The T-wave in an ECG represents

A) Electrical excitation of atria

B) Return of the ventricles from excited state

C) Depolarization of ventricles

D) Beginning of systole

Option A: Electrical excitation of atria

• The P wave of the electrocardiogram (ECG) represents atrial depolarization, i.e., the electrical excitation of atria, which causes atrial contraction.
• The electrical impulse travels through the conducting system, stimulating atria and ventricles. The AV node transmits the signal to the ventricles, leading to ventricular contraction.
• Therefore, Option A is not correct.

Option B: Return of the ventricles from excited state

• The T wave represents ventricular repolarization, i.e., the return of the ventricles to their resting state after excitation.
• This phase resets the ventricles for the next contraction. The T wave shows a positive deflection because the ventricular cells that depolarize first also repolarize first.
• Therefore, Option B is correct.

Option C: Depolarization of ventricles

• Ventricular depolarization is represented by the QRS complex on the ECG.
  • Q wave: first negative deflection
  • R wave: first positive deflection
  • S wave: negative deflection following R wave
  • Additional positive deflection after S is called R′ wave
• This is not the return from the excited state but the process of excitation itself.
• Therefore, Option C is not correct.

Option D: Beginning of systole

• The QRS complex also marks the onset of ventricular systole (isovolumetric contraction).
• Systole has two phases:
  • Atrial systole (0.1 sec): atria contract, pushing blood into ventricles.
  • Ventricular systole (0.3 sec): ventricles contract, pumping blood to lungs (via pulmonary trunk) and body (via aorta).
• However, this is not the same as the “return of ventricles from excited state.”
• Therefore, Option D is not correct.

Correct Answer: Option B – Return of the ventricles from excited state