Evaluation of graft patency by computed tomographic angiography in symptom-free post-coronary artery bypass surgery patients

Background  Accelerated atherosclerosis occurs in aortocoronary saphenous vein grafts, contributing to increased morbidity and mortality rates. We estimated the prevalence of asymptomatic graft failure in patients 5 years or more after coronary artery bypass grafting (CABG) using electron-beam computed tomographic angiography (EBA). Methods and Results  EBA was performed in 45 symptom-free patients (mean age, 66±9 year; 87% male; mean time interval after CABG, 8±5 years). A total of 102 vein grafts and 37 internal mammary artery grafts were evaluated. Patients with graft stenosis or occlusion on EBA underwent myocardial perfusion scintigraphy and invasive angiography. Six grafts were unevaluable by EBA. Twenty patients had evidence of graft stenosis or occlusion on EBA. Of 20 asymptomatic patients with graft disease, 17 (85 %) had abnormal myocardial perfusion, with moderate to severe reversible ischemia occurring in one third of subjects. Fourteen occluded and eleven stenosed vein grafts were correctly diagnosed by EBA. There were 2 false-positive EBA diagnoses of graft stenosis, resulting in a 100 % positive predictive accuracy for detecting graft occlusion and 85% positive predictive accuracy for detecting graft stenosis. All occluded internal mammary artery grafts (n=3) were accurately diagnosed. Conclusion  Computed tomographic coronary angiography permits reliable identification of by pass graft stenoses and occlusion in symptom-free patients more than 5 years after CABG. Future studies are needed to assess the prognostic benefit of early detection of graft disease and intervention in asymptomatic patients The study was supported by research grants from the Harrow Cardiovascular Research Trust     

Thallium-201 myocardial scintigraphic evidence of ischemia in a patient with angina pectoris and normal coronary arteriogram: Significance of thallium-201 washout analysis

We present a patient who had anginal pain and an abnormal exercise electrocardiogram but a normal coronary arteriogram. We thought that myocardial ischemia was responsible for this symptom in view of the exercise left ventriculogram, exercise thallium-201 myocardial scintigraphy and effect of nitroglycerin on the anginal pain. The left ventriculogram at rest was normal but exercise worsened the entire left ventricular wall motion. Exercise thallium-201 myocardial images showed minimal reduction of radio-activity in the anterior, apical, antero-lateral and postero-lateral wall. Myocardial thallium-201 washout analysis revealed washout abnormalities all over the left ventricular myocardium similar to those of triple vessel disease, supporting the exercise left ventriculographic finding. Myocardial thallium-201 washout analysis as well as the visual method should be performed in patients with angina pectoris and normal coronary arteriograms.     

Contrast-enhanced magnetic resonance imaging of hypoperfused myocardium.

Contrast-enhanced magnetic resonance (MR) imaging can define myocardial perfusion defects due to acute coronary occlusion. However, since most clinically important diagnostic examinations involve coronary arteries with subtotal stenoses, we investigated the ability of MR imaging with a manganese contrast agent to detect perfusion abnormalities in a canine model of partial coronary artery stenosis. The contrast agent was administered after the creation of a partial coronary artery stenosis with the addition of the coronary vasodilator dipyridamole in six of 12 animals. The hearts were imaged ex situ using gradient reversal and spin-echo sequences, and images were analyzed to determine differences in signal intensity between hypoperfused and normally perfused myocardium. Comparison of MR images with regional blood flow and thallium-201 measurements showed good concordance of hypoperfused segments in those animals given dipyridamole, with 75% of the abnormal segments correctly identified. In those animals not given dipyridamole, 48% of segments were correctly identified. Thus, ex vivo MR imaging with a paramagnetic contrast enhancement can be used to detect acute regional myocardial perfusion abnormalities due to severe partial coronary artery stenoses.     

Polar presentation of coronary angiography and thallium-201 single photon emission computed tomography. A method for comparing anatomic and pathologic findings in coronary angiography with isotope distribution in thallium-201 myocardial SPECT

Individual results of coronary angiography were compared with tomographic myocardial scintigraphy (SPECT) in 99 patients. Coronary angiography findings were transferred to polar maps. Borders between arteries were assigned angles in a coordinate system constructed as a compass-rose. Areas perfused by different arteries were described by sectors. Findings were visually compared with the perfusion defects in a polar presentation of thallium-201 SPECT also described by angles. The mean values and SD for the angles representing arterial borders and perfusion defects were presented. The left ventricular myocardium was perfused by 3 coronary arteries in 92/99 patients. Dominant left artery was present in 7/99 patients; 79 perfusion defects were related to 118 arterial sectors 84 per cent had totally or partially matched stenotic arteries. Inter-individual differences in distribution of coronary arteries influence the localization of perfusion defects in myocardial SPECT and can be estimated with this polar presentation method.     

Reliability of technetium-99m Q12 and thallium-201 myocardial activity measurements after triphenyl tetrazolium chloride myocardial staining by perfusion

RATIONALE AND OBJECTIVES: Investigations in animal models of severe myocardial ischemia or infarction use triphenyl tetrazolium chloride (TTC) staining to document infarction size histologically and to correlate these data with uptake measurements of radiolabeled tracers. Previously published data suggest that TTC staining itself has an important impact on myocardial tracer activity measurements. The authors hypothesized that TTC staining by perfusion has no significant effect on relative regional myocardial activity measurements of technetium-99m Q12 and thallium-201 in an open-chest canine model. METHODS: Eight dogs underwent left anterior descending artery occlusion for 2 hours with 30 minutes of reperfusion, followed immediately by injection of technetium-99m Q12 (n = 4) or thallium-201. Total myocardial activity was recorded in a dose calibrator, and regional myocardial samples were obtained by Cope needle biopsies from the ischemic and normal zones, both before and after TTC staining. RESULTS: The mean percent activity retention for the whole heart after perfusion staining with TTC was significantly reduced when compared to the preperfusion value for both technetium-99m Q12 and thallium-201. Regional measurements revealed no significant difference between the mean percent retention of technetium-99m Q12 in the ischemic and normal zones. After TTC perfusion, regional mean percent retention of thallium-201 was similar in the ischemic and normal zones. CONCLUSIONS: In a canine model of myocardial ischemia and infarction with reperfusion, TTC staining can be performed by coronary artery perfusion without significantly affecting comparative regional measurements of either technetium-99m Q12 or thallium-201. Whole heart tracer retention is significantly reduced by TTC perfusion staining, but thallium-201 is more affected than technetium-99m Q12.     

Comparison of flow capacities of arterial and venous grafts for coronary artery bypass grafting: evaluation with exercise thallium-201 single-photon emission tomography

Stress thallium-201 tomography was performed to compare the flow capacities of arterial and saphenous vein grafts in patients with coronary artery bypass grafting (CABG). One hundred and seven consecutive patients (95 male and 12 female; mean age 58±9.1 years) underwent exercise-redistribution ²⁰¹Tl myocardial single-photon emission tomography 4–5 weeks after CABG. When a reversible perfusion defect was present in the area covered by a patent bypass graft, the flow capacity of the graft was defined as insufficient. Of all 285 grafts, 211 were considered as complete bypass. Reversible perfusion defects were present in 29 (27%) of 108 myocardial areas supplied by patent arterial grafts but in only 5 (5%) of 103 myocardial areas supplied by patent saphenous vein grafts (P<0.0001). In the LAD area reversible defects were observed in 22 of 82 areas covered by arterial grafts, in contrast to only 1 of 29 areas covered by venous grafts (P<0.01); in the RCA area reversible defects were observed in 7 of 17 and 4 of 41 areas respectively (P<0.01). There was no difference between the native coronary artery stenosis bypassed by patent arterial and venous grafts (88%±12% vs 86%±14% respectively, P=0.27). In conclusion, flow capacities during peak myocardial demand were more frequently insufficient in arterial bypass grafts than in saphenous vein grafts. Received 23 May and in revised form 7 August 1997     

Diffuse subendocardial ischemia in a patient with aortic valve stenosis without coronary artery disease by exercise 201Tl SPECT]

A case of aortic valve stenosis without coronary artery disease was confirmed to have diffuse subendocardial ischemia by exercise Thallium-201 myocardial single photon emission computed tomography. A 72-year-old woman, who had been diagnosed as aortic valve stenosis, was admitted because of chest pain during exercise. In cardiac catheterization findings, the patient angiographically had normal coronary arteries and no asynergy of left ventricular wall motion. The peak flow velocity in continuous wave Doppler echocardiography was about 5.0 m/sec at aortic valve level, providing a pressure drop of 100 mmHg across a stenotic valve with calculating on a modified Bernoulli equation (PG = 4V2). Thallium-201 myocardial SPECT images during exercise showed a transient "dilation and a widespread wall thinning" of left ventricle with apical perfusion defect. Simultaneous electrocardiogram showed further ST depression and the patient had chest pain. In 6 months after aortic valve replacement the patient no longer demonstrated both apical perfusion defect and "wall thinning" in postoperative thallium-201 myocardial SPECT images and also had neither ST depression nor chest pain. Thus; a transient "dilation and wall thinning" of left ventricle in this patient is suspected to be a sign of diffuse subendocardial ischemia.     

Evaluation of myocardial perfusion abnormalities with gadolinium-enhanced snapshot MR imaging in humans. Work in progress.

To determine whether myocardial perfusion abnormalities could be detected in patients with coronary artery disease by means of contrast material-enhanced magnetic resonance (MR) images, a snapshot imaging technique was used in six patients with coronary artery disease and four healthy subjects in conjunction with pharmacologic stress (dipyridamole infusion) and bolus injection of gadopentetate dimeglumine. MR images from all patients and healthy subjects were quantitatively analyzed to define spatial changes in signal intensity after administration of dipyridamole and gadopentetate dimeglumine. The resultant findings were compared with findings on thallium-201 scintigrams obtained after administration of dipyridamole and on coronary arteriograms in all patients. Nine myocardial regions supplied by stenosed arteries showed diminished levels of signal intensity after infusion of the contrast agent compared with those of normally perfused regions. These findings were in agreement with those obtained with T1-201 scintigraphy (in eight of nine regions) and arteriography. Thus, contrast-enhanced high-speed MR imaging with use of dipyridamole enabled detection of regional perfusion abnormalities in humans.     

Coronary flow reserve evaluated by 201Tl myocardial perfusion SPECT after coronary artery bypass grafting (CABG) for angina pectoris

We compared the flow reserves of the coronary bypass vessels between arterial and venous grafts by 201Tl myocardial perfusion SPECT on the patients with angina pectoris who had no past history of myocardial infarction or intervention therapy such as PTCA. Thirty two patients had undergone a total of 70 bypass grafts and 66 of them were proved to be patent at postoperative CAG. Reversible defects were observed in 6 of 40 segments (15.0%) covered by patent venous grafts, and in 11 of 26 segments (42.3%) by patent arterial grafts. The rate of postoperative reversible defects was higher in the areas grafted by artery but this had no relation with the severity of coronary artery stenosis before CABG. This reversible defect is most likely to be caused by the character of artery graft itself and this should not be considered to highly suggest the restenosis or occlusion of the graft vessel.     

冠状动脉旁路移植术后心绞痛复发的桥血管造影分析

目的分析冠状动脉旁路移植术(CABG)后心绞痛复发患者的自体血管及桥血管的变化特点。方法对CABG术后因心绞痛复发的病例行选择性血管造影,检查冠状动脉和桥血管情况。结果24例均发现桥血管病变,血管病变以闭塞为主,占38.2%(26/68),狭窄占10.3%(7/68)。静脉桥24支完全闭塞,5支狭窄。乳内动脉桥完全闭塞和狭窄各2支。心绞痛复发还可由再血管化不完全和自体血管病变加重引起。结论CABG术后仍可以复发心绞痛,桥血管病变是主要原因,术后如发生心绞痛应该及时检查。     

Single injection thallium-201 stress and redistribution myocardial perfusion imaging: comparison with stress electrocardiography and coronary arteriography.

The efficacy of single injection thallium-201 exercise stress and rest redistribution imaging in the evaluation of myocardiacl ischemia was compared with stress electrocardiography and coronary arteriography. Thallium-201 imaging was interpreted at two levels of sensitivity in order to define the circumstances under which it best serves as a screening modality for coronary arteriography. With the prevalence of coronary disease usually found in patients referred for coronary arteriography (75%), unprocessed thallium-201 imaging is as good as stress electrocardiography in identifying patients apt to show coronary artery abnormalities, but not much better than stress electrocardiography in delineating those patients unlikely to show coronary artery disease. In contrast, processed lesion enhanced images showing normal results virtually eliminate the possibility of significant arteriographic findings. With this screening technique, many patients may be spared unnecessary coronary arteriography.     

Tc-99m tetrofosmin myocardial SPECT combined with a modified exercise protocol in an unusual case of steal phenomenon

A 61-year-old diabetic woman was referred for myocardial perfusion single photon emission computed tomographic (SPECT) imaging 4 years after coronary artery bypass grafting to the left anterior descending (LAD) artery using a left internal mammary artery (LIMA) graft. She had 3 months' angina associated with fatigue of her left upper extremity (the patient is left-handed). Stress myocardial imaging using a Bruce protocol did not exhibit significant myocardial ischemia, but because of her typical angina symptoms, she underwent repeat stress myocardial imaging in combination with exercise of her left arm. During the aforementioned modified stress protocol, the patient reported angina, and radionuclide perfusion imaging showed extensive myocardial ischemia. The patient underwent coronary angiography and arteriography of the left subclavian artery, which revealed severe stenosis before the origin of the LIMA, resulting in reversed blood flow from the LAD artery through the LIMA graft to the left subclavian artery.     

Gated thallium tomography--potential for improved accuracy in the detection of coronary artery disease

Gated thallium-201 myocardial tomography incorporating perfusion profile analysis was used alone, to assess left ventricular wall perfusion and left ventricular wall movement together in 29 consecutive patients, without prior infarction, who presented with chest pain. All patients had had coronary and left ventricular angiography. The proportion of false positive perfusion defects was reduced when an analysis of corresponding wall movement was made. This combined technique resulted in an improved specificity compared with standard 201Tl myocardial tomography. This approach shows the functional effect of reversible ischaemia on regional myocardial contractility and would appear to be particularly useful in the assessment of patients who present with atypical chest pain.     

双源CT冠状动脉成像评价冠状动脉搭桥术后桥血管通畅情况

目的探讨双源 CT 冠状动脉成像对冠状动脉搭桥术后桥血管通畅状况的诊断价值.资料与方法38例患者于冠状动脉搭桥术后行双源 CT 冠状动脉成像与冠状动脉造影检查,以冠状动脉造影作为“金标准”,对双源 CT 冠状动脉成像结果进行分析.结果38例患者共检出桥血管92支,其中内乳动脉桥31支,大隐静脉桥61支;31支内乳动脉桥中,26支(83.9%)桥血管通畅,5支(16.1%)管腔狭窄、闭塞;61支大隐静脉桥血管中35支(57.4%)桥血管通畅;26支(42.6%)管腔狭窄、闭塞.大隐静脉桥血管狭窄、闭塞的发生率明显高于内乳动脉桥血管(P<0.05).双源 CT 冠状动脉成像评价桥血管狭窄、闭塞的敏感性为93.9%,特异性为100.0%.结论双源 CT 冠状动脉成像对冠状动脉搭桥术后桥血管通畅状况的评价有较高的诊断价值,是一种快速、无创、准确、安全的检查方法.     

Multivessel coronary artery disease (CAD): Coronary bypass surgery versus coronary angioplasty

With jeopardized viable myocardium in the distributions of the left anterior descending and right coronary arteries, it was decided to perform bypass surgery. Saphenous venous bypass grafts were placed to the left anterior descending, right and obtuse marginal coronary arteries. The patient had an uneventful postoperative course and was discharged. The case shows how nuclear myocardial perfusion imaging can be a useful adjunct in the clinical decision-making process when coronary anatomy reveals occlusion of one or more arteries associated with severe regional wall motion abnormalities suggesting scar. In this case, if only the angiographic and echocardiographic data had been evaluated, the inferior wall would have been assessed as nonviable and might not have been revascularized. The perfusion imaging, however, clearly defined persistent jeopardized viable myocardium involving the inferior wall as well as in the left anterior descending artery territory. This allowed the patient to have complete revascularization.     

Clinical significance of 201Tl reverse redistribution in patients with aorto-coronary bypass surgery

Detection of myocardial ischemia by the stress thallium scan has traditionally been performed using transient defect analysis on exercise, followed by redistribution studies. Worsening of the 201Tl myocardial image from exercise to redistribution is referred to as reverse redistribution. In this study, we found reverse redistribution in 10 (21%) of 48 angina pectoris patients who had undergone aortocoronary bypass surgery. The clinical significance of this phenomenon in these patients was investigated in relation to angiographic and surgical findings. Reverse redistribution was found to occur in regions which were supplied by bypass grafts. These areas showed increased coronary blood flow and rapid thallium washout. Our results indicate that a perfusion defect in the bypass region of the redistribution image might be caused by relatively rapid washout in the bypass graft region compared to the adjacent normal myocardium. These results should be considered in the clinical interpretation of stress thallium scans.     

Double right coronary artery diagnosed by computed tomographic angiography: A case report and systematic review of the literature

Double right coronary artery (RCA) is an extremely uncommon anomaly that is mostly detected incidentally in patients undergoing coronary angiography. It can be a benign and isolated anomaly or associated with other congenital abnormalities, mostly other coronary anomalies. Although atherosclerosis and myocardial ischemia have been frequently reported in patients with double RCA, this likely reflects that the patients were evaluated for chest pain rather than the predisposition to atherosclerosis in double RCA. Paralleling the increased awareness of this entity and the availability of non-invasive and cost-effective imaging of the coronary arteries, the diagnosis of double RCA has increased recently. Here, we present a case of double RCA diagnosed by coronary computed tomographic angiography, and provide a mini-review on the demography, anatomic variants, and clinical significance of double RCA.     

Rubidium-82 myocardial uptake and extraction after transient ischemia: PET characteristics

The effects of transient regional ischemia on monovalent cation uptake and extraction by the myocardium were studied in seven open chest dogs. Following a 10-20% stenosis of the left anterior descending coronary artery to prevent reactive hyperemia, the regional myocardial uptake of the monovalent cation 82Rb (ml/min/g X extraction) was measured before, during, and at 10, 30, and 60-80 min after a 10 min total occlusion of the left anterior descending coronary artery using positron emission tomography. Regional myocardial blood flow was also measured at the same time interval using radiolabeled carbonized microspheres. The regional myocardial extraction of 82Rb was calculated as uptake/flow. In normally perfused myocardial regions there was an inverse relationship between 82Rb extraction and blood flow [extraction = -0.56 (In flow) + 0.46, r = 0.93] over a range of flow from 0.3 to 4 ml/min/g. During the prolonged recovery of 82Rb uptake in the transiently ischemic region, flow had returned to normal levels but 82Rb extraction at a given value of flow was significantly decreased at the 30 and 60-80 min times after release of the occlusion compared with normally perfused regions. Thus, prolonged abnormalities in the 82Rb uptake and extraction occur in myocardium recovering from transient ischemia.     

双源CT在冠状动脉搭桥术后随访中的临床应用

目的 评价双源CT冠状动脉造影对冠状动脉搭桥术后桥血管病变随访的应用价值.方法 50例冠状动脉搭桥患者,术后6～20个月行双源CT冠状动脉造影检查;对原始数据行VR、CPR、MIP多种图像后处理技术进行重建.由2位有经验的放射科医生对重建图像进行观察,对桥血管通畅性进行分级诊断.结果 50例患者总计140支桥血管,134支桥血管显示良好,其中通畅或狭窄＜50％的桥血管共127支（91％）,狭窄≥50％的桥血管7支（5％）,闭塞未显示的桥血管共6支（4％）.结论 DSCT冠状动脉造影能够清晰显示并评价冠状动脉桥血管病变,尤其是重度狭窄和闭塞的桥血管,可作为冠状动脉搭桥术后随访的有效评价手段.     

Myocardial redistribution of technetium-99m-methoxyisobutyl isonitrile (SESTAMIBI)

To determine whether technetium-99m-hexakis-2-methoxyisobutyl isonitrile (SESTAMIBI) remains fixed in the myocardium following its initial uptake or undergoes time-related redistribution, anesthetized dogs underwent occlusion of the anterior descending coronary artery for 6 min, followed by 3-hr reperfusion. Technetium-99m-SESTAMIBI and thallium-201 (201Tl) were injected intravenously after 1 min occlusion and regional myocardial blood flow was measured with radioactive microspheres. Tomographic imaging of Tc-SESTAMIBI revealed a perfusion defect with slight but definite filling in over 2 hr. Quantitative analysis indicated a significant rise in the nadir and decrease in the width of the defect in circumferential profile curves. After 3-hr of reperfusion, Tc-SESTAMIBI activity in the previously ischemic area was always greater than the activity of microspheres injected during coronary occlusion (mean normalized values, 0.32 versus 0.11, p less than 0.0001). Our results indicate that following transient ischemia and reperfusion, Tc-SESTAMIBI clearly undergoes myocardial redistribution, although more slowly and less completely than 201Tl.