Gated xenon scans for right ventricular function.

The complex geometry of the right ventricle makes the use of radionuclides an attractive method for assessing right ventricular function. The use of the gated 133Xe technique for this purpose offers several advantages. A short i.v. infusion over 20 sec of 133Xe permits scans to be obtained, gated to the electrocardiogram at rest and during maximal exercise using a standard gamma camera. The method is both reproducible (3.5%) and repeatable (2.8%), and because of the short half-life within the patient with most of the radioisotope being excreted by the lungs, scans may be repeated within a few minutes and the radiation dose to the patient is small. Right ventricular ejection fraction obtained from gated xenon scans is shown to correlate well with measurements obtained from both standard gated technetium scans and first-pass studies.

Quantitation of postexercise lung thallium-201 uptake during single photon emission computed tomography.

To test the hypothesis that analysis of lung thallium uptake measured during single photon emission computed tomography (SPECT) yields supplementary clinical information as reported for planar imaging, quantitative analysis of lung thallium uptake following maximal exercise was performed in 40 clinically normal subjects (Group 1) and 15 angiographically normal subjects (Group 2). Lung thallium uptake was measured from anterior projection images using a ratio of heart-to-lung activities. Seventy subjects with coronary artery disease (CAD) (Group 3) determined by angiography (greater than or equal to 70% luminal stenosis) underwent thallium perfusion SPECT. Thirty-nine percent of these subjects had multivessel and 61% had single vessel CAD. Lung thallium uptake was elevated in 47 of 70 (67%) Group 3 subjects. Group 3 subjects with elevated lung thallium uptake did not differ from Group 3 subjects with normal lung thallium uptake with respect to extent or distribution of coronary artery disease, left ventricular function, or severity of myocardial ischemia as determined by exercise and redistribution thallium SPECT. Thus, the measurement of thallium lung uptake from anterior projection images obtained during SPECT frequently identifies patients with CAD, but it may not provide supplementary information regarding the extent of myocardial ischemia or ventricular dysfunction.

Assessment of right ventricular function in acute inferior myocardial infarction using 133-xenon imaging.

UNLABELLED: The detection of right ventricular dysfunction in acute inferior myocardial infarction is important because of its potentially serious consequences which may be remediable with the appropriate therapeutic manoeuvres. A technique has been developed to assess right ventricular function using 133-xenon. This technique was applied to 26 patients who had sustained an acute inferior myocardial infarction. Right ventricular ejection fractions ranged from 7-54%, mean 30 +/- 11%, which was significantly lower than values obtained from normal volunteers (n = 21), mean 43 +/- 5%, and patients with arteriographically proven coronary artery disease without previous myocardial infarction (n = 12), mean 39 +/- 9%, P less than 0.001, and P less than 0.001, respectively. In the patients with acute inferior myocardial infarction 18 patients (69%) had evidence of right ventricular dysfunction (right ventricular ejection fraction less than 35%). 13/26 patients (50%) had clinical evidence of right ventricular dysfunction with a mean right ventricular ejection fraction 26 +/- 11% (range 7-54%) which was significantly lower than the patients without evidence of right ventricular dysfunction, mean 35 +/- 9% (range 16-49%), P less than 0.001. The clinical signs had a sensitivity of 72% (13/18), a specificity of 87.5% (7/8) and a predictive accuracy of 76% (20/26) when compared to the imaging data. IN CONCLUSION: (1) gated 133-xenon imaging provides a method for assessing right ventricular function in the setting of acute myocardial infarction; (2) a wide spectrum of right ventricular dysfunction occurs following inferior myocardial infarction which may not manifest itself clinically.

The evaluation of right ventricular function in acute myocardial infarction by xenon-133.

Right ventricular performance was assessed in 37 patients with acute myocardial infarction within two hours of admission to Coronary Care and compared to results in 21 normal volunteers and 12 patients undergoing coronary arteriography. Right ventricular ejection fraction (RVEF) was measured from gated xenon-133 scans. The normal range of RVEF (42.8 +/- 5.1%) was significantly higher than in the 30 patients with inferior infarction (26.3 +/- 10.9%; p less than 0.001) and was similar to that in patients with anterior infarct (40.6 +/- 5.4%; ns) and patients undergoing coronary arteriography (39.3 +/- 4.9%; ns). Fifteen of the patients with inferior infarct had clinical evidence of right ventricular dysfunction with a mean RVEF of 18.9 +/- 7.9%, significantly below the fifteen patients with no clinical evidence of right ventricular dysfunction (34.3 +/- 8.3%; p less than 0.001).

The detection of coronary artery disease: a comparison of exercise thallium imaging and exercise equilibrium radionuclide ventriculography.

This study compared the accuracy of rest and exercise gated equilibrium technetium ventriculography with exercise thallium imaging in 50 consecutive male patients undergoing routine coronary angiography for the evaluation of chest pain. No patients were excluded on the basis of prior myocardial infarction, nature of angiographically defined coronary disease or symptoms. Antianginal therapy was continued in all patients. Eight patients had normal coronary arteries, 9 had single vessel, disease, 20 had double vessel disease and 13 had triple vessel disease. Sixteen patients had previously documented myocardial infarction. Using exercise radionuclide ventriculography, 34 patients with coronary disease were detected resulting in a sensitivity of 81%; 6 patients with normal coronary arteries had normal scans, a specificity of 75%, with a predictive accuracy of 80%. In comparison, thallium imaging detected 42 patients with coronary disease resulting in a sensitivity of 100%. Six patients with normal coronary arteries had normal thallium images resulting in a specificity of 75% and a predictive accuracy of 96%. These results suggest that exercise thallium imaging is a more accurate investigation than exercise equilibrium radio-nuclide ventriculography and is the investigation of choice in the noninvasive detection of coronary artery disease.

Improved detection of coronary artery disease by estimated myocardial thallium uptake.

Myocardial thallium uptake has been assessed at the time of thallium scanning in a group of 50 male patients undergoing coronary arteriography and 10 young healthy volunteers. The net thallium dose injected was obtained by counting the dose prior to injection using the gamma camera and counting the syringe and IV cannula after injection. Significantly higher levels of myocardial thallium uptake were obtained in both the volunteers and patients with normal coronary anatomy (1.36% +/- 0.32%, n = 10 and 0.93% +/- 0.26%, n = 9, respectively) compared to patients with single, double or triple vessel coronary artery disease (0.63% +/- 0.19%, n = 11; 0.70% +/- 0.20%, n = 15; 0.67 +/- 0.18, n = 15, respectively). Exercise tests were positive in 46% of patients with coronary artery disease with an overall predictive accuracy of 56%. Thallium scans were positive in 68% of patients at a specificity of 89%. If the range of myocardial thallium uptake from the patients with normal coronary arteries is used to define a lower limit of normal, then the sensitivity of the thallium scan with thallium uptake is 90% with a predictive accuracy of 90% in the detection of significant coronary artery disease in this group of patients. Thus, estimation of total % thallium uptake is a simple index which yields useful diagnostic clinical information.

The effect of exercise on thrombin and plasmin generation in middle-aged men.

Plasma levels of B beta 15-42 peptide and fibrinopeptide A (FPA) were measured as indicators of plasmin-mediated fibrin(ogen)olysis and thrombin activity of fibrinogen in 34 middle-aged men, at rest and following a standard exercise test. In the group as a whole no significant changes in B beta 15-42 or FPA were noted after exercise. When the group was subdivided into men with (n = 20) and without (controls n = 14) coronary heart disease, exercise-stimulated thrombin and plasmin generation was found only in the control group who exercised for a significantly longer duration. The rise in B beta 15-42 was related to both the intensity and duration of exercise. Similar increases in plasma fibrinolytic activity (fibrin plate) occurred in both groups and no other differences in the components of the fibrinolytic system (plasminogen, alpha 2-antiplasmin, fibrin degradation product) were noted either after exercise or between the groups. Exercise in normal middle-aged men is associated with modest thrombin and plasmin activation.

Quantitative rotational tomography with 201Tl and 99mTc 2-methoxy-isobutyl-isonitrile. A direct comparison in normal individuals and patients with coronary artery disease.

We tested the hypothesis that 99mTc 2-methoxy-isobutyl-isonitrile (99mTc MIBI), a new radiopharmaceutical for myocardial perfusion imaging, provides accurate noninvasive detection of coronary artery disease (CAD). Imaging in patients after exercise and at rest with 99mTc MIBI was compared with imaging after exercise and redistribution with 201Tl in 12 normal subjects and 38 patients with angiographic documentation of CAD (greater than or equal to 50% diameter stenosis). We used single-photon emission computed tomography (SPECT) and computer quantitation of regional tracer distribution. The quality of reconstructed images with 99mTc MIBI judged visually was superior to that of 201Tl in 88% of all studies performed and was comparable in the others. With the limits of normal as 2.5 SD below the mean of gender-matched normal volunteers, 201Tl SPECT identified 32 and 99mTc MIBI identified 36 patients with CAD (p = 0.2). 201Tl SPECT identified 45 of 75 (60%) and 99mTc MIBI identified 59 of 75 (79%) stenosed coronary arteries (p less than 0.05). The quantitative severity of perfusion defects was similar for the two tracers. 201Tl SPECT identified 104 reversibly ischemic myocardial segments compared with 134 with 99mTc MIBI (p less than 0.05). Thus, SPECT myocardial perfusion imaging with 99mTc MIBI and computer quantitation provides an accurate method for the noninvasive detection of significant coronary artery disease. Furthermore, image quality is generally superior to 201Tl, and reversibly ischemic myocardial segments may be better identified with 99mTc MIBI.