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Essential ECG Findings in Cardiology

Apr 20, 2025

ECG Findings in Medicine

Introduction

  • Focus on common and must-know ECG findings.
  • Important for diagnosing and understanding cardiac rhythms and disorders.

Sinus Rhythm

  • Normal heart rhythm.
  • Features regular P waves followed by QRS complexes.
  • Indicates normal conduction from sinoatrial node through atrioventricular node to the ventricles.
  • PR Interval: Constant; time between start of P wave and initiation of QRS.
  • QRS Complex: Represents ventricular depolarization; normally narrow (80-100 ms).
  • Sinus Bradycardia: Rate < 60 bpm.
  • Sinus Tachycardia: Rate > 100 bpm.

Atrial Fibrillation

  • Abnormal electrical activity causing uncoordinated atrial muscle contraction.
  • ECG: No clear P waves; irregularly irregular rhythm.
  • Occurs due to substrate like atrial dilatation and a trigger (e.g., electrical activity from pulmonary veins).
  • Rapid Ventricular Response: Rate > 100 bpm.
  • Slow Ventricular Response: Rate < 60 bpm.

Atrial Flutter

  • Similar to atrial fibrillation but features coordinated atrial activity.
  • Re-entry Circuit: Leads to rapid atrial contraction (~300 bpm).
  • ECG: Sawtooth pattern; inverted P waves in inferior leads.
  • Conduction Ratio: Ratio of P waves to ventricular contractions (e.g., 2:1).
  • 1:1 Conduction: Associated with instability, may progress to ventricular fibrillation.

Premature Contractions

  • Premature Ventricular Contractions (PVCs): Originate from histo-Purkinje system; wide QRS; compensatory pause.
    • BiGeminy: PVC every other beat.
    • Sequence of PVCs can lead to ventricular tachycardia.
  • Premature Atrial Contractions (PACs): Different P wave morphology; narrow QRS.

Bundle Branch Blocks

  • Left and Right Bundle Branch Blocks: Wide QRS (> 120 ms).
  • Left Bundle Branch Block: Deep S wave in V1; prolonged R wave in V6.
  • Right Bundle Branch Block: RSR' pattern in V1; prolonged S wave in V6.
  • Mnemonic: William Marrow (LBBB: W in V1, M in V6; RBBB: M in V1, W in V6).

Atrioventricular (AV) Blocks

  • First Degree AV Block: Prolonged PR interval (> 200 ms).
  • Second Degree AV Block:
    • Mobitz 1 (Wenckebach): Progressive PR lengthening till a non-conducted P wave.
    • Mobitz 2: Non-conducted P wave without PR variation; high risk for progression to third degree.
  • Third Degree AV Block: No association between P waves and QRS complexes; escape rhythms.

Ventricular Tachycardia and Fibrillation

  • Ventricular Tachycardia (VT): Broad complex tachycardia.
    • Monomorphic VT: Single source; similar QRS complexes.
    • Polymorphic VT: Variable QRS complex morphologies; example: Torsades de Pointes.
  • Ventricular Fibrillation: Chaotic ECG activity; minimal cardiac output.

ST Elevation

  • Indicates acute myocardial infarction among other causes like pericarditis, LBBB, LV hypertrophy.
  • Definition: Elevation > 1 mm from isoelectric baseline (1.5 mm for V2/V3).
  • Territories:
    • Lateral Leads: I, aVL, V5, V6.
    • Inferior Leads: II, III, aVF.
    • Anterior/Septal Leads: V1-V4.
    • Posterior View: Additional leads V7-V9.

Further Reading

  • Recommend sources: "Life in the Fast Lane" and "ECG Waves".
  • Expert videos available for deeper understanding.

These notes provide an overview of key ECG findings and how they relate to various heart conditions, serving as a useful guide for medical study and review.

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