T Wave

The normal morphology of the T wave is not symmetrical. 

In the frontal axis:

• The T wave has a slow upstroke followed by a rapid downstroke. 
• The T wave has a positive deflection in all limb leads except aVR. 
• If the ÅQRSF is 0° or less, the T wave may be negative in aVL. 
• The T wave is never negative in lead I.

In the horizontal axis: 

• The T wave in the precordial leads may be negative, positive, or isoelectric in lead V₁. 
• T waves have a positive deflection in leads V₂ to V₆. 
• A negative T wave in leads V₂ and V₃ is common in young women. 
• A negative deflection of the T wave in leads V₄ to V₆ is a normal variant, provided there is no evidence of any pathological medical conditions. 

Tall and symmetric T waves in the precordial leads (especially in leads V₂, V₃, and V₄) in younger people with sinus bradycardia is a normal variant.

General Guidelines to Diagnose Pathologic T Waves

Any T wave alterations in the presence of normal QRS morphologies must be considered as a nonspecific diagnosis. 

Patients with CAD exhibit symmetric and negative T waves known as the coronary T waves. This may also be seen in pericarditis and severe anemia. It is impossible to distinguish between CAD and left ventricular overload using the morphology of the T wave alone. 

Asymmetric negative T waves are mostly seen in patients with ventricular overload. Patients with left ventricular overload may have discordant negative T waves in leads I, aVL, V₅, and V₆. 

On the ECG of patients with right ventricular overload, the T waves may be negative in V₂ and V₃. Negative T wave deflection is also seen in V₁ through V₃ in cases of arrhythmogenic right ventricular dysplasia and in patients with funnel chest.

U Wave

A U wave is a positive flat deflection after the T wave, and they are more pronounced in V₅ and V₆. The U wave represents an impulse from the Purkinje fibers. Some causes of the U wave include:

• Acute ischemia and aortic valve incompetence: a U wave with a negative deflection
• Hypokalemia and long QT syndrome: the fusion of a T wave with a U wave forming a TU segment

ECG Tracing of U Wave