Ability of dipyridamole-thallium-201 imaging one to four days after acute myocardial infarction to predict in-hospital and late recurrent myocardial ischemic events

Pharmacologic radionuclide myocardial perfusion imaging

Pharmacologic stress testing with myocardial perfusion imaging has enabled patients who cannot complete adequate exercise to undergo diagnostic and prognostic evaluation for coronary artery disease. Pharmacologic stress agents belong to two groups: vasodilators (such as adenosine and dipyridamole), and inotropes (such as dobutamine). All have similar sensitivity (89%-91%) and specificity (78%-86%) for the diagnosis of coronary disease. For risk stratification, the risk of future cardiac events is related to the extent and severity of perfusion abnormalities. Pharmacologic stress testing permits risk stratification as early as 1 to 4 days following an acute myocardial infarction, and is superior to exercise stress testing in this regard. Similarly, it identifies patients at high risk for perioperative cardiac events prior to noncardiac surgery. This review summarizes the current evidence available regarding the diagnostic and prognostic use of pharmacologic stress testing.

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.

Cardiac nuclear medicine in monitoring patients with coronary heart disease

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

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.

Prognostic value of stress-gated Tc-99m sestamibi SPECT after acute myocardial infarction

Stress-gated technetium-99m (Tc-99 m) sestamibi single-photon emission computed tomography (SPECT) is used to risk stratify patients after acute myocardial infarction (AMI). In clinical practice, results of this test are used primarily to identify patients with myocardial ischemia for intervention. The value of this test to risk stratify patients with AMI not at high ischemic risk has not been addressed. More than 1-year follow-up was undertaken in 124 patients who underwent predischarge gated Tc-99m sestamibi SPECT studies and who did not undergo subsequent revascularization. Clinical variables and test-derived variables were evaluated to predict cardiac death, recurrent AMI, and hospitalization for unstable angina, congestive heart failure, or coronary revascularization. Independent predictors by multivariate analysis for cardiac death or recurrent AMI were a history of prior AMI (relative risk [RR] = 5.32, confidence interval [CI] 2.17 to 12.96), a low exercise capacity (RR = 6.84, CI 1.99 to 23.48), and left ventricular (LV) ejection fraction (EF) <40% (RR = 2.63, CI 1.04 to 6.38). The incidence of cardiac death or recurrent AMI was 29.8% in patients with a low exercise capacity versus 4.5% in those with good exercise capacity, and 38.1% in patients with LVEF <40% versus 9.4% in those with LVEF >40%. Independent predictors of cardiac death, AMI, or hospitalization for unstable angina, congestive heart failure, or revascularization were a history of prior AMI (RR = 2.24, CI 1.11 to 4.50) and LVEF <40% (RR = 3.13, CI 1.64 to 5.95). Among patients followed after AMI without revascularization Tc-99m sestamibi SPECT can identify a high-risk subset. The strongest independent predictors are poor exercise capacity and LVEF < 40%.

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.

Stress nuclear myocardial perfusion imaging versus stress echocardiography: prognostic comparisons

The use of noninvasive stress cardiac imaging for stratifying risk in patients with known or suspected coronary artery disease is growing as a tool for identification of the subgroup most likely to benefit from the expense and risk of more invasive procedures, including cardiac catheterization and coronary revascularization. In this setting, it is especially important that a test be able to identify patients with sufficiently low risk that clinicians are comfortable in deferring such interventions, especially in those with other markers of increased risk. Previous data have shown that cardiac risk is most closely related to the presence and extent of jeopardized viable myocardium on noninvasive stress cardiac imaging. Although stress echocardiography may have comparable ability to detect coronary artery disease, current data suggest that stress echocardiography detects significantly less jeopardized viable myocardium than stress nuclear myocardial perfusion imaging and consequently fewer patients at risk for cardiac events. Stress nuclear myocardial perfusion imaging may therefore have important advantages for risk stratification and the direction of future care of patients with known or suspected coronary artery disease.

Early dipyridamole (99m)Tc-sestamibi single photon emission computed tomographic imaging 2 to 4 days after acute myocardial infarction predicts in-hospital and postdischarge cardiac events: comparison with submaximal exercise imaging

BACKGROUND

Because of its brief hemodynamic effects and minor effect on determinants of myocardial oxygen demand, vasodilator stress myocardial perfusion imaging (MPI) can be applied very early after acute myocardial infarction (AMI) for risk stratification, allowing management decisions to be made earlier and thus potentially shortening hospitalization stays, reducing costs, and preventing early cardiac events. This multicenter randomized trial compared the prognostic value of early dipyridamole MPI and standard predischarge submaximal exercise MPI in patients who presented with AMI.

METHODS AND RESULTS

Patients who presented with their first AMI (n=451) were randomized in a 3:1 ratio to undergo either both an early (day 2 to 4) dipyridamole (99m)Tc-sestamibi MPI study and a predischarge (day 6 to 12) submaximal exercise (99m)Tc-sestamibi MPI study or only the predischarge study. Multivariate predictors of in-hospital cardiac events included nuclear imaging summed stress and summed reversibility scores and peak creatine kinase. For postdischarge cardiac events, multivariate predictors in patients undergoing dipyridamole MPI included only the summed stress, reversibility, and rest imaging scores and anterior MI. For a given summed stress score, the interaction of reversibility score further improved the predictive value. Dipyridamole MPI showed better risk stratification than submaximal exercise MPI.

CONCLUSIONS

Dipyridamole MPI very early after MI predicts early and late cardiac events, with superior prognostic value compared with submaximal exercise imaging. The extent and severity of the stress defect and reversibility of the defect were the most important predictors of cardiac death and recurrent MI. This technique can allow management decisions to be made earlier with regard to AMI patients and could have important economic impact if applied widely.

Diagnostic and Prognostic Use of Stress Echocardiography and Radionuclide Scintigraphy

Stress echocardiography and radionuclide scintigraphy are effective diagnostic and prognostic techniques in patients with known or suspected coronary artery disease (CAD), myocardial infarction (MI), chronic left ventricular dysfunction (LVD), and those undergoing noncardiac surgery. Both are sensitive and specific for the detection and extent of CAD. Negative tests confer a high negative predictive value for cardiac events irrespective of clinical risk. Positive studies confer a high positive predictive value for ischemic events in patients with intermediate to high clinical risk. Both provide incremental diagnostic and prognostic information relative to clinical, resting echocardiographic, and angiographic data. Meta-analysis studies have shown that the diagnostic and prognostic information provided by stress echocardiography is comparable with radionuclide scintigraphic stress tests. Stress echocardiography may be more specific for the detection and extent of CAD, whereas radionuclide scintigraphy may be more sensitive for single-vessel disease. Sensitivities are similar for the detection and extent of disease in patients with multivessel CAD.

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

Prediction of functional recovery and prognosis in patients with acute myocardial infarction by 123I-BMIPP and 201Tl myocardial single photon emission computed tomography: a multicenter trial

123I-BMIPP [15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid] was developed for metabolic imaging with SPECT. A multicenter collaborative study was conducted on a large patient series to determine whether 123I-BMIPP and 201Tl myocardial SPECT are of use in predicting the prognosis and ventricular function after acute myocardial infarction (AMI). Patients with uncomplicated first AMI underwent resting 123I-BMIPP and 201Tl myocardial SPECT in the subacute phase after the onset of AMI. Of these, 167 patients who had been followed up for an average of 22 months were retrospectively reviewed to predict serious cardiac events and recurrent ischemia. In addition, the association between changes in radionuclide parameters and recurrent ischemia was investigated in Subgroup A (58 patients) who had repeated SPECT in the chronic phase. Furthermore, prediction of the ejection fraction (EF) was investigated in Subgroup B (94 patients) and Subgroup C (76 patients) in whom left ventriculography was performed at the time of discharge and 90 days or more after the onset, respectively. The prognosis was generally favorable, with 4 cases of cardiac death (2%), 3 of heart failure (2%), 4 of nonfatal reMI (2%), and 25 of recurrent ischemia (15%). The results of Cox multivariate regression analysis revealed a high probability of serious cardiac events in patients who were elderly (p = 0.04), who had 90% or more residual stenosis of the infarct-related artery (p = 0.09), and who had a high BMIPP defect score (p = 0.17). There was a high probability of recurrent ischemia in elderly patients (p = 0.10) who had multi-vessel disease (p = 0.03), but no association was found with radionuclide parameters in the subacute phase. In Subgroup A, however, the probability of recurrent ischemia tended to be high in patients with a large mismatch scorebetween 123I-BMIPP and 201Tl in the subacute to chronic phase. An important observation was that the extent of BMIPP defect was more strongly correlated with EF at the time of discharge and 90 days or more after the onset than the extent of Tl defect (r = -0.60 vs. r = -0.47, and r = -0.53 vs. r = -0.43, respectively). In addition, multiple regression analysis showed that parameters related to the BMIPP defect were also better predictive factors of EF both at the time of discharge and 90 days or more after the onset. In conclusion, resting 123I-BMIPP and 201Tl myocardial SPECT performed in the subacute phase of AMI were shown to be useful in predicting prognosis and ventricular function for patient management.

Thallium reinjection versus standard stress/delay redistribution imaging for prediction of cardiac events

OBJECTIVES

The purpose of this study was to compare thallium reinjection with standard stress/delay redistribution for the prediction of cardiac events.

BACKGROUND

Although thallium reinjection enhances the detection of viable myocardium, its contribution to prognosis over stress/delay redistribution in a general referral population has not been clearly evaluated.

METHODS

This retrospective analysis included 366 consecutive patients with coronary artery disease who underwent stress/delay redistribution imaging and thallium reinjection scintigraphy, with a mean follow-up of 33+/-12 months.

RESULTS

Cardiac events occurred in 48 patients (40 deaths, 8 myocardial infarctions). Of the 366 original patients, 159 demonstrated ischemia by stress/delay redistribution, 107 showed ischemia by reinjection only, and 100 showed infarction only. Cardiac events occurred in 20 patients (12.6%) with stress/delay redistribution, 13 patients (12%) with ischemia detected by thallium reinjection only and 15 patients (15%) with infarction only. The size of the reversible thallium defect by either stress/delay redistribution imaging or reinjection scintigraphy did not predict cardiac events. Independent predictors of cardiac events included left ventricular cavity size, the size of the abnormal perfusion defect and patient age.

CONCLUSIONS

Thallium reinjection does not contribute independent prognostic utility for cardiac events when compared with stress/delay redistribution. Left ventricular dilation and the size of the post-stress defect were predictors of cardiac events.

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.

Superiority of nitrate-enhanced 201Tl over conventional redistribution 201Tl imaging for prognostic evaluation after myocardial infarction and thrombolysis

BACKGROUND

201Tl imaging has been widely used for postinfarction risk stratification. However, thrombolytic therapy and aspirin have significantly changed outcome, and there are few nuclear imaging studies that assess prognosis in such patients. Furthermore, newer techniques of 201Tl imaging, such as reinjection and nitrate-enhanced rest 201Tl imaging, have been shown to improve the detection of viable but jeopardized myocardium.

METHODS AND RESULTS

We studied 100 consecutive patients, who remained event free 6 weeks after myocardial infarction and thrombolysis. Patients underwent conventional exercise and 4-hour redistribution imaging, followed on a separate day by nitrate-enhanced rest 201Tl study. Planar images were reported semiquantitatively by two experienced observers blinded to clinical data. Redistribution and rest injection images were classified as demonstrating reversible ischemia if they showed improvement in uptake by at least two grades in at least two segments in comparison with the initial exercise scintigram. Patients were followed up for 8 to 32 months (mean, 21 months); during this period, 37 patients had first cardiac events. Reversible ischemia was present in 29 patients on redistribution, of whom 14 (48%) had events; of 71 without reversible defects, 23 (32%) had events (hazard ratio, 1.5; 95% CI, 0.8 to 3.0; P=NS). Nitrate-enhanced rest 201Tl imaging detected reversible defects in 68 patients, of whom 33 (49%) had events, whereas of 32 without reversible defects, only 4 (13%) had subsequent cardiac events (hazard ratio, 8.1; 95% CI, 2.7 to 23.8; P<.001).

CONCLUSIONS

Thus, after myocardial infarction and thrombolysis, even "stable" patients have a high (68%) incidence of viable but jeopardized myocardium, causing a high event rate. Those identified to be at high risk by perfusion imaging may benefit from early intervention.

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.

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.

Relation between ambulatory electrocardiographic monitoring and myocardial perfusion imaging to detect coronary artery disease and myocardial ischemia: an ACIP ancillary study. The Asymptomatic Cardiac Ischemia Pilot (ACIP) Investigators

OBJECTIVES

This study sought to explore the relation between markers of ischemia detected by ambulatory electrocardiographic (AECG) monitoring and stress myocardial perfusion single-photon emission computed tomography (SPECT).

BACKGROUND

Stress myocardial SPECT and AECG monitoring are both utilized in evaluating patients with coronary artery disease. However, information is limited regarding the relation between the presence and extent of ischemia as detected by these two modalities.

METHODS

This was an ancillary study of the Asymptomatic Cardiac Ischemia Pilot (ACIP) trial. One hundred six patients with previous coronary angiography underwent AECG monitoring and stress SPECT within a close temporal time period. The frequency and duration of ischemia as assessed by AECG monitoring and the total and ischemic stress-induced myocardial perfusion defect sizes as assessed by SPECT were quantified in separate core laboratories. Multivariate logistic regression and linear regression analysis were used to determine associations between AECG and SPECT abnormalities with regard to angiographic, demographic and treadmill exercise variables.

RESULTS

Seventy-four percent of patients with significant (> or = 50%) coronary artery stenosis had SPECT abnormalities, whereas 61% had ischemia by AECG monitoring. The most important predictors of SPECT abnormalities were severity (p < 0.001) of coronary artery stenosis, followed by total exercise duration (p = 0.016) and patient age (p = 0.04). The only predictor of AECG abnormalities was the presence of ST segment depression on the initial exercise treadmill test (p = 0.021). Only a 50% concordance for normalcy or abnormalcy was observed between the SPECT and AECG results, and no relation was observed between the frequency or duration of AECG ischemia and the quantified total or ischemic myocardial perfusion defect size as assessed by SPECT.

CONCLUSIONS

Ischemia as detected by AECG monitoring does not correlate with the presence and extent of ischemia as quantified by stress SPECT. Because these techniques appear to detect different pathophysiologic manifestations of ischemia, they may be complementary in more fully defining the functional significance of coronary artery disease and, in particular, which patients are at highest risk for adverse cardiac events.

Clinical application of coronary flow reserve using an intracoronary Doppler guide wire

Coronary flow reserve (CFR) is a critical measurement in the assessment of the coronary circulation. The development of this physiologic variable in animal and human studies is reviewed. Human studies documenting the limitations of coronary angiography, especially in the setting of severe diffuse coronary artery disease, are analyzed. Furthermore, the important variables that must be accounted for when CFR is measured are examined. With this background, the application of CFR in a variety of clinical settings and the development and use of the Doppler FloWire for its measurement are discussed.

Myocardial contrast echocardiography in acute myocardial infarction using aortic root injections of microbubbles in conjunction with harmonic imaging: potential application in the cardiac catheterization laboratory

OBJECTIVES

The aim of this study was to evaluate myocardial contrast echocardiography using aortic root injections with harmonic imaging in experimental acute myocardial infarction to determine the potential of this approach in the cardiac catheterization laboratory.

BACKGROUND

It would be desirable to have an adjunctive procedure that could evaluate myocardial perfusion at the time of cardiac catheterization in patients with acute myocardial infarction. A single injection of contrast medium in the aortic root would provide complete information on myocardial perfusion in a cross section of the heart. High quality images would provide on-line assessment of myocardial perfusion without recourse to image processing. These data could be very valuable for determining patient management.

METHODS

Perfusion defects on myocardial contrast echocardiography were measured during coronary occlusion and reflow, using fundamental and harmonic imaging in both continuous and intermittent modes in nine open chest dogs. These defects were compared with risk area on technetium-99m autoradiography and infarct size on tissue staining.

RESULTS

Whereas harmonic imaging increased myocardial video intensity by more than twofold (p < 0.001) compared with fundamental imaging after aortic root injection of contrast medium, intermittent imaging was not superior to continuous imaging. The improved signal to noise ratio of harmonic imaging allowed on-line definition of risk area (r = 0.98) and infarct size (r = 0.93) without recourse to off-line processing. Similar results could be obtained with fundamental imaging only after off-line processing.

CONCLUSIONS

Aortic root injection of contrast medium coupled with harmonic imaging can be used to provide accurate on-line assessment of risk area and infarct size during acute myocardial infarction. These results have important implications for the catheterization laboratory.

A metaanalysis of predischarge risk stratification after acute myocardial infarction with stress electrocardiographic, myocardial perfusion, and ventricular function imaging

We assessed the relation of abnormal predischarge non-invasive test results to outcomes in postmyocardial infarction patients. We included series published from 1980 to 1995 containing only myocardial infarction patients, enrolling most patients after 1980, testing within 6 weeks of infarction, having follow-up rates > 80%, and having 2 x 2 frequency outcome rates for test results, that were the latest of multiple reports. Sensitivity, specificity, and predictive values were calculated for test results for 1-year outcomes (cardiac death, cardiac death or reinfarction). Univariable and summary odds were calculated for test results. Reports (n = 54) included a total of 19,874 patients and were primarily retrospective (76%) and small series (35% of reports included < 5 deaths). One-year mortality ranged from 2.5% for pharmacologic stress echocardiography to 9.3% for exercise radionuclide angiography. Positive predictive values for most noninvasive risk markers were < 0.10 for cardiac death and < 0.20 for death or reinfarction. Electrocardiographic, symptomatic, and scintigraphic risk markers of ischemia (ST-segment depression, angina, a reversible defect) were less sensitive (< or = 44%) for identifying morbid and fatal outcomes than markers of left ventricular dysfunction or heart failure (exercise duration, impaired systolic blood pressure response, and peak left ventricular ejection fraction). The positive predictive value of predischarge noninvasive testing is low. Markers of left ventricular dysfunction appear to be better predictors than markers of ischemia. Limitations of the literature-small samples and widely varying event rates-impede our ability to discern the accuracy of pre-discharge noninvasive testing. More rigorous, controlled trials are required to elucidate the relative value of these tests for risk stratification.

Prognostic value of exercise 201Tl tomography in patients treated with thrombolytic therapy during acute myocardial infarction

BACKGROUND

Although myocardial perfusion scintigraphy is of proven value in the risk stratification of patients with a recent myocardial infarction who receive conventional therapy, its value in patients undergoing thrombolytic therapy remains controversial.

METHODS AND RESULTS

Seventy-one patients who received thrombolytic therapy for acute myocardial infarction had exercise 201Tl tomography and coronary angiography before hospital discharge. Eleven (15%) of 71 patients had ischemic ST-segment depression during exercise, whereas 27 patients (38%) had scintigraphic ischemia. Twenty-five (37%) of 68 patients had a cardiac event consisting of either death (n = 2), recurrent myocardial infarction (n = 5), congestive heart failure (n = 7), or unstable angina (n = 11) during a follow-up of 26 +/- 18 months. Univariate predictors of cardiac events were as follows: Killip class (P = .04); left ventricular ejection fraction (P < .0005); total (P = .002) and ischemic (P < .0005) perfusion defect size; percent thallium lung uptake (P = .001); presence of infarct-zone redistribution (P = .02); and multivessel coronary artery disease (P = .01). By multivariate analysis, the significant joint predictors of risk were ejection fraction (P < .0005) and ischemic perfusion defect size (P = .005). The combination of ejection fraction and thallium tomography added significant incremental prognostic information to the clinical data, whereas angiography did not further improve a model that included clinical, ejection fraction, and tomographic variables.

CONCLUSIONS

Quantitative exercise 201Tl tomography provides important incremental, long-term prognostic information in patients receiving thrombolytic therapy for acute myocardial infarction.

Comparison of pharmacologic stress agents

In choosing a pharmacologic agent for stress testing, the clinician must keep a number of things in mind, such as the diagnostic utility of the agent or in what situations a vasodilator or catecholamine will be the better choice. Although all stress agents produce similar diagnostic accuracy for CAD, vasodilators have a higher cardiac uptake than catecholamines, and the addition of exercise improves the heart/background contrast ratios. With regard to physiologic comparisons, exercise or dobutamine will double coronary perfusion compared with baseline flow, but vasodilators produce a threefold or fourfold increase. The clinician should also keep in mind that adenosine will produce the shortest duration of hyperemia, whereas dobutamine and arbutamine produce a longer effect, and dipyridamole has the longest duration. If electrophysiologic considerations are important, exercise and catecholamines accelerate sinoatrial and atrioventricular conduction and are not typically associated with heart block. In contrast, adenosine can cause transient atrioventricular block, but this rarely occurs with dipyridamole. Clinical factors also must be considered. Although clinical utility of pharmacologic stress agents in the first 24 hours after infarction has not been demonstrated, the prognostic utility of vasodilators in the subsequent 2- to 4-day period has been shown. With patients with pulmonary disease (asthma) who do not have wheezing, dipyridamole can be used, but dobutamine or arbutamine should be used in patients with recent respiratory failure or bronchospasm before testing. In patients with left bundle branch block, vasodilators are the preferred stress agents rather than synthetic catecholamines or dynamic exercise. In the first crossover thallium imaging, there was good overall agreement in segmental perfusion comparing adenosine and dipyridamole, but there was a tendency for adenosine to detect more ischemia. The clinical significance (if any) for these findings has yet to be determined.

Value of thallium-201 imaging in detecting adverse cardiac events after myocardial infarction and thrombolysis: a follow up of 100 consecutive patients

OBJECTIVE

To determine the prognostic role of thallium-201 imaging compared with that of exercise electrocardiography in patients with acute myocardial infarction treated by thrombolysis.

DESIGN

Patients who remained free of adverse cardiac events six weeks after myocardial infarction had stress and rest 201TI imaging and exercise electrocardiography and were followed up for 8-32 months. Adverse cardiac events (death, reinfarction, unstable angina, and congestive heart failure) were documented.

SETTING

Large district general hospital, Middlesex.

SUBJECTS

100 consecutive male and female patients who were stable six weeks after thrombolysis for myocardial infarction.

MAIN OUTCOME MEASURES

Prediction of occurrence of adverse cardiac events after myocardial infarction by exercise cardiography and 201TI myocardial perfusion imaging.

RESULTS

Reversible ischaemia on 201TI imaging predicted adverse cardiac events in 33 out of 37 patients with such events during follow up (hazard ratio 8.1 (95% confidence interval 2.7 to 23.8), P < 0.001). Exercise electrocardiography showed reversible ischaemia in 33 patients, of whom 13 had subsequent events, and failed to predict events in 24 patients (hazard ratio 1.1 (0.56 to 2.2), P = 0.8).

CONCLUSION

201TI imaging is a sensitive predictor of subsequent adverse cardiac events in patients who have received thrombolysis after acute myocardial infarction, whereas exercise electrocardiography fails to predict outcome.

Coronary reserve abnormalities in the infarcted myocardium. Assessment of myocardial viability immediately versus late after reflow by contrast echocardiography

BACKGROUND

The aim of this study was to determine whether myocardial contrast echocardiography (MCE) during exogenous vasodilation can accurately delineate infarct size, and hence the extent of myocardial viability, both immediately (15 minutes) and late (3 hours) after reperfusion when postreflow coronary hyperema is still present.

METHODS AND RESULTS

Twenty-one open-chest anesthetized dogs underwent 3 to 6 hours of coronary occlusion followed by reperfusion. MCE was performed 15 minutes after reflow before and during infusion of 0.2 mg.kg-1.min-1 adenosine i.v.. In 12 dogs, infarct size was measured at this time. In the remaining 9 dogs, reperfusion was continued for 3 hours, when MCE was repeated before and after an infusion of 0.56 mg.kg-1.min-1 dipyridamole i.v. and infarct size was measured. In the absence of adenosine, MCE perfusion defect at 15 minutes underestimated infarct sizes at both 15 minutes and 3 hours, whereas in the presence of adenosine, the estimate of infarct size was more accurate. Similarly, in the absence of dipyridamole, although MCE perfusion defect underestimated infarct size (both measured 3 hours after reflow), in the presence of dipyridamole, the estimate of infarct size was more accurate.

CONCLUSIONS

By unmasking abnormalities in flow reserve within the infarct bed, MCE in conjunction with coronary vasodilators can accurately predict infarct size both 15 minutes and 3 hours after reperfusion. Thus, MCE can be used for assessing the extent of myocardial viability both immediately and late after reperfusion when postreflow coronary hyperemia is still present.

Left ventricular cavity size determined by preoperative dipyridamole thallium scintigraphy as a predictor of late cardiac events in vascular surgery patients

We hypothesized that left ventricular (LV) cavity size measured on dipyridamole thallium scintigraphy identifies patients at risk for late nonfatal myocardial infarction and cardiovascular death. Accordingly, we retrospectively evaluated the predictive value of clinical and scintigraphic variables, including transendocardial LV cavity measurement performed on formatted images, in 335 vascular surgery patients. A nonhomogeneous perfusion pattern and enlarged LV cavity size were the most significant predictors of late events, and the interaction between these two variables was more predictive than was either variable alone. Life-table analysis demonstrated that patients with normal perfusion patterns had the lowest incidence of late events regardless of cavity size (p < 0.0005). Conversely, patients with a nonhomogeneous perfusion pattern and the largest LV cavity measurements were at the highest risk for late cardiac events (p < 0.0001). Therefore, this study demonstrated that a measurement of LV scintigraphic cavity size can provide important risk stratification for late cardiac events.

Prediction of in-hospital cardiac events using dipyridamole-thallium scintigraphy performed very early after acute myocardial infarction

BACKGROUND AND HYPOTHESIS

Ischemic complications occur frequently during hospitalization after acute myocardial infarction. Dipyridamole-thallium scintigraphy performed early after admission can detect residual ischemia, may have additional prognostic value and be useful in the management of these patients.

METHODS

Dipyridamole infusion and 201thallium imaging were performed on the third day of infarction in 114 consecutive patients. Coronary angiography was performed before hospital discharge in 90% of patients and exercise testing was performed at the time of discharge in patients without contraindications.

RESULTS

Side effects occurred in 28 patients, but they were mild and transient or rapidly reversed with intravenous aminophylline. During hospitalization, three patients died and four had a nonfatal reinfarction. Patients with these major cardiac events had previously shown a higher prevalence of reversible perfusion defects during testing (71 vs. 31%, p < 0.05). In addition, 19 patients had early recurrent ischemia requiring early in-hospital revascularization. Overall, cardiac events defined as death, reinfarction, or early myocardial revascularization occurred in 22 patients. Of the patients with these events, 68% had thallium redistribution on initial myocardial scanning compared with 25% of patients without events (p = 0.0001). Patients with cardiac events also showed a higher number of myocardial segments with reversible perfusion defects (1.8 +/- 2.2 vs. 0.6 +/- 1.3, p = 0.001). Logistic regression analysis revealed that among all the other clinical, scintigraphic, and angiographic variables, the presence of thallium redistribution on the dipyridamole-thallium scan was the only independent predictor of cardiac events, increasing the risk by sixfold. Furthermore, during a 1-year follow-up, 14 other patients had ischemic events. Of these, 64% had previously shown thallium redistribution during early dipyridamole testing compared with 19% of patients without cardiac events (p < 0.001).

CONCLUSIONS

Intravenous dipyridamole-thallium-scintigraphy performed very early after myocardial infarction is safe and useful to predict in-hospital ischemic events.

Myocardial contrast echocardiography: relation of collateral perfusion to extent of injury and severity of contractile dysfunction in a canine model of coronary thrombosis and reperfusion

OBJECTIVES

This study sought to determine whether myocardial contrast echocardiography could be used to detect and quantitate collateral blood flow capable of limiting the effects of ischemia in an experimental model of coronary thrombosis and reperfusion.

BACKGROUND

Myocardial contrast echocardiography has been used to assess collateral blood flow in humans, but this technique has not been extensively validated in the experimental laboratory.

METHODS

Myocardial ischemia occurred after electrically induced left circumflex coronary artery thrombosis in a canine model. Ischemia was intensified by administration of vasodilators. Reperfusion was induced with recombinant tissue-type plasminogen activator. Myocardial perfusion was assessed with contrast echocardiography and radiolabeled microspheres. Infarct size was determined by histochemical staining methods. Myocardial samples were evaluated histologically.

RESULTS

The dogs were classified into two groups on the basis of contrast echocardiographic detection of perfusion in the ischemic region: those with (n = 13) and without collateral flow (n = 10). Collateral perfusion detected by contrast echocardiography paralleled changes detected by radiolabeled microspheres during thrombosis and vasodilator administration. A 91% agreement was observed between the two techniques in detecting collateral flow > 0.3 ml/min per g (p < 0.0001). Collateral perfusion correlated directly with radial shortening fractions of the ischemic myocardium (p < 0.01). Recovery of function after reperfusion was faster, infarct size was smaller (mean [+/- SD] 4 +/- 1% vs. 11 +/- 3%, p = 0.05), and histopathologic injury was less in dogs with than without collateral flow, respectively (p < 0.05).

CONCLUSIONS

Myocardial contrast echocardiography can identify physiologically significant collateral vessels capable of limiting the degree of ischemic damage during coronary thrombosis. The magnitude of collateral flow and the change in flow induced by vasodilators can be assessed and compares favorably with the microsphere standard.

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.

Positive high-dose dipyridamole echocardiography test after acute myocardial infarction is an excellent predictor of cardiac events

To determine the prognostic value of the high-dose (0.84 mg/kg over a 10-minute period) dipyridamole echocardiography test (DET) after a first acute myocardial infarction (AMI) in comparison with clinical, electrocardiographic, echocardiographic, and angiographic variables, follow-up data over an average period of 16 months were obtained in 93 consecutive patients. There were 41 total cardiac events (TCE): one death, two reinfarctions, 13 postinfarction anginas, five percutaneous transluminal coronary angioplasty procedures, and 20 coronary artery bypass graft procedures. TCE without revascularization procedures were considered adverse cardiac events (ACE). The DET result was positive in 28 of 41 patients with TCE and in only 4 of 52 patients without TCE (p < 0.001). The sensitivity, specificity, and accuracy of positive DET in predicting TCE were 68%, 92%, and 82%, respectively. According to Cox's proportional regression model the best predictor of TCE was positivity of DET (p = 0.002, relative risk ratio 4.3), followed by multivessel coronary artery disease (p = 0.018, relative risk ratio 2.9) and patent infarct-related artery (p = 0.042, relative risk ratio 2.9). DET was positive in 12 of 16 patients with ACE and 20 of 77 patients without ACE (p = 0.001). The sensitivity, specificity, and accuracy of DET in predicting ACE were 75%, 74%, and 74%, respectively. According to Cox's proportional regression model significant predictors of ACE were positivity of DET (p = 0.002, relative risk ratio 29.4) and ejection fraction < or = 40% at the time of DET (p = 0.017, relative risk ratio 22.2).(ABSTRACT TRUNCATED AT 250 WORDS)

Preoperative clinical assessment and dipyridamole thallium-201 scintigraphy for prediction and prevention of cardiac events in patients having major noncardiovascular surgery and known or suspected coronary artery disease

The aim of this study was to assess the relative prognostic use of clinical risk stratification and intravenous dipyridamole thallium-201 scintigraphy in patients with an intermediate to high prevalence of coronary artery disease (CAD) who have undergone major noncardiovascular surgery, and to assess the effects of medical therapy or coronary revascularization based on the result of this clinical scintigraphic screening on perioperative cardiac morbidity and mortality. Patients (n = 161) with an intermediate to high likelihood of CAD had clinical assessment and intravenous dipyridamole planar thallium-201 testing which was analyzed semiquantitatively. Cardiac events were cardiac death (n = 9), nonfatal myocardial infarction (n = 6), acute pulmonary edema (n = 6), and unstable angina (n = 4). Multiple (> or = 2) clinical risk variables predicted any cardiac event (p = 0.04). Presence of multiple (> or = 2) abnormal thallium-201 segments was the only independent predictor of cardiac death or nonfatal myocardial infarction (p < 0.001), and was the most powerful multivariate predictor of any cardiac event (p < 0.002). Patients with an abnormal dipyridamole thallium-201 scan had a higher risk of perioperative cardiac death, myocardial infarction (18% vs 2%; p < 0.001), or any perioperative cardiac event (27% vs 6%; p < 0.001) when compared with those with a normal scan. Preoperative changes in anti-ischemic therapy or coronary revascularization in 36 of 72 patients with abnormal dipyridamole thallium-201 studies reduced perioperative death or myocardial infarction from 31% to 6% (p < 0.01), and all cardiac events from 47% to 8% (p < 0.001) compared with those in patients without intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Unstable angina: prognosis, noninvasive risk assessment, and strategies for management

Risk stratification in patients with unstable angina is a major clinical problem with important therapeutic implications. Antiplatelet therapy is clearly effective in reducing the occurrence of myocardial infarction and death in this syndrome. Interventions including coronary bypass surgery and coronary angioplasty are frequently recommended for these patients, but the most appropriate application of these techniques needs to be further defined. After a brief discussion of the value of medical and interventional therapies, this review focuses on the clinical and noninvasive predictors of adverse events in unstable angina. An overall management strategy for these patients, based on current information, will be proposed.

Prevalence of right ventricular perfusion defects after inferior myocardial infarction assessed by low-level exercise with technetium 99m sestamibi tomographic myocardial imaging

To assess the prevalence of right ventricular perfusion defects after a recent inferior wall myocardial infarction, 33 patients were studied 6 to 14 days after infarction with low-level exercise testing and technetium 99m (99mTc) sestamibi (SPECT) imaging. Twenty-two control subjects with a < 5% likelihood of coronary artery disease undergoing exercise 99mTc sestamibi imaging were also studied. For each image the right ventricle was computer isolated from reconstructed transverse cardiac slices, followed by reorientation into oblique slices. Both right and left ventricular images were visually assessed for defects. A quantitative method of defect detection was also applied to the right ventricle. For the right ventricle, 100% of the stress images and 96% of the rest images were adequate for interpretation. Right ventricular stress perfusion defects were identified in 10 (30%) of 33 patients with recent inferior infarction, with 50% completely or partially normalizing on rest images, consistent with ischemia. Of 14 patients with left ventricular inferoseptal defects, eight (57%) had right ventricular defects compared with 2 (11%) of 19 without inferoseptal defects (p < 0.005). We concluded that the right ventricle can be adequately assessed for perfusion defects by means of exercise with 99mTc sestamibi SPECT imaging. Defects of the right ventricle after inferior myocardial infarction occur frequently, and many have evidence of ischemia. Right ventricular perfusion defects are closely associated with left ventricular inferoseptal defects.

Prognostic value of dipyridamole technetium-99m sestamibi myocardial tomography in patients with stable chest pain who are unable to exercise

Unlike dipyridamole testing with thallium-201, the ability of technetium-99m sestamibi (MIBI) myocardial imaging to evaluate risk of later cardiac events has not been established. In this study, the prognostic value of dipyridamole MIBI myocardial tomography (same-day, rest-stress protocol) was assessed in 534 patients with stable chest pain consistent with angina pectoris. During follow-up (mean 13 +/- 5 months), 58 patients (11%) had a major cardiac event--nonfatal myocardial infarction (n = 14) or cardiac death (n = 44). A history of congestive heart failure, prior myocardial infarction or diabetes mellitus, and either a reversible or fixed myocardial perfusion defect on MIBI scans were univariate and multivariate predictors of increased cardiac risk. Cardiac events occurred in 2% of patients with normal MIBI scans, compared with 15% with abnormal scans, 17% with reversible perfusion defects and 16% with fixed defects (all p < 0.01). Relative risks (univariate Cox analysis) associated with an abnormal MIBI scan, a reversible perfusion defect and a fixed defect were 8.4 (95% confidence interval [CI] 2.6 to 26.8), 1.9 (95% CI 1.1 to 3.2) and 2.4 (95% CI 1.4 to 4.3), respectively. Patients with any kind of perfusion abnormality (reversible or fixed) had a significantly lower cardiac event-free survival than those with normal scans (all p < 0.0001). It is concluded that, as with thallium-201 myocardial scintigraphy, a normal MIBI scan is associated with low cardiac risk, whereas dipyridamole-induced myocardial perfusion defects identify patients with significantly increased risk.