Armamentarium of heart tests
Electrocardiogram (ECG/EKG) – Cardiac Catheterization
Echocardiogram – CT Coronary Angiogram including coronary calcium scoring
Stress ECG – CAT/CT scan of heart
Nuclear scan – MRI of heart
24-48 hour holters and Loop Recorders – Tilt table test
The electrocardiogram is the most basic heart test that can be done, and is performed routinely as an extension of a cardiac evaluation. Together with your history and physical examination findings, it may help point to the cause of your symptoms. The ECG mainly gives information about the electrical activity of the heart and may also give clues about heart wall thickness, heart chamber enlargement, and heart circulation. The accuracy of the ECG though, is limited and so a normal ECG may not mean a normal heart. So, depending on your symptoms, and examination findings, your cardiologist may suggest additional testing.
Note: The ECG may be normal in up to 40 per cent of persons having a heart attack.
Echocardiogram or echo
The echocardiogram is probably the single most useful general heart test that may be ordered. It is an ultrasound examination of the heart and major vessels. It gives details of the structure of the heart, including heart size, pumping function, heart valve structure, and function. It can also diagnose congenital heart defects atrial and ventricular septal defects (commonly called hole in the heart), as well as other birth defects affecting the heart. It is useful in follow-up of patients who have been started on treatment to look for improvement, or to follow-up patients who may not need heart surgery at the moment, but may need in the future. The echocardiogram becomes an important tool in determining when this may be needed.
There are two main ways in which the echocardiogram may be performed. The most common way is called a “transthoracic echo” where the ultrasound images of the heart are obtained through the chest wall and also from the abdomen. Less commonly, the doctor may order a “trans-oesophageal echo” or TOE or TEE for short. The TEE is not widely available, as it requires additional specialised training of the cardiologist. The ultrasound images are obtained by passing the probe (the camera of the ultrasound) down the oesophagus ad taking a close look at the heart through the oesophagus. It gives more details of the heart than can be seen on a regular trans-thoracic echocardiogram, such as presents of small clots in the heart, small holes in the heart etc.
Stress tests include a group of tests, which challenges the heart by increasing the heart rate either through the use of exercise or medications. Typically a stress test is used to diagnose coronary artery disease (blocked coronary arteries) as well as some heart rhythm problems. Sometimes, circulation or rhythm problems of the heart will only show up when the heart is under “stress”. We are not referring to emotional stress here, but physical stress.
1. Exercise Stress ECG: Most commonly performed is the treadmill exercise stress test, but a bicycle (ergometer) may also be used. The patient is asked to walk on a treadmill while the heart is being continuously monitored on ECG. During the test, the patient’s blood pressure, heart rate, and ECG are closely monitored as the technician or doctor tries to get the heart rate up to its highest level. The average time spent on the treadmill is five to seven minutes, but is completely dependent on how quickly the heart rate goes up. In general, fitter people have a slower heart rate at rest that takes longer to peak. For example, Usain Bolt’s heart rate may be 40 beats per minute at rest and may take morethan 12 minutes to get to 180 beats per minute, while a 70-year-old man who doesn’t do much may have a heart rate of 90 at rest that goes to 130 within two minutes. So the test is individualised.
Note: A stress test may be normal in up to 40 per cent of persons who have significant coronary artery disease.
One scenario that creates a lot of excitement and casts a lot of doubt on a doctor’s judgement involves the stress test. You hear of persons who went to their doctor and had a stress test which was normal and then a few days later collapse from a severe heart attack. How can this happen you say?
A stress test is designed to pick up blockage in an artery that is at least 70 per cent. The person who has a 70 per cent blocked artery may have chest pain when they exert themselves, but none at rest. Similarly, they may have a normal ECG at rest, but when they exercise, because the circulation to the heart cannot increase through that 70 per cent blocked artery, the problem manifest at a higher heart rate.
It is important to understand how a heart attack happens and the limitations of a stress test. When someone has a heart attack, there is sudden break-up of plaque (which causes hardening of the arteries). In an attempt to heal this area of the lining of the artery, which has been damaged, the body forms a clot. Depending on the size of the clot, it can block off the circulation to heart muscle completely or partially within a matter of seconds.
An artery with a 15 or even 45 per cent blockage by plaque, does not have significant enough blockage to create symptoms or cause an abnormality on the ECG at rest or with exercise. As a result a person with this “minor blockage” can have no symptoms and normal ECG and stress test and still have a heart attack if the plaque ruptures or breaks up. It is therefore important to cut down the risk of that through proper cardiac risk management.