Tall T-waves

ECG: Sinus rhythm with fixed and prolonged PR-interval (220 ms, first degree atrioventricular block); tall and symmetrical T-waves in V2-V6; T-wave amplitude in V3 (> 15 mm) is greater than the size of the preceding S wave or R wave;

ECG 2: 79-year-old man receiving inttermittend hemodialysis for chronic renal failure, hospitalized for syncope;

ECG 2: High grade atrioventricular block with several consecutive blocked P-waves followed by 1 to 2 conducted P-waves; moderate prolongation of QRS with right bundle branch block pattern; tall and symmetrical T-waves from V2 to V5; relatively short QT-interval in keeping with bradycardia; this ECG is evocative of a hyperkalemia which was confirmed by blood analysis;

Comments: There are several values in the literature defining a hyperacute T-wave although the size of the T-wave is generally indexed to that of the R wave preceding it; the amplitude of the T-wave must not exceed 75% of the R wave or S wave. The ECG shows positive T-waves of increased amplitude in various clinical situations: variant of normal, subendocardial ischemia and very early phase myocardial infarction, left or right ventricular hypertrophy, aortic insufficiency (diastolic hypertrophy), left bundle branch block, pericarditis, hyperkalemia, intracranial bleeding, acute alcoholism;

• Variant of normal: tall T-waves can be observed physiologically in mid-precordial leads (V2, V3, V4); the morphology of the T-wave is not modified (regular and asymmetrical); the remainder of the ECG is normal (absence of modification of the QRS-complex);
• Tall ischemic T-wave: the typical pattern of a subendocardial ischemia corresponds to the highlighting of positive, symmetrical, peaked and tall T-waves (> 5 mm) in several concordant leads, losing their proportionality with the amplitude of the QRS-complex;
• Very early signs of myocardial infarction: from the first 30 minutes after the appearance of chest pain, before any abnormality of the QRS-complex or ST segment, it is possible to record, albeit inconsistently (about 50% of cases), isolated T-wave changes of the subendocardial ischemia type, the subendocardial zone being the first to suffer from the lack of oxygen; tall, peaked T-waves, sometimes symmetrical or with a less steep upward slope than the downward slope; this pattern of “giant” T-waves without elevation is fleeting and never exceeds the fourth hour; in effect, the giant T-wave is subsequently transformed into a ST segment elevation;
• Prinzmetal’s angina: a fleeting increase in the amplitude of the T-wave has been described during a coronary spasm mainly from 24-hour Holter tracings (episodes too short to be recorded on a 12-lead electrocardiogram);
• Hyperkalemia: the T-waves can be tall and peaked in several precordial leads, and associated with a shortened QT-interval, an ST elevation, a prolonged QRS or a sinus bradycardia;

Take-home message: Ample T-waves in a context of chest pains should trigger the diagnosis of myocardial infarction.