Electrocardiogram (ECG)

What is the P wave in an ECG?

Shows small upward deflection that represents atrial depolarization

- If the P wave is large: enlarged atria (like in RAV stenosis).

- If the P wave is missing or upside down: SA node (normal pacemaker) is damaged, and the AV node is setting the pace (nodal rhythm)

What does the QRS complex show in an ECG?

Small downward deflection, large upward deflection, small downward deflection—this represents ventricular depolarization

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It represents the depolarization (activation) of the ventricles (lower heart chambers).

- A larger R wave can indicate enlarged ventricles, often due to high blood pressure or aortic stenosis (narrowed heart valve).

What does the T wave represent?

Upward deflection that represents ventricular repolarization (the atria repolarized during ventricular depolarization)

- A flat T wave = myocardial ischemia (low blood flow to the heart).

What is the P-Q segment?

This is the time when the atria are contracting, right after the P wave. It’s when the electrical signal moves through the atria and pauses before going to the ventricles.

What is the S-T segment?

When the ventricles are contract, after the QRS complex. It's when the ventricles are in their plateau phase.

What is the P-Q (P-R) interval?

The start of the P wave to the start of the QRS complex. This shows how long it takes for the electrical signal to travel from the atria to the ventricles.

- A longer P-R interval (>0.2 sec) can mean an AV block (signal delay between atria and ventricles).

What is the Q-T interval?

It’s the time from the start of the QRS complex to the end of the T wave, showing the time it takes for the ventricles to contract and then recover. (depolarize to repolarize)

- It’s usually 0.2 to 0.4 seconds.

What are the typical time durations of different heart events?

- 0.12-0.2 sec: Atria contract (SA node to AV node).

- 0.25-0.4 sec: Ventricles contract (signal travels through Bundle of His → Bundle Branches → Purkinje fibers).

- 0.2-0.4 sec: The time between heartbeats.

What is Tachycardia?

Increased heart rate (too fast) (>100 bpm).

- It can happen due to stress, anemia, hyperthyroidism, or too much caffeine.

What is Bradycardia?

Decreased heart rate (too slow) (<50 bpm).

- This can happen in athletes, from beta blockers (a type of medication), or with hypothyroidism (low thyroid function).

What is Fibrillation?

heart muscle does not have synchronized depolarization, causing it to quiver rather than pump properly.

- Atrial fibrillation: Inefficient pumping to the ventricles, making you feel fatigue or dizzy.

- Ventricular fibrillation: Inefficient pumping to the circuits.

• A dangerous type that requires defibrillation to restore normal rhythm.