ECG

Introduction

Electrocardiogram (ECG) is a way of reading electrical movement of the heart. Electrical impulse started from Sinoatrial node (SA node) causing atrial contraction. Move to Atrioventricular node (AV node), Bundle of His then Bundle Branch and end at Purkinje fiber in which cause ventricular contraction. In this blog, i will present a systematic approach to reading an ECG. Knowledge and illustration from this blog was extracted from The Ecg Workbook (Angela Rowlands, Andrew Sargent), The ECG Made Easy 8th edition and Live In The Fastlane (LITFL) website

Flow of reading

1. Rhythm strip
2. Limb lead
3. Chest lead
4. Heart injury
5. Bundle branch block
6. Chamber enlargement

Rhythm Strip

Rhythm strip is the Lead ll in the ECG Normal sinus rhythm

Rate

• Normal: 60 - 100 bpm
• Arrhythmia: Tachycardia > 100, Bradycardia < 60
• Calculate peak R wave in 6 seconds / 30 large box

Rhythm

• Normal: regular rhythm / equal distance between peak R wave
• Abnormal: Regularly irregular, Irregularly irregular

P wave

• Normal: present, < 120 msec
• Abnormal: absent / inverted / prolong / P-mitral / P-pulmonale

QRS complex

• Normal: narrow, < 120 msec
• Abnormal: broad / prolong

PR interval

• Normal: 120 - 200 msec
• Abnormal: < 120 msec / > 200 msec

P:QRS ratio

• Normal: 1:1
• Abnormal: 1:0 / 3:1 / others

Arrhythmia

• Sinus origin / physiological
  • Complete visualization of PQRST complex with normal morphology
  • Sinus tachycardia / sinus bradycardia
• Atrial fibrillation
  • Most common cardiac arrhythmia
  • ECG finding: tachycardia, irregularly irregular, absent P wave, narrow QRS ~150 bpm irregularly irregular, no discrete P wave, narrow QRS, N/A PR, N/A P:QRS, (irregular irregular tachycardia with no discrete P wave and narrow QRS) *Atrial Fibrillation
• Atrial flutter
  • ECG finding: tachycardia, broad multi P wave / F wave, P:QRS ratio is 2:1 / 3:1, narrow QRS ~100bpm regular, broad multi P wave / F wave / saw tooth, narrow QRS, N/A PR, P:QRS 3:1, (saw tooth appearance with P:QRS ratio of 3:1) *Atrial flutter
• Supraventricular tachycardia *AV node origin
  • ECG finding: tachycardia, absent P wave, narrow QRS complex ~150bpm regular, absent P wave, narrow QRS, N/A PR, N/A P:QRS (tachycardia with narrow QRS) *supraventricular tachycardia
• Ventricular tachycardia *Ventricular node origin
  • ECG finding: tachycardia, absent P wave, bizarre broad QRS complex ~150bpm regular, absent P wave, broad QRS, n/a PR, n/a P:QRS, (tachycardia with broad QRS) *ventricular tachycardia
• Ventricular fibrillation
  • ECG finding: no P wave, no QRS complex, chaotic activity no rate and rhythm, no P wave, no QRS, n/a PR, n/a P:QRS

Heart Block

• 1st degree heart block (QRS complex present)
  • ECG finding: PR < 200 msec, others normal PR interval 360 msec
• 2nd degree heart block (QRS complex absent)
  • Mobitz type l (Wenckebach phenomenon)
    • ECG finding: PR interval progressively prolong until missing a QRS complex ~60bpm irregular ventricular rhythm regular atrial rhythm , normal P wave, narrow QRS, PR interval progressively prolong until missing a QRS, *second degree heart block - Mobitz type l
  • Mobitz type ll
    • ECG finding: PR interval constant with intermittent absent QRS complex, P:QRS not 1:1 ratio, ~60bpm irregular ventricular rhythm regular atrial rhythms, normal P waves, narrow QRS, constantly prolong PR, P:QRS intermittent absent QRS *second degree heart block - Mobitz type ll
• 3rd degree heart block (Complete heart block)
  • ECG finding: P:QRS independent, broad QRS ~60bpm regular, intermittent absent P wave, broad QRS, prolong PR, P:QRS independent *third degree heart block

Limb Lead

Limb lead ECG

Cardiac Axis

• Normal cardiac axis
  • ECG finding: Lead l and aVF being positive Normal axis deviation
• Right axis deviation
  • ECG finding: Lead l negative and aVF positive (Reaching = Right) Right axis deviation
• Left axis deviation
  • ECG finding: Lead l positive and aVF negative (Leaving = Left) Left axis deviation
• Extreme axis deviation
  • ECG finding: Lead l and aVF being negative Extreme axis deviation
• Hexaxial Reference System
  • Find the most equiphasic complex, then move 90 degrees around the Hexaxial Reference System towards the quadrant that you first decided your axis would fall in.
  • Normal range -30 to +90 Hexaxial Reference System

Chest Lead

Chest lead ECG Visual of the chest lead

QRS Complex

• R wave: 1st positive deflection
  • Progression V1 - V4, regression V5 - V6
• S wave: negative deflection after R wave
  • Regression until V6, absent at V6
• Q wave: 1st negative deflection
  • 1st present at V4, biggest at V6 Good R progression with transition at V4, good S regression with total absent at V6, Q wave present at V4-V6

Heart Injury

• Include ischemia, infarction and necrosis.
• Injury can happen at any part of the heart.
• Locate pathological change at the respective site of ECG. ECG territories

Ischemic heart injury

• ST depression, T inversion and T flattening ST depression T inversion

Myocardial infarction

• ST elevation
• Reciprocal ST depression at counter site; PAILS ST elevation at V2-V6, l and aVL, reciprocal change lll and aVF *anterolateral myocardial infarction

Heart necrosis

• Deep Q wave (> 25% depth of R wave) Deep Q wave at V1-V4 with ST elevation *anterior myocardial necrosis with myocardial infarction

Bundle Branch Block

• Right Bundle Branch Block
  • ECG finding: V1= RSR pattern (letter M), V6= wide slurred S wave (MaRRoW) RSR pattern at V1, slurred S wave at V6 *RBBB
• Left Bundle Branch Block
  • ECG finding: V1= rS pattern, V6= M pattern / monophasic R wave (WiLLiaM) rS pattern at V1, M pattern at V6 * LBBB

Chamber Enlargement

• Right atrial enlargement
  • ECG finding: Lead ll= P-pulmonale, V1= P-pulmonale
• Left atrial enlargement
  • ECG finding: Lead ll= P-mitrale, V1= P-biphasic
• Right ventricular hypertrophy
  • ECG finding: V1= Big R, V5= Big S, Right axis deviation
• Left ventricular hypertrophy
  • ECG finding: V1= Huge S, V5/V6= Huge R, S + R > 35mm Huge S wave at V1, huge R wave at V6, total < 35mm