What is ECG?
• An ECG is a non-invasive diagnostic tool that records the heart’s electrical activity over a period of time.
• It is primarily used to:
• Detect irregular heart rhythms (arrhythmias).
• Identify poor blood supply to the heart (ischemia).
• Monitor heart conditions (e.g., after a heart attack or during certain illnesses).
Historical Background:
• 1800s: Early studies by physiologists like Luigi Galvani and Augustus Waller laid the groundwork for understanding electrical activity in muscles.
• 1903: Willem Einthoven invented the first practical ECG machine using his string galvanometer.
• Advancements:
• Over time, the equipment evolved into the portable 12-lead ECG machines we use today.
ECG Waves: Detailed Explanation
a. P Wave
• Represents atrial depolarization (spreading of electrical activity through the atria).
• Characteristics:
• Duration: <0.12 seconds.
• Amplitude: 0.1–0.2 mV.
• Clinical Significance:
• Enlarged P wave → atrial enlargement.
• Absent P wave → atrial fibrillation.
b. QRS Complex
• Represents ventricular depolarization (contraction of the ventricles).
• Characteristics:
• Duration: 0.06–0.12 seconds.
• Components:
• Q wave: First negative deflection (pathological if >0.04 sec or >25% of the R wave).
• R wave: First upward deflection.
• S wave: Downward deflection following R wave.
• Clinical Significance:
• Prolonged QRS → bundle branch block.
• Deep Q wave → myocardial infarction.
c. T Wave
• Represents ventricular repolarization (relaxation of ventricles).
• Characteristics:
• Upright in most leads (except aVR).
• Amplitude: 0.2–0.5 mV.
• Clinical Significance:
• Tall, peaked T waves → hyperkalemia.
• Flattened T waves → ischemia or hypokalemia.
d. PR Interval
• Represents the time taken for electrical activity to travel from atria to ventricles.
• Duration: 0.12–0.20 seconds.
• Clinical Significance:
• Prolonged → first-degree heart block.
• Shortened → pre-excitation syndromes (e.g., Wolff-Parkinson-White syndrome).
e. ST Segment
• Represents the pause between ventricular depolarization and repolarization.
• Characteristics:
• Isoelectric (flat) in normal conditions.
• Elevation or depression → ischemia or infarction.
f. U Wave
• Sometimes seen following the T wave.
• Clinical Significance:
• Prominent U wave → hypokalemia.
Detailed Step-by-Step ECG Procedure
Preparation:
• Ensure a private, quiet environment.
• Inform the patient about the procedure:
• Non-invasive.
• Takes 5–10 minutes.
• Remove items like jewelry or metallic objects that could interfere with the machine.
Electrode Placement:
1. Limb Leads (4 electrodes):
• RA (Right Arm): Right wrist/forearm.
• LA (Left Arm): Left wrist/forearm.
• RL (Right Leg): Right ankle (ground electrode).
• LL (Left Leg): Left ankle.
2. Chest (Precordial) Leads (6 electrodes):
• V1: 4th intercostal space (ICS), right of the sternum.
• V2: 4th ICS, left of the sternum.
• V3: Between V2 and V4.
• V4: 5th ICS, midclavicular line.
• V5: Same level as V4, anterior axillary line.
• V6: Same level as V4, midaxillary line.
Recording:
• Instruct the patient to remain still.
• Ensure proper lead connections.
• Record the ECG using the machine’s automatic mode.
Precautions During ECG
1. Skin Preparation:
• Clean with alcohol to remove oils or sweat.
• Avoid placing electrodes over thick hair (shave if necessary).
2. Electrode Adhesion:
• Ensure good contact to avoid “artifacts” or noise in the recording.
3. Patient Comfort:
• Keep the room warm to prevent shivering.
• Position patient comfortably.
4. Avoid External Interference:
• Keep the ECG machine away from other electronic devices.
Common ECG Abnormalities
1. Sinus Bradycardia: Slow heart rate (<60 bpm).
2. Sinus Tachycardia: Fast heart rate (>100 bpm).
3. Atrial Fibrillation: No distinct P waves, irregular rhythm.
4. Myocardial Infarction (Heart Attack):
• ST elevation.
• Pathological Q waves.
5. Heart Blocks: Prolonged PR interval or dropped QRS complexes.
References
1. Einthoven W. (1903). “The Galvanometer and Electrocardiography.” Nobel Lecture.
2. Goldberger, A. L. (2018). Clinical Electrocardiography: A Simplified Approach.
3. American Heart Association (AHA): Guidelines on ECG interpretation.
4. World Health Organization (WHO): Standards for ECG recording and interpretation.
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