Incremental prognostic value of exercise thallium-201 myocardial single-photon emission computed tomography late after coronary artery bypass surgery

Non-invasive Ischaemia Testing in Patients With Prior Coronary Artery Bypass Graft Surgery: Technical Challenges, Limitations, and Future Directions

Coronary artery bypass graft (CABG) surgery effectively relieves symptoms and improves outcomes. However, patients undergoing CABG surgery typically have advanced coronary atherosclerotic disease and remain at high risk for symptom recurrence and adverse events. Functional non-invasive testing for ischaemia is commonly used as a gatekeeper for invasive coronary and graft angiography, and for guiding subsequent revascularisation decisions. However, performing and interpreting non-invasive ischaemia testing in patients post CABG is challenging, irrespective of the imaging modality used. Multiple factors including advanced multi-vessel native vessel disease, variability in coronary hemodynamics post-surgery, differences in graft lengths and vasomotor properties, and complex myocardial scar morphology are only some of the pathophysiological mechanisms that complicate ischaemia evaluation in this patient population. Systematic assessment of the impact of these challenges in relation to each imaging modality may help optimize diagnostic test selection by incorporating clinical information and individual patient characteristics. At the same time, recent technological advances in cardiac imaging including improvements in image quality, wider availability of quantitative techniques for measuring myocardial blood flow and the introduction of artificial intelligence-based approaches for image analysis offer the opportunity to re-evaluate the value of ischaemia testing, providing new insights into the pathophysiological processes that determine outcomes in this patient population.

Hybrid coronary computed tomography angiography and positron emission tomography myocardial perfusion imaging in evaluation of recurrent symptoms after coronary artery bypass grafting

Aims

Recurrent chest pain after coronary artery bypass grafting (CABG) poses a diagnostic challenge. We hypothesized that combining anatomy of bypass grafts and native coronary arteries with ischaemia detection by hybrid imaging could be used to gain valuable and complementary information in patients with recurrent symptoms after CABG.

Methods and results

We analysed 36 consecutive patients (67 ± 9 years, 81% male) who had undergone hybrid imaging using coronary computed tomography angiography (CCTA) and [15O]H2O positron emission tomography (PET) myocardial perfusion imaging due to recurrent symptoms after CABG. Coronary tree and left ventricular myocardium were divided into three main territories, yielding a total of 108 coronary territories in 36 patients. The presence of obstructive (≥50%) stenosis and the patency of grafts were evaluated by CCTA, while myocardial ischaemia was assessed by quantitative adenosine-stress PET. Altogether 28 (78%) of the 36 study patients presented with matched PET/CCTA abnormalities. Forty-one coronary territories were supplied by non-obstructed bypass grafts or native coronary arteries (protected territory). However, 12 (29%) of these presented with a perfusion defect. In six cases, the perfusion defect involved myocardium distal to the graft-coronary anastomosis, as interpreted on the PET/CCTA fusion images. In turn, in 48 coronary territories the supplying artery was obstructed on CCTA (unprotected territory). Of these, 41 (85%, P < 0.001 vs. protected) presented with abnormal perfusion, involving myocardium distal to the anastomosis in 29 cases.

Conclusion

Hybrid imaging provides complementary information on the presence and localization of atherosclerotic lesions and myocardial perfusion abnormalities in symptomatic patients with previous CABG.

Prediction of all-cause mortality from gated-SPECT global myocardial wall thickening: comparison with ejection fraction and global longitudinal 2D-strain

BACKGROUND

The aim of this study was to assess the correlation between global wall thickening (GWT) obtained by gated-single photon emission computed tomography (SPECT) and echocardiographic measures [ejection fraction (EF), global longitudinal strain (GLS), and strain rate (GLSR)] and to compare their prognostic value for all-cause mortality.

METHODS AND RESULTS

Seventy-four patients with referral for dipyridamole myocardial perfusion SPECT were prospectively included and underwent transthoracic echocardiography to measure left ventricular EF, GLS, and GLSR. The strongest correlation with GWT was for EF (R = 0.63, P < .001), followed by GLSR (R = -0.57, P < .001) and GLS (R = -0.53, P < .001). There were ten deaths over a period of 14.6 ± 5.7 months. Using the multivariate Cox analysis, summed stress score (HR 1.108; P = .023), EF (HR 1.01, P = .031), GLS (HR 1.593, P = .001), and GWT (HR 0.898, P = .034) remained independent predictors of mortality. Mean survival rate evaluated by Kaplan-Meier analysis was longer in patients with GWT ≥ 24% (21.9 ± 0.6 months) than those with GWT < 24% (13.6 ± 2.7 months; P < .001).

CONCLUSIONS

GWT assessed is a highly sensitive tool to detect early myocardial systolic dysfunction and may bring additional prognostic information.

Prognostic value of stress imaging after revascularization: a systematic review of stress echocardiography and stress nuclear imaging

BACKGROUND

Risk assessment may be important in patients being considered for repeat revascularization after prior coronary intervention or surgery. We sought the prognostic value of radionuclide stress myocardial perfusion imaging or echocardiography among patients with previous revascularization.

METHODS

Studies on the outcomes of stress imaging tests after revascularization were selected from an electronic search if they reported the odds or hazard ratio (HR) of an abnormal stress test in the prediction of mortality (cardiac or total), hard cardiac events (cardiac death and myocardial infarction [MI]), total hard events (total mortality and MI]), or overall events (cardiac death, MI, and repeat revascularization).

RESULTS

In 29 studies (12,874 patients, 63 ± 3 years, 80% men), an abnormal test result was associated with hard cardiac events (HR 1.2, 95% CI 1.1-1.3), cardiac mortality (HR 5.8, 95% CI 0.8-10.8), total mortality (HR 2.2, 95% CI 1.3-3.1), total hard events(HR 2.4, 95% CI 1.4-3.3), and overall events (HR 1.2, 95% CI 1.1-1.3). The nature of the end point was not associated with differences in the prediction of events, but the type of revascularization showed a significant association with outcome, with percutaneous intervention portending a worse outcome. Age and the timing of the stress imaging postrevascularization were inversely associated with survival. Gender, length of follow-up after testing, symptom status, past infarction, and risk factor status did not explain interstudy heterogeneity.

CONCLUSIONS

In patients with previous revascularization, abnormal results at stress echocardiography or radionuclide myocardial perfusion imaging are predictive of subsequent events, with age, type of revascularization, and the timing of the stress imaging after revascularization being important sources of heterogeneity between studies.

A combination of anatomical and functional evaluations improves the prediction of cardiac event in patients with coronary artery bypass

OBJECTIVE

To study the usefulness of combined risk stratification of coronary CT angiography (CTA) and myocardial perfusion imaging (MPI) in patients with previous coronary-artery-bypass grafting (CABG).

DESIGN

A retrospective, observational, single centre study.

SETTING AND PATIENTS

204 patients (84.3% men, mean age 68.7±7.6) undergoing CTA and MPI.

MAIN OUTCOME MEASURES

CTA defined unprotected coronary territories (UCT; 0, 1, 2 or 3) by evaluating the number of significant stenoses which were defined as the left main trunk ≥50% diameter stenosis, other native vessel stenosis ≥70% or graft stenosis ≥70%. Using a cut-off value with receiver-operating characteristics analysis, all patients were divided into four groups: group A (UCT=0, summed stress score (SSS)<4), group B (UCT≥1, SSS<4), group C (UCT=0, SSS≥4) and group D (UCT≥1, SSS≥4).

RESULTS

Cardiac events, as a composite end point including cardiac death, non-fatal myocardial infarction, unstable angina requiring revascularisation and heart-failure hospitalisation, were observed in 27 patients for a median follow-up of 27.5 months. The annual event rates were 1.1%, 2%, 5.7% and 12.9% of patients in groups A, B, C and D, respectively (log rank p value <0.0001). Adding UCT or SSS to a model with significant clinical factors including left ventricular ejection fraction, time since CABG and Euro SCORE II improved the prediction of events, while adding UCT and SSS to the model improved it greatly with increasing C-index, net reclassification improvement and integrated discrimination improvement.

CONCLUSIONS

The combination of anatomical and functional evaluations non-invasively enhances the predictive accuracy of cardiac events in patients with CABG.

Impact of repeat myocardial revascularization on outcome in patients with silent ischemia after previous revascularization

OBJECTIVES

This study sought to compare the survival of asymptomatic patients with previous revascularization and ischemia, who subsequently underwent repeat revascularization or medical therapy (MT).

BACKGROUND

Coronary artery disease is progressive and recurring; thus, stress myocardial perfusion scintigraphy (MPS) is widely used to identify ischemia in patients with previous revascularization.

METHODS

Of 6,750 patients with previous revascularization undergoing MPS between January 1, 2005, and December 31, 2007, we identified 769 patients (age 67.7 ± 9.5 years; 85% men) who had ischemia and were asymptomatic. A propensity score was developed to express the associations of revascularization. Patients were followed up over a median of 5.7 years (interquartile range: 4.7 to 6.4 years) for all-cause death. A Cox proportional hazards model was used to identify the association of revascularization with all-cause death, with and without adjustment for the propensity score. The model was repeated in propensity-matched groups undergoing MT versus revascularization.

RESULTS

Among 769 patients, 115 (15%) underwent revascularization a median of 13 days (interquartile range: 6 to 31 days) after MPS. There were 142 deaths; mortality with MT and revascularization were 18.3% and 19.1% (p = 0.84). In a Cox proportional hazards model (chi-square test = 89.4) adjusting for baseline characteristics, type of previous revascularization, MPS data, and propensity scores, only age and hypercholesterolemia but not revascularization were associated with mortality. This result was confirmed in a propensity-matched group.

CONCLUSIONS

Asymptomatic patients with previous revascularization and inducible ischemia on MPS realize no survival benefit from repeat revascularization. In this group of post-revascularization patients, an ischemia-based treatment strategy did not alter mortality.

Population-based study of the use of cardiac stress imaging and referral for coronary angiography and repeated revascularization after coronary artery bypass graft surgery

OBJECTIVE

To assess stress single-photon emission computed tomography (SPECT) and stress echocardiography use after coronary artery bypass grafting (CABG) and their effect on referral for coronary angiography and revascularization.

PATIENTS AND METHODS

The referral, timing, and results of stress imaging after CABG; referral for coronary angiography and revascularization; and all-cause mortality were assessed in this longitudinal, population-based, retrospective study of 1138 Olmsted County, Minnesota, patients undergoing CABG between January 1, 1993, and December 31, 2003.

RESULTS

A total of 570 patients (50.1%) underwent a stress imaging study (341 SPECT and 229 echocardiography) during the study period. Of the 1138 patients, 372 (32.7%) were referred for coronary angiography, and 144 of those patients (12.7%) underwent repeated revascularization (132 percutaneous revascularization and 12 CABG). The median interval between CABG and the index stress imaging study was 3.0 years (25th-75th percentile, 1.2-5.7 years). The results of 75.7% (258 of 341) of the stress SPECT studies and 70.7% (162 of 229) of the stress echocardiograms were abnormal. Seventy-six of 570 patients (13.3%) referred for stress imaging underwent coronary angiography within 180 days after the stress test. Repeated coronary revascularization was performed in 25 patients (4.4%) who underwent a stress imaging study within the preceding 180 days. The 5- and 10-year survival rates in the entire study cohort (83.5% and 65.1%, respectively) were not significantly different than predicted for the age- and sex-matched Minnesota population.

CONCLUSION

Half of this community-based population of patients with CABG underwent stress SPECT or echocardiography during median follow-up of 8.9 years. Despite that approximately 75% of the results of stress imaging studies were abnormal, subsequent referral for coronary angiography within 180 days was low (13.3%), and the yield for repeated revascularization was very low (4.4%).

Utility of nuclear stress imaging for detecting coronary artery bypass graft disease

Background

The value of Single Photon Emission Computed Tomography stress myocardial perfusion imaging (SPECT-MPI) for detecting graft disease after coronary artery bypass surgery (CABG) has not been studied prospectively in an unselected cohort.

Methods

Radial Artery Versus Saphenous Vein Graft Study is a Veterans Affairs Cooperative Study to determine graft patency rates after CABG surgery. Seventy-nine participants agreed to SPECT-MPI within 24 hours of their coronary angiogram, one-year after CABG. The choice of the stress protocol was made at the discretion of the nuclear radiologist and was either a symptom-limited exercise test (n = 68) or an adenosine infusion (n = 11). The SPECT-MPI results were interpreted independent of the angiographic results and estimates of sensitivity, specificity and accuracy were based on the prediction of a graft stenosis of ≥70% on coronary angiogram.

Results

A significant stenosis was present in 38 (48%) of 79 patients and 56 (22%) of 251 grafts. In those stress tests with an optimal exercise heart rate response (>80% maximum predicted heart rate) (n = 26) sensitivity, specificity and accuracy of SPECT-MPI for predicting the graft stenosis was 77%, 69% and 73% respectively. With adenosine (n = 11) it was 75%, 57% and 64%, respectively. Among participants with a suboptimal exercise heart rate response, the sensitivity of SPECT-MPI for predicting a graft stenosis was <50%. The accuracy of SPECT-MPI for detecting graft disease did not vary significantly with ischemic territory.

Conclusions

Under optimal stress conditions, SPECT-MPI has a good sensitivity and accuracy for detecting graft disease in an unselected patient population 1 year post-CABG.

A stepwise approach to the visual interpretation of CT-based myocardial perfusion

Cardiovascular anatomic and functional testing have been longstanding and key components of cardiac risk assessment. As part of that strategy, CT-based imaging has made steady progress, with coronary computed tomography angiography (CTA) now established as the most sensitive noninvasive strategy for assessment of significant coronary artery disease. Myocardial CT perfusion imaging (CTP), as the functional equivalent of coronary CTA, is being tested in currently ongoing multicenter trials and is proposed to enhance the accuracy of coronary CTA alone. However, unlike coronary CTA that has published guidelines for interpretation and is rapidly gaining applicability in the noninvasive risk assessment paradigms, myocardial CTP is rapidly evolving, and guidance on a standard approach to its interpretation is lacking. In this article we describe a practical stepwise approach for interpretation of myocardial CTP that should add to the clinical applicability of this modality. These steps include (1) coronary CTA interpretation for potentially obstructive atherosclerosis, (2) reconstruction and preprocessing of myocardial CTP images, (3) image quality assessment and the identification of potentially confounding artifacts, (4) rest and stress image interpretation for enhancement patterns and areas of hypoattenuation, and (5) correlation of coronary anatomy and myocardial perfusion deficits. This systematic review uses already published methods from multiple clinical studies and is intended for general usage, independent of the platform used for image acquisition.

Exercise technetium 99m sestamibi single-photon emission computed tomography late after coronary artery bypass surgery: long-term follow-up

BACKGROUND AND HYPOTHESIS

The prognostic value of exercise technetium 99m sestamibi single-photon emission computed tomography (SPECT) imaging in patients with previous bypass surgery is unknown. The aim of our study was to assess the prognostic information obtained with exercise scintigraphy performed for routine follow-up or reappearance of symptoms.

METHODS

We studied 75 patients referred to our Center at a mean of 38 +/- 53 months from the revascularization procedure and prospectively followed them for 38 +/- 24 months.

RESULTS

Fifteen patients (20%) had events at follow-up: there were 4 cardiac deaths, 3 nonfatal acute myocardial infarctions, 8 late revascularization procedures (4 percutaneous transluminal angioplasty and 4 repeat bypass surgery). Univariate analysis identified a history of typical angina (p = 0.001), a clinically positive ergometric test (p = 0.009), peak exercise heart rate (p = 0.0003), percentage of maximal predicted heart rate (p = 0.0001), peak exercise double product (p = 0.048), therapy during exercise (p = 0.003), scintigraphic summed reversibility score (i.e., the summation of the segmental differences between stress and rest) (p = 0.014), as significant predictors of events. Three multivariate models were built, with clinical variables (Model 1, chi square 15.97), ergometric variables (Model 2, chi square 19.66), and with scintigraphic variables added to clinical/ergometric variables (Model 3, chi square 31.13). The scintigraphic variable selected in the model as significant predictor of events was the summed reversibility score (p = 0.008).

CONCLUSIONS

Exercise sestamibi SPECT scintigraphy provides optimal prognostic information after clinical and ergometric parameters in patients with previous bypass surgery.

Evidence based medicine: role of multidetector CT in the follow-up of patients receiving coronary artery bypass graft

PURPOSE

The aim of this study was to define the role of multidetector computed tomography (MDCT) in the follow-up assessment of patients undergoing coronary artery bypass grafting (CABG) using an evidence-based medicine (EBM) approach.

MATERIALS AND METHODS

We performed a literature search of the most reputable studies published in the period 1990-2005 on the clinical follow-up of patients after myocardial revascularisation by CABG. Relevant studies were ranked according to levels of evidence using EBM criteria. A similar search was also conducted on the Internet to identify and review the guidelines posted by the major international scientific societies.

RESULTS

A total of 29 papers meeting the basic reliability requirements of EBM were identified. The reported sensitivity and specificity for electrocardiogram (ECG) testing, stress echocardiography and radionuclide myocardial perfusion imaging were 45% and 82%, 86% and 90%, and 68% and 84%, respectively. All 16 CT studies (one retrospective, the remaining prospective) were validation studies comparing MDCT with conventional coronary angiography. The total number of patients and graft segments studied were 705 and 1,974, respectively. The total number of assessable graft segments were 62%-100%, with a sensitivity and specificity of 75%-100% and 76.9%-100%, respectively.

CONCLUSIONS

The applications of MDCT in the follow-up assessment of patients after CABG are derived from indirect evidence only. The efficacy of the method should be evaluated in randomised clinical trials comparing MDCT not only with conventional coronary angiography but also with other noninvasive stress imaging methods. On the basis of the clinical evidence reported in the literature, the indications for the use of MDCT are still limited. In our view, the completion of such randomised trials combined with the development of new-generation scanners is required to correctly define the role of MDCT in the follow-up assessment of patients who have undergone CABG.

Midterm follow-up of patients receiving radial artery as coronary artery bypass grafts using 16-detector-row CT coronary angiography

PURPOSE

The study was undertaken to evaluate the 3-year outcome of patients undergoing coronary artery bypass grafting (CABG) involving the use of the radial artery (RA) in comparison with the left internal mammary artery (LIMA) and saphenous vein (SV) grafts by using 16-slice multidetector computed tomography (MDCT).

MATERIALS AND METHODS

Fifty-one patients underwent electrocardiogram (ECG)-gated 16-MDCT 32+/-4 months after surgery. A total of 50 LIMA grafts, 55 SV grafts and 51 RA grafts were studied. Approximately 68.6% or RAs were free, 21.5% sequential and 9.8% composite. Grade 0 was defined as complete patency, grade 1 as focal stenosis (>70%) and grade 2 as graft occlusion. The Fisher exact test was used to analyse variables (p<0.05 significant). Concordance between readers for the detection of patency was calculated by the kappa-value.

RESULTS

LIMA had the best patency rate (94.0%), followed by SV (83.6%) and RA (74.5%). Regarding RA, the patency rate by territory was 79.4% in the left circumflex coronary artery (LCX), 72.7% in the left anterior descending (LAD) and 50% in the right coronary artery (RCA); the occlusion rate was 20.0% among free grafts, 18.2% among sequential grafts and 20.0% among composite grafts. The kappa-value was 0.86.

CONCLUSIONS

Sixteen-slice MDCT scanners enable accurate analysis of CABG status and are a useful noninvasive diagnostic tool for midterm clinical follow-up of patients who have undergone CABG involving the use of RA.

Role of nuclear cardiology in advancing cardiac surgery

Cardiac surgeons are commonly faced with issues regarding the balance between the potential risk and the potential benefit of a surgical procedure. Nuclear cardiology procedures [myocardial perfusion SPECT (MPS) and positron emission tomography (PET)] provide the surgeon with objective information that augments standard clinical and angiographic assessments with respect to diagnosis, prognosis, and potential benefit from intervention. Development of the technology and methodology of gated MPS acquisition and interpretation allows assessment of the extent and severity of hypoperfused but viable myocardium, as well as global LVEF and LV volume measurements, diastolic function, and LV geometry. With PET, myocardial metabolism and blood flow reserve can also be measured. This chapter provides insight into the current evidence regarding settings in which nuclear cardiology procedures are helpful to the surgeon in assessment of patients having or being considered for cardiac surgery in the setting of coronary artery disease (CAD). Overall, a risk-benefit approach to MPS results is proposed, with principal focus on identifying patients at risk for major cardiac events who may benefit from a surgical procedure.

Use of Stress Testing Early After Coronary Artery Bypass Graft Surgery

The American College of Cardiology/American Heart Association guidelines for exercise testing do not take a position regarding the utility of routine stress testing after coronary artery bypass grafting (CABG). Our purposes were (1) to document the patterns of use of stress testing after CABG and (2) to establish whether the choice of stress testing strategy is associated with clinical characteristics of patients. The Routine versus Selective Exercise Treadmill Testing after Coronary Artery Bypass Graft Surgery (ROSETTA-CABG) Registry is a prospective multicenter study that examined the use of stress testing after CABG among 395 patients at 16 clinical centers in 6 countries. During the 12 months after CABG, 37% of patients underwent stress testing (range across centers 0% to 100%). Among patients who underwent stress testing, 24% had a clinical indication and 76% had it as a routine follow-up. A total of 65% of stress tests involved exercise treadmill testing alone, 17% involved stress nuclear perfusion imaging, 13% involved stress echocardiographic imaging, and 5% involved other types of stress tests, such as positron emission tomographic scans. The first stress test was performed at a median of 13 weeks after CABG, with 20% of patients having second tests at a median of 28 weeks and 6% having additional tests at a median of 34 weeks. Univariate and multivariate analyses demonstrated that the chief determinant of using routine stress testing was the clinical center. In conclusion, these results suggest that there is little consensus on the appropriate use of stress testing soon after CABG. Practice patterns vary widely; poorly diagnostic tests are used routinely; and the clinical center at which the procedure is performed, rather than the clinical characteristics of the patient, determines the use of stress testing after CABG.

Diagnostic accuracy of myocardial perfusion imaging in a study population without post-test referral bias

BACKGROUND

Most previous studies on the accuracy of myocardial perfusion imaging (MPI) are hampered by post-test referral bias, in that referral for coronary angiography was influenced by the MPI result. In this way, patients with a normal MPI result less frequently underwent catheterization, a tendency supposed to cause an underestimation of test specificity and an overestimation of test sensitivity.

METHODS AND RESULTS

MPI by use of a gated dual-isotope protocol was undertaken before angiography in 357 patients referred for angiography for suspected stable angina pectoris. The MPI reports were kept secret to prevent post-test referral bias. The MPI study was normal in 215 patients (60%) and showed reversible perfusion abnormalities in 118 (33%) and fixed defects in 24 (7%). Angiography was normal in 231 patients (65%) and revealed 1 or more significant stenoses in 126 (35%). With angiography as the reference, the sensitivity and specificity of MPI for detecting significant coronary artery stenosis were 75% and 79%, respectively.

CONCLUSIONS

In this prospective study without post-test referral bias, we found a lower sensitivity and slightly higher specificity than in studies with post-test referral bias. The imperfect accuracy may reflect differences between anatomic and physiologic imaging.

A New Anatomic Score for Prognosis After Cardiac Catheterization in Patients with Previous Bypass Surgery

OBJECTIVES

The purpose of this study was to determine the value of a new anatomic score for prognosis after diagnostic catheterization in patients with previous coronary artery bypass grafting (CABG).

BACKGROUND

Previous CABG patients comprise a growing proportion of patients with coronary artery disease (CAD). Whereas prognostic scores are available to adjust for native CAD, there are no comparable scores for patients with previous CABG.

METHODS

We studied 3,178 previous CABG patients (2,729 in a training set) who underwent cardiac catheterization. With a Cox model to develop relative weights in the training set, we created a graft index that adjusted native anatomy for territories with grafts free of significant (> or =75%) stenoses. Scaling the regression coefficients by the maximum coefficient created an index ranging from 0 to 100, where 100 was three-vessel CAD with no patent grafts.

RESULTS

The graft index was significantly associated with all-cause death (chi-square = 121.9, p < 0.001). In combined models, the index was more strongly associated with all-cause death than either number of diseased vessels (chi-square = 68.0 and 1.7, respectively) or the Duke CAD index (chi-square = 54.3 and 9.5, respectively). In models for death using an independent validation set, the index was also associated more strongly than either native disease descriptors. In a model including other clinical variables, the graft index remained significantly associated with all-cause death (chi-square = 40.1, p < 0.001).

CONCLUSIONS

For previous CABG patients, the Duke graft index was significantly more associated with prognosis than native anatomy alone and quantifies the effect of patent grafts on survival. This tool has the potential to help determine prognosis and inform the referral of post-CABG patients to repeat revascularization procedures.

Prediction of death or myocardial infarction by exercise single photon emission computed tomography perfusion scintigraphy in patients who have had recent coronary artery stenting

BACKGROUND

Although practice guidelines do not recommend routine exercise testing of patients after coronary stenting, several small studies have suggested that stress myocardial perfusion imaging can provide prognostic information about future adverse cardiac events. We sought to determine if exercise nuclear testing provides independent prognostic information in patients after coronary stenting.

METHODS

We analyzed the outcomes of 370 patients who underwent dual isotope exercise nuclear scintigraphy at least 1 month after coronary stenting and had testing between April 1996 and May 2002. Patients were classified according to presence or absence of any ischemia. The primary endpoint was all-cause mortality or myocardial infarction (MI) during a median of 30 months (range 6-59) of follow-up.

RESULTS

There were 86 patients (23%) who had ischemia. Major events--death or MI--occurred in 62 patients including 22 deaths. Among patients with no ischemia, the 30-month event rate was 9.1%, whereas among patients with ischemia, the event rate was 17.0% (P = .001). After adjusting for age, sex, standard cardiac risk factors, cardiac history, left ventricular ejection fraction, angiographic findings, procedural variables, exercise capacity, and heart-rate dynamics, the presence of scintigraphic evidence of ischemia predicted death or MI (adjusted hazard ratio 2.08, 95% CI 1.21-3.56, P = .008). The presence of ischemia similarly predicted events in asymptomatic patients (adjusted hazard ratio 2.19, 95% CI 1.17-4.11, P = .015).

CONCLUSIONS

In patients with recent coronary stent placement, reversible nuclear perfusion defects independently predicted risk of death or MI.

Prognostic value of dobutamine stress echocardiography in patients with previous coronary revascularisation

OBJECTIVE

To assess the prognostic value of dobutamine stress echocardiography (DSE) in patients with previous myocardial revascularisation.

DESIGN

Prospective study.

SETTING

Tertiary referral centre in Rotterdam, the Netherlands.

PATIENTS

332 consecutive patients with previous percutaneous or surgical coronary revascularisation underwent DSE. Follow up was successful for 331 (99.7%) patients. Thirty eight patients who underwent early revascularisation (<or= 3 months) after the test were excluded from analysis.

MAIN OUTCOME MEASURES

Cox proportional hazards regression models were used to identify independent predictors of the composite of cardiac events (cardiac death, non-fatal myocardial infarction, and late revascularisation).

RESULTS

During a mean (SD) of 24 (20) months, 37 (13%) patients died and 89 (30%) had at least one cardiac event (21 (7%) cardiac deaths, 11 (4%) non-fatal myocardial infarctions, and 68 (23%) late revascularisations). In multivariate analysis of clinical data, independent predictors of late cardiac events were hypertension (hazard ratio (HR) 1.7, 95% confidence interval (CI) 1.1 to 2.6) and congestive heart failure (HR 2.1, 95% CI 1.3 to 3.2). Reversible wall motion abnormalities (ischaemia) on DSE were incrementally predictive of cardiac events (HR 2.1, 95% CI 1.3 to 3.2).

CONCLUSIONS

Myocardial ischaemia during DSE is independently predictive of cardiac events among patients with previous myocardial revascularisation, after controlling for clinical data.

Myocardial perfusion scintigraphy: the evidence

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Discrepancy between myocardial ischemia and luminal stenosis in patients with left internal mammary artery grafting to left anterior descending coronary artery

BACKGROUND

Left internal mammary artery (LIMA) grafting to the left anterior descending artery (LAD) is known to have long-term patency. However, myocardial ischemia in the territories supplied by LIMA to LAD is still demonstrated. The aim of this study is to examine the relationships between the extent, location, and clinical outcome of myocardial ischemia in LAD territories (ILAD) by use of myocardial perfusion imaging (MPI) and angiographic characteristics of such a bypass conduit.

METHODS AND RESULTS

We studied 38 consecutive patients with prior coronary artery bypass grafting who showed stress-induced ischemia in LIMA to LAD territories by MPI single photon emission computed tomography between the years 1996-2000. All patients underwent quantitative coronary angiography within 6 months of the nuclear study. Single photon emission computed tomography parameters of ILAD were assessed by location (septum, apex, anterior, and anterolateral) and included extension score (1-4 per patient), severity score (0-3 per territory), and total sum score. LIMA to LAD quantitative coronary angiography parameters included minimal lumen diameter, lesion length, reference diameter, and diameter stenosis (percentage). LAD and LIMA diameters and ratio (in normal segments) were determined within 10 mm proximal and distal to the anastomotic site. The study group was compared with 18 control subjects without ischemia or stenosis treated with LIMA to LAD. The patients were followed up for cardiac death at an interval of 3.2 +/- 1.5 years from the time of MPI testing. The patients' mean age was 66 +/- 12 years (31 men and 7 women); the mean period after surgery was 6.2 +/- 1.5 years. The ILAD distribution was as follows: septum, 12 (32%); apex, 20 (52%); anterior, 24 (63%); and anterolateral, 18 (47%). The mean extension score was 1.9 +/- 1.0, and the mean total sum score was 3.4 +/- 2.3. Of 38 patients with ILAD, only 17 (45%) had greater than 50% luminal stenosis (2 LIMA and 15 anastomosis or distal). Among clinical variables during stress testing, the prevalence of angina was significantly higher in the luminal stenotic patients versus patients without stenosis (P =.04). A significant correlation was found between anterior wall ischemia and reference diameter (r = -0.7, P =.002) and between total sum score and minimal lumen diameter (r = -0.48, P =.05). Of note, the LAD-to-LIMA ratio was significantly lower in patients with ILAD and without luminal stenosis compared with the control group (0.73 +/- 0.16 vs 0.87 +/- 0.15, P =.004). Cardiac death occurred in 8 patients (21%), 5 patients with luminal stenosis versus 3 patients without stenosis (P = not significant).

CONCLUSIONS

In patients with LIMA to LAD anastomosis, myocardial ischemia could occur even without angiographic luminal stenosis and apparently reflects a mismatch between LAD and LIMA diameters at distal anastomotic sites. Regarding the similar prevalence of cardiacdeath, invasive evaluation and aggressive treatment are recommended in all patients with ischemia in LIMA/LAD territories.

Increased resting Tl-201 lung-to-heart ratio is associated with invasively determined measures of left ventricular dysfunction, extent of coronary artery disease, and resting myocardial perfusion abnormalities

BACKGROUND

Stress lung thallium 201 uptake correlates with left ventricular (LV) dysfunction and extent of coronary artery disease (CAD). Although Tl-201 is used less commonly for stress imaging, dual-isotope stress and viability protocols continue to use Tl-201 for rest imaging. We sought to investigate the association between increased resting Tl-201 lung-to-heart ratio (LHR) and hemodynamic indices of LV dysfunction, indices of myocardial perfusion, and extent of CAD.

METHODS AND RESULTS

Over a 1-year period, we identified 192 consecutive patients who underwent dual-isotope stress perfusion imaging and cardiac catheterization within 30 days, without interim events or revascularization. Resting LHR was measured, and its association with invasively measured hemodynamic parameters, extent of CAD, and indices of myocardial perfusion at rest and stress was examined. Increased resting Tl-201 LHR was weakly but significantly associated with lower LV ejection fraction (EF) (r = 0.209, P <.05), higher pulmonary capillary wedge pressure (r = 0.25, P <.005), and LV end-diastolic pressure (r = 0.215, P <.01) but not with pulmonary artery systolic pressure. Increased LHR was also weakly associated with rest perfusion abnormalities including the sum rest score (r = 0.271, P <.001) and number of abnormally perfused segments (r = 0.25, P <.001) bud did not correlate with stress perfusion indices or ischemic burden. The 76 patients (40%) with LHR greater than 0.5 were more likely to have LVEF lower than 40% and 3-vessel/left main CAD.

CONCLUSIONS

Increased rest Tl-201 LHR is weakly associated with higher LV end-diastolic pressure and pulmonary capillary wedge pressure and lower LVEF. LHR is also associated with the extent of previously infarcted myocardium and may indicate the presence of 3-vessel/left main CAD.

Risk assessment by myocardial perfusion imaging for coronary revascularization, medical therapy, and noncardiac surgery

Stress myocardial perfusion imaging (MPI) has become an important tool in risk stratification of patients with known coronary artery disease. A normal myocardial perfusion scan has a high negative predictive value and is associated with low annual mortality rate (< 1%). Patients with extensive ischemia (> 20% of the left ventricle), defects in more than 1 coronary vascular territory, transient or persistent left ventricular cavity dilation, and ejection fraction less than 45% have a high annual mortality rate (> 3%). Those patients should undergo coronary revascularization whenever feasible, as the cardiac event rate increases in proportion to the magnitude of the jeopardized myocardium. Stress MPI can be used to demonstrate ischemia in patients with symptoms early after coronary artery bypass surgery (< 5 years) or in those without symptoms late (>/= 5 years) after coronary artery bypass surgery. With respect to patients who underwent percutaneous interventions, stress MPI can help detect in-stent restenosis early after the intervention (3-6 months) or assess the progression of native coronary disease afterward. Since preliminary data suggest that a reduction in the perfusion defect size may translate to a reduction of coronary events, stress MPI can help assess the efficacy of medical management of coronary disease. Finally, stress MPI is indicated for perioperative cardiac risk stratification for noncardiac surgery in patients with intermediate risk predictors (mild angina, prior myocardial infarction or heart failure symptoms, diabetes mellitus, renal insufficiency) and poor functional capacity or in those who undergo high-risk surgery with significant implications in further preoperative management.

Prognostic value of exercise cardiac tomography performed late after percutaneous coronary intervention in symptomatic and symptom-free patients

The long-term prognostic value of single-photon emission computed tomography (SPECT) performed late after percutaneous coronary intervention (PCI) has not been extensively evaluated. Moreover, the role of myocardial ischemia at SPECT in symptom-free patients after PCI is not clear. This study was designed to determine the long-term prognostic value of SPECT in predicting cardiac events after PCI in symptomatic and symptom-free patients. Exercise technetium-99m sestamibi SPECT was performed in 206 patients between 12 and 18 months after PCI. All patients were followed for a mean period of 37 +/- 16 months. Cardiac death, nonfatal myocardial infarction, and late revascularization procedures were considered to be events. Myocardial ischemia at SPECT was detectable in 44 patients. During follow-up, 24 patients experienced events (cardiac death in 4 patients, myocardial infarction in 10, and late revascularization in 10). At univariate analysis, the summed stress score (p <0.05) and summed difference score (p <0.001) were significant predictors of cardiac events. Event-free survival curves showed a higher event rate in patients with than without ischemia (p <0.001). The occurrence of cardiac events was higher in the presence of ischemia at SPECT in symptomatic and symptom-free patients (both p <0.001). The results of this study demonstrate that the extent and severity of myocardial ischemia at exercise SPECT performed between 12 and 18 months after PCI predicts cardiac events during long-term follow-up in symptomatic and symptom-free patients.

Long-term outcome of a residual scar from myocardial infarction after coronary artery bypass grafting: a 100-month study using myocardial perfusion scintigraphy

The prognosis for patients with a residual scar from myocardial infarction (MI) after coronary artery bypass grafting surgery (CABG) has not been fully evaluated, so the present study retrospectively evaluated such patients with stress myocardial single photon emission computed tomography (SPECT) at 100 months after CABG. The study group consisted of 24 subjects (23 males, 1 female; mean age, 59+/-9 years) in whom CABG had been performed more than 100 months (mean follow-up period 135+/-25 months) previously. The 24 subjects were classified into 3 groups according to their summed stress score (SSS) and summed reversibility score (SRS) in the early period after CABG. Eight subjects with MI (SSS> or =2 and SRS<2) were classified into the group MI, 8 subjects with ischemic myocardium (SSS> or =2 and SRS> or =2) was classified into the group RE, and 8 subjects with normal perfusion (SSS<2 and SRS<2) was classified into group N. None of the subjects in group MI required revascularization. Cardiac events occurred in 4 of the group RE patients and all required revascularization. As to the SPECT scoring system, the long-term SSS of group MI (6.4+/-3.1) was not different from that in the early periods (4.3+/-4.0; NS). However, the long-term SSS values of group RE (8.8+/-6.2) were significantly greater than those soon after CABG (3.4+/-1.8; p=0.03). In group N, there was also no difference in the SSS values between the early period (0.3+/-0.5) and the long-term period (0.0+/-0.0; NS). Patients with a residual scar from MI in the early period after CABG did not worsen over a period of 100 months. Moreover, there was no significant difference in the SPECT score in the segment with the residual scar in the short or long term after CABG. However, the extent of reversibility was directly associated with the presence of clinical events. Therefore scintigraphic imaging remains an important and clinically relevant risk stratification tool. Stress myocardial SPECT, early after CABG, can be used to predict the possibility of future cardiac events or the need for revascularization.

Prognostic value of exercise echocardiography in patients after coronary artery bypass surgery

To assess the prognostic value of exercise echocardiography in patients with prior coronary artery bypass surgery, follow-up was obtained in 718 patients (591 men [82%] and 127 women [18%], aged 67 +/- 9 years) who underwent clinically indicated exercise echocardiography 5.7 +/- 4.7 years after coronary bypass surgery. Resting wall motion abnormalities were present in 479 patients (67%). New or worsening wall motion abnormalities developed with exercise in 366 patients (51%). During a median follow-up of 2.9 years, cardiac events included cardiac death in 36 patients and nonfatal myocardial infarction in 40 patients. The addition of the exercise echocardiographic variables, abnormal left ventricular end-systolic volume response and exercise ejection fraction to the clinical, resting echocardiographic and exercise electrocardiographic model provided incremental information in predicting cardiac events (chi-square 37 to chi-square 42, p = 0.02) and cardiac death (chi-square 38 to chi-square 43, p <0.02). Exercise echocardiography provides prognostic information in patients after coronary artery bypass surgery, incremental to clinical, rest echocardiographic, and exercise electrocardiographic variables.

Prognostic value of 201Tl myocardial scintigraphy after coronary artery bypass grafting

BACKGROUND

201Tl myocardial scintigraphy (201Tl SPECT) is of strong prognostic value in various populations with suspected or known coronary artery disease. However, its value in patients with coronary artery bypass grafting (CABG) is not fully assessed.

METHODS

We examined 115 consecutive patients to determine the relation between clinical data/stress 201Tl SPECT performed 5+/-3 years after CABG, and subsequent cardiac events.

RESULTS

Thirteen patients (11%) had stress-induced angina, 22 (19%) had electrical positivity, and 97 (84%) had abnormal scintigraphy, including 62 (54%) with reversible defects. During follow-up (35+/-22 months), there were nine cardiac deaths, seven myocardial infarctions, and 20 revascularization procedures. Multivariate Cox analysis identified the delay between CABG and scintigraphy (P<0.01, relative risk (RR) = 1.01), the extent of stress 201Tl defects (P = 0.04, RR = 1.18), and increased stress 201Tl lung uptake (P = 0.03, RR = 3.56) as significant predictors of cardiac deaths/infarctions. Delay between CABG and scintigraphy (P < 0.001, RR = 1.01), the extent of stress 201Tl defects (P = 0.03, RR = 1.15), and that of reversible defects (P = 0.05, RR = 1.13) were the only significant predictors of total events.

CONCLUSIONS

Besides the delay between CABG and scintigraphy, the scintigraphic parameters were the only significant and additive predictors of cardiac events in 115 patients with CABG.

Principal uses of myocardial perfusion scintigraphy in the management of patients with known or suspected coronary artery disease

The use of myocardial perfusion single photon emission computed tomography (SPECT) has undergone considerable expansion and evolution over the past 2 decades. Although myocardial perfusion imaging was first conceived as a noninvasive diagnostic tool for determining the presence or absence of coronary artery disease, its prognostic value is now well established. Thus, identification of patients at risk for future cardiac events has become a primary objective in the noninvasive evaluation of patients with chest pain syndromes and among patients with known coronary artery disease. In particular, the ability of myocardial perfusion SPECT to identify patients at low (< 1%), intermediate (1% to 5%) or high (> 5%) risk for future cardiac events is essential to patient management decisions. Moreover, previous studies have conclusively shown the incremental prognostic value of myocardial perfusion SPECT over clinical and treadmill exercise data in predicting future cardiac events. This report addresses the current role and new developments, with respect to the use of myocardial perfusion imaging, in determining patient risk for cardiac events and the cost-effective integration of such information into patient management decisions.

When to stress patients after coronary artery bypass surgery? Risk stratification in patients early and late post-CABG using stress myocardial perfusion SPECT: implications of appropriate clinical strategies

OBJECTIVES

The study compared the prognostic significance of myocardial perfusion single-photon emission computed tomography (SPECT) (MPS) in patients early and late after coronary artery bypass graft surgery (CABG).

BACKGROUND

The long-term effectiveness of CABG is limited by graft stenosis. The greatest incidence of graft occlusion occurs between five and eight years after surgery. However, little is known regarding the appropriate time to stress patients post-CABG with respect to risk stratification.

METHODS

We identified 1,765 patients, who underwent MPS 7.1 +/- 5.0 years post-CABG. All patients underwent rest T1-201/stress Tc-99m sestamibi MPS and were followed up > or =1 year after testing. Patients with early CABG or PTCA (<60 days after MPS) were censored. The prognostic population consisted of 1,544 patients. A semiquantitative visual analysis employing a 20-segment model was used to define summed stress score (SSS), summed rest score (SRS), summed difference score (SDS), and the number of nonreversible segments (NRS).

RESULTS

During follow-up, 53 cardiac deaths (CD) occurred. There was a significant increase in annual CD rates as a function of SSS. A multivariate analysis identified age, ischemia (SDS), and infarct size (NRS) as independent predictors of CD. Nuclear variables added incremental value to prescan information. The annual CD rate was relatively low (1.3%) in patients < or =5 years post-CABG. In this subgroup only age and infarct size (NRS) were predictive of CD.

CONCLUSION

MPS is strongly predictive of subsequent CD in post-CABG patients and adds incremental value over clinical and treadmill test information. Our data suggest that symptomatic patients < or =5 years and all patients >5 years post-CABG may benefit from testing.

Long-term prognostic value of Duke treadmill score and exercise thallium-201 imaging performed one to three years after percutaneous transluminal coronary angioplasty

The value of exercise nuclear perfusion imaging performed beyond the 6-month restenosis window for percutaneous transluminal coronary angioplasty (PTCA) has not been explored. This study evaluates the long-term prognostic value of exercise thallium (Tl)-201 imaging after PTCA. We studied the late outcome of a series of 211 patients with tomographic Tl-201 exercise studies performed between 1 to 3 years after PTCA. Follow-up was 96% complete at a median duration of 7.3 years. Most (73%) had 1- or 2-vessel coronary artery disease and normal left ventricular function and 193 (91%) had successful PTCA. Two thirds of the patients were symptomatic at the time of testing. The mean Duke score was 5+/-6 and 125 (60%) patients had a low-risk Duke score. Mean summed stress score was 50+/-9 and mean summed reversibility score was 3+/-4. The 5-year overall survival was 95%, yielding a low annual mortality rate of 1%/year. The summed stress score exhibited a significant association (p = 0.047) with the end point of cardiac death or myocardial infarction. The Duke score was predictive of the combination end point of hard and soft cardiac events (p = 0.002). This study demonstrates that exercise Tl-201 perfusion imaging performed 1 to 3 years after PTCA was predictive of cardiac events.

The role of nuclear cardiology in clinical decision making

This review suggests that the field of nuclear cardiology is alive, well, and thriving, providing relevant information that aids in everyday clinical decision making for nuclear medicine and referring physicians alike. Despite the competition from other modalities, the clinically appropriate applications of nuclear cardiology techniques are likely to increase. The foundation of this optimism is based on the vast amount of data documenting cost-effective clinical applications for diagnosis, risk stratification, and assessing therapy in both chronic and acute coronary artery disease (CAD), the powerful objective quantitative analysis of perfusion and function provided by the technique, and the increasing general availability of the approach.

Increased stress right ventricular activity on dual isotope perfusion SPECT: a sign of multivessel and/or left main coronary artery disease

OBJECTIVES

This study sought to determine the anatomic and physiologic correlates of increased right ventricular (RV) activity on exercise single-photon emission computed tomography (SPECT) perfusion imaging in patients with coronary artery disease (CAD).

BACKGROUND

Because SPECT perfusion imaging delineates relative myocardial blood flow, patients with global left ventricular (LV) hypoperfusion but normal RV perfusion may have increased relative RV tracer uptake as an indicator of multivessel CAD.

METHODS

Rest thallium-201 and exercise 99mTc-sestamibi or 99mTc-tetrofosmin SPECT perfusion images were analyzed for peak RV and LV activity (RV:LV index) in 315 patients, including 240 patients with documented CAD, 39 patients with no significant CAD on arteriography, and a "normalcy" group of 36 patients with a low pre- and posttest probability of CAD.

RESULTS

Resting RV:LV perfusion index ranged from 0.32 to 0.34 in each group, increasing to 0.36 with exercise in control and normalcy groups. CAD patients with the highest exercise RV:LV were those with severe left main CAD (or "left main equivalent"), with a lesser degree of proximal right CAD (0.51, n = 14, p < 0.001 vs. other groups). An exercise RV:LV >0.42 with a exercise:rest ratio >1.2 was present in 93% patients with this pattern of CAD, but was absent in 97% of the normalcy group, 92% of patients without significant angiographic CAD, and 100% of patients with proximal right CAD tighter than stenoses in the left system.

CONCLUSIONS

Increased RV:LV activity exercise may occur in patients with acute RV strain, but is otherwise an indicator of exercise-induced RV:LV perfusion imbalance associated with severe CAD, particularly high-grade left main with less severe proximal right CAD.

Prognosis of "clandestine" myocardial ischemia, silent myocardial ischemia, and angina pectoris in medically treated patients

The aim of this study was to assess the prognosis of medically treated patients with "clandestine" myocardial ischemia (perfusion defect without angina and no ST depression > 1 mm during exercise test) compared to those with silent myocardial ischemia (ST-segment depression > 1 mm, without angina) and those with angina pectoris. One hundred twelve patients without previous myocardial infarction were included. All patients underwent a symptom-limited exercise test on a bicycle ergometer, myocardial perfusion technetium-99m-methoxy-isobutyl-isonitrile single-photon emission computed tomography (SPECT), and coronary angiography. They were classified into 3 groups (angina group, 34 patients; silent group, 20 patients; and the clandestine group, 58 patients). The mean follow-up was 3.6 years (range 6 months to 5.5 years). Patients with clandestine ischemia had a lower scintigraphic and angiographic score than patients with silent ischemia (25+/-8 vs 31+/-9 and 24+/-8 vs 29+/-7, p = 0.008, respectively), but the prognosis was similar. Only angina and severe reversible SPECT defects were predictive for cardiac events: death + myocardial infarction + revascularization. We conclude that in medically treated patients without previous myocardial infarction, angina and severe reversible SPECT defects are predictive for cardiac events only when the need for revascularization is included as a cardiac event.

Dobutamine-atropine stress myocardial perfusion SPECT imaging in the diagnosis of graft stenosis after coronary artery bypass grafting

OBJECTIVE

To assess the accuracy of dobutamine stress myocardial perfusion single photon emission computed tomographic imaging (SPECT) for the diagnosis of vascular stenosis after coronary artery bypass grafting (CABG).

BACKGROUND

Exercise thallium scintigraphy is a clinically useful method for the diagnosis of graft stenosis after CABG. Although dobutamine perfusion scintigraphy is an alternative method for the evaluation of patients with limited exercise capacity, its value in the diagnosis of vascular stenosis after CABG has not been studied.

METHODS

Dobutamine (up to 40 lg/kg/min)-atropine (up to 1 mg) stress test in conjunction with myocardial perfusion SPECT imaging (201T1 or 99m technetium sestamibi [MIBII) was performed in 71 patients (mean age 58 9 years, 57 men) with limited exercise capacity referred for evaluation of myocardial ischemia 3.7 3.5 years after CABG. Significant vascular stenosis was defined as >50% luminal diameter stenosis of a graft or a native nongrafted coronary artery and was predicted on the basis of reversible perfusion abnormalities.

RESULTS

Significant vascular stenosis was detected in 52 patients. Sensitivity, specificity, and accuracy of reversible perfusion defects at dobutamine SPECT for the overall diagnosis of vascular stenosis were 81%, confidence interval (CI) 72 to 90, 79%, CI 69 to 88, and 80%, CI 71 to 90, respectively. Significant vascular stenosis was detected in 73 arterial regions. Sensitivity, specificity, and accuracy of dobutamine SPECT for the diagnosis of regional vascular stenosis were 66%, CI 58 to 74, 83%, CI 76 to 89, and 74%, CI 67 to 81, respectively. Patients with multivessel stenosis had a higher number of ischemic segments (1.6 + 1.3 vs 1 + 1, P < .05) and ischemic perfusion score (3.2 2.7 vs 2.2 + 2.3, P < .05) than patients with single-vessel stenosis, respectively. Significant graft stenosis was detected in 67 graft regions. Sensitivity, specificity, and accuracy of dobutamine SPECT for the diagnosis of regional graft stenosis were 64%, CI 56 to 73, 85%, CI 78 to 91, and 74%, CI 66 to 82, respectively.

CONCLUSION

Dobutamine stress myocardial perfusion SPECT imaging is a useful method for the diagnosis of significant vascular stenosis after CABG in patients with limited exercise capacity.

Prognostic value of exercise thallium-201 imaging performed within 2 years of coronary artery bypass graft surgery

OBJECTIVES

We sought to determine the prognostic capabilities of exercise thallium (Tl)-201 tomographic imaging performed relatively early (within 2 years) after coronary artery bypass graft surgery (CABG).

BACKGROUND

Exercise testing is commonly performed after CABG, but few data exist demonstrating its prognostic value in this setting.

METHODS

Four hundred eleven patients were followed up for a median duration of 5.8 years. Eleven prospectively chosen clinical, exercise and Tl-201 variables were tested for their associations with outcome end points by means of proportional hazards regression models.

RESULTS

During follow-up there were 60 deaths from any cause, 53 initial cardiac deaths or nonfatal myocardial infarctions (MIs) and 22 late (>3 months after the Tl-201 study) revascularization procedures. The number of abnormal Tl-201 segments on the postexercise image was the only variable in the multivariate analyses to show a significant association with all three outcome end points: chi-square 7.3, p = 0.007 for overall mortality; chi-square 8.1, p = 0.004 for cardiac death or MI; chi-square 7.8, p = 0.005 for any cardiac event. Other independent predictors of outcome were exercise duration (chi-square 10.7, p = 0.001) and age (chi-square 3.9, p = 0.049) for overall mortality and exercise angina score (chi-square 8.7, p = 0.003) for cardiac death or MI. The 5-year survival rate free of cardiac death or MI was 93% for patients without angina and a normal image or small postexercise perfusion defect versus 71% for patients with angina and a medium or large defect.

CONCLUSIONS

Exercise Tl-201 imaging performed within 2 years of CABG can stratify patients into low and high risk subgroups.

Prediction of death and myocardial infarction by screening with exercise-thallium testing after coronary-artery-bypass grafting

BACKGROUND

The role of myocardial-perfusion imaging in calculating risk in symptom-free patients who have had coronary-artery-bypass grafting (CABG) is unclear. Practice guidelines have argued against routine screening of these patients. We sought to find out the independent and incremental prognostic value of exercise thallium-201 single-photon-emission computed tomography (SPECT) for prediction of death and non-fatal myocardial infarction (MI) in these patients.

METHODS

Analyses were based on 873 symptom-free patients undergoing symptom-limited exercise thallium-201 SPECT between September, 1990, and December, 1993. All had undergone CABG and none had recurrent angina or other major intercurrent coronary events. Exercise and thallium-perfusion variables were analysed to determine their prognostic importance during 3 years of follow-up.

FINDINGS

Myocardial-perfusion defects were noted in 508 (58%) patients. There were 57 deaths and 72 patients had major events (death or non-fatal MI). Patients with thallium-perfusion defects were more likely to die (9% vs 3%, p=0.0004) or suffer a major event (11% vs 4%, p=0.0002). Reversible defects were also predictive of death (12% vs 5%, p=0.002) and major events (13% vs 7%, p=0.004). The exercise variable with the strongest predictive power was an impaired (< or = 6 METs [measure of oxygen consumption equal to 3.5 mL/kg/min]) exercise capacity; poor exercise capacity was predictive of death (18% vs 4%, p<0.0001) and death or non-fatal MI (19% vs 5%, p<.00001). After adjusting for baseline clinical variables, surgical variables, time elapsed since CABG, and standard cardiovascular risk factors, thallium-perfusion defects remained predictive of death (adjusted relative risk 2.78, 95% CI 1.44-5.39) and major events (2.63, 1.49-4.66). Similarly, impaired exercise remained strongly predictive of death (4.16, 2.38-7.29) and major events (3.61, 2.22-5.87) after adjusting for confounders.

INTERPRETATION

In this group of patients who were symptom-free after CABG, thallium-perfusion defects and impaired exercise capacity were strong and independent predictors of subsequent death or non-fatal MI. Recommendations against routine screening exercise myocardial-perfusion studies in this setting should be reconsidered.

Utility of stress single-photon emission computed tomography (SPECT) perfusion imaging in predicting outcome after coronary artery bypass grafting

Previous studies have examined the predictors of outcome in medically treated patients with coronary artery disease (CAD). There is limited information on predictors of outcome after coronary artery bypass grafting (CABG). This study examined the predictors of outcome of 255 patients with CAD, at a mean time of 5 years after CABG for angina pectoris. The 255 patients underwent coronary angiography and stress single-photon emission computed tomography (SPECT) myocardial perfusion imaging after CABG. During a mean follow-up of 41 +/- 28 months after stress testing, there were 34 hard events (24 cardiac deaths and 10 nonfatal myocardial infarctions). The hemodynamics during stress testing, and age and gender were not predictors of events. The SPECT variables of multivessel perfusion abnormality, perfusion deficit size, and increased lung thallium uptake were predictors of death and total events by uni- and multivariate survival analysis. There were 14 events in 45 patients (31%) with multivessel abnormality and increased lung thallium uptake, 14 events in 101 patients (14%) with either multivessel abnormality or increased lung uptake, and 6 events in 109 patients (6%) with neither of these 2 variables (p = 0.0001). The annual mortality and total event rates were 7.5% and 9.5% with both variables, 3.4% and 4.3% with either variable, and 0.6% and 1.7% with neither of the variables (p = 0.01). Thus, stress SPECT perfusion imaging is useful to stratify patients after CABG into low, intermediate, and high risk groups for future cardiac events.

Actuarial outcome after catheter balloon commissurotomy in patients with mitral stenosis

BACKGROUND

The goal of the present study was to determine the intermediate-term survival and the independent predictors of survival and event-free survival for patients who undergo catheter balloon commissurotomy (CBC).

METHODS AND RESULTS

CBC for the treatment of mitral stenosis was performed in 132 patients from 1986 through 1994. The use of CBC increased the mitral valve area (MVA) from 1.0 +/- 0.3 to 1.9 +/- 0.6 cm2 (P < .001). There were six early deaths (4.5%) up to 1 month after CBC ("hospital" deaths). In the past 4.5 years, there have been no hospital deaths. Four late deaths occurred after elective mitral valve replacement (MVR). Actuarial 7-year survival was 95 +/- 1%; when mortality after MVR is included, 7-year survival was 83 +/- 6%. Actuarial 1-, 3-, 5-, and 7-year event-free survival (survival without MVR or repeat CBC) was 80 +/- 4%, 77 +/- 4%, 65 +/- 6%, and 65 +/- 6%. On multivariate analysis, the only two independent predictors (both after CBC) of 7-year event-free survival were MVA of > or = 1.5 versus < 1.5 cm2 (75 +/- 7% versus 32 +/- 12%) and mean pulmonary artery wedge pressure of < or = 18 versus > 18 mm Hg (84 +/- 6% versus 38 +/- 11%) (P < .001 for both). Patients with MVA of > or = 1.5 cm2 (n = 96) could be further subdivided into high- and low-risk subgroups for 7-year event-free survival by two post-CBC variables: mean pulmonary artery wedge pressure of < or = 18 versus > 18 mm Hg (90 +/- 6% versus 48 +/- 14%) (P = .0002) and cardiac index of > or = 2.5 versus < 2.5 L.min-1.m-2 (82 +/- 8% versus 61 +/- 13%) (P = .004). Patients with post-CBC MVA of < 1.5 cm2 (n = 24) had no additional predictors of event-free survival. Of patients who did not undergo MVR or repeat CBC, 8% were in New York Heart Association functional class III and 92% were in class I or early class II at the last follow-up.

CONCLUSIONS

The rates for intermediate-term survival and event-free survival after CBC are very encouraging. Most patients without events were asymptomatic or minimally symptomatic. Thus, in selected patients with mitral stenosis who require an interventional procedure, CBC is the procedure of choice at centers with physicians who have experience and skill in performing this procedure.