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Myocardial Perfusion Scintigraphy
with Tc-MIBI in the Diagnosis of
Coronary Heart Disease in Women

Peix, Amalia; Chacón, Deylis; Ponce, Felizardo;
López, Adlin; Llerena, Lorenzo; Villafranca, Orlando;
Cabrera, Omar; Maltas, Ana María; Carrillo, Regla

Instituto de Cardiología y Cirugía Cardiovascular, La Habana, Cuba

SUMMARY
Introduction: Coronary Heart Disease (CHD) is frequent in postmenopausal women, but its diagnosis is difficult due to atypical clinical presentation, as well as anatomical differences which originate false positives in noninvasive cardiological tests. The myocardial perfusion scintigraphy can help in the CHD diagnosis, but there are two main problems: smaller hearts, with small defects in the lower limit of the detector resolution, and breast attenuation defects.
Objectives: To assess the sensibility and specificity of myocardial perfusion scintigraphy for CHD diagnosis in women, we compared the results of a Tc-MIBI scintigraphy with those of a coronary angiography in a group of women referred for evaluation of chest pain.
Material and Methods: Eighteen women (mean age: 54±6 years) with a previous coronary angiography were included. A Tc-MIBI myocardial scintigraphy with one-day protocol (rest-stress) was performed. When needed, a combined stress (ergometric bicycle plus 0,28 mg/kg of I.V. dypyridamole) was used. All patients also did some spinal passive movements before starting the test. Both qualitative and quantitative regional uptake analysis was done. Sensibility and specificity values for CHD diagnosis were calculated.
Results: Change in regional uptake (stress/rest) was as follows: during stress Tc-MIBI, 105 segments had normal uptake (from 93±9 to 94±7%); 46 had moderately reduced uptake (from 67±9 to 75±8%), and 11 had severely reduced uptake (from 33±9 to 64±28%). Qualitative and quantitative analysis coincided in 16 cases. Sensibility and specificity for the CHD diagnosis were of 100% and 50%, respectively. Breast attenuation defects were detected in 4 cases.
Discussion: Myocardial scintigraphy with Tc-labeled compounds had a higher sensibility for CHD diagnosis in women compared with Tl-201 scintigraphy. However, it is important to be careful with positive scintigraphies in women with typical chest pain and normal coronaries, taking into account a higher frequency of microvascular angina in women.
Conclusion: Tc-MIBI myocardial scintigraphy can help in the CHD diagnosis in postmenopausal women.

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INTRODUCTION
   Coronary Heart Disease (CHD) is the leading cause of death among middle-aged men, but is an equally important cause of death among postmenopausal women.

   Noninvasive diagnosis of myocardial ischemia in women poses a significant challenge. The clinical presentation is frequently atypical and women are more likely to have false-positive or nondiagnostic results on standard exercise tests, related to lower pretest probability of disease, poor exercise capacity and greater probability of repolarization abnormalities on electrocardiogram. Exercise - and dobutamine - echocardiography may have some advantages in women but it depends on good echocardiographic windows. Myocardial perfusion scintigraphy has better sensitivity and specificity, but there are two main interpretation problems: smaller hearts, with small defects in the lower limit of the detector resolution, and breast attenuation defects.

OBJECTIVES
   To assess the sensibility and specificity of myocardial perfusion scintigraphy for CHD diagnosis in women, we compared the results of a technetium-99m (99mTc) - methoxi-isobutyl-isonitrile (MIBI) scintigraphy with those of a coronary angiography in a group of women referred for evaluation of chest pain.

MATERIAL AND METHODS
Study Population
   Eighteen women (mean age: 54±6 years), 15 of them postmenopausal, who were referred for evaluation of chest pain, were included.

Coronary Angiography
   Cardiac catheterization, including selective coronary angiography in multiple projections, was performed within 15 days prior to the scintigraphy. The main epicardial coronary arteries were evaluated by two observers, and each vessel was graded as having significant stenosis if the lesion restricted the lumen by 50%.

Technetium 99m - MIBI Scintigraphy
   Two 99mTc-MIBI scintigraphies were performed by planar technique on the same day: at rest and after a signs and/or symptoms-limited ergometric bicycle stress. When needed, a combined stress (ergometric bicycle plus 0.28 mg/kg of intravenous dypyridamole) was used. The mean time between the injection (15 mCi 99mTc-MIBI at rest and 30 mCi at stress) and image acquisition, depending on the laboratory availability, was 80±24 minutes at rest, and 62±23 minutes post-stress. All patients did some spinal passive movements before starting the test.

   Anterior, 45-degrees left anterior oblique (LAO), and 70-degrees lateral projections were obtained with a 128x128 word matrix until 500,000 counts per image were accumulated. The images were smoothed with a 9-point filter, and each projection was divided as follows: anterior (anterolateral, inferior, and apical segments); 45-degrees LAO (septal, inferoapical, and posterolateral segments); 70-degrees lateral (anterior, posterior, and apical segments).

   Both qualitative and quantitative regional uptake analysis was done. For quantitative analysis, in each projection the myocardial segment with the maximum counts was considered the normal reference region. 99mTc-MIBI uptake in all other segments was then expressed as the percentage of the activity measured in the reference region. A myocardial segment was considered abnormal if stress 99mTc-MIBI uptake was > 2 standard deviation (SD) below the mean observed in the same region for normal subjects. Segments with abnormal uptake were subgrouped (on the basis of severity of reduction in tracer activity) as moderate ( 50% of peak activity) and severe (< 50% of peak activity) defects. A segment with reduced activity on stress 99mTc-MIBI was considered reversible if the activity increased 10% at rest.

Statistical Analysis
   Values were expressed as mean±SD. The continuous variables were analyzed with a paired Student t-test. A probability value of p<0.05 was considered significant.

   Sensibility (Sens) and Specificity (Spec) values were calculated as follows:
Sens = TP / TP + FN                         Spec = TN / TN + FP
Where: TP = true-positive (positive both scintigraphy and coronary angiography); TN = true-negative (negative both scintigraphy and coronary angiography); FN = false-negative (negative scintigraphy and positive coronary angiography) and FP = false-positive (positive scintigraphy and negative coronary angiography).

RESULTS
   A total of 162 segments (100%) were analyzed. On stress 99mTc-MIBI images, 105 had normal uptake (93±7% of peak activity), while 46 showed moderate (67±9% of peak activity), and 11 showed severe reduction (33±9% of peak activity) of tracer uptake. Normal segments at stress did not show significant differences in myocardial uptake at rest, whereas segments with moderate and severe defects significantly increased uptake (Table 1).

   Qualitative and quantitative analysis of tracer uptake coincided in 16 cases. The two non-coincident cases were patients in whom qualitative analysis and coronary angiography were normal, but on quantitative analysis it appeared a reversible defect on posterolateral segment in one case and a "reverse redistribution" phenomenon in the other. There were other two cases of "reverse redistribution" in patients with coronary stenosis on left anterior descendent and right coronary arteries.

   Sensibility and specificity for CHD diagnosis were of 100% and 50%, respectively.

   Breast attenuation defects were detected in four cases (100% by quantitative and 50% by qualitative analysis of tracer uptake).

   Among patients with negative coronary angiography, myocardial scintigraphy was coincident only in 50% (Figure 1). Characteristics of patients with reversible perfusion defects are presented in Table 2.

DISCUSSION
   Diagnosis of CHD is largely based on symptoms. Angina pectoris among women frequently occurs in the absence of angiographically demonstrable coronary disease. Among women with typical angina, only 60% to 75% have angiographically significant disease; among those with probable angina it is only 30% to 40%.

   Myocardial scintigraphy with Tc-labeled compounds had a higher sensibility for CHD diagnosis in women compared with thallium-201(201Tl) scintigraphy. The 140 keVmonoenergetic photopeak of 99mTc is associated with less scatter and less attenuation than 201Tl. The sensibility of the 99mTc-MIBI scintigraphy was very good in our study, but it was not the same with the specificity.

   It is important to be careful with positive scintigraphies in women with typical chest pain and normal coronaries, taking into account a higher frequency of microvascular angina in women. This clinical picture is part of the so-called cardiac syndrome X, whose mechanism has not yet been totally clarified. In our cases, the 100% of this kind of patients were postmenopausal and with some kind of chest pain at rest. Besides that, there was 66% with systolic hypertension (sign of atherosclerosis) and 66% with positive stress test.

   The lack of natural estrogens during the postmenopause affects the preservation of endothelium-dependent vasodilatation mediated by nitric oxide. In the postmenopausal women, endothelial dysfunction, which already exists in systolic hypertension and diabetes, might be worsened. In addition, there can be a worse lipid profile.

CONCLUSION
   Tc-MIBI myocardial scintigraphy can help in the CHD diagnosis in postmenopausal women.

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
Scientific Committee
President
Dr. Armando Pacher
Technical Committee - CETIFAC
President
fgaro@fac.org.ar
fgaro@satlink.com
rbretal@fac.org.ar
rbretal@netverk.com.ar
apacher@fac.org.ar
apacher@satlink.com

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