Jack E. Juni

The aims of this study were to validate invasive coronary Doppler flows against noninvasive PET assessments of myocardial perfusion and to examine the timing and degree of regional coronary vasodilator reserve recovery in patients who are successfully reperfused with primary angioplasty (PTCA) for acute myocardial infarction. PTCA was performed in 21 consecutive patients with acute myocardial infarction; the final diameter stenosis was 25% +/- 7%. After restoration of TIMI Grade 3 flow, all patients underwent quantitative coronary angiography and distal Doppler coronary blood flow studies (basal and after adenosine-induced hyperemia) in the infarct and noninfarct vessels. Regional myocardial perfusion and vasodilator function were quantitated after intravenous adenosine infusion PET in all patients at 26 +/- 9 hr after acute PTCA. These were repeated in 17 patients 9 +/- 3 days later. Post-PTCA resting coronary flow was 35 +/- 15 ml/min in the infarct-related vessels and 50 +/- 24 ml/min during peak hyperemia (p < 0.05). Coronary flow reserve (CFR) was 1.48 +/- 0.34 and 2.08 +/- 0.62 in the infarct and noninfarct vessels, respectively (p < 0.001). Early (< 36 hr) PET myocardial perfusion reserves (MPR) in the infarct and noninfarct regions were 1.59 +/- 0.33 and 2.03 +/- 0.62 (p < 0.01). Doppler CFR and PET MPR were correlated in the infarct (r = 0.61, p < 0.01) and noninfarct (r = 0.77, p < 0.0001) regions. Follow-up PET studies demonstrated improved MPR in both infarct and noninfarct regions (1.93 +/- 0.52 versus 2.54 +/- 0.97, p < 0.01). The improvement in coronary vasodilator function from the time of acute PTCA to follow-up PET in the infarct region was significant (p = 0.005). After successful mechanical revascularization by PTCA after acute myocardial infarction, intracoronary Doppler blood flows and noninvasive PET regional myocardial perfusion are correlated within the wide range of reperfusion blood flows observed in patients with contrast angiographic TIMI Grade 3 flow. Serial PET studies demonstrated a trend towards continued improvement in the vasodilator response in infarct-related myocardial regions after the restoration of blood flow by PTCA. PET offers the potential for accurate noninvasive serial assessment of reperfusion blood flow after primary angioplasty for acute myocardial infarction.

Summary The clinical outcome of 68 patients with unexplained chest pain triaged with emergency centre (EC) SPET myocardial perfusion imaging (MPI) was assessed at 9 month follow-up. Based on clinical presentation and EC-MPI, 63% (43/68) of patients were discharged from the EC; 84% (36/43) of these patients reported no further symptoms at follow-up. There were no adverse clinical events in patients with totally normal EC-MPI.

To determine the cost-effectiveness of promptly performing myocardial perfusion (MP) imaging with single photon emission computed tomography (SPECT) in patients presenting to the emergency department with unexplained chest pain. Fifty patients with unexplained chest pain underwent MP imaging with SPECT and technetium-99m sestamibi. The cardiologists' management plans before and after receipt of imaging findings were compared. Costs were determined from analysis of comparable admissions for the 6 months before the start of the study. The cardiologists' confidence in their clinical diagnosis significantly increased with use of MP imaging (P<.0001). MP imaging results altered management decisions in 34 patients. Twenty-nine patients were sent home on the basis of imaging findings. None of the patients with a normal MP image experienced a serious adverse cardiac event. The total savings to the hospital was $39,296, or $786 per patient. Performing MP imaging in patients with unexplained chest pain while in the emergency department is cost-effective.

To assess the use of modified PIOPED scintigraphic criteria for lung scan (V/Q) interpretation to detect pulmonary embolism (PE), we prospectively applied these criteria in suspected PE patients referred for V/Q from 9/1/92 to 2/7/94. PIOPED criteria were modified by placing a moderate segmental perfusion mismatch in the intermediate instead of low probability of PE category and using the "stripe sign." Patients were studied by six-view V/Q imaging using 74 MBq (2 mCi) 99mTc-MAA followed by 148-370 MBq (4-10 mCi) 99mTc-DTPA aerosol, contrast pulmonary selective angiography and Doppler sonography with leg compression as needed. Patients underwent follow-up (mean 13.9 mo) to detect subsequent thromboembolic events. In this study group, 1000 patients were studied by V/Q followed by angiography in 133 patients. The distribution of V/Q-assigned PE probabilities was: high probability 5.7%, intermediate 17.4%, low 41.4% and normal 35.5%. Group A patients (133) underwent angiography, which resulted in the determination of a 27.1% PE prevalence. Group B patients (867) did not have angiograms; the clinical prevalence of PE was 7.5%. In the total study population, the positive predictive value of a high probability V/Q study for PE (10.1% prevalence) was 98.2%, intermediate probability V/Q study for PE was 24.1% and a low probability study for PE was only 0.5%. Modified PIOPED V/Q interpretation criteria afford better angioproven PE discrimination between intermediate (31.8% PE prevalence) and low (5.5% PE prevalence) probability V/Q results than reported for PIOPED intermediate (32.6% PE prevalence) and low (16.3% PE prevalence) probability V/Q interpretation criteria.

This study determined the feasibility of performing a multicenter trial using quantitative SPECT myocardial perfusion imaging in patients with acute myocardial infarction. The feasibility was assessed by a cardiac phantom. Twenty-two gamma camera systems in 19 laboratories were evaluated. Each laboratory performed nine studies on the cardiac phantom and performed quality control tests of system uniformity, collimator quality and gantry alignment on their gamma camera system. Defects simulating "hypoperfused" myocardium of differing amounts were placed in the myocardium for eight of the nine studies. Measured defect size was compared to true defect size. A total of 198 studies from 22 systems were analyzed. Three studies were technically inadequate. For all 22 systems, the average correlation coefficient between true and measured defect size was 0.992 +/- 0.009, with a range from 1.00 to 0.97. Three systems were rejected due to slopes of the regression line outside the limits 1.00 +/- 0.10 and mean errors > 5% in estimating defect size. The remaining systems had a correlation coefficient of 0.995 + 0.008 with an average slope of 1.00 +/- 0.04 and an intercept of 0.11% +/- 1.57%. The mean error in estimating defect size was 2.08% +/- 0.69%. The small interlaboratory variation and the close correlation with true defect size observed in a cardiac phantom indicate the feasibility of quantitative myocardial SPECT as a useful tool in multicenter trials evaluating therapy in acute myocardial infarction. Preliminary objective testing is required, however, to identify systems with technical deficiencies.