ECG Findings in Medicine

Sinus Rhythm

• Normal Heart Rhythm: Regular P waves followed by QRS complex.
• Electrical Signal Pathway: From sinoatrial node (right atrium) to atrioventricular node and bundle of His into ventricles.
• PR Interval: Constant time between start of P wave and initiation of QRS.
• QRS Complex: Represents ventricular depolarization, typically narrow (80-100 ms).
• Sinus Bradycardia: Rate < 60 bpm.
• Sinus Tachycardia: Rate > 100 bpm.

Atrial Fibrillation

• Abnormal Electrical Activity: Atrial muscle fibers contract at different times.
• ECG Characteristics: No clear P waves; QRS complexes not preceded by P waves.
• Heart Rhythm: Irregularly irregular rhythm.
• Causes: Substrate like atrial dilatation, triggering event from regions like pulmonary veins.
• Subtypes:
  • Rapid Ventricular Response: Rate > 100 bpm.
  • Slow Ventricular Response: Rate < 60 bpm.

Atrial Flutter

• Difference from Atrial Fibrillation: Coordinated electrical activity due to re-entry circuit.
• Atrial Rate: Around 300 bpm, narrow complex tachycardia.
• ECG Pattern: Sawtooth pattern from inverted P waves, usually in inferior leads.
• Conduction Ratio: Commonly 2:1, ventricular rate ~150 bpm.
• Instability: 1:1 conduction associated with instability and progression to ventricular fibrillation.

Premature Contractions

• Types:
  • Premature Ventricular Contractions (PVCs): Wide complex beats (>120 ms), compensatory pause.
  • Premature Atrial Contractions (PACs): Different P wave morphology, narrow QRS complex.

Bundle Branch Blocks

• Types:
  • Left Bundle Branch Block (LBBB): Deep S wave in V1, prolonged R wave in V6.
  • Right Bundle Branch Block (RBBB): RSR pattern in V1, prolonged S wave in V6.

Atrioventricular (AV) Blocks

• First Degree AV Block: Prolonged PR interval (>200 ms), generally benign.
• Second Degree AV Block:
  • Mobitz Type 1 (Wenckebach): Progressive PR lengthening until non-conducted P wave.
  • Mobitz Type 2: Non-conducted P wave, no PR variation, higher risk for progression.
• Third Degree AV Block: No association between atrial and ventricular contractions, regular P waves and QRS complexes without linkage.

Ventricular Tachycardia and Fibrillation

• Ventricular Tachycardia (VT): Broad complex regular tachycardia.
  • Monomorphic VT: Single source, uniform QRS complexes.
  • Polymorphic VT: Multiple sources, varying QRS morphologies (e.g., Torsades de Pointes).
• Ventricular Fibrillation: Chaotic activity, minimal cardiac output, leads to asystole.

ST Elevation

• ECG Feature: Elevation between S wave end and T wave start.
• Causes: Myocardial infarction, pericarditis, LBBB, LVH, benign early repolarization.
• Elevation Threshold: >1 mm from isoelectric baseline, different criteria for V2, V3.
• Territory Representation: Different leads represent lateral, inferior, anterior, septal territories.
• Reciprocal Changes: Opposite territory ST depressions indicate blocked coronary artery.

Additional Resources

• Recommended reading and resources:
  • Life in the Fast Lane
  • ECG Waves
• Further learning through dedicated videos on specific ECG topics.