Interrelation of coronary calcification, myocardial ischemia, and outcomes in patients with intermediate likelihood of coronary artery disease: a combined positron emission tomography/computed tomography study

Long-term prognostic value of 13N-ammonia myocardial perfusion positron emission tomography added value of coronary flow reserve

OBJECTIVES

The goal of this study was to assess the predictive value of myocardial perfusion imaging with (13)N-ammonia positron emission tomography (PET) and coronary flow reserve (CFR) on long-term prognosis in patients with suspected myocardial ischemia.

BACKGROUND

No prognostic data exist on the predictive value of CFR and (13)N-ammonia PET.

METHODS

Perfusion and CFR were assessed in 256 patients using (13)N-ammonia PET, and follow-up was obtained in 245 (96%) patients. Sixteen early revascularized patients were excluded and 229 were assigned to normal versus abnormal perfusion or normal versus abnormal CFR (<2.0). Major adverse cardiac events (MACE) (cardiac death, nonfatal myocardial infarction, late revascularization, or hospitalization for cardiac reasons) were assessed using the Kaplan-Meier method. Cox proportional hazard regression was used to identify independent predictors for cardiac events.

RESULTS

During follow-up (5.4 +/- 2.2 years), 78 patients had at least 1 cardiac event, including 29 cardiac deaths. Abnormal perfusion (n = 126) was associated with a higher incidence of MACE (p < 0.001) and cardiac death (p < 0.05). In patients with normal perfusion, abnormal CFR was independently associated with a higher annual event rate over 3 years compared with normal CFR for MACE (1.4% vs. 6.3%; p < 0.05) and cardiac death (0.5% vs. 3.1%; p < 0.05). In abnormal perfusion, CFR remained predictive throughout the 10-year follow-up (p < 0.001).

CONCLUSIONS

Perfusion findings in (13)N-ammonia PET and CFR are strong outcome predictors. CFR allows further risk stratification, suggesting a "warranty" period of 3 years if normal CFR is associated with normal perfusion. Conversely, in patients with abnormal perfusion, an impaired CFR has added value for predicting adverse outcomes.

Cardiac positron emission tomography

Positron emission tomography (PET) is a powerful, quantitative imaging modality that has been used for decades to noninvasively investigate cardiovascular biology and physiology. Due to limited availability, methodologic complexity, and high costs, it has long been seen as a research tool and as a reference method for validation of other diagnostic approaches. This perception, fortunately, has changed significantly within recent years. Increasing diversity of therapeutic options for coronary artery disease, and increasing specificity of novel therapies for certain biologic pathways, has resulted in a clinical need for more accurate and specific diagnostic techniques. At the same time, the number of PET centers continues to grow, stimulated by PET's success in oncology. Methodologic advances as well as improved radiotracer availability have further contributed to more widespread use. Evidence for diagnostic and prognostic usefulness of myocardial perfusion and viability assessment by PET is increasing. Some studies suggest overall cost-effectiveness of the technique despite higher costs of a single study, because unnecessary follow-up procedures can be avoided. The advent of hybrid PET-computed tomography (CT), which enables integration of PET-derived biologic information with multislice CT-derived morphologic information, and the key role of PET in the development and translation of novel molecular-targeted imaging compounds, have further contributed to more widespread acceptance. Today, PET promises to play a leading diagnostic role on the pathway toward a future of high-powered, comprehensive, personalized, cardiovascular medicine. This review summarizes the state-of-the-art in current imaging methodology and clinical application, and outlines novel developments and future directions.

First experience of combined cardiac PET/64-detector CT angiography with invasive angiographic validation

PURPOSE

Despite modern CT systems and expert evaluators, the diagnostic performance of coronary CT angiography is limited by overestimation of vessel stenosis which reduces the positive predictive value (PPV) of the test. The aim of this study was to evaluate the performance of combined cardiac PET/64-detector CT angiography.

METHODS

Included in this retrospective study were 33 consecutive patients (5 women, 28 men; mean age 61.6 years, range 47-87 years, mean BMI 27.3+/-5.2 kg/m(2)) with clinically suspected flow-limiting coronary artery disease who underwent combined cardiac PET/64-detector CT angiography and invasive angiography. Combined PET/CT images were reported by an experienced dual-accredited radiologist/nuclear physician. An experienced cardiac CT radiologist re-read the CT images without PET. Stenotic disease was defined as >50% vessel narrowing. Invasive coronary angiography was used as a reference standard. Local ethics committee approval and patient consent were obtained.

RESULTS

CT angiography (without PET data) was concordant with invasive angiography in 31/33 patients and at a patient level, the sensitivity in detecting significant coronary artery lesions was 100%, the specificity was 82%, the PPV was 92% and the negative predictive value (NPV) was 100%. Using combined PET/CT angiography the findings were concordant with invasive angiography in 32/33 patients and at a patient level, the sensitivity was 96%, the specificity was 100%, the PPV was 100% and the NPV was 91%.

CONCLUSION

The use of integrated cardiac PET/64-detector CT angiography is feasible and appears to improve some aspects of the diagnostic performance of 64-detector coronary artery angiography in detecting coronary artery disease.

Incremental prognostic value of multi-slice computed tomography coronary angiography over coronary artery calcium scoring in patients with suspected coronary artery disease

AIMS

The purpose of this study was to assess the relationship between calcium scoring (CS) and multi-slice computed tomography coronary angiography (MSCTA) and to determine if MSCTA has an incremental prognostic value to CS.

METHODS AND RESULTS

In 432 patients (59% male, age 58 +/- 11 years) referred for cardiac evaluation owing to suspected coronary artery disease (CAD), CS and 64-slice MSCTA were performed. The following events were combined in a composite endpoint: all-cause mortality, non-fatal infarction, and unstable angina requiring revascularization. CS was 0 in 147 (34%) patients, CS 1-99 was present in 122 (28%), CS 100-399 in 75 (17%), CS 400-999 in 56 (13%), and CS > or = 1000 in 32 (7%). MSCTA was normal in 133 (31%) patients, MSCTA 30-50% stenosis was observed in 190 (44%), and MSCTA > or =50% stenosis in 109 (25%). During follow-up [median 670 days (25th-75th percentile: 418-895)], an event occurred in 21 patients (4.9%). After multivariate correction for CS, MSCTA > or = 50% stenosis, the number of diseased segments, obstructive segments, and non-calcified plaques were independent predictors with an incremental prognostic value to CS.

CONCLUSION

MSCTA provides additional information to CS regarding stenosis severity and plaque composition. This additional information was shown to translate into incremental prognostic value over CS.

Witnessing ischemia or proofing coronary atherosclerosis: two different windows on the same or on different pathways precipitating cardiovascular events?

Risk stratification and prevention of future cardiac events is an extremely relevant part of the daily medical practice in the large population of asymptomatic or scarcely symptomatic patients. The strategies available to this purpose encompass programs intended either to reduce progression and complications of atherosclerosis, and revascularization procedures aimed to reduce total ischemic burden. The former represents a primary prevention approach and fights the substrate of ischemic heart disease. The latter, instead, is used to reduce the total ischemic burden and thus implies to identify those patients in whom ischemia can be life threatening because of its severity and extension. Today, at least two imaging methods are available for this task: coronary calcium scoring by x-ray CT and ischemia assessment by myocardial perfusion imaging. Although both approaches can accurately estimate cardiovascular risk, from a theoretical point of view, the assessment of ischemia evaluates the functional consequences of coronary obstructions and thus the target of revascularization procedure, while estimating the total atherosclerotic burden represents an indirect index of it. This difference might appear academic in its nature, given the current model of ischemic heart disease pathophysiology that assumes and predicts a very tight correlation between the severity of a coronary stenosis and its capability to cause ischemia. However, the majority of studies focused on the combined risk assessment with both approaches confirm the relevance of this issue. In fact, among 7785 patients reported in the literature, coronary calcium scoring most often resulted in positive findings (78%). However, this sign of atherosclerosis was associated with inducible ischemia in only one-fifth of patients. In the near future, coronary calcium scoring will be easily and immediately completed by the noninvasive definition of coronary stenoses. At that time we will face a still largely unknown risk: the presence of a stenosis in the absence of symptoms and of ischemia. Evaluating the effectiveness of different protocols will thus be needed to improve our capability to help these patients.

Integrated imaging of cardiac anatomy, physiology, and viability

Technologic developments in imaging will have a significant impact on cardiac imaging over the next decade. These advances will permit more detailed assessment of cardiac anatomy, complex assessment of cardiac physiology, and integration of anatomic and physiologic data. The distinction between anatomic and physiologic imaging is important. For assessing patients with known or suspected coronary artery disease, physiologic and anatomic imaging data are complementary. The strength of anatomic imaging rests in its ability to detect the presence of disease, whereas physiologic imaging techniques assess the impact of disease, such as whether a coronary atherosclerotic lesion limits myocardial blood flow. Research indicates that physiologic data are more prognostically important than anatomic data, but both may be important in patient management decisions. Integrated cardiac imaging is an evolving field, with many potential indications. These include assessment of coronary stenosis, myocardial viability, anatomic and physiologic characterization of atherosclerotic plaque, and advanced molecular imaging.

Novel clinical applications of state-of-the-art multi-slice computed tomography

Recent years have witnessed a rapid development of multi-slice computed tomography (MSCT) technology. The number of detector rows has increased from 4-slices to the current availability of 64-slice and even 320-slice systems. In addition, images are acquired with thinner slices and faster rotation times resulting in substantially improved image quality and diagnostic accuracy. Simultaneously, effective dose reduction acquisition techniques have been developed allowing considerable reduction of the radiation dose. Conceivably, these advancements may allow further expansion of the use of MSCT beyond the visual assessment of the presence or absence of significant coronary artery disease. Indeed, a particular advantage of the technique is that in addition to evaluation of the coronary arteries it also allows assessment of cardiac structures and function. The purpose of the current review is to discuss several novel applications of cardiac MSCT, including stenosis quantification, atherosclerotic plaque imaging and prognostification as well as imaging of left ventricular function, aortic and mitral valve anatomy using state-of-the-art technology.

The evolving role of molecular imaging for coronary artery disease: where do we stand today?

The landscape of cardiac imaging is changing rapidly. There are promising new developments in molecular imaging on the horizon. It is likely that nuclear cardiology will continue to play an important role in the evaluation of CAD, but that role must evolve to meet clinical needs, competing technologies and the increasing emphasis on ensuring that imaging adds value and improves outcomes. This review offers some suggestions on the optimal role nuclear imaging can play vis-à-vis alternative options such as CT, but more data are needed before definitive recommendations can be made. Randomised trials comparing different diagnostic strategies can and should be performed to strengthen the foundations of clinical practice in nuclear cardiology. An evidence-based approach to imaging is here to stay.

Noninvasive assessment of coronary anatomy and myocardial perfusion: going toward an integrated imaging approach

Many noninvasive imaging techniques are available for the evaluation of patients with known or suspected chronic coronary artery disease. Among these, computed tomography-based techniques allow the quantification of coronary atherosclerotic calcium and noninvasive imaging of coronary arteries, whereas nuclear cardiology is the most widely used noninvasive approach for the assessment of myocardial perfusion. The available single-photon emission computed tomography flow agents are characterized by a cardiac uptake proportional to myocardial blood flow. In addition, different positron emission tomography tracers may be used for the quantitative measurement of myocardial blood flow and coronary flow reserve. Extensive research is currently being performed in the development of noninvasive coronary angiography and myocardial perfusion imaging using cardiac magnetic resonance. Finally, new multimodality imaging systems have been recently developed, bringing together anatomical and functional information. This review sought to provide a description of the relative merits of noninvasive imaging techniques in the assessment of coronary anatomy and myocardial perfusion in patients with known or suspected coronary artery disease.

Analytic system matrix resolution modeling in PET: an application to Rb-82 cardiac imaging

This work explores application of a novel resolution modeling technique based on analytic physical models which individually models the various resolution degrading effects in PET (positron range, photon non-collinearity, inter-crystal scattering and inter-crystal penetration) followed by their combination and incorporation within the image reconstruction task. In addition to phantom studies, the proposed technique was particularly applied to and studied in the task of clinical Rb-82 myocardial perfusion imaging, which presently suffers from poor statistics and resolution properties in the reconstructed images. Overall, the approach is able to produce considerable enhancements in image quality. The reconstructed FWHM for a Discovery RX PET/CT scanner was seen to improve from 5.1 mm to 7.7 mm across the field-of-view (FoV) to approximately 3.5 mm nearly uniformly across the FoV. Furthermore, extended-source phantom studies indicated clearly improved images in terms of contrast versus noise performance. Using Monte Carlo simulations of clinical Rb-82 imaging, the resolution modeling technique was seen to significantly outperform standard reconstructions qualitatively, and also quantitatively in terms of contrast versus noise (contrast between the myocardium and other organs, as well as between myocardial defects and the left ventricle).

Coronary artery calcium scores: current thinking and clinical applications

Most incident coronary disease occurs in previously asymptomatic individuals who were considered to be at a lower risk by traditional screening methods. There is a definite advantage if these individuals could be reclassified into a higher risk category, thereby impacting disease outcomes favorably. Coronary artery calcium scores have been recognized as an independent marker for adverse prognosis in coronary disease. Multiple population based studies have acknowledged the shortcomings of risk prediction models such as the Framingham risk score or the Procam score. The science behind coronary calcium is discussed briefly followed by a review of current thinking on calcium scores. An attempt has been made to summarize the appropriate indications and use of calcium scores.