Question

The T-wave of an ECG indicates:

• A. Atrial contraction
• B. Ventricular contraction
• C. Ventricular repolarization
• D. Atrial depolarization

Hint:

The T-wave marks the end of the ventricular systole. If the T-wave is flat or inverted, it may indicate myocardial ischemia (lack of oxygen to the heart muscle).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
An Electrocardiogram (ECG) records the electrical impulses that travel through the heart. Each wave corresponds to a specific electrical event that triggers a mechanical action (contraction or relaxation).

Step 2: Detailed Explanation:
A standard ECG consists of three main components:
1. P-wave: Represents atrial depolarization, which is the electrical signal that triggers the contraction of the atria.
2. QRS complex: Represents ventricular depolarization, which is the electrical signal that triggers the contraction of the ventricles (systole).
3. T-wave: Represents ventricular repolarization. This is the stage where the ventricular muscle cells recover from their excited state and return to their resting state, which leads to ventricular relaxation.

Step 3: Final Answer:
The T-wave is indicative of ventricular repolarization.

Answer 2

Here each wave of the ECG is checked against where it falls in the electrical timeline of one heartbeat, rather than just listing the standard wave to event mapping.

1. Atrial contraction: Atrial contraction is triggered by atrial depolarization, which appears on the ECG as the P-wave, occurring well before the T-wave, so atrial contraction cannot be what the T-wave represents.
2. Ventricular contraction: Ventricular contraction is triggered by ventricular depolarization, seen as the sharp QRS complex. The T-wave appears distinctly after the QRS complex, during the plateau and recovery of the ventricular action potential, not during the contraction triggering event itself.
3. Ventricular repolarization: After the QRS complex, ventricular muscle fibres remain depolarized for a short refractory period and then repolarize, restoring their resting membrane potential so the muscle can relax. This recovery process is exactly what generates the T-wave, its position right after the QRS complex and before the next P-wave fits a recovery, not a triggering, event.
4. Atrial depolarization: Atrial depolarization corresponds to the P-wave at the very start of the cycle, long before the T-wave appears, and atrial repolarization itself is actually hidden inside the QRS complex because it is masked by the much larger ventricular depolarization signal.

Placing each wave on the electrical timeline of the heartbeat confirms that the T-wave marks the recovery phase of the ventricles.

So the correct answer is Ventricular repolarization.