Quantitative planar thallium-201 stress scintigraphy: a critical evaluation of the method

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Randomized, controlled trial of long-term moderate exercise training in chronic heart failure: effects on functional capacity, quality of life, and clinical outcome

BACKGROUND

It is still a matter of debate whether exercise training (ET) is a beneficial treatment in chronic heart failure (CHF).

METHODS AND RESULTS

To determine whether long-term moderate ET improves functional capacity and quality of life in patients with CHF and whether these effects translate into a favorable outcome, 110 patients with stable CHF were initially recruited, and 99 (59+/-14 years of age; 88 men and 11 women) were randomized into 2 groups. One group (group T, n=50) underwent ET at 60% of peak &f1;O2, initially 3 times a week for 8 weeks, then twice a week for 1 year. Another group (group NT, n=49) did not exercise. At baseline and at months 2 and 14, all patients underwent a cardiopulmonary exercise test, while 74 patients (37 in group T and 37 in group NT) with ischemic heart disease underwent myocardial scintigraphy. Quality of life was assessed by questionnaire. Ninety-four patients completed the protocol (48 in group T and 46 in group NT). Changes were observed only in patients in group T. Both peak &f1;O2 and thallium activity score improved at 2 months (18% and 24%, respectively; P<0. 001 for both) and did not change further after 1 year. Quality of life also improved and paralleled peak VO2. Exercise training was associated both with lower mortality (n=9 versus n=20 for those with training versus those without; relative risk (RR)=0.37; 95% CI, 0.17 to 0.84; P=0.01) and hospital readmission for heart failure (5 versus 14; RR=0.29; 95% CI, 0.11 to 0.88; P=0.02). Independent predictors of events were ventilatory threshold at baseline (beta-coefficient=0.378) and posttraining thallium activity score (beta-coefficient -0.165).

CONCLUSIONS

Long-term moderate ET determines a sustained improvement in functional capacity and quality of life in patients with CHF. This benefit seems to translate into a favorable outcome.

Effects of moderate exercise training on thallium uptake and contractile response to low-dose dobutamine of dysfunctional myocardium in patients with ischemic cardiomyopathy

BACKGROUND

There is evidence that exercise training can induce myocardial and coronary adaptations in both animals and humans. However, the significance of these potentially important changes remains to be determined in patients with ischemic heart disease and left ventricular (LV) systolic dysfunction.

METHODS AND RESULTS

To investigate whether exercise training can improve thallium uptake and the contractile response to low-dose dobutamine of dysfunctional myocardium, 46 patients (42 men, 4 women; mean age, 57+/-9 years) with chronic coronary artery disease and impaired LV systolic function (ejection fraction < 40%) were randomly assigned to two groups. The exercise group (n = 26) underwent exercise training at 60% of peak oxygen uptake for 8 weeks. The control group (n = 20) was not exercised. At baseline and after 8 weeks all patients underwent an exercise test with gas exchange analysis and stress echocardiography using low-dose dobutamine (5 to 10 microg/kg per minute) followed by thallium myocardial scintigraphy. Coronary angiography was performed in 23 patients at baseline and after 8 weeks. After 8 weeks, peak oxygen uptake increased significantly only in trained patients (24%). Significant improvements in the contractile response to dobutamine and thallium activity were observed in trained patients (28% and 31%, respectively; trained versus control: P<.001 for both). In a subgroup of trained patients, both improvements were correlated with an increase in the coronary collateral score (P<.005 and P<.001, respectively).

CONCLUSIONS

Moderate exercise training improves both thallium activity and the contractile response of dysfunctional myocardium to low doses of dobutamine in patients with ischemic cardiomyopathy. The implication of this study is that even a short-term exercise training may improve quality of life by improvement of LV systolic function during mild-to-moderate physical activity in patients with ischemic cardiomyopathy.

Cardiac function, perfusion, and morbidity in irradiated long-term survivors of Hodgkin's disease

PURPOSE

The incidence of cardiotoxicity and clinical cardiac events following mantle irradiation (RT) in patients with Hodgkin's disease using modern techniques is controversial. The use of quantitative, prognostically validated noninvasive tests to assess systolic and diastolic cardiac function and regional myocardial blood flow may reveal preclinical abnormalities associated with subsequent clinical events of myocardial infarction, cardiac death, or angina. The goals of this study are to determine, through noninvasive measures, the presence and time course of alterations in cardiac systolic and diastolic function and of relative myocardial blood flow in long-term survivors of Hodgkin's disease, and assess their correlation with subsequent clinical cardiac end points.

METHODS AND MATERIALS

Equilibrium radionuclide angiocardiography (ERNA) was used to assess left ventricular (LV) systolic and diastolic function by measuring LV ejection fraction (LVEF) and peak filling rate (PFR), respectively, in patients without known ischemic heart disease who received RT. Electrocardiography was performed to assess electrical cardiac function under conditions of rest and either exercise or dipyridamole vasodilator stress. Quantitative rest/stress myocardial perfusion imaging with thallium-201 and/or Tc-99m sestamibi was used to assess myocardial perfusion. Patients at least 1.0 year after RT were eligible if they were <50 years old at RT, had no known cardiac disease, and remained free of clinical recurrence of Hodgkin's disease. Fifty patients, ages 10.2-46.1 years (mean 26.0 +/- 8.6) at RT, were tested 1.1 to 29.1 years (mean 9.1 +/- 7.5) after RT. Seventeen of these patients were tested two times separated by 1.1 to 8.1 years. The mean central cardiac RT dose was 35.1 +/- 7.8 Gy (range 18.5-47.5) in daily 15-2.0 Gy fractions. Twelve patients were concomitantly irradiated to the left ventricle, usually through partial transmission left lung shields (mean 17.0 +/- 2.2 Gy, range 14.3-21.3).

RESULTS

No patients had signs or symptoms of cardiac disease at the time of evaluation. The mean LVEF at the time of initial testing was 59.6 +/- 6.2% (n = 50; range 42-73%; normal > or =50%), and the mean peak filling rate (PFR) was 3.46 +/- 0.88 end diastolic volumes per second (EDV/s) (range 1.5-5.4 EDV/s; normal > or =2.54 EDV/s). The 12 patients also treated to the left ventricle had a normal mean ejection fraction that was lower (56.6 +/- 5.0%) than that of the other 38 patients (LVEF = 60.6 +/- 6.3%, p = 0.051) when initially evaluated. Average PFR was similar in the two groups. For the 15 patients who had repeat tests, changes in LVEF were generally modest in individual patients, and there was no change in the group mean. For all patients, no significant association was found between cardiac function indices and age at RT, dose, or interval from RT to testing. Myocardial perfusion scintigraphy demonstrated mild ischemia in one or more segments in two patients, and borderline normal perfusion in three patients. Rest and stress ECG testing demonstrated mild repolarization abnormalities in three, and one patient was abnormal at rest and had nondiagnostic changes with stress.

CONCLUSIONS

Patients irradiated to the heart incidental to the treatment of Hodgkin's disease using modern techniques have generally normal measures of left ventricular function and myocardial perfusion. Modest differences in the normal left ventricular ejection fraction observed may be attributable to the cardiac volume irradiated. Some patients may manifest improved cardiac function as time from RT elapses, while a significant deterioration of ejection fraction was not observed and reduction in diastolic peak filling rate is uncommon. The previously reported increased risk of cardiac death may relate to use of older techniques of RT employing higher doses and lack of cardiac shielding, and uncontrolled patient selection with additional behaviors and cardiac risk factors.

Comparison of thallium scintigraphy and positron emission tomography

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

Relevance of increased lung thallium uptake on stress imaging in patients with unstable angina and non-Q wave myocardial infarction: results of the Thrombolysis in Myocardial Infarction (TIMI)-IIIB Study

OBJECTIVES

This study sought to determine the significance of abnormal thallium-201 (Tl-201) lung uptake on stress imaging in the absence of perfusion abnormalities.

BACKGROUND

Abnormal Tl-201 lung uptake, represented by an increased lung/heart ratio (LHR), on stress imaging is a marker of stress-induced left ventricular dysfunction and poor prognosis in patients with coronary artery disease.

METHODS

We evaluate 1,271 patients from the Thrombolysis in Myocardial Infarction (TIMI)-IIIB trial (86% of TIMI-IIIB cohort) with unstable angina or non-Q wave myocardial infarction, who underwent predischarge exercise (92%) or dipyridamole stress (8%) Tl-201 imaging. An increased LHR (> or = 0.50) was related to perfusion abnormalities and adverse cardiac events at 1 year.

RESULTS

Of 1,271 patients, there were 762 (60%) with and 509 (40%) without perfusion abnormalities. An increased LHR was seen in 227 patients (18%) (173 [23%] with, 54 [11%] without perfusion abnormalities). Patients with an increased LHR had a lower left ventricular ejection fraction, higher body weight, lower exercise capacity and a higher prevalence of angina on exercise than patients with a normal LHR. In the two groups with increased LHR, there was no difference in age, hypertension, previous myocardial infarction, total exercise time, frequency of angina and ST segment depression on exercise. However, the group with an increased LHR and normal myocardial perfusion had a preponderance of women (65% vs. 30%, p < 0.001). At 1-year follow-up, patients with an increased LHR had a higher cardiac event rate than those with a normal LHR (18% vs. 10%, respectively, p = 0.001) despite a higher revascularization rate (28% vs. 15%, p < 0.001). An increased LHR was associated with increased adverse cardiac events, irrespective of the presence or absence of perfusion abnormalities.

CONCLUSIONS

An increased LHR continues to be associated with higher adverse cardiac events in the current era of aggressive interventional management of coronary artery disease. An increased LHR in the absence of myocardial perfusion abnormality is seen mostly in women and overweight patients. However, despite the apparent absence of perfusion abnormalities, an increased LHR in this group is also associated with a higher rate of adverse cardiac events.

Clinical implications of silent versus symptomatic exercise-induced myocardial ischemia in patients with stable coronary disease

OBJECTIVES

This study was undertaken to better understand the functional and prognostic significance of silent relative to symptomatic ischemia.

BACKGROUND

Previous studies have reached conflicting conclusions as to whether painless ischemia identified during noninvasive cardiac testing is related to a lesser extent of myocardial ischemia or a different prognosis than ischemia accompanied by angina, or both.

METHODS

Nine hundred thirty-six clinically stable patients 1 to 6 months after an acute coronary event, either myocardial infarction or unstable angina, underwent ambulatory monitoring, exercise treadmill testing and stress thallium-201 scintigraphy. They were then followed up prospectively for a mean of 23 months for recurrent cardiac events (cardiac death, nonfatal myocardial infarction or unstable angina).

RESULTS

Compared with patients with symptomatic ischemia during testing (n = 125), those with silent ischemia (n = 378) demonstrated less severe and extensive reversible defects on stress thallium scintigraphy (p = 0.0008), less functional impairment during treadmill testing manifested by longer exercise duration (640 +/- 173 vs. 529 +/- 190 s, p = 0.002) and longer time to ST segment depression (530 +/- 215 vs. 419 +/- 205 s, p = 0.0001) and less frequent ST segment depression during ambulatory monitoring (9% vs. 19%, p = 0.005). Patients with symptomatic ischemia had a significantly (p = 0.004) increased number of subsequent recurrent cardiac events (28.8%) versus those with silent (18.0%) or no (17.3%) ischemia. Adverse outcomes were especially concentrated in the subgroup with symptomatic ischemia and poor exercise tolerance. The difference in cardiac event rates between patients with silent versus symptomatic ischemia persisted after adjustment for baseline clinical characteristics by Cox regression analysis.

CONCLUSIONS

Patients with painless ischemia during exercise testing 1 to 6 months after recovery from a coronary event have less jeopardized ischemic myocardium and fewer recurrent cardiac events than patients with symptomatic ischemia.

Comparison of optimised planar scintigraphy with SPECT thallium, exercise ECG and angiography in the detection of coronary artery disease

BACKGROUND

Thallium SPECT has been shown to be more sensitive than planar imaging in the detection of coronary heart disease (CAD) in a number of reported series. Early (< 10 minutes) redistribution on planar imaging has been demonstrated in clinical studies and this may partly contribute to its lower sensitivity.

AIM

To determine whether thallium SPECT is superior to planar scintigraphy (with the timing of imaging performed optimally so that it was commenced within five minutes of injection) in the detection of CAD.

METHODS

Planar and SPECT studies were performed in 44 patients with significant (> 70% stenosis) CAD, seven patients with borderline stenoses (50-69%) and in 18 patients with no significant CAD.

RESULTS

The sensitivity of planar imaging was 66% which was higher than exercise ECG 54% (ns) but significantly lower than SPECT 86% (p < 0.005). The specificity of planar thallium scintigraphy was 100% which was higher than SPECT (83%) and significantly higher than exercise ECG 72% (p < 0.05). SPECT had a significantly higher sensitivity for LAD and single vessel disease than planar imaging and this was unrelated to a history of prior myocardial infarction.

CONCLUSION

Even when planar imaging is timed optimally to minimise the impact of early redistribution, SPECT is more sensitive than either planar imaging or exercise ECG in the detection of CAD, but its specificity is lower.

Quantitative evaluation of myocardial single-photon emission tomographic imaging: application to the measurement of perfusion defect size and severity

A new method is described for precise quantitative analysis of the relative three-dimensional distribution of myocardial tracers. The system uses a 360 degrees elliptical sampling of radial slices to create activity profiles. These are then positioned onto a common centre at the same angular coordinates as the corresponding radial slice reconstruction planes to generate a two-dimensional polar summary display. Abnormal distribution is then identified by automatic comparison of the patient polar map with the threshold of a normal database defined on a pixel by pixel basis as the normal mean -2.5 SD. Our stress and rest databases currently comprise 34 and 24 studies for sestamibi and tetrofosmin respectively. The present method differs from currently available software in two major respects. First, radial slices are used rather than short-axis slices to minimize operator intervention and to allow quantitative evaluation of the left ventricle volume independent of the heart size and without truncation, in particular near the apex and at the base. This sampling scheme also results in a more homogeneous and sampling-independent partial volume effect. Secondly, quantitative analysis is improved by calculating perfusion defect severity, extent and size in a precise manner. Severity is evaluated relative to a standardized background measurement and to the mean normal value rather than to the threshold value. This parameter was underestimated up to a defect extent of 32 cm2 in our phantom studies. Calculation of defect extent takes into account the surface distortion resulting from planar projection by using pixel by pixel weighted factors but it is otherwise overestimated as a result of the limited resolution of the imaging system. Integrating defect severity and extent, our hypoperfusion index appeared to accurately estimate the true defect size in our phantom model (r=0.993). The reproducibility of analysis was 6.24% in phantom studies and 3.10% in patient studies including repeated acquisitions. Applied to a well-documented population of 80 patients, this method resulted in an 86% sensitivity and a 78% specificity for overall coronary artery disease detection with reference to the angiographic data.

Prognostic value of noninvasive testing one year after orthotopic cardiac transplantation

OBJECTIVES

We sought to evaluate the prognostic value of routine noninvasive testing--stress thallium-201 imaging, rest two-dimensional echocardiography and rest equilibrium radionuclide angiography--1 year after cardiac transplantation.

BACKGROUND

Coronary artery vasculopathy is the most important cause of late death after orthotopic cardiac transplantation. Several clinical variables have been identified as risk factors for development of coronary vasculopathy. Traditional noninvasive diagnostic testing has been shown to be relatively insensitive for identifying patients with angiographic vasculopathy.

METHODS

Results of prospectively acquired noninvasive testing in 47 consecutive transplant recipients alive 1 year after transplantation were related to subsequent survival. Other clinical variables previously shown to be associated with the development of coronary artery vasculopathy were also included in the analysis.

RESULTS

The 5-year survival rate after cardiac transplantation was 81%. By univariate analysis, echocardiography (chi-square 9.21) and stress thallium-201 myocardial perfusion imaging (chi-square 16.76) were predictive for survival, whereas rest equilibrium radionuclide angiography was not. Clinical contributors to survival were donor age (chi-square 4.56), number of human leukocyte antigen mismatches (chi-square 3.06) and cold ischemic time (chi-square 3.23). By multivariate analysis, stress myocardial imaging remained the only significant predictor of survival (risk ratio 0.27; 95% confidence interval 0.06 to 0.89).

CONCLUSIONS

Normal thallium-201 stress myocardial perfusion imaging 1 year after cardiac transplantation is an important predictor of 5-year survival.

Nuclear cardiology, current applications in clinical practice

The clinical applications of nuclear cardiology have rapidly expanded since the introduction of suitable imaging cameras and readily applicable isotopes. The currently available methods can provide useful data on estimates of ventricular function and detection of myocardial ischemia for adequate patient management. Two standard procedures are routinely used: (1) myocardial perfusion scintigraphy, eg, with thallium 201; and (2) radionuclide angiocardiography by using technetium 99m-labeled red blood cells. Myocardial perfusion scintigraphy provides information on regional viability and estimates regional myocardial perfusion by measuring regional tracer activity. Thallium 201 is the agent used for noninvasive assessment of myocardial perfusion and for improving the results of exercise electrocardiography. Alternative tests, such as pharmacologic stress testing with dipyridamole, have been proposed as a reliable substitute for exercise testing. Additional quantitative analysis and computed tomography have increased the sensitivity and specificity of thallium scintigraphy. Radionuclide angiography techniques are used for the noninvasive evaluation of cardiac function, right and left ventricular function, and wall motion abnormalities. As in perfusion scintigraphy, radionuclide angiography has proven its value for the detection of coronary artery disease (CAD). Abnormal regional wall motion abnormalities are specific for CAD.

Prognostic implications of mental stress-induced silent left ventricular dysfunction in patients with stable angina pectoris

Thirty patients with stable angina pectoris and ischemia on stress perfusion imaging underwent continuous ambulatory left ventricular (LV) function monitoring. Mental stress was induced by mental arithmetic. Fifteen patients developed transient LV dysfunction during mental arithmetic. Patients were followed for 2 years for adverse cardiac events. Twelve patients had cardiac events over 1 year (myocardial infarction in 4, and unstable angina in 8). Nine of 15 patients (60%) with and only 3 of 15 (20%) without mental stress-induced LV dysfunction developed cardiac events (p = 0.025). A higher proportion of patients with cardiac events were taking beta blockers (p = 0.01) and had lower resting heart rates (p = 0.002) than those without cardiac events. There was no difference in the baseline characteristics between the groups of patients with and without cardiac events. At 2-year follow-up, 10 of 15 patients (67%) with mental stress-induced LV dysfunction had adverse events compared with only 4 of 15 (27%) with no mental stress-induced LV dysfunction (p = 0.025). Thus, in this cohort of patients with stable angina pectoris, mental stress-induced LV dysfunction was associated with higher cardiac events on follow-up. The exact mechanism of this association is not clear. Mental stress may be a trigger for adverse cardiac events in these patients. Transient LV dysfunction in response to mental stress may be a marker of abnormal cardiovascular reactivity to emotional and psychological stimuli in patients with coronary artery disease and may be useful for risk stratification.

Prospective evaluation of viable myocardium by quantitative dipyridamole-thallium-201 scintigraphy and radionuclide ventriculography

Improvement of myocardial function is a major goal of coronary revascularization. Considerable interest remains in the preoperative identification of viable myocardium. We examined 26 consecutive patients with left ventricular dysfunction undergoing coronary artery bypass grafting. Serial dipyridamole-thallium imaging and radionuclide ventriculography was performed preoperatively and postoperatively. The relationship between preoperative and postoperative thallium perfusion and segmental wall motion was analyzed. The mean preoperative ejection fraction was 32 +/- 9 (21 to 51%) and increased to 41 +/- 12 (17 to 67%) postoperatively (p > 0.01). Seventy-seven percent of patients improved their global ejection fraction postoperatively by > 5%. Thallium perfusion improved postoperatively in 84% of reversible defects vs 63% of partially reversible defects and 35% of fixed defects. Segments with either reversible or partially reversible thallium defects showed an improved postoperative wall motion in 71% and 68%, respectively. Postoperative wall motion improved in 43% of fixed defects. Overall, 67% of hypokinetic segments showed improved postoperative wall motion while only 29% of akinetic or dyskinetic segments improved postoperatively. Preoperative thallium redistribution coupled with preserved wall motion was predictive of improvement in wall motion was predictive of improvement in wall motion postoperatively and indirectly indicates myocardial viability. However, 43% of fixed defects also showed improved postoperative wall motion. A significant improvement in global ejection fraction was found and could be predicted by a linear regression analysis utilizing clinical and thallium parameters.

The growing flood of technetium-99m myocardial perfusion agents. More water ... or more mud?

“Ol’ man river, dat ol’ man river,

He must know sumpin’, but don’t say nothin’,

He just keeps rollin’, he keeps on rollin’ along.”

Ol’ Man River

—Oscar Hammerstein II

© 1927 T.B. Harms Co. Copyright renewed.

Limited usefulness of exercise testing and thallium scintigraphy in evaluation of ambulatory patients several months after recovery from an acute coronary event: implications for management of stable coronary heart disease. Multicenter Myocardial Ischemia Research Group

OBJECTIVES

This study evaluated the value of noninvasive testing to predict cardiac events in patients with stable coronary disease after hospital admission (and risk stratification) for an acute coronary event.

BACKGROUND

Exercise testing with thallium perfusion imaging identifies patients with obstructive coronary artery disease and has been used to stratify patients after myocardial infarction. Its usefulness for predicting cardiac events in patients with stable coronary disease after recovery from an acute coronary event was explored.

METHODS

Nine hundred thirty-six patients were enrolled 1 to 6 months after hospital admission for a coronary event. Patients underwent exercise treadmill testing with planar thallium-201 scintigraphy and were followed up for an average of 23 months (range 6 to 43). End points were 1) unstable angina requiring hospital admission, nonfatal myocardial infarction or cardiac death; 2) nonfatal infarction or cardiac death; or 3) cardiac death alone.

RESULTS

Twelve patients died of cardiac causes (1.2%); 32 had a nonfatal myocardial infarction (3.4%); and 79 patients (8.4%) developed unstable angina in the first year. Exercise testing improved proportional hazards models constructed from clinical variables for all three end points (p < 0.05). The perfusion scan further improved models for the end points (nonfatal infarction or cardiac death and cardiac death alone, p < 0.05). However, the exercise test with or without thallium added little to the overall prediction of primary events (area under the receiver operating curve increased from 0.649 to 0.663), and only 2% to 13% of patients with abnormal results either had a nonfatal infarction or died.

CONCLUSIONS

Thallium-201 scintigraphy and exercise testing variables identify patients at risk for subsequent cardiac events. However, the poor predictive performance of these tests in this group of patients with stable coronary disease severely limits their usefulness. These results suggest a limited role for exercise and thallium testing in predicting cardiac events in patients with known coronary disease.

Reduced variability of interpretation and improved image quality with a technetium 99m myocardial perfusion agent: comparison of thallium 201 and technetium 99m-labeled tetrofosmin

BACKGROUND

The purpose of this study was to determine the relative image quality and interobserver variability among four readers for 201Tl and 99mTc-labeled tetrofosmin myocardial perfusion images. 99mTc-labeled perfusion agents, with near-optimal physical characteristics for gamma camera imaging, may allow for superior image quality and improved consistency of interpretation. However, most studies to date have demonstrated only similarity in the diagnostic accuracy between technetium agents and thallium. Tetrofosmin is a recently developed 99mTc-labeled agent that has shown promising results in early clinical trials.

METHODS AND RESULTS

A multicenter, open-label trial was performed during which treadmill exercise thallium and tetrofosmin scintigraphy was performed within a 2-week period of each other in 216 subjects. Image quality was evaluated subjectively and scans were interpreted in a blinded, independent fashion by four readers. Perfusion abnormalities were graded as consistent with ischemia, infarction, or mixed and were described both globally and regionally. Interobserver variability was assessed by use of the kappa statistic, and receiver-operator curves were compared for each observer for the diagnostic accuracy of each agent. More tetrofosmin images were of excellent quality than with thallium (52% vs 28%; p < 0.05), and when differences in quality were noted between the agents, tetrofosmin was more often superior (p < 0.0001). The interobserver variability was lower with tetrofosmin scintigraphy because generally higher kappa values were noted, especially in the lateral wall. Higher receiver-operator curve areas indicative of improved diagnostic accuracy were noted among the four readers for tetrofosmin in 80% of vascular territories.

CONCLUSIONS

99mTc-labeled tetrofosmin scintigraphy yields images of improved quality compared with thallium, and there is an overall improvement in the consistency of image analysis associated with the use of tetrofosmin.

One-year prognosis of patients with normal planar or single-photon emission computed tomographic technetium 99m-labeled sestamibi exercise imaging

BACKGROUND

The favorable prognostic significance of normal 201Tl stress perfusion images, even in the presence of known coronary artery disease, has been well documented. Relatively few data are available with regard to the prognostic significance of normal planar and single-photon emission computed tomographic (SPECT) stress 99mTc-labeled sestamibi (99mTc-sestamibi) images.

METHODS AND RESULTS

The prognostic significance of normal exercise 99mTc-sestamibi myocardial perfusion imaging was evaluated in 208 consecutive patients. All patients were referred for evaluation of chest pain syndrome. One hundred eight patients (52%) underwent SPECT imaging, 79 patients (38%) underwent planar imaging, and 21 patients (10%) underwent both planar and SPECT imaging. One hundred seventy-five patients (84%) had a normal or nondiagnostic exercise electrocardiogram, and 33 patients (16%) had a positive exercise electrocardiogram. Follow-up was 13.5 +/- 2 months and was complete in 99.5% of patients. No patient died of cardiac causes during follow-up. One patient (0.5%) had a nonfatal myocardial infarction and four patients (2%) had unstable angina necessitating revascularization. There was no difference in rate of cardiac events between men and women or whether SPECT or planar imaging was used. However, 33 patients with normal 99mTc-sestamibi imaging and a positive exercise electrocardiogram had a significantly higher cardiac event rate than had patients with negative exercise electrocardiograms (9% vs 1%, p < 0.025).

CONCLUSION

Patients with normal 99mTc-sestamibi exercise SPECT or planar imaging results and a normal or nondiagnostic exercise electrocardiogram have a favorable 1-year prognosis. Patients with normal 99mTc-sestamibi images and a positive stress electrocardiogram have a less favorable outcome.

Thallium-201 redistribution after early reinjection in patients with severe stress perfusion defects and ventricular dysfunction

Early poststress thallium-201 reinjection to obviate the need for two sets of redistribution images has been proposed as an alternative reinjection protocol although, in a preliminary study, it did not reduce the frequency of late redistribution. The efficacy of the early reinjection protocol was assessed in 102 patients with chronic ischemic heart disease and left ventricular dysfunction who showed severe thallium-201 defects on planar stress images. Thallium-201 was reinjected immediately after the poststress study, and redistribution images were acquired 4 and 24 hours later. By quantitative analysis, a further increase in thallium-201 uptake on 24-hour imaging was documented in only 48 (6%) of 740 segments still abnormal on 4-hour images, 26 (54%) of which were represented by partially reversible or not severe fixed defects. Overall, late thallium-201 uptake was less frequently observed in patients with depressed ejection fraction (p < 0.05). Clinically relevant late reversibility was found in only 3 (3%) of 94 patients. Scans were repeated after revascularization in 20 patients. Tracer uptake improved in 40 (34%) of 118 segments with 4-hour defect: the improvement mainly (85%) involved those segments already showing partial 4-hour reversibility or mild fixed defects on the preoperative study. Thus a negligible late tracer redistribution was found in patients with severe stress thallium-201 defects undergoing early reinjection and 4-hour imaging; no significant 24-hour improvement was observed in those patients with depressed ventricular function and fixed 4-hour defects. This simpler imaging protocol could obviate the need for additional late imaging to detect residual viability.

X-syndrome: is there impairment of myocardial perfusion during stress?

Stress T1-201 myocardial scintigraphy was carried out in 16 patients with x-syndrome. Eleven patients having IHD with single-vessel disease served as the control. With bicycle exercise test all 16 patients with x-syndrome had some type of myocardial perfusion abnormality. These perfusion defects were situated in the vascular beds of different coronary arteries. Myocardial perfusion defects in patients with x-syndrome were similar to those patients with moderate, but haemodynamically significant, single-vessel disease. At the same time, these perfusion defects were significantly less pronounced than those in patients with a subtotal occlusion of one coronary artery. Thus, patients with x-syndrome have not only the clinical features of IHD (anginal attacks), but also marked stress-induced, myocardial perfusion defects.

Exercise and redistribution thallium-201 myocardial scintigraphy: changes in distribution qualitatively unaffected by previous infarction

Eighteen patients with stable exertional angina pectoris were investigated by thallium-201 (201Tl) exercise and redistribution single photon emission computed tomography (SPECT) after coronary angiography. Eight of the patients had a previous myocardial infarct. Six patients had single-, eight double- and four triple-vessel disease. An exercise SPECT was acquired 10 min after the administration of isotope, injected 1-2 min before the termination of a symptom-limited exercise test. A redistribution SPECT was recorded 3 h later. 201Tl activity per pixel was compared between the exercise and redistribution SPECT in relative and absolute terms. For each patient there was a good correlation between activity per pixel in the redistribution SPECT and the corresponding pixels in the exercise SPECT (mean correlation coefficient 0.86 +/- 0.08), irrespective of the extent of coronary artery disease or presence of a previous infarction in the pixel region. Relative wash-out correlated to the degree of coronary artery stenosis (r = 0.48), but did not differ between infarcted and non-infarcted myocardial regions. A similar relationship was documented for pixels with visual 'refill' in the redistribution SPECT. This implies that most of the information in the redistribution SPECT was present already in the exercise SPECT. Thus, qualitative information of a similar kind is obtained from images acquired immediately after exercise and after 3-4 h of redistribution.

Effects of altered left ventricular geometry on quantitative technetium 99m sestamibi defect size in humans: perfusion imaging during coronary angioplasty

BACKGROUND

Serial myocardial perfusion imaging is used to assess exercise-induced myocardial ischemia and myocardial risk area, salvage, and viability in patients with myocardial infarction. In an experimental animal model it has been shown that abnormal regional wall motion and altered left ventricular geometry can produce apparent perfusion defects independent of changes in blood flow. The effects of regional alteration in ventricular geometry on perfusion images in humans are not defined. The purpose of our investigation was to evaluate quantitatively the effect of altered left ventricular geometry on myocardial perfusion imaging with technetium 99m sestamibi during coronary angioplasty.

METHODS AND RESULTS

Nine patients with normal baseline left ventricular function referred for angioplasty of the left anterior descending coronary artery were studied. 99mTc sestamibi was administered intravenously before angioplasty. Baseline planar electrocardiographic-gated imaging was performed. Imaging was repeated in the catheterization laboratory during angioplasty vessel occlusion when altered left ventricular geometry was produced and again later after angioplasty. Summed static, end-systolic, and end-diastolic images were generated from the electrocardiographic-gated acquisitions. Circumferential count profiles of images obtained during percutaneous transluminal coronary angioplasty (PTCA) were compared with those of a normal 99mTc sestamibi database and their own baseline images. Defect integral (the area below the reference profile) and nadir (maximum percent decrease in activity) were derived. Compared with a normal database, new quantitative defects appeared on PTCA-summed images in only two patients. The defects were small to moderate in size. However, compared with their own baseline profile, six patients had quantitative defects during PTCA (mean defect integral 3 +/- 2; mean defect nadir 12% +/- 7%). Defect nadir was larger on end-diastolic images compared with summed images (22% +/- 7% and 12% +/- 7%, respectively; p < 0.05).

CONCLUSIONS

Altered left ventricular geometry may create apparent, albeit small, planar myocardial perfusion defects in humans. Changes in defect size on serial images may be only partially caused by changes in regional wall motion or geometry.

Myocardial risk area defined by technetium-99m sestamibi imaging during percutaneous transluminal coronary angioplasty: comparison with coronary angiography

OBJECTIVES

The purpose of this study was to compare the assessment of myocardial area at risk in patients with coronary artery stenosis by coronary angiography and quantitative myocardial perfusion imaging with technetium-99m sestamibi.

BACKGROUND

Decisions concerning patient management frequently rely on semiquantitative angiographic estimation of the myocardial area at risk, although this approach has not been well validated. Technetium-99m sestamibi is a perfusion imaging agent with little redistribution after initial myocardial uptake. This characteristic allows for injection during angioplasty and later imaging for visualization and quantitation of the nonperfused area at risk.

METHODS

Thirty-nine patients referred for coronary angioplasty were studied. Technetium-99m sestamibi was injected intravenously during angioplasty balloon inflation. Planar (33 patients) or tomographic (6 patients) imaging was performed after completion of angioplasty. Imaging was repeated 24 to 48 h later. Myocardial risk area (perfusion defect on angioplasty image) was quantified as an integral using circumferential count distribution profiles and normal reference. Angiographic risk area was assessed using five scoring methods.

RESULTS

The scintigraphic risk area was 14 +/- 15 on planar images and 39 +/- 16 on tomography. Scintigraphic risk area of patients with infarction was larger than in patients without (22 +/- 17 versus 7 +/- 8, p = 0.003). The left anterior descending coronary artery had a larger mean risk area than other vessels (22 +/- 15 versus 7 +/- 11, p = 0.002). The presence of angiographic collateral channels was associated with smaller risk areas. Angiographic risk scores correlated only moderately with the technetium-99m sestamibi risk area (r = 0.54 to 0.65), with considerable spread of data.

CONCLUSIONS

Area at risk estimated from coronary angiography does not correlate well with that from quantitative myocardial perfusion imaging with technetium-99m sestamibi. These findings emphasize that the functional significance of coronary artery disease is not predicted by coronary anatomy alone.

Role of behavioral and psychological factors in mental stress-induced silent left ventricular dysfunction in coronary artery disease

OBJECTIVES

We examined the relationship of the psychological profile to left ventricular dysfunction induced during mental stress.

BACKGROUND

The contribution of psychological factors to mental stress-provoked silent myocardial ischemia has not been explored.

METHODS

Thirty patients with chronic stable coronary artery disease and a reversible defect on stress thallium-201 imaging completed a psychological assessment by questionnaire and Structured Interview, serially administered mental stress and brief walking exercise. Blood pressure, electrocardiogram (ECG) and left ventricular indexes were obtained by ambulatory serial radionuclide ventriculography. Silent ventricular dysfunction was defined by a decrease > or = 0.05 in ejection fraction or > or = 1 mm in ST segment on the ECG in the absence of symptoms.

RESULTS

Of the 30 patients, 15 (Group I) had evidence of silent left ventricular dysfunction during mental arithmetic. The other 15 (Group II) showed no change. In addition, 18 of 30 patients had this dysfunction during the Structured Interview. Both ischemic and nonischemic groups developed comparable and significant increases in heart rate and blood pressure. Group I patients were distinguished by higher scores on measures of aggressive responding (p < 0.001), trait anger (p < 0.0001), hostile affect (p < 0.003) and an index of behavioral reactivity (p < 0.003) and a lower score on anger control (p < 0.001). No other variables, including historical and clinical indexes, discriminated between the two groups.

CONCLUSIONS

Patients with coronary artery disease and mental stress-provoked silent ventricular dysfunction were distinguished by a psychological profile consistent with emotional reactivity to social interaction and mental provocation, with anger as the predominant affective state. Patients with such a profile may be at risk of frequent silent left ventricular dysfunction.

Planar 201Tl scintigraphy in ischaemic heart disease: a critical re-evaluation of qualitative and quantitative data analysis

The aims of the present study were to examine the observer agreement of qualitative (visual) and quantitative (computer-assisted) analysis of planar 201Tl imaging and to compare the diagnostic values of these methods in the detection of infarcted and exercise-induced ischaemic myocardium. The study population comprised of 119 patients (aged 24-77 years) referred consecutively for stress thallium scintigraphy for either diagnostic reasons (n = 42, 35%) or for further evaluation of known coronary artery disease (CAD) (n = 77, 65%). The interobserver agreement was low with the qualitative method and significantly higher with the quantitative method: Kappa-values 0.29-0.39 vs. 0.80-0.92, P < 0.00001. Sensitivity and specificity for the detection of previous Q-wave infarct was significantly higher with the quantitative method (94% and 94%) compared to the qualitative method (77% and 74%), P < 0.01. The corresponding predictive values of a positive and a negative test were 96% and 92% vs. 80% and 70% (P < 0.01). In 86 patients in whom coronary angiography was performed the two methods did not differ significantly regarding sensitivity, specificity and predictive values for the diagnosis of reversible ischaemia or rather CAD. However, when 22 patients with a maximal exercise heart rate < 80% of the predicted target heart rate were excluded the sensitivity was increased with both techniques and was significantly higher with the quantitative method. We conclude that qualitative image analysis has an unacceptably low reproducibility and that quantitative image analysis increases the diagnostic value of 201Tl scintigraphy considerably in both the detection of previous infarcts and, provided a sufficient exercise level is achieved, in the disclosure of reversible myocardial ischaemia.

Comparison between reference values for 201thallium uptake and washout from the myocardium after exercise and after dipyridamole

A slow washout of 201Thallium has a high diagnostic and prognostic value for coronary artery disease. The aim of the present work was to contribute with reference data on 201Tl uptake and washout from the myocardium. With a quantitative method using circumferential profiles and interpolative background subtraction we performed 201Tl myocardial imaging in two groups of subjects with a low probability of coronary artery disease. Washout in per cent is defined as (1-D/I).100, where D is the delayed uptake rate and I the initial uptake rate. In group A (n = 16) myocardial hyperaemia was induced by maximal exercise, in group B (n = 15) by intravenous infusion of dipyridamole. In group A, the mean washout was 52%, and in group B it was 34% (P < 0.001). The delayed uptake rate D was significantly higher after dipyridamole, 58.4 cps, than after exercise, 44.5 cps (P < 0.05). There was no significant differences in I between the two groups. The findings regarding D and I explain that the washout is slower after dipyridamole than after exercise, as the mean D/I ratio was 0.48 in group A and 0.66 in group B (P < 0.001).

The role of scintigraphic techniques in the evaluation of functional results of coronary bypass grafting and percutaneous transluminal coronary angioplasty

Scintigraphic techniques can be used first, to guide appropriate referral for interventional procedures, and second to predict the effect of revascularization on regional perfusion and function prior to the intervention, thereby being able to assess efficacy of revascularization and to assess whether ischemia is the origin of recurrence of symptoms. Of increasing importance is the ability of nuclear techniques to identify those myocardial regions with abnormal function which might benefit from revascularization by showing improvement in regional wall motion. Positron emission tomography is considered to be the gold standard to assess regional myocardial perfusion and metabolism. The introduction of the reinjection technique makes 201Tl-scintigraphy the method of choice to detect jeopardized myocardium and to guide appropriate referral for revascularization procedures in those institutes where PET is not available. Even when the costly PET-instrumentation is available, cost-benefit analysis is indicated to assess the additional value of PET compared with 201Tl reinjection imaging.

Extent of jeopardized viable myocardium determined by myocardial perfusion imaging best predicts perioperative cardiac events in patients undergoing noncardiac surgery

OBJECTIVES

This study was undertaken to test the hypothesis that the risk of perioperative cardiac events is not simply determined by the presence of myocardium at risk, but is directly related to the extent of myocardium at risk as reflected in thallium-201 myocardial imaging.

BACKGROUND

The risk of perioperative cardiac events in patients undergoing noncardiac surgery has been related to the presence of transient defects on dipyridamole thallium-201 myocardial imaging, reflecting jeopardized viable myocardium.

METHODS

The study cohort consisted of 231 consecutive patients who underwent noncardiac surgery and had a preoperative dipyridamole thallium-201 imaging study. Patients with vascular reconstruction or bypass constituted the largest surgical subgroup (n = 140). For thallium-201 imaging data, each of three planar projections was divided into three segments (total nine segments) and each segment was interpreted as normal or showing a transient or fixed defect. The ability of clinical and thallium-201 imaging data to predict perioperative cardiac events was compared with stepwise multivariate logistic regression analysis.

RESULTS

Perioperative cardiac events occurred in 19 patients, including 5 with cardiac death, 7 with nonfatal myocardial infarction and 7 with unstable angina. For cardiac death or nonfatal myocardial infarction, the only significant multivariate predictors were the number of myocardial segments with transient thallium-201 defects (p < 0.0005) and a history of diabetes mellitus (p < 0.05). For all cardiac events, the only significant multivariate predictors were the number of myocardial segments with transient defects (p < 0.0001), diabetes mellitus (p < 0.05) and calcium channel blocker use (p < 0.05).

CONCLUSIONS

The probability of important cardiac events in patients undergoing noncardiac surgery is best predicted by the extent of myocardium at risk as reflected on thallium-201 myocardial perfusion imaging. A history of diabetes mellitus also has a significant influence on perioperative risk.

The use of computer-assisted diagnosis in cardiac-perfusion nuclear medicine studies: a review

The use of computer-assisted diagnosis has become widespread in cardiac nuclear medicine. Quantitative programs are commercially available for ventriculography, phase analysis, and thallium 201 perfusion studies. The goal of these programs is to eliminate interobserver variability by objectively analyzing the studies without causing a loss of accuracy. In addition, by using quantitative data not apparent on visual inspection, some programs attempt to increase sensitivity for disease above that possible by the visual reading of images. Programs that analyze perfusion studies to detect coronary artery disease have received the most interest. Results have varied, but sensitivities as high as 95% have been reported. This review discusses the techniques of computer-assisted diagnosis for thallium 201 myocardial-perfusion studies. The circumferential and washout profile methods are discussed in detail.

Does diffuse coronary atherosclerosis affect the relation between coronary stenoses and uptake of thallium-201 after exercise?

It has been proposed that diffuse coronary atherosclerosis influences the myocardial perfusion. We performed a study of 94 young men with previous myocardial infarction in order to find out whether the presence and extent of diffuse coronary atherosclerosis affected the relation between maximal stenosis and myocardial perfusion in areas remote from the infarction. The patients were examined by planar-imaging thallium-201 scintigraphy, following exercise, and coronary angiography within 6 months after myocardial infarction. The maximal distinct stenosis and diffuse coronary atherosclerosis, comprising both plaque size and extent, were semiquantitatively assessed. The correlation coefficients between maximal stenosis within the LAD, RCA, and LCX vascular territories and the corresponding initial uptake of thallium were 0.52 (P = 0.0001), 0.30 (P = 0.04), and 0.46 (P = 0.02), respectively. No change of the correlations was found, except for a slight increase of the r-value from 0.30 to 0.37 in regions corresponding to RCA, after controlling for the diffuse atherosclerosis score in a multiple stepwise regression analysis. These findings indicate no impact of diffuse coronary atherosclerosis on regional myocardial perfusion in areas remote from the infarction.

Thallium-201 for assessment of myocardial viability: quantitative comparison of 24-hour redistribution imaging with imaging after reinjection at rest

Redistribution thallium-201 imaging 2 to 4 h after exercise may be incomplete and therefore may be inadequate to fully assess myocardial variability. Late redistribution imaging 24 h after exercise has been proposed to overcome this limitation of thallium stress imaging. However, because of poor count density the image quality on these studies is often suboptimal. In the present study the diagnostic information on 24-h planar thallium redistribution images was compared with that on images obtained after a reinjection of thallium at rest. Eighty-four patients with a stress thallium-201 defect had delayed redistribution imaging after 2 to 4 h and 24 h later, and again after an injection of thallium at rest. Defect reversibility on 24-h redistribution images was compared quantitatively with that on images after injection of thallium at rest. The quality of thallium images at rest was consistently better than that of 24-h redistribution images. Poor quality studies occurred in 13% of 24-h redistribution images compared with 0.4% of the studies at rest. Significantly more defect reversibility was detected on images after the reinjection at rest. Of 41 patients who appeared to have a fixed defect at 2- to 4-h redistribution imaging, 11 (27%) had a reversible defect by 24-h redistribution imaging compared with 29 (71%) after thallium-201 reinjection. No clinical variables at the time of stress testing were predictive of late defect reversibility. It is concluded that in patients with fixed a thallium defect at 2 to 4 h after exercise, reimaging after a reinjection at rest provides better diagnostic information than does 24-h late redistribution imaging.

Prognostic value of thallium-201 myocardial perfusion imaging in patients with unstable angina who respond to medical treatment

Although the prognostic value of thallium-201 imaging is well established, its ability to risk stratify patients who present with unstable angina is unclear. Fifty-two consecutive patients admitted with unstable angina who responded to medical treatment and underwent stress thallium-201 imaging within 1 week of discharge were studied. Patients were followed up for 39 +/- 11 months. Cardiac events included cardiac death (n = 3), nonfatal myocardial infarction (n = 4) and admission for unstable angina or revascularization (n = 17). The ability of thallium-201 data (redistribution, fixed defects, normal) to predict cardiac events was compared with clinical data (age, gender, prior myocardial infarction, anginal syndrome, rest and stress electrocardiogram) and cardiac catheterization data using logistic regression. Thallium-201 redistribution was the only significant predictor of cardiac death or nonfatal myocardial infarction (p less than 0.05). The number of myocardial segments with thallium-201 redistribution (p less than 0.0005) and a history of prior myocardial infarction (p less than 0.05) were the only significant predictors of all cardiac events. Cardiac death or nonfatal myocardial infarction occurred more frequently in patients with thallium-201 redistribution (6 [26%] of 23) than in those without redistribution (1 [3%] of 29, p less than 0.05). Similarly, total cardiac events developed more frequently in patients with thallium-201 redistribution (p less than 0.001). Stress thallium-201 imaging has important prognostic value in patients admitted with unstable angina who respond to medical therapy and can identify subgroups at high versus low risk for future cardiac events.

Circumferential quantitative analysis of planar 201T1 myocardial scintigraphy in the diagnosis of coronary artery disease

Methodology for the computer analysis of 201T1 myocardial perfusion images has been developed by several laboratories. Substantial evidence of the advantage of this approach over visual inspection alone has been reported. The currently available computer analyses use different algorithms to analyze 201T1 kinetics in the myocardium. The authors evaluated and compared two widely used software programs, Medical Data System (MDS): a mean-count profile, and the Cedars Sinai (CS): a maximal-count profile, of planar 201T1 scintigraphy for their ability to detect coronary artery disease (CAD).

Silent myocardial ischemia and infarction in diabetics with peripheral vascular disease: assessment by dipyridamole thallium-201 scintigraphy

We investigated the incidence of silent myocardial ischemia and infarction as assessed by dipyridamole thallium scintigraphy in 30 diabetic patients with peripheral vascular disease and without clinical suspicion of coronary artery disease. Seventeen patients (57%) had thallium abnormalities, with reversible thallium defects compatible with ischemia in 14 patients (47%) and evidence of prior, clinically silent myocardial infarction in 11 patients (37%). Thallium abnormalities were most frequent in patients with concomitant hypertension and cigarette smoking (p = 0.001). These results suggest that unsuspected coronary artery disease is common in this particular group of patients with diabetes mellitus.

Quantification of area at risk during coronary occlusion and degree of myocardial salvage after reperfusion with technetium-99m methoxyisobutyl isonitrile

Serial myocardial imaging with technetium-99m methoxyisobutyl isonitrile (99mTc-MIBI) has been proposed for evaluating myocardial salvage after reperfusion. To define 99mTc-MIBI uptake before and after reperfusion, 17 open-chest dogs underwent 3 hours of left anterior descending artery occlusion and 3 hours of reperfusion. 99mTc-MIBI was injected during occlusion (group 1) or after 90 minutes of reperfusion (group 2). Myocardial 99mTc-MIBI activity was correlated with microsphere flow during occlusion and reperfusion. Anatomic risk area and infarct area were defined by postmortem vital staining and correlated with the perfusion defects defined by analysis of 99mTc-MIBI macroautoradiographs and gamma camera images of myocardial slices. The left ventricle was divided into 96 segments for gamma well counting. Flow and 99mTc-MIBI activity were normalized to nonischemic values. Myocardial segments were grouped, based on occlusion flow, into zones: severely ischemic (less than or equal to 30% nonischemic), moderately ischemic (greater than 30%, less than or equal to 60% nonischemic), mildly ischemic (greater than 60%, less than or equal to 90% nonischemic), and nonischemic (greater than 90%, less than or equal to 120% nonischemic). Among dogs injected with 99mTc-MIBI during coronary occlusion (group 1), myocardial 99mTc-MIBI activity correlated linearly with occlusion flow for both endocardial (r = 0.91) and transmural (r = 0.91) segments. The risk area defined by 99mTc-MIBI autoradiography (group 1) correlated with the postmortem risk area (rho = 0.94) but was 29% smaller than the anatomic risk area (p = 0.03), reflecting the contribution of collateral flow. Among dogs injected with 99mTc-MIBI after reperfusion (group 2), myocardial 99mTc-MIBI did not correlate with reperfusion flow in either endocardial or transmural segments. Among group 2 dogs, myocardial 99mTc-MIBI activity was significantly less than reperfusion flow at the time of injection in the severely ischemic (25 +/- 5% versus 74 +/- 24% nonischemic, p = 0.002), moderately ischemic (54 +/- 12% versus 96 +/- 15% nonischemic, p = 0.001), and mildly ischemic (84 +/- 6% versus 93 +/- 3% nonischemic, p = 0.002) zones. The defect area defined by 99mTc-MIBI autoradiography (group 2) correlated very closely with the postmortem infarct area (rho = 0.98). Thus, the myocardial uptake of 99mTc-MIBI during coronary occlusion correlates with occlusion flow and reflects the "area at risk." When 99mTc-MIBI was given after 90 minutes of reperfusion following 3 hours of coronary occlusion, the myocardial activity was significantly reduced compared with reperfusion flow in both necrotic and perinecrotic regions, reflecting myocardial viability more than the degree of reperfusion.

Radiation effects on left ventricular function and myocardial perfusion in long term survivors of Hodgkin's disease

We evaluated systolic and diastolic indices of left ventricular performance by radionuclide angiocardiography and myocardial perfusion with exercise/rest thallium scintigraphy in 16 patients previously irradiated for Hodgkin's disease. These commonly used indices of left ventricular (LV) performance included LV ejection fraction (LVEF) as a measure of systolic function, and LV peak filling rate (PFR) as a measure of diastolic function. The presence of coronary artery disease (CAD) was evaluated by ECG treadmill testing (13 patients) and by quantitative planar thallium scintigraphy (12 patients). Patients were 16-38 years old (mean 24.9 +/- SD 6.2) at the tim eof irradiation, and were evaluated 2.5-21.5 years (mean 9.3 +/- 6.3) after radiation therapy (RT). RT was delivered with beam energies of 2-18 MV, equally weighted AP-PA mantle fields with both fields treated daily for most patients (13 patients), and fraction sizes of 1.5-2.0 Gy. Six patients received radiation to th entire cardiac volume, most commonly via left-sided partial transmission lung blocks (PTLB). Patient data were analyzed according to the volume of heart treated. Individuals who had the entire cardiac volume irradiated were assigned to group I (N = 6), and those patients who had some portion of the heart shielded throughout treatment comprised group II (N = 10). In this series, no perfusion defects were evident in either group by quantitative planar thallium scintigraphy. Mean LVEF for all patients studied was 60% (normal LVEF greater than or equal to 50%). Patients in group I had a lower mean LVEF than those in group II, 55 +/- 4% versus 63 +/- 6% (p = 0.01). Mean PFR for all patients studied was normal at 3.5 EDV/sec (normal PFR greater than or equal to 2.54 EDV/sec). Patients in group I had a lower mean PFR than those in group II, 3.0 +/- 0.6 vs 3.8 +/- 0.7 EDV/sec (p = 0.04). Thus, patients irradiated to large cardiac and pulmonary volumes had lower LVEF and PFR within the normal range compared to patients who had some portion of the cardiac volume shielded. These differences are statistically significant in the relatively small groups studied but do not appear to be associated at the present time with clinically significant effects.

Assessment of "silent" restenosis and long-term follow-up after successful angioplasty in single vessel coronary artery disease: the value of quantitative exercise electrocardiography and quantitative coronary angiography

Exercise electrocardiographic (ECG) testing during follow-up after coronary angioplasty is widely applied to evaluate the efficacy of angioplasty, even in asymptomatic patients. One hundred forty-one asymptomatic patients without previous myocardial infarction underwent quantitative exercise ECG testing and quantitative coronary angiography 1 to 6 months after successful angioplasty in single vessel coronary artery disease to 1) determine the value of exercise ECG testing to detect "silent" restenosis, and 2) assess the long-term prognostic value of exercise ECG testing and coronary angiography. The prevalence of restenosis (defined as greater than or equal to 50% luminal narrowing at the dilation site) was 12% in this selected study group. Of 26 patients with an abnormal exercise ECG (ST segment depression greater than or equal to 0.1 mV), only 4 (15%) showed recurrence of stenosis. Sensitivity and specificity for detection of restenosis were 24% and 82%, respectively. One hundred thirty-four patients (95%) were followed up 1 to 64 months (mean 35) after exercise ECG testing and coronary angiography. Thirty-two patients (24%) experienced a cardiac event: in 25 patients (78%) the initial event was recurrent angina pectoris (New York Heart Association class III or IV) and in 7 patients (22%) it was myocardial infarction, although cardiac death did not occur. The mean interval between exercise ECG testing and the initial cardiac events was 14 months (range 1 to 55), whereas 47% of the initial events took place less than or equal to 6 months after exercise ECG testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial perfusion scintigraphy as an aid in understanding electrocardiographic changes of ischemia and infarction

In summary, myocardial perfusion scintigraphy with either thallium or the isonitriles has added substantially to electrocardiographic definition of both myocardial infarction and acute and chronic myocardial ischemia. Using perfusion scintigraphy, one can define infarct zones, risk zones, and the presence of reperfusion following thrombolytic therapy. When perfusion scintigraphy is combined with physiologic or pharmacologic stress, myocardial ischemia can be documented, irrespective of electrocardiographic documentation of the phenomenon. Delayed imaging may be important for defining viability even in the presence of significant Q waves. Myocardial perfusion scintigraphy provides prognostic evaluation of patients with both acute and chronic coronary syndromes. When the current cumulative experience is looked at critically, it is clear that myocardial perfusion scintigraphy has helped in the development of an understanding of the limitations of electrocardiography in the diagnostic and functional categorization of patients with acute and chronic coronary disease.