Accuracy of exercise stress technetium 99m sestamibi SPECT imaging in the evaluation of the extent and location of coronary artery disease in patients with an earlier myocardial infarction

Lung-to-heart ratio analysis using virtual planar images obtained from myocardial perfusion SPECT data: A phantom and clinical studies

BACKGROUNDS

The lung-to-heart ratio (L/H ratio) in myocardial perfusion scintigraphy (MPS) is a useful marker that complements the sensitivity of ischemia detection. However, it requires planar imaging acquired following a separate protocol in addition to single-photon emission computed tomography (SPECT). We developed a novel method for constructing virtual planar image (VPI) from SPECT data.

METHODS

Myocardial phantoms using Tl-201 were built with different amounts of radioactivity in the lungs. SPECT data and conventional planar images of these phantoms were collected with an Anger-type gamma camera. VPIs were constructed by adding all coronal images reconstructed from SPECT data. The clinical utility of VPIs obtained from 52 patients who underwent MPS with Tc-99m sestamibi was evaluated.

RESULTS

The radioactivity linearity of VPIs was satisfactory, with a correlation coefficient of r ≥ .99 between the measured amounts of radioactivity and image counts. The L/H ratios obtained from VPI analysis were strongly correlated with those of conventional planar images with a correlation coefficient of r ≥ .99 in the phantom study and r = .929 in clinical application.

CONCLUSION

The accuracy of VPI-based L/H ratio analysis was comparable to that of conventional planar image-based analysis. VPIs could be used as an alternative method of obtaining planar images in clinical settings.

Standardizing the Definition and Analysis Methodology for Complete Coronary Artery Revascularization

Guideline‐based medical therapy is the foundation of treatment for individuals with coronary artery disease. However, revascularization with either percutaneous coronary intervention or coronary artery bypass grafting may be beneficial in patients with acute coronary syndromes, refractory symptoms, or in other specific scenarios (eg, left main disease and heart failure). While the goal of percutaneous coronary intervention and coronary artery bypass grafting is to achieve complete revascularization, anatomical and ischemic definitions of complete revascularization and their methodology for assessment remain highly variable. Such lack of consensus invariably contributes to the absence of standardized approaches for invasive treatment of coronary artery disease. Herein, we propose a novel, comprehensive, yet pragmatic algorithm with both anatomical and ischemic parameters that aims to provide a systematic method to assess complete revascularization after percutaneous coronary intervention or coronary artery bypass grafting in both clinical practice and clinical trials.

Accuracy of myocardial perfusion imaging in detecting multivessel coronary artery disease: A cardiac CZT study

BACKGROUND

Myocardial perfusion imaging (MPI) performed on traditional single-photon emission computed-tomography cameras has been shown to have a sub-optimal accuracy in detecting multivessel coronary artery disease (CAD).

METHODS

Six-hundred and ninety-five patients were submitted to MPI on a novel cadmium-zinc-telluride (CZT) camera and coronary angiography. A coronary stenosis >70% was considered obstructive. In every patient, the summed stress score (SSS) was computed. Moreover, the regional stress scores were also calculated for every coronary territory.

RESULTS

Four-hundred and forty-one patients had obstructive CAD in one (28%), two (19%), or three (17%) vessels. At per-patient analysis, the SSS showed a significant accuracy in detecting obstructive CAD (AUC 0.87, P < .001). Specifically, its accuracy was maintained also in patients with double (AUC 0.83; P < .001) or triple-vessels disease (AUC 0.79, P < .001), where CZT was able to correctly identify CAD extent in 64% of patients. On a per-vessel basis, CZT confirmed its high accuracy in detecting obstructive CAD (AUC 0.88, P < .001), independently from the involved coronary vessel.

CONCLUSIONS

MPI performed on a CZT camera is highly accurate in detecting obstructive CAD, independently from the coronary artery involved and the overall disease burden.

Patients with left bundle branch block pattern and high cardiac risk myocardial SPECT: does the current management suffice?

INTRODUCTION

Myocardial perfusion SPECT (MPS) is frequently used for cardiovascular risk stratification. The significance of MPS in patients with abnormal electrical ventricular activation is often questionable. This review assesses the value of MPS for risk stratification of patients with intrinsic left bundle branch block or that due to right ventricular apical pacing.

METHODS

We reviewed the literature by a search of the MEDLINE database (January 1980 to September 2010). The terms prognosis or prognostic value were combined with SPECT and LBBB or pacing or pacemakers. MPS was categorised as low and high risk according to the original definitions.

RESULTS

We identified 11 studies suitable for review. A low-risk MPS is associated with a low risk of cardiac events whereas high-risk MPS carries a 4.8-fold increased risk, 95% CI [3.2 - 7.2] (p < 0.0001). Despite secondary prevention and an improved medical and interventional care, these figures have hardly changed over time.

CONCLUSION AND CLINICAL IMPLICATIONS

A low-risk MPS permits a policy of watchful waiting whereas a high-risk MPS requires further analysis and treatment. The persistent high cardiac death and acute myocardial infarction rate after a high-risk MPS suggest that the current management of these patients does not suffice and needs reconsideration.

Incremental value of combining 64-slice computed tomography angiography with stress nuclear myocardial perfusion imaging to improve noninvasive detection of coronary artery disease

BACKGROUND

To compare the accuracy of combined 64-slice computed tomography angiography (CTA) and stress nuclear myocardial perfusion imaging (MPI) in the noninvasive detection of coronary artery disease (CAD) with that of 64-slice CTA alone.

METHODS AND RESULTS

One hundred thirty symptomatic patients with suspected CAD underwent both 64-slice CTA and stress thallium-201 MPI before invasive coronary angiography (ICA). Coronary lesions with >or=50% luminal narrowing were considered as significant stenoses on CTA and ICA. Of 390 arteries in 130 patients, 54 (14%) were nonevaluable by CTA due to severe calcifications, motion artifacts, and/or poor opacification. All nonevaluable arteries were considered positive. The sensitivity, specificity, PPV and NPV were 95%, 80%, 69%, and 97%, respectively, for CTA alone and 94%, 92%, 85%, and 97%, respectively, for CTA with stress nuclear MPI for all nonevaluable arteries on CTA. Per-patient analysis showed significant increase in specificity and PPV. The majority (75%, 9/12) of nonevaluable severely calcified vessels in the left anterior descending artery were positive on stress nuclear MPI, whereas the majority (89%, 8/9) of nonevaluable vessels with motion artifacts in the right coronary artery were negative.

CONCLUSIONS

Combined CTA and stress nuclear MPI provide improved diagnostic accuracy for the noninvasive detection of CAD.

The validity of multi-center common normal database for identifying myocardial ischemia: Japanese Society of Nuclear Medicine working group database

PURPOSE

The Japanese Society of Nuclear Medicine (JSNM) working group has created a myocardial perfusion imaging database applicable to standard acquisition protocol. The aim of this study is to validate the diagnostic accuracy of the common normal database compared with the expert interpretation of each institute.

METHODS

Five institutions participated in this study and used different acquisition settings which included 360 degrees /180 degrees rotation, camera configuration and camera orbits. The software and its version used in each institution also varied. The working group database was applied to detect the culprit coronary territory from a total of 166 patients with coronary artery disease (CAD) and 145 patients with low-likelihood of CAD.

RESULTS

When summed stress score > or =4 was defined as significant abnormality, overall sensitivity, specificity and accuracy of patient-based analysis were 77, 72 and 75%, respectively, based on quantitative analysis using the common database, whereas those by institutional visual expert reading were 72, 79 and 75%, respectively.

CONCLUSION

The common database, which was created by a multi-center working group and separated between male/female with 180/360 degrees acquisitions, demonstrated comparable diagnostic accuracy to expert interpretation by each institute, and it may be applicable to multi-center studies.

Variability of myocardial ischemic responses to mental versus exercise or adenosine stress in patients with coronary artery disease

BACKGROUND

Mental stress precipitates myocardial ischemia in a significant percentage of coronary artery disease (CAD) patients. Exercise or adenosine stresses produce different physiologic responses and cause myocardial ischemia via different mechanisms. Little is known about the comparative severity and location of myocardial ischemia provoked by these different stressors. In this study we sought to compare the within-individual ischemic responses to mental versus exercise or adenosine stress in a cohort of CAD patients.

METHODS AND RESULTS

All patients underwent mental stress and either exercise or adenosine testing within a 1-week period. Mental stress was induced via a public speaking task. Rest-stress myocardial perfusion imaging was used with all testing protocols. Participants were 187 patients (65 women [35%]) with a documented history of CAD and a mean age of 64 +/- 9 years. Mental stress-induced myocardial ischemia (MSIMI) was less prevalent and frequently of less magnitude than exercise- or adenosine-induced ischemia. Ischemia induced by exercise or adenosine testing did not accurately predict the development or the location of MSIMI. The overall concordance between these stressors for provoking ischemia was weak (percent agreement, 71%; kappa [+/- SE], 0.26 +/- 0.07). In a minority of patients (11%) mental stress provoked ischemia in the absence of exercise- or adenosine-induced ischemia. Moreover, in patients who had myocardial ischemia during both stressors, there were significant within-individual differences in the coronary artery distribution of the ischemic regions. MSIMI was more likely to occur in a single-vessel distribution (86%) compared with exercise- or adenosine-induced ischemia (54%). The stressors had moderate agreement if the ischemic region was in the right coronary artery territory (percent agreement, 76%; kappa, 0.52 +/- 0.19) or the left anterior descending coronary artery (percent agreement, 76%; kappa, 0.51 +/- 0.19) and significantly lower agreement in the left circumflex territory (percent agreement, 62%; kappa, 0.22 +/- 0.18).

CONCLUSIONS

Our findings indicate that mental and exercise or adenosine stresses provoke different myocardial ischemic responses. These observations suggest that exercise or adenosine testing may not adequately assess the likelihood of occurrence or severity of MSIMI and that different mechanisms are operative in each condition.

Frequency and severity of myocardial perfusion abnormalities using Tc-99m MIBI SPECT in cardiac syndrome X

Background

Cardiac syndrome X is defined by a typical angina pectoris with normal or near normal (stenosis <40%) coronary angiogram with or without electrocardiogram (ECG) change or atypical angina pectoris with normal or near normal coronary angiogram plus a positive none-invasive test (exercise tolerance test or myocardial perfusion scan) with or without ECG change. Studies with myocardial perfusion imaging on this syndrome have indicated some abnormal perfusion scan. We evaluated the role of myocardial perfusion imaging (MPI) and also the severity and extent of perfusion abnormality using Tc-99m MIBI Single Photon Emission Computed Tomography (SPECT) in these patients.

Methods

The study group consisted of 36 patients with cardiac syndrome X. The semiquantitative perfusion analysis was performed using exercise Tc-99m MIBI SPECT. The MPI results were analyzed by the number, location and severity of perfusion defects.

Results

Abnormal perfusion defects were detected in 13 (36.10%) cases, while the remaining 23 (63.90%) had normal cardiac imaging. Five of 13 (38.4%) abnormal studies showed multiple perfusion defects. The defects were localized in the apex in 3, apical segments in 4, midventricular segments in 12 and basal segments in 6 cases. Fourteen (56%) of all abnormal segments revealed mild, 7(28%) moderate and 4 (16%) severe reduction of tracer uptake. No fixed defects were identified. The vessel territories were approximately the same in all subjects. The Exercise treadmill test (ETT) was positive in 25(69%) and negative in 11(30%) patients. There was no consistent pattern as related to the extent of MPI defects or exercise test results.

Conclusion

Our study suggests that multiple perfusion abnormalities with different levels of severity are common in cardiac syndrome X, with more than 30 % of these patients having at least one abnormal perfusion segment. Our findings suggest that in these patients microvascular angina is probably more common than is generally believed.

Noninvasive detection of coronary allograft vasculopathy by myocardial contrast echocardiography

BACKGROUND

Noninvasive detection of coronary allograft vasculopathy is still challenging. To determine the accuracy of myocardial contrast echocardiography (MCE) in detecting coronary allograft vasculopathy after heart transplantation, we studied 35 asymptomatic patients (30 men, aged 46 +/- 12.7 years) with normal left ventricular function.

METHODS

Patients underwent MCE with continuous contrast (perfluorocarbon-exposed sonicated dextrose albumin) administration. Images were obtained at baseline and during peak dobutamine (up to 40 mg/kg/min) with intermittent harmonic imaging. Areas failing to increase contrast enhancement during peak stress were regarded as abnormal. Coronary artery obstructions greater than 50% at angiography were considered significant.

RESULTS

Seven out of 10 patients with coronary artery disease had a positive MCE and one patient with a positive MCE had no angiographically detected disease (sensitivity = 70%, specificity = 96%, accuracy = 88.6%). Agreement between the vascular territory and perfusion defects was good for the left anterior descending coronary artery (kappa = 0.56), but not for other arteries. Although 5 patients had multivessel disease, multiple perfusion defects were detected in only one patient.

CONCLUSION

MCE showed good accuracy in detecting the presence of coronary allograft vasculopathy after heart transplantation; however, it failed to identify the extent of the disease.

Head-to-head comparison of uncorrected and scatter corrected, summed and end diastolic myocardial perfusion SPECT in coronary artery disease

OBJECTIVES

Compared with other non-invasive methods for diagnosing coronary artery disease (CAD), myocardial perfusion imaging (MPI) suffers from some lack of specificity, especially in patients with a small heart. Allowing the assessment of perfusion on end diastolic images instead of summed images, gated single photon emission computed tomography (SPECT) constitutes an attractive method for increasing the accuracy of MPI. Scatter correction, known to improve image contrast, might also be interesting. The present study aimed at comparing scatter corrected to uncorrected gated MPI for CAD diagnosis.

METHODS

The results for 100 patients referred for gated 99mTc sestamibi SPECT were analysed. They were divided into two subgroups according to their end systolic volume (ESV) measured by QGS analysis (group A, ESV > or =30 ml, n=65; group B, ESV <30 ml, n=35). For each patient, a total defect score (TDS) was quantified on four polar maps (uncorrected and scatter corrected, summed, and uncorrected and scatter corrected, end diastolic). The optimal TDS separating non-CAD from CAD patients was calculated by analysis of the receiver operating characteristic (ROC) curve for the four data sets, using the coronary angiogram as a 'gold standard'.

RESULTS

In the whole patient population, the accuracy of the uncorrected data was 67% for the end diastolic images and 71% for the summed images (sensitivity, 66% and 70%; specificity, 71% and 79%, respectively). After scatter correction, the accuracy did not change for the end diastolic data (accuracy, 67%; sensitivity, 63%; specificity, 93%) and increased to 74% for the summed data (sensitivity, 73%; specificity, 79%). In group A, the uncorrected data were 72% accurate for the end diastolic images and 78% for the summed images (sensitivity, 72% and 79%; specificity, 75% and 75%, respectively). After correction, the accuracy of end diastolic images increased to 77% (sensitivity, 77%; specificity, 75%), and did not change for the summed images (accuracy, 78%; sensitivity, 79%; specificity, 75%). In group B, the accuracy of uncorrected images amounted to 51% for both end diastolic and summed data (sensitivity, 48% and 40%; specificity, 60% and 80%, respectively). After correction, it increased to 57% for the end diastolic images and to 63% for the summed images (sensitivity, 48% and 64%; specificity, 80% and 60%, respectively).

CONCLUSIONS

Despite lower blurring on end diastolic compared with summed images, non-scatter corrected end diastolic data were least accurate for the diagnosis of coronary artery disease in patients with a high prevalence of disease. Scatter correction, by improving the delineation of perfusion defects, increased the accuracy of quantitative MPI for the diagnosis of CAD in a large number of patients, more particularly in those with a small heart.

Prognostic value of stress Tc-99m tetrofosmin SPECT in patients with previous myocardial infarction: impact of scintigraphic extent of coronary artery disease

BACKGROUND

Our objective was to assess the prognostic value of the scintigraphic extent of coronary artery disease on stress technetium 99m tetrofosmin single photon emission computed tomography in patients with previous myocardial infarction.

METHODS AND RESULTS

We studied 383 patients (280 men and 103 women; mean age, 60 +/- 11 years) more than 3 months after an acute myocardial infarction by exercise bicycle or dobutamine (up to 40 mug . kg -1 . min -1 ) stress Tc-99m tetrofosmin myocardial perfusion tomography. Stress images were acquired 1 hour after stress, and rest images were acquired 24 hours after stress testing. An abnormal study was defined as one demonstrating a reversible or fixed perfusion abnormality. Myocardial segments were assigned to corresponding coronary arteries as follows: the apex, anterior wall, and anterior septum were assigned to the left anterior descending coronary artery; the posterolateral wall was assigned to the left circumflex artery; and the basal posterior septum and inferior wall were assigned to the right coronary artery. During a mean follow-up of 4.3 +/- 2.1 years, 48 cardiac events occurred (36 cardiac deaths and 12 nonfatal myocardial infarctions). Myocardial perfusion was normal in 51 patients, abnormal in a single-vessel distribution in 170 patients, and abnormal in a multivessel distribution in 162 patients. The annual cardiac event rates in these groups were 0.4%, 2.6%, and 4%, respectively. In a multivariate analysis model, independent predictors of cardiac events were diabetes mellitus (odds ratio [OR], 2.3; 95% confidence interval [CI], 1.4-4.5), history of congestive heart failure (OR, 2.7; 95% CI, 1.4-4), age (OR, 1.05; 95% CI, 1.01-1.08), and scintigraphic extent of coronary artery disease (OR, 4.2; 95% CI, 1.8-9.1).

CONCLUSION

Stress Tc-99m tetrofosmin myocardial perfusion imaging provides independent prognostic information for the risk stratification of patients with previous myocardial infarction. The event rate is directly related to the scintigraphic extent of coronary artery disease. Patients with normal perfusion have an excellent event-free survival rate.

Incidence and predictors of heart failure during long-term follow-up after stress Tc-99m sestamibi tomography in patients with suspected coronary artery disease

BACKGROUND

Heart failure is a major cause of morbidity and death in patients with coronary artery disease (CAD). The aim of this study was to define the incidence and predictors of heart failure during long-term follow-up in patients with suspected CAD referred for stress myocardial perfusion imaging.

METHODS AND RESULTS

We studied 787 patients (mean age, 57 +/- 12 years; 470 men) with suspected CAD who had no history of previous myocardial infarction or heart failure with exercise (n = 508) or dobutamine (n = 279) stress technetium 99m sestamibi single photon emission computed tomography. Patients were followed up for the occurrence of heart failure, nonfatal myocardial infarction, and death. An abnormal perfusion scan (reversible or fixed perfusion defect) was detected in 341 patients (43%). During a mean follow-up of 6.7 +/- 2.3 years, heart failure occurred in 46 patients (6%), 170 patients (22%) died, and 52 patients (7%) had nonfatal myocardial infarction. Patients in whom heart failure developed were older (mean age, 60 +/- 12 years vs 56 +/- 12 years; P = .01) and were more likely to be men (34 [74%] vs 436 [59%], P = .01) and to have an abnormal scan (32 [70%] vs 309 [42%], P = .0002) compared with patients without heart failure. Nonfatal myocardial infarction occurred before the onset of heart failure in only 3 patients (7%). By multivariate analysis, predictors of heart failure were age (risk ratio [RR], 1.04 [95% CI, 1.01-1.08]), male gender (RR, 2 [95% CI, 1.3-4.5]), resting heart rate (RR, 1.1 [95% CI, 1.05-1.2]), and abnormal scan (RR, 2.3 [95% CI, 1.4-3.9]). The annual mortality rate was 15% after the diagnosis of heart failure.

CONCLUSION

In patients with suspected CAD and no history of myocardial infarction, late heart failure is predicted by age, gender, resting heart rate, and abnormal perfusion, and it is associated with a substantial mortality rate. The majority of heart failure events are heralded by perfusion abnormalities on sestamibi single photon emission computed tomography but not by an earlier myocardial infarction.

Differential prognostic significance of peri-infarction versus remote myocardial ischemia on stress technetium-99m sestamibi tomography in patients with healed myocardial infarction

Peri-infarction and remote myocardial ischemia involve different myocardial substrates, but their differential clinical implications have not been previously studied. We assessed the differential prognostic significance of peri-infarction and remote ischemia during long-term follow-up in patients with healed myocardial infarction. We studied 345 patients (59 +/- 12 years old; 282 men) with previous myocardial infarction who demonstrated reversible perfusion abnormalities on exercise or dobutamine stress technetium-99m sestamibi tomography. Follow-up events for 5.5 +/- 2.6 years were 60 deaths (17%; 40 cardiac deaths) and 25 reinfarctions (7%). Reversible perfusion abnormalities were detected in the remote region in 129 patients (37%), the peri-infarction region in 142 patients (41%), and in both regions in 74 patients (21%). The annual rates of cardiac death in these groups were 1.2%, 2.8%, and 2.9%, respectively (p <0.01). The annual rates of reinfarction were 1%, 1.5%, and 0.9%, respectively (p = NS). In a multivariate analysis model, independent predictors of cardiac death were history of heart failure (risk ratio [RR] 2.8, 95% confidence interval [95% CI] 1.2 to 7), diabetes mellitus (RR 4.1, 95% CI 1.9 to 8.9), summed score at rest (RR 1.4, 95% CI 1.1 to 3.1), and peri-infarction ischemia (RR 2.6, 95% CI 1.1 to 6.1). Predictors of reinfarction were age (RR 1.03, 95% CI 1.01 to 1.07) and diabetes mellitus (RR 3.3, 95% CI 1.2 to 9.1). Peri-infarction ischemia assessed by stress technetium-99m sestamibi tomography is associated with a greater risk of cardiac death than is remote ischemia. The risk of reinfarction is not related to the location of ischemia.

Myocardial perfusion assessment in patients with medium probability of coronary artery disease and no prior myocardial infarction: comparison of myocardial contrast echocardiography with 99mTc single-photon emission computed tomography

BACKGROUND

No previous studies have compared myocardial contrast echocardiography (MCE) and single-photon emission computerized tomography (SPECT) for the detection of coronary artery disease (CAD) in patients with a medium likelihood of CAD. This study was developed to test the hypothesis that MCE is superior to SPECT for the detection of CAD.

METHODS

Fifty-five patients with a medium probability of CAD and no previous myocardial infarction were recruited. Results of MCE and SPECT were compared to quantitative coronary arteriography, where CAD was defined as >50% stenosis. Each patient was examined for the anterior and posterior circulations.

RESULTS

On a coronary circulation basis (n = 110), the sensitivity of MCE was significantly greater than that of SPECT for the detection of CAD (86% vs 43%, P <.0001). However, the specificities were similar (88% and 93%, P =.52). Both techniques were marginally more accurate in the anterior compared to the posterior circulation (88% vs 76%, P =.07 for MCE and 79% vs 63%, P =.19, for SPECT). On a patient basis (n = 55), MCE had a higher sensitivity than SPECT for the detection of CAD (83% vs 49%, P <.05). Although specificity tended to be higher for SPECT than MCE (92% vs 58%), it was not significant (P =.33). When CAD was defined as >40% coronary stenosis, the specificity of MCE increased to 83% without any change in sensitivity.

CONCLUSION

In this preliminary study, MCE was found to be superior to SPECT during dipyridamole stress for the diagnosis of CAD in patients with a medium pretest probability of CAD. Larger studies are required to confirm these findings.

Sensitivity, specificity and accuracy of stress SPECT myocardial perfusion imaging for detection of coronary artery disease in the distribution of first-order branch vessels, using an anatomical matching of angiographic and perfusion data

We sought to investigate the utility of stress single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) for the identification of coronary artery disease (CAD) in the distribution of first-order branch vessels. We evaluated 135 consecutive patients with coronary angiography and stress SPECT MPI. We anatomically matched angiography and SPECT to assess the sensitivity, specificity and accuracy of SPECT MPI for the detection of CAD in the distribution of first-order branches. Subgroup analysis for stress test performance and previous coronary artery bypass grafting (CABG) was also performed. The sensitivity, specificity and accuracy of stress SPECT MPI for the detection of CAD in the distribution of first-order branch vessels were all 67%. For isolated branch vessel CAD, stress SPECT MPI had a sensitivity of 44%. In patients without CABG, the sensitivity, specificity and accuracy for the detection of CAD in the distribution of first-order branch vessels were 71%, 67% and 68%, compared with 60%, 67% and 64% for patients with CABG. The sensitivity for isolated branch vessel CAD was 50% for patients without CABG, but only 29% for patients with CABG. The sensitivity and specificity for CAD in the distribution of branch vessels were similar for all patients for all stress test modalities and heart rate response (sensitivity, 64-69%; specificity, 61-69%). Stress SPECT MPI offers intermediate sensitivity, specificity and accuracy for the detection of CAD in the distribution of first-order coronary artery branch vessels. However, for isolated branch vessel CAD, stress SPECT has a lower sensitivity, particularly in patients with previous CABG.