Use of technetium-99m isonitrile (RP-30A) in assessing left ventricular perfusion and function at rest and during exercise in coronary artery disease, and comparison with coronary arteriography and exercise thallium-201 SPECT imaging

Combined assessment of technetium-99m SESTAMIBI planar myocardial perfusion images at rest and during exercise with rest/exercise left ventricular wall motion studies evaluated from gated myocardial perfusion studies

The favorable physical characteristics of technetium-99m-labeled 2-methoxy-2-methylisopropyl-1-isonitril (Tc-SESTAMIBI) enable the combined evaluation of both myocardial perfusion and left ventricular wall motion. To assess the potential of rest and exercise regional myocardial function as an adjunct to planar myocardial perfusion imaging, 60 patients with coronary artery disease and documented arteriographic findings were studied with both protocols during a single study. Exact segmental concordance between myocardial perfusion and wall motion studies was 77% (701/900 segments). Overall sensitivity and specificity to detect hemodynamically significant coronary artery disease with Tc-SESTAMIBI myocardial perfusion imaging were 89% and 79%, respectively, with resting wall motion studies 83% and 71%, respectively, and with rest/exercise wall motion studies, 85% and 71%, respectively. If the results of both perfusion and rest/exercise studies were combined, sensitivity increased to 96% and specificity decreased to 64%. The differences with perfusion studies alone were not statistically significant. Thus despite a good correlation between regional left ventricular function and perfusion, no statistically significant incremental diagnostic value was found when the results of both perfusion and wall motion studies were combined.

Radiopharmaceucticals for cardiovascular imaging

Radionuclide cardiac imaging is a noninvasive technique routinely used to detect coronary artery disease (CAD). This imaging modality includes techniques such as planar, single photon emission computed tomography (SPECT), positron emission tomography (PET) and radionuclide ventriculography--each technique having unique features of its own. Each technique employs various radiopharmaceuticals suitable for assessing different physiological and functional parameters that may become abnormal in the presence of CAD. Various cardiac imaging techniques include myocardial perfusion or blood flow, myocardial metabolism and cardiac function and wall motion. While radionuclide ventriculography gives the global functional status of the heart, SPECT and PET techniques provide information as to the regional blood flow and metabolic status of the myocardium. The following is a review of radiopharmaceuticals that are utilized clinically and in research in different types of nuclear cardiac imaging. Radiopharmaceuticals have been grouped according to the technique employed in which they are used. Various characteristics, merits and disadvantages of each radiopharmaceutical are discussed in detail.

The clinical usefulness of electrocardiogram-gated Tc-99m methoxy-isobutyl-isonitrile images in the detection of basal wall motion abnormalities and reversibility of stress induced perfusion defects

Technetium-99m methoxy-isobutyl-isonitrile (SESTAMIBI) has been recently introduced to trace regional myocardial perfusion. Beyond blood flow distribution, a quantitative index of regional myocardial wall motion from SESTAMIBI electrocardiogram (ECG)-gated images was obtained, according to the assumption that changes in the detected radioactivity reflect changes in myocardial wall thickness during the cardiac cycle. As a preliminary study, 20 patients with coronary artery disease and regional wall motion abnormalities and 15 normal subjects were studied by SESTAMIBI scintigraphy and contrast ventriculography. Regional wall motion was analyzed by a radial method applied to both techniques. Absolute systolic changes in radioactivity and its ratio to reference normal values (wall thickening index, WTI) were determined in 9 anatomical cardiac regions according to the formula (endsystolic counting profile-enddiastolic counting profile/enddiastolic counting profile) x 100. The overall agreement between radioisotopic and ventriculographic techniques was 88% (158 of 180 segments). Normal, hypokinetic and akinetic ventriculographic segments showed WTI values of 1.1 +/- 0.2, 0.8 +/- 0.2 and 0.4 +/- 0.3 respectively (P less than 0.001). A second clinical study was performed in 25 patients studied by stress/rest ECG-gated SESTAMIBI scintigraphy. The assumption of this part of the study was to investigate if a preserved wall thickening in segments with stress defects might predict those areas with normal resting perfusion. Partial or total normalization of regional perfusion was observed in 90% of segments with a WTI greater than or equal to 0.8. These studies indicate the ECG-gated SESTAMIBI may represent a suitable technique for the simultaneous analysis of flow distribution and function. Analysis of post-exercise ECG-gated SESTAMIBI can predict the reversibility of transient perfusion defects.

Technetium-99m sestamibi tomography in patients with spontaneous chest pain: correlations with clinical, electrocardiographic and angiographic findings

The sensitivity and specificity of technetium-99m hexakis-2-methoxy-2-isobutyl-isonitrile (sestamibi) single-photon emission computed tomographic (SPECT) imaging for the diagnosis of coronary artery disease were studied in 45 patients admitted to the hospital for clinical suspicion of unstable angina. Only patients without prior myocardial infarction were included and all patients had technetium-99m sestamibi injection and a 12-lead electrocardiogram (ECG) during and less than or equal to 4 h after an episode of chest pain. Coronary angiography performed in all patients during hospitalization showed significant coronary artery disease (greater than or equal to 50% luminal diameter reduction) in 26 of the 45 patients. The SPECT studies obtained after injection of technetium-99m sestamibi during an episode of spontaneous chest pain showed a sensitivity of 96% for the detection of coronary artery disease; the 12-lead ECG obtained at the time of the injection had a sensitivity of 35%. With the patient in the pain-free state, respective sensitivity values were 65% and 38%. Specificity for the radionuclide study was 79% during pain and 84% in the pain-free state; for the ECG, it was 74% both during and between episodes of pain. The site of the perfusion defect corresponded to the most severe coronary artery lesion in 88% of patients. The severity of the perfusion defect correlated with the extent of coronary artery disease: the defect score was 5.3 +/- 3.3 with one-vessel disease, 4.9 +/- 2.8 with two-vessel disease and 10.5 +/- 5.0 with three-vessel disease (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of technetium-99m-MIBI and thallium-201 in tomographic imaging combined with high-dose dipyridamole and handgrip exercise for detecting coronary artery disease

Forty-two patients with known stable coronary artery disease, referred for coronary angiography, were examined with technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile (MIBI) tomography combined with a high-dose dipyridamole infusion (0.7 mg/kg) and handgrip stress. MIBI tomography was unable to show coronary artery disease only in 2 patients, thus yielding a sensitivity figure of 95%. MIBI tomography correctly identified 27 (82%) of 33 stenotic lesions (greater than or equal to 50% diameter stenosis) of the left anterior descending artery, 17 (61%) of 28 of those of the left circumflex artery, and 28 (90%) of 31 of those of the right coronary artery. The overall vessel sensitivity was 78%. The computed lumen diameter stenoses were more advanced in cases detected than in those not detected with MIBI tomography: 87 +/- 14 vs 76 +/- 14% (p less than 0.01). The 50 to 69% stenoses did not show any tendency to produce less positive findings than those with greater than or equal to 70% stenoses. In the subgroup of 21 patients who also presented for thallium scintigraphy, the overall diseased vessel identification rate was 76% for thallium tomography and 83% for MIBI tomography (p = not significant). Minor noncardiac side effects related to the dipyridamole-handgrip test occurred only in 5% of 63 study sessions. A high-dose dipyridamole combined with isometric exercise is a safe stress method, and when used during scintigraphy, MIBI tomography is at least as efficient a tool as thallium tomography in detecting diseased vessel territories in patients in coronary artery disease.

Technetium 99m sestamibi in the assessment of chronic coronary artery disease

Extensive work has already been performed with regard to both planar and single photon emission computed (SPECT) technetium 99m sestamibi studies. Before widespread application of optimized acquisition and processing methods, clinical results between 99mTc sestamibi and thallium 201 were remarkably similar. It is anticipated that as techniques for 99mTc sestamibi planar and SPECT imaging become optimized, improvements in sensitivity and specificity for detection of coronary artery disease, over those observed with 201TI, might be forthcoming. This expectation is based on the improved image quality inherent in the use of the 99mTc agent with its higher count rate and higher energy. This improvement in image quality may be a principal reason for laboratories to switch from 201TI to 99mTc sestamibi imaging. It is anticipated that, with improved imaging characteristics, it will be easier for the average community hospital to obtain higher quality planar or SPECT imaging using 99mTc sestamibi rather than 201TI. In addition to improved image quality, the characteristics of 99mTc sestamibi allow gated planar or SPECT perfusion images to be obtained. It has been suggested that stress-gated SPECT sestamibi studies may provide all the information contained in a stress-rest nongated 99mTc sestamibi study, thereby potentially increasing patient throughput, a major concern with SPECT. Throughput can also be increased by using dual-isotope approaches with rest 201TI and stress technetium sestamibi acquisitions, employing either separate or simultaneous imaging with which the entire study can be accomplished in less than 2 hours. With simultaneous dual-isotope acquisition, camera time can be reduced by 50%. Finally, 99mTc sestamibi offers the advantage of the ability to perform first-pass exercise ventricular function and SPECT myocardial perfusion studies with a single injection of tracer. Regarding the assessment of myocardial viability, results to date suggest a very high degree of concordance between 201TI and 99mTc sestamibi studies using either planar or SPECT acquisition techniques. Correlative rest studies with both tracers will be of particular interest, as will preoperative and postoperative and position emission tomography correlation studies.

Assessment of the extent of jeopardized myocardium during acute coronary artery occlusion followed by reperfusion in man using technetium-99m isonitrile imaging

We tested the feasibility of technetium-99m methoxyisobutyl isonitrile (Tc-MIBI) imaging for delineating jeopardized myocardium during acute coronary occlusion and reperfusion in man. This new perfusion agent was injected in 25 patients during elective percutaneous transluminal coronary angioplasty (PTCA) of a single-vessel left anterior descending (LAD) coronary artery stenosis. Distinct perfusion defects were present on "occlusion" images but not on "open vessel" images obtained 20 to 24 hours later in 21 patients (84%). The extent and severity of perfusion defects were significantly smaller in patients with distal versus proximal LAD occlusions (3.4 +/- 1.2 versus 5.2 +/- 1.5 segments; p less than 0.001). The only factor that was significantly related to the presence or absence of such "ischemic" perfusion defects was the absence or presence of visible collateral vessels to the LAD (p less than 0.03). The site of occlusion, presence of wall motion abnormalities, or occlusion time did not influence the results significantly. Thus the myocardial area at risk could be visualized and quantitated by Tc-MIBI imaging even after occlusion times as short as 15 seconds, but functioning collateral vessels are capable of protecting jeopardized myocardium in this setting.

Assessment of coronary artery disease using single-photon emission computed tomography with thallium-201 during adenosine-induced coronary hyperemia

Thallium-201 myocardial imaging during dipyridamole-induced coronary hyperemia has been an accepted method for diagnosing coronary artery disease (CAD) and risk stratification. Adenosine is a powerful short-acting coronary vasodilator. Initial results of thallium imaging during adenosine infusion have been encouraging. In 132 patients with CAD and in 16 patients with normal coronary angiograms, adenosine was given intravenously at a dose of 0.14 mg/kg/min for 6 minutes and thallium-201 was injected at 3 minutes. The thallium images using single-photon emission computed tomography were abnormal in 47 of the 54 patients (87%) with 1-vessel, in 34 of 37 patients (92%) with 2-vessel and in 40 of 41 patients (98%) with 3-vessel CAD. The sensitivity was 92% in the 132 patients with CAD (95% confidence intervals, 86 to 96%). In patients with normal coronary angiograms, 14 of 16 patients had normal thallium images (specificity, 88%; 95% confidence intervals, 59 to 100%). The results were very similar when subgroups of patients were analyzed: those without prior myocardial infarction, elderly patients and women. The nature of the perfusion defects (fixed or reversible) was assessed in relation to whether the 4-hour delayed images were obtained with or without the reinjection technique. In patients who underwent conventional delayed imaging, there were more fixed perfusion defects than in patients with reinjection delayed imaging (16 vs 0%, p less than 0.0001). The adverse effects were mild, transient and well tolerated. Thus, adenosine thallium tomographic imaging provides a high degree of accuracy in the diagnosis of CAD. The use of the reinjection technique enhances the ability to detect reversible defects.

Myocardial perfusion imaging with technetium-99m-labeled agents

Thallium-201 (201Tl) is suboptimal as a single-photon emitting agent for myocardial perfusion imaging, in view of its low-energy photons and long half-life. To circumvent these limitations, two new myocardial perfusion imaging agents labeled with technetium-99m (99mTc) have been developed. They are Tc-sestamibi and Tc-teboroxime. Clinical trials of myocardial perfusion with both tracers have shown results similar to those obtained with 201Tl for detection of coronary artery disease. Results to date indicate that Tc-sestamibi accurately detects and locates myocardial infarction and can accurately assess both left and right ventricular ejection fractions by the first-pass technique. In addition, research has shown that rest-stress studies can be performed on the same day and that Tc-sestamibi can be used to assess the results of thrombolytic therapy. Tc-teboroxime has excellent myocardial tracer uptake characteristics but is cleared very rapidly from the myocardium. These features make Tc-teboroxime well suited to rapid serial studies. These new technetium myocardial perfusion agents have just become available for routine clinical use and are likely to replace 201Tl in many of its clinical applications.

Myocardial imaging with Tc-99m teboroxime: technique and initial results

This study examined the results of Tc-99m teboroxime imaging in 22 patients aged 59 +/- 9 years and compared the results with those of thallium-201. The exercise and rest teboroxime studies were obtained within 3 hours of each other using a dose of 15 mCi/study. Because of the very short wash-out half-life of teboroxime, imaging was begun within 1 to 2 minutes after injection. Both SPECT and planar images were obtained; the SPECT protocol was modified by changing the number of frames, the time per frame, or the filters used for reconstruction of images. The planar images were obtained in the supine or upright position. Shorter acquisition time for SPECT (10 sec/frame) and the use of a Butterworth filter with a frequency cutoff of 0.3 cycle/cm and a power of 10 yielded best image quality. There was a close agreement with thallium results in identifying an abnormal or normal perfusion pattern in 89% of vascular territories. The scans were abnormal by both techniques in 12 patients, normal in nine patients, and discordant in only one patient. Thus Tc-99m teboroxime myocardial imaging is feasible at rest and during exercise using either SPECT or planar imaging. Shorter acquisition time and appropriate filtering for SPECT imaging and the upright position in planar imaging improve image quality and are convenient for the patient.

Reproducibility of quantitative hexakis-2-methoxyisobutylisonitrile single photon emission tomography in stable coronary artery disease

The quantification of myocardial perfusion abnormalities is necessary to allow comparison of repeated studies, especially in the evaluation of the success of medical, interventional or combined treatment in stable coronary artery disease or in evolving myocardial infarction. The purpose of this study was to assess inter-observer reproducibility of tomographic study processing using a semi-automatic quantitative programme. Technetium 99m hexakis-2-methoxyisobutylisonitrile (99mTc-Sestamibi) was chosen for tomographic imaging of repeated rest-stress studies in patients with stable coronary artery disease. The quantification was performed using a modification of the Cedars polar coding and comparison with the normal data base. The perfusion defects were quantified separately for each standard perfusion area [left anterior descending (LAD), right coronary (RCA) and left circumflex (LCX) arteries] and total area of hypoperfused myocardium. The inter-observer variability for 40 tomographic studies was accomplished. The defects were the largest in the LAD perfusion area (average 19.7% of the normalized LAD supply area) with an inter-observer correlation of 0.84 for this region. The greatest variability was found for the LCX region (r = 0.55) and is attributed to a small average perfusion defect (7.1%), only 18 studies having abnormal perfusion in this area. In total, an average 14.3% of the left ventricular myocardium was significantly hypoperfused, and the inter-observer correlation was 0.87. These results show good inter-observer reproducibility using semi-automatic quantitation of perfusion defects. Careful interpretation of smaller defects in the evaluation of treatment results is advised when repeated 99mTc-Sestamibi single photon emission tomography studies are processed by more than one observer.

Comparison of thallium-201 and technetium-99m hexakis 2-methoxyisobutyl isonitrile single-photon emission computed tomography for estimating the extent of myocardial ischemia and infarction in coronary artery disease

Single-photon emission computed tomography (SPECT) using thallium-201 (Tl-201) was compared with technetium-99m hexakis 2-methoxyisobutyl isonitrile (Tc-99m MIBI) in 24 patients with coronary artery diseaes. Patients exercised to the same work load as each isotope was studied. Normal and hypoperfused left ventricular mass was determined with an automated method. Estimated total left ventricular mass was similar for both stress/redistribution Tl-201 and stress/rest Tc-99m MIBI images. The mean estimated defect size in the redistribution Tl-201 images was 32 +/- 34.7 vs 33 +/- 38.4 g in the resting Tc-99m MIBI studies (difference not significant). The individual determinations of defect mass were highly correlated (r = 0.93; p less than 0.0001). Estimated defect size in the stress Tl-201 images (52 +/- 46.2 g) was significantly larger than the exercise Tc-99m MIBI estimates of defect mass (42 +/- 39.9 g; p less than 0.05). A linear correlation existed between stress thallium and technetium estimates of defect size (r = 0.85) but 15 of 24 Tc-99m MIBI defects were smaller than the Tl-201 defects. Partial redistribution of Tc-99m MIBI could explain the discordance. Stress Tc-99m MIBI SPECT defect size determined by visual interpretation or by the use of isocount analysis may be smaller than what is seen with stress Tl-201 SPECT.

Development and prospective application of quantitative 2-day stress-rest Tc-99m methoxy isobutyl isonitrile SPECT for the diagnosis of coronary artery disease

The clinical diagnostic accuracy of 2-day stress/rest quantitative Technetium-99m (Tc-99m) methoxy-isobutyl-isonitrile (Tc-sestamibi) single photon emission computerized tomography (SPECT) was assessed in a validation population of 61 patients from two different sites using two different camera/computer systems. The study population was made up of 53 catheterized patients, 29 from Cedars-Sinai Medical Center (CSMC) and 24 from the University of Texas Southwestern Medical Center (UTSMC), and eight UTSMC patients with a less than 5% pre-test likelihood of coronary artery disease. Interpretation employed gender-specific normal limits developed in an additional 15 men and 8 women at CSMC with less than a 5% likelihood of significant coronary artery disease. The results from CSMC compared with those from UTSMC were not different from each other. The overall sensitivity for detection of patients with coronary artery disease (greater than or equal to 50% stenosis) was 94% (CSMC: 92%, UTSMC: 95%). Overall specificity in the five patients with normal coronary arteriograms was 80% (CSMC: 67%, UTSMC: 100%). The normalcy rate in patients with a low likelihood of coronary artery disease was 88%. Vessel sensitivity was 85% (CSMC: 84%, UTSMC: 85%), while vessel specificity was 71% (CSMC: 72%, UTSMC: 69%). There was also no significant difference in the sensitivities and specificities between male and female populations. In addition, the agreement with coronary angiography for assessment of disease extent (normal coronary arteriogram, single or multivessel disease) was 75% (kappa = 0.6 +/- 0.1). This study demonstrated that Tc-sestamibi SPECT by quantitative analysis is accurate for the detection and localization of coronary artery disease. Furthermore, the CSMC quantitative method was shown to provide similar diagnostic accuracy when applied to data acquired at a different site using a different camera/computer system.

Are the kinetics of technetium-99m methoxyisobutyl isonitrile affected by cell metabolism and viability?

To investigate the role of cell viability and metabolism on the myocardial kinetics of a new tracer, technetium-99m-methoxyisobutyl isonitrile (Tc-99m-MIBI), 250 microCi/l Tc-99m-MIBI was infused in isolated rat hearts under constant flow conditions. The hearts were studied after inducing irreversible damage by cytochrome c oxidase inhibitor sodium cyanide (n = 8) or sarcolemmal membrane detergent Triton X-100 (n = 8). The control hearts (n = 6) received no toxins. Mean Tc-99m-MIBI peak accumulation activity was significantly reduced after cyanide (51.1 +/- 44.2% of control, p less than 0.01) and Triton (13.8 +/- 2.7% of control, p less than 0.001) administration. Kinetic studies also showed marked reduction in accumulation rates and marked increase in clearance rates for cyanide (p less than 0.01) and Triton (p less than 0.01) groups compared with controls. Potential changes in regional flow distribution were assessed using microspheres. When peak accumulation activity was corrected for these changes, there remained significant differences between the groups. In the cyanide and Triton groups, irreversible cell injury was confirmed by creatine kinase and lactate dehydrogenase release, triphenyl tetrazolium chloride staining, and electron microscopy. All the cells were viable in the control group. We conclude that the accumulation and clearance kinetics of Tc-99m-MIBI are significantly affected by cell viability. Tc-99m-MIBI kinetics appear to be dependent on sarcolemmal integrity and to a lesser extent on aerobic metabolism.

Myocardial perfusion imaging with technetium-99m sestamibi SPECT in the evaluation of coronary artery disease

Technetium-99m (Tc-99m) sestamibi is a new myocardial perfusion imaging agent that offers significant advantages over thallium-201 (Tl-201) for myocardial perfusion imaging. The results of the current clinical trials using acquisition and processing parameters similar to those for Tl-201 and a separate (2-day) injection protocol suggest that Tc-99m sestamibi and Tl-201 single photon emission computed tomography (SPECT) provide similar information with respect to detection of myocardial perfusion defects, assessment of the pattern of defect reversibility, overall detection of coronary artery disease (CAD) and detection of disease in individual coronary arteries. Tc-99m sestamibi SPECT appears to be superior to Tc-99m sestamibi planar imaging because the former provides a higher defect contrast and is more accurate for detection of disease in individual coronary arteries. Research is currently under way addressing optimization of acquisition and processing of Tc-99m sestamibi studies and development of quantitative algorithms for detection and localization of CAD and sizing of transmural and nontransmural myocardial perfusion defects. It is expected that with the implementation of the final results of these new developments, further significant improvement in image quality will be attained, which in turn will further increase the confidence in image interpretation. Development of algorithms for analysis of end-diastolic myocardial images may allow better evaluation of small and nontransmural myocardial defects. Furthermore, gated studies may provide valuable information with respect to regional myocardial wall motion and wall thickening. With the implementation of algorithms for attenuation and scatter correction, the overall specificity of Tc-99m sestamibi SPECT should improve significantly because of a substantial decrease in the occurrence of attenuation-related image artifacts.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of SPECT using technetium-99m agents and thallium-201 and PET for the assessment of myocardial perfusion and viability

This report reviews the applications of tomographic imaging with current and new tracers in assessing myocardial perfusion and viability. Multiple studies with thallium-201 (TI-201) single photon emission computed tomography (SPECT) imaging for the detection of coronary artery disease (CAD) have demonstrated high sensitivity, high rates of normalcy and high reproducibility. In assessing viability, fixed defects are frequently detected in viable zones in 4-hour studies with TI-201 imaging. Redistribution imaging performed 18 to 72 hours after injection or reinjection of TI-201 before 4-hour redistribution imaging has been shown to improve accuracy of viability assessment. TI-201 SPECT studies are limited by the suboptimal physical properties of TI-201, which result in variable image quality. The 2 new technetium-99m (Tc-99m) - labeled myocardial perfusion tracers offer the ability to inject much higher amounts of radioactivity, making it possible to assess ventricular function as well as myocardial perfusion from the same injection of radiotracer. Tc-99m sestamibi has very slow myocardial clearance, which allows for prolonged imaging time and results in image quality superior to that obtained with TI-201 and Tc-99m teboroxime. The combination of minimal redistribution of Tc-99m sestamibi and high count rates makes gated SPECT imaging feasible, and also permits assessment of patients with acute ischemic syndromes by uncoupling the time of injection from the time of imaging. The combination of high image quality and first-pass exercise capabilities may lead to a choice of this agent over TI-201 for assessment of chronic CAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Technetium-99m sestamibi in chronic coronary artery disease: the European experience

Since the introduction of technetium-99m methoxy-isobutyl isonitrile (Tc-99m sestamibi) in Europe, there has been a growing interest in its use. Several European multicenter trials have been conducted to evaluate this new agent in relation to the traditional perfusion marker thallium-201, and other studies are in progress to understand the use of this perfusion marker for the diagnosis of coronary disease, for use in conjunction with pharmacologic vasodilation, for use in the assessment of ventricular function and wall motion and for the assessment of interventions.

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

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

Effect of exercise level on the ability of thallium-201 tomographic imaging in detecting coronary artery disease: analysis of 461 patients

This study examined the effect of the level of exercise on the ability of thallium-201 imaging with single photon emission computed tomography (SPECT) to detect coronary artery disease. Patients in group 1 (n = 164) achieved adequate exercise end points, defined as positive exercise electrocardiograms or greater than or equal to 85% of maximal predicted heart rate. Patients in group 2 (n = 108) had submaximal exercise. The SPECT thallium-201 images showed perfusion defects in 74%, 88%, and 98%, respectively, of patients with one, two and three vessel coronary artery disease in group 1, compared with 52%, 84% and 79%, respectively, of such patients in group 2 (p less than 0.05). Perfusion defects showed partial or complete redistribution consistent with ischemia in 56%, 80% and 88%, respectively, of patients with one, two and three vessel coronary artery disease in group 1 compared with 35%, 58% and 56%, respectively, of such patients in group 2 (p = 0.08, less than 0.03 and less than 0.001, respectively). Of 58 patients with normal coronary angiograms or less than 50% diameter stenosis, 36 (62%) had normal SPECT images. In a separate group of 131 patients with less than 5% pretest probability of coronary artery disease, the specificity was 93%. The sensitivity of exercise SPECT imaging in group 1 was higher than that of ST segment depression (p less than 0.001). Thus, the level of exercise affects the results of SPECT thallium imaging in the localization and evaluation of the extent of coronary artery disease and the detection of ischemia.