Thallium reinjection after stress-redistribution imaging. Does 24-hour delayed imaging after reinjection enhance detection of viable myocardium?

Determining myocardial viability in chronic ischemic left ventricular dysfunction: a prospective comparison of rest-redistribution thallium 201 single-photon emission computed tomography, nitroglycerin-dobutamine echocardiography, and intracoronary myocardial contrast echocardiography

BACKGROUND

Detection of viable myocardium (VM) has important therapeutic implications for chronic ischemic left ventricular (LV) systolic dysfunction. We compared the ability of nitroglycerin-dobutamine echocardiography (NTG-DE), intracoronary myocardial contrast echocardiography (MCE), and rest-redistribution thallium 201 single-photon emission computed tomography (RRT-SPECT) to detect VM in this setting.

METHODS

Patients with LV ejection fraction (LVEF) <40% and multivessel coronary disease suitable for revascularization underwent NTG-DE, MCE, RRT-SPECT, and radionuclide ventriculography to determine baseline LVEF. Myocardial contrast echocardiography was performed using intracoronary injection of Albunex. Patients who underwent revascularization had 3-month postprocedural radionuclide ventriculography and transthoracic echocardiography to assess functional recovery.

RESULTS

Of 512 myocardial segments in the 32 patients studied, 309 were akinetic or dyskinetic at baseline. Nitroglycerin alone increased regional thickening in 20% of segments with contractile reserve. By RRT-SPECT, 93% of nitroglycerin-responsive segments were viable. Myocardial contrast echocardiography had up to 85% sensitivity and 74% specificity for detection of VM diagnosed by RRT-SPECT. In the 23 patients who underwent revascularization, 54% of akinetic segments showed improved contractility, and mean LVEF increased from 32% to 37% (P = .04). Sensitivities and specificities for detecting functional recovery were 95% and 37% for RRT-SPECT, up to 87% and 48% for MCE, and 63% and 83% for a biphasic response during NTG-DE.

CONCLUSIONS

In patients with chronic ischemic LV dysfunction, RRT-SPECT had the highest sensitivity, and NTG-DE, the best specificity for detection of VM. Nitroglycerin facilitated detection of VM and may be a useful adjunct to dobutamine stimulation.

Detection of hibernate myocardium by 99mTc sestamibi gated SPECT during low-dose dobutamine infusion plus nitrate in patients with first acute myocardial infarction

AIM

To investigate the role of Tc-MIBI gated SPECT imaging following the administration of low-dose dobutamine plus nitrate (LDD+nitrate) in the assessment of left ventricular function and the perfusion of hibernate myocardial tissue.

METHODS

The study group comprised 29 patients diagnosed as having acute myocardial infarction. In the first month post-infarction, Tc-MIBI gated SPECT imaging was performed in all patients at rest-dobutamine stress and LDD+nitrate. Ejection fraction, end diastolic volume (EDV), end systolic volume (ESV), stroke volume, volume, extent score, and reversibility score values were calculated.

RESULTS

The findings of Tc-MIBI gated SPECT imaging following the administration of LDD+nitrate and the rest Tc-MIBI gated SPECT findings revealed that while the levels of ejection fraction (P=0.004) and reversibility score (P=0.000) increased significantly, there was a significant decrease in EDV (P=0.001), ESV (P=0.001), volume (P=0.017), stroke volume (P=0.257) and extent score (P=0.039) values.

CONCLUSION

The use of Tc-MIBI gated SPECT concomitantly with the administration of LDD+nitrate is useful in the determination of myocardial hibernation in patients with left ventricular failure following acute myocardial infarction.

An overview of contemporary nuclear cardiology

Myocardial perfusion single photon emission computed tomography (SPECT) is a widely utilized noninvasive imaging modality for the diagnosis, prognosis, and risk stratification of coronary artery disease. It is clearly superior to the traditional planar technique in terms of imaging contrast and consequent diagnostic and prognostic yield. The strength of SPECT images is largely derived from the three-dimensional, volumetric nature of its image. Thus, this modality permits three-dimensional assessment and quantitation of the perfused myocardium and functional assessment through electrocardiographic gating of the perfusion images.

Value of linsidomin in assessing myocardial viability with thallium-201 SPECT

Myocardial viability can be assessed with rest/24 h redistribution (201)Tl myocardial single photon emission computed tomography (SPECT). The intravenous injection of vasodilators induces an early redistribution of (201)Tl and shortens the total examination time. The aim of this study was to compare the images after injection of linsidomin with the 24 h images. We studied 51 consecutive patients (38 males, 13 females), aged 66+/-11 years, referred for assessment of myocardial viability after acute myocardial infarction. SPECT acquisition at rest (30 projections over 180 degrees, 30 s per projection) was performed 20 min after injection of (201)Tl. A second acquisition (same parameters) was performed 2 min after intravenous injection of linsidomin (2 mg). A delayed acquisition was performed on the following day (50 s per step). Myocardial perfusion at rest was normal in 111 of 255 segments. For the 144 other segments, 24 h images were similar to the images acquired after the injection of linsidomin in 94% of cases (136 of 144 segments). The 24 h images showed partial redistribution that was not present after linsidomin in only eight segments (6%). Injection of linsidomin after rest acquisition can provide a reliable and more rapid assessment of myocardial viability. This very simple protocol (rest/linsidomin (201)Tl myocardial SPECT) can be performed in less than 1 h.

Immediate thallium re-injection after stress imaging for the detection of myocardial viability

Myocardial perfusion imaging with thallium is an established method to assess the presence of ischaemic and viable myocardium. Using planar imaging, images acquired 1 h after immediate thallium re-injection have been shown to be comparable to those of 3 h redistribution. The aim of this study was to clarify this using SPET. Twenty patients with chronic coronary artery disease with at least two perfusion defects on post-exercise images participated in this study. All patients received thallium re-injection after post-stress SPET and all had 1 h, 3 h and 24 h redistribution imaging. The thallium myocardial tomograms were divided into 14 segments for each patient. A total of 78 segments were studied. When the frequency of reversibility on 1 h, 3 h and 24 h redistribution images is compared, of the 78 SPET defects 18 (23.1%) showed reversibility by 1 h, 34 (43.6%) by combined 1 h and 3 h imaging (P < 0.05) and 50 (64.1%) by combined 1 h, 3 h and 24 h imaging (P < 0.05). Our results show that, compared to 3 h images, images acquired 1 h after immediate thallium re-injection underestimate the extent of viable myocardial segments and the incidence of late reversibility was not reduced by the immediate re-injection of thallium.

Nitrate-enhanced thallium 201 single-photon emission computed tomography imaging in hibernating myocardium

OBJECTIVES

This study tested the usefulness of nitrate-enhanced thallium 201 imaging for detecting myocardial viability.

BACKGROUND

Previous work suggests that nitrates enhance the ability of (201)Tl imaging to detect viable myocardium.

METHODS

Eighteen patients with coronary artery disease underwent (201)Tl imaging at rest, after 4 hours of redistribution, and during intravenous nitroglycerine infusion (mean dose = 5.96 +/- 5.37 microgram/kg/min). Twelve patients had their echocardiograms repeated after revascularization. Perfusion and wall motion were scored from 0 to 2 (absent to normal).

RESULTS

All the regions identified as viable by the rest/redistribution pair of scans were identified as viable by the rest/nitroglycerine pair of scans. Ninety-one percent of these regions were identified as viable by the single nitroglycerine scan alone. In patients who underwent revascularization, the total (201)Tl perfusion score improved from 193 to 214 after revascularization (P =.009). Wall motion score improved from 151 to 168 after revascularization (P =.09). Both the rest/nitroglycerine and rest/redistribution studies correctly predicted 14 (88%) of 16 regions that improved after revascularization. Most importantly, the rest/nitroglycerine and rest/redistribution studies were able to predict postrevascularization myocardial viability (absence of akinesis or dyskinesis after revascularization), with a sensitivity of 95% and 92%, respectively, and a predictive accuracy of 84.4%.

CONCLUSIONS

Nitroglycerine infusion during (201)Tl imaging is a useful technique for detecting underperfused, viable myocardium, requires less time to perform than rest/redistribution imaging, and may allow detection of viable myocardium with a single (201)Tl single-photon emission computed tomographic study.

SPECT and PET in the evaluation of coronary artery disease

Cardiac positron emission tomography (PET) is an accurate method for assessing myocardial perfusion and metabolism in the evaluation of coronary heart disease. PET allows more accurate detection of myocardial ischemia than single photon emission tomography (SPECT). In addition, PET has higher spatial resolution and allows attenuation correction and the quantification of various physiologic parameters. PET with 2-(fluorine-18) fluoro-2-deoxy-D-glucose is considered the standard of reference for predicting improvement in regional or global left ventricular function after revascularization by identifying hibernating viable myocardium that shows diminished perfusion and preserved metabolism. Other less commonly used clinical applications of cardiac PET include assessment of myocardial oxygen consumption and fatty acid metabolism. The use of PET in myocardial imaging is expected to increase in the near future with the regional distribution of positron-emitting radiotracers and the emergence of relatively low-cost PET systems.

Rest-redistribution 201-Tl single-photon emission CT imaging for determination of myocardial viability: relationship among viability, mode of therapy, and long-term prognosis

BACKGROUND

The diagnosis of viable myocardium in the setting of ischemic left ventricular systolic dysfunction might indicate which patients have the greatest prognostic benefit from myocardial revascularization. Single-photon emission CT (SPECT) thallium-201 (201Tl) scintigraphy for the detection of viable myocardium is widely available in the community, but outcome data using this imaging modality are limited.

METHODS

Thirty-seven patients (mean [+/- SD] age, 62+/-12 years) with ischemic left ventricular dysfunction (mean ejection fraction, 30+/-9%) initially referred for rest-redistribution SPECT thallium scintigraphy were evaluated 29+/-19 months after coronary bypass surgery (n = 15) or medical therapy alone (n = 22). The relationship among myocardial viability, mode of therapy, and long-term prognosis was evaluated.

RESULTS

Significant myocardial viability (defined as a viability index [VI] of > 0.5) was present in 19 patients. Among patients with a VI > 0.5, the 48-month actuarial event-free survival was 89+/-10% for patients undergoing surgical revascularization, compared with 0% for the medical treatment subgroup (p = 0.005). In contrast, patients in the low-viability subgroup tended to have intermediate event-free survival rates, which were not statistically different for patients receiving either surgical (62+/-21%) or medical therapy (50+/-14%; p = 0.55).

CONCLUSIONS

Survival is significantly more favorable for surgically revascularized patients with ischemic left ventricular dysfunction and myocardial viability as detected by SPECT 201Tl scintigraphy.

Quantification of Viable Myocardium in Multivessel Coronary Disease: Effects of the Redistribution Time after Reinjection Of Thallium-201 and Comparison with Postrevascularization Defect Size

Reinjection of 201Tl is used for improved detection of viable myocardium. Prospectively the effect of the redistribution time after injection for the quantification of the definitive perfusion defect size in multivessel coronary heart disease and severely impaired left ventricular function was examined. Thirty patients were included preoperatively before CABG. The study was performed with 80-90 MBq 201Tl-Cl and reinjection (40-50 MBq). Imaging was performed after an exercise test and 3 hours afterwards. Thereafter, the reinjection dose was given and repeated studies were performed 10 minutes, 2 hours, and 20 hours later. Defect sizes were compared with the 3-hour rest-study without reinjection. Imaging studies were repeated postoperatively. The defect size was expressed as % of left ventricular total myocardium. Perfusion defect sizes were as follows: post-stress study (27%), 3 hour rest-study (17%), post-reinjection-10 min (12%), 2 hours (9%), and 20 hours (7%). Compared with the 3 hour rest-study, the perfusion defect was reduced only in 7/30 patients in the study immediately after reinjection. In the delayed studies, defect sizes were markedly smaller (p < 0.05) both in studies 2 hours and 20 hours after reinjection. In 15/30 patients there was a marked reduction of 50% of defect sizes in the study 2 hours post-reinjection vs the 3 hour rest-study. The residual defects at 2 hours after reinjection were identical to the postoperative defect sizes (10%). Further prolongation of the redistribution time to 20 horus caused an additional small reduction in defect size only in two patients compared with the 2-hour post-reinjection images (n.s.). Using a marker as 201Tl with redistribution characteristics, the redistribution time after reinjection is of utmost importance to correctly identify the definitive size of the perfusion defect vs viable myocardium in patients with multivessel disease. A delay of 2 hours for redistribution after the reinjection most correctly corresponds to the postop defect size; a longer redistribution time did not provide additional advantages.

Comparison of filled-in myocardial segments after early and late reinjection of thallium-201--influence of the timing of reinjection on fill-in

Thallium-201 (201Tl) late reinjection after stress-redistribution imaging improves the detection of viable myocardium. Recently, early reinjection of 201Tl immediately after stress imaging was proposed as a new method for distinguishing ischemic myocardium, hibernating myocardium, and myocardial scar. However, there are no data on the influence of the timing of reinjection on "fill-in." This study was designed to assess whether the reinjection time influences "fill-in" in chronic coronary artery disease. Thirty-three patients with chronic coronary artery disease were studied. All patients underwent exercise 201Tl tomography. Immediately after stress imaging, 37 MBq of thallium was reinjected earlier than usual and early reinjection delayed image (ERDI) was acquired 3 h later. With the same protocol, all patients also underwent a second study involving late reinjection of 201Tl within 1 week. An additional 37 MBq of thallium was reinjected 3 h after stress imaging, and late reinjection delayed image (LRDI) was obtained 10 min later. All images were analyzed qualitatively using a 4-point grading uptake score. Of the 72 hypoperfused segments on stress images, 66 segments showed fill-in and 6 showed persistent defects on ERDI, and of the same 72 segments 55 segments displayed fill-in and the remaining 17 showed persistent defects on LRDI (p<0.05). The delta uptake score (the uptake score of the delayed image minus that of stress image) in early reinjection was 1.60+/-0.80, which was significantly higher than that in late reinjection (1.24+/-0.94, p<0.01). A small dose of thallium reinjected immediately after stress imaging with delayed images obtained 3 h later is convenient and might provide another technique for determining myocardial viability.

Assessment of myocardial viability in patients with previous myocardial infarction by using single-photon emission computed tomography with a new metabolic tracer: [123I]-16-iodo-3-methylhexadecanoic acid (MIHA). Comparison with the rest-reinjection thallium-201 technique

OBJECTIVES

We compared the ability of rest single-photon emission computed tomography (SPECT) with [123I]-16-iodo-3-methylhexadecanoic acid (MIHA) and the thallium-201 (Tl-201) rest-reinjection technique to detect myocardial viability after infarction.

BACKGROUND

After myocardial infarction, MIHA frequently shows increased uptake in the areas with exercise Tl-201 defects (mismatch), even in patients with an irreversible Tl-201 reinjection defect. Whether such increased uptake is indicative of ischemic but viable myocardium is not known.

METHODS

We studied 38 patients who 1) underwent exercise SPECT Tl-201 with rest-reinjection and rest SPECT with MIHA before undergoing percutaneous transluminal coronary angioplasty (PTCA) of an infarct-related coronary artery, and 2) were found to have successful revascularization at follow-up angiography. The relation between SPECT results before PTCA and subsequent improvement in left ventricular wall motion was assessed.

RESULTS

A mismatch was evident before PTCA in 51 of 76 infarct-related segments and correlated with subsequent improvement in wall motion (overall accuracy 71%), even for the 27 segments whose exercise defects remained irreversible after Tl-201 reinjection (overall accuracy 81%). The finding of a mismatch clearly enhanced the results provided by the finding of > or = 50% Tl-201 uptake as determined at redistribution (p < 0.05), but not as determined at reinjection, although there was a trend toward a better specificity for the findings of a mismatch.

CONCLUSIONS

MIHA is an efficient marker of viability inside exercise-underperfused areas after infarction, even in patients with irreversible Tl-201 reinjection defects. Assessment by conventional SPECT of a mismatch between results obtained with a metabolic tracer (MIHA) and a flow tracer analyzed at exercise (Tl-201) as a marker of myocardial viability is a promising area of research.

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.

Prognostic value of coronary angiography in patients with chronic ischemic left ventricular dysfunction and evidence of viable myocardium on thallium reinjection imaging

BACKGROUND

We evaluated the independent and incremental prognostic value of cardiac catheterization and coronary angiographic data over thallium reinjection after stress redistribution imaging in patients with myocardial infarction and left ventricular dysfunction.

METHODS AND RESULTS

Sixty-nine patients with a first myocardial infarction (> 8 weeks) and left ventricular ejection fraction < or = 40% underwent thallium-201 reinjection after stress redistribution tomographic imaging and cardiac catheterization. During follow-up (mean 26 months) 11 cardiac events (8 cardiac deaths and 3 nonfatal myocardial infarctions) occurred. On Cox regression analysis independent predictors of cardiac events were the sum of reversible and moderately irreversible defects at thallium reinjection (chi 2, 16.4, p < 0.005) and the number of reversible defects at stress redistribution (chi 2, 5.1, p < 0.05). Moreover, thallium reinjection imaging improved the prognostic power of clinical, exercise, and stress redistribution data (p < 0.01). The inclusion of left ventricular ejection fraction produced a borderline improvement (p = 0.06), whereas the number of vessels with coronary disease did not. In contrast, in patients at high risk such as those with at least 25% of viable myocardium at reinjection, the number of diseased vessels provided additional prognostic information (p < 0.05).

CONCLUSIONS

In patients with chronic ischemic left ventricular dysfunction, left ventricular ejection fraction, but not the number of diseased vessels, provides additional prognostic information to thallium imaging. Therefore coronary angiography seems unnecessary in these patients, unless a significative amount of viable myocardium is detectable.

Nitrate administration to enhance the detection of myocardial viability by technetium-99m tetrofosmin single-photon emission tomography

A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with 99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent 201Tl rest-injection and 99mTc-tetrofosmin baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >/=50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of 99mTc-tetrofosmin at baseline correlated with that of 201Tl (r=0.82, P <0.001). On baseline 99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peak activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in 99mTc-tetrofosmin uptake from 40%+/-9% to 57%+/-9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on 201Tl studies, but 20 segments that were non-viable on 99mTc-tetrofosmin studies were viable on 201Tl studies. Using a threshold value of >/=40% of peak activity, only seven segments remained non-viable on 99mTc-tetrofosmin studies. Overall agreement between 99mTc-tetrofosmin with nitrates and 201Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with 99mTc-tetrofosmin was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.

Amrinone stimulation test: ability to predict improvement in left ventricular ejection fraction after coronary bypass surgery in patients with poor baseline left ventricular function

OBJECTIVES

This study sought to determine whether the response to amrinone in patients with severe baseline left ventricular dysfunction can predict improvement in left ventricular ejection fraction after coronary artery bypass graft surgery.

BACKGROUND

Previous studies have suggested that the inotropic response to dobutamine can identify viable myocardium in the setting of chronic coronary disease and left ventricular dysfunction. However, increased oxygen demand stimulated by dobutamine can lead to superimposition of ischemia on the hibernating state, potentially confounding interpretation of results. Amrinone is an inotropic agent that does not critically augment myocardial oxygen demand and may be useful for identification of hibernating myocardium in the chronically ischemic state.

METHODS

Forty-four consecutive patients with coronary artery disease and left ventricular ejection fraction < 40% referred for coronary artery bypass graft surgery underwent amrinone stimulation (1 mg/kg body weight). Left ventricular ejection fraction was determined before amrinone stimulation, 20 min after infusion and 21 days after bypass surgery.

RESULTS

Baseline ejection fraction was 28 +/- 7% (mean +/- SD). Ejection fraction increased to 35 +/- 5% after amrinone stimulation (p < 0.0001) and to 33 +/- 6% after bypass surgery (p < 0.0001). Postbypass ejection fraction was significantly correlated with postamrinone ejection fraction (r = 0.65, p < 0.0001). Furthermore, the change in ejection fraction from baseline to after bypass surgery was highly correlated with the change in ejection fraction after amrinone stimulation (r = 0.75, p < 0.0001). Of 13 patients with an increase in ejection fraction > or = 10% after amrinone, all 13 had an increase of at least 8% and 11 (85%) of 13 had an increase > or = 10% after bypass surgery. In contrast, of 31 patients with an increase in ejection fraction < 10% after amrinone, only 2 (6%) had an increase > or = 10% (p < 0.0001) and 28 (90%) of 31 had an increase < 5% after bypass surgery.

CONCLUSIONS

Augmentation of myocardial contraction by amrinone in patients with chronic coronary artery disease and severe baseline left ventricular dysfunction predicts improvement in left ventricular ejection fraction after coronary artery bypass graft surgery.

Present assessment of myocardial viability by nuclear imaging

Prospective delineation of viable from nonviable myocardium in patients with coronary artery disease in an important factor in deciding whether a patient should be revascularized or treated medically. Two common techniques--single-photon emission computed tomography (SPECT) and positron-emission computed tomography (PET)--are used in nuclear medicine using various radiopharmaceuticals for the detection of myocardial viability in patients. Thallium-201 (201Tl) and technetium-99m (99mTc)-sestamibi are the common radiopharmaceuticals used in different protocols using SPECT, whereas fluoride-18 (18F)-fluorodeoxyglucose (FDG) and rubidium-82 (82Rb) are most widely used in PET. The SPECT protocols involve stress/redistribution, stress/redistribution/reinjection, and rest/redistribution imaging techniques. Many studies have compared the results of 201Tl and (99mTc)-sestamibi SPECT with those of FDG PET; in some studies, concordant results have been found between delayed thallium and FDG results, indicating that 201Tl, although considered a perfusion agent, shows myocardial viability. Discordant results in a number of studies have been found between sestamibi and FDG, suggesting that the efficacy of sestamibi as a viability marker has yet to be established. Radiolabeled fatty acids such as iodine-123 (123I)-para-iodophenylpentadecanoic acid and carbon-11 (11C)-palmitic acid have been used for the assessment of myocardial viability with limited success. 11C-labeled acetate is a good marker of oxidative metabolism in the heart and has been used to predict the reversibility of wall motion abnormalities. (18F)-FDG is considered the marker of choice for myocardial viability, although variable results are obtained under different physiological conditions. Detection of myocardial viability can be greatly improved by developing new equipment and radiopharmaceuticals of better quality.

Prognostic value of predischarge dipyridamole technetium 99m sestamibi myocardial tomography in medically treated patients with unstable angina

Recently developed unstable angina clinical practice guidelines have recommended risk stratification with dipyridamole thallium-201 myocardial imaging in patients at "intermediate" pretest clinical risk who cannot exercise maximally. The prognostic value of predischarge dipyridamole technetium 99m sestamibi (MIBI) tomography has not been assessed in this clinical setting. To this end, 128 medically treated patients with unstable angina at intermediate pretest clinical risk underwent follow-up for 16 +/- 11 (mean +/- SD) months after predischarge intravenous dipyridamole MIBI tomography. An abnormal MIBI scan result was present in 99 patients (77%), of whom 47 had one or more reversible and 76 had one or more fixed perfusion defects. Cardiac events occurred in 68 (53%) patients after dipyridamole testing: recurrent unstable angina (n = 36), nonfatal acute myocardial infarction (n = 6), or death (n = 26). A cardiac event occurred in 10% of patients with normal MIBI tomography results compared with 69% of those with abnormal results (p < 0.01). Event rates associated with specific perfusion defects were similar (reversible = 68%; fixed = 71%) and were greater than rates in patients without defects (both p < 0.05). Clinical variables associated with increased risk of cardiac events by univariate analysis included a history of congestive heart failure, prior myocardial infarction, and diabetes mellitus (all p < 0.05). Independent multivariable predictors (Cox proportional hazards model) of any cardiac event were an abnormal result of MIBI scan (relative risk [RR] = 4.3, 95% confidence interval [CI] 1.5 to 12.0) and a reversible (RR = 1.8, 95% CI 1.1 to 2.9) or a fixed perfusion defect (RR = 2.9, 95% CI 1.6 to 5.4).(ABSTRACT TRUNCATED AT 250 WORDS)

Thallium 201 for detection of viable myocardium: comparison of different reinjection protocols

BACKGROUND

The finding fo false fixed 201Tl defects by the conventional stress-redistribution protocol is a well-known phenomenon. The aim of this study was to compare two different 201Tl reinjection protocols to identify viable myocardium in the same group of patients.

METHODS AND RESULTS

Twenty-seven patients with ischemic heart disease and at least one persistent defect on 201Tl uptake redistribution images 3 hours after stress were investigated. In the same-day protocol (R1) patients were reinjected with 1 mCi 201Tl immediately after redistribution images, with imaging starting 15 minutes later; in the different-day protocol the patients were reinjected with 2 mCi 48 to 96 hours later. Two sets of images were obtained, 30 (R2) and 180 (R3) minutes after reinjection. The comparison of redistribution and reinjection versus stress images showed a significant (p < 0.01) frequency distribution. The uptake of 201Tl of the 111 irreversible segments at redistribution was enhanced in 35.1% with R1, 43.2% with R2, and 49.5% with R3. The agreement among the three procedures in classifying the segmental defects was high between R2 and R3 (r = 0.81) and lower between the same- and different-day protocols. Of the 19 patients with a dominant scar pattern demonstrated by the conventional stress-redistribution study, 37%, 47%, and 53% were judged mainly ischemic after R1, R2, and R3, respectively. All but three of the 55 segments-showing an increased 201Tl uptake by R3 had an echocardiographic score of 2 or greater.

CONCLUSION

The best technique to differentiate scarred from viable myocardium seems to be the reinjection of a second dose of 201Tl on a different day followed by imaging 3 hours later.

Dobutamine stress echocardiography predicts reversible dysfunction and quantitates the extent of irreversibly damaged myocardium after reperfusion of anterior myocardial infarction

OBJECTIVES

This study was designed to evaluate dobutamine stress echocardiography in identifying reversible dysfunction and assessing the extent of irreversibly damaged myocardium early in acute myocardial infarction.

BACKGROUND

Several experimental and clinical studies have suggested that dobutamine enhances contractile function of stunned or hibernating, or both, myocardium. It is important for clinical strategy to predict the magnitude of improvement in myocardial function early in acute myocardial infarction.

METHODS

We studied 21 patients with a reperfused first anterior myocardial infarction. Two-dimensional echocardiography was performed before and during dobutamine infusion (10 micrograms/kg body weight per min) at a mean of 3 days after the infarction. Follow-up echocardiography was performed at a mean of 25 days later. To assess segmental wall motion, we divided the left ventricle into 17 segments and assigned a wall motion abnormality score: 3 = dyskinesia or akinesia; 0 = normal. Improvement in wall motion was indicated by a decrease of at least one grade in segmental score. For quantitative assessment, the ratio of endocardial length showing dyskinesia or akinesia to a left ventricular endocardial length (akinetic length ratio) was determined in the apical long-axis view at each stage.

RESULTS

Sensitivity and specificity of dobutamine infusion in detecting improvement in wall motion at follow-up echocardiography were 83% (55 of 66 segments) and 86% (43 of 50 segments), respectively. Excellent correlation was found (r = 0.93, p < 0.001; absolute difference [mean +/- SD] 0.03 +/- 0.05) between the akinetic length ratios measured during dobutamine infusion and in the late convalescent stage.

CONCLUSIONS

In the early stage of acute myocardial infarction, low dose dobutamine stress echocardiography provides a useful method for predicting reversible dysfunction with excellent sensitivity and specificity and can also be used to quantitate the extent of irreversibly damaged myocardium.

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.

Value of thallium-201 early reinjection for assessment of myocardial viability

To assess the efficacy of early reinjection for predicting post intervention improvement in thallium-201 (T1) uptake and regional wall motion, we reinjected a small dose of T1 following post-stress imaging and obtained reinjection early images (10 min after early reinjection) and reinjection delayed images (3 hr afterwards) in 40 patients who were referred to us for revascularization (group I). Twenty-nine patients in group I also underwent conventional stress-redistribution T1 scintigraphy (group II). Conventional stress-redistribution T1 scintigraphy was repeated after intervention. Contrast left ventriculography was performed before and after intervention and changes in regional wall motion were assessed in 22 of 40 patients. In group I, the predictive value for improvement and no improvement (the accuracy) of reinjection early images in perfusion was 83%, while that of reinjection delayed images was 91%. Furthermore, the accuracy of reinjection early images in regional wall motion was 80%, while it was 91% for reinjection delayed images. In group II, the accuracy in perfusion was 78% and the value in regional wall motion was 70%. Both accuracy in perfusion and in regional wall motion obtained from reinjection delayed images were significantly higher than the values in group II (p < 0.05). These data suggest that early reinjection is useful for predicting postintervention thallium uptake and regional wall motion.

Comparison of teboroxime and thallium for the reversibility of exercise-induced myocardial perfusion defects

To determine the optimal technique for the scintigraphic detection of exercise-induced myocardial perfusion defects, we compared teboroxime scanning to both stress/redistribution thallium imaging and the thallium reinjection method following exercise in 35 patients. The overall concordance for the presence of a perfusion defect between teboroxime and thallium scanning was 91% (p < 0.01) and 89% when teboroxime was compared with stress/reinjection thallium imaging (p < 0.01). More segments per scan with fixed defects were observed with redistribution imaging than with teboroxime or thallium reinjection (2.9 vs 2.0 vs 1.9; p < 0.02). Additionally, more transient defects were present with teboroxime than thallium, but less than with reinjection imaging. One half of the 52 fixed perfusion abnormalities on stress/redistribution thallium imaging demonstrated reversibility with both teboroxime imaging and thallium reinjection scanning, but less than 50% of these segments were concordant. Teboroxime allows for improved detection of reversible perfusion defects compared with stress/redistribution thallium scanning, but more ischemia is noted with thallium reinjection. The variation in the detection of segmental ischemic defects between teboroxime scintigraphy and thallium reinjection scanning probably reflects different physiologic properties and imaging protocols of these perfusion agents.

Nitrogen-13 ammonia perfusion imaging: relation to metabolic imaging

PET provides an advanced imaging technology that permits the accurate definition of regional tracer distribution. In combination with N-13 ammonia, PET allows for the sensitive and specific detection of coronary artery disease. Results of several studies indicate the superiority of this approach compared with standard thallium-201 tomographic imaging. In addition, regional blood flow can be accurately measured with N-13 ammonia PET, and this approach can be used in conjunction with pharmacologic stress imaging to quantify regional flow reserve. In combination with metabolic markers, N-13 ammonia is capable of assessing myocardial viability. Furthermore, the N-13 ammonia PET approach may differentiate among various forms of cardiomyopathy. More studies are needed to define the cost-benefit ratio of the N-13 ammonia PET technique for the management of patients with coronary artery disease or cardiomyopathy.

Reinjection as an alternative to rest imaging for detection of exercise-induced ischemia with thallium-201 emission tomography

Exercise thallium-201 single photon emission computed tomography images were compared prospectively with 4-hour redistribution images, with 4-hour reinjection images, and with images obtained at rest on a separate day in 37 patients with documented coronary artery disease. Exercise images were abnormal in 35 patients (95%). On the basis of an improvement in thallium-201 distribution between exercise and nonexercise images, overall sensitivity for the detection of coronary artery stenosis was significantly higher with reinjection at 4 hours (p < 0.05) or with a rest injection on a separate day (p < 0.05) than with redistribution imaging (84%, 83%, and 70%, respectively). Reinjection and rest injection were positive more frequently in patients with a wall-motion abnormality (76% and 80%, respectively, vs 64% at redistribution; p < 0.05 for both) or with > 90% stenosis (77% and 76%, respectively, vs 58% at redistribution; p < 0.05 for both). Among the 11 patients who had no evidence of redistribution at 4 hours, five (45%) demonstrated ischemia with reinjection and five demonstrated ischemia in the separate rest study; a total of seven patients showed improvement either at reinjection or rest. Among these 86% had a wall-motion abnormality associated with stenosis of > 90%, whereas in the other 30 patients these two conditions were observed concomitantly in only 43%. This study demonstrates that the thallium-201 4-hour postexercise reinjection technique is as sensitive as the 2-day rest/exercise method for the detection of coronary artery stenosis and provides additional information when a severe stenosis is associated with a wall-motion abnormality.

Myocardial hibernation in the infarcted region cannot be assessed from the presence of stress-induced ischemia: usefulness of delayed image of exercise thallium-201 scintigraphy

To examine the relationship between the improvement of wall motion in infarcted regions after percutaneous transluminal coronary angioplasty (PTCA) and thallium-201 uptake in the delayed image of exercise thallium-201 scintigraphy before PTCA, 14 patients with anterior old myocardial infarction were studied. Exercise thallium-201 scintigraphy was performed before PTCA of left anterior descending artery, and mean percent thallium-201 uptake of abnormal segments was calculated in the initial and 4-hour delayed images. Left ventricular angiography was performed during catheterization, before, and 4 to 13 months after PTCA; and regional ejection fraction of anterior wall was calculated. Atrial pacing stress test with the measurement of lactate concentration of aorta and great cardiac vein was performed during catheterization before PTCA. In five patients with mean percent thallium-201 uptake in the delayed image < or = 50% (group I), regional ejection fraction did not increase after PTCA (23% +/- 9% to 24% +/- 12%). In the other nine patients with mean percent thallium-201 uptake > 50% (group II), regional ejection fraction increased significantly after PTCA (39% +/- 18% to 47% +/- 14%; p < 0.05). There was no significant difference in regional ejection fraction, lactate extraction ratio during maximal pacing, and the redistribution of exercise thallium-201 scintigraphy between the two groups before PTCA. Thus the delayed image before PTCA is useful to detect reversible nonfunctioning viable myocardium (hibernating myocardium) in the infarcted region. However, the wall-motion abnormality and the degree of stress-induced ischemia in the infarcted region before PTCA may not be necessarily useful for the detection of hibernating myocardium.

Assessing viable myocardium with thallium-201

Patients with chronic coronary artery disease and potentially reversible left ventricular dysfunction can often be successfully identified by one or more clinical indicators of myocardial viability, including regional wall motion, systolic wall thickening, regional myocardial perfusion as determined by perfusion tracers, and redistribution of thallium-201. In some patients, however, viable but "hibernating" myocardium will exist even when none of the above are evident. Myocardial viability in this situation can be detected with a high degree of accuracy by the demonstration of preserved metabolic activity by positron emission tomography (PET) scanning. Additionally, modifications of the standard exercise-redistribution thallium protocol may also produce accurate results. These modifications include late thallium-201 redistribution imaging, performed 8-72 hours following initial thallium injection, and thallium reinjection at rest after early (3-4 hours) or late (8-72 hours) redistribution imaging. These methods can identify viable myocardium in many thallium defects that appear to be irreversible on a standard 3-4 hour redistribution image. In addition, serial imaging after administration of thallium-201 at rest may also provide valuable insights into myocardial viability. These imaging modalities have important practical applications in the evaluation and management of patients with coronary artery disease and left ventricular dysfunction.

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.

Complementarity of magnetic resonance spectroscopy, positron emission tomography and single photon emission tomography for the in vivo investigation of human cardiac metabolism and neurotransmission

The three techniques allowing the noninvasive study of cardiac metabolism, namely magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single photon emission computed tomography (SPET), all use external detection with stable or radioactive isotopes. These techniques yield different information. PET is quantitative and very sensitive, and therefore only tracer amounts of molecules need to be injected. It allows neurotransmitters and receptors to be studied and a global view of metabolism (oxygen consumption, glucose and fatty acid utilization) to be obtained. SPET also has good sensitivity, but uses gamma-emitting isotopes of heteroatoms. Their longer half-lives allow follow-up for hours or days. MRS is based on stable elements with high (hydrogen 1, phosphorus 31, fluorine 19...) or low (carbon 13, Deuterium) natural abundance. It has very low sensitivity and only millimolar concentrations of substrates can be detected, but various parts of metabolism can be studied. The in vivo measurement of myocardial concentration of substances has many problems that are common to all three techniques (measurement of the volume, measurement of the quantity of each molecule, resolution, partial volume effect, improvement of the signal-to-noise ratio, movement of the organ). The complementarity of the techniques is illustrated by their applications to the study of cardiac metabolism. For instance, the energy metabolism can be studied by 31P-MRS, which detects the high-energy compounds ATP and phosphocreatine, and 13C-MRS yields information on the tricarboxylic acid cycle activity. PET and SPET allow the utilization of fatty acids, the normal fuels of the heart, to be studied. During ischaemia, PET with 18F-fluorodeoxyglucose (18FDG) can determine the glucose consumption and 1H-MRS shows the increase in lactic acid, reflecting anaerobic glycolysis. Comparison of the use of acetate labelled with 11C for PET or 13C for MRS shows the potentials and limitations of each technique. Myocardial perfusion can be evaluated directly with various PET tracers or indirectly with thallium 201 or various technetium-99m-labelled tracers by SPET. No MRS marker of perfusion is so far clinically available. Mainly SPET and PET are used clinically for the investigation of ischaemic heart disease as well as cardiomyopathies, but some initial results using 31P-MRS are being obtained.

Comparison of exercise radionuclide angiography with thallium SPECT imaging for detection of significant narrowing of the left circumflex coronary artery

Although quantitation of exercise thallium tomograms has enhanced the noninvasive diagnosis and localization of coronary artery disease, the detection of stenosis of the left circumflex coronary artery remains suboptimal. Because posterolateral regional wall motion during exercise is well assessed by radionuclide angiography, this study determined whether regional dysfunction of the posterolateral wall during exercise radionuclide angiography is more sensitive in identifying left circumflex disease than thallium perfusion abnormalities assessed by single-photon emission computed tomography (SPECT). One hundred ten consecutive patients with CAD were studied, of whom 70 had a significant stenosis of the left circumflex coronary artery or a major obtuse marginal branch. Both regional function and segmental thallium activity of the posterolateral wall were assessed using visual and quantitative analysis. Left ventricular regional function was assessed objectively by dividing the left ventricular region of interest into 20 sectors; the 8 sectors corresponding to the posterolateral free wall were used to assess function in the left circumflex artery distribution. Similarly, using circumferential profile analysis of short-axis thallium tomograms, left ventricular myocardial activity was subdivided into 64 sectors; the 16 sectors corresponding to the posterolateral region were used to assess thallium perfusion abnormalities in the left circumflex artery territory. Qualitative posterolateral wall motion analysis detected 76% of patients with left circumflex coronary artery stenosis, with a specificity of 83%, compared with only 44% by qualitative thallium tomography (p less than 0.001) and a specificity of 92%. Whereas quantitation of thallium activity increased the sensitivity for detecting left circumflex coronary artery stenosis to 80% with a specificity of 55%, it did not achieve statistical significance when compared with qualitative wall motion analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Thallium 201 for assessment of myocardial viability

Left ventricular (LV) performance is reduced in a large subset of patients with chronic coronary artery disease (CAD) and LV dysfunction on the basis of regionally ischemic or hibernating myocardium rather than irreversibly infarcted tissue. The detection of dysfunctional but viable myocardium is clinically relevant since regional and global LV function in such patients will improve after revascularization procedures; however, the identification of patients with such potentially reversible LV dysfunction is difficult. Although thallium 201 imaging may be of value in detecting viable myocardium if regions with perfusion defects during exercise demonstrate redistribution of thallium on a 3- to 4-hour resting image, thallium defects often appear persistently "fixed" within regions of severely ischemic or hibernating myocardium. It has been shown that up to 50% of regions with apparently irreversible thallium defects will improve in function after revascularization. Thus, standard exercise-redistribution thallium scintigraphy may not differentiate LV dysfunction arising from infarcted versus hibernating myocardium. The precision with which thallium imaging identifies viable myocardium can be improved greatly by additional studies once 4-hour redistribution imaging demonstrates an irreversible thallium defect. These additional studies include late (24-hour) redistribution imaging, repeat imaging after thallium reinjection, or a combination of thallium reinjection followed by late imaging. Several recent studies suggest that thallium reinjection techniques, by demonstrating thallium uptake in dysfunctional regions with apparently irreversible defects, predict improvement after revascularization with similar predictive accuracy as that achieved using metabolic imaging with positron emission tomography (PET). Studies directly comparing such thallium methods and PET, which thus far involve only small numbers of patients, suggest that the assessment of regional metabolic activity using PET and the assessment of regional thallium activity using single photon emission computed tomography provide concordant results. These findings, if confirmed by larger ongoing studies, suggest that thallium reinjection imaging is a convenient, clinically accurate, and relatively inexpensive method with which to identify viable myocardium in patients with chronic CAD and LV dysfunction.