Approximately 50% of first heart attacks are fatal. Waiting for the first event to decide on treatment strategies is not recommended! Diet and lifestyle are central recommendations, and cholesterol lowering medications are common (centred around statins). Risk prediction models (e.g. Australian Cardiovascular Risk Calculator www.cvdcheck.org.au) should be used in every patient. These probability and population-based tools may not reflect an individual’s actual disease burden so further testing can help guide management.
Coronary Artery Calcium Score (CACS) is inexpensive, fast, low radiation, providing an absolute score (approximately $150, no Medicare rebate). A CACS score of zero is normal. Any non-zero score (1- 10 minimal, 10 -100 mild 101-400 moderate and over 401 large plaque burden) is abnormal indicating the presence of atherosclerosis. Decisions to treat are often made based on CACS, which makes intuitive sense but is not strictly evidence based. A large randomised trial (the CAUGHT-CAD study) testing this approach is currently underway in Australia.
CT coronary angiography (CTCA) involves a contrast injection during coronary CT. The coronary arteries are reconstructed using 3D imaging, and an accurate assessment of plaque burden is reported along with CACS. CTCA is about $500, but provides more information than CACS alone. It is best suited to asymptomatic moderate risk individuals, to evaluate atypical chest pain, or for assessment of prior coronary bypass grafts.
Conventional coronary angiography, invasive, requiring arterial puncture and catheters inserted into the coronary arteries, is well suited for acute coronary syndromes or evaluation of a haemodynamically significant stenosis. It should not be performed in asymptomatic individuals at low to moderate risk. Mild coronary disease (without stenosis) may be completely missed.
Stress ECG (continuous 12 lead ECG monitoring during exercise) is well suited for patients with angina symptoms, and to assess exercise tolerance. It is not recommended for asymptomatic moderate to low risk individuals, being neither sensitive nor specific. The most likely abnormal result in this group is a false positive test, which inevitably leads to further testing, expense and un-necessary concern.
Stress Echo or Stress Nuclear Imaging have superior sensitivity and specificity compared with stress ECG, but are most suited to patients with classic symptoms. Stress echo has some advantages over stress nuclear in that it is free of radiation, cheaper, and can assess functional changes (e.g. valve gradients and diastolic filling) with exercise. Stress imaging does not exclude subclinical coronary disease so is not recommended in asymptomatic low to moderate risk individuals.
Resting Echo assesses structure and function of the heart, including systolic and diastolic function, pulmonary pressures and valve disease but not coronary disease unless there is severe disease or prior infarction, resulting in abnormal left ventricular function at rest.
Asymptomatic 60-year-old male: Risk factors: LDL 3.6. BP 140/80. Fasting BSL 5.5, Mild visceral obesity, BMI 30, non-smoker, no family history of premature CVD. A prior exercise stress echo, requested by another General Practitioner for cardiovascular risk prediction, showed good exercise tolerance (8 min, 30 sec), normal LV augmentation, and no ECG abnormalities at rest or with exercise. The patient asked you whether he should take cholesterol medication.
Which test best decides whether atherosclerosis is present? In this case, a CT coronary angiogram. In the absence of symptoms or impaired exercise tolerance, there is no reason to expect the stress echo to be abnormal, even if atherosclerosis is present. The CT coronary angiogram showed a calcium score of 837, with multiple areas of calcified and noncalcified plaque throughout his coronary tree. This is an important result, suggesting a significantly increased long term cardiovascular risk.
Which treatment? There is no absolute answer. Diet and lifestyle advice should be given and followed closely. It is common to treat with aspirin and statin, plus or minus blood pressure treatment. Whilst a CT based management approach makes sense and appears the clearest “individualised” treatment approach available, it has not been fully validated by clinical trials, the results of which are eagerly awaited.
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