ECG also known as Electrocardiogram or EKG in most of the cases can diagnose a heart attack and helps determine the right treatment depending on the type of heart attack. The medical test records the electrical activity of the heart. The heart produces electrical impulses that regulate its rhythm and coordinate the contraction of its different chambers. An ECG measures and graphically represents these electrical signals. However, there are times when ECG fails to detect a heart attack and many people may believe that their heart attack symptoms could be due to some other reason and fail to get the required treatment. 

Noted cardiologist Dr Gaurav Gandhi who died of heart attack on Tuesday morning had felt chest discomfort at 2 am and got an ECG done which came normal; Dr Gandhi mistook the symptoms as acidity and took an injectable for the same, reported Indian Express. After staying in the hospital for some time, he went back home and was found collapsed on the bathroom floor at 6 am in the morning.

Can ECG be normal during heart attack?

"Yes. Whenever a patient comes in with an emergency of a heart attack 70% of the time, the initial ECG is not normal, but in 30% cases the ECG can be normal. So, the patient thinks that they are normal and that they can go home. But that is not the case. Patients who have critical blocks in the blood vessels of the heart or patients with major heart attacks can have a normal ECG when the report to hospital for the first time. ECG must be repeated in regular intervals every 15-30 minutes for up to 2-3 hours after the initial attack. The patient should stay in the hospital for the repeat ECGs and other necessary investigations like ECHO and blood tests. Sometimes all may be normal and only coronary angiogram can reveal a critical lesion in a patient with chest pain," says Dr. V. Vinoth Kumar, Senior Consultant Interventional Cardiologist, CARE Hospitals, Hi-Tec City, Hyderabad.

"During a heart attack, also known as myocardial infarction, the blood supply to a part of the heart is severely reduced or completely blocked. This blockage usually occurs due to a blood clot that forms in a coronary artery. An electrocardiogram (ECG) is a medical test used to measure the electrical activity of the heart and can be a valuable tool in diagnosing a heart attack. However, it is possible for an ECG to appear normal during a heart attack in some cases," says Dr. Dixit Garg, Consultant - cardiology, Manipal Hospital, Gurugram.

Dr Garg explains that in many instances of a heart attack, the ECG will show characteristic changes that indicate a problem and these changes may include ST-segment elevation, ST-segment depression, or the appearance of abnormal Q-waves. These abnormalities on the ECG suggest that a heart attack is occurring or has recently occurred.

"However, there are situations where an ECG can be normal during a heart attack. This phenomenon is more likely to occur in the early stages of a heart attack or in certain circumstances," he adds.

Reasons why ECG may appear normal in case of heart attack

Dr Garg lists reasons why an ECG may appear normal during a heart attack include,

Timing: The ECG may be performed during the initial stages of a heart attack when the changes on the ECG may not have fully developed yet. It takes time for the electrical changes to become apparent on the ECG.

Location: The ECG leads may not be positioned correctly to detect the specific area of the heart affected by the heart attack. Depending on the location of the blockage, the changes on the ECG may be subtle or not present in the leads being monitored.

Silent heart attack: Some heart attacks may be 'silent' or 'asymptomatic,' meaning the person does not experience the typical symptoms of a heart attack. In these cases, the ECG may be normal, or the changes may be so subtle that they are not easily detectable.

Coronary artery collateral circulation: In rare instances, a person may have developed alternative blood supply pathways called collateral vessels, which can provide some blood flow to the affected area of the heart. This collateral circulation can help maintain the ECG within normal limits despite the presence of a heart attack.

"ECG can be absolutely normal in a case of heart disease you have, you can have all the three arteries blocked and yet your ECG can be absolutely normal. The accuracy of ECG to predict a heart attack is only 33%. An abnormal ECG has a lot of significance but a normal ECG in presence of chest pain can be misleading and it can mask a significant heart attack also. We have seen patients with absolutely normal ECGs but they have major heart attacks. So do not go by a normal ECG, specially single ECG. It is always better to get the ECG repeated after one hour or two hours if you have a strong suspicion and let your doctor decide about it," says Dr. Sanjeev Chaudhary, Director - Cardiology at Marengo Asia Hospitals, Gurugram.