There are now safer alternatives to the old gold standard, invasive coronary angiography. By Michael Lim
YOU have chest pain on exertion or you have just been told that your treadmill stress test is abnormal, and you are advised to undergo a procedure called invasive coronary angiography (ICA) which involves the insertion of specially designed plastic tubes through your leg artery to take pictures of your heart arteries using iodine based contrast media under X-ray imaging. ICA is one of the most commonly performed diagnostic tests for patients suspected to have heart disease. In light of the advances in imaging of the heart arteries over the last decade, is ICA, which has been the “gold” standard for imaging of the heart arteries, still the best choice for you?
The updated July 2014 American College of Cardiology and American Heart Association guideline for the diagnosis and management of patients with stable heart disease due to blockage of the heart artery provides answers to this question. The irony is that although ICA has been performed for decades, there is as yet no strong scientific data to provide the basis for recommending an ICA. Furthermore, the guideline states that the potential additional benefit of confirming the presence or absence of blockage of heart arteries by ICA has yet to be confirmed by well designed studies. Hence, the guideline states that there is no strong evidence to support the routine recommendation of ICA for those with suspected blockage of heart arteries. ICA has been the “gold” standard by virtue of the fact that it was the only method that could allow the visualisation of the heart arteries in the past. It was basically a case of Hobson’s choice. The advancing tide of technology has gradually eroded the value of ICA as a diagnostic tool for heart artery disease in the last decade as seen through the evolution of safer non-invasive methods to visualise the heart arteries, namely the use of computed tomography (CT) scan and magnetic resonance imaging (MRI).
What should one do when chest pain occurs and there is reason to suspect underlying heart disease after clinical risk assessment? The current guidelines recommend that the most appropriate first test of choice should be a non-invasive test. Wherever practical, an exercise stress test should be the first test of choice for women with chest pain suspected to have heart disease. For women in particular, tests that involve exposure to X-ray radiation should be avoided and if these tests are necessary, these tests should not result in an X-ray radiation exposure of more than three millisieverts (equivalent to the average background ionising radiation that a person is exposed to annually)
In practice, if the results of non-invasive testing such as treadmill test, stress echocardiography (ultrasound) or stress nuclear heart scan are inconclusive or of borderline significance, it is a common practice to proceed to do ICA. While this has been a prevalent practice, advances in medical science have provided alternative options. CT scan of the heart arteries may be a more appropriate and a safer alternative than ICA in this situation. Rapid advances in CT technology have resulted in increasing indications for the use of CT scan in place of ICA. CT scan has several advantages over ICA; it can be performed as an outpatient within seconds, is non-invasive, is of lower cost, has lower radiation dosage (for new generation scanners), is three dimensional and can visualise detailed characteristics of the plaque (such as soft or hard plaque, presence and severity of calcium deposits). MRI of the heart arteries is a relatively newer modality which is less readily available but it has the advantages of being non-invasive, performed as outpatient procedure, has absolutely no X-ray radiation, and does not require any injection.
ICA carries real risks. The 2012 American College of Cardiology National Cardiovascular Data Registry CathPCI Registry recorded a 1.5 per cent incidence of complications from ICA. Complications included death, stroke, heart attacks, bleeding, infection, allergic reactions, damage to vessels, kidney damage due to contrast, abnormal heart rhythms, and emergency heart bypass surgery. The risk factors are age over 70, severe heart failure , severe valve disease, serious medical conditions, bleeding abnormalities, or allergies to contrast dye. The risk of contrast-induced kidney damage is increased in those with kidney disease or diabetes mellitus. In addition, there are at least six prospective studies that have demonstrated 5 to 22 per cent incidence of silent strokes detected on MRI of the brain following ICA. The long term consequence of silent strokes is memory impairment and cognitive decline. Hence, before ICA is recommended, the patient needs to fully understand the risks associated with the procedure and the results of the ICA must have a significant impact on management decisions. If a patient decides not to have any definitive procedure, such as bypass surgery or stent placement, performed no matter what the findings are or if the general condition of the patient makes bypass surgery or stenting of heart arteries a non-viable option, it is best not to perform an ICA , as there are safer alternatives.
So when should one consider undergoing an ICA? ICA is considered appropriate in the following situations.
• Those with suspected blocked heart arteries (ischaemic heart disease or IHD) who have unacceptable symptoms despite optimal medication and who are willing and suitable for heart bypass surgery or stenting
• Those whose non-invasive tests (other than treadmill test) indicate a high likelihood of severe IHD and are willing and suitable for heart bypass surgery or stenting
• Those suspected of symptomatic IHD who are unsuitable for stress testing, or have non-diagnostic stress tests, and if it is very likely that the ICA findings will result in important changes to treatment
• Those with impaired heart pump function
• Those with life threatening heart rhythms
• Those undergoing transplant surgery.
However, studies published in recent years have questioned the wisdom of doing an ICA instead of using non-invasive tests such as CT scan, as published registries on ICA in the USA have shown that in the real world experience, for every 100 patients that undergo ICA, about 40 per cent have normal heart arteries and only slightly more than one third have significant heart artery disease. In other words, about 60 per cent of real world patients who underwent ICA do not need an ICA.
In the past, when the choices were limited, ICA was deemed a “gold” standard despite its significant risks and limitations. Unlike CT scan of the heart arteries which provide three dimensional assessment of the heart arteries, ICA can only allow two dimensional visualisation of the lumen of the artery and has significant limitations as the vessel wall cannot be seen. Hence, if there is diffuse disease, it is not possible to quantify the severity of vessel narrowing accurately as there may not be any adjacent normal vessel segment for comparison. Multiple studies have shown that there is significant variability in the assessment of arterial narrowing, especially overestimation of severity for visually assessed narrowing of >50 per cent. ICA is also unable to identify which plaques are likely to result in a heart attack and is also unable to define the functional significance of the narrowing.
Hence, if you have chest pain on exertion or you have just been told that your treadmill stress test is abnormal, you should consider safer non-invasive alternatives especially if you fall into the category of those at higher risk of complications of ICA. For women and the young, tests that involve exposure to ionising or X-ray radiation should be avoided and where it is necessary, the radiation dosage resulting from the tests should preferably be not more than three millisieverts. CT scan is increasingly used by many physicians as an alternative to ICA and in this 2014 guideline, the committee explicitly wrote that CT scan is “appropriate and safer” than ICA in the diagnosis of IHD. Where expertise for MRI of heart arteries is available, it is a good alternative for the young and for women as there is no X-ray radiation. Remember, before confirming a decision on ICA, always look for safer alternatives.