Ischemic Cardiac Disease

X-Ray (Chest X-Ray, Invasive Coronary Angiography)

In most patients presenting to the emergency department, an initial chest x-ray is obtained. Although not routinely used to detect ischemic cardiac disease, it can provide certain indicators of CAD because extensive coronary calcification may be visible or characteristic enlargement of certain cardiac chambers may indicate valvular disease and heart failure.

In routine clinical practice assessment of ischemic cardiac disease, x-ray technology is usually used more during ICA. This invasive approach remains the gold standard to assess CAD, especially because FFR measurements also allow for an accurate evaluation of the hemodynamic significance of coronary stenosis. CAD detected on CCTA may be reaffirmed using ICA, the severity can be quantified using FFR, and it can be simultaneously treated with balloon angioplasty and stent placement when appropriate.

Computed Tomography (Coronary CT Angiography, CT Myocardial Perfusion Imaging)

Due to several major technical improvements over the last decades, CT has evolved into a routinely used modality to detect multiple cardiac pathologies. Currently, it is still mostly used to detect or rule out CAD. For an initial evaluation, a low-dose, unenhanced calcium scoring scan is usually performed to detect calcified coronary plaques ( Fig. 30.1 ). The resulting Agatston score based on this dataset can be used for risk stratification based on an extensive body of research regarding the prognostic value of this calcium score. Nevertheless, especially in younger patients, noncalcified coronary soft plaque or, in the acute setting, a clot or embolus may be present, which would remain undetected on a noncontrast scan. Therefore, a contrast-enhanced CCTA study may be necessary to assess coronary artery patency and high-risk coronary anomalies (e.g., interarterial or intramural course). CCTA is also used to evaluate CABG patency, and newer scanner generations allow for the detection of in-stent thrombosis due to higher spatial and temporal resolution and improved metal artifact reduction algorithms. The combination of recently introduced dose-saving technologies has allowed for a substantial dose reduction, down to submillisievert levels in clinical practice. Thus CCTA has been established as an adequate first-line, rule-out test in patients with suspected CAD, with low to intermediate probability.

In an effort to provide comprehensive cardiac assessment, static and dynamic MPI using CT (CTMPI) has been made feasible ( Fig. 30.2 ). A growing body of evidence demonstrates that additional CTMPI may be helpful to identify patients with hemodynamically relevant coronary artery stenosis. An advantage of CTMPI over other established myocardial viability imaging modalities is the opportunity for a comprehensive, single-modality cardiac assessment. By performing both examinations in the same time slot, without additional patient positioning, this may ultimately prove to be a more time-efficient and cost-effective imaging solution.

Cardiac Magnetic Resonance

Due to several major technical improvements over the last decades, cardiac magnetic resonance (CMR) has evolved into the gold standard for the assessment of left and right ventricular function and myocardial viability without the use of ionizing radiation. There is growing evidence that stress myocardial perfusion CMR is a superior alternative to SPECT for the detection of perfusion deficits. Some have even suggested that this modality may also be particularly useful in women, whose epicardial coronary arteries show no obstruction but who have suspected coronary microvascular dysfunction. An increasing number of pacemakers and intravascular stents are MR-compatible, and several single-shot, free-breathing protocols and motion correction algorithms are available for most imaging indications. In addition, CMR late gadolinium enhancement (LGE) imaging remains the examination of choice for the visualization of myocardial necrosis and scar, as well as the myocardial involvement in a variety of other structural diseases (e.g., cardiac amyloidosis, sarcoidosis, myocarditis). Furthermore, stress dobutamine CMR is a viable alternative to stress dobutamine echocardiography.

Nevertheless, CMR still tends to be more time-consuming than cardiac CT, and some patients still refuse or abort MR examinations due to severe claustrophobia. Thus some of the concepts of CMR, including late-enhancement imaging, have been transferred to CT to allow for similar examination characteristics in selected patients, although such techniques are still under development.

Nuclear Studies

SPECT remains an established MPI technique to detect myocardial ischemia due to the substantial body of research regarding its value as a prognostic indicator. Nevertheless, its relatively high radiation exposure, requirement for a radionuclide tracer, and rather low specificity have led to the development of the other aforementioned MPI techniques. Although cardiac positron emission tomography using ⁸² Rb or ¹³ N-ammonia is also feasible, it is only used by a minority in clinical routine, primarily due to the logistical difficulties in obtaining these radiotracers.