Clinical application of cardiac computed tomography: implications for chest pain assessment

Chest pain is a common and potentially life-threatening symptom that represents a global health and economic challenge. The prompt and accurate evaluation of chest pain has considerable implications for patient morbidity and mortality as well as on health care economics, however accurate identification of the aetiology of a patient’s chest pain is associated with many diagnostic challenges and potential pitfalls. Most current diagnostic strategies for chest pain focus on the detection of acute coronary syndromes and are based on the premise that other potential diagnoses can be excluded with careful clinical assessment. Therefore, efforts to improve the efficacy of the evaluation of chest pain patients have incorporated newer diagnostic strategies and modalities, such as new cardiac biomarkers and non-invasive imaging techniques. These approaches are typically used in various combinations as part of diagnostic protocols for patients admitted to chest pain units. If the initial evaluation shows no evidence of acute coronary syndrome or myocardial ischaemia, a confirmatory study is usually performed to exclude obstructive coronary artery disease or ischaemia. Although exercise treadmill testing (often with echocardiography or myocardial perfusion imaging) is widely used as a confirmatory test, coronary computed tomography angiography (CCTA) is becoming increasingly used as an alternative, primarily due to its very high sensitivity and negative predictive value in excluding obstructive coronary artery disease as a cause of chest pain. However, CCTA is a relatively new technique compared to established stress testing techniques, and has not yet demonstrated safe long-term outcomes in the acute chest pain setting. Since the introduction of CCTA imaging approximately 15 years ago there has been a steady improvement in image acquisition time, number of x-ray detectors employed, spatial and temporal resolution as well as a reduction in radiation and contrast dose. This has resulted in improved image quality and diagnostic accuracy for the detection of obstructive coronary artery disease, non-coronary structural heart disease and myocardial ischaemia, all of which are important aspects in determining the aetiology of a patient’s chest pain with the potential to change risk stratification of coronary artery disease. This includes patients with stable chest pain syndromes, as well as patients at low to intermediate risk of an acute coronary syndrome who present to an Emergency Department with acute chest pain. In addition there is growing interest in applications beyond assessment of coronary anatomy, including evaluation of non-coronary cardiac anatomy and extracardiac structures that may identify an alternate cause for the patient’s chest pain, as well as assessment of myocardial perfusion, which simultaneously allows a single examination to identify coronary artery anatomy, coronary artery stenosis and the functional significance of coronary artery stenoses. Whether recent CCTA advances translate into more accurate diagnosis of the cause of patients’ chest pain is yet to be fully determined. Similarly, it is not yet known whether the use of this technology will result in acceptable long-term safety outcomes in the chest pain population presenting to the Emergency Department. A more in depth exploration of the potential role of novel CCTA techniques in these areas is essential to establish the place and appropriateness of this technology in contemporary cardiac practice. This thesis, which explores the clinical application of CCTA and other novel imaging techniques in the contemporary assessment of chest pain, has the following specific aims: 1. To provide an in-depth review of the current evidence regarding the clinical utility of CCTA in the assessment of stable and acute chest pain syndromes, considering the latest advances in CCTA techniques and their potential clinical application to improve patient care in a cost-effective manner (chapter 2). 2. To provide a comprehensive overview of the role of multidetector computed tomography in the assessment of structural heart disease, including the detection of alternate causes of chest pain beyond coronary artery disease, the evaluation of myocardial perfusion and the assessment of emerging peri-procedural clinical applications (chapter 3). 3. To evaluate the long-term safety outcomes and hospital readmission rates of patients presenting to the Emergency Department with possible acute coronary syndrome after investigation with a novel CCTA-guided algorithm (chapter 4). 4. To establish the prevalence and anatomic characteristics of coronary arteries arising from an anomalous location detected by CCTA and determine the impact of high-risk anatomic characteristics on patient management and medium-term safety outcomes (chapter 5). 5. To determine the diagnostic accuracy of combined 320-detector CCTA and adenosine stress computed tomography perfusion imaging in detecting perfusion abnormalities caused by obstructive coronary artery disease in symptomatic patients; and to investigate whether 320-detector computed tomography perfusion imaging, when added to resting CCTA, provides incremental diagnostic accuracy to CCTA alone in detecting myocardial ischaemia (chapter 6). 6. To investigate whether patients undergoing treadmill stress echocardiography with an abnormal left ventricular contractile response to exercise without obstructive coronary artery disease or other established causes have resting left ventricular long-axis dysfunction, and to determine independent associations with this abnormal response (chapter 7)