Quantitative adenosine 201Tl single-photon emission computed tomography for the early assessment of patients surviving acute myocardial infarction

Clinical significance of right ventricular activity on treadmill thallium-201 myocardial single-photon emission computerized tomography using cadmium-zinc-telluride cameras

OBJECTIVE

Identification of right ventricular (RV) abnormalities is important in patients with suspected coronary artery disease (CAD). RV activity can be better visualized on myocardial single-photon emission computerized tomography (SPECT) using a higher sensitivity cadmium-zinc-telluride (CZT) detector. The aim of this study was to investigate the clinical significance of RV/left ventricular (LV) uptake ratios during exercise thallium-201 SPECT using CZT detectors.

PATIENTS AND METHODS

A total of 102 patients underwent treadmill ECG-gated SPECT, coronary angiography, and echocardiography. SPECT myocardial perfusion was interpreted using a 17-segment model and a 0-4-point scale. RV/LV uptake ratios were calculated on the basis of maximum counts per pixel within the entire RV and LV walls. The relationships between RV/LV uptake ratio and gated SPECT, presence of CAD (≥50% stenosis in the left main or ≥70% in the main branches), demographics, and echocardiographic parameters were analyzed.

RESULTS

Stress RV/LV ratios correlated positively with the presence of left main or multivessel disease, and tricuspid regurgitation maximum pressure gradient. After multivariate regression, stress/rest RV/LV ratios correlated positively with mitral flow deceleration time, age, female sex, and use of β-blockers.

CONCLUSION

RV/LV uptake ratios on the basis of exercise myocardial perfusion SPECT imaging using CZT cameras are useful for the detection of severe CAD and could serve as an indicator of pulmonary hypertension and LV diastolic dysfunction.

Surgical ventricular restoration improves the left ventricle basal wall function using quantitative gated SPECT

OBJECTIVE

It is not clear whether surgical ventricular restoration (SVR) or procedures approaching mitral complex for controlling functional mitral regurgitation (MR) affect the regional left ventricular wall function. The purpose of the present study was to evaluate the regional LV function after SVR using overlapping left ventriculoplasty (OLVP) using quantitative gated myocardial perfusion SPECT (QGS).

PATIENTS AND METHOD

Forty-one heart failure patients, including those with ischemic cardiomyopathy (ICM) (n = 25) and non-ICM (NICM) (n = 16), underwent SVR and/or papillary muscle approximation (PMA). The rest myocardial perfusion SPECT were performed before and early after operation (mean 25.8 ± 10.6 days). These patients were divided into 4 groups based on the surgical procedures (SVR and/or PMA) and etiology of patients (ICM or NICM) as follows: SVR (with or without PMA) of ICM, SVR of NICM, PMA of ICM and PMA of NICM groups. The regional wall thickening was compared before and after the operation between the four groups.

RESULTS

NYHA functional classes were improved after the operation in all four groups. MR grade was also improved in three groups other than SVR of the ICM group. The left ventricular basal wall thickening was improved postoperatively in following three groups (SVR of ICM: 12.7 ± 3.8% to 16.5 ± 4.6% p <0.05, PMA of ICM: 11.1 ± 4.3% to 14.9 ± 4.8% p <0.05, SVR of NICM: 5.8 ± 6.6% to 12.3 ± 6.4% p <0.05), whereas PMA of the NICM group did not show an improvement. Wall thickening in the middle and distal levels was not improved in all groups.

CONCLUSION

OLVP improved NYHA functional classes, and also improved the regional wall function at the basal level of the left ventricle. In contrast, lone PMA did not improve or impair the regional wall function at any of the levels.

Predicting clinically unrecognized coronary artery disease: use of two- dimensional echocardiography

BACKGROUND

2-D Echo is often performed in patients without history of coronary artery disease (CAD). We sought to determine echo features predictive of CAD.

METHODS

2-D Echo of 328 patients without known CAD performed within one year prior to stress myocardial SPECT and angiography were reviewed. Echo features examined were left ventricular and atrial enlargement, LV hypertrophy, wall motion abnormality (WMA), LV ejection fraction (EF) < 50%, mitral annular calcification (MAC) and aortic sclerosis/stenosis (AS). High risk myocardial perfusion abnormality (MPA) was defined as >15% LV perfusion defect or multivessel distribution. Severe coronary artery stenosis (CAS) was defined as left main, 3 VD or 2VD involving proximal LAD.

RESULTS

The mean age was 62 +/- 13 years, 59% men, 29% diabetic (DM) and 148 (45%) had > 2 risk factors. Pharmacologic stress was performed in 109 patients (33%). MPA was present in 200 pts (60%) of which, 137 were high risk. CAS was present in 166 pts (51%), 75 were severe. Of 87 patients with WMA, 83% had MPA and 78% had CAS. Multivariate analysis identified age >65, male, inability to exercise, DM, WMA, MAC and AS as independent predictors of MPA and CAS. Independent predictors of high risk MPA and severe CAS were age, DM, inability to exercise and WMA. 2-D echo findings offered incremental value over clinical information in predicting CAD by angiography. (Chi square: 360 vs. 320 p = 0.02).

CONCLUSION

2-D Echo was valuable in predicting presence of physiological and anatomical CAD in addition to clinical information.

International variations in the ischemic burden post-acute myocardial infarction: prognostic implications

OBJECTIVES

To determine if there is a variation in the ischemic burden post-acute myocardial infarction (AMI), as assessed by myocardial perfusion imaging (MPI), between different populations in different geographic locations and to see if this variation is associated with different clinical outcomes.

METHODS AND RESULTS

We characterized the MPI findings in 104 stable patients who were hospitalized with AMI at the American University of Beirut Medical Center (AUBMC), a tertiary referral hospital in an East Mediterranean country and we compared them to 126 patients who were enrolled according to a similar protocol in a previous study done at Baylor College of Medicine (BCM), Houston, Texas. There were no differences between the two populations with respect to prevalence of diabetes, hypertension, smoking, the use of thrombolysis, percentage of anterior MIs, Q-wave MIs, and multivessel disease on coronary angiography. However, the quantified ischemic defect size in the BCM population was double that in the AUBMC population (12 +/- 12% vs 6 +/- 8%, P < .01). This was associated with almost doubling of the 1 year event rate of death/myocardial infarction (18.3% vs 10.6%, P = .02) in the BCM population.

CONCLUSION

Our study suggests that the ischemic burden post-AMI, as assessed by MPI, might vary between different populations in different geographic locations. This variation carries important prognostic implications and is associated with different patient outcomes.

Prognostic value of adenosine Tl-201 myocardial perfusion imaging after acute myocardial infarction: results of a prospective clinical trial

BACKGROUND

We have previously shown in retrospective studies that adenosine myocardial perfusion imaging (MPI) done after acute myocardial infarction (AMI) can effectively predict the risk of future cardiac events in these patients. The objective of this study was to validate these observations in a prospective clinical trial.

METHODS AND RESULTS

One hundred twenty-six stable patients underwent quantitative adenosine MPI at a mean of 4.5 +/- 2.9 days after AMI. On the basis of the MPI results, they were divided into 3 risk groups: low risk (< 20% perfusion defect), intermediate risk (> or = 20% perfusion defect with < 10% ischemia), and high risk (> or = 20% perfusion defect with > 10% ischemia). The patients were followed up for 11 +/- 5 months for the occurrence of cardiac events: death, myocardial infarction, unstable angina, or congestive heart failure. The actual event rates correlated very well with the prespecified risk groups (19% for the low-risk group, 28% for the intermediate-risk group, and 78% for the high-risk group; P < .001). The significant multivariate predictors for events were female gender (relative risk [RR], 2.90; P = .002), left ventricular ejection fraction (RR, 1.34; P = .04), and ischemic defect size (RR, 1.46; P = .001), with a global chi2 value of 26.7.

CONCLUSION

This study demonstrates, in a prospectively designed clinical trial, that quantitative adenosine MPI performed soon after AMI can effectively predict the risk of future cardiac events. These findings are currently being validated in an ongoing, large, multicenter, international clinical trial.

Adenosine sestamibi SPECT post-infarction evaluation (INSPIRE) trial: A randomized, prospective multicenter trial evaluating the role of adenosine Tc-99m sestamibi SPECT for assessing risk and therapeutic outcomes in survivors of acute myocardial infarction

BACKGROUND

Preliminary studies indicate that adenosine myocardial perfusion single photon tomography (SPECT) can safely and accurately stratify patients into low and high risk groups early after acute myocardial infarction (AMI).

METHODS AND RESULTS

INSPIRE is a prospective, randomized multicenter trial which enrolled 728 clinically stable survivors of AMI. Following baseline adenosine sestamibi gated SPECT, patients were classified as low, intermediate or high risk based on the quantified total and ischemic left ventricular (LV) perfusion defect size (PDS). A subset of high risk patients with a LV ejection fraction > or =35% were randomized to a strategy of either intensive medical therapy or coronary revascularization. Adenosine SPECT was repeated at 6-8 weeks to determine the relative effects of anti-ischemic therapies on total and ischemic PDS (primary endpoint). All patients were followed for one year. The baseline demographic, clinical and scintigraphic characteristics of the study population are presented. Adenosine SPECT was performed within 1 day of admission in 12% of patients and in 64% by Day 4.

CONCLUSION

The unique study design features of INSPIRE will further clarify the role of adenosine sestamibi SPECT in defining initial patient risk after AMI and in monitoring the benefits of intensive anti-ischemic therapies.

A randomized, double-blind, placebo-controlled trial of Ad5FGF-4 gene therapy and its effect on myocardial perfusion in patients with stable angina

OBJECTIVES

The primary objective of this study was to determine whether intracoronary administration of the adenoviral gene for fibroblast growth factor (Ad5FGF-4) can improve myocardial perfusion compared with placebo.

BACKGROUND

Animal studies and observational clinical studies have shown improvement in perfusion of the ischemic myocardium using genes encoding angiogenic growth factors; however, randomized, double-blind data in humans are lacking.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of intracoronary injection of 10(10) adenoviral particles containing a gene encoding fibroblast growth factor (Ad5FGF-4) to determine the effect on myocardial perfusion. Fifty-two patients with stable angina and reversible ischemia comprising >9% of the left ventricle on adenosine single-photon emission computed tomography (SPECT) imaging were randomized to gene therapy (n = 35) or placebo (n = 17). Clinical follow-up was performed, and 51 (98%) patients underwent a second adenosine SPECT scan after 8 weeks.

RESULTS

Overall (n = 52), the mean total perfusion defect size at baseline was 32.4% of the left ventricle, with 20% reversible ischemia and 12.5% scar. At eight weeks, Ad5FGF-4 injection resulted in a significant reduction of ischemic defect size (4.2% absolute, 21% relative; p < 0.001) and placebo-treated patients had no improvement (p = 0.32). Although the change in reversible perfusion defect size between Ad5FGF-4 and placebo was not significant (4.2% vs. 1.6%, p = 0.14), when a single outlier was excluded a significant difference was observed (4.2% vs. 0.8%, p < 0.05). Ad5FGF-4 was well tolerated and did not result in any permanent adverse sequelae.

CONCLUSIONS

Intracoronary injection of Ad5FGF-4 showed an encouraging trend for improved myocardial perfusion; however, further studies of therapeutic angiogenesis with Ad5FGF-4 will be necessary.

Selective A2A adenosine receptor agonist as a coronary vasodilator in conscious dogs: potential for use in myocardial perfusion imaging

The authors sought to demonstrate the advantages of a selective, potent, short-acting A adenosine receptor agonist, CVT-3146 (2-(N-pyrazolyl)Ado derivative), for potential clinical use as a coronary vasodilator during myocardial perfusion imaging. The use of adenosine in a pharmacological stress test during myocardial imaging is limited by side effects mediated by A1 and A2B adenosine receptors and by its ultrashort duration of action. CVT-3146 (0.1-5 microg/kg) and adenosine (13-267 microg/kg) were given as peripheral intravenous injections in 10 awake dogs instrumented for measurement of coronary blood flow (CBF). CVT-3146 caused a dose-dependent increase of CBF (ED50 = 0.34 +/- 0.08 microg/kg, maximal increase = 221 +/- 18%, n = 6). Adenosine was less potent (ED = 51 +/- 15 microg/kg, p < 0.05) but equieffective (maximal increase in CBF = 227 +/- 11%). The increase in CBF caused by 2.5 microg/kg CVT-3146 reached 84 +/- 5% of the maximal reactive hyperemia following 20 s of coronary occlusion (n = 4). After a 10-s injection of CVT-3146 (2.5 microg/kg), the increase in CBF remained at least twofold above baseline for 97 +/- 14 s, whereas for adenosine (267 microg/kg), the twofold increase in CBF lasted only 24 +/- 2 s (p < 0.01, n = 6). A 30-s injection of 2.5 microg/kg CVT-3146 prolonged the twofold increase in CBF up to 221 +/- 20 s. No atrioventricular block was noted. At 2.5 microg/kg, the peak effect of CVT-3146 on CBF was associated with a short-lasting (20 +/- 6 s) increase in heart rate (78 +/- 9 bpm) and decrease in mean arterial blood pressure (13 +/- 6 mm Hg, p < 0.05, n = 6). CVT-3146 is a potent coronary vasodilator. Its short duration of action, minimal and transient systemic hemodynamic effects, and ease of administration may make this agonist suitable for pharmacological coronary vasodilation during myocardial perfusion imaging for noninvasive detection of subcritical arterial stenosis.

Adenosine myocardial perfusion single photon emission computed tomographic stress testing 24-72 h after uncomplicated myocardial infarction

Safety of performing adenosine myocardial perfusion stress testing as early as 24 h after acute uncomplicated myocardial infarction is not known. We evaluated 31(14 females and 17 males, average age 72, range 46-89 years) consecutive patients with uncomplicated myocardial infarction, who underwent adenosine myocardial perfusion stress imaging, 24-72 h after infarction for risk stratification. Adenosine was infused at a rate of 140 microg/kg/min for 6 min. Twenty patients were presented with non-ST-elevation myocardial infarction. Eleven patients were admitted with acute ST-elevation myocardial infarction. Patients were monitored for signs of complication during and immediately after the stress test. The average time from admission to performance of stress tests was 51 +/- 19 h, ranging from the minimum of 24 h to maximum 72 h. No complications related to adenosine infusion were detected. In conclusion, our data suggest that a further large study of early adenosine myocardial perfusion SPECT imaging may be safe in a carefully selected group of patients after uncomplicated myocardial infarction.

Risk stratification post-myocardial infarction: is early coronary angiography the more effective strategy?

The primary management strategy for the post-myocardial infarction patient continues to be controversial despite published guidelines. In part, this is the consequence of study designs that are not directly applicable to individual patients, but also to the rapidly changing pharmacological and mechanical device armamentarium that rapidly renders clinical trial results obsolete within a few years. This review attempts to highlight those areas where there is consensus as well as to explicate those situations where common clinical practice appears to be in conflict with accepted guidelines.

Dobutamine stress echocardiography versus quantitative technetium-99m sestamibi SPECT for detecting residual stenosis and multivessel disease after myocardial infarction

OBJECTIVE

To compare the relative accuracy of dobutamine stress echocardiography (DSE) and quantitative technetium-99m sestamibi single photon emission computed tomography (mibi SPECT) for detecting infarct related artery stenosis and multivessel disease early after acute myocardial infarction.

DESIGN

Prospective study.

SETTING

University hospital.

METHODS

75 patients underwent simultaneous DSE and mibi SPECT at (mean (SD)) 5 (2) days after a first acute myocardial infarct. Quantitative coronary angiography was performed in all patients after imaging studies.

RESULTS

Significant stenosis (> 50%) of the infarct related artery was detected in 69 patients. Residual ischaemia was identified by DSE in 55 patients and by quantitative mibi SPECT in 49. The sensitivity of DSE and mibi SPECT for detecting significant infarct related artery stenosis was 78% and 70%, respectively, with a specificity of 83% for both tests. The combination of DSE and mibi SPECT did not change the specificity (83%) but increased the sensitivity to 94%. Mibi SPECT was more sensitive than DSE for detecting mild stenosis (73% v 9%; p = 0.008). The sensitivity of DSE for detecting moderate or severe stenosis was greater than mibi SPECT (97% v 74%; p = 0.007). Wall motion abnormalities with DSE and transient perfusion defects with mibi SPECT outside the infarction zone were sensitive (80% v 67%; NS) and highly specific (95% v 93%; NS) for multivessel disease.

CONCLUSIONS

DSE and mibi SPECT have equivalent accuracy for detecting residual infarct related artery stenosis of >/= 50% and multivessel disease early after acute myocardial infarction. DSE is more predictive of moderate or severe infarct related artery stenosis. Combined imaging only improves the detection of mild stenosis.

Tolerance and diagnostic accuracy of an abbreviated adenosine infusion for myocardial scintigraphy: a randomized, prospective study

BACKGROUND

The objectives of this study were 2-fold: (1) to determine the tolerance of adenosine perfusion tomography with the use of an abbreviated (3-minute) infusion in comparison to the standard (6-minute) infusion, and (2) to assess the relative diagnostic accuracy of a 3-minute adenosine infusion in patients referred for arteriography. An abbreviated adenosine infusion may decrease the frequency and duration of side effects and be a more cost-effective alternative.

METHODS AND RESULTS

We prospectively randomized 599 patients undergoing adenosine myocardial perfusion tomography to either a 3-minute or 6-minute adenosine infusion at 140 microg/kg per minute. Among the 599 enrolled patients, 142 subsequently underwent coronary angiography. Patients randomized to the 3-minute adenosine infusion tolerated the procedure better than those randomized to the standard infusion (P <.01). Flushing, headache, neck pain, and atrioventricular block were all significantly less frequent (P <.01) with the abbreviated infusion. Moreover, patients receiving the abbreviated infusion had less hypotension and tachycardia (P <.05). The sensitivity of the test for detection of coronary artery disease was 88% for both the 3- and 6-minute infusions. In patients with abnormal scan results, perfusion defect size was slightly larger in those receiving a 6-minute infusion versus those receiving a 3-minute infusion (P =.05).

CONCLUSIONS

An abbreviated 3-minute adenosine infusion, in combination with perfusion tomography, has similar sensitivity for detection of coronary artery disease and is better tolerated than the standard 6-minute infusion.

Risk assessment in patients with acute myocardial infarction treated with thrombolytic therapy

OBJECTIVE

Several noninvasive methods have prognostic information regarding mortality and new coronary events after an acute myocardial infarction (AMI). The practical for clinical decision-making in the immediate postmyocardial infarction (MI) period is, however, less evident. We investigated consecutive patients with AMI treated with thrombolysis to further clarify this issue.

DESIGN

A total of 100 patients (27% women) aged 64 +/- 9 years (mean +/- SD) were studied. Risk assessment based on a clinical score system, myocardial perfusion scintigraphy single photon emission computed tomography (SPECT) at rest and during adenosine stress, echocardiography, radionuclide angiography, symptom-limited exercise stress test, and 24-h Holter ECG recording with ST-analysis and analysis of heart rate variability (HRV) were performed 5-8 days after hospital admission. Mortality, nonfatal reinfarction, and the need for revascularization were followed during 12 months.

SETTING

A university hospital.

RESULTS

A total of 6 patients died, seven had a nonfatal reinfarction, and 23 were revascularized. Inability to perform an exercise test (P = 0.004) and an ejection fraction (EF) < 40% (P = 0.002) were the only parameters separating those who died from the survivors. No method could predict a nonfatal reinfarction. Patients suffering either death or nonfatal reinfarction had a clinical risk assessment score 2 points higher (8.8 vs. 6.7, P = 0.05) than the group without such events. A positive symptom-limited exercise stress test (P = 0.027), ST-depressions on Holter ECG (P = 0.04), and reversibility on myocardial perfusion scintigraphy (P = 0.029) predicted the need for revascularization.

CONCLUSION

Risk assessment based on clinical information, exercise stress testing, and an estimate of left ventricular function (e.g. via echocardiography) contribute with prognostic information in thrombolysed MI-patients. Additional noninvasive investigations such as adenosine-SPECT, analysis of HRV, and Holter-monitoring do not add to these commonly available tools in risk stratification of subjects at low to medium risk.

Principal uses of myocardial perfusion scintigraphy in the management of patients with known or suspected coronary artery disease

The use of myocardial perfusion single photon emission computed tomography (SPECT) has undergone considerable expansion and evolution over the past 2 decades. Although myocardial perfusion imaging was first conceived as a noninvasive diagnostic tool for determining the presence or absence of coronary artery disease, its prognostic value is now well established. Thus, identification of patients at risk for future cardiac events has become a primary objective in the noninvasive evaluation of patients with chest pain syndromes and among patients with known coronary artery disease. In particular, the ability of myocardial perfusion SPECT to identify patients at low (< 1%), intermediate (1% to 5%) or high (> 5%) risk for future cardiac events is essential to patient management decisions. Moreover, previous studies have conclusively shown the incremental prognostic value of myocardial perfusion SPECT over clinical and treadmill exercise data in predicting future cardiac events. This report addresses the current role and new developments, with respect to the use of myocardial perfusion imaging, in determining patient risk for cardiac events and the cost-effective integration of such information into patient management decisions.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

[The impact of the clinical data and the interhospital agreement in the interpretation of myocardial perfusion tomography]

INTRODUCTION AND OBJECTIVES

The aim of this study is to analyze the impact of clinical data and the interhospital agreement in the interpretation of myocardial perfusion single photon emission tomography (SPECT) images and polar mapping.

METHODS

150 patients from 5 hospitals were studied. Each center contributed with tomographic images and polar maps of 99mTc-tetrofosmin exercise SPECT and clinical reports of 30 patients. Thus, 300 images (150 of tomographic images and 150 of polar maps) were interpreted by each center without knowledge of clinical data of the patient ("blinded" report).

RESULTS

90 (60%) out of 150 patients had a coronary stenosis > or = 50%. Sensitivity and specificity of "non blinded" report were 91% and 86%, respectively. Sensitivity determined by majority decision (three or more centers) was 82% for tomographic images and 83% for polar maps (p = 0.002 and p = 0.03, respectively, regarding the "non-blinded" report). Specificity was 88% for tomographic images and 79% for polar map (p = 0.05 with respect to tomographic images). Interhospital agreement was good not only for tomographic images (kappa: 0.625) but for polar maps (kappa: 0.7) as well.

CONCLUSIONS

Sensitivity of clinical or "non blinded" report of myocardial perfusion SPECT is significantly higher than the "blinded" report. Specificity of the "blinded" report of polar mapping is lower than that of tomographic images. A good interhospital agreement in interpretation of both types of images was observed.

Pharmacological stress testing

Pharmacological stress in conjunction with radionuclide myocardial perfusion imaging has become a widely used noninvasive method of assessing patients with known or suspected coronary artery disease. In the United States, over one third of perfusion imaging studies are performed with pharmacological stress. Pharmacological stress agents fall into two categories: coronary vasodilating agents such as dipyridamole and adenosine, and cardiac positive inotropic agents such as dobutamine and arbutamine. For both, in the presence of coronary artery disease (CAD), perfusion image abnormalities result from heterogeneity of coronary blood flow reserve. Vasodilating agents work directly on the coronary vessels to increase blood flow, whereas inotropic agents work indirectly by increasing myocardial work load, which then leads to an increase in coronary blood flow. Both classes of agents have high accuracies for diagnosing coronary artery disease, and they have excellent safety records with acceptably low occurrences of side effects. For dipyridamole planar thallium imaging, pooled analysis yields a sensitivity of 85% and a specificity of 87% for diagnosis of coronary disease, but there is a large variation in reported values depending on various factors, such as the extent of postcatheterization referral bias, the type of imaging (planar versus single photon emission computed tomography [SPECT]), the types of patients being studied (single versus multivessel disease, men versus women), and the imaging agent used (thallium versus one of the technetium-based agents). Diagnostic accuracies for adenosine are similar to those of dipyridamole, with reported overall sensitivities ranging from 83% to 97%, and specificities ranging from 38% to 94%. For dobutamine, pooled analyses yield a sensitivity of 82% and a specificity of 75%. There is some concern that dobutamine may interfere with uptake of technetium-99m sestamibi, lowering the sensitivity for detection of disease, and thus the vasdodilating agents are generally preferred. Pharmacological stress testing has high clinical use for risk stratifying patients with known or suspected CAD, in patients after myocardial infarction, and in patients needing noncardiac surgery. Vasodilating agents are particularly advantageous in assessing post-myocardial infarction patients, allowing testing as soon as 2 days after the event. Like patients undergoing exercise stress testing, patients with normal perfusion images by pharmacological stress have a <1% annual incidence of cardiac events. The likelihood of an event increases with the extent and severity of perfusion abnormalities. However, it is important to consider clinical variables when using perfusion imaging for risk stratification, particularly in the presurgery patients. As with exercise testing, adjunct markers such as ST segment depression during testing, lung uptake of radiotracer (if thallium is used), and ventricular cavity dilatation add additional prognostic information to that available from the perfusion images alone. The aim of current research is to find better agents that are easier to use and that have fewer side effects. MRE-0470 is an experimental vasodilating agent that is more receptor selective than adenosine and promises a lower incidence of hypotension. Arbutamine more closely simulates exercise than dobutamine, and it can be administered by a closed-loop computerized delivery device. Work is also underway to look at novel uses of pharmacological stress agents, such as acquiring gated SPECT images during dobutamine infusion to enhance detection of myocardial viability. With increasing use of noninvasive testing in elderly patients and in patients with comorbidities that preclude adequate exercise, pharmacological stress testing has become an indispensable tool for radionuclide myocardial perfusion imaging studies. A good understanding of pharmacological stress testing is essential for performing high-quality nuclear cardiology

Stress myocardial perfusion imaging versus echocardiography for the diagnosis and risk stratification of patients with known or suspected coronary artery disease

Stress perfusion imaging and stress echocardiography (ECHO) are both very useful for assessment of diagnosis and risk stratification of patients with coronary artery disease (CAD). Both techniques have been well validated during exercise and inotropic stress, but coronary vasodilation stress is better used in combination with perfusion imaging. The overall sensitivity for detection of CAD is slightly higher by single photon emission computed tomography (SPECT) than by two-dimensional (2D) ECHO during all stress modalities, whereas the specificity is slightly higher by ECHO, although the differences in general are not statistically significant. SPECT, however, appears to be superior to ECHO in the diagnosis of isolated circumflex stenosis, as well as for the correct identification of multivessel CAD. A substantially greater amount of information is available regarding risk stratification with SPECT than with 2D ECHO. Although the data suggest that both techniques are very useful for risk stratification of patients with stable CAD, after myocardial infarction, and for preoperative risk stratification, the risk for cardiac events is lower in the presence of a normal stress SPECT study than of a normal stress ECHO.

Increased stress right ventricular activity on dual isotope perfusion SPECT: a sign of multivessel and/or left main coronary artery disease

OBJECTIVES

This study sought to determine the anatomic and physiologic correlates of increased right ventricular (RV) activity on exercise single-photon emission computed tomography (SPECT) perfusion imaging in patients with coronary artery disease (CAD).

BACKGROUND

Because SPECT perfusion imaging delineates relative myocardial blood flow, patients with global left ventricular (LV) hypoperfusion but normal RV perfusion may have increased relative RV tracer uptake as an indicator of multivessel CAD.

METHODS

Rest thallium-201 and exercise 99mTc-sestamibi or 99mTc-tetrofosmin SPECT perfusion images were analyzed for peak RV and LV activity (RV:LV index) in 315 patients, including 240 patients with documented CAD, 39 patients with no significant CAD on arteriography, and a "normalcy" group of 36 patients with a low pre- and posttest probability of CAD.

RESULTS

Resting RV:LV perfusion index ranged from 0.32 to 0.34 in each group, increasing to 0.36 with exercise in control and normalcy groups. CAD patients with the highest exercise RV:LV were those with severe left main CAD (or "left main equivalent"), with a lesser degree of proximal right CAD (0.51, n = 14, p < 0.001 vs. other groups). An exercise RV:LV >0.42 with a exercise:rest ratio >1.2 was present in 93% patients with this pattern of CAD, but was absent in 97% of the normalcy group, 92% of patients without significant angiographic CAD, and 100% of patients with proximal right CAD tighter than stenoses in the left system.

CONCLUSIONS

Increased RV:LV activity exercise may occur in patients with acute RV strain, but is otherwise an indicator of exercise-induced RV:LV perfusion imbalance associated with severe CAD, particularly high-grade left main with less severe proximal right CAD.

Comparative prognostic value of automatic quantitative analysis versus semiquantitative visual analysis of exercise myocardial perfusion single-photon emission computed tomography

OBJECTIVES

The purpose of this study was to determine the prognostic value of automatic quantitative analysis in exercise dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT) and to compare the prognostic value of quantitative analysis to semiquantitative visual SPECT analysis.

BACKGROUND

Extent, severity and reversibility of exercise myocardial perfusion defects have been shown to correlate with prognosis. However, most studies examining the prognostic value of SPECT in chronic coronary artery disease (CAD) have been based on visual analysis by experts.

METHODS

We studied 1,043 consecutive patients with known or suspected CAD who underwent rest Tl-201/exercise Tc-99m sestamibi dual-isotope myocardial perfusion SPECT and were followed up for at least 1 year (mean 20.0+/-3.7 months). After censoring 59 patients with early coronary artery bypass grafting or percutaneous transluminal coronary angioplasty, <60 days after nuclear testing, the final population consisted of 984 patients (36% women, mean age 63+/-12 years).

RESULTS

During the follow-up period, 28 hard events (14 cardiac deaths, 14 nonfatal myocardial infarctions) occurred. Patients with higher defect extent (>10%), severity (>150) and reversibility (>5%) by quantitative SPECT defect analysis, as well as those with an abnormal scan (>2 abnormal segments, summed stress score >4 and summed difference score >2) by semiquantitative visual SPECT analysis, had a significantly higher hard event rate compared to patients with a normal scan (p < 0.001). With both visual and quantitative analyses, hard event rates of approximately 1% with normal scans and 5% with abnormal scans (p > 0.05) were observed over the 20-month follow-up period. A Cox proportional hazards regression model showed that chi-square increased similarly with the addition of quantitative defect extent and visual summed stress score variables after considering both clinical and exercise variables (improvement chi-square = 11 for both, p < 0.0007). There were no significant differences in the areas under receiver operating characteristic curves between quantitative and visual analysis (p > 0.70). Linear regression analysis also indicated that quantitative assessments correlated well with visual semiquantitative assessments.

CONCLUSIONS

The findings of this study indicate that automatic quantitative analysis of exercise stress myocardial perfusion SPECT is similar to semiquantitative expert visual analysis for prognostic stratification. These findings may be of particular clinical importance in laboratories with less experienced visual interpreters.

Myocardial perfusion scintigraphy (SPECT) during adenosine stress can be performed safely early on after thrombolytic therapy in acute myocardial infarction

The objective of this study was to evaluate the safety of myocardial perfusion scintigraphy with Tc-99 m sestamibi during adenosine stress in patients with recent thrombolytically treated myocardial infarction. Eighty-four patients with thrombolytically treated myocardial infarction, 59 males and 25 females, aged 62.9 +/- 8.4, were eligible for myocardial perfusion scintigraphy during adenosine provocation. Exclusion criteria for adenosine stress were hypotension, unstable angina pectoris, cardiac failure, pericarditis and atrioventricular block (AV block) II-III. Adenosine-stress and resting myocardial perfusion scintigraphy was performed 2-5 days after thrombolysis. Scintigraphy at rest was done 24 h after the stress study. Sixty patients (71%) experienced some kind of side-effects during adenosine infusion. The most frequent side-effects were dyspnoea in 43/84 patients (51%) and unspecific chest discomfort in 26/84 patients (31%). During infusion, ST depressions or elevations on ECG were seen in 9 patients (11%), 5 of whom experienced atypical chest discomfort. Five patients (6%) described typical angina but none of them showed electrographic signs of myocardial ischaemia during infusion. Six patients (7%) developed transient AV block I-II. Reversible scintigraphic perfusion defects were seen in 67 patients (79%). No serious complications, such as death, reinfarction or severe arrhythmias, occurred during adenosine infusion or during a 3-day clinical follow-up period. In conclusion, MIBI-SPECT during adenosine stress is a safe diagnostic method that can be performed in most patients early on after thrombolytically treated acute myocardial infarction. Side-effects are common but benign, and not different from those seen in patients with chronic coronary artery disease.

Dipyridamole thallium-201 scintigraphy for early risk stratification of patients after uncomplicated myocardial infarction

OBJECTIVE

To determine the safety and prognostic value of dipyridamole thallium-201 scintigraphy performed in patients within three to five days of acute myocardial infarction, including those receiving thrombolytic treatment.

DESIGN

A prospective study of dipyridamole thallium-201 scintigraphy in patients early after acute myocardial infarction.

SETTING

University hospital.

PATIENTS

200 patients who were clinically uncomplicated at day 3 after infarction, 92 (46%) of whom had received thrombolysis.

MAIN OUTCOME MEASURES

Incidence of cardiac death, non-fatal reinfarction, readmission to hospital for unstable angina, or non-elective revascularisation procedure within six months' follow up.

RESULTS

No patient had a serious complication from the dipyridamole study. At six month follow up, 55 patients (28%) had suffered a defined cardiac event. Patients who received thrombolysis had the same extent of thallium-201 redistribution and the same occurrence of subsequent cardiac events as those not receiving thrombolysis. Patients who subsequently had an event had more myocardial segments showing thallium-201 redistribution than event free patients: 2.7 (SD 1.9) v 1.2 (1.4), respectively (p < 0.001). Among all clinical and scintigraphic variables, multivariate analysis identified the extent of thallium-201 redistribution as the only independent predictor of outcome (p < 0.001). Among 63 patients (32%) of the study cohort who showed more than two myocardial segments with thallium-201 redistribution, the adjusted risk ratio for a cardiac event was 7.5 (95% confidence interval 2.9 to 19.1) compared with patients without any redistribution.

CONCLUSIONS

Dipyridamole thallium-201 scintigraphy can be performed safely within a few days of the event in patients with uncomplicated myocardial infarction, including those who received thrombolysis, and can identify a subgroup of patients at high risk of future ischaemic events.

[Clinical prediction of the early prognosis in acute myocardial infarct]

Several clinical factors can influence the pathophysiology, clinical course and prognosis of acute myocardial by different means. Some of them may be easily detected through the history, physical examination or ECG in an early phase. The knowledge of these factors may help the therapeutic decision making of patients with myocardial infarction. The influence for the main clinical factors (age, sex, risk factors, cardiologic antecedents and evolutive findings) on the short-term prognosis of acute myocardial infarction is reviewed. An analysis of the likely mechanisms of the influence of these factors on infarct prognosis is also performed.

Adenosine technetium-99m sestamibi single-photon emission tomography for the assessment of jeopardized myocardium early after acute myocardial infarction. Paradoxical scintigraphic underestimation of jeopardized myocardium in patients with a severe infarct-related stenosis

This study investigated the value of technetium-99m sestamibi scintigraphy in identifying patients at risk for post-infarct ischaemia (=jeopardized myocardium), especially within the reperfused infarct region. In 51 patients with a recent (<1 month) myocardial infarction, adenosine 99mTc-sestamibi single-photon emission tomography (SPET) and dobutamine stress echocardiography (DSE) were performed and correlated with the presence of significant coronary artery stenosis [% diameter stenosis (DS) >50%] on quantitative coronary angiography. Regional perfusion activity was analysed semi-quantitatively (score 0-4) on a 13-segment left ventricular model. DSE was used for the estimation of the infarct size (low-dose DSE) and for concomitant evaluation of ischaemia (high-dose DSE). A reversible perfusion defect within the infarct region was observed in 20 of the 37 patients with a significant infarct-related lesion (sensitivity of 54%) and only in one patient without a significant infarct-related lesion (specificity of 93%). Further analysis revealed that the scintigraphic assessment of jeopardized myocardium was fairly good in patients with a moderate (DS 51%-64%) infarct-related stenosis but was inadequate in patients with a severe (DS>/=65%) infarct-related stenosis (sensitivity of 80% vs 36%, P<0.01), while the echocardiographic detection of ischaemia was not influenced by stenosis severity (sensitivity of 73% in both subgroups). This scintigraphic underestimation of jeopardized myocardium was mainly related to a severely impaired myocardial perfusion under baseline conditions, as was evidenced by a significantly more severe rest perfusion score in the infarct region in patients with a severe stenosis as compared to those with a moderate stenosis (average score: 1.5+/-0.7 vs 2.1+/-0.6, P<0.01), while infarct size on echocardiography was similar for both subgroups. It may be concluded that early after an acute myocardial infarction, adenosine 99mTc-sestamibi SPET may underestimate reperfused but still jeopardized myocardium, particularly in patients with a severe infarct-related stenosis. In these patients the evaluation of the ischaemic burden on rest-stress scintigraphy is hampered by the presence of a severely impaired myocardial perfusion in resting conditions.

Safety of early intravenous dipyridamole technetium 99m sestamibi SPECT myocardial perfusion imaging after uncomplicated first myocardial infarction. Early Post MI IV Dipyridamole Study (EPIDS)

We assessed the safety of early (2 to 4 days) intravenous dipyridamole infusion in conjunction with technetium 99m sestamibi tomographic myocardial perfusion imaging in patients with first myocardial infarction (MI). Early risk stratification with myocardial perfusion imaging of patients after acute MI may be useful to identify patients who either require further evaluation or may be safely discharged. Because of minimal hemodynamic effects, intravenous dipyridamole may be a safe means of producing hyperemia for myocardial perfusion imaging. Stable patients with first acute MI who met entry criteria were randomized (3:1) to either intravenous dipyridamole infusion (0.56 mg/kg over a 4-minute period) 48 to 96 hours after onset of symptoms or a control (no test) group. Adverse cardiac events (unstable angina, recurrent MI, or cardiac death) were evaluated during and 24 hours after the dipyridamole infusion and during the corresponding 24 hours for the control group. Two hundred eighty-four patients received dipyridamole infusion a mean time of 3.3 +/- 0.7 days after MI. There were no adverse clinical events either during or immediately after the infusion. During the 24 hours after infusion, three patients had symptoms of unstable angina pectoris, one patient had a recurrent MI, and no patients died. The earliest event occurred 4.2 hours after the dipyridamole infusion. Three patients had unstable angina pectoris, whereas no patients had either recurrent MI or died in the control group. There were no statistically significant differences between the two groups. In a multicenter trial, dipyridamole infusion administered early after the first acute MI resulted in no increased evidence of cardiac events either immediately or 24 hours after the procedure compared with a control group. Therefore intravenous dipyridamole can be safely used as a pharmacologic vasodilator for myocardial perfusion imaging soon after uncomplicated MI.

Risk stratification in coronary artery disease: implications for stabilization and prevention

Noninvasive nuclear imaging techniques, including dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT), have been employed in the development of strategies for diagnosis and risk stratification of patients with suspected or known coronary artery disease. These risk-stratification strategies are based on studies in which known outcome has been linked to diagnostic and prognostic information provided by myocardial perfusion SPECT. This article describes a validated dual-isotope exercise protocol for assessment of perfusion and function and reviews the evidence on which a cost-effective risk management strategy is based.

Adenosine thallium-201 tomography in evaluation of graft patency late after coronary artery bypass graft surgery

OBJECTIVES

We sought to ascertain the utility of adenosine thallium-201 tomography for assessing graft stenoses late after coronary artery bypass graft surgery.

BACKGROUND

Although pharmacologic perfusion imaging has been increasingly used in the assessment of patients with coronary artery disease, the value of this stress modality for detecting coronary artery bypass graft stenosis late after surgery is unknown.

METHODS

We studied 109 patients who underwent both adenosine thallium-201 tomography and coronary angiography at 6.7 +/- 4.8 (mean +/- SD) years after coronary artery bypass graft surgery. Adenosine thallium-201 tomography was assessed quantitatively by computer-generated polar maps of the myocardial thallium-201 activity.

RESULTS

On coronary angiography, significant graft stenoses were present in 68 patients, 65 of whom had a corresponding perfusion defect as shown by thallium-201 tomography (sensitivity 96%). Significant stenoses were present in 107 (37.8%) of 283 grafts. The overall specificity by quantitative tomography was 61%. Seventy percent of the apparently false positive perfusion defects could be explained on the basis of unbypassed native disease or by the presence of fixed defects in patients with previous myocardial infarction.

CONCLUSIONS

Thus, results of adenosine thallium-201 tomography are nearly always abnormal in patients with late coronary graft stenosis. Most of the false positive defects appear to be due to either unbypassed native disease or a previous myocardial infarction.

Role of adenosine in pathogenesis of syndrome X: assessment with coronary hemodynamic measurements and thallium-201 myocardial single-photon emission computed tomography

OBJECTIVES

This study was performed 1) to examine the role of adenosine in the pathogenesis of syndrome X in patients with this syndrome and abnormal results on myocardial scintigrams during exercise, and 2) to determine the susceptibility to myocardial ischemia in this subset of patients with syndrome X.

BACKGROUND

A role for adenosine in the pathogenesis of syndrome X has recently been postulated, but there are few clinical data supporting this hypothesis.

METHODS

Exercise thallium-201 myocardial scintigraphy after intravenous administration of aminophylline, an adenosine receptor blocking agent, or saline solution and adenosine thallium-201 scintigraphy were performed in 26 patients with syndrome X. Hemodynamic variables during exercise and perfusion defect size after aminophylline and saline infusions were compared. At cardiac catheterization, coronary hemodynamic variables during separate infusions of adenosine and doubutamine were also examined and were compared among patients with abnormal or normal scintigrams and 10 control subjects.

RESULTS

Perfusion abnormalities on exercise-thallium-201 scintigraphy occurred in 14 of 26 patients with syndrome X. Intravenous infusion of aminophylline suppressed the scintigraphic perfusion defect and prolonged the time to 1-mm ST segment depression in patients with syndrome X with abnormal exercise scintigrams. Intravenous infusion of adenosine induced a perfusion defect in the same myocardial area where the perfusion defect was observed at exercise in 7 of the 14 patients with syndrome X. At cardiac catheterization, patients with syndrome X with abnormal exercise scintigrams had lower coronary flow reserve and a greater frequency of myocardial lactate production and ST segment depression in response to the infusions of adenosine and doubtamine than did the other two groups. During adenosine infusion, great cardiac vein blood flow and oxygen content were significantly increased and myocardial oxygen consumption and lactate extraction were significantly reduced from baseline without a significant increase in rate-pressure product in this subset of patients with syndrome X.

CONCLUSIONS

Patients with syndrome X with abnormal exercise scintigrams have high susceptibility to myocardial ischemia during exercise or pharmacologic stress tests, probably owing to reduced coronary flow reserve. A heterogeneous response to endogenous adenosine may contribute to scintigraphic perfusion abnormalities and myocardial ischemia during exercise in this subset of patients with syndrome X.

Clinical and angiographic significance of a normal thallium-201 tomographic study in patients with a strongly positive exercise electrocardiogram

Among 23,059 patients who underwent exercise myocardial tomography between 1985 and 1994 at our institution, there were 817 (3.5%) with a strongly positive exercise electrocardiogram and normal myocardial tomograms. Among these, 52 patients had no conditions known to be associated with a false-positive exercise electrocardiogram and no previous coronary revascularization, and underwent coronary angiography. Of the 32 patients with significant coronary stenoses, 50% had 1-vessel disease and only 22% had 3-vessel disease (p < 0.05). Among 55 stenosed arteries, 56% were of moderate severity (50 to 74%), whereas only 9% had subtotal or total occlusion (95 to 100%) (p < 0.001). There was a significant gender difference in the prevalence of significant coronary stenoses (80% in male vs 24% in female patients, p < 0.0001). A strongly positive exercise electrocardiogram coupled with normal exercise myocardial tomograms is a rare clinical finding. In women, this finding is usually associated with normal coronary arteries, whereas in men it often denotes coronary artery disease, usually of mild to moderate degree.

Stress echocardiography in elderly patients with coronary artery disease: applicability, safety and prognostic value of dobutamine and adenosine echocardiography in elderly patients

OBJECTIVES

Our aim was to determine the applicability, safety and prognostic value of adenosine and dobutamine stress echocardiography in patients > or = 70 years old.

BACKGROUND

These tests are sometimes mandatory because of difficulties and inaccuracies in interpreting traditional electrocardiographic stress tests. Furthermore, if these tests could be used to avoid coronary arteriography and cardiac catheterization, they would become essential in the care of the elderly, whose numbers are increasing.

METHODS

We performed coronary arteriography and dobutamine and adenosine stress echocardiographic tests in 120 patients (72 men) > or = 70 years old who entered the hospital because of chest pain and had known or suspected coronary artery disease. The stress tests were performed on separate days, within 2 weeks of coronary arteriography. Both the arteriograms and the echocardiograms were analyzed by two experts who had no knowledge of the patients' other data or the other interpreter's report. Tests were judged to have positive or negative results, and the patients were followed up for the development of cardiac events. Univariate and multivariate analyses and other statistical modalities were applied for comparisons.

RESULTS

Documented coronary artery disease was found in 89 patients. During the 14 +/- 7 of follow-up, cardiac events developed in 50 patients, including 3 (7.9%) of 38 patients with negative dobutamine and 12 (20.7%) of 58 patients with negative adenosine test results. Demonstration of any abnormality on stress echocardiography was an independent factor for cardiac events, both for dobutamine (relative risk 7.3) and for adenosine (relative risk 3.0). Both cessation of dobutamine or adenosine tests and diagnosis of disease in two or more coronary vessels were also independent predictors. ST segment depression > or = 1mm was related to future events only with the dobutamine test.

CONCLUSIONS

These echocardiographic stress tests proved safe and well tolerated. They successfully stratified this cohort of elderly patients with coronary artery disease to low or high risk subgroups for subsequent cardiac events.

Simultaneous assessment of myocardial perfusion and left ventricular function during transient coronary occlusion

OBJECTIVES

We used technetium-99m sestamibi imaging to evaluate the magnitude of changes in left ventricular function and perfusion and to investigate their interdependence during transient coronary occlusion.

BACKGROUND

Transient coronary occlusion during coronary angioplasty provides a unique opportunity for examining the effects of acute myocardial ischemia on left ventricular function and perfusion.

METHODS

Thirty-five patients with normal left ventricular function underwent first-pass radionuclide angiography with technetium-99m sestamibi using a multicrystal gamma camera during balloon occlusion of a coronary artery. Single-photon tomography was performed 2.1 +/- 1.7 h later. Subsequently, all scans were repeated at rest.

RESULTS

The mean size +/- SD of the perfusion defect during coronary occlusion was 23 +/- 18%, with significantly larger defects observed for occlusions of the left anterior descending coronary artery (39 +/- 20%) than for occlusions of the left circumflex (15 +/- 11%) or right (15 +/- 9%) coronary artery (p < 0.05). The mean change in ejection fraction from recovery to occlusion was -17 +/- 17% and was significantly larger for left anterior descending (-26 +/- 21%) and left circumflex (-15 +/- 11%) than for right (-8 +/- 10%) coronary artery occlusions (p < 0.05). For the entire group, ejection fraction during occlusion correlated significantly with perfusion defect size (r = 0.63, p = 0.0004), whereas the extent of ischemic myocardium correlated with the decrease in ejection fraction (r = 0.69, p = 0.0001). The defects present during occlusion reversed within a few hours.

CONCLUSIONS

Changes in left ventricular function and perfusion develop pari passu during coronary occlusion and are more severe when the left anterior descending artery is occluded. Although a significant correlation exists between the extent of the perfusion defect and the severity of the decrease in ejection fraction, there is a substantial individual variation with respect to changes in both myocardial perfusion and ventricular function during acute coronary occlusion.

High reproducibility of myocardial perfusion defects in patients undergoing serial exercise thallium-201 tomography

The purpose of this study was to define the reproducibility of sequential quantitative exercise thallium-201 tomography. This was an ancillary study of a randomized, double-blind, placebo-controlled trial evaluating the short-term efficacy of transdermal nitroglycerin patches in stable patients with angiographic coronary artery disease and no prior myocardial infarction. All 18 patients had a baseline tomographic perfusion defect involving > or = 5% of the left ventricle after treadmill exercise. At a minimum of 3 days (mean 6.1 +/- 1.8) after double-blind randomization to placebo, exercise thallium-201 tomography was repeated (study 2) using the same exercise protocol as in the baseline study (study 1). No significant differences in exercise parameters were observed from studies 1 to 2. Seventeen of 18 patients (94%) had an abnormal repeat exercise perfusion scan and 96% of initially abnormal vascular territories remained abnormal. The mean tomographic perfusion defect size was not significantly different from studies 1 (17.4 +/- 13.3%) to 2 (16.6 +/- 15.3%), nor were the components defined as scar and ischemia. A > or = 10% change in total perfusion defect size in an individual patient defined the 95% confidence interval for exceeding the variability of the tomographic technique. Quantitative exercise thallium-201 tomography is highly reproducible and can be used to accurately interpret temporal changes in myocardial perfusion in individual patients.

Role of adenosine thallium-201 tomography for defining long-term risk in patients after acute myocardial infarction

OBJECTIVES

This study prospectively evaluated whether early assessment with adenosine thallium-201 tomography could better refine risk stratification on the basis of absolute extent of myocardial ischemia in postinfarction patients in clinically stable condition.

BACKGROUND

Postinfarction patients are at increased risk for subsequent cardiac events. However, identifying high risk patients among those with residual myocardial ischemia is suboptimal.

METHODS

All 146 patients enrolled underwent assessment of left ventricular function and had adenosine tomography performed early (mean [+/- SD] 5 +/- 3 days) after infarction. Excluded from analysis were 51 patients with revascularization after scintigraphy and 3 lost to follow-up. Statistical risk models were therefore generated from the remaining 92 patients.

RESULTS

Cardiac events occurred in 30 (33%) of 92 patients over 15.7 +/- 4.9 months. Univariate predictors of all events were quantified perfusion defect size (p < 0.0001), absolute extent of left ventricular ischemia (p < 0.000001) and ejection fraction (p < 0.0001). Risk was best predicted by Cox analysis on the basis of 1) absolute extent of ischemia and ejection fraction (chi-square 24.6); 2) percent infarct zone ischemia and ejection fraction (chi-square 24.4); or 3) total perfusion defect size and percent infarct zone ischemia (chi-square 18.9). The variables that predicted all cardiac events were equally powerful at predicting only death and nonfatal reinfarction. Death was best predicted by total perfusion defect size.

CONCLUSIONS

Risk analysis of individual patients early after infarction is feasible on the basis of the quantified extent of scintigraphic ischemia and severity of left ventricular dysfunction.

Rest-redistribution thallium-201 scintigraphy to determine myocardial viability early after myocardial infarction

OBJECTIVES

This study attempted to determine the utility of early rest-redistribution thallium-201 imaging in detecting residual myocardial viability after myocardial infarction.

BACKGROUND

The early detection of myocardial viability after myocardial infarction would have clinical relevance.

METHODS

Thirty-one patients with acute myocardial infarction had early (mean [+/- SD] 2 +/- 1 day) rest-redistribution thallium-201 imaging followed by radionuclide and coronary angiography. Late studies included stress-redistribution-reinjection thallium-201 imaging or radionuclide angiography, or both. Viability was defined by the rest thallium-201 scan as an initial mild rest defect or any defect that demonstrated redistribution.

RESULTS

Group 1 (n = 15) was predicted to have viable and Group 2 (n = 16) nonviable myocardium in the infarct zone. Group 1 patients were more likely to have a patent infarct-related artery (15 of 15 vs. 10 of 16, p < 0.03), higher initial ejection fraction (61 +/- 12% vs. 53 +/- 9%, p < 0.05), higher infarct wall motion score (p < 0.0001) and fewer abnormal thallium-201 segments (p < 0.0001). On follow-up studies, ejection fraction improved in Group 1 (from 57 +/- 13% to 66 +/- 10%, p < 0.05, n = 9) and deteriorated in Group 2 (from 53 +/- 10% to 46 +/- 8%, p < 0.05, n = 13). On late stress testing with thallium-201 reinjection, Group 1 patients had fewer abnormal segments (p < 0.03) and higher infarct zone counts during exercise (p < 0.05) and after reinjection (p < 0.05) than Group 2 patients.

CONCLUSIONS

If confirmed by larger studies, early rest-redistribution thallium-201 imaging may be a useful technique for identifying residual viability after myocardial infarction.

Should all patients undergo cardiac catheterization after a myocardial infarction?

Between one half and two thirds of patients who survive an acute myocardial infarction (AMI) may be at low risk for future complications and hence can be managed with medical therapy. However, the remaining patients are prone to future complications, which by and large occur within the subsequent 3 months and include cardiac death, recurrent AMI, unstable angina, and congestive heart failure. Current available methods for risk stratification include a good clinical evaluation, rest and stress electrocardiograms (preferentially combined with radionuclide imaging), and possibly two-dimensional stress echocardiography. In patients unable to exercise, pharmacologic perfusion scintigraphy affords a powerful means to identify high-risk patients. Patients deemed to be at high risk should be referred for cardiac catheterization and myocardial revascularization. The practice of performing routine cardiac catheterization after an AMI has led to an over use of resources in the United States. Such a practice is not based on any scientific evidence of enhanced benefit. In fact, in other Western world countries where only selected patients are referred for cardiac catheterization, patient survival appears to be similar to that in the United States. In conclusion, most patients after AMI, whether treated with thrombolytic therapy or not, can be managed conservatively and risk stratified on the basis of noninvasive testing, after which patients deemed to be at high risk should undergo invasive evaluation.

Transdermal nitroglycerin patch therapy reduces the extent of exercise-induced myocardial ischemia: results of a double-blind, placebo-controlled trial using quantitative thallium-201 tomography

OBJECTIVES

This study prospectively evaluated whether transdermal nitroglycerin patches could limit the extent of exercise-induced left ventricular ischemia as assessed by quantitative thallium-201 tomography.

BACKGROUND

Although antianginal medications are effective at reducing chest pain symptoms in patients with coronary artery disease, there is limited evidence that these agents can also reduce myocardial ischemia.

METHODS

This was a randomized, double-blind, parallel, placebo-controlled trial evaluating nitroglycerin patch therapy in patients in stable condition with angiographic coronary artery disease and no previous myocardial infarction. All patients were weaned from antianginal agents and had a baseline symptom-limited treadmill test followed by thallium-201 tomography. Forty patients with perfusion defects involving > or = 5% of the left ventricle were randomized to receive either intermittent (12 h on/off) active nitroglycerin patch therapy (0.4 mg/h) or placebo. Exercise tomography was repeated a mean (+/- SD) of 6.1 +/- 1.8 days after randomization.

RESULTS

Patients randomized to receive active patch therapy had a significant reduction in their total perfusion defect size (-8.9 +/- 11.1%) compared with placebo-treated patients (-1.8 +/- 6.1%, p = 0.04), which was most apparent in those with the largest (> or = 20%) baseline perfusion defects (-11.4 +/- 13.4% vs. 1.0 +/- 3.6%, respectively, p < 0.02). Furthermore, 7 (33%) of 21 patients receiving active therapy had a > or = 10% decrease in their perfusion defects compared with only 1 (5%) of 19 patients randomized to receive placebo (p = 0.002). Nitrate therapy did not significantly reduce heart rate, blood pressure or double product, indicating benefit through enhancement of coronary blood flow.

CONCLUSIONS

Short-term, intermittent nitroglycerin patch therapy significantly reduces myocardial ischemia, particularly in patients with large ischemic perfusion defects. Thallium-201 tomography can be used to assess sequential changes in the extent of exercise-induced left ventricular ischemia.