The first thing to know is what an Electrocardiogram (ECG) is before getting to what a T-wave is. An ECG is a medical device that is used to measure the electricity of the heart and the electrical signals from the heartbeats. The different parts within the ECG wave can be broken down into the P, Q, R, S, and T waves all represent a function of the heart. The P-wave represents the atrial depolarization of the heart and is shown as an upward bump at the beginning of the wave. The Q-wave represents the depolarization of the interventricular septum and is shown as a small downward spike before the R wave. The R-wave represents the electrical current of the heart traveling down the ventricles during depolarization and is shown as a large peak in the middle of the wave. The S-wave represents the depolarization of the Purkinje fibers and is shown as a downward spike after the R-wave. The final section we intend to focus on is the T-wave which represents the ventricular repolarization of the heart and is shown as an upward bump at the end of the wave, similar to the P-wave.

“Normal EKG showing P waves (green arrows), QRS complex (blue arrows), and T waves (red arrows).” Contributed by Yasar Sattar, MD.

Abnormalities of the T-wave can be an indication of serious problems within the heart. These abnormalities include a tall T-wave which can indicate myocardial infarction. A biphasic T-wave which represents two ventricle repolarizations in one cycle. An inverted T-wave which can be a sign that there is not enough blood reaching the heart and a sign that a person is suffering from ischemia. Lastly, a flat T-wave which can be a sign of many different heart conditions like ischemia, coronary artery disease, myocardial infarction, and other conditions.

“Example ECGs of the three phenotypes of Brugada ECG with various ST and T wave alterations.”  Reprinted from European Heart Journal with permission (2004;25:874–878).