Reversal of rest myocardial asynergy during exercise: a radionuclide scintigraphic study

While exercise-induced segmental left ventricular wall motion abnormalities are well described, the phenomenon of improvement in certain asynergic segments during exercise in some patients remains a curiosity. To assess this unexpected finding, results were analyzed in 85 patients with wall motion abnormalities at rest who underwent two view (45 degrees left anterior oblique and anterior) exercise radionuclide ventriculography and exercise thallium-201 myocardial perfusion imaging. Wall motion was scored with a 5 point system (from 3 [normal] to - 1 [dyskinesia]); normalization or increase of 2 or more points with exercise signified improvement. Forty-eight patients (56%) had no change or further deterioration of wall motion at peak exercise, 15 (18%) showed both improvement of wall motion and deterioration and 22 (26%) showed only improvement of wall motion. Wall motion improvement during exercise was found in 57 (20%) of 279 segments with asynergy at rest. Of these 57 segments improving with exercise, 45 (79%) showed mild and 12 (21%) showed severe asynergy at rest. Only seven segments (12%) were associated with pathologic Q waves. Thallium-201 perfusion was normal in 44 segments (77%) while only 6 segments (11%) had reversible and only 7 (12%) had nonreversible thallium-201 defects. In conclusion: 1) wall motion that is abnormal at rest can sometimes improve with exercise; 2) this phenomenon generally occurs in zones without a Q wave or nonreversible thallium-201 defect. Hence, segments with abnormal wall motion at rest that show improvement with exercise appear to represent viable nonischemic segments.     

Reverse redistribution of thallium-201: a sign of nontransmural myocardial infarction with patency of the infarct-related coronary artery

The pattern of reverse redistribution on the day 10 poststreptokinase resting thallium-201 myocardial scintigrams is a common finding in patients who have undergone streptokinase therapy in evolving myocardial infarction. To investigate this phenomenon, 67 patients who underwent streptokinase therapy were studied pre- and 10 days poststreptokinase therapy resting thallium-201 studies, poststreptokinase therapy resting radionuclide ventriculography and coronary arteriography (60 of the 67 patients). Of the 67 patients, 50 (75%) showed the reverse redistribution pattern on the day 10 thallium-201 study (Group I), 9 (13%) had a nonreversible defect (Group II) and the remaining 8 (12%) had a normal study or showed a reversible defect (Group III). The reverse redistribution pattern was associated with patency of the infarct-related artery (100%), quantitative improvement in resting thallium-201 defect size from day 1 to day 10 study (94%) and normal or near normal wall motion on day 10 radionuclide ventriculography (80% of segments with marked and 54% of those with mild reverse redistribution). In contrast, nonreversible defects were associated with significantly less frequent patency of the infarct-related artery (67%, p = 0.01), improvement in defect size (11%, p less than 0.001) and normal or near normal wall motion (21%, p less than 0.05). Group III patients were similar to Group I with respect to these variables. The quantitated thallium-201 percent washout was higher in the regions with the reverse redistribution pattern (49 +/- 15%) compared with the contralateral normal zone (24 +/- 15%, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of myocardial ischemia and left ventricular wall motion abnormalities as contributory factors in the genesis of exercise-induced ST-segment elevation in Q-wave myocardial infarction.

In patients with a previous myocardial infarction, controversy exists regarding the significance of postexercise ST-segment elevation in the infarct-related leads. Although usually admitted to be a sign of left ventricular dysfunction or myocardial aneurysm, other studies however have related this finding to transient myocardial ischemia and to the presence of jeopardized but viable myocardium in the infarct area. The aim of the present study was to assess the significance of postexercise ST-segment elevation in Q-wave leads as a marker of transmural ischemia or left ventricular dysfunction in 36 consecutive patients, 16 with exercise-induced ST-segment elevation in infarct-related leads. Patients were evaluated by treadmill exercise testing, coronary angiography and ventriculography, thallium-201 tomographic scintigraphy and radionuclide ventriculography within 3 months of the first myocardial infarction. Sixteen patients (group I) had exercise-induced ST segment elevation and 20 (group II) postexercise inversion, no change or pseudonormalization of the T wave in infarct-related leads. The study showed no difference in infarct-related artery, vessel disease or luminal diameter stenosis in groups I and II. The overall agreement between ST shifts and myocardial perfusion in the infarct area was 30.56% with a kappa coefficient of -0.33 (p = NS). The overall agreement between ST shifts and wall motion abnormalities was 69.44% with a kappa coefficient of 0.39 (p < 0.01), stress-induced ST-segment elevation being associated with severe wall contractile disorders in 85% of the patients. In conclusion stress-induced ST-segment elevation in Q wave leads, although not a marker of wall motion abnormalities, is associated with akinesia or dyskinesia of the left ventricular wall.     

再注射201铊心肌显像检测冬眠心肌的价值

目的探讨再注射２０１铊（Ｔｌ）心肌单光子发射计算机断层显像检测冬眠心肌的价值。方法对２２例冠心病心肌梗塞患者进行了运动再分布再注射２０１Ｔｌ心肌显像、心血池显像、冠状动脉（冠脉）造影及冠脉血运重建术，术后复查心血池及运动再分布２０１Ｔｌ心肌显像。结果１８个（４５％）在运动再分布影像上呈不可逆缺损节段在再注射影像上有再分布。再注射２０１Ｔｌ心肌显像预测冬眠心肌血运重建术后血流灌注与功能改善的阳性预测值为８８．９％和８３．３％，阴性预测值为７７．３％和８１８％，两者符合率为８４８％。术后患者运动耐量及左室射血分数改善。结论再注射２０１Ｔｌ心肌显像是检测冬眠心肌较可靠和实用的方法     

Positron emission tomography--usefulness in assessing myocardial viability.

Positron emission tomography (PET) using N-13 ammonia and F-18 fluorodeoxyglucose (FDG) has been used to evaluate myocardial viability in comparison with thallium-201 single photon emission computed tomography (SPECT), and left ventricular wall motion in comparison with contrast ventriculography. Forty patients with anterior myocardial infarction underwent stress and delayed resting perfusion imaging using Tl-201 SPECT and ammonia PET, a glucose metabolism study using FDG PET, and wall motion assessment with left ventriculography. Out of a total of 600 segments of left ventricular imaging, SPECT demonstrated 197 fixed perfusion defects, 99 with redistribution on delayed imaging and 304 normal segments. Of 197 segments with fixed defects, 24 (12%) were normal and 71 (36%) ischemic according to PET criteria. Nineteen of 28 with infarction and all of 12 with non-Q wave infarction showed a viable myocardium. Left ventricular wall motion was significantly better in patients with normal PET findings compared with those with ischemia or scar on PET. Post-PTCA PET revealed improved ammonia PET in 6 of 11 patients but reduced FDG uptake was noted only in 3. These data suggests that Tl-201 SPECT significantly underestimates myocardial viability and that PET imaging is a promising tool for assessing the presence of salvaged myocardium.     

Dual myocardial imaging with technetium-99m pyrophosphate and thallium-201 for detecting, localizing and sizing acute myocardial infarction.

In order to assess and compare the sensitivity and accuracy of technetium (Tc)-99m pyrophosphate and thallium-201 (Tl-201) in detecting, locating and sizing acute myocardial infarction with respect to the biochemically measured extent of infarction, myocardial imaging with both agents using a gamma scintillation camera was performed in 35 patients with documented acute myocardial infarction within 1 to 5 days after the onset of acute symptoms. Tc-99m pyrophosphate scintigrams were abnormal in 30 patients (86 percent) and the location of uptake corresponded to the electrocardiographic site of the infarct in 23 of the 30 patients (77 percent). The five negative Tc-99m pyrophosphate scintigrams included two from patients with a subendocardial infarction. By contrast, all 35 TI-201 myocardial images showed areas of decreased uptake and 33 (94 percent) corresponded to the electrocardiographic location of the infarct. In three patients with a prior myocardial infarction, separate defects were noted in addition to areas of decreased TI-201 uptake corresponding to new Q waves and ST-T wave changes. Additional abnormal areas in the scintigrams not suggested by the electrocardiogram were noted with Tc-99m pyrophosphate in 9 patients and with TI-201 in 16 patients; in 6 of these patients these areas were identical in extent and location in both radionuclide studies. In patients with negative Tc-99m pyrophosphate scintigrams, the average infarct size obtained from completed creatine kinase (CK) curves using serial serum CK values was smaller at 3.2 ± 0.5 (standard error) IU/literhour than in those with positive images (26.9 ± 4.1 IU/literhour; P <0.02). The planimetered area of Tc-99m pyrophosphate uptake that projected largest in one of the three views averaged 33.2 ± 4.6 cm² in patients with anterior or lateral infarction but only 18.9 ± 2.5 cm² (P <0.03) in patients with inferior infarction, whereas mean infarct size as assessed with CK values was not different in both groups. Correlation between infarct size as assessed with CK curve and area as assessed with Tc-99m pyrophosphate uptake was good (r = 0.90) in anterior infarctions but only fair (r = 0.64) in inferior infarctions.     

Comparison of radionuclide and enzymatic estimate of infarct size in patients with acute myocardial infarction

A comparison was made of the estimated size of the myocardial infarction occurring in 26 patients with a first infarction using creatine kinase (CK) enzyme release between radionuclide gated blood pool measurement of total and regional ventricular function and thallium-201 scintigraphic measurement of myocardial perfusion defects. Creatine kinase estimates of infarct size (enzymatic infarct size) correlated closely with the percent of abnormal contracting regions, left ventricular ejection fraction and thallium-201 estimates of percent of abnormal perfusion area (r = 0.78, 0.69 and 0.74, respectively, p less than 0.01). A close correlation also existed between percent abnormal perfusion area and percent of abnormal contracting regions (r = 0.81, p less than 0.01) and left ventricular ejection fraction (r = 0.69, p less than 0.01). Enzymatic infarct size was larger in anterior (116 +/- 37 CK-g-Eq) than inferior (52 +/- 29 CK-g-Eq) myocardial infarction (p less than 0.01) and was associated with significantly more left ventricular functional impairment as determined by left ventricular ejection fraction (33 +/- 7 versus 60 +/- 10%) (p less than 0.01) and percent abnormal perfusion area (58 +/- 14 versus 13 +/- 12) (p less than 0.01). No significant correlation was observed between enzymatic infarct size and right ventricular ejection fraction. These different methods of estimating infarct size correlated closely with each other in these patients with a first uncomplicated myocardial infarction.     

Radionuclide assessment of regional differences in left ventricular wall motion and myocardial perfusion in idiopathic dilated cardiomyopathy

Regional variations in left ventricular contractility and myocardialperfusion are frequent in idiopathic dilated cardiomyopathyand might result from an increase in left ventricular wall stressresponsible for regional wall motion abnormalities. The aimof the study was to perform radionuclide studies in patientswith idiopathic dilated cardiomyopathy to assess regional leftventricular wall motion and myocardial perfusion abnormalitiesin this myocardial disease. We studied 29 men referred withidiopathic dilated cardiomyopathy and normal coronary angiograms.Rest radionuclide left ventriculography and exercise thallium-201tomography were performed in all patients. The thallium-201tomograms were divided into 20 segments for each patient. Meanleft ventricular ejection fraction was 27±11%; 17 patientshad diffuse hypokinesia (mean left ventricular ejection fraction:24±9%) and 12 patients had predominant regional hypokinesia(mean left ventricular ejection fraction: 32±12%). Ofall 580 tomographic segments, 186 had a reduction of thallium-201uptake at exercise. Among them, reversibility was found in 53%.On the whole, 68% (158/232) of anterior, inferior and apicalsegments had a perfusion abnormality, compared with 8% (28/348)of septal and lateral segments (P<0.0001). Left ventricular wall motion and myocardial perfusion abnormalitiesare heterogeneous and not evenly distributed in dilated cardiomyopathy.The alterations are predominant on the myocardial regions delineatingthe antero-posterior axis of the left ventricle. These findingssuggest the possible role of increased left ventricular wallstress on this axis.     

Utility of various radionuclide techniques for distinguishing ischemic from nonischemic dilated cardiomyopathy.

BACKGROUND--Clinically, ischemic and nonischemic (idiopathic) dilated cardiomyopathy may be difficult to distinguish. Radionuclide ventriculography and exercise testing with thallium-201 scintigraphy are often used in an attempt to differentiate them noninvasively. With these techniques, the presence of (1) left ventricular (LV) regional asynergy, (2) depressed LV systolic function with normal right ventricular function, and/or (3) thallium-201 perfusion abnormalities traditionally has been regarded as evidence of ischemic heart disease. We assessed the incidence with which these abnormalities occur in patients with nonischemic-dilated cardiomyopathy. METHODS--Seventy-six patients (45 men, 31 women, aged 18 to 75 years) with invasively proven nonischemic-dilated cardiomyopathy underwent radionuclide ventriculography (n = 75) and provocative thallium-201 perfusion imaging (n = 17). RESULTS--Regional LV wall motion abnormalities were noted in 48% of patients, and 54% had LV systolic dysfunction without concomitant right ventricular dysfunction. Reversible and/or fixed exercise-induced thallium-201 perfusion abnormalities occurred in 94% of the patients studied. CONCLUSIONS--Radionuclide ventriculography and exercise testing with thallium perfusion imaging cannot be used reliably to differentiate ischemic from nonischemic dilated cardiomyopathy, since many patients with the latter have radionuclide evidence of LV segmental wall motion abnormalities, selective LV systolic dysfunction, and segmental perfusion abnormalities.     

Magnetic resonance imaging of myocardial infarction: correlation with enzymatic, angiographic, and radionuclide findings

Spin-echo cardiac magnetic resonance imaging studies were performed in 20 patients with a first 7- to 14-day-old (mean 10) myocardial infarction. The magnetic resonance imaging findings were compared with coronary angiography (14 patients), myocardial enzyme release (18 patients), radionuclide angiography (19 patients), and thallium-201 perfusion scintigraphy (19 patients). Regional T2 relaxation times determined from the signal intensities at echo times 30 msec and 90 msec were significantly prolonged in the infarcted areas. Based on abnormal T2 times for every patient, a regional and a total myocardial damage score was determined. The infarct-related artery was correctly identified in 93% of patients by magnetic resonance imaging, in 79% of patients by thallium-201 scintigraphy, and in 62% of patients by radionuclide angiography. The total damage score correlated well with enzymatic infarct size (r = 0.75, p less than 0.001). The correlation between left ventricular end-systolic volume index determined by magnetic resonance imaging and by radionuclide angiography was r = 0.89 (p less than 0.002). The left ventricular end-systolic volume index correlated significantly with enzymatic infarct size (r = 0.72, p less than 0.001), total damage score (r = 0.68, p less than 0.002), and radionuclide left ventricular ejection fraction (r = -0.68, p less than 0.002). Correlations between the magnetic resonance damage score and the thallium-201 perfusion score were r = 0.60 (p less than 0.01) for the exercise images, and r = 0.72 (p less than 0.001) for the redistribution images. This study shows that spin-echo magnetic resonance imaging is quite comparable with the established noninvasive imaging modalities currently used in patients with acute myocardial infarction.     

Usefulness and limitations of thallium-201 myocardial scintigraphy in delineating location and size of prior myocardial infarction.

In order to evaluate the usefulness of thallium-201 (201TI) myocardial scintigraphy in delineating the location and size of prior myocardial infarction, 32 patients were evaluated at a mean of 7 +/- 2 months after infarction with a 12-lead ECG, resting 201TI myocardial scintigram, biplane left ventriculogram and coronary angiograms. From the left ventriculogram, asynergy was quantified as percent abnormally contracting segment (% ACS), the percent of end-diastolic circumference which was either akinetic or dyskinetic. Using a computerized planimetry system, we expressed 201TI perfusion defects as a percentage of total potential thallium uptake. Of 21 patients with ECG evidence of prior transmural infarction, a 201TI defect was present in 20 (95%), and angiographic asynergy was present in all 21 (100%). The site of prior infarction by ECG agreed with the 201TI defect location in 24 of 32 patients (75%) and with site of angiographic asynergy in 23 of 32 patients (72%). Scintigraphic defects were present in only four of 10 patients (40%) with ACS less than or equal to 6%, but scintigraphic defects were found in 20 to 22 patients (91%) with ACS greater than 6% (p less than 0.01). Thallium defect size correlated marginally with angiographic left ventricular ejection fraction (r = -0.60) but correlated closely with angiographic % ACS (r = 0.80). Thallium defect size was similar among patients with one-, two-, or three-vessel coronary artery disease (greater than or equal to 70% stenosis), but thallium defect size was larger in patients with electrocardiographic evidence of transmural infarction (p less than 0.01) or pulmonary capillary wedge pressure greater than 12 mm Hg (p less than 0.001). Thus, resting 201TI myocardial scingigraphy is useful in localizing and quantifying the extent of prior myocardial infarction, but is insensitive to small infarcts (ACS less than 6%).     

Submaximal exercise testing after acute myocardial infarction: myocardial scintigraphic and electrocardiographic observations.

The relation between global and regional left ventricular function and electrocardiographic signs of ischemia at rest and during submaximal supine exercise was studied in 27 patients 2 to 3 weeks after acute myocardial infarction. Dynamic myocardial scintigraphy was performed at rest and during submaximal exercise utilizing an in vivo method of labeling red blood cells with technetium-99m pertechnetate. Gated radionuclide blood pool scintigrams were obtained in a modified left anterior oblique, and in some patients also in the right anterior oblique projection, to measure left ventricular ejection fraction and segmental wall motion. Electrocardiographic monitoring of heart rate and rhythm was provided during the exercise. The submaximal exercise test was terminated when the patient's heart rate reached 125 beats/min or if angina, malignant ventricular ectopy or electrocardiographic evidence of myocardial ischemia developed before this rate was reached. The data demonstrate that patients with a recent anterior myocardial infarct, in contrast to patients with a recent inferior or nontransmural infarct, manifest a significant reduction in left ventricular ejection fraction with submaximal exercise. Of the eight patients with an anterior infarct, seven had segmental wall motion abnormalities at rest. Four of these eight manifested more severe abnormalities with submaximal exercise; three had abnormalities at rest that did not change with exercise. Four of the eight had a positive electrocardiographic response during exercise (two were taking digoxin). Of these four, only two had more marked wall motion abnormalities with effort. Of the 13 patients with an inferior infarct, 11 had apparently normal wall motion in the modified left anterior oblique projection at rest, including 2 who manifested segmental wall motion abnormalities with submaximal exercise; the 2 remaining patients had wall motion abnormalities at rest that, on exercise, became more marked in one and were unchanged in one. Four of the 13 had a positive electrocardiographic response with exercise (one was taking digoxin); only one of these had a detectably more severe wall motion abnormality with exercise. Of the six patients with a nontransmural infarct, four had no identifiable wall motion abnormalities at rest; in one of these, an abnormality developed with exercise. The remaining two patients had wall motion abnormalities at rest; in one, a positive electrocardiographic ischemic response developed with exercise. Patients with an anterior infarct appear to have a different functional ventricular response to submaximal exercise at the time of hospital discharge than patients with an inferior or nontransmural infarct. To identify ischemic responses with submaximal exercise in these patients one should ideally use both electrocardiographic monitoring and dynamic myocardial scintigraphy.     

Uncomplicated first myocardial infarction: strategy for comprehensive prognostic studies

To evaluate the prognostic role of combined cardiac studies (submaximal exercise test, thallium-201 scintigraphy, radionuclide exercise ventriculography, two-dimensional echocardiography, Holter monitoring and cardiac catheterization) in patients with a first acute myocardial infarction without complications during hospital admission, 115 consecutive patients aged less than 65 years were prospectively evaluated. The studies were carried out before hospital discharge and the patients were then clinically followed up for 12 months. During the follow-up period, 69 patients (60%) developed complications, which were severe in 23 (20%). Half of all complications and 70% of severe complications developed during the 1st follow-up month. Logistic regression analysis disclosed that the combination of studies with the highest predictive power for complications (probability of complications 99%) and severe complications (probability of severe complications 95%) was the association of exercise test + thallium-201 + echocardiogram. Four decision models (exercise test + echocardiography, exercise test + radionuclide ventriculography, thallium-201 scintigraphy + echocardiography, thallium-201 scintigraphy + radionuclide ventriculography) allowed the stratification of all patients in a particular risk category (high, intermediate or low). The best decision model was the association of thallium-201 scintigraphy + radionuclide ventriculography (probability of complications if both tests were positive 84%; probability of absence of severe complications if both tests were negative 88%), but there were no significant differences with the other models. Any association of a test detecting residual ischemia or functional capacity, or both (exercise test or thallium-201) and a test assessing ventricular function (echocardiography or radionuclide ventriculography) results in significant prognostic information in patients with an uncomplicated first acute myocardial infarction. Additional cardiac catheterization does not improve the predictive power of noninvasive studies, which should ideally be performed before hospital discharge because most complications develop during the 1st follow-up month.     

Gated technetium-99m sestamibi for simultaneous assessment of stress myocardial perfusion,postexercise regional ventricular function and myocardial viability: Correlation with echocardiography and rest thallium-201 scintigraphy

Objectives. This study compares technetium-99m sestamibi (sestamibi) electrocardiographic (ECG) gated single-photon emission computed tomography (gated SPECT) and echocardiography for the evaluation of myocardial function and assesses the feasibility of single-injection, single-acquisition stress perfusion/rest function technetium-99m sestamibi-gated SPECT as an alternative to conventional stress/rest imaging for assessment of myocardial perfusion and viability.Background. Simultaneous assessment of stress perfusion and rest function is possible with gated SPECT acquisition of stress-injected technetium-99m sestamibi.Methods. Rest thallium-201 SPECT followed by stress sestamibigated SPECT (acquired 0.5 to 1 h after sestamibi injection) was performed in 58 patients. Echocardiography was performed immediately after or before gated SPECT in 43 of the patients. All studies were analyzed by semiquantitative visual scoring. Sestamibi-gated SPECT studies were read for stress perfusion and rest wall motion and thickening. Reversibility on sestamibi-gated SPECT was defined as the presence of a definite stress defect with normal or mildly impaired wall motion or thickening on gated SPECT.Results. There was high segmental score agreement between gated SPECT and echocardiography for wall motion (91%, kappa = 0.68, p < 0.001) and thickening (90%, kappa = 0.62, p < 0.001). Correlation for global wall motion (r = 0.9S, p < 0.001) and thickening (r = 0.96, p < 0.001) scores between the two modalities was excellent. In 32 patients without previous myocardial infarction, there was excellent agreement for reversibility between stress sestamibi-gated SPECT and rest thallium-201/stress sestamibi (98%, kappa = 0.93, p < 0.01). However, in 26 patients with previous infarction, discordance between the two approaches was frequent, with 26% (20 of 78) of nonreversible defects by stress sestamibi-gated SPECT being reversible by rest thallium-201/stress sestamibi and 21% (23 of 112) of reversible defects by stress sestamibi-gated SPECT being nonreversible by rest thallium-201/stress sestamibi.Conclusions. Gated SPECT of stress-injected sestamibi correlates well with echocardiographic assessment of regional function and thus adds information to perfusion SPECT. In patients without previous myocardial infarction, a single-injection stress perfusion/rest function approach using sestamibi-gated SPECT can substitute for conventional stress/rest myocardial perfusion imaging, adding a rest perfusion study only if there are nonreversible defects or consideration of attenuation artifacts. In patients with previous myocardial infarction, the gated SPECT approach does not replace the need for a rest perfusion study.     

Serial myocardial scintigraphy after a single dose of thallium-201 in men after acute myocardial infarction

Serial myocardial scintigraphy after a single dose of thallium-201 in the period immediately after myocardial infarction may demonstrate redistribution of thallium-201 into perfusion defects that were evident in the initial scan. This study tested the hypothesis that evaluation of this redistribution, available within hours of infarction, could provide a more accurate estimate of the eventual perfusion defect than a single thallium-201 Image obtained immediately after infarction. The study group comprised 14 patients with a diagnosis on admission of probable acute myocardial infarction. The patients received thallium-201 a mean of 1.3 hours after admission to the coronary care unit. Imaging began 10 minutes after the thallium injection and was repeated 4 to 8 hours later.Eight patients with acute myocardial infarction had a definite reduction in one or more perfusion defects on serial scintigraphy, possibly indicating reperfusion of transiently Ischemic zones. Two patients with acute infarction had an increase in perfusion defects in a second study performed 6 hours after the initial scintigram. In the interval between scans, one patient had a cardiac arrest with clinical evidence of infarct extension after successful resuscitation; the other sustained a lateral extension of the infarct. One patient with acute aortic dissection had normal scans on both studies. All three patients with unstable angina had an abnormal initial scan; on repeat scan, the thallium-201 defect was unchanged in one patient, increased in one and decreased in the third. In the patients with myocardial infarction, repeat thallium-201 scans corresponded more nearly than the initial scans to the extent of technetilum-99m stannous pyrophosphate uptake by the heart.These data suggest that serial myocardial imaging with thallium-201 immediately after myocardial infarction can overcome some of the limitations of a single thallium-201 scintigram and may be useful in delineating ischemic from infarcted myocardium in the postinfarction period.     

Myocardial salvage by intracoronary thrombolysis in evolving acute myocardial infarction: evaluation using intracoronary injection of thallium-201

Immediate objective assessment of viabillty of reperfused myocardium following intracoronary (IC) thrombolysis by evaluation of ventricular function may be limited due to delay in restoration of function. Thus we assessed myocardial uptake of thallium-201 (TI-201) following IC injection postreperfusion as an index of myocardial salvage in 12 experimental dogs and in five patients with evolving acute myocardial infarction (AMI). In seven dogs with mean of 313 minutes of experimental coronary occlusion, immediate postreperfusion IC TI-201 images revealed absence of myocardial uptake in prevlously occluded zones. These TI-201 defects correlated with presence of necrosis as demonstrated by histochemical staining with triphenyl-tetrazolium chloride (TTC). In contrast, in five dogs with mean of 37 minutes of coronary occlusion, reperfused myocardium showed normal TI-201 uptake following its IC injection; this normal TI-201 uptake pattern correlated with absence of necrosis by TTC technique in all five dogs. In five patients with evolving AMI, control TI-201 images obtained following IV injection prior to IC thrombolysis showed myocardial perfusion defects corresponding to distribution of the occluded vessel. Following reperfusion, 30 to 50 mCi of TI-201 was injected into the reopened coronary artery. In two patients with mean symptom onset of reperfusion time of $\text{2}\text{1}\text{2}\text{hours}$, immediate postreperfusion IC TI-201 images demonstrated normal or improved TI-201 uptake in reperfused myocardium. By radionuclide ventriculography, segmental wall motion remained abnormal in the reperfused regions 6 hours postreperfusion and showed improvement by the time of 10-day study. In the remaining three patients with symptom onset to reperfusion time of 5 hours, immediate postreperfusion IC TI-201 images did not show improvement, correlating with persistent wall motion abnormalities 10 days postreperfusion. In all five patients, repeat 10-day IV TI-201 images were unchanged from the immediate postreperfusion IC TI-201 images. We conclude that (1) prereperfusion TI-201 imaging with repeat TI-201 injection into the reopened coronary artery appears to delineate the extent of myocardial salvage in both experimental and clinical studies and (2) this method of IC TI-201 imaging allows immediate assessment of myocardial viabillty which may facilltate decisions regarding the need for additional myocardial revascularization modalities.     

Thallium-201 imaging with color display computer system in old myocardial infarction

In 13 patients with old myocardial infarction diagnosed with use of the electrocardiogram, coronary angiogram and left ventriculogram and in 11 patients without infarction, thallium-201 imaging with a color display computer system was carried out. In the group without infarction the average ratio of activities in two regions of interest within the myocardial wall, excluding the apex, was 1.14 (1.08 to 1.23). In the group with infarction the average ratio of noninfarcted to infarcted areas was 1.44 (1.23 to 1.78). Objective detection of infarction was possible in 12 patients (92 percent) in the group with infarction. In two patients, the earlier electrocardiographic pattern of infarction had resolved by the time of imaging. These results suggest that the sensitivity of thallium-201 imaging in the diagnosis of old myocardial infarction may be greatly enhanced by objective and quantitative analysis using a color display computer system.     

Simultaneous assessment of left ventricular wall motion and myocardial perfusion at rest and during exercise by technetium-99m methoxy isobutyl isonitrile.

First-pass radionuclide ventriculography followed by myocardial SPECT with technetium-99m methoxy isobutyl isonitrile (Tc-99m MIBI) was performed on 12 patients with suspected coronary artery disease at rest and during exercise. Left ventricular wall motion and myocardial perfusion were assessed simultaneously and compared on a segment-by-segment basis. Segmental agreement between Tc-99m MIBI and Tl-201 with regard to the presence of perfusion defects was 95% (57/60) at rest and 93% (37/40) during exercise. With respect to the assessment of myocardial ischemia and/or infarction, abnormalities in regional wall motion agreed with the presence of myocardial perfusion defects in 18 out of 21 segments (86%). Simultaneous evaluation of regional wall motion and myocardial perfusion by Tc-99m MIBI may provide useful information for the assessment of myocardial ischemia.     

Predicting the extent and location of coronary artery disease during the early postinfarction period by quantitative thallium-201 scintigraphy

The ability of quantitative thallium-201 scintigraphy to predict the extent and location of coronary artery disease before hospital discharge after acute myocardial infarction was evaluated in 52 patients. All patients underwent coronary angiography and serial thallium-201 imaging either at rest (10 patients) or after submaximal exercise stress (42 patients; target heart rate 120 beats/min). Two or three vessel disease was designated if abnormal thallium-201 uptake or washout patterns, or both, were seen in two or three vascular segments, respectively. Of 156 vessels analyzed in the 52 patients, 91 stenoses of 70 percent or greater were found by angiography. Seventy-four (81 percent) of these were predicted by scintigraphy. The specificity of scintigraphy for identifying vessel stenoses was 92 percent. Sensitivity for detecting and localizing stenoses supplying an infarct zone was 96 percent compared with 62 percent for stenoses supplying myocardium remote from the acute infarct. Perfusion abnormalities were more frequently seen in the distribution of vessels with severe (90 percent or greater) stenoses than in those with moderate (70 to 90 percent) stenoses (87 versus 53 percent, p <0.01). Scintigraphy detected a greater proportion of left anterior descending and right coronary arterial stenoses than circumflex stenoses (91 and 87 versus 63 percent, respectively, p <0.006).In the 42 patients who underwent submaximal exercise testing, multivariate analysis of 23 clinical and laboratory variables identified multiple thallium-201 defects as the best predictor of multivessel disease. The predictive accuracy of exercise-induced S-T segment depression was only 45 percent compared with 88 percent (p <0.05) for thallium-201 scintigraphy. Thus, 2 weeks after myocardial infarction, exercise thallium-201 scintigraphy is useful for predicting the extent and location of coronary artery disease, particularly stenoses in the left anterior descending and right coronary arteries. Moreover, thallium-201 imaging at rest is reliable in assessing the extent of coronary disease in hospitalized patients who cannot undergo exercise testing because of unstable angina, uncompensated heart failure, poorly controlled arrhythmias or physical limitations.     

Poststress redistribution of thallium-201 in patients with coronary artery disease, with and without prior myocardial infarction

To elucidate patterns of thallium-201 redistribution with and without myocardial infarction, to determine the value of thallium-201 redistribution scintigrams in identifying additional ischemic myocardium in the presence of prior myocardial infarction and to delineate the relation of collateral vessels to redistribution, thallium-201 myocardial perfusion scintigraphy was performed immediately after exercise and 4 to 6 hours after exercise in 46 patients with coronary artery disease and 12 normal control subjects. Scintigrams were interpreted in the conventional visual manner as well as with use of computer-processed myocardial perfusion ratios. Normal control subjects demonstrated uniform thallium-201 distribution with regional perfusion ratios approximating unity in both the early and delayed scintigrams.

Of 27 patients with prior myocardial infarction, 5 (19 percent) had complete redistribution on delayed imaging, 17 (62 percent) had partial redistribution and 5 (19 percent) had no redistribution. Of 25 regions corresponding to electrocardiographlc evidence of infarction, 8 (32 percent) had total, 8 (32 percent) had partial and 9 (36 percent) had no redistribution. Collateral vessels were absent or of poor quality in seven of eight infarct areas with no redistribution; three of four infarct regions with normal early thallium uptake were supplied by collateral vessels of good quality. Of 12 regions supplied with good collateral vessels, 9 had complete redistribution, 2 partial and 1 no redistribution. In contrast, only 2 of 21 hypoperfused zones without redistribution (10 percent) were supplied by good collateral vessels. Of 19 patients without prior myocardial infarction, 10 (53 percent) had complete redistribution, 6 (31 percent) had partial redistribution and 3 (16 percent) had no redistribution. Of the 34 abnormal areas in the immediate postexercise image, 22 (65 percent) showed total redistribution, 3 (9 percent) showed partial redistribution and 9 (26 percent) showed no redistribution.

Thus, considerable overlap in redistribution scintigrams occurs in patients with coronary artery disesase with and without prior infarction; a high incidence rate of transient stress-induced hypoperfusion occurs in both infarcted and noninfarcted myocardium. Further, good quality collateral vessels afford redistribution, even to some areas of prior infarction. These data indicate that because delayed postexercise redistribution imaging may not discriminate between myocardial scar and ischemia resting scintigrams may be needed in a substantial number of patients.