Preventing Coronary Artery Disease
Coronary artery disease (CAD) is the number one killer of Australians and is due to the presence of atheroma, or “plaque”, in the heart’s arteries. Plaque is mainly composed of cholesterol and/or calcium and can cause angina (exertion-related chest discomfort due to progressive narrowing of a heart artery) or a “heart attack” (sudden chest pain at rest due to sudden blockage of a heart artery by blood clot). In up to two-thirds of patients who die suddenly from a CAD-related cardiac arrest, there are no preceding symptoms, meaning that accurate risk assessment to implement timely preventative measures is crucial.
Established risk factors for CAD are either non-modifiable or modifiable;
- Non-modifiable
- Male gender
- Increasing age
- Family history of CAD (esp. first-degree relatives)
- Modifiable
- Elevated blood pressure (hypertension)
- Elevated blood lipids (inc. cholesterol & triglycerides)
- Diabetes
- Smoking
CAD risk calculators, such as the “Australian Absolute Cardiovascular Disease Risk Calculator” (http://www.cvdcheck.org.au/calculator/) use population-based data to predict whether an individual’s risk of cardiovascular disease in the following years is “low”, “moderate” or “high”. These risk calculators, while clinically useful, only provide an estimate of CAD risk. These estimates are far from perfect – for example, at the time of their first “heart attack”, up to 75% of patients would not have qualified for preventive therapy.
Prevention strategies, comprised of risk factor modification ± aspirin and cholesterol lowering medications, can significantly reduce the risk of CAD. However, selecting who should be targeted for more aggressive preventative strategies remains problematic as a relatively large proportion of the asymptomatic population are classed as “moderate” risk using the aforementioned risk calculators and hence the benefit of preventative therapy is uncertain.
Coronary artery calcium (CAC) scoring can better personalise an individual’s CAD risk. Using a simple, quick and non-invasive CT scan performed at a radiology facility, an individual’s CAC score can be calculated by counting the overall burden of calcium plaque in their heart arteries. A score of 0 implies the absence of calcium-containing plaque whereas any score >0 indicates the presence of plaque, with a higher score equating to higher CAD risk.
A CAC score, however, does not assess how narrowed by plaque an artery is. Blood flow to the heart muscle is limited when a plaque obstructs an artery by >70%. To determine whether a plaque is “obstructive” a stress echocardiogram can be performed. A stress echocardiogram consists of ultrasound imaging of the heart before and after exercise on a treadmill. Normally, both heart rate and heart contractility increase with exercise. However in the presence of an “obstructed” artery, parts of the heart muscle fail to contract appropriately. For these patients, an invasive coronary angiogram may be performed, with heart artery stenting or bypass surgery to follow if obstruction is confirmed.
For patients with coronary artery plaque, regardless of whether it is obstructive, aggressive risk factor optimisation is essential. This includes lowering blood pressure (preferably to <130/80 mmHg), lowering LDL cholesterol, preventing/controlling diabetes and cessation of smoking. Conservative approaches to achieve this include increased exercise, improved dietary habits and weight loss – these measures may be combined with medications at your doctor’s discretion.
You can prevent CAD – please consider discussing your CAD risk with your GP.