𝟏𝟎 Rules of A Normal ECG

Rule 1: PR Interval

• Definition: The PR interval represents the time from the onset of atrial depolarization (P wave) to the onset of ventricular depolarization (QRS complex).
• Normal Range: 120–200 milliseconds (ms) or 3–5 small squares on ECG paper.
• Clinical Importance:
  • A prolonged PR interval (>200 ms) suggests first-degree AV block.
  • A short PR interval (<120 ms) may indicate pre-excitation syndromes like Wolff-Parkinson-White (WPW) syndrome.

Rule 2: QRS Complex Width

• Definition: The QRS complex represents ventricular depolarization.
• Normal Width: Should not exceed 120 ms (or less than 3 small squares).
• Clinical Importance:
  • A wide QRS (>/=120 ms) may indicate bundle branch block, ventricular tachycardia, or hyperkalemia.

Rule 3: QRS Complex in Leads I and II

• Observation:
  • The QRS complex should be predominantly upright (positive deflection) in leads I and II.
• Clinical Importance:
  • If QRS is negative in these leads, it may indicate axis deviation, chamber enlargement, or conduction abnormalities.

Rule 4: QRS and T Wave Direction

• Observation:
  • QRS and T waves should typically be in the same direction in limb leads.
• Clinical Importance:
  • If T wave is opposite to QRS, it may suggest ischemia, electrolyte imbalance, or repolarization abnormalities.

Rule 5: aVR Lead

• Observation:
  • All waves (P, QRS, and T) should be negative in lead aVR.
• Clinical Importance:
  • If the waves are positive, it suggests incorrect lead placement or a rare condition affecting ventricular activation.

Rule 6: R and S Wave Progression in Precordial Leads

• Observation:
  • The R wave should progressively increase from V1 to V4.
  • The S wave should progressively decrease from V1 to V3 and disappear in V6.
• Clinical Importance:
  • Poor R wave progression may indicate old anterior myocardial infarction or left ventricular hypertrophy.

Rule 7: ST Segment

• Observation:
  • The ST segment should be isoelectric (flat), except in V1 and V2, where it may be slightly elevated.
• Clinical Importance:
  • ST elevation may indicate acute myocardial infarction (STEMI).
  • ST depression suggests ischemia or electrolyte imbalances.

Rule 8: P Wave Morphology

• Observation:
  • The P wave should be upright in leads I, II, and V2 to V6.
• Clinical Importance:
  • Inverted P waves in these leads may indicate ectopic atrial rhythms.

Rule 9: Q Wave Characteristics

• Observation:
  • There should be no pathological Q wave, or only a small q wave (<0.04 seconds) in leads I, II, V2-V6.
• Clinical Importance:
  • Deep Q waves (>0.04s and >25% of R wave height) may suggest previous myocardial infarction.

Rule 10: T Wave Morphology

• Observation:
  • The T wave must be upright in leads I, II, V2 to V6.
• Clinical Importance:
  • Inverted T waves may indicate ischemia, strain patterns, or electrolyte abnormalities.

Do not forget to leave a comment, if this helped you in anyways… THANK YOU !!!