📘 Notes: Electrocardiogram (ECG)

What is ECG?

ECG (Electrocardiogram) is the electrical recording of the potentials (tiny voltages) generated by the cardiac impulses (heart’s electrical signals).

Electrocardiogram (ECG): Waves, Interpretation, and Cardiac Conduction Explained

How ECG Works

·        When a cardiac impulse passes over the surface of the heart, it produces a minute electrical current.

·        This current spreads into surrounding tissues and reaches the surface of the body.

·        Electrodes (metal sensors) are placed on the skin → they detect these electrical potentials.

·        Electrodes connect to an electrocardiograph (ECG machine), which records the electrical activity as waves.

·        ECG is used to diagnose abnormalities in the conduction system of the heart.

📊 Waves of ECG (With Meaning & Function)

1. P Wave

·        Shows beginning of atrial depolarization (depolarization = electrical activation).

·        Initiated by SA node (pacemaker).

·        Indicates atrial contraction.

·        Irregular or absent P wave → arrhythmia (lack of rhythmic heartbeat).

2. PR Segment

·        Shows completion of atrial depolarization.

·        Duration: 0.12–0.20 sec.

·        Prolonged PR → first-degree heart block (slow conduction from SA to AV node).

3. QRS Complex

·        Shows beginning of ventricular depolarization → causes ventricular contraction.

·        Atrial repolarization (return to resting state) also occurs but is hidden under QRS.

·        QRS abnormalities may indicate:

o   Bundle branch block (block in bundle of His branches)

o   Ventricular tachycardia (very fast ventricular rate)

o   Other ventricular conduction defects

4. ST Segment

·        Represents completion of ventricular depolarization.

·        Duration: ≈ 0.08 sec.

·        ST segment changes:

o   Depressed ST → ischemia (reduced blood flow to heart muscles)

o   Elevated ST → myocardial infarction (heart attack)

5. T Wave

·        Shows beginning of ventricular repolarization (ventricles returning to resting state).

·        T wave changes indicate:

o   Electrolyte imbalance

o   Hyper-acute T wave → earliest sign of acute myocardial infarction

6. QT Interval

·        Measured from start of QRS to end of T wave.

·        Represents total time taken for depolarization + repolarization of ventricles.

·        Normal value: ≈ 0.40 sec.

·        Abnormal QT → risk of dangerous arrhythmias.

📍 Cyanosis (Blue Babies) — Short Note

·        Cyanosis = blueness of skin due to supply of mixed oxygenated + deoxygenated blood to newborn body.

·        Caused by failure of temporary fetal openings to close:

1.     Interatrial foramen (between right & left atria)

§  Normally closes during development.

2.     Ductus arteriosus (channel between pulmonary artery & aorta)

§  Should constrict after birth.

 

📘 Electrocardiogram (ECG) — MCQs, Short Questions, Long Questions

✔ MCQs (with answers + explanations)

1. The electrical recording of heart activity is called:

a) EMG
b) EEG
c) ECG
d) EPG
Answer: c) ECG
Explanation: ECG records electrical potentials generated by cardiac impulses.

2. Electrodes in ECG are placed on:

a) Chest only
b) Head only
c) Skin on opposite sides of heart
d) Hands only
Answer: c)
Explanation: Electrodes detect surface electrical currents from heart.

3. P wave represents:

a) Ventricular depolarization
b) Atrial depolarization
c) Ventricular repolarization
d) Atrial repolarization
Answer: b)
Explanation: P wave = atrial activation.

4. QRS complex shows:

a) Atrial contraction
b) Ventricular depolarization
c) Ventricular repolarization
d) Atrial repolarization only
Answer: b)
Explanation: QRS is the main electrical impulse for ventricular contraction.

5. A prolonged PR segment indicates:

a) Ventricular tachycardia
b) Cyanosis
c) First-degree heart block
d) Ischemia
Answer: c)
Explanation: Slow SA → AV conduction lengthens PR.

6. ST elevation is a sign of:

a) Normal rhythm
b) Fever
c) Myocardial infarction
d) Electrolyte imbalance
Answer: c)
Explanation: Heart attack elevates the ST segment.

7. T wave represents:

a) Atrial depolarization
b) Ventricular depolarization
c) Atrial repolarization
d) Ventricular repolarization
Answer: d)

8. Normal QT interval is about:

a) 0.08 sec
b) 0.12 sec
c) 0.20 sec
d) 0.40 sec
Answer: d)

9. Hyper-acute T waves are early signs of:

a) Fever
b) Acute myocardial infarction
c) Cyanosis
d) Stroke
Answer: b)

10. ST depression indicates:

a) Heart block
b) Ischemia
c) Tachycardia
d) Cyanosis
Answer: b)

✔ Short Questions (with answers)

1. What is ECG?

An electrical recording of potentials generated by cardiac impulses.

2. What instrument records an ECG?

Electrocardiograph.

3. What does the P wave represent?

Beginning of atrial depolarization.

4. What does the QRS complex show?

Beginning of ventricular depolarization.

5. What does the T wave represent?

Beginning of ventricular repolarization.

6. What does a prolonged PR segment indicate?

First-degree heart block.

7. What does ST elevation indicate?

Myocardial infarction.

8. What causes cyanosis in newborns?

Incomplete closure of interatrial foramen or ductus arteriosus, causing mixing of blood.

9. What is the normal QT interval?

About 0.40 seconds.

10. Why are electrodes placed on opposite sides of the heart?

To detect electrical potentials spreading to the body surface.

✔ Long Questions (without answers)

1.

Describe in detail the process of ECG recording. Include the placement of electrodes, role of electrocardiograph, and significance of electrical potentials.

2.

Explain the different waves of ECG (P wave, PR segment, QRS complex, ST segment, T wave, QT interval) with their clinical importance.

3.

Discuss the abnormalities indicated by changes in P wave, PR segment, QRS complex, ST segment, and T wave.

4.

Write a detailed note on how ECG helps in diagnosing conduction disorders of the heart.

5.

Describe cyanosis in newborns, its causes, and how failure of temporary fetal structures leads to this condition.