An ECG — or electrocardiogram — is the most commonly performed cardiac test. However, a normal ECG does not mean that the patient has no heart problem. It is just a useful screening tool for a variety of cardiac abnormalities since ECG machines are readily available in most medical facilities and the test is simple to perform, risk-free and inexpensive. Since the ECG is a test that records the rhythm and electrical activity of your heart, it can detect problems you may have with your heart rhythm. It helps doctors to tell if you are having a heart attack or if you’ve had a heart attack in the past. Sometimes an ECG can indicate if your heart is enlarged or thickened. It is therefore the first investigation of a suspected heart problem.
However having said this, there is no doubt that for a full assessment of the heart, other tests may be needed. What also needs to be stressed is that despite its limitations with regard to its sensitivity and specificity in many settings, the ECG still has a lot of value in diagnosis, prognosis and treatment decisions. In addition, it is a test that most physicians can read.
The resting electrocardiogram is the first, foremost and readily available in the variety of tests meant to diagnose near disease modalities.
An all-useful test
As mentioned before, the information obtained from an electrocardiogram can be used to discover different types of heart disease. It may be useful in seeing how well a patient is responding to treatment. It is done to check the heart’s electrical activity, find the cause of unexplained chest pains — which could be caused by a heart attack; inflammation of the sac surrounding the heart (pericarditis), or angina; find the cause of the symptoms of heart disease, such as shortness of breath, dizziness, fainting, or rapid, irregular heartbeats (palpitations); find out if the walls of the heart chambers are too thick (hypertrophied); check how well medicines are working and whether they are causing side effects that affect the heart; check how well mechanical devices that are implanted in the heart, such as pacemakers, are working to control a normal heart beat; check the health of the heart when other diseases or conditions are present, such as high blood pressure, high cholesterol, cigarette smoking, diabetes, or a family history of early heart disease. Some diseases present from birth are diagnosed absolutely correctly by just a simple ECG test. So, one cannot simply brush this test aside.
In addition to its diagnostic value for an abnormal heart and palpitations, ECGs at rest are important tools for ruling out almost all acute heart emergency settings viz. an ongoing chest discomfort which could be a “heart attack” or the bad effect of angina; a clot going to the lungs (pulmonary embolism); symptoms like palpitations, sweating, dizziness or loss of consciousness in a patient arising from important cardiac ailments.
However, though the test can show evidence of disease in the coronary arteries, sadly in many people who have a significant narrowing of the arteries supplying the heart muscle, an ECG recording made at rest is often normal. Therefore, if a significant narrowing is suspected, an ECG recording is often made when the patient is exercising (an exercise stress test) as this is more likely to reveal the problem.
Important reference tool
A simple ECG done as a routine preventive health test serves as a baseline and reference tool for future comparisons. It also serves as a very useful tool in making a diagnosis by comparing new changes to an old ECG. Several ECG abnormalities like left ventricular hypertrophy (LVH), Q waves, ST segment changes, left bundle branch block, atrial fibrillation or QT interval prolongation can predict heart problems for the future. But having said this, there are of course other modalities of non-invasive tests like the echocardiogram, stress tests and CT coronary angiography.
The writer is Chairman & Chief Cardiologist, Cardiology Council, Fortis Group of Hospitals and President Elect, Cardiological Society of India
