J. Maddahi

Separate acquisition rest thallium-201/stress technetium-99m sestamibi dual-isotope myocardial perfusion single-photon emission computed tomography: A clinical validation study

OBJECTIVESnThis study assessed the validity of a novel approach to myocardial perfusion scintigraphy that provides the opportunity to avoid the drawbacks of standard same-day rest/stress technetium-99m sestamibi myocardial perfusion studies by using separate-acquisition dual-isotope rest thallium-201 and exercise technetium-99m sestamibi single-photon emission computed tomography (SPECT).nnnBACKGROUNDnStandard same-day rest/stress technetium-99m sestamibi myocardial perfusion studies are cumbersome, associated with a potential decrease in perceived stress defect severity compared with thallium-201 due to the presence of rest technetium-99m sestamibi and may be unable to differentiate hibernating from infarcted myocardium.nnnMETHODSnThe dual-isotope procedure was performed in 63 patients without previous myocardial infarction undergoing coronary angiography to evaluate sensitivity and specificity for coronary artery disease and in 107 patients with a low (< 5%) likelihood of coronary artery disease to evaluate normalcy rate. To validate defect reversibility, the dual-isotope SPECT study was compared with stress/rest technetium-99m sestamibi SPECT studies in a separate group of 31 patients with previous documented myocardial infarction who underwent a rest technetium-99m sestamibi study in addition to the dual-isotope SPECT study.nnnRESULTSnIn angiographic correlations, dual-isotope SPECT demonstrated high sensitivity for detecting patients with > or = 50% stenosis (91%, 55 patients) and > or = 70% stenosis (96%, 52 patients). In a small group of patients, high specificity was also observed (75% for < 50% stenosis [8 patients] and 82% for < 70% stenosis [11 patients]). A very high normalcy rate of 95% was also found. In the patient group assessed for defect reversibility, in zones with no previous myocardial infarction, segmental agreement for defect type between rest thallium-201 and rest technetium-99m sestamibi studies was 97% (kappa = 0.79, p < 0.001). In myocardial infarct zones, segmental agreement for defect type was 98% (kappa = 0.93, p < 0.001). Image quality was generally good to excellent.nnnCONCLUSIONSnOur findings demonstrate that separate-acquisition dual-isotope myocardial perfusion SPECT is accurate for coronary artery disease detection, correlates well with rest-stress sestamibi studies for assessment of defect reversibility and results in good to excellent image quality. This approach provides an excellent method for the combined assessment of stress myocardial perfusion and myocardial viability.

Improved noninvasive assessment of coronary artery disease by quantitative analysis of regional stress myocardial distribution and washout of thallium-201

Visual interpretation of stress-redistribution thallium-201 (201T1) scintigrams is subject to observer variability and is suboptimal for evaluation of extent of coronary artery disease (CAD). An objective, computerized technique has been developed that quantitatively expresses the relative space-time myocardial distribution of 201TI. Multiple-view, maximum-count circumferential profiles for stress myocardial distribution of 201T1 and segmental percent washout were analyzed in a pilot group of 31 normal subjects and 20 patients with CAD to develop quantitative criteria for abnormality. Subsequently, quantitative analysis was applied prospectively to a group of 22 normal subjects and 45 CAD patients and compared with visual interpretation of scintigrams for detection and evaluation of CAD. The sensitivity and specificity of the quantitative technique (93% and 91%, respectively) were not significantly different from those of the visual method (91% and 86%). The quantitative analysis significantly (p < 0.05) increased the sensitivity of 20Tl imaging over the visual method in the left anterior descending artery (from 56% to 80%), left circumflex artery (from 34% to 63%) and right coronary artery (from 65% to 94%) without significant loss of specificity. Using quantitative analysis, sensitivity for detection of diseased vessels did not diminish as the number of vessels involved increased, as it did with visual interpretation. In patients with one-vessel disease, 86% of the lesions were detected by both techniques; however, in patients with three-vessel disease, quantitative analysis detected 83% of the lesions, while the sensitivity was only 53% for the visual method. Seventy percent of the coronary arteries with moderate (50-75%) stenosis were detected quantitatively, compared with 35% by the visual method.We conclude that this quantitative technique for analysis of stress-redistribution 201T1 scintigrams is objective and more sensitive than the visual method, especially in patients with multiple-vessel disease and those with moderate coronary artery stenosis.

A new technique for assessing right ventricular ejection fraction using rapid multiple-gated equilibrium cardiac blood pool scintigraphy. Description, validation and findings in chronic coronary artery disease.

A reproducible, noninvasive technique for determining right ventricular ejection fraction (RVEF) was developed using multiple-gated equilibrium blood pool scintigraphy, which allows serial rapid measurements without reinjection of radioactivity. Studies were obtained using in vitro labeled technetium- 99m red blood cells, gamma camera and computer. In 20 patients, RVEF determined by multiple-gated equilibrium imaging in the left anterior oblique view was compared with RVEF measured by first-pass scintigraphy. For both types of imaging, multiple regions of interest (ROIs) were used for RVEF. The accuracy of RVEF using equilibrium scintigraphy was also evaluated using a single ROI. In 20 additional patients, rapid (2-minute) equilibrium scintigraphy for RVEF was compared with standard (6-minute) imaging. Excellent correlation (r = 0.94) for RVEF was found between multiple-gated equilibrium scintigraphy and the first-pass technique when multiple ROIs were used. Inter- and intraobserver variations for the equilibrium method were small (r = 0.91 and r = 0.98, respectively). RVEF with the 2-minute equilibrium technique correlated well with the 6-minute method (r = 0.98). In contrast to the high correlation when multiple ROIs were used, analysis of equilibrium scintigraphy by single ROI severely underestimated first-pass RVEF and showed poor correlation (r = 0.60).In 15 normal subjects and 21 patients with significant coronary artery disease and different degrees of right coronary artery stenosis, simultaneous left ventricular ejection fraction (LVEF) and RVEF were measured. RVEF was less than LVEF in normal subjects (0.48 ± 0.05 vs 0.63 ± 0.08, mean ± SD). In patients with coronary artery disease, RVEF was not significantly different from that in the normal group, regardless of the degree of stenosis of the right coronary artery. We conclude that 1) multiple-gated equilibrium scintigraphy is a very accurate and reproducible new technique for determining RVEF; 2) the technique may be performed rapidly, and is therefore well suited to serial assessment of right ventricular function during exercise; 3) multiple ROIs are necessary for accurate measurement with this technique; and 4) RVEF is normally less than LVEF and is not significantly affected at rest by right coronary artery disease.

Left ventricular performance in septic shock: Reversible segmental and global abnormalities

Left ventricular dysfunction has been implicated in the pathogenesis of septic shock, but little is known about its natural history, cause, and prognostic significance. Left ventricular performance was assessed by serial radionuclide and hemodynamic studies in 35 patients with culture-proven septic shock. The mean age (+/- S.D.) of the group was 64 +/- 18 years; 16 of the subjects were women, and 15 had antecedent heart disease. On the first study, the left ventricular stroke work index was depressed in 33 (94%) patients, and nineteen (54%) had a left ventricular ejection fraction less than 0.48. Twenty-two (63%) of the patients had segmental and four had generalized wall motion abnormalities. Conventional hemodynamic parameters were of no value in predicting the patients who had a depressed left ventricular ejection fraction or segmental abnormalities. Patients with underlying heart disease had a much higher frequency (87%) of segmental dysfunction than those without underlying heart disease (45%; p = 0.016), but no differences were noted in the left ventricular ejection fraction or left ventricular stroke work index of these two groups. Segmental abnormalities and low ejection fractions were seen more often in patients with a large left ventricular end-diastolic volume index. Only five subjects had a systemic vascular resistance index greater than 2580 dynes X sec X cm-5 per m2, and the correlation between systemic vascular resistance index and left ventricular ejection fraction was poor. No difference was found in the mean coronary perfusion pressure of those with segmental abnormalities and those with normal wall motion.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous streptokinase in evolving acute myocardial infarction

Eighty-one consecutive patients presenting within 3 hours of the onset of acute myocardial infarction (AMI) and without contraindications to thrombolytic or anticoagulant therapy received a 15- to 30-minute intravenous infusion of 750,000 or 1.5 million units of streptokinase (STK) followed by anticoagulation. Treatment was instituted 130 +/- 41 minutes after the onset of symptoms and reperfusion was achieved 36 +/- 26 minutes later. Reperfusion of the infarct artery was recognized by indirect clinical criteria in 78 patients (96%). In all 66 patients who underwent coronary angiography 3 to 7 days later, there was complete concordance between indirect and angiographic evidence of reperfusion. In 6 patients there was early reocclusion within 24 hours of treatment; in 4 of these patients, the artery was reopened with an additional dose of STK. Two elderly patients suffered an intracranial hemorrhage and there were 8 other major hemorrhagic complications, of which 7 were related to procedural trauma. Five patients (6.2%) died in the hospital. The results of intravenous STK thrombolytic therapy are compared with those of our previous study using intracoronary STK.

ST elevations in leads V1 to V5 may be caused by right coronary artery occlusion and acute right ventricular infarction

In 5 of 69 patients (7%) undergoing intracoronary or intravenous streptokinase treatment, the ST-segment elevations in leads V1 to V5 were caused by occlusion of the right rather than the left anterior descending coronary artery and by myocardial infarction (MI) of the right ventricular (RV) wall rather than the anterior left ventricular (LV) wall or the ventricular septum. RV involvement was documented by technetium pyrophosphate uptake, hypokinesia, dilatation and depressed RV ejection fraction. The left anterior descending artery was patent and the anterior LV wall had normal thallium-201 uptake, no technetium uptake and normal wall motion. ST-segment elevation was highest in lead V1 or V2 and decreased toward lead V5; in patients with anterior LV MI, the ST-segment elevations are usually lowest in lead V1 and increase toward the V5 lead. In contrast to anterior LV infarcts, the R waves in leads V1 to V5 did not decrease and Q waves did not evolve with progression of the MI. The ST-segment elevations in leads V1 to V5 in our patients were associated with small or absent ST-segment elevations in leads, II, III and aVF, suggesting that in other cases of RV infarction, the appearance of ST-segment elevations in leads V1 to V5 is blocked by the dominant electrical forces of the LV inferior MI. This suggestion was confirmed in a canine model. Recognition of the presence of RV infarction may be therapeutically important.

Use of thallium-201 redistribution scintigraphy in the preoperative differentiation of reversible and nonreversible myocardial asynergy

Thallium-201 (ITI) redistribution scintigraphy might differentiate reversibly from nonreversibly asynergic myocardial segments and thus predict the response of these segments to coronary artery bypass grafting (CABG). To test this hypothesis, 25 consecutive patients undergoing CABG, preoperative stress-redistribution 2lTI scintigraphy, and both pre- and postoperative resting equilibrium radionuclide Yentriculography were evaluated. For both types of scintigraphic study, each patient was imaged in the same three views. Because of the effects of CABG on septal motion, this region was considered separately.Postoperative improvement was noted in 54% of 72 preoperative asynergic segments. Improvement was common not only in hypokinetic but also in akinetic and dyskinetic segments, and occurred in a similar proportion of studies performed early (less than 2 weeks) or late (3-6 months) after CABG. Thallium-201 redistribution scintigraphy was highly predictive of the pattern of postoperative asynergy: The redistribution pattern was normal in 90% of segments with reversible asynergy and abnormal in 76% of segments with nonreversible asynergy. The presence or absence of pathologic Q waves was less sensitive in this differentiation. Septal segments, however, frequently demonstrated abnormal wall motion postoperatively, despite normal 20Tl redistribution scintigraphy. Resting left ventricular ejection fraction (LVEF) was generally unchanged postoperatively, but in some patients with multiple areas of reversible asynergy it did improve.Thus, 20TI redistribution scintigraphy appears to reliably distinguish viable from nonviable asynergic myocardial zones, and predicts the response of these segments to CABG.

Significance of dipyridamole-induced transient dilation of the left ventricle during thallium-201 scintigraphy in suspected coronary artery disease

The occurrence and significance of transient dilation of the left ventricle during dipyridamole stress-redistribution thallium-201 scintigraphy was studied in 73 patients who underwent both dipyridamole thallium-201 study and coronary angiography. Transient dilation ratio was calculated from planar anterior images by dividing the computer-derived left ventricular area on the initial image by that of the 4-hour image. In 11 patients with normal coronary arteriograms or less than 50% coronary stenosis, the transient dilation ratio was 0.98 +/- 0.046. An abnormal transient dilation ratio was defined as greater than or equal to 1.12, representing greater than or equal to 3 standard deviations above the mean normal value. When the 15 patients with an abnormal ratio were compared with the 58 with a normal ratio, the former group had a significantly higher frequency of 3 critical (greater than or equal to 90%) coronary stenoses (33 vs 5%), higher prevalence of collaterals (67 vs 24%), more extensive myocardial reversible defects by planar (71 vs 10%) or by single-photon emission computed tomography (87.5 vs 35%) imaging and a higher incidence of dipyridamole-induced anginal chest pain (53 vs 22%). No significant difference between the 2 groups was noted with respect to age, gender, prior myocardial infarction, single or double critical coronary stenosis, dipyridamole-induced ischemic electrocardiographic response and increased lung uptake. An abnormal transient dilation ratio of greater than or equal to 1.12 was a specific marker of multivessel (87%) or 3-vessel (85%) critical coronary artery disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Right ventricular ejection fraction during exercise in normal subjects and in coronary artery disease patients: assessment by multiple-gated equilibrium scintigraphy.

SUMMARYThe response of right ventricular ejection fraction (RVEF) during exercise and its relationship to the location and extent of coronary artery disease are not fully understood. We have recently developed and validated a new method for scintigraphic evaluation of RVEF using rapid multiple-gated equilibrium scintigraphy and multiple right ventricular regions of interest. The technique has been applied during upright bicycle exercise in 10 normal subjects and 20 patients with coronary artery disease. Resting RVEF was not significantly different between the groups (0.49 ± 0.04 vs 0.47 ± 0.09, respectively, mean ± SD). In all 10 normal subjects RVEF rose (0.49 ± 0.04 to 0.66 ± 0.08, p < 0.01) at peak exercise. At peak exercise in coronary artery disease patients, the group RVEF remained unchanged (0.47 ± 0.09 to 0.50 + 0.11, p = NS), but the individual responses varied. In the coronary artery disease patients, the relationship between RVEF response to exercise and exercise left ventricular function, septal motion and right coronary artery stenosis were studied. Significant statistical association was found only between exercise RVEF and right coronary artery stenosis. RVEF rose during exercise in seven of seven patients without right coronary artery stenosis (0.42 ± 0.06 to 0.58 ± 0.08, p = 0.001) and was unchanged or fell in 12 of 13 patients with right coronary artery stenosis (0.50 + 0.09 to 0.45 ± 0.10, p = NS). We conclude that (1) in normal subjects RVEF increases during upright exercise and (2) although RVEF at rest is not necessarily affected by coronary artery disease, failure of RVEF to increase during exercise, in the absence of chronic obstructive pulmonary disease or valvular heart disease, may be related to the presence of significant right coronary artery stenosis. The possibility that severe left ventricular dysfunction in the absence of proximal right coronary artery obstruction may cause abnormal RVEF response to stress requires further evaluation in a larger, more varied patient population.

Analysis of the degree of pulmonary thallium washout after exercise in patients with coronary artery disease

An abnormal increase in pulmonary thallium activity may be visualized on post-stress thallium images in patients with coronary artery disease. Because this increased pulmonary thallium activity usually disappears by the time of redistribution imaging, this study was designed to assess whether measurement of the degree of pulmonary thallium washout between stress and redistribution might improve the detection of increased pulmonary thallium activity in patients with coronary artery disease. Quantitative analysis revealed abnormal (that is, greater than 2 standard deviations of normal values) pulmonary thallium washouts in 59 (64%) of 92 patients with coronary artery disease, but in only 2 (25%) of 8 subjects with angiographically normal arteries (p less than 0.06). By comparison, the visual analysis of pulmonary thallium washout and use of initial pulmonary to myocardial thallium ratio were significantly (p less than 0.05) less sensitive in detecting abnormality in patients with coronary artery disease. Abnormal pulmonary thallium washout was related to both the anatomic extent and functional severity of disease: it occurred with greatest frequency in patients with multivessel disease and in those with exercise-induced left ventricular dysfunction (p less than 0.005). When added to the quantitative analysis of myocardial scintigraphy, the analysis of pulmonary thallium washout increased the detection of coronary artery disease from 84 to 93% (p less than 0.05), but the sample size was too small to assess specificity. Thus, the analysis of pulmonary thallium washout is a useful diagnostic variable because it: 1) provides an objective measurement of abnormal pulmonary thallium activity and is more sensitive than other methods; 2) correlates with both the extent of coronary artery disease and the degree of exercise-induced left ventricular dysfunction, and 3) improves the sensitivity of quantitative myocardial thallium scintigraphy to detect the presence of coronary artery disease.