Regional perfusion, glucose metabolism, and wall motion in patients with chronic electrocardiographic Q wave infarctions: evidence for persistence of viable tissue in some infarct regions by positron emission tomography

Principles and techniques of imaging in identifying the substrate of ventricular arrhythmia

Life-threatening ventricular arrhythmias (VA) are a major cause of death in patients with cardiomyopathy. To date, impaired left ventricular ejection fraction remains the primary criterion for implantable cardioverter-defibrillator therapy to prevent sudden cardiac death. In recent years, however, advanced imaging techniques such as nuclear imaging, cardiac magnetic resonance imaging, and computed tomography have allowed for a more detailed evaluation of the underlying substrate of VA. These imaging modalities have emerged as a promising approach to assess the risk of sudden cardiac death. In addition, non-invasive identification of the critical sites of arrhythmias may guide ablation therapy. Typical anatomical substrates that can be evaluated by multiple advanced imaging techniques include perfusion abnormalities, scar and its border zone, and sympathetic denervation. Understanding the principles and techniques of different imaging modalities is essential to gain more insight in their role in identifying the arrhythmic substrate. The current review describes the principles of currently available imaging techniques to identify the substrate of VA.

Late percutaneous coronary intervention prevents left ventricular remodeling and improves clinical outcomes in patients with ST-elevation myocardial infarction

BACKGROUND

The optimal strategy for treating late presenters of ST-elevation myocardial infarction (STEMI) remains uncertain.

HYPOTHESIS

percutaneous coronary intervention (PCI) has a favorable effect on left ventricular (LV) remodeling and clinical outcomes in late presenters of STEMI.

METHODS

Patients with STEMI who were hospitalized between 2009 and 2011 at 7 PCI-capable hospitals in China were selected. Cardiac characteristics were reassessed by echocardiography between August 2013 and January 2014. The clinical endpoints were evaluated during a median follow-up period of 36 months.

RESULTS

1090 patients who either underwent late PCI (n = 786) or received standard medical therapy alone (n = 304) was analyzed. Left ventricular remodeling was more pronounced in the conservative-treatment group. Logistic regression revealed that late PCI was independently and negatively correlated with LV remodeling (odds ratio: 0.356, 95% confidence interval [CI]: 0.251-0.505, P < 0.001). Kaplan-Meier analysis showed the lower risks of major adverse cardiovascular events (MACE), all-cause death, and rehospitalization for heart failure in the late-PCI group. Multivariate Cox regression revealed that late PCI was significantly associated with lower risks for MACE, all-cause death, and rehospitalization for heart failure both in all patients (hazard ratio [HR]: 0.507, 95% CI: 0.412-0.625, P < 0.001; HR: 0.419, 95% CI: 0.314-0.559, P < 0.001; and HR: 0.583, 95% CI: 0.379-0.896, P = 0.014, respectively) and in the matched patients (HR: 0.466, 95% CI: 0.358-0.607, P < 0.001; HR: 0.398, 95% CI: 0.277-0.571, P < 0.001; and HR: 0.498, 95% CI: 0.283-0.878, P = 0.016, respectively) by propensity-score analysis.

CONCLUSIONS

Late-PCI strategy prevents LV remodeling and improves clinical outcomes in STEMI patients compared with conservative strategies.

Is it Feasible to Use the Commercially Available Autoquantitation Software for the Evaluation of Myocardial Viability on Small-Animal Cardiac F-18 FDG PET Scan?

PURPOSE

To evaluate the reliability of quantitation of myocardial viability on cardiac F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) scans with three different methods of visual scoring system, autoquantitation using commercially available autoquantitation software, and infarct-size measurement using histogram-based maximum pixel threshold identification on polar-map in rat hearts.

METHODS

A myocardial infarct (MI) model was made by left anterior descending artery (LAD) ligation in rat hearts. Eighteen MI rats underwent cardiac FDG-PET-computed tomography (CT) twice within a 4-week interval. Myocardium was partitioned into 20 segments for the comparison, and then we quantitated non-viable myocardium on cardiac FDG PET-CT with three different methods: method A-infarct-size measurement using histogram-based maximum pixel threshold identification on polar-map; method B-summed MI score (SMS) by a four-point visual scoring system; method C-metabolic non-viable values by commercially available autoquantitation software. Changes of non-viable myocardium on serial PET-CT scans with three different methods were calculated by the change of each parameter. Correlation and reproducibility were evaluated between the different methods.

RESULTS

Infarct-size measurement, visual SMS, and non-viable values by autoquantitation software presented proportional relationship to each other. All the parameters of methods A, B, and C showed relatively good correlation between each other. Among them, infarct-size measurement (method A) and autoquantitation software (method C) showed the best correlation (r = 0.87, p < 0.001). When we evaluated the changes of non-viable myocardium on the serial FDG-PET-CT- however, autoquantitation program showed less correlation with the other methods. Visual assessment (method B) and those of infarct size (method A) showed the best correlation (r = 0.54, p = 0.02) for the assessment of interval changes.

CONCLUSIONS

Commercially available quantitation software could be applied to measure the myocardial viability on small animal cardiac FDG-PET-CT scan. This kind of quantitation showed good correlation with infarct size measurement by histogram-based maximum pixel threshold identification. However, this method showed the weak correlation when applied in the measuring the changes of non-viable myocardium on the serial scans, which means that the caution will be needed to evaluate the changes on the serial monitoring.

Acipimox-enhanced ¹⁸F-fluorodeoxyglucose positron emission tomography for characterizing and predicting early remodeling in the rat infarct model

The rat myocardial infarction (MI) model is widely used to study left ventricular (LV) remodeling. In this study, acipimox-enhanced (18)F-Fluorodeoxyglucose (FDG) gated-positron emission tomography (PET) was assessed for characterizing and predicting early remodeling in the rat infarct model. Nineteen Wistar rats had surgical occlusion of the left anterior descending coronary artery and 7 were sham-operated. PET was scheduled 48 h and 2 weeks later for quantifying MI area and LV function. Segments with <50% of FDG uptake had histological evidence of MI (74 ± 9% decrease in parietal thickness, fibrosis development). At 48 h, MI area was large (>35% of LV) in 6 rats, moderate (15-35% of LV) in 8 rats, limited (<15% of LV) in 5 rats and absent in the 7 sham rats. LV remodeling, assessed through the 2 weeks increase in end-diastolic volume, increased between rats with limited, moderate and large MI (+72 ± 25, +109 ± 56, +190 ± 69 μl, respectively, P = 0.007). This 3-groups classification allowed predicting 44% of the 2 weeks increase in end-diastolic volume, and additional 34% were predicted by heart rate at 48 h. The acipimox-enhanced FDG gated-PET technique provides efficient characterization and prediction of early remodeling in the rat infarct model.

Acute and chronic myocardial infarction in a pig model: utility of multi-slice cardiac computed tomography in assessing myocardial viability and infarct parameters

OBJECTIVES

The aim of this study was to determine the feasibility of multi-slice computed tomography (MSCT) biphasic imaging in assessing myocardial viability and infarct parameters in both acutely and chronically infarcted pig models.

MATERIALS AND METHODS

Seven pigs underwent ligation of the distal left anterior descending artery. Imaging was performed on the day of infarction and 3 months post-infarct, with contrast infusion followed by MSCT scan acquisition at different time-points. Left ventricular ejection fractions (LVEFs) were obtained by left ventriculography (LVG) after 3 months. Infarcted locations found using MSCT were compared with those obtained using SPECT. Infarcted areas were also analysed histopathologically and compared with the findings from MSCT.

RESULTS

Chronic phase images had perfusion defects with lower CT values relative to normal myocardium (43±10HU vs. 156±13HU, p=0.001) on the early images but no residual defects on delayed images. However, we found hyperenhancing regions on delayed images (244±20HU vs. 121±25HU, p=0.001), and good correlation between MSCT- and LVG-derived LVEFs (60.56±7.56%). The areas identified by MSCT corresponded to the location of (201)Tl SPECT-/pathologic staining-derived regions in all models. Infarct size was in good agreement with MSCT and pathological analyses of chronic phase models.

CONCLUSIONS

Necrotic myocardium in different stages after infarction could be qualitatively and quantitatively assessed using MSCT biphasic imaging, as could the status of microcirculation formation. MSCT-measured LVEFs matched well with other modalities, and hence MSCT is a useful tool in assessing post-infarct cardiac function.

Is detection of hibernating myocardium necessary in deciding revascularization in systolic heart failure?

Although the prognosis of systolic heart failure, also called heart failure with reduced ejection fraction, has improved with advances in therapy, the prognosis remains poor in patients who become refractory to such therapies. That cardiac transplantation improves the quality of life and survival of such patients has been established, but it is available to a very small number of patients. Thus, newer pharmacologic and nonpharmacologic therapies for patients with refractory systolic heart failure are being explored. Because chronic ischemic heart disease is the most common cause of systolic heart failure, potential exists for revascularization therapy. Although revascularization can be performed with low procedural mortality, improvement in left ventricular function, relief of symptoms, and long-term prognosis appear to be related to the presence and extent of viable ischemic hibernating myocardium. In conclusion, the detection of hibernating myocardium is highly desirable before revascularization treatment is undertaken.

Practical assessment of myocardial viability with a positron coincidence gamma camera using 18F-fluorodeoxyglucose in acute myocardial infarction: comparison with dedicated positron emission tomography and 201Tl single photon emission computed tomography

OBJECTIVE

2-[(18)F] fluoro-2-deoxy-D-glucose ((18)F-FDG) began to be supplied commercially to our hospital, which does not have a cyclotron, in autumn of 2005. The purpose of this study was to compare the utility of a dual-head positron coincidence detection (PCD) gamma camera in the detection of myocardial viability using (18)F-FDG with that of dedicated positron emission tomography (PET) and with that of thallium-201 ((201)Tl) single photon emission computed tomography (SPECT).

METHODS

A total of 15 patients (14 men and 1 woman, mean age: 60+/-7 years, range: 46-73) with a large acute myocardial infarction (AMI) underwent (18)F-FDG PET, (18)F-FDG PCD imaging after oral glucose loading (75 g) and (201)Tl SPECT imaging. We divided the SPECT and PET images into a total of 20 segments, and semiquantitative visual analysis was performed by assessing regional tracer activities on a 4-point scoring system (DS): 0=normal uptake, 1=mildly reduced uptake, 2=severely reduced uptake, and 3=no uptake. We summed the DS in each patient as the total DS (TDS).

RESULTS

The TDS of the (18)F-FDG PET image was 14.4+/-7.7. The TDS of the (18)F-FDG PCD image was 18.7+/-7.7. The TDS of the (201)Tl SPECT image was 24.1+/-11.5. The TDS of the (18)F-FDG PET image was significantly smaller than that of the (18)F-FDG PCD image. The TDS of the (18)F-FDG PET image was significantly smaller than that of the (201)Tl SPECT image. The TDS of the (18)F-FDG PCD image was significantly smaller than that of the (201)Tl SPECT image.

CONCLUSION

The findings of the project suggest that (18)F-FDG PCD is a good modality based on its accuracy, convenience, and cost-performance for detecting myocardial viability in hospitals that do not have a PET system.

Late percutaneous coronary intervention for the totally occluded infarct-related artery: a meta-analysis of the effects on cardiac function and remodeling

BACKGROUND

Late percutaneous coronary intervention (PCI) of a totally occluded infarct-related artery (IRA) in stable patients is currently not recommended based on the lack of clear clinical benefits in randomized controlled trials. We sought to perform a systematic review and meta-analysis of randomized controlled trials comparing PCI with optimal medical therapy in patients with IRA occlusion more than 12 hr after onset of acute myocardial infarction (AMI), focusing on left ventricular function and remodeling.

METHODS AND RESULTS

PubMed, CENTRAL, and mRCT were searched for eligible studies. Studies were included in the analysis if they were randomized controlled trials comparing conservative medical management with PCI performed at least 12 hr after the onset of symptoms of AMI, and data on left ventricular ejection fraction (LVEF) at baseline and follow-up were available. Studies were excluded if randomization occurred less than 12 hr after symptom onset, or if patients were hemodynamically unstable. Change in LVEF was the primary outcome of interest, with changes in left ventricular end-diastolic volume index (LVEDVI) and end-systolic volume index (LVESVI) analyzed as secondary endpoints. We retrieved five studies in which baseline and follow up LVEF data were available enrolling a total of 648 patients: 342 patients randomized to PCI and 306 to medical treatment. There was a statistically significant difference in LVEF changes over time favoring PCI (+3.1%, 95% CI +1.0 to +5.2, P = 0.0004). In addition, there were statistically significant differences changes in both LVEDVI (-5.1 ml in favor of PCI, 95% CI of -9.4 to -0.8, P = 0.020) and LVESVI (-5.3 ml in favor in PCI, 95% CI of -8.3 to -2.4, P = 0.0005).

CONCLUSIONS

This meta-analysis suggests that late revascularization of an occluded IRA may improve left ventricular systolic function and remodeling, supporting the "open artery hypothesis." The reason why these changes have not resulted in clinical benefits in large clinical trials is subject to debate.

Survival and cardiac remodeling benefits in patients undergoing late percutaneous coronary intervention of the infarct-related artery: evidence from a meta-analysis of randomized controlled trials

OBJECTIVES

Our purpose was to perform a systematic review and meta-analysis of randomized trials comparing percutaneous coronary intervention (PCI) of the infarct-related artery (IRA) with medical therapy in patients randomized >12 h after acute myocardial infarction (AMI).

BACKGROUND

There is ongoing uncertainty about the risk-benefit ratio of late PCI in stable patients with AMI.

METHODS

PubMed, CENTRAL, and other databases were searched (July 2007). Studies were included if they compared PCI with medical management and randomized patients >12 h and up to 60 days after AMI, and were excluded if patients were hemodynamically unstable. Odds ratios (ORs) were pooled for dichotomous outcomes, with all-cause mortality as the primary end point. Left cardiac remodeling parameters were also pooled with generic inverse-variance weighting.

RESULTS

We retrieved 10 studies that enrolled 3,560 patients, with median time from AMI to randomization of 12 days (range 1 to 26 days), and follow-up of 2.8 years (42 days to 10 years). Randomization allocated 1,779 subjects to PCI and 1,781 to medical treatment. There were 112 (6.3%) and 149 (8.4%) deaths in the 2 groups, respectively, yielding significantly improved survival in the PCI group (OR 0.49 [95% confidence interval (CI) 0.26 to 0.94], p = 0.030). These benefits were associated with similarly favorable effects on cardiac remodeling, such as improved left ventricular ejection fraction in the PCI group (+4.4% change [95% CI 1.1 to 7.6], p = 0.009).

CONCLUSIONS

Percutaneous coronary intervention of the IRA performed late (12 h to 60 days) after AMI is associated with significant improvements in cardiac function and survival.

Late myocardial enhancement assessed by 64-MSCT in reperfused porcine myocardial infarction: diagnostic accuracy of low-dose CT protocols in comparison with magnetic resonance imaging

The purpose was to assess the practicability of low-dose CT imaging of late enhancement in acute infarction. Following temporary occlusion of the second diagonal branch, seven pigs were studied by multislice computed tomography (MSCT) and magnetic resonance imaging (MRI). Thus, 64-slice CT was performed at 3, 5, 10 and 15 min following the injection of contrast medium according to a bolus/low-flow protocol. Standard parameters of 120 kV and 800 mAs were compared with 80 kV and 400 mAs in various combinations. Infarct volumes were assessed as percentage of the ventricle for both MSCT and MR images. CT density values for viable and infarcted myocardium were obtained and image quality assessed. Mean infarct volume as measured by MRI was 12.33+/-7.06%. MSCT achieved best correlation of volumes at 5 and 10 min. Whilst lowering of tube current resulted in poor correlation, tube voltage did not affect accuracy of infarct measurement (r (2)=0.92 or 0.93 at 5 min, 800 mAs and 80 or 120 kV). In terms of image quality, greater image noise with 80 kV was compensated by significantly better contrast enhancement between viable and non-viable myocardium at lower voltage. Myocardial viability can accurately be assessed by MSCT at 80 kV, which ensures higher contrast for late enhancement and yields good correlation with MRI.

Relation of T-wave inversion in Q-wave acute myocardial infarction to myocardial viability on resting rubidium-82 and 18-fluoro-deoxyglucose positron emission tomography imaging

T-wave inversion in areas of Q-wave myocardial infarction has been advocated as a predictor of myocardial viability. However, the predictive value of this electrocardiographic finding in distinguishing viable from nonviable muscle is not fully defined. Thus, we correlated electrocardiographic Q waves and a measure of T-wave inversion with the results of rubidium-82 (Rb-82) and 18-fluoro-deoxyglucose-positron emission tomography (FDG-PET) imaging at rest. We analyzed 35 Q-wave myocardial infarct regions in 25 patients. Nineteen of the 35 (54%) were judged viable by Rb-82/FDG-PET. Using the Novacode T-wave score, T-wave inversion was present in 11 of 19 regions (58%) with viability and 5 of 16 regions (31%) without viability. Thus, neither Q waves nor T-wave inversion can accurately predict myocardial viability in patients with Q-wave myocardial infarction.

Which parameters on magnetic resonance imaging determine Q waves on the electrocardiogram?

Studies have demonstrated that patients with Q-wave infarctions on the electrocardiogram (ECG) frequently have nontransmural scar formation, whereas non-Q-wave infarctions may have transmural scars. The precise pathophysiologic substrate that underlies Q waves remains unclear. Magnetic resonance imaging (MRI) is the preferred technique to evaluate patients who have infarction because information can be obtained on function, contractile reserve (viability), and scar tissue. Consecutive patients (n = 69) who had coronary artery disease and a history of myocardial infarction underwent MRI; the protocol included MRI at rest, small-dose dobutamine MRI, and contrast-enhanced MRI. Parameters included left ventricular ejection fraction, left ventricular volumes, end-diastolic wall thickness and contractile reserve in the infarct region, transmurality and spatial extent of scar tissue, total scar score, and quantified percent left ventricular scar tissue. MRI data were related to the presence/absence of Q waves on the ECG. Q waves were present in 39 patients (57%). Univariate analysis identified transmurality, spatial extent, total scar score, and quantified percent scar tissue as predictors of Q waves. Multivariate analysis demonstrated that quantified percent scar tissue was the single best predictor of Q waves on the ECG. A cut-off value of 17% infarcted tissue of the left ventricle yielded a sensitivity and specificity of 90% to predict the presence/absence of Q waves. When quantified percent scar tissue was removed from the model, spatial extent of infarction was the best predictor. Thus, Q waves on the ECG correlate best with quantified percent scar tissue on contrast-enhanced MR images.

Clinical decision-making and myocardial viability: current perspectives

Not all myocardium involved in a myocardial infarction is dead or irreversibly damaged. The balance between the amount of scar and live tissue, and the nature of the live tissue, determine the likelihood that contractile function will improve after revascularisation. This improvement (which defines viability) may be predicted with about 80% accuracy using several techniques. This review examines the determinants of functional recovery and how they may be integrated in making decisions regarding revascularisation.

Viable Myocardium: How Much Is Enough? A Comparison of Viability by Comparative Imaging Techniques to Assess the Quantity and Functionality of Ischemic Myocardium

Left ventricular systolic dysfunction is mainly a result of coronary artery disease (CAD). Decrease in myocardial contractility results as a response to a chronic hypoperfusion state that produces a change in cardiac myocyte metabolism, resulting in a perfusion-contraction mismatch in which function is sacrificed for survival. If revascularization is performed in a timely fashion, metabolism can be restored leading to recovery of function. Through the use of noninvasive imaging modalities, assessing myocardial viability can be easily performed and will aid in selecting those patients who will benefit from revascularization. Viable myocardium can be identified by nuclear modalities that have a high sensitivity but a lower specificity, such as thallium-201 single photon emission computed tomography and positron emission tomography (PET); or by the use of dobutamine stress echocardiogram (DSE), which has a decreased sensitivity but a better specificity. A modality that is increasingly being used with an overall good sensitivity and specificity is contrast-enhanced magnetic resonance imaging. The purpose of this review is to explore the amount of myocardial viability that is relevant to pursue revascularization, since as myocardial function improves there is a decrease in morbidity and mortality from heart failure and arrhythmias.

Prognostic value of predischarge electrocardiographic measurement of infarct size after thrombolysis: insights from GUSTO I Economics and Quality of Life substudy

BACKGROUND

Current methods for risk stratification after acute myocardial infarction (MI) include several noninvasive studies. In this cost-containment era, the development of low-cost means should be encouraged. We assessed the ability of an electrocardiogram (ECG) MI-sizing score to predict outcomes in patients enrolled in the Economics and Quality of Life (EQOL) sub study of the Global Utilization of Streptokinase and Tissue plasminogen activator for Occluded coronary arteries -I (GUSTO-I) trial.

METHODS

We classified patients by electrocardiographic Selvester QRS score at hospital discharge: those with a score 0-9 versus > or =10. Endpoints were 30-day and 1-year mortality, resource use, and quality-of-life measures.

RESULTS

Patients with a QRS score <10 were well-matched with those with QRS score > or =10 with the exception of a trend to more anterior MI in the higher scored group. Patients with QRS score > or =10 had increased risk of death at 30-days (8.9% vs. 2.9% P < .001), and this difference persisted at 1 year (12.6% vs. 5.4%, P = .001). Recurrent chest pain, use of angiography, and angioplasty were similar during follow-up. However, there was a trend toward less coronary bypass surgery in patients with a QRS score > or =10. Readmission rates were higher at 30 days but similar at 1 year.

CONCLUSIONS

Stratification of patients after acute MI by a simple measure of MI size identifies populations with different long-term prognoses; patients with a QRS score > or =10 (approximately 30% of the left ventricle infarcted) at discharge have poorer outcomes in both the short- and long-term. The standard 12-lead ECG provides a simple, economical means of risk stratification at discharge.

Contrast-enhanced MR imaging of the heart: overview of the literature

The use of magnetic resonance (MR) imaging for cardiac diagnosis is expanding, aided by the administration of paramagnetic contrast agents for a growing number of clinical applications. This overview of the literature considers the principles and applications of cardiac MR imaging with an emphasis on the use of contrast media. Clinical applications of contrast material-enhanced MR imaging include the detection and characterization of intracardiac masses, thrombi, myocarditis, and sarcoidosis. Suspected myocardial ischemia and infarction, respectively, are diagnosed by using dynamic first-pass and delayed contrast enhancement. Promising new developments include blood pool contrast media, labeling of myocardial precursor cells, and contrast-enhanced imaging at very high fields.

Q-wave regression after acute myocardial infarction assessed by Tl-201 myocardial perfusion SPECT

BACKGROUND

The actual relationship between the interval change of myocardial thallium 201 (Tl-201) radioactivity in the infarct area and the pattern of Q-wave regression is still unknown. This study was conducted to evaluate their relationship after acute myocardial infarction (AMI).

METHODS AND RESULTS

A total of 30 patients who had a first Q-wave AMI (11 without Q-wave regression and 19 with Q-wave regression) were retrospectively included. Two sets of 12-lead surface electrocardiograms and Tl-201 myocardial perfusion images were obtained 0 to 2 months and 14 to 84 months after the AMI event, respectively. The acute/subacute redistribution Tl-201 radioactivity was similar between the patients with and those without Q-wave regression. However, the patients with Q-wave regression had higher chronic redistribution Tl-201 radioactivity than those without Q-wave regression. Moreover, the patients with Q-wave regression presented a higher gradient in the redistribution Tl-201 radioactivity between the chronic and acute/subacute images than those without Q-wave regression.

CONCLUSIONS

This study supports the role of functional recovery of stunning and/or hibernating myocardium in the disappearance of Q waves after AMI.

F-18-FDG uptake is a reliable predictory of functional recovery of akinetic but viable infarct regions as defined by magnetic resonance imaging before and after revascularization

Identification of akinetic but viable myocardium is important for the selection of patients for coronary revascularization. In order to assess predictive values of end-diastolic wall thickness and dobutamine induced wall thickening obtained by magnetic resonance imaging (MRI) and [18F]Fluorodeoxyglucose uptake assessed by positron emission tomography (F-18-FDG-PET), these parameters were compared to recovery of left ventricular function after successful revascularization. Forty patients with chronic myocardial infarction and regional a- or dyskinesia by ventriculography underwent rest- and dobutamine-MRI studies (10 microg dobutamine/kg body weight/min) and F-18-FDG-PET. Viability of the infarct region was considered to be present if; 1) end-diastolic wall thickness was > or =5.5 mm; 2) dobutamine induced wall thickening > or =2 mm could be measured; and 3) normalized F-18-FDG-uptake was > or =50% in > or =50% of akinetic segments. Preserved end-diastolic wall thickness was found in 32/40 patients, functional improvement during dobutamine infusion in 26/40 patients and preserved F-18-FDG-uptake in 29/40 patients. After revascularization regional left ventricular function improved in 25/40 patients. Positive and negative predictive values and diagnostic accuracy were 78%, 100%, and 83% for preserved end-diastolic wall thickness, 92%, 93%, and 93% for dobutamine inducible contraction reserve and 86%, 100%, and 90% for preserved F-18-FDG-uptake. Quantitative assessment of dobutamine induced systolic wall thickening by MRI and F-18-FDG-uptake by PET are highly accurate techniques for the identification of viable myocardium and prediction of functional recovery after successful revascularization. Preserved end-diastolic wall thickness results in an overestimation of viable myocardium compared to functional improvement, but wall thickness <5.5 mm excludes recovery of regional function.

Evaluation of Salvaged Myocardium After Acute Myocardial Infarction Using Single Photon Emission Computed Tomography After 201Tl-Glucose-Insulin Infusion

BACKGROUND

GIK-201Tl imaging reportedly improves the detection of viable myocardium, so the present study evaluated whether it can detect myocardial viability after acute myocardial infarction (AMI).

METHODS AND RESULTS

Resting 201Tl and 99mTc-pyrophosphate (PYP) dual single photon emission computed tomography (SPECT) and 201Tl SPECT after 201Tl with GIK (10% glucose, insulin 5 U, and KCl 10 mmol) infusion (GIK-201Tl) were performed in 25 AMI patients within 10 days of admission. GIK-201Tl SPECT images were obtained immediately and 4 h after infusion. Left ventriculography (LVG) was performed within 3 weeks and at 6 months when follow-up 201Tl SPECT was also performed. From 20 SPECT segments, both the summed defect score (RDS) and the number of defect segments (ES) were calculated. The infarcted area was defined as 99mTc-PYP uptake segments. Wall motion was estimated in 7 LVG segments. The ES of R-201Tl (5.5 +/- 2.8), immediate GIK-201Tl (4.0 +/- 2.3), and 4-h GIK-201Tl (5.6 +/- 2.7) were lower than that of 99mTc-PYP (7.5 +/- 4.1) (p<0.05), and the ES had significantly declined 6 months later on 201Tl (3.5 +/- 2.8) (p<0.05). Although the RDS of R-201Tl (11.3 +/- 7.9) and 4-h GIK-201Tl (11.2 +/- 6.3) were greater than at the 6-month 201Tl (7.1 +/- 6.5), immediate GIK-201Tl (7.4 +/- 6.5) was equivalent to follow-up 201Tl. The sensitivity of immediate GIK-201Tl was highest among the imaging methods.

CONCLUSION

To detect myocardial viability after AMI, early imaging with GIK-201Tl is more useful than resting 201Tl imaging.

The contribution of hibernation to heart failure

For many years the functional sequelae of chronic coronary artery disease (CAD) were considered irreversible. Evidence accrued over the past three decades proves that this concept is not necessarily true. Non-randomised studies demonstrated that coronary revascularisation (CR) confers symptomatic and prognostic benefits to patients with CAD and heart failure. Based on available studies, one can assume that the beneficial effect of CR in heart failure derives primarily from recovery of contractile function in 'hibernating myocardium' (HM), i.e., chronically dysfunctional, but viable, myocardium subtended by stenosed coronary arteries which recovers after CR. Cardiac imaging with echocardiography, single photon and positron emission tomography (PET) and magnetic resonance allows the identification of HM. These techniques have comparable predictive values in patients with moderate left ventricular impairment. PET studies have shown that resting myocardial blood flow is preserved in most cases of HM while its main feature is a severe impairment of coronary flow reserve. Thus, the pathophysiology of HM is more complex than initially postulated. Recent evidence that repetitive ischaemia in patients can be cumulative and lead to more severe and prolonged stunning, lends further support to the hypothesis that, at least initially, stunning and HM are two facets of the same coin.

Quantification of regional left ventricular function in Q wave and non-Q wave dysfunctional regions by tissue Doppler imaging in patients with ischaemic cardiomyopathy

OBJECTIVE

To quantify regional left ventricular (LV) function and contractile reserve in Q wave and non-Q wave regions in patients with previous myocardial infarction.

DESIGN

An observational study.

SETTING

Tertiary care centre.

PATIENTS

81 patients with previous myocardial infarction and depressed LV function.

INTERVENTIONS

All patients underwent surface ECG at rest and pulsed wave tissue Doppler imaging at rest and during low dose dobutamine infusion. The left ventricle was divided into four major regions (anterior, inferoposterior, septal, and lateral). Severely hypokinetic, akinetic, and dyskinetic regions on two dimensional echocardiography at rest were considered dysfunctional.

MAIN OUTCOME MEASURES

Regional myocardial systolic velocity (Vs) at rest and the change in Vs during low dose dobutamine infusion (DeltaVs) in dysfunctional regions with and without Q waves on surface ECG.

RESULTS

220 (69%) regions were dysfunctional; 60 of these regions corresponded to Q waves and 160 were not related to Q waves. Vs and DeltaVs were lower in dysfunctional than in non-dysfunctional regions (mean (SD) Vs 6.2 (1.9) cm/s v 7.1 (1.7) cm/s (p < 0.001), and DeltaVs 1.9 (1.9) cm/s v 2.6 (2.5) cm/s (p = 0.009), respectively). There were no significant differences in Vs and DeltaVs among dysfunctional regions with and without Q waves (Q wave regions: Vs 6.2 (1.8) cm/s, DeltaVs 1.6 (2.2) cm/s; non-Q wave regions: Vs 6.3 (1.9) cm/s, DeltaVs 2.0 (2.0) cm/s).

CONCLUSIONS

Quantitative pulsed wave tissue Doppler demonstrated that, among dysfunctional regions, Q waves on the ECG do not indicate more severe dysfunction, and myocardial contractile reserve is comparable in Q wave and non-Q wave dysfunctional myocardium.

Endocardial cryotherapy as a novel strategy of improving myocardial perfusion in a patient with severe coronary artery disease

Patients with intractable angina pectoris due to end-stage coronary artery disease who are not amenable to conventional revascularization provide a therapeutic challenge. We describe the first published case of a young patient with intractable coronary artery disease that was successfully treated by endocardial cryotherapy.

Pathophysiology and diagnosis of hibernating myocardium in patients with post-ischemic heart failure: the contribution of PET

Identification and treatment of hibernating myocardium (HM) lead to improvement in LV function and prognosis in patients with post-ischemic heart failure. Different techniques are used to diagnose HM: echocardiography, MRI, SPECT and PET and, in patients with moderate LV impairment, their predictive values are similar. There are few data on patients with severe LV dysfunction and heart failure in whom the greatest benefits are apparent after revascularization. Quantification of FDG uptake with PET during hyperinsulinemic euglycemic clamp is accurate in these patients with the greatest mortality risk in whom other techniques may give high false negative rates. The debate on whether resting myocardial blood flow to HM is reduced or not has stimulated new research on heart failure in patients with coronary artery disease. PET with H2(15)O or 13NH3 has been used for the absolute quantification of regional blood flow in human HM. When HM is properly identified, resting blood flow is not different from that in healthy volunteers although a reduction of approximately 20% can be demonstrated in a minority of cases. PET studies have shown that the main feature of HM is a severe impairment of coronary vasodilator reserve that improves after revascularization in parallel with LV function. Thus, the pathophysiology of HM is more complex than initially postulated. The recent evidence that repetitive ischemia in patients can be cumulative and lead to more severe and prolonged stunning, lends further support to the hypothesis that, at least initially, stunning and HM are two facets of the same coin.

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.

Assessment of myocardial viability with a positron coincidence gamma camera using fluorodeoxyglucose in comparison with dedicated PET

The use of dual-head gamma camera modified positron coincidence detection (PCD) is a new, alternative method of 2-[18F]fluoro-2-deoxy-D-glucose (FDG) imaging. This study investigated the potential ability of evaluating myocardial viability in patients with ischaemic heart disease by FDG imaging using PCD. A total of 21 patients (18 male, three female; mean age 59.7+/-8.5 years) with a history of previous myocardial infarction and confirmed coronary angiography underwent FDG PCD and FDG PET after oral glucose loading (75 g). Quantitative analysis was compared between images of FDG PCD and FDG PET. A significant linear correlation between the segmental percentage of FDG uptake obtained by PCD and PET was observed (r=0.63, P<0.001). By receiver operating characteristic (ROC) analysis, using FDG PET as the 'gold standard', at the 50% threshold value in PET, FDG PCD showed a sensitivity of 92% and specificity of 63% in detecting myocardial viability. Regional analysis showed lower agreement of FDG PCD and FDG PET in the inferior (79%) and septal (70%) walls compared with the other walls. Quantitative evaluation of myocardial viability using FDG PCD yielded comparable clinical results in apex, anterior and lateral walls to that of FDG PET. However, the agreement was lower in the inferior and septal walls. Therefore, results of FDG PCD should be carefully interpreted in evaluating myocardial viability in the inferior and septal walls. The application of a measured attenuation correction and scatter correction are needed to improve the detectability of myocardial viability in FDG imaging by coincidence gamma camera.

Assessment of myocardial perfusion abnormalities by intravenous myocardial contrast echocardiography with harmonic power Doppler imaging: comparison with positron emission tomography

BACKGROUND

Intravenous myocardial contrast echocardiography with harmonic power Doppler imaging (HPDI) enables assessment of myocardial perfusion. Its accuracy in comparison with positron emission tomography (PET), which is one of the most reliable clinical gold standards for myocardial perfusion, remains to be determined.

OBJECTIVE

To assess the ability of HPDI to identify myocardial perfusion abnormalities, using PET as a gold standard.

METHODS

23 patients with myocardial infarction underwent HPDI. Images were obtained from the apical two and four chamber views at pulsing intervals of one to eight cardiac cycles with continuous infusion of Levovist (Schering, Germany). PET was done within two weeks of HPDI. The left ventricle was divided into 12 segments and myocardial opacification by HPDI and uptake of NH(3) by PET in each segment was graded as normal, mildly reduced, or severely reduced.

RESULTS

Of the 276 segments examined, adequate image quality was obtained in 226 (82%) by HPDI; 50 segments were excluded because of inadequate image quality. There were more exclusions in the basal segments than in the mid or apical segments (p < 0.0001). Of the 226 segments analysed, overall concordance between HPDI and PET was 82% (chi = 0.70). In the apex, more segments were overestimated by HPDI than were underestimated (chi(2) = 6.25, p = 0.012).

CONCLUSIONS

HPDI and PET gave similar results in the assessment of myocardial perfusion abnormalities. However, poor image quality in the basal segments and overestimation of perfusion in the apical segments are current limitations of HPDI.

Assessment of residual myocardial viability in regions with chronic electrocardiographic Q-wave infarction

BACKGROUND

Q waves on the electrocardiogram are often considered to be reflective of irreversibly scarred myocardium due to antecedent transmural myocardial infarction. However, there are some indications that residual viable tissue may be present in Q-wave-infarcted regions. It is clinically relevant to know how many Q-wave regions contain viable tissue because these patients may benefit from revascularization in terms of improvement of function and long-term survival.

METHODS

Patients (n = 150) with chronic electrocardiographic Q-wave infarction, heart failure symptoms, and chronic coronary artery disease underwent dobutamine-atropine stress echocardiography to assess myocardial viability. Residual viability in regions with Q-wave infarction was considered present when the end-diastolic wall thickness (EDWT) was >6 mm and the response during dobutamine infusion indicated viable tissue.

RESULTS

Baseline echocardiography revealed 517 dysfunctional myocardial regions; 202 of the dysfunctional regions were related to Q waves on the electrocardiogram and the other 315 dysfunctional regions were not. EDWT was < or =6 mm in 13 regions with a Q wave on the electrocardiogram, with only 1 region exhibiting viable tissue during dobutamine stress echocardiography. EDWT was >6 mm in 189 regions with a Q wave, with 118 (62%) having viable tissue on dobutamine stress echocardiography. In 6 dysfunctional regions without a Q wave, EDWT was < or =6 mm, with all being nonviable on dobutamine stress echocardiography; of the 309 regions without a Q wave and EDWT >6 mm, 204 (66%) exhibited viability on dobutamine stress echocardiography.

CONCLUSIONS

Fifty-eight percent of dysfunctional regions related to chronic Q waves were viable according to the combined information of EDWT and dobutamine stress echocardiography. EDWT </=6 mm virtually excludes viability; regions with EDWT >6 mm need additional testing to detect or exclude viability.

Assessment of viable tissue in Q-wave regions by metabolic imaging using single-photon emission computed tomography in ischemic cardiomyopathy

Chronic electrocardiographic Q waves are often believed to reflect irreversibly scarred, transmurally infarcted myocardium. The aim of this study was to evaluate whether residual viable tissue persists in dysfunctional myocardial regions related to chronic Q waves on the surface electrocardiogram. A total of 148 patients with healed myocardial infarction and impaired left ventricular (LV) function with heart failure symptoms underwent electrocardiography and metabolic imaging using technetium (Tc-99m) tetrofosmin/F18-fluorodeoxyglucose (FDG) single-photon emission computed tomography (SPECT). The left ventricle was divided into 4 major regions to compare myocardial viability in regions with and without chronic Q waves on surface electrocardiography. According to FDG SPECT metabolic imaging, residual viable tissue persisted in a high proportion (61%) of dysfunctional myocardial regions with chronic Q waves. Regions with chronic Q waves were more often dysfunctional than regions without Q waves. Moreover, dysfunctional regions with chronic Q waves were less frequently viable compared with dysfunctional regions without Q waves on the electrocardiogram. This study demonstrates that chronic Q waves on electrocardiography do not necessarily imply irreversibly scarred myocardium. Residual viable tissue persists in a high proportion of dysfunctional ventricular regions according to FDG SPECT metabolic imaging.

Myocardial hibernation in coronary artery disease

Coronary artery disease (CAD) is very prevalent in Western societies and is a leading cause of mortality and morbidity. Despite decreases in mortality rates from CAD over the past 30 years, ischemic heart failure remains an important problem because people with CAD are now living longer. Hibernating myocardium may be defined as reversible left ventricular dysfunction due to chronic CAD that shows improvement in function after revascularization. Many patients with ischemic cardiomyopathy have areas of hibernating myocardium, and thus can potentially show improvement in left ventricular regional and global function if they are revascularized. Whether hibernating myocardium represents an adaptive response to hypoperfusion in the face of chronic ischemia or whether it is a degenerative process is not entirely clear. Clearly, ultrastructural changes of de-differentiation are seen, and include loss of sarcomeres and the appearance of small mitochondria and glycogen accumulation. Although the mechanisms underlying the changes in morphology and depressed contractility, and the factors governing recovery of function are not clear, changes in adrenergic receptor density, cytokine upregulation, and the degree of fibrosis may all play a role. Identification of viability is commonly performed with dobutamine echocardiography or nuclear imaging. Because patients with extensive CAD and poor left ventricular systolic function are high-risk candidates for coronary bypass surgery, the preoperative identification of viability provides important prognostic information. Patients with viable myocardium who are treated with revascularization rather than medical therapy have better outcomes in terms of survival, left ventricular function, symptoms, and exercise capacity.

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.

Myocardial FDG-PET examination during fasting and glucose loading states by means of a one-day protocol

We propose a new method to measure the myocardial FDG uptake during fasting and glucose loading in one day, a myocardial FDG-PET one-day protocol, with both 2- and 3-dimensional data acquisition (2D and 3D) without background activity subtraction. To confirm it, we evaluated the effect of scatter correction in the 2D and 3D modes of a PET scanner both in phantom and patient studies. In the phantom study, we used a cardiac phantom with six divided chambers and two cylindrical phantoms placed as the activity outside the field of view. Each chamber was filled with a different concentration of F- 18 solution. Regions of interest (ROI) were placed on a polar map generated from reconstructed images and were compared to the concentration of the solution in each chamber in both 2D and 3D. In the patient study, 10 non-diabetic patients with coronary artery disease were studied. Each patient received a myocardial FDG study during fasting (F) and glucose loading (L). L images with background subtraction (Lsub(+)) and without background subtraction (Lsub(-)) were compared by polar map analysis. The ROI counts for the true activity in 2D and 3D demonstrated a linear relationship, and quite similar slopes were observed (0.72 in 2D, 0.69 in 3D). The background fraction in Lsub(-) was 3.59+/-1.83%. There were significant differences between Lsub(-) or Lsub(+) and F in both normal and ischemic myocardium. Scatter correction was successfully performed in both 2D and 3D modes. Background activity is thought to be negligible and this proposed method is simple touse in measuring the myocardial FDG uptake in one day.

Ischemically compromised myocardium displays different time-courses of functional recovery: correlation with morphological alterations?

OBJECTIVE

It has been demonstrated that positron emission tomography (PET) predicts the functional recovery of viable but ischemically compromised myocardium. Reversible contractile dysfunction after revascularization has been reported for 'hibernating myocardium' and stunned myocardium, however, there are little data concerning the time-course and the extent of improvement of the two different pathophysiological conditions.

METHODS

Twenty-nine patients with advanced coronary artery disease and severely reduced left ventricular function (EF 18--35%) who were referred for isolated coronary artery bypass grafting underwent preoperative PET viability assessment and were functionally assessed by two-dimensional echocardiography preoperatively at 11 days, 14 weeks, and more than 12 months after surgical revascularization. Intraoperative biopsies were taken from dysfunctional areas defined by PET as segments of normal perfusion and normal metabolism (stunned myocardium) and from areas with a 'mismatch' between perfusion and metabolism (hibernating myocardium). The degree of morphological alterations was evaluated by electron microscopy.

RESULTS

In 70% of the 240 dysfunctional segments, 'stunned myocardium' was present whereas 'hibernating myocardium' could be detected in only 24% (P < 0.01). Hibernating myocardium was associated with more severe preoperative wall motion abnormalities and incomplete postoperative recovery. After 1 year, 31% of 'stunned' segments vs. only 18% of 'hibernating' segments showed complete functional restoration (P < 0.05). This incomplete improvement was associated with more severe morphological alterations including depletion of sarcomeres, accumulation of glycogen, loss of sarcoplasmatic reticulum, and cellular sequestration.

CONCLUSIONS

These data indicate that in patients with severe ischemic left ventricular dysfunction 'stunned myocardium' is more prevalent than 'hibernation'. Functional normalization is more frequent in 'stunned' segments, whereas areas of 'hibernation' showed more severe tissue injury and protracted recovery. Different degrees of myocardial injury coexist in most patients, which determines the time-course and the extent of improvement after revascularization.

Cardiac nuclear medicine in monitoring patients with coronary heart disease

Patient monitoring is a major indication for cardiac nuclear medicine procedures. Stress myocardial perfusion scintigraphy was initially used for diagnosis, but monitoring patients with coronary artery disease has become more common. Stress myocardial perfusion scintigraphy has been shown to provide a considerable amount of incremental prognostic information, which may be useful in selecting patients for therapy. In patients being considered for revascularization, fluorodeoxyglucose can be used to identify regions of dysfunctional but viable myocardium, even within regions that show fixed defects on stress perfusion imaging. It can be used to select a group of patients who will improve function with revascularization and who may have an improved outcome. Thus, cardiac nuclear medicine plays a pivotal role in monitoring patients with coronary artery disease.

Relevance of 99mTc-MIBI rest uptake, ejection fraction and location of contractile abnormality in predicting myocardial recovery after revascularization

The aim of this study was to analyse the influence of rest technetium-99m-methoxy-isobutyl-isonitrile (99mTc-MIBI) uptake, left ventricular ejection fraction (EF) and dysfunctional location in the prediction of myocardial viability. Rest 99mTc-MIBI single photon emission computed tomography (SPECT) was analysed in 82 patients (59+/-9 years, 70 men, 12 women) with one or more segments showing severe hypokinesia, akinesia or dyskinesia who had undergone coronary revascularization. Before and within 3-6 months after the revascularization, gated blood pool scintigraphy was performed. In the post-revascularization control, contractile recovery was observed in 48.7% (155/318) of the segments with severe hypokinesia, akinesia or dyskinesia. Significant increases in sensitivity (53%, 72% and 91%, P<0.0001) and negative predictive value (62%, 68% and 79%, P = 0.01) were observed with decreasing rest uptake 99mTc-MIBI levels of 50%, 40% and 30%, respectively. The decrease in specificity was also significant (67%, 53% and 32%, P<0.0001). The negative predictive value was higher than the positive predictive value mainly in patients with EF < or = 0.35 and with anterior dysfunction. In logistic regression analysis, uptake levels and EF were independent variables that influenced sensitivity and specificity. The negative predictive value was influenced by EF and the positive predictive value only by dysfunctional location. This study suggests that the negative predictive value of 99mTc-MIBI SPECT is higher than the positive predictive value, mainly in patients with EF < or = 0.35, and that the rest uptake level, EF and dysfunctional location are factors that must be considered when results of 99mTc-MIBI SPECT are analysed.

The contribution of positron emission tomography to the study of ischemic heart failure

Cardiac imaging with positron emission tomography offers unrivaled sensitivity and specificity to probe cardiovascular physiology in health and disease. The use of positron emission tomography to noninvasively measure regional myocardial blood flow and assess myocardial viability in patients with ventricular dysfunction and coronary artery disease has contributed greatly to our understanding of the pathophysiology of ischemic heart failure. The advances and the need for further studies to establish both the natural history of such ventricular dysfunction and the role of coronary revascularization are discussed.

Detecting viable hibernating myocardium in chronic coronary artery disease--a comparison of resting 201Tl single photon emission computed tomography (SPECT), 99mTc-methoxy-isobutyl isonitrile SPECT after nitrate administration, and 201Tl SPECT after 201Tl-glucose-insulin infusion

To identify and quantify the amount of viable hibernating myocardium in patients with chronic coronary artery disease, resting 201Tl single photon emission computed tomography (SPECT) was compared with 99mTc-methoxy-isobutyl isonitrile (MIBI) SPECT after nitrate infusion (nitrate-99mTc-MIBI) and 201Tl SPECT after 201Tl with glucose-insulin-potassium infusion (201Tl-GIK) in 25 patients. Twenty-one patients also underwent completely left ventriculography beforehand and 5+/-4 months afterwards. SPECT images were divided into 9 segments and scored visually from 0 (normal uptake) to 3 (absent). The defect score was calculated as the summation of the total scores (TDS) in each patient. The TDS of nitrate-99mTc-MIBI images (6.3+/-4.3) and 201Tl-GIK images (5.8+/-4.2) were significantly lower than the 7.4+/-4.3 of resting 201Tl images (p<0.01). Based on the improvement of wall motion after coronary revascularization, the sensitivity of 201Tl-GIK imaging (85%) was significantly higher (p<0.05), and that of nitrate-99mTc-MIBI imaging (79%) also tended to be higher (p=0.08), than that of 201Tl imaging (62%) in detecting viable myocardium. The specificity of the 3 methods was almost the same. The nitrate-99mTc-MIBI and 201Tl-GIK methods were more useful than the resting 201Tl method for evaluating viable hibernating myocardium. Furthermore, the 201Tl-GIK method may provide a more accurate estimate of the amount of viable myocardium than the nitrate-99mTc-MIBI method.

Time course and extent of improvement of dysfunctioning myocardium in patients with coronary artery disease and severely depressed left ventricular function after revascularization: correlation with positron emission tomographic findings

OBJECTIVES

This study was performed to evaluate the prevalence, time course of recovery and extent of improvement of segments with a positron emission tomographic (PET) flow-metabolism mismatch and match pattern, as well as of PET segments with normal perfusion but with impaired myocardial function.

BACKGROUND

Previous studies have shown that scintigraphic techniques evaluating myocardial viability provide predictive information about the improvement of regional wall motion. However, there are little data concerning the time course and extent of improvement of segments according to preoperative scintigraphic patterns.

METHODS

Twenty-nine patients with ischemic cardiomyopathy (ejection fraction 18% to 35%) underwent preoperative PET viability assessment and were functionally assessed by two-dimensional echocardiography preoperatively and at 11 days, 14 weeks and >12 months after coronary artery bypass graft surgery.

RESULTS

In 168 (70%) of 240 dysfunctional segments, a "normal" scintigraphic pattern was present, whereas a "mismatch" pattern was observed in 24% (p<0.01). Mismatch areas were associated with more severe preoperative wall motion abnormalities and incomplete postoperative recovery. After one year, 31% of normal scintigraphic segments, compared with only 18% of mismatch segments, showed complete functional restoration (p<0.05).

CONCLUSIONS

These data suggest that in patients with severe left ventricular dysfunction, a scintigraphic pattern of normal perfusion and normal metabolism is more prevalent than a flow-metabolism mismatch pattern. Functional recovery is more frequent in normal scintigraphic segments, whereas in mismatch segments, postoperative recovery remains incomplete even after one year.

18-Fluorodeoxyglucose imaging with positron emission tomography and single photon emission computed tomography: cardiac applications

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with extensive viable myocardium, patients with predominantly scar tissue should be treated medically or evaluated for heart transplantation. Among the many viability tests, noninvasive assessment of cardiac glucose use (as a marker of viable tissue) with F18-fluorodeoxyglucose (FDG) is considered the most accurate technique to detect viable myocardium. Cardiac FDG uptake has traditionally been imaged with positron emission tomography (PET). Clinical studies have shown that FDG-PET can accurately identify patients with viable myocardium that are likely to benefit from revascularization procedures, in terms of improvement of left ventricular (LV) function, alleviation of heart failure symptoms, and improvement of long-term prognosis. However, the restricted availability of PET equipment cannot meet the increasing demand for viability studies. As a consequence, much effort has been invested over the past years in the development of 511-keV collimators, enabling FDG imaging with single-photon emission computed tomography (SPECT). Because SPECT cameras are widely available, this approach may allow a more widespread use of FDG for the assessment of myocardial viability. Initial studies have directly compared FDG-SPECT with FDG-PET and consistently reported a good agreement for the assessment of myocardial viability between these 2 techniques. Additional studies have shown that FDG-SPECT can also predict improvement of LV function and heart failure symptoms after revascularization. Finally, recent developments, including coincidence imaging and attenuation correction, may further optimize cardiac FDG imaging (for the assessment of viability) without PET systems.