ABSTRACT
Tall ‘hyperacute’ T waves may be seen in the early stages of an acute coronary syndrome. Increased T wave height may be a result of potassium released from damaged myocytes, leading to a localized hyperkalaemia. There is no clearly defined normal range for T wave height, although, as a general guide, a T wave should be no more than half the size of the preceding QRS complex. Tall T waves are particularly characteristic of acute posterior myocardial infarction. Infarction of the posterior wall of the left ventricle leads to reciprocal changes when viewed from the perspective of the anterior chest leads. Hypothyroidism can cause small QRS complexes and small T waves, but the most characteristic finding is sinus bradycardia. There are also several conditions in which T wave inversion occurs in combination with other electrocardiogram abnormalities. T wave inversion can occur not only as a temporary change in myocardial ischaemia but also as a more prolonged change in myocardial infarction.
