International guidelines around the world have positioned the cardiac CT as a first line test for evaluation of stable chest pain.
General practitioners commonly encounter patients with stable chest pain, and coronary artery disease is always a serious cause that should be considered. Fortunately, coronary artery disease is a preventable cause of morbidity and mortality in Australia.
The choice of initial test for investigating coronary artery disease in stable chest pain often depends on the patient characteristics, local availability and cost. Currently, available tests include exercise stress electrocardiogram or echocardiogram, dobutamine stress echocardiogram, myocardial perfusion stress imaging and cardiac CT.
Although the coronary artery calcium score is increasingly used for risk-stratification in asymptomatic patients, it should not be used in isolation in patients with chest pain, as non-calcified plaque is not detected.
Catheter coronary angiography has traditionally been seen as the gold-standard test for diagnosing coronary artery disease but is an invasive procedure that carries risks. Studies have shown that many patients with stable chest pain referred for this procedure do not actually have obstructive coronary artery disease. Thus, when evaluating chest pain, it is important that non-invasive tests can risk-stratify patients and assist in deciding whether further testing or medical therapy is required.
The cardiac CT is a robust non-invasive imaging modality that provides a 3-dimensional assessment of the coronary arteries, atherosclerotic plaque burden and degree of stenosis. American and European guidelines now support cardiac CT as a first line test in low-intermediate risk patients with stable chest pain. Due to its very high sensitivity, a normal CT coronary angiogram provides clinicians with confidence in ruling-out coronary artery disease. The clinician can then consider alternate causes for the patient’s symptoms. In addition, patients with a normal scan are at low short-term risk of cardiac events and may avoid unnecessary stress testing or preventive therapies.
When coronary artery disease is detected, the cardiac CT can provide information on overall plaque burden, plaque location and can assess whether plaque is causing significant stenosis or obstruction, which could be the cause of chest pain. If a severe stenosis is identified in a major coronary artery, cardiology referral and invasive coronary angiography may be indicated. If a moderate (50-69%) stenosis is identified in the setting of stable chest pain, further evaluation can be undertaken with a stress test to determine whether the stenosis is haemodynamically significant.
Stress tests are very commonly performed in general practice to assess for obstructive coronary artery disease, which is seen as inducible ischaemia on the test. In patients with a high probability of obstructive coronary artery disease, or who have known coronary artery disease, stress testing may be preferred over cardiac CT. However, stress tests can also be positive for other reasons such as microvascular disease or coronary vasospasm.
Importantly, patients with diffuse and non-obstructive coronary artery disease are likely to go undetected by stress tests. The ability to identify non-obstructive plaque, even if it is not the cause of chest pain, is a crucial advantage of cardiac CT. Patients with mild coronary artery disease are at increased cardiovascular risk and plaque rupture causing myocardial infarction can occur even in non-obstructive plaque. Cardiac CT has been shown to guide the use of preventive therapies such as statins and aspirin. In the patients with coronary artery disease, prognosis can be improved by implementing these preventive therapies.
Remarkably, technological advances and analysis of plaque morphology and composition have allowed patients a more personalised approach to cardiac assessment. Artificial intelligence helps to optimise image acquisition, analysis and diagnostic accuracy. Radiation exposure has significantly reduced, such that scans can be performed at doses <5 mSv.
The cardiac CT can now be used to identify high-risk or “vulnerable” plaque (prone to rupture) and perivascular inflammation, both of which are predictive of myocardial infarction. Although not yet widely available, CT-derived fractional flow reserve can turn the CT coronary angiogram into a stress test as well, by using computational fluid dynamics to assess whether a stenosis is haemodynamically significant.
Although cardiac CT is available in many imaging practices throughout Australia, Medicare reimbursement is only available via specialist referral. With increasing evidence and support from international guidelines, there should be strong consideration for incorporating cardiac CT into Australian clinical pathways for the evaluation of patients presenting with stable chest pain.
Dr Abdul Ihdayhid is a consultant cardiologist at Fiona Stanley Hospital, research leader in cardiovascular biology at Curtin University and a clinical advisor at Artrya Ltd.
