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Biomedical subjects

F J Wackers

Publications and source records attributed to F J Wackers.

At least 73 records · Page 4Linked to original sources
PubMed1992

Technetium-99m sestamibi myocardial imaging at rest for assessment of myocardial infarction and first-pass ejection fraction. Multicenter Cardiolite Study Group.

The ability of technetium (Tc)-99m sestamibi myocardial perfusion imaging at rest to evaluate myocardial infarction and first-pass ejection fraction was studied in a trial involving 18 institutions. Protocol I compared regional perfusion with occurrence of infarction by Q wave or by gated blood pool scan wall motion abnormality in 146 patients. Protocol II assessed first-pass right and left ventricular ejection fraction in 85 patients. In protocol I, Tc-99m sestamibi images were abnormal in 104 of 111 patients (94%) with both a Q wave and a gated scan wall motion abnormality and was normal in 23 of 25 patients (92%) in whom both were normal. Therefore, concordance existed in 105 (94%) patients. Of 115 patients with a Q wave, 107 (93%) had an abnormal Tc-99m sestamibi study. Of 115 patients with a gated scan wall motion abnormality, 108 (94%) had an abnormal Tc-99m sestamibi study. Tc-99m sestamibi imaging showed corresponding perfusion abnormalities in 81% of 69 anterior Q-wave infarcts, 73% of 55 inferior Q-wave infarcts and 88% of 8 posterior infarcts. Specificity in normal regions on electrocardiography and wall motion was 91, 100 and 100%, respectively, for anterior, inferior and posterior regions, respectively, between wall motion and perfusion. Of 17 myocardial segments per patient, there was concordance in 74% of patients. First pass Tc-99m sestamibi imaging of ejection fraction agreed well with conventional first-pass imaging for the right and left ventricle. It is concluded that Tc-99m sestamibi myocardial imaging at rest reliably diagnoses and localizes infarction and assesses ejection fraction by first-pass imaging.

Adult↗
PubMed1991

Thallium-201 for assessment of myocardial viability: quantitative comparison of 24-hour redistribution imaging with imaging after reinjection at rest.

Redistribution thallium-201 imaging 2 to 4 h after exercise may be incomplete and therefore may be inadequate to fully assess myocardial variability. Late redistribution imaging 24 h after exercise has been proposed to overcome this limitation of thallium stress imaging. However, because of poor count density the image quality on these studies is often suboptimal. In the present study the diagnostic information on 24-h planar thallium redistribution images was compared with that on images obtained after a reinjection of thallium at rest. Eighty-four patients with a stress thallium-201 defect had delayed redistribution imaging after 2 to 4 h and 24 h later, and again after an injection of thallium at rest. Defect reversibility on 24-h redistribution images was compared quantitatively with that on images after injection of thallium at rest. The quality of thallium images at rest was consistently better than that of 24-h redistribution images. Poor quality studies occurred in 13% of 24-h redistribution images compared with 0.4% of the studies at rest. Significantly more defect reversibility was detected on images after the reinjection at rest. Of 41 patients who appeared to have a fixed defect at 2- to 4-h redistribution imaging, 11 (27%) had a reversible defect by 24-h redistribution imaging compared with 29 (71%) after thallium-201 reinjection. No clinical variables at the time of stress testing were predictive of late defect reversibility. It is concluded that in patients with fixed a thallium defect at 2 to 4 h after exercise, reimaging after a reinjection at rest provides better diagnostic information than does 24-h late redistribution imaging.

Adult↗
PubMed1991

Validation of continuous radionuclide left ventricular functioning monitoring in detecting silent myocardial ischemia during balloon angioplasty of the left anterior descending coronary artery.

Silent myocardial ischemia has been inferred from transient ST-segment depression during continuous electrocardiographic monitoring. Recently, continuous ambulatory monitoring of left ventricular (LV) function using a radionuclide technique (VEST) has demonstrated episodes of significant silent LV dysfunction in the absence of electrocardiographic changes. To validate the demonstration of silent LV dysfunction with this technique, 12 men were studied during percutaneous transluminal coronary angioplasty. A total of 18 left anterior descending coronary artery balloon inflations were performed. Balloon inflations at 8 +/- 2 atm (4 to 10 atm) lasted 70 +/- 16 seconds. Seventeen of 18 inflations were associated with a decrease in LV ejection fraction greater than 0.10. Mean LV ejection fraction decreased from 0.53 +/- 0.08 to 0.28 +/- 0.11 (p less than 0.0001). In contrast, there was pain in only 10 inflations and ST-segment changes in 7. LV dysfunction was associated with a minimal increase in end-diastolic volume (4 +/- 3%, p less than 0.003), and a major increase in relative end-systolic volume (69 +/- 43%, p less than 0.001). These data suggest that continuous monitoring of LV function with the VEST can sensitively detect silent ischemic decreases in LV function occurring during angioplasty, and provide further validation of the use of this technique for detecting silent myocardial ischemia.

Aged↗
PubMed1991

Myocardial perfusion imaging in ischemic heart disease anno 1990.

The field of radionuclide myocardial perfusion imaging is in a rapid state of change. Stress-rest myocardial imaging is important not only for the detection of coronary artery disease but also for prognostic stratification of patients. In particular, assessment of myocardial viability in patients with left ventricular dysfunction is a recent focus of investigation. Single-photon emission computed tomography has become widely accepted as the preferred (albeit challenging) imaging modality for myocardial perfusion imaging. Silent myocardial ischemia and its clinical significance continues to be an intriguing aspect of the clinical manifestation of coronary artery disease. Myocardial perfusion imaging is an invaluable independent method to unravel this problem. Dipyridamole was approved for pharmacologic vasodilation in conjunction with myocardial perfusion imaging. At the same time, direct infusion of adenosine was proposed as an alternative method of effecting vasodilatory stress. In 1990, several new technetium-99m-labeled myocardial perfusion imaging agents have been introduced (teboroxime and hexakis-2-methoxyisobutyl-isonitrile [sestaMIBI]) that may have a profound impact on imaging techniques and applications of myocardial perfusion imaging.

Coronary Disease↗
PubMed1991

False-negative dipyridamole-thallium-201 myocardial imaging after caffeine infusion.

The vasodilator effect of intravenously administered dipyridamole may be caused by an increase in endogenous plasma adenosine levels. We evaluated the effect of caffeine, an adenosine receptor antagonist, on the diagnostic results of dipyridamole-201Tl myocardial imaging in eight patients with coronary artery disease. Caffeine infusion significantly attenuated the dipyridamole-induced fall in blood pressure and the accompanied increase in heart rate. The infusion of dipyridamole alone resulted in chest pain and ST-segment depressions on the electrocardiogram in four patients, whereas none of these problems occurred when the tests were repeated after caffeine. In six of eight patients, caffeine was responsible for false-negative dipyridamole-201Tl tests. Semiquantitive scores of the dipyridamole-induced 201Tl perfusion defects were decreased by caffeine from 9.0 +/- 0.9 to 2.0 +/- 1.1 points (p less than 0.05). Computerized analysis revealed a caffeine-mediated reduction in the percent reversibility of the images from 46% +/- 16% to 6% +/- 10% (p less than 0.05). We conclude that the use of caffeinated products prior to dipyridamole-201Tl testing may be responsible for false-negative findings.

Caffeine↗
PubMed1991

Reproducibility of quantitative planar thallium-201 scintigraphy: quantitative criteria for reversibility of myocardial perfusion defects.

Fifty-two paired stress/delayed planar 201TI studies (27 exercise studies, 25 dipyridamole studies) were processed twice by seven technologists to assess inter- and intraobserver variability. The reproducibility was inversely related to the size of 201TI perfusion abnormalities. Intraobserver variability was not different between exercise and dipyridamole studies for lesions of similar size. Based upon intraobserver variability, objective quantitative criteria for reversibility of perfusion abnormalities were defined. These objective criteria were tested prospectively in a separate group of 35 201TI studies and compared with the subjective interpretation of quantitative circumferential profiles. Overall, exact agreement existed in 78% of images (kappa statistic k = 0.66). We conclude that quantification of planar 201TI scans is highly reproducible, with acceptable inter- and intraobserver variability. Objective criteria for lesion reversibility correlated well with analysis by experienced observers.

Coronary Disease↗
PubMed1991

Orbit-related variation in spatial resolution as a source of artifactual defects in thallium-201 SPECT.

The cause of 180-degree diametrical artifactual defects in clinical thallium-201 SPECT imaging was investigated using phantom simulation. This artifact was observed on SPECT images acquired with a "body contour" or "peanut" orbit. It was hypothesized that this artifact was caused by differences in spatial resolution that occur when the heart-to-detector distance changes employing noncircular orbits. To test this hypothesis, a series of planar static images of a normal cylindrical phantom was obtained at varying distances from the camera detector head. From these images, tomographic acquisition files were created that simulated tomographic data acquired with circular orbits and elliptical orbits. The reconstructed phantom short-axis slices showed no artifacts for circular orbits. However, for various elliptical orbits, significant regional nonuniformity, similar to the artifacts noted in patients, was observed. The degree of nonuniformity correlated with the long-short axis ratio of elliptical orbits (r = 0.98). In addition, circular orbits with the phantom in an eccentric position resulted in similar nonuniformities. It is concluded that a noncircular tomographic orbit can create characteristic artifacts on thallium-201 SPECT images. For rotational thallium 201 SPECT, a circular orbit with the heart in the center of rotation should be employed.

Coronary Disease↗
PubMed1990

Thrombolytic therapy for myocardial infarction: assessment of efficacy by myocardial perfusion imaging with technetium-99m sestamibi.

Technetium-99m (Tc-99m) sestamibi has been used to evaluate the efficacy of thrombolytic therapy. Improved image quality due to the higher photon energy of Tc-99m and the increased allowable doses of this radiopharmaceutical along with its lack of redistribution makes Tc-99m sestamibi an acceptable imaging agent for such studies. This imaging agent was used for serial quantitative planar and tomographic imaging to assess the initial risk area of infarction, its change over time and the relation to infarct-related artery patency in patients with a first acute myocardial infarction. Twenty-three of 30 patients were treated with recombinant tissue-type plasminogen activator (rt-PA) within 4 hours after onset of acute chest pain. Seven patients were treated in the conventional manner and did not receive thrombolytic therapy. The initial area at risk varied greatly both in patients treated with rt-PA and in those who received conventional therapy. Patients with successful thrombolysis and patient infarct arteries had a significantly greater reduction of Tc-99m sestamibi defect size than patients who had persistent coronary occlusion. Serial imaging with Tc-99m sestamibi could find important application in future clinical research evaluating the efficacy of new thrombolytic agents. Direct measurements of the amount of hypoperfused myocardium before and after thrombolysis could provide rapid and unequivocal results using fewer patients and avoiding the use of "mortality" as an end point. This approach has not yet been widely tested in the clinical arena.

Heart↗
PubMed1990

Silent left ventricular dysfunction during routine activity after thrombolytic therapy for acute myocardial infarction.

To investigate prospectively the occurrence and significance of postinfarction transient left ventricular dysfunction, 33 ambulatory patients who underwent thrombolytic therapy after myocardial infarction were monitored continuously for 187 +/- 56 min during normal activity with a radionuclide left ventricular function detector at the time of hospital discharge. Twelve patients demonstrated 19 episodes of transient left ventricular dysfunction (greater than 0.05 decrease in ejection fraction, lasting greater than or equal to 1 min), with no change in heart rate. Only two episodes in one patient were associated with chest pain and electrocardiographic changes. The baseline ejection fraction was 0.52 +/- 0.12 in patients with transient left ventricular dysfunction and 0.51 +/- 0.13 in patients without dysfunction (p = NS). At follow-up study (19.2 +/- 5.4 months), cardiac events (unstable angina, myocardial infarction or death) occurred in 8 of 12 patients with but in only 3 of 21 patients without transient left ventricular dysfunction (p less than 0.01). During submaximal supine bicycle exercise, only two patients demonstrated a decrease in ejection fraction greater than or equal to 0.05 at peak exercise; neither had a subsequent cardiac event. These data suggest that transient episodes of silent left ventricular dysfunction at hospital discharge in patients treated with thrombolysis after myocardial infarction are common and associated with a poor outcome. Continuous left ventricular function monitoring during normal activity may provide prognostic information not available from submaximal exercise test results.

Acute Disease↗
PubMed1990

Myocardial perfusion scintigraphy as an aid in understanding electrocardiographic changes of ischemia and infarction.

In summary, myocardial perfusion scintigraphy with either thallium or the isonitriles has added substantially to electrocardiographic definition of both myocardial infarction and acute and chronic myocardial ischemia. Using perfusion scintigraphy, one can define infarct zones, risk zones, and the presence of reperfusion following thrombolytic therapy. When perfusion scintigraphy is combined with physiologic or pharmacologic stress, myocardial ischemia can be documented, irrespective of electrocardiographic documentation of the phenomenon. Delayed imaging may be important for defining viability even in the presence of significant Q waves. Myocardial perfusion scintigraphy provides prognostic evaluation of patients with both acute and chronic coronary syndromes. When the current cumulative experience is looked at critically, it is clear that myocardial perfusion scintigraphy has helped in the development of an understanding of the limitations of electrocardiography in the diagnostic and functional categorization of patients with acute and chronic coronary disease.

Coronary Disease↗
PubMed1990

Comparison of immediate invasive, delayed invasive, and conservative strategies after tissue-type plasminogen activator. Results of the Thrombolysis in Myocardial Infarction (TIMI) Phase II-A trial.

To assess the value and timing of percutaneous transluminal coronary angioplasty (PTCA) after thrombolytic therapy for acute myocardial infarction (AMI), 586 patients in the Thrombolysis in Myocardial Infarction Study Phase II-A were randomized among three treatment strategies, one using immediate coronary arteriography followed by PTCA if appropriate (immediate invasive strategy group, n = 195), a second that deferred angiography and PTCA for 18-48 hours (delayed invasive strategy group, n = 194), and a third, more conservative, approach in which PTCA was used only if ischemia occurred spontaneously or at the time of predischarge exercise testing (conservative strategy group, n = 197). Predischarge contrast left ventricular ejection fraction, the primary study end point, was similar among the patients in all three treatment groups and averaged 49.3%. The finding of a patent infarct-related artery at the time of predischarge arteriography was equally common among the patients in the three groups (mean, 83.7%); however, the mean residual infarct artery stenosis was greater in the patients in the conservative strategy group (67.2%) as compared with the patients in the immediate invasive (50.6%) and the delayed invasive strategy groups (47.8%) (p less than 0.001). Immediate invasive strategy led to a higher rate of coronary artery bypass graft surgery (CABG) after PTCA (7.7%) than did delayed invasive and conservative strategies (2.1% and 2.5%, respectively; p less than 0.01). Furthermore, among patients not undergoing CABG during the first 21 days, blood transfusion of more than 1 unit was used in 13.8% of the patients in the immediate invasive strategy group, 3.1% of the patients in the delayed invasive strategy group, and 2.0% of the patients in the conservative strategy group (p less than 0.001). At 1-year follow-up, the three treatment groups had similar cumulative rates of mortality (8.7%, pooled over all groups), fatal and nonfatal reinfarction (8.5%), combined death and reinfarction (14.5%), and CABG (17.2%), although the cumulative performance rate of PTCA remained higher in the invasive groups (immediate invasive strategy group, 75.8%; delayed invasive strategy group, 64.3%; and conservative strategy group, 23.9%; p less than 0.001). Thus, because conservative strategy achieves equally good short- and long-term outcome with less morbidity and a lower use of PTCA, it seems to be the preferred initial management strategy.

Aged↗
PubMed1990

Serial changes in myocardial perfusion using tomographic technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile imaging following reperfusion therapy of myocardial infarction.

Resting tomographic myocardial perfusion images using technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile (Tc-Sestamibi) were obtained in 25 patients during their first myocardial infarction. Tc-Sestamibi was injected intravenously before acute reperfusion therapy, and repeated twice, at 18-48 hr, and at 6 to 14 days. Reperfusion was successful in 19 patients. In the patients with successful reperfusion, there was a mean decrease in the amount of hypoperfused myocardium between the initial and second studies (-9% +/- 12%, p = 0.004) and a further decrease between the second and final studies (-10% +/- 12%, p = 0.002). Nine of these 19 patients (47%) had evidence of significant improvement at the time of the second study. In six patients, significant improvement was not evident until the final study. Although tomographic imaging with Tc-Sestamibi following reperfusion therapy may show improvement in perfusion at 18-48 hr, the full extent of improvement is usually not evident until later.

Adult↗
PubMed1990

Quantitative analysis of planar technetium-99m-sestamibi myocardial perfusion images using modified background subtraction.

Standard interpolative background subtraction, as used for thallium-201 (201Tl), may create artifacts when applied to planar technetium-99m-Sestamibi (99mTc-Sestamibi) images, apparently because of the oversubtraction of relatively high extra-cardiac activity. A modified background subtraction algorithm was developed and compared to standard background subtraction in 16 patients who had both exercise-delayed 201Tl and exercise-rest 99mTc-Sestamibi imaging. Furthermore, a new normal data base was generated. Normal 99mTc-Sestamibi distribution was slightly different compared to 201Tl. Using standard background subtraction, mean defect reversibility was significantly underestimated by 99mTc-Sestamibi compared to 201Tl (2.8 +/- 4.9 versus -1.8 +/- 8.4, p less than 0.05). Using the modified background subtraction, mean defect reversibility on 201Tl and 99mTc-Sestamibi images was comparable (2.8 +/- 4.9 versus 1.7 +/- 5.2, p = NS). We conclude, that for quantification of 99mTc-Sestamibi images a new normal data base, as well as a modification of the interpolative background subtraction method should be employed to obtain quantitative results comparable to those with 201Tl.

Algorithms↗