Women who have heart artery disease are often under diagnosed as they usually do not display typical symptoms. By Michael Lim
THE differences between women and men extend to the nature of heart artery disease. Most of the research data that has been published on heart artery disease was mainly based on study populations that had a predominantly male bias and it is only more recently that there has been evidence that women often do not have typical symptoms. This has resulted in under diagnosis and under treatment of women with heart artery disease, leading to higher death rates and increased complications.
Non-chest pain symptoms
While men with blockage of their heart arteries usually experience chest pain or chest tightness on physical exertion, women may have symptoms that are precipitated by mental or emotional stress rather than physical exertion. In addition to chest pain, women may suffer from upper abdominal discomfort, pain radiating to neck or arm, tiredness or shortness of breath. Due to the non-specific symptoms of women, there may be a possibility of an increasing referral of women for diagnostic testing to determine more accurately those who have a higher likelihood for heart attacks in the future.
To address this concern, a June 2014 American Heart Association (AHA) Consensus Statement on the role of non-invasive diagnostic testing for women addresses the choice of diagnostic testing in the most cost effective manner based on current evidence.
The use of questionnaire-based risk scoring systems, also termed global risk assessment, attempts to determine the likelihood of heart artery disease. Much of the data used was old and hence less applicable to current situations. The Framingham risk score, which was the most commonly used, has been abandoned in favour of a new risk scoring system proposed by the AHA. The new system is meant for use in specific population groups in the US and is not meant to be applied to Asian populations. Furthermore, risk assessment scoring systems are meant for asymptomatic populations and are not meant to be used for those with symptoms.
How then should women decide when to seek assessment for heart artery disease? A few general principles prevail based on current evidence. The likelihood of significant heart artery disease increases with age and with increased number of risk factors such as smoking, high cholesterol, diabetes, high blood pressure and family history of heart disease. Women who are symptomatic but are premenopausal are considered low risk unless they have diabetes. Those in their 50s to 60s who are limited in their activities by symptoms are considered of intermediate risk and those in their 70s or older who are symptomatic are considered high risk. If they have multiple risk factors, the risk category will be increased by one category. Those considered high risk will also include those with stroke, impairment of kidney function, smoking related lung disease, and blockage of leg arteries.
Choice of tests
Low risk premenopausal women generally do not require diagnostic testing although there may be exceptions. For low risk premenopausal women with symptoms very typical of heart artery disease, a treadmill stress test can be considered as the first choice test. The most important consideration for premenopausal women undergoing diagnostic assessment for their heart is to avoid the use of tests that require exposure to X-ray or ionising radiation which means that nuclear and X-ray scans of the heart should be avoided, and other alternatives should be considered.
For those who are considered to be of intermediate risk (premenopausal women with risk factors or women in their 50s to 60s with typical symptoms), a treadmill exercise stress test can be the first option for diagnostic assessment provided that the resting electrocardiogram (ECG) is normal and the person is able to perform a treadmill test. The ECG is a recording of the heart’s electrical pattern and if the ECG at rest is abnormal, it may affect the accuracy of the treadmill test. Those with intermediate to high risk who are unsuitable for treadmill test should be considered for a nuclear scan, cardiac magnetic resonance imaging (MRI) scan or computed tomography (CT) scan to assess the heart.
Exercise stress test
Many women in their 50s and 60s find the standard treadmill protocol too physically demanding and hence, these women should discuss with their doctors about using modified protocols (such as the modified Bruce protocol) which provide a more gradual increase in exercise level. However, if despite using a physically less demanding protocol, they are unable to achieve 85 per cent of the maximum predicted heart rate, heart disease should be suspected. The new formula for calculation of maximum heart rate is 206 – (0.88 x age). Those who are unable to complete 85 per cent or more of their age-predicted heart rate have at least two times increased risk of death. If a standard Bruce protocol is used, the inability to go beyond stage one of the Bruce protocol or achieve more than five metabolic equivalents of exercise predicts increased risk of death and other events related to blockage of heart arteries independent of traditional risk factors.
One needs to understand the limitations of a treadmill test. In meta-analysis of 19 exercise treadmill stress tests, the average sensitivity and specificity of the tests were 61 per cent and 70 per cent for women respectively, and 72 per cent and 77 per cent among men. It means that for every 100 women with significant blockage of the heart arteries, the treadmill test will be abnormal for 61 and 39 may go undetected.
Of the other non-invasive tests available, stress echocardiography (ultrasound imaging of the heart) and MRI scans have no X-ray radiation and are options for symptomatic women at intermediate to high risk of heart artery disease, and can even be used for premenopausal women. Nuclear scans and CT scan of the heart arteries have X-ray radiation. A stress nuclear scan of the heart has X-ray radiation exposure of about 11 mSv. (millisievert or mSv is the unit used to measure radiation exposure to the body). The potential impact of this radiation dose is an estimated additional three to eight persons at risk of cancer for every 10,000. CT scan of the heart arteries will typically result in three to five mSv using low dose scanning protocols and 12 to 25 mSv for standard protocols.
Invasive coronary angiography, which involves inserting tubings into the heart arteries, has an average radiation dose of about seven mSv depending on the number of views taken. Real world accuracies for these tests can differ substantially from reported published data from high volume centres. As stated in this June’s AHA statement, “the issue of local expertise guides test performance and selection for all imaging modalities” and this means that local expertise has an impact on the accuracy of the tests chosen.
For symptomatic women with intermediate risk with abnormal resting ECG or uncertain or abnormal treadmill test, CT scan of the heart arteries is a reasonable option as it allows visualisation of the heart arteries unlike, stress echocardiography or nuclear scans. For premenopausal women with functional disability, CT of the heart arteries can also be considered if the centre is able to achieve a radiation dose of not more than three mSv. Unlike men, symptomatic women with non-significantly blocked heart arteries are at increased risk of heart attacks and can benefit from medical treatment. One of the advantages of CT is that women with non-significant blockage of the heart arteries can be identified. Last but not least, MRI of the heart arteries is an option where no X-ray radiation and no injection is required but it is only available in few specialised centres. As it is not associated with any X-ray radiation, it can be used even for premenopausal women with suspected heart disease.
In summary, symptomatic premenopausal women do not require testing unless they have risk factors. If testing is required, a treadmill test is the first choice. However, if the treadmill test cannot be performed because of physical limitations or abnormal resting ECG, other options such as MRI scan or stress echocardiography which do not have any X-ray radiation should be considered. CT scan should only be considered if a radiation dose of 3 mSv or less can be achieved. For those with intermediate to high risks, the choice of the test should take into consideration the cancer risk of X-ray radiation and the accuracy and expertise of the centres providing the tests.