The value of 24-hour images after rest thallium injection.

Rest (201) Tl imaging has been used for detecting viability, but the ideal timing for imaging after injection to maximally estimate viability is not well established. Thirty patients with fixed or incompletely reversible defects on 4 h redistribution SPECT imaging after thallium rest injection underwent 24 h imaging. Global redistribution was subjectively rated none, minimal or meaningful by two experienced observers. Fourteen patients had no meaningful redistribution at either 4 h or 24 h. Ten patients had meaningful redistribution at 4 h only. Six patients had no meaningful redistribution at 4 h but did at 24 h. Defect size was quantified using a 70% threshold. For the total group, defect size was smaller at 4 h compared to immediate imaging (38+/-18% vs 41+/-19%, P=0.06) and smaller still at 24 h (36+/-16% vs 38+/-18%, P=0.02). Later (24 h) redistribution images detected additional redistribution in 30% of the patients who did not have meaningful redistribution on early (4 h) images, and in 8% of the segments which were abnormal at 4 h. It is concluded that, in patients who have incompletely reversible defects on early redistribution imaging at 4 h, late redistribution imaging after 24 h will demonstrate additional redistribution in 30% of the patients.

Prediction of severe coronary artery disease and long-term outcome in patients undergoing vasodilator SPECT.

BACKGROUND: Vasodilator perfusion imaging has not been extensively evaluated for predicting severe coronary artery disease (CAD) or long-term prognosis. METHODS AND RESULTS: The goals of this study were to develop a model to predict left main/3-vessel CAD in patients undergoing vasodilator thallium 201 imaging and coronary angiography (angiographic population) and to test the long-term prognostic value of this model in a separate cohort of patients who were not referred for angiography (prognostic population). In the angiographic population (n = 653) the chi2 value of the clinical model (containing the variables age, sex, and prior myocardial infarction) in the prediction of severe CAD was 32. The addition of 3 vasodilator Tl-201 variables (magnitude of ST-segment depression, summed reversibility score, and increased lung uptake) increased the model chi2 value to 114 (P <.001). Only 9% of predicted low-risk patients versus 57% of predicted high-risk patients had severe CAD. In the prognostic population (n = 521) survival rates free of cardiac death or myocardial infarction at 7 years were 91%, 73%, and 51%, respectively, for patient groups predicted to be at low, intermediate, and high risk of severe CAD (P <.001). CONCLUSIONS: Clinical and vasodilator Tl-201 variables can accurately predict the risk of severe CAD. Stress Tl-201 variables add incremental information to clinical variables. The same model also predicts patient outcome.

The impact of time to thrombolytic treatment on outcome in patients with acute myocardial infarction. For the CORE investigators (Collaborative Organisation for RheothRx Evaluation).

OBJECTIVES: To examine the impact of time to thrombolytic treatment on multiple acute outcome variables in a single trial of thrombolysis in acute myocardial infarction. DESIGN AND PATIENTS: Mortality and reinfarction rate were measured in 2770 patients with acute myocardial infarction who received thrombolysis within 12 hours in CORE, an international, dose ranging trial of poloxamer 188. Tc-99m sestamibi infarct size and radionuclide angiographic ejection fraction substudies included 1099 and 1074 patients, respectively. RESULTS: Time to thrombolysis, subgrouped by intervals (< 2, 2-4, > or = 4-6, and > or = 6 hours), was significantly associated with infarct size (median 15.0%, 18.5%, 22.0%, 18.5% of left ventricle; p = 0.033), mean (SD) ejection fraction (51.5 (12.0)%, 48. 3 (13.9)%, 48.2 (13.3)%, 48.2 (15.0)%; p = 0.006), 35 day mortality (5.7%, 7.1%, 7.9%, 12.5%; p = 0.0004), six month mortality (7.3%, 8. 6%, 10.4%, 15.5%; p < 0.0001), and 35 day reinfarction rate (6.1%, 3. 2%, 4.0%, 0.9%; p = 0.0001). CONCLUSIONS: In this single large trial, the beneficial effect of time to thrombolysis on infarct size and ejection fraction was restricted to treatment given within two hours of symptom onset, while the effect on mortality was evident over all time intervals. Reinfarction rate was higher in patients treated with earlier thrombolysis.

The effect of collateral flow and myocardial viability on the distribution of technetium-99m sestamibi in a closed-chest model of coronary occlusion and reperfusion.

Myocardial uptake of technetium-99m sestamibi at low coronary flow rates overestimates blood flow, but the relative impact of flow and viability on 99mTc-sestamibi kinetics is unclear. The objective of this study was to determine the effect of myocardial viability and the degree of collateral blood flow on the uptake and retention of 99mTc-sestamibi by examining three animal models of coronary occlusion and reperfusion, each reflecting a different state of viability and collateral blood flow. Three closed-chest animal models were studied: canine (high collateral flow, preserved viability), porcine (low collateral flow, absent viability) and porcine with slowly occlusive coronary stents producing infarction and enhanced collateral blood flow (high collateral flow, absent viability). There were seven dogs, seven pigs and six pigs, respectively, in each animal model. Animals from all three models were subjected to a 40-min total left anterior descending artery (LAD) occlusion followed by 2 h of reperfusion. 99mTc-sestamibi and radiolabelled microspheres were injected during LAD occlusion 10 min prior to reperfusion. Animals were sacrificed after 2 h of reperfusion flow. Ex situ heart slice imaging to determine risk area was followed by viability staining to determine infarct size. Slices were subsequently sectioned into equally sized radial segments and placed in a gamma well counter. Risk area as determined by ex situ 99mTc-sestamibi imaging was not significantly different by model. Pathological infarct size differed significantly by model [canine = 1%+/-1% of the left ventricle (LV); porcine = 13%+/-8% LV; porcine with stent = 14%+/-7% LV; P = 0.002)]. Collateral blood flow by microspheres during occlusion tended to differ among models (overall P = 0.08), with the canine and porcine with stent models having relatively high flow rates compared with the acute porcine model. 99mTc-sestamibi activity correlated with microsphere blood flow in all three models, with r values for individual animals (n = 20) ranging from 0.86 to 0.96 (all P<0.0001). There was a significant difference in the regression line intercepts (P<0.0001) and slopes (P<0.01) among the three models comparing 99mTc-sestamibi uptake with myocardial blood flow. 99mTc-sestamibi uptake overestimated blood flow to a greater extent in the canine model (high flow with viability) than in the porcine model (low flow, absent viability). Despite enhanced collateral flow, there was significantly less overestimation of flow in the porcine stent model (high flow, absent viability). In conclusion, at low flow rates 99mTc-sestamibi activity overestimates myocardial blood flow. This effect is most pronounced in myocardium with significant collateral flow and preserved viability, consistent with over-extraction or redistribution of the tracer. The effect is markedly decreased in non-viable myocardium regardless of blood flow.

Identification of severe coronary artery disease in patients with a single abnormal coronary territory on exercise thallium-201 imaging: the importance of clinical and exercise variables.

OBJECTIVES: The aim of this study was to determine which clinical, exercise and thallium variables can aid in the identification of three-vessel or left main coronary artery disease (3VLMD) in patients with one abnormal coronary territory (either a reversible or fixed defect) on exercise thallium testing and to test the prognostic value of these variables. BACKGROUND: Although the sensitivity of detection of coronary artery disease by thallium-201 imaging is high, the actual detection of 3VLMD by thallium tomographic images alone is not optimal. METHODS: A multivariate model for prediction of 3VLMD was developed from several clinical, exercise and thallium-201 variables in a training population of 264 patients who had one abnormal coronary artery territory on exercise thallium testing and had undergone coronary angiography. Using this model, patients were stratified into risk groups for prediction of 3VLMD. A separate validation cohort of 474 consecutive patients who were treated initially with medical therapy and who had one abnormal coronary territory were divided into identical risk groupings by the variables derived from the training population, and they were followed for a median of 7.0 years to evaluate the prognostic value of this model. RESULTS: The prevalence of 3VLMD was 26% in the training population despite one abnormal thallium coronary territory. Four clinical and exercise variables--diabetes, hypertension, magnitude of ST segment depression, and exercise rate-pressure product-were found to be independent predictors of 3VLMD. In the training population, the prevalence of 3VLMD in low-, intermediate- and high-risk groups was 15%, 22% and 51%, respectively. When the multivariate model was applied to the validation population, the eight-year overall survival rates in the low-, intermediate- and high-risk groups were 89%, 73% and 75%, respectively (p < 0.001). CONCLUSIONS: A substantial proportion of patients with one abnormal thallium coronary territory have 3VLMD with subsequent divergent outcomes based upon risk stratification by clinical and exercise variables. Consequently, the finding of only a single abnormal coronary territory by thallium-201 perfusion imaging does not necessarily confer a benign prognosis in the absence of consideration of nonimaging variables.

Infarct size measured by single photon emission computed tomographic imaging with (99m)Tc-sestamibi: A measure of the efficacy of therapy in acute myocardial infarction.

BACKGROUND: Use of mortality as an end point in randomized trials of reperfusion therapy requires increasingly large sample sizes to test advances compared with existing therapy, which is already highly effective. There has been a growing interest in infarct size measurements by (99m)Tc-sestamibi SPECT (single photon emission computed tomographic) imaging as a surrogate end point. METHODS AND RESULTS: We reviewed the reports published in English regarding infarct size measurements by (99m)Tc-sestamibi. Four separate lines of published evidence support the validity of SPECT imaging with (99m)Tc-sestamibi for determination of infarct size. This end point has been used in a total of 7 randomized trials-1 single center and 6 multicenter. The end point compares favorably with left ventricular function and infarct size measurements with the use of other radiopharmaceuticals. The most important limitation of this approach is the absence thus far of a randomized trial that has shown a corresponding decrease in mortality in association with a therapy that reduces infarct size. CONCLUSIONS: SPECT imaging with (99m)Tc-sestamibi is the best available measurement tool for infarct size. It has already served as an end point in early pilot studies to evaluate potential efficacy and in dose-ranging studies. It has the potential to serve as a surrogate end point to uncover advantages of new therapies that may be equivalent to existing therapies with respect to early mortality.

Is rest or exercise hypertension a cause of a false-positive exercise test?

STUDY OBJECTIVES: To determine if a history of hypertension or an exaggerated rise in exercise systolic BP is associated with a false-positive exercise ECG. DESIGN, SETTING, AND PATIENTS: Retrospective analysis of the associations between exercise-induced ST-segment depression and a history of hypertension, exercise systolic BP, and several other clinical and exercise test variables. Among 20,097 patients referred for exercise tomographic thallium imaging in a nuclear cardiology laboratory at a tertiary care center, 1,873 patients met inclusion criteria for this study, which included no history of myocardial infarction or coronary artery revascularization, a normal resting ECG, and normal exercise thallium images. RESULTS: False-positive ST-segment depression occurred in 20% of the population. A history of hypertension was actually associated with a lower likelihood of ST-segment depression (odds ratio, 0.70; 95% confidence interval [CI], 0.55 to 0.89; p = 0. 004). A higher peak exercise systolic BP was associated with a higher likelihood of ST-segment depression (odds ratio, 1.08 for each 10-mm Hg increase in systolic BP; 95% CI, 1.03 to 1.14; p < 0. 001). However, the association between peak exercise systolic BP and ST-segment depression was so weak that this measurement could not be predictive in the individual patient (R(2) = 0.2%). For every 20-mm Hg increase in peak exercise systolic BP, the percentage of patients with ST-segment depression increased by only 3%. CONCLUSIONS: In patients with normal resting ECGs, we conclude the following: (1) a history of hypertension is not a cause of a false-positive exercise test, and (2) higher exercise systolic BP is a significant but weak predictor of ST-segment depression.

A systematic analysis of factors which may impact upon tomographic perfusion imaging measurements: implications for the use of Tc-99m sestamibi in acute myocardial infarction.

BACKGROUND: The use of acute Tc-99m sestamibi imaging has provided a valuable methodology to assess myocardium at risk and collateral blood flow. OBJECTIVE: The purpose of this study was to determine the impact of physical, physiologic, and reconstruction factors on the extent and severity of Tc-99m sestamibi images in a porcine model of coronary occlusion and reperfusion. METHODS AND RESULTS: Eleven pigs underwent 40 min of coronary occlusion using a balloon catheter followed by reperfusion. Radiolabeled microspheres were injected during occlusion for blood flow determination and 20-30 mCi of Tc-99m sestamibi was injected intravenously for cardiac imaging. Each animal underwent four modes of gamma camera imaging: a cardiac and respiratory gated SPECT study, an ungated SPECT study, a post-mortem SPECT study and an ex-situ study where the heart was sliced into five short axis slices and directly imaged. All animals had extensive wall motion abnormalities at the time of imaging. Myocardial risk area by ex-situ imaging was 32 +/- 9% LV and did not significantly change with the addition of a chest cavity and tomographic reconstruction (post-mortem and gated imaging) or cardiac and respiratory motion (ungated imaging). Defect severity was significantly underestimated with the addition of a chest cavity and tomographic reconstruction but was unaltered by cardiac and respiratory motion. CONCLUSIONS: The assessment of risk area acutely by SPECT Tc-99m sestamibi imaging is unaffected by cardiac motion obviating the necessity for gated imaging. Estimated defect severity (which has been used as a measure of collateral flow) is significantly reduced by the chest wall and tomographic acquisition and reconstruction suggesting a role for scatter and attenuation algorithms for this measure.

Threshold values for preserved viability with a noninvasive measurement of collateral blood flow during acute myocardial infarction treated by direct coronary angioplasty.

BACKGROUND: Quantitative measures of myocardial perfusion defect severity from acute (99m)Tc-sestamibi tomographic images (nadir) have correlated closely with collateral and residual antegrade blood flow during acute myocardial infarction. The purpose of this study was to determine whether a viability threshold could be identified from this measure in patients with acute myocardial infarction treated in a homogeneous manner with successful reperfusion therapy. METHOD AND RESULTS: The study group consisted of 61 patients with acute myocardial infarction with a risk area of >6% LV treated with primary angioplasty between 120 and 240 minutes after symptom onset. All patients were injected with 20 to 30 mCi of (99m)Tc-sestamibi before primary angioplasty and imaged after the procedure. Acute myocardium at risk (MAR) and subsequent infarct size (IS) were quantified by a threshold program. Severity (nadir) from the acute image was the lowest ratio of minimal/maximum counts from 5 short-axis slices. Infarct location was anterior in 22 and inferior in 39 patients. MAR was 33+/-15% LV and IS was 13+/-15% LV: 23 patients had no infarction despite MAR similar to those with infarction. Receiver-operator characteristic curve analysis identified a nadir value of 0.26 as providing the best separation of patients with and without infarction (sensitivity, 74%; specificity, 74%). This nadir threshold varied by infarct location: anterior defect, 0.21; inferior defect, 0.31. The sensitivity and specificity for absent infarction for these values were anterior, 69% and 67%, and inferior, 88% and 84%, respectively. CONCLUSIONS: In a time frame in which the presence of residual blood flow is important, the severity of the acute (99m)Tc-sestamibi defect can be used to predict whether infarction will develop despite successful reperfusion.

Comparison of acute myocardial infarct size to two-year mortality in patients <65 to those > or =65 years of age.

Older patients have higher in-hospital and longer term mortality after myocardial infarction. To determine if larger infarct size correlates with this observation, myocardium at risk was measured on arrival to the hospital in 347 patients with acute myocardial infarction, and final infarct size was measured at hospital discharge in a subset of 274 of these patients. Myocardium at risk and final infarct size were quantified by tomographic technetium-99m sestamibi imaging. Statistical analyses examined the associations between age, myocardium at risk, final infarct size, and both in-hospital and postdischarge mortality. Median value for age was 64 years, and myocardium at risk was 24% and final infarct size was 12% of the left ventricle. There was no correlation between age and myocardium at risk (r = 0.04, p = NS) or final infarct size (r = 0.06, p = NS). In-hospital mortality was 4% overall and was 2% for patients <65 years old versus 6% for those > or =65 years old (chi-square 11.3, p<0.001). In-hospital mortality was not associated with myocardium at risk (chi square <1, p = NS). For the subset of 274 patients in whom final infarct size was measured, the subsequent 2-year mortality rate was 3% and was independently associated with both age (chi-square 15.6, p<0.001) and final infarct size (chi-square 9.7, p = 0.002). Survival was excellent for patients who were either <65 years old (2-year mortality 1%) or had an infarct size <12% (2-year mortality 0%). For patients > or =65 years old with infarct size > or =12%, 2-year mortality was 13%. These results demonstrate that older patients do not have larger infarcts. Advanced age is associated with higher in-hospital and postdischarge mortality, independent of infarct size.

Independent and incremental value of coronary artery calcium for predicting the extent of angiographic coronary artery disease: comparison with cardiac risk factors and radionuclide perfusion imaging.

OBJECTIVES: The study was done to test the ability to predict the extent of angiographically determined coronary artery disease (CAD) by quantification of coronary calcium using electron-beam computed tomography (EBCT) and to compare it with more conventional parameters for delineating the angiographic extent of CAD, that is, cardiovascular risk factors and radionuclide single-photon emission computed tomography (SPECT). BACKGROUND: The angiographic extent of CAD is a powerful predictor of subsequent events. Use of EBCT may be able to define it by virtue of its ability to determine plaque burden. METHODS: We examined 308 patients presenting with suspected but not previously known CAD who underwent selective coronary angiography. As measures of the angiographic extent of CAD, coronary artery greater even 20 (CAGE > or =20) and CAGE > or =50 scores represented the total number of coronary segments with > or =20% or > or =50% stenoses, respectively. The EBCT-derived total calcium scores were obtained in 291 patients, risk factors as defined by the National Cholesterol Education Program in 239 patients, and SPECT scans in 136 patients. RESULTS: Using multiple linear regression analysis, total calcium scores were better independent predictors of both CAGE > or =20 and CAGE > or =50 scores than either a SPECT-derived radionuclide perfusion score or the risk factors age, male gender and ratio of total/high-density lipoprotein (HDL) cholesterol. The association between EBCT and angiographic scores remained highly significant after excluding the influence of all interrelated risk factors and SPECT variables (r = 0.65; p < 0.001 for CAGE > or =20 scores, r = 0.50; p < 0.001 for CAGE > or =50 scores). CONCLUSIONS: Coronary calcium predicts the angiographic extent of CAD in symptomatic patients and provides independent and incremental information to the more conventional clinical parameters derived from SPECT or risk assessment.

Prognostic value of a treadmill exercise score in symptomatic patients with nonspecific ST-T abnormalities on resting ECG.

CONTEXT: Exercise testing of patients with ST-T abnormalities on the resting electrocardiogram (ECG) is problematic because in the presence of pre-existing ST-T abnormalities, the exercise test is less specific for the diagnosis of coronary artery disease. The prognostic capability of the Duke treadmill score in patients with ST-T abnormalities vs those with normal findings on resting ECG has, to our knowledge, not been evaluated. OBJECTIVE: To compare the prognostic accuracy of the Duke treadmill score in patients with nonspecific ST-T abnormalities vs those with normal results on resting ECG. DESIGN: Inception cohort study with 7 years of follow-up. SETTING: Nuclear cardiology laboratory of a US referral center. PATIENTS: All symptomatic patients who underwent exercise thallium testing between 1989 and 1991,939 of whom had nonspecific ST-T abnormalities and 1466 of whom had normal findings on resting ECG. Exclusion criteria included congenital, valvular, or cardiomyopathic heart disease; prior coronary artery revascularization; resting ECG with secondary ST-T abnormalities; or missing data. MAIN OUTCOME MEASURES: Rates of overall mortality and cardiac death for subjects classified by Duke treadmill score risk group. RESULTS: For the end point cardiac death, 7-year survival in the study population in the low-, intermediate-, and high-risk groups was 97%, 92%, and 76%, respectively (P<.001). Compared with the control group, the study group had lower 7-year survival (94% vs 98%; P<.001), fewer low-risk patients (426 [45%] vs 811 [55%]; P<.001) with worse 7-year survival (97% vs 99%; P= .008), and more high-risk patients (49 [5%] vs 34 [2%];P<.001) with a nonsignificant trend toward worse 7-year survival (76% vs 93%; P= .36). CONCLUSIONS: The Duke treadmill score can effectively risk-stratify patients with ST-T abnormalities on the resting ECG. In classified risk categories, patients with ST-T abnormalities have a worse prognosis than those with normal results on resting ECG.

Determinants of infarct size after thrombolytic treatment in acute myocardial infarction.

Both experimental and single-center clinical studies have shown that myocardium at risk, residual collateral flow, and duration of coronary occlusion are important determinants of final infarct size. The purpose of this study was to replicate these results on a multicenter basis to demonstrate that perfusion imaging using different camera and computer systems can provide reliable assessments of myocardium at risk and collateral flow. Sequential tomographic myocardial perfusion imaging with technetium-99 (Tc-99m) sestamibi was performed in 74 patients with first time myocardial infarction, who were enrolled in a multicenter, randomized, double-blind, placebo-controlled pilot study of poloxamer 188 as ancillary therapy to thrombolysis. All patients underwent thrombolysis within 6 hours of the onset of chest pain. Tc-99m sestamibi was injected intravenously at the initiation of thrombolytic therapy, and tomographic imaging was performed 1 to 6 hours later to assess myocardium at risk. Collateral flow was estimated noninvasively from the acute sestamibi images by 3 methods that assess the severity of the perfusion defect. Final infarct size was determined at hospital discharge by a second sestamibi study. Myocardium at risk (r = 0.61, p <0.0001) and radionuclide estimates of collateral flow (r = 0.58 to 0.66, all p <0.0001) were significantly associated with final infarct size. These associations were independent of the treatment center. On a multivariate basis, myocardium at risk (p = 0.003), the radionuclide estimate of collateral flow (p = 0.03), and treatment arm (p = 0.04) were all independent determinants of infarct size. Time to thrombolytic therapy showed only a trend (p = 0.10). The treatment center was not significant (p = 0.42). Myocardium at risk and collateral flow are important determinants of infarct size that are independent of treatment center. Tomographic imaging with Tc-99m sestamibi can provide noninvasive assessments of these parameters in multicenter trials of thrombolytic therapy.

Variability of myocardium at risk for acute myocardial infarction.

The objective of this study was to assess the variability in myocardium at risk and relate this to coronary angiographic variables. One hundred ninety-seven patients with > or = 1-mm ST-segment elevation in 2 contiguous electrocardiographic leads, without prior myocardial infarction, were injected with technetium-99m sestamibi acutely before reperfusion therapy. The perfusion defect was quantified to determine myocardium at risk for infarction. Patients underwent coronary angiography to determine the infarct-related artery and to classify the occlusion as proximal or not proximal. Collateral and anterograde (Thrombolysis In Myocardial Infarction [TIMI] trial) flow were assessed in a subset of 83 patients with angiography before direct angioplasty. Myocardium at risk for infarction in the distribution of the left anterior descending coronary artery was significantly greater (p <0.0001) than that in the circumflex or right coronary artery. In the left anterior descending coronary artery distribution, myocardium at risk for infarction was significantly larger for proximal occlusions (p <0.0001). There was a trend toward greater myocardium at risk for infarction of proximal occlusions (p = 0.14) of the left circumflex but not for proximal occlusions in the right coronary artery distribution (p = 0.47). Multivariate analysis revealed that the infarct-related artery (p <0.0001), TIMI flow (p = 0.0002), and proximal location (p = 0.09) in the infarct-related artery were independent predictors of myocardium at risk for infarction. Thus, infarct-related artery, TIMI flow, and proximal location of occlusion in the infarct-related artery influence the myocardium at risk for infarction, which is highly variable for given location of occlusion.

Twelve-year outcome of patients with an abnormal exercise radionuclide left ventricular angiogram and angiographically insignificant coronary artery disease.

This study examines the long-term prognosis of patients with an abnormal exercise radionuclide angiogram in the absence of significant angiographic coronary artery disease (CAD). In general, patients without significant CAD have an excellent prognosis, but the long-term outcome for the subset of patients with an "ischemic" exercise test is not known. In this study, 161 patients with normal coronary arteries or insignificant CAD (< 50% left main and < 70% left anterior descending, left circumflex, or right), resting left ventricular (LV) ejection fraction > or = 0.50, and an abnormal exercise radionuclide angiogram (LV ejection fraction that decreased with exercise or peak exercise LV ejection fraction < 0.60) were followed for a median duration of 11.3 years. The mean delta LV ejection fraction was -0.07, 98 patients (61%) had a decrease in LV ejection fraction of > or = 5 units, and 40 patients (25%) had peak exercise LV ejection fraction < 0.50. During follow-up there were 19 deaths (only 1 of which was cardiac), 7 nonfatal myocardial infarctions, and 9 revascularization procedures. At 12 years, overall survival was 88%, better than the expected survival for the age- and sex-matched general population. Survival free of cardiac death or myocardial infarction was 94% and survival free of any cardiac event including revascularization was 88%. Thus, patients with an abnormal exercise radionuclide angiogram but without significant CAD have an excellent long-term prognosis.

Measurement of myocardial infarct size by electron beam computed tomography: a comparison with 99mTc sestamibi.

RATIONALE AND OBJECTIVES: The authors sought to determine, using a variety of regional left ventricular ejection fraction (EF) and wall thickening (WTh) criteria, the applicability to measure left ventricular (LV) infarct size using electron-beam CT (EBCT) in patients as compared with technetium 99m (99mTc) sestamibi scanning as reference standard. METHODS: Twelve patients (age 57 +/- 11 years) underwent 99mTc sestamibi scanning and EBCT at hospital discharge after an acute index anterior myocardial infarction. Left ventricular infarct size was defined using standard 99mTc sestamibi scanning. Regional EF and WTh were analyzed on each EBCT scan with use of a floating epicardial centroid method. In five contiguous LV tomograms, the amount of infarcted myocardium was estimated using the following EF and WTh criteria: EF < or = 35%, 30%, 25%, 20%, and WTh < or = 2 mm, 1 mm, and 0 mm. RESULTS: Infarct size measured with 99mTc sestamibi was 33.3% (+/- 18.3%) (mean +/- SD, range 6%-54%) of the LV. Using an EF < or = 35% or absolute WTh < or = 2 mm as criteria for infarcted myocardium, EBCT yielded 28% (+/- 17%) and 27% (+/- 16%), respectively (P = NS, paired Student's t test, versus 99mTc sestamibi). Although, with use of the other criteria, EBCT tended to underestimate infarct size compared with 99mTc sestamibi, a close correlation across the entire range of infarct size determinations (range, 0.72-0.82) regardless of the underlying criteria suggested an internal consistency of the data. CONCLUSIONS: Quantitative analysis of regional myocardial function by EBCT allows an estimate of anterior infarct size when compared with 99mTc sestamibi. This suggests that in addition to previously established applications after acute myocardial infarction such as examination of cardiac volumes and mass, EBCT also may provide for infarct size determination.

Reversible perfusion defects on exercise tomographic thallium imaging in patients with and without collateral flow.

A consecutive series of patients underwent exercise thallium imaging and coronary angiography that identified single-vessel right coronary artery disease. Redistribution in the left anterior descending territory was significantly associated with the presence of left-to-right collaterals, whereas collaterals were significantly less frequent in individuals who did not exhibit redistribution.

Correlation of resting first-pass left ventricular ejection fraction and resting myocardial infarct size.

This study determined the correlation between the extent of the resting perfusion defect by technetium-99m sestamibi tomographic imaging and the first-pass left ventricular (LV) ejection fraction (EF). A total of 1,955 patients underwent technetium-99m sestamibi tomographic imaging with measurement of first-pass resting LVEF. Twenty-five percent of patients had a prior history of myocardial infarction. First-pass LVEF was measured using a peripheral intravenous injection and a multicrystal gamma camera with standard software. Resting tomographic perfusion defect size (infarct size) was quantitated using previously published methods. Mean LVEF for the study group was 0.60 +/- 0.11. Mean LV infarct size was 5 +/- 11%. For the 1,265 patients (65% of the study group) with no measurable perfusion defect, the prevalence of a normal (> or = 0.50) LVEF was 96% (1,212 of 1,265 patients). For patients with a measurable defect (n = 690, 35%), the inverse linear correlation with LVEF was highly significant (r = -0.60, p <0.0001) but with wide confidence limits (SEE = 10 LVEF points), thereby limiting the predictive value in individual patients. Thus, in the absence of known cardiomyopathy, valvular heart disease, or left bundle branch block, patients without a quantifiable resting perfusion defect are highly likely to have a normal resting LVEF and may not require determination of LV function. For patients with resting perfusion defects, LVEF cannot be predicted with confidence and should therefore be measured.

Prognostic value of vasodilator myocardial perfusion imaging in patients with left bundle-branch block.

BACKGROUND: The prognostic value of tomographic myocardial perfusion imaging with dipyridamole or adenosine in patients with left bundle-branch block has not been established. METHODS AND RESULTS: The study group consisted of 245 patients with left bundle-branch block who underwent tomographic (single photon emission tomography) myocardial perfusion imaging with thallium-201 (n=173) or technetium-99m sestamibi (n=72) and either dipyridamole (n=153) or adenosine (n=92) stress. Patients were prospectively classified into two groups. Patients were classified as "high risk" if they had (1) a large severe fixed defect (n=28), (2) a large reversible defect (n=36), or (3) cardiac enlargement and either increased pulmonary uptake (thallium) or a decreased resting ejection fraction (sestamibi) (n=20). The remaining 161 patients (66% of the study group) were at "low risk." Follow-up was 99% complete at 3+/-1.4 years. Three-year overall survival was 57% in the high-risk group compared with 87% in the low-risk group (P<.0001). Survival free of cardiac death/nonfatal myocardial infarction/cardiac transplantation was 55% in the high-risk group and 93% in the low-risk group (P<.0001). The presence of a high-risk scan had significant incremental prognostic value after adjustment for age, sex, diabetes, and previous myocardial infarction (P<.0001). Patients with a low-risk scan had an overall survival that was not significantly different from that of a US age-matched population (P=.86). CONCLUSIONS: Tomographic myocardial perfusion imaging with adenosine or dipyridamole stress provides important prognostic information in patients with left bundle-branch block, which is incremental to clinical assessment.