## BACKGROUND

The worldwide burden of coronary artery disease (CAD) remains substantial. Annually, an estimated 1.5% of the US population visits the primary care services with symptoms of chest pain.1 Each year over 660,000 patients in the United States present to hospital with either a first myocardial infarction (MI) or sudden cardiac death (SCD) due to CAD.2 Of these 305,000 will have had a recurrent MI. An estimated 160,000 will also suffer a silent first MI.2 CAD is the leading cause of death across the world and is predicted to remain so for the next 20 years. Annually, approximately 3.8 million men and 3.4 million women die from CAD. The number is estimated to rise to 11.1 million deaths globally by 2020.3 An estimated $108.9 billion is spent annually on treatment of CAD and is expected to exceed$320 billion by the year 2030.2 Thus, means and methods to reduce the prevalence, morbidity, and mortality associated with CAD remain of great importance to health care providers.

For these reasons, a systematic approach for early diagnosis and risk stratification of CAD is important for patients to benefit from preventive and therapeutic strategies. Over the past two decades, radionuclide myocardial perfusion imaging (MPI) has become clinical mainstay for the noninvasive evaluation of CAD. In this chapter, the role of nuclear cardiac perfusion including both single-photon emission computed tomographic (SPECT) and positron emission tomographic (PET) imaging will be discussed in relation to the diagnosis, risk stratification, and patient management decisions in patients with suspected CAD.

## ASSESSMENT OF RISK FOR CAD

To optimize the use of testing for suspected CAD, the initial step involves stratifying the likelihood of such a patient to have underlying disease. Although a variety of tools are available for this purpose, the evaluation of risk factors and the nature of presenting chest pain and associated symptoms are often used to estimate the pretest likelihood of CAD in patients (Table 14-1).4 Modifiable cardiac risk factors include hypercholesterolemia, tobacco smoking, hypertension, diabetes mellitus, physical inactivity, and obesity, while nonmodifiable risk factors are family history of CAD in first-degree relatives under the age of 60 years, advanced age, and male gender.5,6 Multiple clinical prediction models have been developed to stratify asymptomatic patients into low, intermediate, and high risk for presence of CAD. The most commonly used risk score in the United States is the Framingham Risk Score (FRS) which predicts a 10-year risk for nonfatal MI and cardiac death based on the presence or absence of cardiac risk factors.7 Using the FRS, patients can be categorized into low-risk (age-specific risk level below average; 10-year absolute risk of CAD <6%), intermediate-risk (age-specific risk level average or above average; 10-year absolute risk of CAD between 6% and 20%), or high-risk (patients with coronary risk equivalents; 10-year absolute risk >20%) groups. A modified version of the ...

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