Regional myocardial perfusion defects during exercise, as assessed by three dimensional integration of morphology and function, in relation to abnormal endothelium dependent vasoreactivity of the coronary microcirculation

Epicardial and microvascular coronary vasomotor dysfunction and its relation to myocardial ischemic burden in patients with non-obstructive coronary artery disease

AIM

To assess the relative contribution of epicardial endothelium-dependent (EDD) and microvascular endothelium-independent (EIMVD) coronary vasomotor dysfunction to the extent of myocardial ischemia in patients with normal angiograms or non-obstructive coronary artery disease (NOCAD).

METHODS

Coronary vasomotion was evaluated by quantitative angiography and blood flow (CBF) measurements during intracoronary acetylcholine, nitroglycerine, and adenosine in 101 patients. Myocardial SPECT ischemic burden was evaluated by semi-quantitative scoring of summed stress (SSS) and summed ischemic (SDS) perfusion defect size.

RESULTS

Coronary vasomotor dysfunction was found in most patients (83; 77%) with a divergent behavior of EDD and EIMVD in one half of them (52.4%). There was no significant difference in SDS between patients with and without EIMVD, whereas SDS was significantly greater in subjects with EDD as compared to patients with normal response to acetylcholine (4.31 ± 2.44 vs 1.35 ± 1.45; P < .0001). Patients with EDD, either alone or in combination with EIMVD, had significantly higher SSS as compared to patients with lone EIMVD or normal vasomotor function (8.50 ± 5.32; 5.55 ± 3.21; 2.60 ± 2.14; and 1.74 ± 1.66, respectively; P < .0001). Acetylcholine CBF correlated inversely with both SDS (r = -0.545; P < .001) and SSS (r = 0.538; P < .001).

CONCLUSIONS

In NOCAD patients with symptoms and signs of myocardial ischemia, vasomotor dysfunction is common. EDD is associated with greater extent of ischemia as compared to isolated EIMVD. Thus, assessment of both EIMVD and EDD is needed to recognize mechanisms of ischemia and identify patients with greater ischemic burden.

A narrative overview: Have clinical trials of PCI vs medical therapy addressed the right question?

BACKGROUND

In RCTs about revascularization, the terms "coronary artery disease" and "ischemic heart disease" are sometimes used interchangeably. This can create confusion concerning inclusion and exclusion criteria, which may lead to uncertain results.

OBJECTIVE

Our purpose is to investigate whether the study populations in randomized controlled trials (RCTs) which compared percutaneous coronary revascularization to medical therapy for stable ischemic heart disease specifically enrolled patients with demonstrable ischemia, and how many patients were included in trials with evidence of coronary atherosclerosis but without evidence of ischemia.

METHODS

Trial published data were obtained from ACME I, ACME II, RITA I, RITA II, MASS I, MASS II, AVERT, ACIP, COURAGE and FAME2. Published data were used to calculate the number of patients included in the trials with a negative stress test but significant coronary artery stenosis and the number of patients excluded from the trials with a positive stress test or angina, but without significant coronary artery stenosis at the time of angiography.

RESULTS

A total of 196,433 patients were screened between 1998 and 2011. Overall about 30% of patients were excluded if they did not meet the angiographic criteria, even though the presence of inducible ischemia or angina, and, about 20% of patients were included without inducible ischemia.

CONCLUSION

RCTs have contributed to the confusion between coronary artery disease and ischemic heart disease. This may limit the ability to interpret the results and apply them in practice.

Altered transmural contractility in postmenopausal women affected by cardiac syndrome X

BACKGROUND

Cardiac syndrome X (CSX) is characterized by typical angina and abnormal exercise test results, with normal coronary arteries. Cardiovascular magnetic resonance imaging has shown subendocardial hypoperfusion in patients with CSX after adenosine. The aim of this study was to investigate the contribution of separate myocardial layers to global function under stress in women with CSX.

METHODS

Twenty-two postmenopausal women with CSX were studied and compared with 20 healthy women matched for age and body mass index. All subjects underwent clinical evaluations and exercise echocardiography. Left ventricular systolic and diastolic parameters were evaluated at rest and at peak exercise. Layer-specific global longitudinal strain (GLS) and strain rate (SR) were assessed from the endocardium, midmyocardium, and epicardium using two-dimensional speckle-tracking echocardiography.

RESULTS

All subjects showed normal contractile function at rest and at peak exercise. Significant increases in GLS and SR in all myocardial layers were observed at peak exercise in the control group, whereas patients with CSX showed significantly lower increases in endocardial GLS and SR compared with the control group (endocardial ΔSR, 0.17 ± 0.19 vs 0.33 ± 0.13 [P < .01]; endocardial ΔGLS, 1.33 ± 2.93 vs 6.64 ± 2.62 [P < .001]). Moreover, significantly impaired diastolic function (ΔE', 1.1 ± 3.3 vs 4.0 ± 2.03) was observed in patients with CSX.

CONCLUSIONS

The results of this study show subendocardial impairment of contractile function during exercise in patients with CSX, confirming the existence of reduced myocardial perfusion reserve in patients with CSX and suggesting layer-targeted exercise echocardiography as a sensitive diagnostic tool in the assessment of suspected CSX.

Four-Dimensional Image Reconstruction Strategies in Cardiac-Gated and Respiratory-Gated PET Imaging

Cardiac and respiratory movements pose significant challenges to image quality and quantitative accuracy in PET imaging. Cardiac and/or respiratory gating attempt to address this issue, but instead lead to enhanced noise levels. Direct four-dimensional (4D) PET image reconstruction incorporating motion compensation has the potential to minimize noise amplification while removing considerable motion blur. A wide-ranging choice of such techniques is reviewed in this work. Future opportunities and the challenges facing the adoption of 4D PET reconstruction and its role in basic and clinical research are also discussed.

The influence of endothelial function and myocardial ischemia on peak oxygen consumption in patients with coronary artery disease

Impaired endothelial function has been shown to limit exercise in coronary artery disease (CAD) patients and has been implicated in myocardial ischemia. However, the association of endothelial function and ischemia on peak exercise oxygen consumption (VO₂) has not been previously reported. A total of 116 CAD patients underwent standard exercise stress testing, during which VO₂ was measured. On a separate day, endothelial-dependent and -independent function were assessed by ultrasound using flow-mediated arterial vasodilation (FMD) and sublingual glyceryl trinitrate administration (GTNMD) of the brachial artery. Patients with exercise-induced myocardial ischemia had lower FMD than nonischemic patients (3.64 ± 0.57 versus 4.98 ± 0.36, P = .050), but there was no difference in GTNMD (14.11 ± 0.99 versus 15.47 ± 0.63, P = .249). Analyses revealed that both FMD (P = .006) and GTNMD (P = .019) were related to peak VO₂. However, neither the presence of ischemia (P = .860) nor the interaction of ischemia with FMD (P = .382) and GTNMD (P = .151) was related to peak VO₂. These data suggest that poor endothelial function, potentially via impaired NO production and smooth muscle dysfunction, may be an important determinant of exercise capacity in patients with CAD, independent of myocardial ischemia.

Nitroglycerin-induced heterogeneous subendocardial myocardial blood flow observed by cardioscopy in patients with coronary artery disease

It is controversial as to whether or not nitroglycerin (NTG) increases subendocardial myocardial blood flow (SMBF), and if it does, whether arterial or venous blood flow is increased in patients with coronary artery disease. This study was performed to examine NTG-induced changes in SMBF.Changes in SMBF induced by NTG (200 µg, i.v.) were examined by cardioscopy in 58 left ventricular wall segments of 58 patients with coronary artery disease. NTG-induced red and purple endocardial colors were defined as increased arterial and venous SMBF, respectively. Endocardial color before NTG administration was classified into brown, light brown, pale and white. Endomyocardial biopsy of the observed portion and (201)Tl scintigraphy were performed in 40 of these patients immediately after cardioscopy and several days after cardioscopy, respectively.Upon administration of NTG, SMBF increased in 48 of 58 wall segments; arterial SMBF in 34 and venous SMBF in 12 wall segments; arterial SMBF in all 24 brown to light brown segments; venous SMBF, arterial SMBF and no change in 12, 10 and 5 of pale segments, respectively; and no change in all 10 white wall segments. (201)Tl-scintigraphy and endomyocardial biopsy revealed that brown, light brown, pale and white endocardial color represented no ischemia, mild ischemia, severe ischemia and fibrosis, respectively.NTG caused an increase in either arterial or venous SMBF depending on control endocardial color, wall motion and severity of coronary stenosis.

Interrelationship between myocardial perfusion imaging, coronary calcium score, and endothelial function in asymptomatic diabetics and controls

BACKGROUND

Coronary artery disease is a leading cause of death among diabetics, and silent ischemia is a major concern in patients with diabetes mellitus (DM).

METHODS

To detect the prevalence of ischemia in diabetics by myocardial perfusion imaging (MPI), and compare it to a control group without DM but with coronary risk factors, as well as to explore the relationship between silent ischemia, endothelial dysfunction, and coronary calcium, 59 patients (Group I) and 42 controls (Group II) were included. All underwent clinical and laboratory evaluations, gated MPI, brachial artery vasodilation measured by ultrasonography, and coronary calcium score (CCS).

RESULTS

Twenty diabetics showed perfusion defects, vs seven controls (P = .04). There was no significant difference between both groups regarding the brachial artery vasodilator responsiveness: 4.49% ± 4.26% (diabetics) vs 4.70% ± 4.98% (controls). Mean CCS was 74 in diabetics vs five in controls (P = .01). The only risk factor significantly associated with an abnormal MPI was the presence of diabetes (P = .03). In the whole population of patients and in diabetics, the abnormal endothelium-dependent vasodilation, the CCS >100, and the cholesterol/HDL ratio >4, showed an OR >1. CCS exhibited the higher OR among the whole population: OR 2.15 [95% CI 0.42-10.99]; while for diabetics it was the cholesterol/HDL ratio: OR 3.95 [95% CI 0.71-21.84].

CONCLUSIONS

Reversible perfusion defects and coronary calcium are more frequent in diabetics. CCS, abnormal endothelium-dependent vasodilation, and cholesterol/HDL ratio higher than 4, showed an association with perfusion abnormalities in asymptomatic diabetics.

The diagnostic yield of exercise stress testing as a screening tool for subclinical coronary artery disease in patients with moderate to severe obstructive sleep apnea

STUDY OBJECTIVE

To address the yield of routine exercise stress testing as a screening tool for subclinical coronary artery disease (CAD) in patients with moderate to severe obstructive sleep apnea (OSA).

DESIGN AND SETTING

A cross-sectional study in a university hospital.

PARTICIPANTS

Of 380 consecutive patients with OSA, data from 206 subjects (mean apnea-hypopnea index [AHI] 41 ± 21 events/h) were studied; data from 78 with a history of CAD and 96 with mild OSA (AHI 5-15 events/h) were excluded.

MEASUREMENTS

Routine exercise stress testing.

RESULTS

Six subjects could not reach maximal exercise capacity. Of the remaining 200 patients, the results of exercise stress testing were normal in 189. Three had a positive stress test, with coronary angiography confirming the diagnosis of CAD. Eight patients had suspected positive findings on the stress test, but the results of the myocardial perfusion study were negative.

CONCLUSION

The prevalence of subclinical CAD in this selected population with OSA was 1.5%, which is not higher than that in a general population. Our results do not support the routine use of exercise stress testing in patients with moderate to severe OSA who do not have symptoms of CAD.

Noncalcified atherosclerotic plaque burden at coronary CT angiography: a better predictor of ischemia at stress myocardial perfusion imaging than calcium score and stenosis severity

OBJECTIVE

The purpose of this study was to examine the relation between the coronary CT angiographic findings of calcified and noncalcified plaque burden and stenosis severity and the myocardial perfusion imaging finding of ischemia.

MATERIALS AND METHODS

Seventy-two patients (41 men, 31 women; mean age, 56 years) underwent coronary CT angiography and stress-rest SPECT myocardial perfusion imaging. Calcium scoring was performed. Coronary CT angiograms were analyzed for stenosis and noncalcified or mixed plaque. A plaque analysis tool was used to calculate the volume of noncalcified plaque components. SPECT images were analyzed for perfusion defects. Data were analyzed per patient and per vessel.

RESULTS

A total of 53 purely noncalcified, 50 mixed, and 201 purely calcified plaques were detected. Forty-five stenoses were rated > or = 50%, 19 of those being > or = 70%. Myocardial perfusion imaging depicted perfusion defects in 37 vessels (13%) in 24 patients (18 reversible, 19 fixed defects). Vessels with > or = 50% stenosis had significantly (p = 0.0009) more perfusion defects in their supplied territories (11 with, 22 without perfusion defects) than did vessels without significant lesions (26 with, 229 without perfusion defects). In vessel-based analysis, the sensitivity of coronary CT angiography in prediction of any perfusion defect on myocardial perfusion images was 30% with 91% specificity, 33% positive predictive value, and 90% negative predictive value. Between vessels with and those without perfusion defects, there was no significant difference in Agatston or calcium volume score (p = 0.25), but there was a significant difference in noncalcified plaque volume (44 +/- 77 vs 19 +/- 58 mm(3); p = 0.03). Multiple stepwise regression analysis showed noncalcified plaque volume was the only significant predictor of ischemia (p = 0.01).

CONCLUSION

At coronary CT angiography, noncalcified plaque burden is a better predictor of the finding of myocardial ischemia at stress myocardial perfusion imaging than are calcium score and degree of stenosis.

Cardiovascular disease and type 2 diabetes mellitus: a multifaceted symbiosis

Chronic hyperglycaemia (e.g. type 2 diabetes mellitus (T2DM) and prediabetes) in humans is associated with an increased risk of cardiovascular (CV) complications, and, vice versa, the presence of CV complications (e.g. myocardial infarction, stroke or intermittent claudication) among patients heightens the risk of T2DM or prediabetes. In both cases (i.e. chronic hyperglycaemia and CV complications), significant diagnostic and treatment challenges resulting from a broad range of factors may serve as barriers to reducing the deleterious societal impact of T2DM and prediabetes. These challenges often include clinicians: failing to intervene early and aggressively enough among patients with T2DM to achieve CV risk factor control; failing to efficaciously identify T2DM patients with already established CV complications; and failing proactively to assess individuals at high risk for T2DM. This review discusses the apparent symbiosis between CV disease and T2DM, with a focus on identifying patients with established T2DM or at risk for T2DM; traditional and novel risk factors and markers for CV disease in T2DM; challenges related to diagnosing CV disease in T2DM; and organization of T2DM care in order to prevent CV complications. These are issues that require attention because identifying patients at high risk for T2DM can halt or reduce their further glycaemic deterioration if addressed properly, and because novel markers and non-invasive tests could be applied in patients with T2DM as a means of detecting and possibly treating unrecognized CV disease in time. Furthermore, several approaches for T2DM care can be effective in controlling the CV risk factors contributing to CV complications.

Ischemia in women with angina and normal coronary angiograms

BACKGROUND

Coronary artery disease is frequent in postmenopausal women. Myocardial ischemia has been induced with stress testing, and a relationship between endothelial dysfunction and perfusion defects has been reported.

OBJECTIVE

To evaluate whether myocardial ischemia can be evidenced both by perfusion and function abnormalities using gated single-photon emission computed-tomography myocardial scintigraphy with technetium-labeled compounds in women with typical angina, normal coronary angiography, and endothelial dysfunction.

METHODS AND RESULTS

Fifty-nine postmenopausal patients were studied. Each underwent technetium-99m methoxy-isobutyl-isonitrile myocardial scintigraphy (protocol: exercise stress-rest), brachial artery endothelial function measured by ultrasonography, lipidogram, and 24-h ambulatory ECG recording (Holter). Twenty-one patients (group I) showed perfusion defects in myocardial scintigraphy, whereas the other 38 patients (group II) did not. Group I patients exhibited endothelial dysfunction more frequently (57 vs. 29%) than those of group II. Among group I patients, 12 showed a reversible perfusion defect that, in 75% of the cases, was associated with poststress left ventricular ejection fraction reduction greater than 5% and a regional hypokinesis. Nine patients had fixed defects, which in 56% of the cases were associated with poststress left ventricular ejection fraction reduction greater than 5%. Left ventricular ejection fraction poststress minus left ventricular ejection fraction at rest was -5.2% in group I patients versus -1.8% in group II (P<0.001). Three patients in group I showed evidence of ischemia by Holter compared with four in group II.

CONCLUSION

Stress-induced ischemia is associated with poststress left ventricular ejection fraction reduction in postmenopausal women with typical angina, normal coronary angiography, and a trend toward abnormal endothelial-mediated vasodilation.

Comparison of the prognostic value of the stress-recovery index versus standard electrocardiographic criteria in patients with a negative exercise electrocardiogram

To verify whether the stress recovery index (SRI) improves risk stratification in patients with a negative exercise electrocardiogram (ECG) using standard criteria, the SRI was derived in 708 consecutive patients with a negative exercise ECG. All-cause mortality and the combination of death or nonfatal myocardial infarction were target end points. The individual effect of clinical and exercise testing data on outcome was evaluated using Cox regression analysis with separate models for each group of variables. Model validation was performed using bootstrap adjusted by degree of optimism in estimates. Survival analysis was performed using a product-limit Kaplan-Meier method. During a 37-month follow-up, 22 deaths and 40 nonfatal acute coronary syndromes occurred. After adjusting for confounding variables, age (hazard ratio 1.62, 95% confidence interval [CI] 1.14 to 2.31 for interquartile difference), hypertension (hazard ratio 1.74, 95% CI 1.04 to 2.89), and SRI (hazard ratio 0.75, 95% CI 0.65 to 0.86 for interquartile difference) were predictive of death or nonfatal myocardial infarction. Moreover, SRI increased the prognostic power of the model on top of clinical and exercise testing variables and provided significant discrimination of survival. In conclusion, the SRI may help refine the prognostic stratification of patients with a negative exercise test result using standard electrocardiographic criteria.

Heart rate adjustments and analysis of recovery patterns of ST-segment depression in type 2 diabetes

AIMS

To investigate the diagnostic value for coronary artery disease (CAD) detection of evaluating time- and heart rate (HR)-related ST-segment changes (the ST/HR-slope) and the post-exercise recovery pattern (the ST/HR-recovery loop) in patients with type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

Ninety-one patients (22 female, age 59+/-9 years) with T2DM (diabetes duration 6+/-6 years) performed an exercise ECG-test that was evaluated using the ST/HR slope (cut-off</=-2.4 microV/bpm) and -recovery loop patterns (abnormal versus normal) and compared to the conventional >/=1 mm ST-segment depression criterion and dobutamine stress echo-cardiography, all evaluated against coronary angiography irrespective of stress test results. Coronary angiography revealed CAD in 20 men and 3 women (25%). Sensitivity for the conventional exercise test and stress echocardiography was low (0.35 and 0.30), but increased significantly using the ST/HR-slope (0.45), the recovery loop (0.86) or the combined ST/HR slope and recovery loop criterion (0.91). The associations between angiographic CAD-detection and the different tests expressed by the Odds ratio demonstrated an added value of performing ST/HR analysis both over pre-test CAD risk profile and the established techniques.

CONCLUSION

T2DM patients capable of performing an exercise test could be assessed with the ST/HR-analysis for selecting patients to angiography. However, further studies including a higher number of patients are needed to confirm the diagnostic value of this approach.

Coronary x-ray angiographic reconstruction and image orientation

We have developed an interactive geometric method for 3D reconstruction of the coronary arteries using multiple single-plane angiographic views with arbitrary orientations. Epipolar planes and epipolar lines are employed to trace corresponding vessel segments on these views. These points are utilized to reconstruct 3D vessel centerlines. The accuracy of the reconstruction is assessed using: (1) near-intersection distances of the rays that connect x-ray sources with projected points, (2) distances between traced and projected centerlines. These same two measures enter into a fitness function for a genetic search algorithm (GA) employed to orient the angiographic image planes automatically in 3D avoiding local minima in the search for optimized parameters. Furthermore, the GA utilizes traced vessel shapes (as opposed to isolated anchor points) to assist the optimization process. Differences between two-view and multiview reconstructions are evaluated. Vessel radii are measured and used to render the coronary tree in 3D as a surface. Reconstruction fidelity is demonstrated via (1) virtual phantom, (2) real phantom, and (3) patient data sets, the latter two of which utilize the GA. These simulated and measured angiograms illustrate that the vessel center-lines are reconstructed in 3D with accuracy below 1 mm. The reconstruction method is thus accurate compared to typical vessel dimensions of 1-3 mm. The methods presented should enable a combined interpretation of the severity of coronary artery stenoses and the hemodynamic impact on myocardial perfusion in patients with coronary artery disease.

Insulin improves myocardial blood flow in patients with type 2 diabetes and coronary artery disease

Insulin infusion improves myocardial blood flow (MBF) in healthy subjects. Until now, the effect of insulin on myocardial perfusion in type 2 diabetic subjects with coronary artery disease (CAD) has been unknown. We studied the effects of insulin on MBF in ischemic regions evaluated by single-photon emission-computed tomography and coronary angiography and in nonischemic regions in 43 subjects (ages 63 +/- 7 years) with type 2 diabetes (HbA(1c) 7.1 +/- 0.9%). MBF was measured at fasting and during a euglycemic-hyperinsulinemic clamp at rest (n = 43) and during adenosine-induced (140 mug . kg(-1) . min(-1) for 7 min) hyperemia (n = 26) using positron emission tomography and (15)O-labeled water. MBF was significantly attenuated in ischemic regions as compared with in nonischemic regions (P < 0.0001) and was increased by insulin as compared with in the fasting state (P < 0.0001). At rest, insulin infusion increased MBF by 13% in ischemic regions (P = 0.043) and 22% in nonischemic regions (P = 0.003). During adenosine infusion, insulin enhanced MBF by 20% (P = 0.018) in ischemic regions and 18% (P = 0.045) in nonischemic regions. In conclusion, insulin infusion improved MBF similarly in ischemic and nonischemic regions in type 2 diabetic subjects with CAD. Consequently, in addition to its metabolic effects, insulin infusion may improve endothelial function and thus increase the threshold for ischemia and partly contribute to the beneficial effects found in clinical trials in these subjects.

Relation of myocardial perfusion defects and nonsignificant coronary lesions by angiography with insights from intravascular ultrasound and coronary pressure measurements

Several studies have demonstrated a correlation between myocardial ischemia and severity of coronary lesions as determined by intravascular ultrasound (IVUS) and fractional flow reserve (FFR) measurements. However, their value for the assessment of mild coronary stenoses that are associated with myocardial perfusion abnormalities has not been well studied. The objective of this study was to prospectively compare the results of myocardial perfusion as determined by exercise/dipyridamole myocardial single-photon emission computed tomography with IVUS and FFR measurements in patients who had angiographically mild coronary stenosis (< 50% diameter stenosis by quantitative coronary angiography). Forty-eight patients who had stable coronary disease (61 +/- 11 years of age; 6 women) were included. All had mild coronary stenosis in the proximal/middle segment of > or = 1 coronary artery and had undergone maximal exercise myocardial technetium-99m tetrofosmin single-photon emission computed tomography within 48 hours before coronary angiography. IVUS measurements included lesion lumen area, external elastic membrane area, lesion plaque burden (calculated as external elastic membrane minus lumen area, divided by external elastic membrane, and multiplied by 100), and lumen area stenosis (calculated as reference lumen area minus lesion lumen area, divided by reference lumen area, multiplied by 100). Fifty-three coronary lesions were studied, with a mean percent diameter stenosis of 34.9 +/- 7.9% on angiography. Myocardial perfusion defects were demonstrated by single-photon emission computed tomography in 11 patients (12 myocardial regions) with no differences in lesion percent diameter stenosis compared with those without perfusion defects. The presence of reversible perfusion defects was associated with a higher lesion plaque burden as evaluated by IVUS (67.4 +/- 8.1% vs 60.2 +/- 9.3%, p = 0.01). FFR values did not differ in the presence or absence of perfusion defects (0.90 +/- 0.06 vs 0.92 +/- 0.07, respectively; p = NS). In conclusion, plaque burden as determined by IVUS may partly explain the presence of myocardial perfusion defects in cases of angiographically nonsignificant coronary lesions. However, the high FFR values associated with these lesions suggest that other mechanisms, such as endothelial/microvascular dysfunction, might also account for perfusion abnormalities in these patients.

Exercise testing in asymptomatic adults: a statement for professionals from the American Heart Association Council on Clinical Cardiology, Subcommittee on Exercise, Cardiac Rehabilitation, and Prevention

Along with coronary artery calcium scanning, ankle-brachial index measurement, and carotid artery ultrasound, exercise electrocardiography has been proposed as a screening tool for asymptomatic subjects thought to be at intermediate risk for developing clinical coronary disease. A wealth of data indicate that exercise testing can be used to assess and refine prognosis, particularly when emphasis is placed on nonelectrocardiographic measures such as exercise capacity, chronotropic response, heart rate recovery, and ventricular ectopy. Nevertheless, randomized trial data on the clinical value of screening exercise testing are absent; that is, it is not known whether a strategy of routine screening exercise testing in selected subjects reduces the risk for premature mortality or major cardiac morbidity. The writing group believes that a large-scale randomized trial of such a strategy should be performed.

Cardiac positron emission tomography imaging

Cardiac positron emission tomography (PET) imaging has advanced from primarily a research tool to a practical, high-performance clinical imaging modality. The widespread availability of state-of-the-art PET gamma cameras, the commercial availability of perfusion and viability PET imaging tracers, reimbursement for PET perfusion and viability procedures by government and private health insurance plans, and the availability of computer software for image display of perfusion, wall motion, and viability images have all been a key to cardiac PET imaging becoming a routine clinical tool. Although myocardial perfusion PET imaging is an option for all patients requiring stress perfusion imaging, there are identifiable patient groups difficult to image with conventional single-photon emission computed tomography imaging that are particularly likely to benefit from PET imaging, such as obese patients, women, patients with previous nondiagnostic tests, and patients with poor left ventricular function attributable to coronary artery disease considered for revascularization. Myocardial PET perfusion imaging with rubidium-82 is noteworthy for high efficiency, rapid throughput, and in a high-volume setting, low operational costs. PET metabolic viability imaging continues to be a noninvasive standard for diagnosis of viability imaging. Cardiac PET imaging has been shown to be cost-effective. The potential of routine quantification of resting and stress blood flow and coronary flow reserve in response to pharmacologic and cold-pressor stress offers tantalizing possibilities of enhancing the power of PET myocardial perfusion imaging. This can be achieved by providing assurance of stress quality control, in enhancing diagnosis and risk stratification in patients with coronary artery disease, and expanding diagnostic imaging into the realm of detection of early coronary artery disease and endothelial dysfunction subject to risk factor modification. Combined PET and x-ray computed tomography imaging (PET-CT) results in enhanced patient throughput and efficiency. The combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and noninvasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

Prevalence of symptomatic and silent stress-induced perfusion defects in diabetic patients with suspected coronary artery disease referred for myocardial perfusion scintigraphy

PURPOSE

Silent myocardial ischaemia--as evaluated by stress-induced perfusion defects on myocardial perfusion scintigraphy (MPS) in patients without a history of chest pain--is frequent in diabetes and is associated with increased rates of cardiovascular events. Its prevalence has been determined in asymptomatic diabetic patients, but remains largely unknown in diabetic patients with suspected coronary artery disease (CAD) in the clinical setting. In this study we therefore sought (a) to determine the prevalence of symptomatic and silent perfusion defects in diabetic patients with suspected CAD and (b) to characterise the eventual predictors of abnormal perfusion.

METHODS

The patient population comprised 133 consecutive diabetic patients with suspected CAD who had been referred for MPS. Studies were performed with exercise (41%) or pharmacological stress testing (1-day protocol, (99m)Tc-sestamibi, 201Tl or both). We used semi-quantitative analysis (20-segment polar maps) to derive the summed stress score (SSS) and the summed difference score (SDS).

RESULTS

Abnormal MPS (SSS> or =4) was observed in 49 (37%) patients (SSS=4.9+/-8.4, SDS=2.4+/-4.7), reversible perfusion defects (SDS> or =2) in 40 (30%) patients [SSS=13.3+/-10.9; SDS=8.0+/-5.6; 20% moderate to severe (SDS>4), 7% multivessel] and fixed defects in 21 (16%) patients. Results were comparable between patients with and patients without a history of chest pain. Of 75 patients without a history of chest pain, 23 (31%, 95% CI=21-42%) presented reversible defects (SSS=13.9+/-11.3; SDS=7.4+/-1.2), indicative of silent ischaemia. Reversible defects were associated with inducible ST segment depression during MPS stress [odds ratio (OR)=3.2, p<0.01). Fixed defects were associated with erectile dysfunction in males (OR=3.7, p=0.02) and lower aspirin use (OR=0.25, p=0.02).

CONCLUSION

Silent stress-induced perfusion defects occurred in 31% of the patients, a rate similar to that in patients with a history of chest pain. MPS could identify these patients with a potentially increased risk of cardiovascular events.

Molecular imaging in nuclear cardiology

State-of-the-art techniques have been used to measure key aspects of cardiovascular pathophysiology from the birth of radionuclide cardiovascular imaging. However, during the last 30 years, there have been few innovative imaging advances to further our understanding of the complex physiologic processes. Molecular imaging now offers an array of tools to develop advanced diagnostic approaches and therapies for patients with coronary artery disease and heart failure. For example, the enhanced understanding of the pathophysiology of atheroma makes it possible to identify vulnerable plaque based on its metabolic signature or the presence of excessive apoptosis. Because the metabolic and apoptotic signals are large, it is likely that even small lesions will be visible. Of the many approaches that are being developed, 2 tracers appear most likely to be tested in the near future: (1) [18F]-fluorodeoxyglucose, to determine macrophage metabolism; and (2) radiolabeled annexin, to measure apoptosis of the inflammatory cells. Using existing techniques such as perfusion imaging, appropriate patients can be selected for treatment with novel therapies, such as stem cell transplantation or vascular gene therapy. Using positron tomography in place of single photon imaging adds the capability for the measurement of absolute perfusion and perfusion reserve to the information on regional perfusion. Flow reserve detects global decreases in perfusion and refines the determination of lesion severity available from perfusion imaging.