Early noninvasive detection of reperfusion and infarct by intravenous technetium 99m pyrophosphate scintigraphy following thrombolysis

To determine whether technetium-99-pyrophosphate accumulation immediately after intravenous thrombolysis can serve as a marker of reperfusion and infarct size, 17 patients with acute myocardial infarction were studied. Immediately after thrombolysis 10 mCi of technetium-99m pyrophosphate were injected intravenously. Coronary and left ventricular angiography were then performed in all patients, revealing patent coronary arteries in 13 patients. In all patients, 0.3 and 0.5 mCi of thallium-201 were injected into the right and left coronary artery, respectively, followed by planar scintigraphy. 6 patients with patent coronary arteries and a large thallium-201 defect had massive (more than one third of the cardiac silhouette) pyrophosphate accumulation (group A), whereas 7 patients with a small or no thallium-201 defect in the presence of a patent infarct artery had either focal or no pyrophosphate accumulation (group B). In contrast, 4 patients with an occluded infarct artery showed no acute pyrophosphate uptake despite a large thallium-201 defect (group C). Emission computed tomography confirmed the planar scintigraphic data in group A patients and revealed small thallium-201 defects and focal pyrophosphate accumulation in group B patients with negative planar scintigrams. Global and regional ejection fractions in the infarct area, measured from the acute and follow-up left ventricular angiograms, were higher in group A than in group B and C patients. It is concluded that early intravenous technetium-99m pyrophosphate scintigraphy in patients with acute myocardial infarction undergoing intravenous thrombolysis may serve as an indicator of reperfusion and infarct size.     

Scintigraphic evidence of the "no reflow" phenomenon in human beings after coronary thrombolysis

To assess whether the absence of new thallium-201 uptake after successful intracoronary thrombolysis reflects a disturbance of myocardial cell function or lack of capillary reperfusion, dual isotope scintigraphic studies with thallium-201 and technetium-99m micro-albumin aggregates were performed in 16 patients with acute anterior myocardial infarction. Intracoronary thallium-201 and technetium-99m scintigraphy performed before intracoronary thrombolysis in 12 of the 16 patients resulted in identical thallium-201 and technetium-99m defect sizes. Immediately after intracoronary thrombolysis, thallium-201 and technetium-99m scintigraphy was repeated in 11 of the 12 patients. In 4 of the 11, the initial thallium and technetium scintigraphic defects were significantly reduced, and in 6 of the 11, they were only slightly reduced; there was no difference in the size of the residual defect as assessed with both radionuclides in all 10 of the 11 patients. In the eleventh patient, there was a significant reduction of the initial technetium-99m scintigraphic defect but no change in the size of the thallium-201 defect. In four other patients, scintigrams were obtained only after intracoronary thrombolysis; these revealed no difference in thallium-201 and technetium-99m defect size. In seven of eight patients restudied 2 to 4 weeks after intracoronary thrombolysis, thallium-201 and technetium-99m defect sizes were identical with those immediately after intracoronary thrombolysis; in the eighth patient there was no difference in thallium-201 and technetium-99m defect size, although such a difference had been present immediately after intracoronary thrombolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thallium-201/technetium-99m pyrophosphate overlap in patients with acute myocardial infarction after thrombolysis: prediction of depressed wall motion despite thallium uptake

Intracoronary thallium-201/technetium-99m pyrophosphate planar scintigraphy was performed in 60 patients with acute myocardial infarction undergoing intracoronary thrombolysis to predict salvage of myocardium immediately after thrombolysis. In eight patients a significant overlap of new thallium uptake and technetium pyrophosphate accumulation was found after thrombolysis. Intravenous planar thallium scintigraphy revealed thallium uptake in the region of overlap in all patients; circumferential profile analysis showed no difference in the thallium scintigrams before and after technetium injections. Both findings indicate that overlap is not the result of scattering of technetium into the thallium window. Emission computed tomography revealed thallium/technetium pyrophosphate uptake in identical slices and regions. Regional wall motion in the area of overlap remained depressed in all patients, in contrast to patients with similar thallium uptake without overlap. These data suggest that thallium/technetium pyrophosphate overlap reflects the close proximity of viable and necrotic myocardial cells and predicts depressed wall motion after thrombolysis.     

Comparison of the predischarge exercise thallium-201 perfusion defect after myocardial infarction with myocardium at risk measured during acute infarction with technetium-99m sestamibi imaging

Background Exercise thallium-201 imaging provides a noninvasive estimate of the amount of myocardium presumed to be at risk of infarcting should a complete occlusion of the coronary stenosis occur. The relationship between the size of the exercise thallium perfusion defect and the extent of myocardium supplied by a diseased coronary artery has not been established. This study evaluates that presumed correlation. Methods Patients were injected intravenously with technetium-99m sestamibi during acute myocardial infarction before thrombolysis or conventional therapy to quantify the myocardium at risk. Twenty-six patients who underwent risk-area assessment subsequently underwent clinically driven, predischarge, submaximal exercise imaging with thallium-201. The exercise testing was performed on day 7 ± 2 days. A conventional polar map display was used to quantify the perfusion defect. Results The myocardium at risk determined by technetium-99m sestamibi at the time of infarction was 30% ± 20% of the left ventricle. The mean exercise thallium-201 defect was 34% ± 22% of the left ventricle. The exercise defect tended to be slightly larger than the myocardium at risk (4% ± 10% of the left ventricle, P = .05). There was a close correlation between the 2 measurements (r = 0.89, SE = 9.4, P < .0001). Conclusions This study shows a close correlation between the myocardium “at risk” assessed acutely by technetium-99m sestamibi and the “presumed at-risk area” determined by thallium-201 imaging on predischarge exercise testing. This finding supports the concept that the size of the exercise thallium defect caused by coronary stenosis indicates the likely size of a myocardial infarction resulting from occlusion of that stenosis. (Am Heart J 2003;145:357-63.)     

Effect of coronary artery recanalization on right ventricular function in patients with acute myocardial infarction

The effects of coronary artery recanalization by intracoronary administration of streptokinase on left ventricular function during acute myocardial infarction have received increasing attention in recent years. Although myocardial dysfunction is often more pronounced in the right ventricle than in the left ventricle in patients with acute inferior wall myocardial infarction, the effect of coronary artery recanalization on right ventricular dysfunction has not been previously addressed. Accordingly, in this investigation, 54 patients who participated in a prospective, controlled, randomized trial of recanalization during acute myocardial infarction were studied. Among 30 patients with inferior wall infarction, 19 had right ventricular dysfunction on admission; 11 of these 19 had positive uptake of technetium-99m pyrophosphate in the right ventricle, indicative of right ventricular infarction. Patients with successful recanalization (n = 6) exhibited improved right ventricular ejection fraction from admission to day 10 (26 +/- 7 to 39 +/- 14%, p less than 0.03). However, control patients (n = 6) and patients who did not undergo recanalization (n = 7) also exhibited improvement (20 +/- 7 to 29 +/- 11% [p less than 0.02] and 30 +/- 8 to 40 +/- 6% [p less than 0.03], respectively). Improvement in several other variables of right ventricular dysfunction evolved at an equal rate with the ejection fraction changes. Patients with or without right ventricular infarction improved similarly. These data indicate that the right ventricular dysfunction commonly associated with inferior wall infarction is often transient, and improvement is the rule, irrespective of early recanalization of the "infarct vessel."     

Derivation and validation of a new angiographic score of right coronary artery perfusion

A semi-quantitative right coronary artery score (RCA score)was derived from the ratio of the number of the major left ventricularbranches of the right coronary artery to the total of the rightcoronary and left circumflex arteries, to stratify the extentof perfusion in patients with right coronary artery dominance.Thirty-seven patients with one-vessel coronary disease involvinga dominant right coronary artery proximal to the left ventricularbranches were selected for study. Thallium scintigraphy wasperformed after right intracoronary injection in 11 patients,and 26 patients underwent conventional stress thallium scintigraphy(24 exercise thallium and two dipyridamole thallium scintigraphy).Thallium scores of perfusion region size after right intracoronarythallium injection and perfusion defect size in stress thalliumstudies were quantitated from planar thallium images. Both theRCA score and the regional thallium scores spanned over a widerange. The RCA score (range 0.23–0.85) correlated best with theposterior (70;° left anterior oblique view) plus lateralsegment (40° left anterior oblique view) thallium score(r = 0.88 and 0.53 for intracoronary and stress thallium studiesrespectively). It also correlated with the summed thallium scoresin the posterior, lateral, apical and inferior segments (r =0.73 and 0.54 respectively) but not with thallium scores inthe apex or inferior segment alone. The proposed RCA score quantitates the variable posterolateralperfusion territory of the right coronary artery, and couldstratify the area of myocardium at risk from coronary stenosisin the majority of patients with right coronary dominance.     

Identification of viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Comparison of thallium scintigraphy with reinjection and PET imaging with 18F-fluorodeoxyglucose

In patients with chronic coronary artery disease and left ventricular dysfunction, the distinction between ventricular dysfunction arising from myocardial fibrosis and ischemic, but viable, myocardium has important clinical implications. By positron emission tomography (PET), enhanced fluorine-18-labeled fluorodeoxyglucose (FDG) uptake in myocardial segments with impaired function and reduced blood flow is evidence of myocardial viability. Reinjection of thallium-201 at rest immediately after stress-redistribution imaging may also provide evidence of myocardial viability by demonstrating thallium uptake in regions with apparently "irreversible" defects. To compare these two methods, we studied 16 patients with chronic coronary artery disease and left ventricular dysfunction (ejection fraction, 27 +/- 9%), all of whom had irreversible defects on standard exercise-redistribution thallium single-photon emission computed tomography (SPECT) imaging. Thallium was reinjected immediately after the redistribution study, and SPECT images were reacquired. The patients also underwent PET imaging with FDG and oxygen-15-labeled water. A total of 432 myocardial segments were analyzed from comparable transaxial tomograms, of which 166 (38%) had irreversible thallium defects on redistribution images before reinjection. FDG uptake was demonstrated in 121 (73%) of these irreversible defects. Irreversible defects were then subgrouped according to the degree of thallium activity, relative to peak activity in normal regions. Irreversible defects with only mild (60-85% of peak activity) or moderate (50-59% of peak) reduction in thallium activity were considered viable on the basis of FDG uptake in 91% and 84% of these segments, respectively. In contrast, in irreversible defects with severe reduction in thallium activity (less than 50% of peak), FDG uptake was present in 51% of segments. In such severe defects, an identical number of segments (51%) demonstrated enhanced uptake of thallium after reinjection. In these severe "irreversible" defects, data on myocardial viability were concordant by the two techniques in 88% of segments, with 45% identified as viable and 43% identified as scar on both PET and thallium reinjection studies. These observations suggest that thallium imaging can be used to identify viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Most irreversible defects with only mild or moderate reduction in thallium activity represent viable myocardium as confirmed by FDG uptake.(ABSTRACT TRUNCATED AT 400 WORDS)     

The noninvasive assessment of myocardial viability

The major objective of noninvasive imaging for detection of myocardial viability is to assist in the improved selection of patients with coronary artery disease and severe left ventricular dysfunction who would benefit most from revascularization. The techniques most commonly used to identify viable myocardium are thallium-201 (TI) scintigraphy, positron emission tomography (PET) using a flow tracer in combination with a metabolic tracer, technetium-99m (Tc) sestamibi imaging, and dobutamine echocardiography. On stress TI scintigraphy, asynergic regions showing normal thallium uptake, an initial defect with delayed redistribution at 3–4 h, late redistribution at 24 h, or defect reversibility after reinjection of a second dose of TI at rest all suggest preserved viability. The greater the final uptake of TI in areas of regional myocardial dysfunction preoperatively, the greater the improvement in ejection fraction after coronary revascularization. Demonstration of uptake of fluoro-18 deoxyglucose (FDG) in regions of diminished blood flow on PET imaging also correlates well with improved systolic function after revascularization. Tc sestamibi may also be useful for assessment of myocardial viability, particularly after thrombolytic therapy for acute myocardial infarction. Dobutamine echocardiography has good positive predictive value for viability determination, but absence of systolic thickening in an akinetic zone in response to intravenous infusion of the drug may still be associated with viable myocardium in 25–50% of segments. Of all the techniques cited above, quantitative resting TI scintigraphy may be the best approach for distinguishing between viable and irreversibly injured myocardium.     

Enhanced detection of proximal right coronary artery stenosis with the additional analysis of right ventricular thallium-201 uptake in stress scintigrams

The value of right ventricular thallium-201 analysis in detecting proximal right coronary artery stenosis in exercise myocardial scintigraphy was analyzed in 52 patients, 27 with and 25 without proximal right coronary artery stenosis. For the detection of proximal right coronary artery stenosis, the sensitivity and specificity of thallium scintigraphic analysis were 59 and 88% for a right ventricular abnormality, 67 and 68% for a left ventricular inferior wall abnormality, and 93 and 56% for an abnormality of either. When both right and left ventricular thallium images were abnormal, all 9 patients had proximal right coronary artery stenoses, and when both were normal, 26 of 28 patients had a normal proximal right coronary artery. The sensitivity and specificity of blood pool scintigraphic variables during exercise (right ventricular ejection fraction and left ventricular inferior wall motion) were not significantly different for detection of proximal right coronary artery stenosis.Thus, the additional analysis of the right ventricle on thallium-201 stress scintigrams can improve the detection of proximal right coronary artery stenosis. When both right ventricular and left ventricular thallium scintigrams are abnormal (or normal), the ability to predict the presence (or absence) of proximal right coronary artery stenosis is very high.     

The scoring system for early technetium-99m pyrophosphate scintigraphy as a method of evaluation of limiting the myocardial infarct size by thrombolysis.

The usefulness of a scoring system with early technetium-99m pyrophosphate scintigraphy as a method for evaluating the efficacy of myocardial preservation after thrombolysis was studied. The mean time from the onset of acute myocardial infarction to injection of the tracer was 5.6 +/- 1.5 h (range 2.8 to 11.9 h). All 36 patients underwent successful recanalization. Patients with strongly positive technetium-99m pyrophosphate uptake in anterior acute myocardial infarction had a significantly lower regional ejection fraction and a significantly larger thallium-201 defect score than those with 2+ positive results in chronic stage. Similarly, in inferior acute myocardial infarction, the thallium-201 defect score was significantly larger in patients with strongly positive uptake than in those with 2+ and negative uptake scores. In conclusion, strongly positive results in early technetium-99m pyrophosphate scintigraphy within 12h after the onset of acute myocardial infarction may indicate failure in limiting the infarct size by coronary thrombolysis.     

Right ventricular myocardial infarction diagnosed by 99 m technetium pyrophosphate scintigraphy: clinical course and follow-up

Out of 178 consecutive patients with acute inferior wall myocardialinfarction submitted to technetium-99 m pyrophosphate scintigraphy,49 (27.5%) were found to have concomitant right ventricularinfarction. Gated blood pool scans showed right ventricularabnormalities in 21 out of 26 patients who were submitted tothis investigation (right ventricular asynergy: 16 cases; rightventricular dilatation: eight cases; decreased right ventricularejection fraction: 16 cases). Complications were common in the acute stage. Shock was notedin 19 cases (eight related to bradycardia, three related torelative hypovolaemia and eight instances of true cardiogenicshock). Atrial fibrillation (seven patients), ventricular fibrillation(eight patients) and severe atrioventricular conduction disorders(13 patients) were also frequent. In spite of this, the in-hospitalmortality was low: three deaths occurred (6.1%), one from heartfailure, two others from posterior septal rupture. All patients were followed up for one year or more. Six additionaldeaths were noted (three from left cardiac failure, two fromrecurrent anterior wall infarction and one from massive pulmonaryembolism). Clinical assessment, haemodynamic measurements andgated blood pool scans showed significant improvement of rightventricular function with return to normal in those cases withsmall right ventricular infarcts as judged from technetium-99m pyrophosphate scintigraphy. In spite of the complications seen in the initial period, patientswith a right ventricular infarction have a good overall prognosisand the long-term outcome, primarily determined by the left-sidedlesions, is often favourable.     

Measurement of myocardium at risk by technetium-99m sestamibi: correlation with coronary angiography.

Previous studies have shown that tomographic perfusion imaging with technetium-99m sestamibi (RP-30A) can accurately measure the myocardium at risk during acute myocardial infarction. The ability of coronary angiography to predict the wide variability in myocardium at risk was studied in 21 patients with their first acute myocardial infarction. In blinded fashion, two experienced angiographers provided an overall "best estimate" of the percent of left ventricular myocardium at risk considering multiple angiographic variables--infarct-related artery, location of stenosis (proximal or nonproximal), vessel diameter, length, territory and the number and size of proximal branches and collateral vessels. Many of these individual variables showed a significant association with myocardium at risk. The most important angiographic variable was the mean best estimate of the two angiographers (r = 0.89, p less than 0.0001). However, the SEE was large (8.6% of the left ventricle) and angiography significantly (p less than 0.002) overestimated myocardium at risk. When patients with an anterior or an inferior infarct were considered separately, the angiographic best estimate had a weaker correlation with myocardium at risk measured by technetium-99m sestamibi in patients in both groups (anterior infarction r = 0.65, p = 0.04; inferior infarction r = 0.65, p = 0.04. Seven patients with an inferior infarct and myocardium at risk ranging from 7% to 32% of the left ventricle had identical angiographic best estimates. Although angiographic estimates correlate closely with measurements of myocardium at risk in groups of patients, their ability to predict the myocardium at risk in individual patients is limited.     

Variability of myocardium at risk for acute myocardial infarction

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

Pure right ventricular infarction.

A 76-year-old man with chest pain was admitted to hospital where electrocardiography (ECG) showed ST-segment elevation in leads V1-4, indicative of acute anterior myocardial infarction. ST-segment elevation was also present in the right precordial leads V4R-6R. Emergency coronary angiography revealed that the left coronary artery was dominant and did not have significant stenosis. Aortography showed ostial occlusion of the right coronary artery (RCA). Left ventriculography showed normal function and right ventriculography showed a dilated right ventricle and severe hypokinesis of the right ventricular free wall. Conservative treatment was selected because the patient's symptoms soon ameliorated and his hemodynamics was stable. 99mTc-pyrophosphate and 201Tl dual single-photon emission computed tomography showed uptake of 99mTc-pyrophosphate in only the right ventricular free wall, but no uptake of 99mTc-pyrophosphate and no perfusion defect of 201Tl in the left ventricle. The peak creatine kinase (CK) and CK-MB were 1,381 IU/L and 127 IU/L, respectively. His natural course was favorable and the chest pain disappeared under medication. Two months after the onset, the ECG showed poor R progression in leads V1-4 indicating an old anterior infarction. Coronary angiography confirmed the ostial stenosis of the hypoplastic RCA. This was a case of pure right ventricular free wall infarction because of the occlusion of the ostium of the hypoplastic RCA, but not of the right ventricular branch. Because the electrocardiographic findings resemble those of an acute anterior infarction, it is important to consider pure right ventricular infarction in the differential diagnosis.     

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

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

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

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

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

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

Myocardial hibernation identified by hyperbaric oxygen treatment and echocardiography in postinfarction patients: comparison with exercise thallium scintigraphy.

To evaluate the potential for hyperbaric oxygen (HBO) to produce transient improvement in function in areas of myocardium ischemic at rest (hibernating myocardium), 24 patients were studied within 1 week of acute myocardial infarction. Results were compared with single-photon emission computed tomography (SPECT) thallium-201 exercise scintigraphy. Echocardiography demonstrated improved contraction following HBO in 20 of 62 damaged left ventricular segments in 12 of 24 patients. Thirteen of the 28 segments and 9 of the 14 patients showing reversible ischemia on SPECT imaging showed improvement with HBO. There were eight segments with apparently normal resting contraction that showed a reversible thallium defect. Of 42 segments with fixed contraction abnormalities following HBO, eight had reversible thallium defects, four had normal thallium kinetics, and 30 had fixed thallium defects. Thus hyperbaric oxygen can demonstrate improvement in function in some segments of left ventricle after infarction. There is some overlap with viability as determined by thallium studies, but the two techniques may be complementary in describing myocardial ischemia.     

Relation between site of origin of ventricular tachycardia and relative left ventricular myocardial perfusion and wall motion

To assess the relation between the site of origin of ventricular tachycardia (VT) and relative myocardial perfusion and wall motion, 18 patients with a history of recurrent sustained VT underwent cardiac catheterization, invasive electrophysiologic study with endocardial mapping, and resting radionuclide ventriculography. In addition, 6 patients had exercise and redistribution thallium-201 scintigraphy, whereas the remaining 12 patients had resting thallium scans. The site of origin of VT (determined by catheter and intraoperative endocardial mapping) was correlated with relative myocardial perfusion (thallium) and left ventricular (LV) wall motion. All patients had significant (>50% narrowing) coronary artery disease and 16 had LV aneurysms.Twenty sites of origin of VT (28 morphologies) were identified in these 18 patients. Of the 9 patients with multiple VT morphologies, the VT originated at disparate sites in 2 patients. All 18 patients had thallium defects at rest and 3 patients had additional reversible (ischemic) defects on exercise. Of the 20 sites of origin of VT, 16 were at the periphery of the thallium defect, 1 was adjacent to it, and 3 were in the center of it. In the 16 patients with LV aneurysm, there were 18 sites of origin: 15 at the border of the aneurysm, 1 adjacent to it, and 2 within it.The data suggest that in patients with VT and coronary artery disease the site of origin is usually the periphery of a resting thallium defect, and in patients with LV aneurysm the site is the border of the aneurysm.     

Role of myocardial perfusion imaging in evaluating thrombolytic therapy for acute myocardial infarction

Myocardial thallium-201 scintigraphy is being increasingly employed as a method for assessing the efficacy of coronary reperfusion in acute myocardial infarction. New thallium uptake after intracoronary tracer administration after successful recanalization indicates that nutrient blood flow has been successfully restored. One may also presume that some myocardial salvage occurred if thallium administered in this manner is transported intracellularly by myocytes with intact sarcolemmal membranes. However, if one injects thallium by way of the intracoronary route immediately after reperfusion, the initial uptake of thallium in reperfused myocardium may predominantly represent hyperemic flow and regional thallium counts measured may not be proportional to the mass of viable myocytes. When thallium is injected intravenously during the occlusion phase the degree of redistribution after thrombolysis is proportional to the degree of flow restoration and myocardial viability. When thallium is injected for the first time intravenously immediately after reperfusion, an overestimation of myocardial salvage may occur because of "excess" thallium uptake in the infarct zone consequent to significant hyperemia. Another approach to myocardial thallium scintigraphy in patients undergoing thrombolytic therapy is to administer two separate intravenous injections before and 24 hours or later after treatment. Clinical studies have demonstrated that the improvement in defect size on serial images predicts improvement in regional function and patency of the infarct-related vessel. Finally, patients with acute myocardial infarction who receive intravenous thrombolytic therapy are candidates for predischarge exercise thallium-201 scintigraphy for risk stratification and detection of residual ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of myocardial necrosis immediately after intracoronary thrombolysis by intracoronary injection of technetium-99m pyrophosphate

To assess myocardial necrosis immediately after intracoronarythrombolysis, thallium-201 (TL-201) and technetium-99m pyrophosphate(Tc-99m PYP) were injected simultaneously into the coronaryartery in 25 patients with acute transmural myocardial infarction.In 17 of the 25 patients, the occluded coronary artery was reopened.Minutes after the intracoronary injection of Tc-99m PYP intothe reopened coronary artery a localized accumulation was seenwithin the area of the Tl-201 defect in all patients. Controlintravenous scintigraphy, which was performed in 8 of these17 patients 1–6 days later, and in 2 patients 18 and 42days after infarction, revealed a Tc- 99m PYP spot similar tothat of the acute intracoronary Tc-99m PYP scintigram in all10 patients. In the 8 of the 25 patients, in whom intracoronary thrombolysisfailed, no localized Tc-99m PYP accumulation was seen afterinjection into the infarct vessel. In 5 of these patients, acontrol intravenous scintigram, performed 1–8 days later,resulted in a Tc-99m PYP spot in the area of the Tl-201 defect. We conclude that, in the presence of therapeutic or spontaneousreperfusion, Tc-99m PYP scintigraphy may provide a useful methodof assessing myocardial necrosis during the early stage of anacute myocardial infarction.     

Thallium-201 re-injection: a new method for the identification of viable myocardium in patients with fixed deficits of myocardial uptake

Fixed defects on thallium-201 myocardial scintigraphy which have been traditionally interpreted as myocardial scar, may in fact be viable myocardium. This has been shown to be the case on 24 hour delayed imaging, positron emission tomography and repeat thallium imaging after coronary angioplasty or bypass surgery. We studied 25 suspected post myocardial infarction ischemia patients who had one or more fixed defects on exercise thallium scintigraphy. Immediately after the conventional delayed images, a second TI-201 injection of 1 mCi (re-injection) was given, followed by an additional set of images. After re-injection, 41% of fixed defects on the conventional delayed images showed increased thallium uptake as evidence of viable myocardium, and 46% of partially reversible defects on the conventional delayed images showed a concordant but increased uptake. Re-injection provided the only evidence for ischemia in 4 patients (16%) and documented ischemia in a new vascular territory in 3 patients (12%). Thus, we conclude that thallium re-injection is an improved technique for assessing myocardial viability in patients after myocardial infarction.