Normal T-waves

ECG: This ECG is normal; the T-wave is normal in all leads in terms of polarity (positive in all leads except for aVR and V1), amplitude (no frontal lead with an amplitude > 5mm or precordial lead with an amplitude > 10 mm) and morphology (asymmetrical pattern, rounded and regular shape);

Comments: The T-wave represents the electrical forces generated during the rapid repolarization phase of the two ventricles. In a healthy left ventricular myocardium, depolarization begins at the endocardium; since the action potential is shorter in the epicardium, repolarization in the opposite direction begins at the level of the epicardium (the repolarization of the epicardium thus physiologically precedes that of the endocardium). A detailed analysis of the axis, amplitude and morphology of the T-wave follows that of the P-wave and the QRS. On the other hand, the T-wave is a relatively slow wave whose duration is not analyzed in current practice given the difficulty in determining the precise onset of the T-wave (progressive connection of its initial branch with the ST segment). The complete analysis of an ECG thus includes the qualification of T-waves (normal T-waves, variant of normal, localized or widespread abnormalities, disease-specific or aspecific abnormalities, secondary repolarization disorders).

• Morphology of the T-wave: the normal T-wave generally has a regular, asymmetrical shape with a slow upward slope (repolarization is a slow process), a more or less rounded peak and a rapid descending slope (more pronounced slope); the asymmetry is all the more pronounced when the heart rate is slow; indeed, physiologically, during an acceleration in heart rate, there is an acceleration of the upward slope yielding a more symmetrical pattern; there are some exceptions to this regular form: in children (most often between 7 and 12 years of age) a physiological T-wave with double peak can be observed in right and mid precordial leads;
• Axis and polarity of the T-wave: the polarity of the T-wave normally follows that of the QRS; the T-wave is therefore always positive in the adult in leads I, II and from V2 to V6, and negative in aVR; the T-wave is often positive in leads III and aVF but can be negative or biphasic in lead III and negative in aVF; the mean axis of the T-wave in the frontal plane varies less than for the QRS, with a norm between -10° and +70° with moderate influence of body morphology (axis a little more to the left in obese subjects); the T-wave is often negative in V1 but may be flat, biphasic or even positive; the direction of the T-wave in the horizontal plane varies significantly according to age with a more or less early and intense gradual forward rotation; the transition zone of the T-wave (transition from a negative T-wave to a positive T-wave) thus travels to the right (child: transition between V3 or V4, adult: transition between V1 and V2); a negative deflection of the T-wave after V1 is very rare beyond 15 years of age; a negative T-wave in V2, V3 may also be observed in obese patients;
• Amplitude of the T-wave: measured from the baseline to the peak of the T-wave and varies physiologically according to age, gender and size of the QRS preceding it; it is generally proportional to the amplitude to the QRS (less than 2/3 and more than 10% of the R wave) and decreases slightly on average with age; there is no formal criterion defining the norm regarding T-wave amplitude but a normal T-wave measures less than 5 mm in limb leads and less than 10 to 15 mm in precordial leads; the amplitude of the T-wave is most often maximal in mid-precordial leads (V2, V3 or V4);

Take-home message: The normal T-wave is asymmetrical, of low voltage and positive in all leads except aVR and occasionally V1. The appearance of negative and symmetrical T-waves and of positive, symmetrical and tall T-waves is therefore abnormal and suspicious.