Assessment of Local Myocardial Perfusion in SPECT Images when Bicycle Exercise Test is Noninterpretable

Transcription

1 e 11 Assessment of Local Myocardial Perfusion in SPECT Images when Bicycle Exercise Test is Noninterpretable Ilona Kulakienė, Zigmundas Satkevičius, Juozas Kiudelis, Irena Milvidaitė 1 Kaunas Medical University, Radiology Clinic; 1 Kaunas Medical University, Institute of Cardiology Key words: Single photon emission computed tomography (SPECT), myocardial perfusion, bicycle exercise tolerance test, 99m Tc MIBI. Summary. The aim of this work was to summarize the data on myocardial perfusion SPECT in a noninterpretable bicycle exercise tolerance test group. Material and methods: It is a retrospective study of 123 patients who underwent myocardial SPECT and bicycle exercise test in the year Only a noninterpretable test group consisting of 34 patients was analysed (23 men, 11 women, mean age ± 9.42). All the patients underwent a bicycle exercise test and in the same day stress-rest myocardial perfusion study according to a standard clinical protocol. SPECT slices were obtained on the vertical long axis, horizontal long axis and short axis planes. The left ventricular myocardium was divided into 19 segments. Myocardial perfusion was analyzed according to five criteria in the three main coronary artery regions: size, severity of defect assessed during the stress and rest, and the score of myocardial recovery at rest. Also five additional values were calculated. Results: Only 7 of 34 patients had normal myocardial perfusion, and even in 18 patients the total defect score was greater than 10. All the patients were divided into four subgroups in accordance with electrocardiographic (ECG) changes. The total and both rest defect scores were significantly higher in the III subgroup than in the IV subgroup (p<0.05). Both the rest defect scores were also significantly higher in the I subgroup than in the IV subgroup. Conclusions: The obtained results have proven a clinical value of myocardial SPECT modality as a good screening tool in patients with rest ECG changes, when bicycle exercise test is noninterpretable, and especially in patients with a history of previous myocardial infarction. Introduction Coronary artery disease (CAD) still remains the biggest killer of both men and women, unfortunately often it manifests as sudden cardiac death. So we need to diagnose CAD and to prevent its complications. Patients with episodes of chest pain undergo a lot of diagnostic procedures in order to reveal CAD and stratify the probability of myocardial infarction. Patients are divided into high- and low-risk groups. When the patient is at high risk, he needs cardiac catheterisation or even further invasive intervention such as coronary angioplasty or coronary artery bypass grafting (CABG). How can we determine the patients at a high risk? We should start with an appropriate cardiovascular history taking and a physical examination of the patients, further they undergo ECG and laboratory tests. Later we perform echocardiography and various stress tests. In cases when stress test causes an episode of typical angina pectoris and/or typical ischaemic changes on ECG, coronary angiography is indicated. The latter is the gold standard for diagnosing CAD, but it is an expensive invasive technique, and radiation dose for the staff and the patient is quite high [1,2]. Stress tests are good screening tools with a possibility to differentiate the patients at high risk of a coronary event (if the test result is pathologic) from those at relatively low risk (if the test result is nonpathologic). Sometimes it is impossible to perform a stress test due to patient s physical condition or other disease, which is a contraindication to stress test. On the other hand, Correspondence to be sent to: I. Kulakienė, Radiology Clinic, Kaunas University of Medicine Hospital, Eivenių pr. 2, LT-3007 Kaunas, Lithuania. nuclear@kmu.lt

2 e 12 Ilona Kulakienė, Zigmundas Satkevičius, Juozas Kiudelis, Irena Milvidaitė sometimes the test result is noninterpretable there are changes on ECG obtained at rest or the test was terminated before reaching submaximal heart rate because of nonspecific limiting symptoms (general weakness, tired legs, breath troubles) when typical ischaemic signs were not recorded. Sometimes the test result is borderline. Then the cardiologist is in a dilemma: to perform coronary angiography, the procedure linked with certain increased morbidity, when the patient probably does not have CAD, or to use drug therapy when it is supposed that the patient should not have a heart attack. A new diagnostic tool myocardial perfusion scintigraphy helps cardiologists who are in the dilemma at Kaunas University of Medicine Hospital from the year It is an accurate, noninvasive, and suitable for screening, diagnostic modality with a radiation dose lower than in coronary angiography. The procedure enables the tester to evaluate the regional myocardial perfusion and contraction [3, 4, 5], and the impact of CAD on the functional state of the patient[6, 7, 8]. This method helps to identify high-risk patients in undiagnosed CAD (with chest pain) and in diagnosed CAD (after revascularization) [6]. The aim of this work was to summarize the data of myocardial perfusion SPECT in a noninterpretable bicycle exercise test group. Methods and Contingent It is a retrospective study of 123 patients, who underwent myocardial SPECT and bicycle exercise test during the year Only the noninterpretable test group (34 patients) was analyzed. It consisted of 23 men (32.4%) and 11 women (67.6%), mean age of whom was ± 9.42, in the range of years. Myocardial perfusion was performed in accordance with the guidelines of the European Association of Cardiology in the presence of the following indications: 1. A nondiagnostic rest ECG because of left ventricular hypertrophy, left or right-bundle branch block, conduction abnormalities, digoxin intoxication and the presence of an artificial pacemaker. 2. A pathological stress ECG in the absence of typical angina pectoris. 3. A suspected false-positive stress test. 4. The patients with a history of previous surgical revascularization, if new ischaemic symptoms and/or signs occur. All the studied patients underwent a bicycle exercise tolerance test and the same day a stress-rest myocardial perfusion study in accordance with a standard clinical protocol. The test was performed with the initial workload increasing every 3 minutes according to the patient s physical condition. The test was terminated after achieving submaximal (85% of the predicted maximal) heart rate or if the first limiting symptoms and/or signs occurred. Patients were divided into four groups according to the bicycle exercise test response: 1. A pathological test group when the stress caused a typical angina or/and typical ischaemic changes on the ECG (39 pts), 2. A nonpathological test group when the submaximal heart rate was achieved in the absence of any ischaemic symptoms and/or signs (23 pts), 3. A borderline test group when some less specific symptoms and/or signs appeared (27 pts), 4. A noninterpretable test group when no ischaemic symptoms were recordered and the stress test was terminated because of nonspecific limiting symptoms (34 pts). After having achieved the predicted submaximal heart rate or in case of terminating the stress test because of appearence of the limiting symptoms and/or signs, we injected MBq of 99m Tc- MIBI intravenously. We recommended our patients to eat some chocolate and to drink. The first part of the myocardial perfusion test (stress test) was performed minutes later after the injection. We used dual-head Siemens gamma camera E.Cam and low-energy collimators. The detectors were positioned at 90 degrees. The patients were laid on their back, arms raised upon the head, in this position the detectors rotated closer to the patient s thorax. The acquisition begins at the 45 degree right oblique projection and ends at 45 the degree left oblique projection after having performed a 180 degree rotation. In this way, 64 images were recordered (32 images from each detector), with 25 second exposure per image. After having performed the first part of the test, the patients were recommended to have some rest, meal and drink. The second part of the test the rest test was performed 3 hours later after the first injection of the radiotracer. Then we repeated the injection of MBq of 99m Tc-MIBI. After a minute interval, we repeated the examination of the patients lying in the same position as during the first part of the test. The images acquired during both examinations were reconstructed using software provided with E.Cam gamma camera by Siemens, SPECT slices

3 Assessment of local myocardial perfusion in SPECT images e 13 Figure 1. The parameters and conclusions determined by long term ECG analysis system Myocardial segments in the short-axis plane: AS anteroseptal; AL anterolateral; LA lateroanterior; LI lateroinferior; IL inferolateral; IS inferoseptal; SI septoinferior. Segments belonging to vertical long-axis plane: PA proximal (or basal) anterior; MA middle anterior; DA distal anterior; IAP inferoapical; I inferior; IB inferobasal. Segments belonging to horizontal long-axis plane: AP apical; DL distal lateral; PL proximal (or basal) lateral; DS distal septal; PS proximal (or basal) septal. were obtained on the vertical long axis, horizontal long axis and short axis planes. 99m Tc-MIBI distributes in the myocardium according to the blood flow - if the perfusion is normal, the distribution is normal. As the right ventricular myocardium is thinner, the accumulation of 99m Tc- MIBI is lower. Because of poor visualisation of the right ventricle, the perfusion is not interpretted. The left ventricular myocardium was divided into 19 segments, corresponding to the area supplied by a discrete artery: the left anterior descending artery (LAD) territory (10 segments), circumflex artery (LCx) territory (4 segments) and right coronary artery (RCA) territory (5 segments). The scheme is shown in the 1 st figure. The stress and rest images were analyzed separately and later compared. The mmyocardial perfusion in the three coronary artery regions was analyzed according to five criteria: the size and severity of the defect revealed during the stress and rest, and the score of defect reversibility at rest. The reduction of perfusion was scored using a 4-point scale: 0 normal perfusion, 1 a slightly reduced perfusion (perfusion reduced to 60-80% of the maximal myocardial perfusion), 2 a moderately decreased tracer uptake (a 40-60% of the maximal uptake in a defect region), 3 a perfusion defect or markedly reduced perfusion (a myocardium uptake lower than 40% in a defect region). The defect reversibility was also scored using a 4-point scale: 0 a complete reversibility (>90% of the defect is reversible), 1 a partial reversibility (30-90 % of the defect is reversible), 2 a primarily fixed defect (10-30 % of the defect is reversible), 3 a fixed defect (<10% of the defect is reversible). We also assessed five additional values: 1. The number of the affected segments at stress. 2. A stress score - severity of perfusion abnormalities summed in all the three main coronary artery regions at stress. 3. The number of the affected segments at rest. 4. The rest score - severity of perfusion abnormalities summed in all the three main coronary artery regions at rest. 5. The total defect score - the sum of the four above-mentioned values. Results Only 7 of 34 patients had normal myocardial perfusion, and even in 18 patients the total defect score was greater than 10. All the patients were divided into four subgroups according to ECG changes: I. History or ECG evidence of previous myocardial infarction (10 pts). II. The previous borderline test results (9 pts). III. Left or right bundle-branch blocks (6 pts). IV. No changes on rest ECG (9 pts). The means of myocardial perfusion criteria with standard deviation in the five subgroups are shown in the 1 st table. There were few patients in the subgroups and the number of them was different, so we compared subgroups using Mann-Whitney test. The number of the affected segments at rest, the total and the rest defect scores were significantly higher in the III subgroup than in the IV subgroup (p<0.05). The number of the affected segments at rest and the rest defect score were also significantly higher in the I subgroup than in the IV subgroup.

4 e 14 Ilona Kulakienė, Zigmundas Satkevičius, Juozas Kiudelis, Irena Milvidaitė Table. Means of myocardial perfusion criteria with standard deviation in subgroups Values I subgroup II subgroup III subgroup IV subgroup All group N Number of affected segments at stress. 4.00± ± ± ± ±2.64 Number of affected segments at rest. 3.50± ± ± ± ±2.66 Stress score 3.10± ± ± ± ±1.96 Rest score 2.90± ± ± ± ±2.06 Total defect score 13.50± ± ± ± ±8.83 I subgroup - history or ECG evidence of previous myocardial infarction. II subgroup - previous borderline test result. III subgroup - left or right-bundle branch block. IV subgroup - no changes on rest ECG. Discussion The results of the present study demonstrate that the patients with noninterpretable stress test result have a high probability of CAD. We found perfusion defects in 27 (79.4%) cases out of 34, and very often these patients are not examined properly. Myocardial perfusion scintigraphy helps to differentiate high-risk from low-risk patients, therefore angiography should be performed when it is really necessary. The analysis of the noninterpretable test group showed that it is not homogenous, so the myocardial SPECT test should be reported in a slightly different way in individual clinical cases. All the patients in the first subgroup had a history or ECG evidence of previous myocardial infarction. Small fixed perfusion defects due to scarring predominated in this subgroup. Such changes in the perfusion scans show a low probability of future cardiac events [8, 9]. On the other hand, the reversible or partly reversible perfusion defects are of the ischaemic origin. Our study data have shown a significantly higher rest score and the number of the affected segments at rest in the I subgroup than in the IV subgroup. So larger areas of significant reversibility on myocardial perfusion scans in IV subgroup increase the risk of a significant myocardial event [8, 9]. Only one patient achieved a submaximal predicted heart rate in the second subgroup, in other cases the test was terminated because of the limiting symptoms and/or signs. So this test result was noninterpretable in spite of the previous borderline test result. The total defect score in this subgroup was low it is possible that not achieved submaximal heart rate could have affected this result. The bicycle exercise test in the III subgroup was performed only as a stress test for myocardial perfusion study. This study is one of a small number of informative tests in patients with rest ECG changes. A considerable number of perfusion abnormalities should prompt the cardiologists to perform myocardial perfusion or other study in order to reveal an ischaemic heart disease in this subgroup patients. Indications for myocardial perfusion study were not clearly defined; maybe it was a question of differential diagnosis. Conclusions The obtained results have confirmed practical clinical value of myocardial SPECT as a good screening tool in the patients with suspected CAD in cases when bicycle exercise test is noninterpretable. The method helps to differentiate the patients at high risk of a coronary event from those at low risk even in cases with rest ECG changes, what is very important especially in the patients with a history of previous myocardial infarction.

5 Assessment of local myocardial perfusion in SPECT images e 15 References 1. Pennell DJ, Prvulovich E. Diagnosis in Coronary Artery Disease. In: Ell PJ, editor. A Handbook of Nuclear Cardiology. London: p Maddahi J, Sanjiv SG. Cost-effective selection of patients for coronary angiography. J Nuclear Cardiology 1997; 4: Danias PG, Ahlberg AW, Clark III BA et al. Combined Assessment of Myocardial Perfusion and Left Ventricular Function With Exercise Technetium-99m Sestamibi Gated Single-Photon Emission Computed Tomography Can Differentiate Between Ischemic and Nonischemic Dilated Cardiomyopathy. Am J Cardiology 1998; 82: Gibbons RJ, Beasley JW, Daley J, et al. ACC/AHA/ACP- ASIM guidelines for management of patients with chronic stable angina. J Am Coll Cardiology 1999;33: Moka D, Baer FM, Theissen P, et al. Non-Q-wave myocardial infarction: impaired myocardial energy metabolism in regions with reduced 99m Tc-MIBI accumulation. European Journal of Nuclear Medicine 2001; 28: Received: , accepted: Bartlett ML, Seaton D, McEwan L, Fong W. Determination of right ventricular ejection fraction from reprojected gated blood pool SPET: comparison with first-pass ventriculography. European Journal of Nuclear Medicine 2001; 28: Sciagra R, Leoncini M, Marcucci G, Dabizzi RP, Pupi A. Technetium-99m sestamibi imaging to predict left ventricular ejection fraction outcome after revascularisation in patients with chronic coronary artery disease and left ventricular dysfunction: comparison between baseline and nitrate-enhanced imaging. European Journal of Nuclear Medicine 2001; 28: Hamada S, Nakamura S, Sugiura T, et al. Accuracy of technetium-99m tetrofosmin myocardial perfusion imaging in the detection of spontaneous recanalization in patients with acute anterior myocardial infarction. European Journal of Nuclear Medicine 2001; 28: Bianko JA, Wilson MA. Myocardial Ischemia and Viability. In:Wilson MA, editor. Textbook of Nuclear Medicine. New York: Lippincott Raven; p