Patients who may have an impending or small heart attack now have more choices of non-invasive diagnostic tests.By Michael Lim

WITHIN the last fortnight, I had two incidents where relatives of patients called me regarding suspected heart attacks. They were asked to make urgent decisions on providing consent for the patients to undergo an invasive coronary angiography (ICA). ICA involves inserting a small plastic tube through the wrist or groin artery into the heart arteries, injecting contrast dye into the heart arteries and taking pictures of the heart arteries using X-rays.

The first patient, Mdm T, was admitted to a hospital for suspected heart attack and was scheduled for an ICA. The following morning, the son was asked to agree to the ICA that had been scheduled at 12 noon. I received a call from the son that morning regarding alternative options. After carefully considering the options, the family took the decision to have a non-invasive test performed. A Computed Tomography (CT) scan of the heart arteries, a non-invasive procedure, was performed. To the relief of her family, there was no significant heart artery disease.

A week after Mdm T’s incident, I received a call from a friend whose nephew, Mr W, was in the Intensive Care Unit for suspected impending heart attack. He insisted on talking to me urgently as the patient had been advised to have an ICA. He wanted to know what non-invasive options were available.

The family then opted for CT coronary angiography (CTCA), which was eventually ordered by his doctor and was performed in the hospital. The family was happy that the CT scan showed that Mr W’s heart arteries were normal and he was spared the pain and risks of an invasive coronary angiography.

While a full blown heart attack presents typical symptoms of chest pain and shortness of breath, and is associated with changes in the electrical pattern of the heart and blood tests demonstrating the presence of heart muscle damage, impending or “small heart attacks” can present significant diagnostic challenges to many doctors. As it is important for doctors not to miss the diagnosis, for some it means doing a diagnostic test, such as invasive coronary angiography, to visualise the heart arteries.

Indirect heart tests that cannot visualise heart arteries

Whether it is a treadmill test, a stress echocardiography or radioactive isotope nuclear scan of the heart, none of these indirect non-invasive tests are able to visualise the heart arteries and the accuracy varies from centre to centre. In the large USA coronary angiography registry data published in the last two years in the New England Journal of Medicine and the Journal of the American College of Cardiology, only about 40 per cent of those who had an abnormal indirect non-invasive test were found to have significant blockage of the heart arteries.

Hence, the accuracy in real world practice varies significantly from published data from large volume experienced centres. It is also a known fact that you can have significant blockage of the heart arteries and yet the indirect non-invasive test may show a normal result.

Invasive coronary angiography – ‘gold standard’ with real risks

For many cardiologists, invasive coronary angiography is the choice of diagnostic investigation for suspected impending or small heart attacks as it can be performed in most hospitals and is currently the “gold standard”. However, it is associated with a-few-in-thousand risk of heart attack, stroke and death.

Research publication where magnetic resonance scan of the brain was performed before and after inserting a plastic tube into the heart from a limb artery showed that there was up to 15 per cent incidence of “silent” strokes. In addition, it requires hospitalisation and is a relatively costly procedure.

Non-invasive visualisation of heart arteries

The last few years have also seen rapid advances and an explosive growth in CTCA, from being only available in few centres and with little acceptance a decade ago, to being routinely available in many hospitals and widely accepted presently. In the latest American Heart Association and American College of Cardiology Report on the criteria for the use of CTCA published in late 2010, the role of CTCA has expanded significantly to not only include the assessment of the heart arteries in many clinical situations but also other types of heart disease.

CTCA has become an important alternative to ICA. It is an outpatient procedure, is non-invasive, is less costly and the scan can be completed in seconds. Like invasive coronary angiography, it also involves the use of X-rays and also the injection of contrast dye, although in this case it is through a forearm vein. However, the X-ray radiation dosage of the newer generation of CT scanners is much lower than that of invasive coronary angiography. Most importantly, it does not carry the risk of stroke, heart attack, bleeding and death that is associated with the ICA procedure.

Visualising heart arteries without X-ray radiation and injections

Other than invasive and CT coronary angiography, the third technique of visualising the heart arteries is MR coronary angiography (MRCA). At an international cardiology meeting a few months ago, Prof Pamela Douglas, director of cardiovascular imaging programme at Duke Clinical Research Institute, was asked on the role of MRCA and she said that when MRCA becomes routinely available, the threshold for use of MRCA will be relatively low.

MRCA is the only non-invasive technique to visualise the heart arteries that does not require any X-ray radiation and does not require any injection. It has great potential as it carries no complication. While it is only available in a few centres presently, it is likely to follow the course of CTCA and become an important alternative technique to visualise heart arteries in the years to come. It is already a very established technique for assessing other aspects of the heart.

These developments mean that patients suspected to have an impending or small heart attack have more choices. It may also mean less pain, less risk, less radiation, less cost and less hospitalisation.

The X-ray radiation dosage of the newer generation of CT scanners is much lower than that of invasive coronary angiography (ICA). Most importantly, it does not carry the risk of stroke, heart attack, bleeding and death that is associated with the ICA procedure.