Waves

Electrocardiography (ECG/EKG)

• Measures electrical activity of the heart.

• Waves:

  • P wave: atrial depolarization.

  • QRS complex: ventricular depolarization (atrial repolarization hidden). pushing blood to the blood to systemic circulation. Venticular pressure but first depolarize

  • T wave: ventricular repolarization. 

• Intervals/segments:

  • P–R interval: time for impulse from atria → ventricles.

  • S–T segment: entire ventricular myocardium depolarized.

  • Q–T interval: ventricular depolarization + repolarization time.

 ⚡ 1. Atrial Depolarization Begins

• The SA node fires, sending an impulse through the atria.

• The atria depolarize and begin to contract, pushing blood into the ventricles.

• ECG event: Start of the P wave.

⚡ 2. Atrial Depolarization Complete

• The impulse reaches the AV node.

• The atria finish contracting and the ventricles finish filling with blood.

• ECG event: End of the P wave (flat PR segment).

• AV node delay: A brief pause allows ventricles to fill completely.

⚡ 3. Ventricular Depolarization Begins at the Apex

• The impulse travels through the AV bundle → bundle branches → Purkinje fibers.

• Depolarization spreads from the apex upward through the ventricles, causing ventricular contraction.

• Atrial repolarization occurs simultaneously but is hidden by the large QRS complex.

• ECG event: QRS complex.

⚡ 4. Ventricular Depolarization Complete

• The ventricles are now fully depolarized and contracting, pumping blood out to the aorta and pulmonary trunk.

• ECG event: End of the S wave, beginning of the ST segment (flat line).

⚡ 5. Ventricular Repolarization

• The ventricles repolarize (reset electrically) as K⁺ exits the cells.

• This allows the ventricles to relax after contraction.

• ECG event: T wave (broad, upward wave).

⚡ 6. Ventricular Repolarization Complete

• The ventricles are now fully repolarized and relaxed.

• The heart is ready for the next depolarization cycle from the SA node.

• ECG event: End of the T wave → back to baseline.

❤ The 4 Heart Rhythms

1⃣ Normal Sinus Rhythm (NSR)

• Origin: SA node (normal pacemaker of the heart).

• Heart rate: 60–100 beats per minute.

• P wave: Present and upright before every QRS complex.

• PR interval: Normal (0.12–0.20 seconds).

• QRS complex: Normal and narrow (<0.12 seconds).

• Meaning:

  • The heart is beating normally and synchronously.

  • Atria and ventricles are working together properly.

✅ Summary:

Regular rhythm, normal rate, every P followed by a QRS.

2⃣ Junctional Rhythm

• Origin: AV node (takes over when the SA node fails).

• Heart rate: 40–60 beats per minute (slower).

• P wave: Often absent, inverted, or appears after the QRS complex.

• QRS complex: Normal.

• Meaning:

  • The AV node is pacing the heart.

  • The SA node isn’t functioning properly.

  • Acts as a backup rhythm to keep blood circulating.

✅ Summary:

AV node takes over → slow rhythm (40–60 bpm) with absent or inverted P waves.

3⃣ Second-Degree Heart Block

• Origin: SA node (normal firing), but some impulses don’t reach the ventricles.

• Heart rate: Often slower, depending on how many beats are dropped.

• P wave: Normal, but not every P wave has a QRS complex following it.

• QRS complex: Normal when present.

• Meaning:

  • Partial block in the AV node.

  • The signal between atria and ventricles is incomplete.

  • Type I (Wenckebach): PR interval gets longer until a beat drops.

  • Type II: PR interval constant, but random beats are dropped.

✅ Summary:

Some atrial signals don’t make it to ventricles → “dropped beats.”

4⃣ Ventricular Fibrillation (V-Fib)

• Origin: Ventricles (multiple areas firing chaotically).

• Heart rate: No effective rate — totally disorganized.

• P wave: None.

• QRS complex: None — just irregular, wavy lines.

• Meaning:

  • The ventricles are quivering, not contracting.

  • No blood is pumped.

  • Life-threatening emergency — requires immediate CPR and defibrillation.

✅ Summary:

Chaotic electrical activity — heart not pumping → cardiac arrest.