stress-induced defects. Among these, the segments whose TF activity increased by 10% from exercise to rest images or exceeded 70% of the maximum uptake were defined as reversible (viable) defects. The remaining defects on the rest image were irreversible (non-viable) defect segments, and were considered for viability study on the basis of %WT. %WT was calculated according to the standard method: [(counts ES - counts ED)/counts ED] x 100. A viable segment on gated SPECT was defined as a segment whose %WT exceeded the lower limit of the normal value (mean - SD). PET viability was defined as FDG uptake exceeding 50% of the maximum count.

RESULTS

Among the 792 segments evaluated in the 33 patients studied, there were 689 PET viable segments. Of the 689 segments analyzed, 198 (29%) were identified as having defects on Ex images. Among these defects, 55 (8%) were reversible or partially reversible, as evidenced by rest images, and 143 (21%) were irreversible. Of the irreversible segments on Ex/rest images, 106 (15%) demonstrated no apparent WT by gated TF SPECT, whereas 37 (6%) segments with irreversible defects did have apparent WT. Overall, the sensitivity of Ex/rest TF perfusion imaging was 79%. Sensitivity was improved from 79% to 85% by combining %WT and perfusion data, but specificity was reduced from 70% to 56%.

CONCLUSION

%WT evaluated from gated TF imaging enhanced myocardial viability assessment in comparison with FDG-PET.

Assessment of regional myocardial wall motion and thickening by gated 99Tcm-tetrofosmin SPECT: a comparison with magnetic resonance imaging

Gated single photon emission computed tomography (SPECT) imaging allows the simultaneous assessment of both perfusion and function by using one single study. The assessment of regional wall motion and thickening pattern with gated SPECT allows viability studies to be performed. Magnetic resonance imaging (MRI) is well validated for the assessment of myocardial wall motion and thickening in patients with normal and impaired ventricular function. The aim of the study was to analyse the concordance between wall motion and thickening scores derived by gated SPECT and MRI imaging. Furthermore, the agreement for myocardial wall motion and thickening according to myocardial perfusion was analysed with both techniques. We studied a group of 21 patients, including 13 with a previous myocardial infarction (all more than 4 months before the study), using both gated SPECT 99Tcm-tetrofosmin myocardial perfusion imaging and MRI. A 13-segment model was used for both gated SPECT and MRI and each segment was visually scored using a scale of 1-3 for wall motion and thickening. There was a high agreement between gated SPECT and MRI for both wall motion (229/273, 84%; k = 0.72, P<0.001) and wall thickening (236/273, 86%; k = 0.77, P<0.001). The agreement for wall motion and thickening was 80% (k = 0.66) and 83% (k = 0.70), respectively, for patients with myocardial infarction; and 90% (k = 0.81) and 92% (k = 0.86), respectively (P = NS), for patients without myocardial infarction. Agreement in segmental wall motion and thickening scores between gated SPECT and MRI was 90% (k = 0.80) and 91% (k = 0.84), respectively, for segments with normal or mild to moderate hypoperfusion; and 71% (k = 0.45) and 77% (k = 0.57), respectively, for segments with severe hypoperfusion or no perfusion. Of the 70 (41%) segments that had severely diminished or no perfusion in post-myocardial infarction patients, 22 (31%) showed preserved wall motion and 17 (24%) showed preserved wall thickening both by gated SPECT and MRI, suggesting residual myocardial viability in malperfused segments. Our results suggest that gated SPECT imaging is a reliable tool for the assessment of regional wall motion and thickening in patients with known or suspected coronary artery disease. In patients with a previous myocardial infarction gated SPECT imaging has the potential to detect preserved wall motion and thickening in regions with fixed perfusion defects indicating the potential presence of residual myocardial viability.

The identification of myocardial hibernation in patients with ischemic heart failure by echocardiography and radionuclide studies

Dobutamine echocardiography and myocardial radionuclide tomography are widely used to assess viability in patients with ischemic cardiomyopathy and left ventricular dysfunction. The main goal of viability evaluation has been the identification of reversible regional dysfunction in the attempt to identify patients in whom revascularization may determine an improvement of global left ventricular ejection fraction. In this application, echocardiographic and radionuclide techniques are used to characterize different pathophysiologic aspects of viable myocardium, ie, integrity of cell membrane and contractile reserve. This explains why the information of the 2 techniques are often divergent and why radionuclide techniques have the highest sensitivity but reduced specificity compared with echocardiography for predicting recovery of regional dysfunction. The identification of residual viable myocardium by either technique is strongly associated with adverse prognosis if the patients are not revascularized, and this substantially contributes to the decision-making process in individual patients. Although it has been assumed that prognostic advantages of revascularization are linked to an increase of ejection fraction, pathophysiologic and clinical observations challenge us with the possibility that benefits of revascularization may also ensue independently on the recovery of ejection fraction through alternative pathophysiologic mechanisms. Therefore, clinical application of viability tests should be evaluated against relevant endpoints, mainly represented by prolongation of life and improvement of life quality, and not by surrogate endpoints as represented by recovery of global ejection fraction. Future studies are needed to assess whether a more clinically oriented approach will provide a better selection of patient candidates for revascularization.

Reverse redistribution of thallium-201 myocardial single photon emission tomography and contractile reserve

The present study investigated the contractile reserve of myocardium exhibiting reverse redistribution (RRD) of thallium-201 (201Tl) after acute myocardial infarction. Forty patients experiencing their first acute myocardial infarction underwent resting 201Tl single-photon emission computed tomography (SPECT) and low-dose (5-10 microgxkg(-1)xmin(-1)) dobutamine stress echocardiography (DSE) within 4 weeks after the onset of infarction. The left ventricle was divided into 13 segments for analysis. The severity of defects in 201Tl SPECT and the extent of wall motion abnormality in DSE were visually assessed and scored. The sum of each defect score and wall motion score of infarct-related segments were defined as total defect score (TDS) and total wall motion score (TWM), respectively. Quantitative analysis of 201Tl uptake was also performed. Resting 201Tl SPECT revealed RRD in 16 patients (group RRD), fixed defect (FIX) in 23 patients (group FIX), and redistribution in one. There was a significant difference in improvement of TWM between rest and stress in TWM in both the RRD and FIX groups (p<0.0001, each case). The improvement of TWM with dobutamine was significantly greater in RRD than in FIX (1.6+/-1.0 vs 0.6+/-0.7, p=0.001). There was a positive correlation between the magnitude of RRD and improvement of TWM with dobutamine (r=0.48, p=0.002). Myocardium exhibiting RRD on 201Tl SPECT in patients with acute myocardial infarction has greater contractile reserve than that exhibiting a fixed defect.

End-diastolic wall thickness as a predictor of recovery of function in myocardial hibernation: relation to rest-redistribution T1-201 tomography and dobutamine stress echocardiography

OBJECTIVES

The study assessed whether end-diastolic wall thickness (EDWT), measured with echocardiography, is an important marker of myocardial viability in patients with suspected myocardial hibernation, and it compared this index to currently established diagnostic modalities of dobutamine stress echocardiography (DSE) and rest-redistribution thallium-201 (T1-201) scintigraphy.

BACKGROUND

Because myocardial necrosis is associated with myocardial thinning, preserved EDWT may provide a simple index of myocardial viability that is readily available from the resting echocardiogram.

METHODS

Accordingly, 45 patients with stable coronary artery disease and ventricular dysfunction underwent rest 2D echocardiograms, DSE and rest-redistribution T1-201 tomography before revascularization and a repeat resting echocardiogram > or =2 months later.

RESULTS

Global wall motion score index decreased from 2.38 +/- 0.73 to 1.94 +/- 0.82 after revascularization (p < 0.001). Thirty-eight percent of severely dysfunctional segments recovered resting function. Compared to segments without recovery of resting function, those with recovery had greater EDWT (0.94 +/- 0.18 cm vs. 0.67 +/- 0.22 cm, p < or = 0.0001) and a higher T1-201 uptake (78 +/- 13% vs. 59 +/- 21%; p < 0.0001). An EDWT >0.6 cm had a sensitivity of 94% and specificity of 48% for recovery of function. Similarly, a T1-201 maximal uptake of > or =60% had a sensitivity of 91% and specificity of 50%. Receiver operating characteristic curves for prediction of recovery of regional and global function were similar for EDWT and maximum T1-201 uptake. Combination of EDWT and any contractile reserve during DSE for recovery of regional function improved the specificity to 77% without a significant loss in sensitivity (88%).

CONCLUSIONS

End-diastolic wall thickness is an important marker of myocardial viability in patients with suspected hibernation, and it can predict recovery of function similar to T1-201 scintigraphy. Importantly, a simple measurement of EDWT < or =0.6 cm virtually excludes the potential for recovery of function and is a valuable adjunct to DSE in the assessment of myocardial viability.

MR imaging of the heart in patients after myocardial infarction: effect of increasing intersection gap on measurements of left ventricular volume, ejection fraction, and wall thickness

PURPOSE

To determine the extent to which the number of planes imaged at magnetic resonance (MR) imaging could be reduced without modifying the calculated volume and thickness of the left ventricle.

MATERIALS AND METHODS

Sixty-one patients were examined after a myocardial infarction. The whole left ventricle was imaged by using 5-mm contiguous breath-hold cine MR short-axis sections with no gap (SAng) (two-dimensional fast low-angle shot sequence, 9/4.8 [repetition time msec/echo time msec]). The effect of omitting one section in two (short-axis sections with 5-mm gap [SA5 mm]) or two sections in three (short-axis sections with 10-mm gap [SA10 mm]) was studied.

RESULTS

In the comparison of SA5 mm or SA10 mm with respect to the reference SAng, the standard error of the estimate (SEE) for the diastolic volume did not exceed the 6.1% interobserver SEE, and the SEE for the ejection fraction remained lower than the 3% interobserver SEE. The measured wall thickness was not affected. In addition, six simple geometric models were compared with SAng and yielded an SEE of 9.5%-28.1% for the diastolic volume and 3.8%-13.3% for the ejection fraction.

CONCLUSION

In the study of left ventricles with heterogeneous contractility, short-axis imaging is more accurate than geometric modeling and permits wall thickness measurements when an intersection gap of 5 or 10 mm is used.

Assessment of myocardial viability by MRI

Assessment of myocardial viability has become an important issue in patients presenting with either acute myocardial infarction or presenting with chronic ischemic left ventricular dysfunction. In patients with viable myocardium recovery of left ventricular function can be anticipatedm, spontaneously in patients with acute myocardial infarction or following revascularization in patients with ischemic cardiomyopathy. In contrast, patients without viable tissue are not likely to improve in left ventricular function. Currently, nuclear imaging techniques and dobutamine stress echocardiography are used for assessment of viability; recent studies with magnetic resonance imaging (MRI) have however demonstrated the potential usefulness of this technique for the assessment of viability. Various parameters, derived from resting MRI, can be used as markers of myocardial viability, including the end-diastolic wall thickness, systolic wall thickening and signal intensity without contrast-enhancement. Other studies have combined the information from resting MRI with the assessment of contractile reserve during dobutamine stimulation. Finally, recent studies have evaluated the use of contrast-enhanced MRI to detect viable myocardium. All of these parameters are potentially useful and MRI provide an alternative approach for the assessment of viable myocardium.

Laminar fiber architecture and three-dimensional systolic mechanics in canine ventricular myocardium

Previous studies suggest that the laminar architecture of left ventricular myocardium may be critical for normal ventricular mechanics. However, systolic three-dimensional deformation of the laminae has never been measured. Therefore, end-systolic finite strains relative to end diastole, from biplane radiography of transmural markers near the apex and base of the anesthetized open-chest canine anterior left ventricular free wall (n = 6), were referred to three-dimensional laminar microstructural axes reconstructed from histology. Whereas fiber shortening was uniform [-0.07 +/- 0.04 (SD)], radial wall thickening increased from base (0. 10 +/- 0.09) to apex (0.14 +/- 0.13). Extension of the laminae transverse to the muscle fibers also increased from base (0.08 +/- 0. 07) to apex (0.11 +/- 0.08), and interlaminar shear changed sign [0. 05 +/- 0.07 (base) and -0.07 +/- 0.09 (apex)], reflecting variations in laminar architecture. Nevertheless, the apex and base were similar in that at each site laminar extension and shear contributed approximately 60 and 40%, respectively, of mean transmural thickening. Kinematic considerations suggest that these dual wall-thickening mechanisms may have distinct ultrastructural origins.

Thallium scintigraphy compared with 18F-fluorodeoxyglucose positron emission tomography for assessing myocardial viability in patients with moderate versus severe left ventricular dysfunction

Thallium-201 reinjection imaging and positron emission tomography provide concordant information regarding myocardial viability in many patients with coronary artery disease and left ventricular (LV) dysfunction. It is unclear whether this concordance applies to patients with severe, as well as those with moderate, LV dysfunction. We studied 44 patients with chronic coronary artery disease and LV dysfunction, subgrouped on the basis of severity of dysfunction: 23 patients had moderate and 21 had severe dysfunction (ejection fractions 34 +/- 6% and 19 +/- 6%). Patients underwent exercise thallium single-photon emission computed tomography (SPECT) with 3- to 4-hour redistribution and reinjection imaging, as well as positron emission tomography (PET) imaging with 18fluorodeoxyglucose and 15O-water. Data were analyzed quantitatively in aligned transaxial PET and SPECT tomograms. A myocardial region was considered nonviable by PET if 18fluorodeoxyglucose activity was <50% of that in a normal region, associated with proportional reduction in blood flow. Similarly, regions were considered nonviable by thallium if activity was <50% of activity in normal regions on redistribution and reinjection studies. Thallium SPECT and PET data were concordant regarding viability in 98% and 93% of myocardial regions, respectively, in patients with moderate and with severe LV dysfunction. Lower concordance was observed only when regions with severe irreversible thallium perfusion defects on redistribution images were considered in both groups: 86% and 78%, respectively (p <0.01). Thus, thallium SPECT with reinjection yields information regarding regional myocardial viability that is similar to that provided by PET in patients with severe as well as moderate LV dysfunction. However, there is discordance in >20% of regions manifesting severe irreversible thallium defects in patients with severely reduced LV function.

Dobutamine magnetic resonance imaging predicts contractile recovery of chronically dysfunctional myocardium after successful revascularization

OBJECTIVES

This study sought to evaluate whether myocardial viability, as assessed by magnetic resonance imaging (MRI), reliably predicts postrevascularization left ventricular (LV) recovery.

BACKGROUND

Compared with positron emission tomographic findings, MRI has proved to be a reliable technique for the identification of residual myocardial viability. However, the predictive accuracy of MRI-assessed preserved end-diastolic wall thickness (DWT) and dobutamine-induced systolic wall thickening (SWT) for LV functional recovery has not yet been evaluated.

METHODS

Rest and low dose dobutamine MRI was performed in 43 patients with a chronic infarct (> or =4 months since ischemic event) and LV dysfunction who had undergone revascularization of the infarct-related vessel. On the basis of segmental evaluation of corresponding short-axis tomograms, infarct regions were graded viable by MRI if 1) DWT was > or =5.5 mm, and 2) dobutamine-induced SWT was > or =2 mm in > or =50% of dysfunctional segments related to the infarct region. Functional recovery was defined as SWT > or =2 mm in > or =50% of infarct-related segments at rest 4 to 6 months after successful revascularization.

RESULTS

Recovery of regional SWT could be observed in 27 (63%) of 43 patients. Comparison MRI grading before and after revascularization indicated that dobutamine-induced SWT was a better predictor of LV functional recovery (sensitivity 89%, specificity 94%) than was preserved DWT (sensitivity 92%, specificity 56%). Segments that remained akinetic after revascularization had significantly lower DWT (6.0+/-3.1 mm [n = 219] vs. 9.8+/-2.6 mm [n = 188], p < 0.001) than those with improved SWT. Left ventricular ejection fraction increased significantly in patients with dobutamine-induced SWT than in those with no contractile reserve (14+/-9% vs. 3+/-9%, p < 0.0002), and the magnitude of this increase was correlated with the number of dobutamine-responsive segments per infarct region (r = 0.68, p < 0.0001).

CONCLUSIONS

Quantitative assessment of dobutamine-induced SWT in chronic infarcts by MRI is a highly accurate predictor of LV functional recovery, and the presence of significantly reduced DWT reliably indicates irreversible myocardial damage. Therefore, dobutamine stress testing for the assessment of myocardial viability can be restricted to patients with preserved DWT.

Effects of myocardial revascularization on regional thallium-201 uptake and systolic function in regions with reverse redistribution on tomographic thallium-201 imaging at rest in patients with chronic coronary artery disease

OBJECTIVES

There is growing evidence that myocardial segments with reverse redistribution are viable in patients with chronic coronary artery disease. The aim of this study was to assess the effects of myocardial revascularization on systolic function and thallium-201 uptake in such segments.

METHODS

Rest-redistribution thallium-201 tomography before and after myocardial revascularization was performed in 47 patients with chronic coronary artery disease. Regional function was evaluated by two-dimensional echocardiography before and after revascularization according to a 3-point scale (1 = normal, 2 = hypokinetic, 3 = a/dyskinetic). Improvement of dysfunctional segments was defined when systolic function score decreased > or =1 after revascularization. Reverse redistribution was defined as >8% decrease in relative thallium-201 uptake between rest and redistribution images.

RESULTS

Reverse redistribution was found in 27 (57%) of 47 patients, corresponding to 60 (11%) of 564 myocardial segments. Of such segments, 24 (40%) had normal systolic function, 19 (32%) were hypokinetic, and 17 (28%) were a/dyskinetic. Thirty-six segments underwent myocardial revascularization, and reverse redistribution was no longer present in 86% of them subsequent to the procedure. Of 26 dyssynergic segments with reverse redistribution subjected to revascularization, 18 (69%) improved at follow-up.

CONCLUSIONS

The findings of the present study indicate that reverse redistribution is a reversible phenomenon and is often associated with improvement of systolic function following revascularization in patients with chronic coronary artery disease.

Assessment of myocardial viability in patients with previous myocardial infarction by using single-photon emission computed tomography with a new metabolic tracer: [123I]-16-iodo-3-methylhexadecanoic acid (MIHA). Comparison with the rest-reinjection thallium-201 technique

OBJECTIVES

We compared the ability of rest single-photon emission computed tomography (SPECT) with [123I]-16-iodo-3-methylhexadecanoic acid (MIHA) and the thallium-201 (Tl-201) rest-reinjection technique to detect myocardial viability after infarction.

BACKGROUND

After myocardial infarction, MIHA frequently shows increased uptake in the areas with exercise Tl-201 defects (mismatch), even in patients with an irreversible Tl-201 reinjection defect. Whether such increased uptake is indicative of ischemic but viable myocardium is not known.

METHODS

We studied 38 patients who 1) underwent exercise SPECT Tl-201 with rest-reinjection and rest SPECT with MIHA before undergoing percutaneous transluminal coronary angioplasty (PTCA) of an infarct-related coronary artery, and 2) were found to have successful revascularization at follow-up angiography. The relation between SPECT results before PTCA and subsequent improvement in left ventricular wall motion was assessed.

RESULTS

A mismatch was evident before PTCA in 51 of 76 infarct-related segments and correlated with subsequent improvement in wall motion (overall accuracy 71%), even for the 27 segments whose exercise defects remained irreversible after Tl-201 reinjection (overall accuracy 81%). The finding of a mismatch clearly enhanced the results provided by the finding of > or = 50% Tl-201 uptake as determined at redistribution (p < 0.05), but not as determined at reinjection, although there was a trend toward a better specificity for the findings of a mismatch.

CONCLUSIONS

MIHA is an efficient marker of viability inside exercise-underperfused areas after infarction, even in patients with irreversible Tl-201 reinjection defects. Assessment by conventional SPECT of a mismatch between results obtained with a metabolic tracer (MIHA) and a flow tracer analyzed at exercise (Tl-201) as a marker of myocardial viability is a promising area of research.

Comparison of thallium scintigraphy and positron emission tomography

Assessment of tissue viability has become an important issue in recent years. Scintigraphic measurements have provided important diagnostic, therapeutic, and prognostic information in patients with myocardial dysfunction, who may improve in left ventricular function after revascularization. For detection of regional myocardial ischemia and viability, thallium 201 (201Tl) has been the most widely used tracer in single-photon scintigraphy. However, 201Tl scintigraphy may underestimate regional viability, especially after myocardial infarction. Positron emission tomography (PET) provides an advanced imaging technology that permits the accurate definition of regional tracer distribution. In combination with nitrogen (13N) ammonia, PET allows for the sensitive and specific detection of coronary artery disease. Several studies indicate the superiority of this approach in comparison with standard 201Tl tomographic (SPECT) imaging. In addition, regional blood flow can be accurately measured with 13N ammonia PET, and this approach can be employed in conjunction with pharmacologic stress imaging to quantify regional flow reserve. In combination with metabolic markers, such as fluorine 18 (18F) deoxyglucose, an indicator of glucose uptake, PET is capable of assessing myocardial viability. Furthermore, the PET approach may differentiate between various forms of cardiomyopathy. More studies are needed to define the cost-benefit ratio of both the 201Tl reinjection and the PET technique for the management of patients with coronary artery disease or cardiomyopathy.

The magnitude of inotropic reserve is unrelated to basal systolic function or wall thickness in patients with chronic ischemic left ventricular dysfunction

Forty-four patients with coronary artery disease and left ventricular dysfunction underwent transesophageal echocardiography with dobutamine infusion to investigate the relation between basal contractile function and inotropic reserve. No significant relation was observed between basal percent systolic thickening or diastolic thickness and the maximum increase in contractile function in response to dobutamine, thus emphasizing the heterogenity of the mechanisms by which coronary stenoses may affect contraction at rest and inotropic reserve in these patients.

Correlation of thallium uptake with left ventricular wall thickness by cine magnetic resonance imaging in patients with acute and healed myocardial infarcts

Myocardial infarction (MI) is characterized by cellular necrosis which undergoes fibrotic transformation over time. Cine magnetic resonance imaging (MRI) offers high-resolution 3-dimensional images of the left ventricular myocardium, allowing sampling of the myocardial wall thickness over the entire left ventricle. Tomographic (single-photon emission computed tomography [SPECT]) thallium images also provide 3-dimensional information on the location and level of thallium uptake, which has been shown to correlate with myocardial viability. The purposes of this study were: (1) to examine the relation between both end-diastolic and end-systolic wall thickness and normalized thallium-201 uptake over the left ventricle in a group of patients with MI, (2) to examine the relation between regional wall thickening and normalized thallium uptake, and (3) to examine the relation between thallium uptake and wall thickness both early and late after infarction. Twenty-four patients with MI underwent stress, redistribution, and reinjection thallium SPECT imaging and cine MRI within several days. Seventeen patients underwent imaging late after infarction and 7 underwent imaging early after infarction. Normalized thallium activity was correlated with MRI wall thicknesses at both end-diastole and end-systole for 18 segments for each ventricle. In addition, end-diastolic and end-systolic wall thicknesses were grouped by their corresponding thallium activity levels into percentiles. End-systolic wall thickness correlated significantly with normalized thallium uptake in 14 of 18 segments, end-diastolic wall thickness in only 4 of 18 segments, and wall thickening in only 3 of 18 segments. Mean values for end-diastolic and end-systolic wall thicknesses corresponding to severely reduced (<50%) normalized thallium activity were 9.9 +/- 1.1 and 8.5 +/- 0.6, respectively. Using receiver-operating curve analysis, end-systolic wall performed as a better diagnostic parameter than end-diastolic wall for identifying severely reduced thallium activity levels. For all levels of thallium activity, end-diastolic wall thicknesses were all thinner late versus early after MI, whereas end-systolic wall thickness was thinner only in the segments corresponding to severely reduced thallium activity. Based on these results, end-systolic wall thickness is the best noninvasive anatomic parameter of myocardial scar.

Assessment of viable myocardium and prediction of postoperative improvement in left ventricular function in patients with severe left ventricular dysfunction by quantitative planar stress-redistribution-reinjection 201-T1 imaging

A noninvasive approach to determine viable but asynergic myocardium will be clinically significant in identifying patients with coronary artery disease and severe left ventricular dysfunction who will benefit most from coronary bypass surgery. Accordingly, 12 patients (mean ejection fraction 0.32 +/- 0.03) underwent quantitative planar stress-redistribution-reinjection thallium scintigraphy and radionuclide ventriculography before and 8 weeks after revascularization for viability and segmental and global left ventricular function assessment, respectively. Reinjection scan showed new fill-in in 63% of segments without redistribution. Postoperative improvement in perfusion and function of asynergic segments were significantly better in viable compared to nonviable segments (P < 0.001, P < 0.01, respectively) with a strong correlation between improvement in 201-T1 uptake and function (P < 0.001). When adequacy of revascularization was considered, the predictive value of a positive preoperative viability test for functional improvement was 83%. Finally, mean ejection fraction and global wall motion score increased significantly after revascularization for the group as a whole (0.32 +/- 0.03 to 0.44 +/- 0.04, P < 0.001 and 24.08 +/- 2.90 to 33.16 +/- 3.32, P < 0.001, respectively). Thus, preoperative quantitative planar stress-redistribution-reinjection thallium imaging detects viable but asynergic segments which improve function postoperatively and may be valuable in selection of patients with severe left ventricular dysfunction for revascularization.

Myocardial stunning, hibernation, and ischemic preconditioning

From the present review, it may be concluded that myocardial ischemia results in far more complicated syndromes than previously realized. Although not all aspects of the issues discussed in this review are currently a clinical reality in the daily practice of cardiovascular anesthesiologists, the understanding and application of these concepts are growing rapidly. Indications for revascularization procedures will be adjusted in patients with evidence of hibernating myocardium. In the future, postoperative myocardial dysfunction may be diminished by the prevention of myocardial stunning, for instance by altering the composition of the cardioplegic solution and other interventions. Finally, additional advances may involve reduction of the extent of perioperative myocardial infarctions by application of ischemic preconditioning.

Inotropic stimulation by dobutamine increases left ventricular regional function at the expense of metabolism in hibernating myocardium

The mechanism by which dobutamine increases the contraction of chronically dysfunctional myocardium and its effects on metabolism are still unknown. The aim of this study was to assess regional myocardial metabolism at rest and during an intracoronary dobutamine infusion in patients with hibernating myocardium. Eleven asymptomatic patients with single proximal stenosis of the left anterior descending coronary artery and persistent left ventricular dysfunction at rest (undergoing percutaneous transluminal coronary angioplasty [PTCA]) were studied prospectively. Regional left ventricular function was assessed by two-dimensional (2D) echocardiography and regional perfusion by thallium-201 single-proton-emission computed tomography. Great cardiac vein and aortic blood samples were obtained for measurements of lactate and plasma free fatty acid (FFA) concentrations. Inotropic challenge, obtained by using intracoronary dobutamine infusion, increases regional left ventricular function. However, the arteriovenous AV lactate difference was 0.206 = 0.070 mmol/L at rest, and it decreased to 0.018 = 0.069 mmol/L (p < 0.05 vs baseline) and 0.066 = 0.068 mmol/L (p < 0.05 vs baseline) at 4 and 10 minutes of dobutamine infusion, respectively. Thus the hibernating myocardium does not produce lactate at rest. However, when regional contraction is stimulated, dobutamine-induced inotropic challenge may cause a perfusion-contraction mismatch with an activation of anaerobic glycolysis.

Regional myocardial motion and thickening assessed at rest by ECG-gated 99mTc-MIBI emission tomography and by magnetic resonance imaging

We have validated ECG-gated emission tomography using technetium-99m methoxyisobutylisonitrile for the assessment of regional ventricular function by comparing it with cine magnetic resonance imaging (MRI). Gated tomography was performed at rest in 24 patients referred for myocardial perfusion imaging [17 males and seven females with a mean age of 58 years, nine of whom had had a previous myocardial infarction (MI)]. Scores were assigned to each of nine myocardial segments for wall motion and for thickening. Cine MRI was analysed in an identical fashion. Four out of 216 (2%) segments were uninterpretable by gated tomography because of inadequate tracer uptake. In eight patients without coronary artery disease (CAD), wall motion and thickening were normal by both methods. Gated tomography showed abnormal wall motion or thickening in all patients with previous MI and in five of seven patients with CAD but no prior MI. Association between wall motion and thickening was good (rs=0. 86). Overall, there was good agreement between gated tomography and MRI for both wall motion (178/212 segments, kappa=0.66) and wall thickening (184/212 segments, kappa=0.69). In segments with severely reduced perfusion, however, there was poorer agreement (kappa=0.31). Interobserver and intraobserver agreement was high (kappa from 0.61 to 0.78). Thus, in patients investigated for CAD, there is good overall agreement between gated tomography and MRI but the agreement is lower in segments with severe perfusion defects.

Predictive value of low dose dobutamine transesophageal echocardiography and fluorine-18 fluorodeoxyglucose positron emission tomography for recovery of regional left ventricular function after successful revascularization

OBJECTIVES

This study was designed to assess the predictive value of myocardial viability diagnosed by dobutamine transesophageal echocardiography and fluorine (F)-18 fluorodeoxyglucose positron emission tomography for left ventricular functional recovery after revascularization in patients with chronic left ventricular dysfunction.

BACKGROUND

The identification of akinetic but viable myocardium is of particular importance for the selection of patients with a compromised left ventricle who will benefit from coronary revascularization.

METHODS

Multiplane rest and dobutamine transesophageal echocardiography (dobutamine, 5 and 10 microg/min per kg) studies and F-18 fluorodeoxyglucose positron emission tomographic studies at rest were performed in 2 patients with 1) previous myocardial infarction and regional akinesia, 2) a stenosed infarct-related coronary artery, and 3) a patent infarct-related vessel after revascularization. A basally akinetic segment was considered viable by transesophageal echocardiography if dobutamine-induced contractile reserve could be observed. Viability by positron emission tomography was defined as F-18 fluorodeoxyglucose uptake > or = 50% of the maximal uptake in a region with normal wall motion. Recovery of regional left ventricular function 4 to 6 months after revascularization was diagnosed by transesophageal echocardiography if > or = 50% of segments akinetic at baseline had improved wall thickening.

RESULTS

Dobutamine transesophageal echocardiography identified viable infarct regions in 25 (59%) of 42 patients, and F-18 fluorodeoxyglucose positron emission tomography in 30 (71%) of 42 patients, yielding diagnostic agreement in 86% of patients. Sensitivity and specificity for prediction of left ventricular functional recovery in individual patients was 92% and 88%, respectively, for dobutamine transesophageal echocardiography versus 96% and 69% for F-18 fluorodeoxyglucose positron emission tomography. Segments remaining akinetic after revascularization had a significantly lower (p < 0.001) F-18 fluorodeoxyglucose uptake (48 +/- 15%) than that (73 +/- 15%) of segments with recovery of regional left ventricular function.

CONCLUSIONS

Both dobutamine transesophageal echocardiography and F-18 fluorodeoxyglucose positron emission tomography were highly sensitive in predicting functional recovery of chronically kinetic or dyskinetic myocardium after successful revascularization. Thus, dobutamine transesophageal echocardiography is a clinically valuable alternative to F-18 fluorodeoxyglucose positron emission tomography for assessing residual viability and predicting functional recovery after revascularization.

Magnetic resonance imaging in ischemic heart disease

The clinical use of MR imaging in ischemic heart disease is still limited, although this is the major cardiac disease afflicting populations of many countries. However, with the recent development of faster MR techniques, MR imaging provides multiple capabilities for the evaluation of most aspects of ischemic heart disease. We described the potential application of MR imaging for identifying and quantifying morphologic and functional alterations caused by myocardial infarction and ischemia; the contribution of MR contrast media to improve tissue characterization and to identify ischemic myocardium; and the application of fast MR imaging techniques for assessing anatomy and blood flow in the native coronary arteries and bypass conduits. With continued development of these capabilities, MR imaging has the potential to be a comprehensive noninvasive imaging modality in ischemic heart disease.

Gated resting Tl-201 SPECT in the evaluation of myocardial viability

Gating of resting Tl-201 SPECT to evaluate myocardial viability is now clinically feasible. Two cases are presented to illustrate the additional information of wall motion and wall thickening obtained from gating. This additional information may improve the classification of viable myocardium and requires further study.