Testing for heart disease

IF you have chest pain and have limited financial resources, what is the single test which can best help you confirm whether you have heart artery disease (coronary artery disease or CAD). The answer can be found in an editorial by Professor Pamela Douglas from the Duke University School of Medicine which was published in the prestigious Circulation journal in August 2016. The article reviewed the major studies that compared the latest advances for diagnosis of heart disease using computed tomography angiogram (CTA) as compared to conventional diagnostic tests.

Stress testing versus direct visualisation

First-line tests to diagnose CAD are non-invasive, and do not involve the insertion of tubes into arteries. Non-invasive tests can be divided into two broad groups. The first group, functional or stress testing, involves stressing the heart by increasing the heart rate with drug infusion or exercise, and indirectly trying to assess whether there is insufficient blood flow to segments of the heart muscle due to significant narrowing of the heart artery when the demand for oxygen supply increases under stress testing. This can take the form of changes in the electrical pattern of the heart (treadmill testing), transient decrease in the motion of the heart pump (stress echocardiography) or uneven distribution of radioactive isotopes in the heart muscle (MIBI scan, Thallium scan or Rubidium PET scan).

The second group are non-invasive tests that allow direct visualisation of the heart arteries. Currently, only CTA and magnetic resonance of the heart arteries are able to accomplish this. CTA involves the injection of iodine based contrast into the veins and taking X-ray images of the heart arteries within seconds. The scan provides two and three-dimensional images of the lumen and wall of the heart arteries. The magnetic resonance scan of the heart arteries provides images of the lumen of the heart arteries but is only performed in a highly specialised system and is not readily available.

Clinical studies on diagnostic testing of the heart

2015 marked an important milestone where the results of several large studies which compared the use of CTA with the use of stress testing for the assessment of chest pain were published. These studies included the PROMISE (Prospective Multicenter Imaging Study for Evaluation of Chest Pain), SCOT-HEART (Scottish Computed Tomography of the Heart), and PLATFORM (Prospective Longitudinal Trial of FFRCT Outcome and Resource Impacts; clinical outcomes of FFRCT-guided diagnostic strategies versus usual care trial).

With regard to patients with chest pain and risk factors for heart disease, current American College of Cardiology/American Heart Association guidelines consider that referral for testing is appropriate in these patients. What was common in all the major studies was that compared to stress testing, CTA results assisted the doctors to make better diagnostic decisions and reduced the need for expensive invasive tests that involve the insertion of plastic tubes into heart arteries (coronary angiogram or CAG).

Avoid unnecessary invasive tests

In the PLATFORM study of patients selected to undergo coronary angiogram following usual stress testing, 73 per cent of these CAG studies did not show significant obstructive coronary artery disease. What it meant was that if we had better non-invasive diagnostic tests, almost three quarters of these CAG studies could have been avoided, resulting in significant cost savings and avoiding unnecessary utilisation of hospital resources.

In this study, CTA augmented by software to analyse flow characteristics during the CTA was able to reduce the incidence of CAG studies with no obstructive disease from 73 per cent in the usual stress testing group to 12 per cent in the CTA group. Hence, CTA is a much more accurate test compared to conventional stress tests and is less likely to give a "false-positive" result. Both PROMISE and SCOT HEART studies also demonstrated similar results with less unnecessary CAG studies when using CTA as compared to the use of stress or functional testing.

Impact on future prognosis

Unlike functional testing which does not allow visualisation of the heart arteries, CTA can provide both two and three dimensional visualisation of the heart arteries. Being able to visually see the degree of obstruction of the heart arteries and the presence of cholesterol deposits (plaques) in the walls of the arteries will not only help the physicians understand the severity and extent of the plaque in all the segments of the heart arteries (not possible with functional testing) but also influence their decisions on giving appropriate treatment based on the extent of disease visualised. In addition, the visual impact will also motivate patients who have extensive disease to take more proactive preventive measures.

In the SCOT HEART study, 23 per cent of patients undergoing CTA had a change in their medications as compared to only 5 per cent in those who underwent stress or functional testing. Hence, non-invasive testing, especially CTA, provided an opportunity for both the physician and the patient to proactively reduce the future risk of heart disease by optimising the medical treatment based on the extent of the disease.

These studies showed that for women, CTA was superior in predicting the prognosis as compared to functional testing. In men, the prognostic value of a CTA was similar to that of stress or functional testing. Presently, the most applicable risk assessment tool used by physicians for calculation of likelihood of significant blockage of the heart arteries prior to doing tests is the Diamond and Forrester risk assessment scoring system. However, the data from PROMISE showed that this widely used tool was also widely off the mark. The risk tool overestimated the likelihood of CAD as 53 per cent whereas the actual prevalence was only less than 15 per cent. Hence, even some of the best risk assessment tools that are widely used are highly inaccurate for predicting the presence of significant CAD.

Stretching your health dollar

For those with chest pain and risk factors, CTA is superior to other non-invasive stress or functional testing. The reasons include:

Hence, based on the results of recently released large scale studies, CTA has certain intrinsic advantages that can allow it to be considered as the single best non-invasive test for the diagnosis of heart disease. Routinely, for full paying patients, many healthcare institutions charge more than S$1,000 for CTA of the heart arteries with the bill going beyond S$1,500 for inpatients in some hospitals. However, there are also healthcare institutions which charge less. Hence, choosing the right test and spending a bit of time to compare prices can help you stretch your health dollar.