Choosing the right test for heart disease

"I'm not afraid of dying; I just don't want to be around when it happens." - Woody Allen

AS HEART doctors, we are often approached by patients with concerns about their risk of developing a heart attack, especially after having heard of a recent sudden event involving a friend or colleague. One common question we get is whether they should undergo screening for heart disease, and what test they should do.

There are many tests for heart disease, ranging from the treadmill test (ECG) to the invasive angiogram. Although it might seem obvious that we should just use the most accurate test, each does have its own strengths and limitations.

The Computed Tomography Angiogram (CTA) is one of these assessments that has recently garnered great interest. It is a non-invasive test using X-ray dye to look for narrowing in the heart arteries.

While accurate, the CTA is less ideal for patients who also present with irregular heart rhythm, impaired kidney function, or heavy calcification of the heart arteries as these factors can affect the results of the test.

Other assessments such as stress testing combined with imaging (stress imaging) are sometimes needed to evaluate blood flow in the heart arteries to ascertain the necessity of further invasive treatment.

At the risk of over-simplification, we can broadly classify these tests into two categories -those that assess the heart's anatomy (presence or absence of narrowing of heart arteries); and those that assess blood flow and function.

Both types of information are sometimes required to tailor the care plans for heart patients.

Expert international guidelines recommend considering patients' symptoms, risk factors and their likelihood of developing heart disease when choosing a suitable test:

For patients with no symptoms, guidelines recommend testing for risk factors such as high cholesterol and diabetes.

Routine testing for heart disease with tests such as CTA is not recommended for asymptomatic individuals.

For patients with a low (less than 10 per cent) likelihood of heart disease (for example, non-anginal chest pain), some guidelines favour treadmill ECG testing, while others recommend not performing any further cardiac testing.

For patients with an intermediate likelihood of heart disease, some guidelines favour using CTA, while others recommend exercise testing with imaging, especially if patients are able to exercise.

For patients with a known history of heart disease (for example, previous heart attack), stress imaging is recommended for evaluating new symptoms.

Why are different tests recommended for different situations? We often need information for both anatomy and blood flow during exercise to make decisions about diagnosis and treatment; no single test is routinely able to provide this information.

It is natural to assume that the degree of narrowing is the most important predictor of a heart attack, but a study of close to 700 patients (PROSPECT) who underwent invasive coronary angiogram and advanced imaging showed that the degree of narrowing does not predict whether a heart attack will occur.

Heart attacks can occur suddenly even in areas of mild narrowing due to blood clots forming in unhealthy arteries.

Recovery outcomes

Ultimately, choosing a test should depend on whether it can lead to better recovery outcomes.

The largest trial (PROMISE) comparing CTA to stress testing with imaging, that is, perfusion scans or echocardiogram (ECG) in 10,000 patients with chest pain, showed no difference in clinical outcomes (death, heart attack or hospitalisation) after two years of follow-up, suggesting that either approach is reasonable.

A trial of 4,000 patients with chest pain (SCOT-HEART) provided evidence favouring CTA for reducing heart attacks.

However, in that study, CTA combined with usual care (mainly treadmill ECG testing) was compared to usual care alone; where only a minority of those patients had undergone stress imaging.

A normal test result can indicate a low risk, but not zero risk. A local review of over 10,000 asymptomatic individuals who took the treadmill ECG test showed that a normal test had an annual less than 0.1 per cent risk of developing a heart attack.

In the PROMISE study, patients with chest pain but a normal CTA result had a low but not zero risk of occurrence (0.9 per cent) over two years.

Since low risk does not mean no risk, it is important to manage risk factors such as high cholesterol, smoking and lifestyle choices, rather than relying on testing alone to prevent heart attacks.

While tests cannot perfectly mitigate these episodes, you can certainly reduce the risk by being aware of symptoms such as exercise-induced chest discomfort, controlling blood sugar and cholesterol levels, as well as other risk factors.