Note: Before doing any of the tests described below, do a study of your full medical profile. This will help the doctor select the most relevant test for you.
I often get asked about the best test to rule out the risk of getting a heart attack.
The truth is that no single test exists that is fool proof. Each cardiac test will give you some information related to current or future risk, and all of it put together, along with a thorough medical history, will give you a good idea of your cardiac risk.
Here are some of the most commonly performed cardiac tests, with their strengths and weaknesses.
Electrocardiogram
Most people consider the electrocardiogram (ECG) to be a magical test which tells us all about the heart. While it is a very useful test, it has its limitations.
Patients and their family and, frankly, even doctors often wonder how a heart attack occurred, even when a recently taken ECG was normal.
The electrocardiogram is a recording of the electrical activity of the heart. The activity is recorded as waves, which are the typical patterns you see on the special ECG paper. This paper is heat sensitive and the recordings fade over time.
So it’s a good idea to take a photocopy of your ECG to preserve it for future reference.
An ECG can fairly accurately give you an idea about your past history but is not good at predicting the future. For example, it can show that you have had a heart attack in the past but will not be able to indicate if you will have one in the next 10 minutes.
Sometimes, it gives you clues of possible future problems, such as indications that some parts of the heart are not receiving adequate blood supply. If the person is in the midst of a heart attack (which can take several hours to evolve), an ECG can pick it up, and in such cases we repeat the test every few hours to track how the attack is progressing and the effect of medication on it.
An ECG is also good at picking up abnormal heart rhythms, such as extra heart beats or abnormally fast or slow heart beats. Therefore, it’s an extremely important test which gives you information about the heart, but is by no means the only heart test that one should do.
The interpretation of the ECG should be left to a trained doctor, who can not only read the ECG, but also is well aware of your clinical situation.
A word of caution here: do not look at the computerized diagnosis printed on your ECG. You will invariably read the phrase, ‘Probably abnormal ECG’, even if there is a minor aberration which has no clinical significance.
Echocardiogram
This test, commonly known as a 2D echo, uses the principle of ultrasound to study the functioning of the heart muscle and valves.
A probe is moved over the left side of your chest, and sound waves are reflected off your heart chambers to form a visual representation of the same on the screen.
This test is great at studying the functioning of the heart valves. It is not used specifically to detect blockages.
However, abnormal movement of the heart muscle during the cardiac cycle can give an indication of inadequate blood supply, indicating blockages.
Stress test
Oftentimes, when patients are told that they need to undergo a stress test, they imagine it’s some sort of mental test, which will put them under great stress.
Actually, the test is done to put your heart under ‘stress’ and see how well it responds.
A stress test is commonly referred to as a TMT, or treadmill test. A resting ECG is taken after which you are made to exercise on a treadmill (or a stationary bike) using a fixed protocol.
The Bruce protocol is most popular worldwide, in which the treadmill goes steeper and faster every three minutes. Your goal is to keep walking (or running) till you are fatigued and can go no further.
This is very different from a regular exercise session on the treadmill and is designed to fatigue you within 6 to 12 minutes.
Stress thallium and stress echo
Both of these tests have a greater degree of accuracy compared to a regular stress test.
In a stress thallium, dye is injected in your veins and images are taken of your heart at rest and during exercise. The doctor studies how well the dye reaches various parts of your heart muscle and looks for areas of reduced dye uptake, which suggest compromised blood flow.
The purpose is to look for areas of ‘reversible’ and ‘fixed’ ischemia—a condition where the heart muscle receives inadequate blood supply.
A fixed defect or ischemia suggests that part of the heart muscle is not receiving blood either at rest or during exercise.
Reversible ischemia suggests that the area is receiving blood during rest, and not during exercise. This has clinical significance, since the decision to carry out an intervention may be based on this information.
Though a fixed defect would mean bad news, it also suggests that there is no point in doing a surgery or angioplasty in that area. After all, opening up the blood supply to that area would be akin to a gardener pouring water on a dead flower.
In a stress echo, the doctor performs a 2D echo study of your heart before and immediately after exercise to look for changes in the contracting pattern of your heart muscle. The pattern of contraction is compared between rest and maximum exercise. If there is a compromise at both rest and exercise, then it’s similar to the fixed defect described above. However, if the compromise is only during maximum exercise, then it’s a reversible problem.
After doing a stress test, patients often want to know if they have passed or failed the test, depending on how long they lasted on the treadmill. There really isn’t any specific cut-off time to indicate that you have passed, but a general rule of thumb suggests that if you are below 60 years, you should be able to last at least eight to nine minutes on the test.
Stress tests are great indicators of cardiorespiratory fitness levels, and the amount of time a person is able to stay on the test also influences treatment decisions. For example, if a person gets mild ECG changes at 11 minutes on a Bruce protocol, we would approach the case very differently compared to changes seen at four minutes.
Angiography
This is considered the gold standard test to detect blockages in your coronary arteries. A small incision is made in your groin, and a thin catheter is passed into the artery opening there, known as the femoral artery.
Currently, the trend is shifting towards passing the catheter through the radial artery by making a small incision in your wrist. Its advantage is that you can be up on your feet almost as soon as the procedure is over, as compared with several hours of bed rest with the groin approach.
CT angiography
In a CT angiography, a CT scan is taken of the heart and blood vessels and a three-dimensional representation of the heart is created. As technology has improved, the correlation between the CT angio and the regular or catheter angio is very close to exact.
However, when advanced tests like a CT scan are done without any clinical indications, they often show up results that can best be described as non-specific.
Another aspect of CT scans that is rarely spoken about is the exposure to radiation. On an average, one cardiac CT scan could equal to 100–200 normal X-rays. This is an extremely high dose of radiation and should not be done without appropriate reason. High radiation has been linked to an increased risk for future cancer.
As technology progresses, some of the newer machines and techniques are able to reduce the amount of radiation, but it is still fairly high. Not just CT scans, even thallium tests lead to large radiation exposure and should not be done without adequate justification.
When should you test further?
The decision on when to test further and which is the best test to perform is often a judgment call on the part of your doctor.
For example, if your stress test was positive, then the next step will depend on how ‘abnormal’ the test was. If the abnormal changes were seen at a very low level of exercise, and the changes were extensive, then it might make sense to go in for an angiography directly.
On the other hand, if the changes were minor or took place at a very high level of exercise, it would be better to undergo a further ‘functional’ test such as a stress echo or stress thallium. If this functional test is abnormal, then an angio is the right choice, but if it is normal, then it’s fine to observe and do no further testing.
Sometimes all tests may be normal, but you may have symptoms related to heart disease, such as chest discomfort. In such situations the decision-making becomes a lot harder.
Symptoms count
Usually, most people like to stay as far away from tests as possible and would rest easy after a negative stress test. But that was not the case with Sunil Joshi. This 60-year-old Prabhadevi resident used to take a daily morning walk for several years.
At one point he experienced mild abdominal discomfort during the walk, for which he diligently went and did a stress test. The test was negative after seven minutes on the treadmill, and he was told that all was well with his heart. He went back to his morning walks, but the uncomfortable sensation still remained. Mentally he knew that something was wrong, and he decided to go in for an angiography since his symptoms were persisting (even though his doctor said there was no need for further testing).
The angiography revealed four blockages and he underwent bypass surgery in January 2013. Unlike most patients, Sunil actually seemed proud of the fact that he had heart disease, because he had self-diagnosed it. He called himself a PhD in heart disease, and when asked to elaborate, said that he had high BP, which made him a graduate, diabetes which made him a double graduate, and his cholesterol was also high, so that got him the PhD degree. They say that laughter is the best medicine, and this description certainly had me in splits. Sunil was obviously enjoying himself and went on to point to his double chin, saying that he had a ‘hereditary double bandho‘, which in Gujarati means he was fat. I have noticed that patients (and people in general) who have the ability to laugh at themselves always end up doing better, and Sunil Joshi was no exception.
No cardiac test is fool proof. The history that a patient gives is often the best guide to diagnosis and if a person is symptomatic, I would advise further testing, even if the initial test was clear.
The flow chart below illustrates the decision-making process in different situations.
You must consult with your doctor when deciding on which test to do.
Decision-making process: Which test should you do?
Pros and cons of commonly performed cardiac tests
Take-home messages
- There are a variety of tests used to detect heart disease, all of which give different information. There is no single test that can be labelled as best.
- The ECG is good at diagnosing heart attacks and rhythm disturbances.
- The 2D echo is best to study the functioning of heart valves and the pumping capacity of the heart.
- A stress test looks at how the heart responds to stress (exercise) and helps detect blockages. Stress thallium and stress echo are more advanced stress tests.
- An angiography looks at the inside of the coronary arteries to detect blockages and their location. It looks at the anatomy (structure), while stress tests look at physiology (function). CT angiography gives you similar information done through a CT scan.
This article is part of a series of articles on the prevention, treatment, and reversal of heart disease by Dr Aashish Contractor.
