Minor clogging of heart arteries: cause for concern?

AS THE population ages, the prevalence of narrowing of the heart arteries (also called coronary artery disease or CAD) becomes more prevalent. If your doctors suspect that you may have narrowing of your heart arteries, to confirm whether you have clogging of your heart arteries, the doctors may use a non-invasive computed tomography (CT) scan of the heart arteries (coronary CT angiogram or CCTA) or an invasive imaging of the heart arteries called coronary angiogram (Invasive coronary angiography or ICA) to record the degree of diameter narrowing of the heart arteries.

Having had one of these tests done and having been told by your doctors that you have minor narrowing of the heart arteries, you may heave a sigh of relief. So the question is, does it mean that you are not at risk of a heart attack in the future?

A research paper published by Chang in July 2018 in the Circulation: Cardiovascular Imaging journal may provide some answers to this question.

Historically, the diagnosis of CAD have been based primarily on the criterion that there is a presence of narrowing of the luminal diameter of at least 50 per cent of a major heart artery, which is defined as obstructive CAD. Little attention is paid to non-obstructive CAD where the luminal diameter narrowing is less than 50 per cent.

Similar - but not the same

Both CCTA and ICA are tests which involve the infusion of contrast into the heart arteries, and X-ray images of the heart arteries are taken when the arteries are filled with contrast. This is where the similarity ends. ICA is an invasive test whereas CCTA is a non-invasive test. ICA involves the insertion of plastic tubes through the wrist or groin artery and contrast is injected after the tubes are manipulated to the opening of the heart arteries. CCTA is non-invasive and involves the injection of contrast into the arm vein and the use of a CT scanner to take pictures of the heart arteries.

ICA is a two-dimensional test and can only allow visualisation of the lumen of the heart artery when it fills with contrast. The degree of stenosis is determined by comparing the narrowed segment with the adjacent segments of the heart artery. It does not allow visualisation of the heart artery wall and hence if there is diffuse disease, the degree of stenosis may be underestimated as the "normal" appearing adjacent segment which is used as the reference diameter for comparison may actually have disease.

The CCTA is a three-dimensional scan allowing not only visualisation of the heart artery lumen but also the wall of the heart artery. Hence, when assessing the degree of stenosis of a narrowed segment, the reference diameter can be the diameter of the vessel at the site of luminal stenosis. So in patients with diffuse disease, do not be surprised if the significant stenosis as measured on the CCTA may not appear so severe on the ICA. It is not that either test is wrong but rather the stenosis as measured on a two-dimensional ICA test may not be the same as that seen on a three-dimensional CCTA.

Non-obstructive coronary artery disease

This research paper by Chang is interesting in that it uses CCTA to quantify the amount of plaque and the characteristics of the plaque to predict progression of heart disease. As CCTA is three-dimensional , the use of CCTA instead of ICA is a better reflection of the amount of clogging in the heart arteries.

In this study, the presence of at-least 50 per cent in diameter-narrowing was considered as clinically significant obstructive CAD. The study found that in patients with non-obstructive CAD, the presence of high plaque burden (quantity of plaque in heart artery) and a rapid rate of plaque progression had the worst outcomes.

In a study by Maddox published in the Journal of the American Medical Association in 2014 entitled Nonobstructive coronary artery disease and myocardial infarction",

patients were divided into a few groups based on the extent of the heart artery disease: no apparent CAD group (coronary luminal diameter narrowing of less than 20 per cent), non-obstructive CAD, obstructive CAD and also taking into account whether it affected one, two or three major heart arteries.

The one-year incidence of heart attack was 0.11 per cent in those with no apparent CAD, 0.24 per cent in those with 1-vessel nonobstructive CAD, 0.56 per cent in those with 2-vessel nonobstructive CAD, 0.56 per cent in those with 3-vessel nonobstructive CAD, 1.18 per cent in those with 1-vessel obstructive CAD, 2.18 per cent in those with 2-vessel obstructive CAD, 2.47 per cent in those with 3-vessel obstructive CAD.

The study also showed that the more extensive the CAD, the higher the incidence of heart attacks and deaths. The one-year death rates ranged from 1.38 per cent among patients without apparent CAD to 4.30 per cent in those with 3-vessel obstructive CAD.

After taking into account the risk profile of the patients and making the appropriate statistical adjustments, it was found that there was no significant association between 1- or 2-vessel non-obstructive CAD and death. However, there were significant associations with death for 3-vessel non-obstructive CAD and all categories of obstructive CAD.

Implications for Heart Health

In an editorial in the same journal accompanying the article by Chang, the view is that CCTA is the only non-invasive test for direct visualisation of clogging in the heart arteries, and there is an increasing impetus to consider this as the first line test for those suspected to have CAD in place of stress-testing such as treadmill tests, nuclear scans (which involve the administration of isotopes) and stress echocardiography (ultrasound assessment of the heart under stress). The fact is that CCTA is more accurate than stress-testing for detecting CAD, and CCTA is superior for risk stratification.

Data from major studies such as the PROMISE (Prospective Multicenter Imaging Study for Evaluation of Chest Pain) and SCOT-HEART (Scottish Computed Tomography of the Heart) trials, as well as a registry with more than 86,000 patients, demonstrated about 30 per cent risk reduction for heart attack in patients with chest pain whose decisions on treatment were guided by CCTA versus conventional care using stress-testing to guide decisions.

CCTA is the only non-invasive test that is able to identify those with early CAD, and hence this allows doctors to prescribe preventive measures. Importantly, in the PROMISE trial, more than two thirds of heart attacks and deaths occurred in patients who had normal stress test results, highlighting the significance of non-obstructive CAD. As such it is not surprising that CCTA is now the first-line test for the evaluation of patients with suspected CAD in the United Kingdom and it is likely that this will soon be the case in the United States.

Hence, if you have chest pain and are making a decision about testing, you should have a discussion with your doctor about the choice of test. In addition, should you have non-obstructive CAD, do not be complacent but rather you should take appropriate changes in lifestyle to prevent heart disease. Remember that making heart attack impossible is not mission impossible.

This series is produced on alternate Saturdays in collaboration with Singapore Heart, Stroke and Cancer Centre.