ECG Interpretation Lecture

Systematic Approach to ECG Interpretation

1. Determine the Heart Rate

   • Indicates if patient is tachycardic, bradycardic, or has a normal heart rate.

2. Determine the Rhythm

   • Assess if the rhythm is narrow regular, narrow irregular, wide regular, or wide irregular.
   • Helps identify arrhythmias.

3. Analyze the Axis

   • Check for left axis deviation, right axis deviation, or extreme right axis deviation.

4. Evaluate the Intervals

   • PR Interval: Helps identify AV blocks and Wolf Parkinson White Syndrome.
   • QT Interval: Indicates risk for Torsades de Pointes.

5. Assess the P-wave

   • Look for evidence of left or right atrial enlargement.

6. Examine the QRS Complex

   • Identify bundle branch blocks or ventricular hypertrophy.

7. Inspect the ST Segment and T-wave

   • Detect signs of myocardial ischemia or infarction.

Heart Rate Calculation Methods

• R-wave Method: Count the number of R-waves in the rhythm strip and multiply by 6.
• Box Method: Count the number of boxes between R-waves, then divide 300 by that number.

Tachycardic Rhythms

• Narrow Regular Tachycardias:

  • Sinus Tachycardia: P-waves present.
  • Atrial Flutter: Flutter waves present, rate around 150.
  • Paroxysmal Supraventricular Tachycardia: No P-waves, can be diagnosed with adenosine.

• Narrow Irregular Tachycardias:

  • Atrial Fibrillation: Fibrillatory waves, no P-waves.
  • Atrial Flutter with Variable Block: Inconsistent R-R intervals.
  • Multifocal Atrial Tachycardia: Different morphological P-waves; common in COPD.

• Wide Regular Tachycardias:

  • Ventricular Tachycardia: Monomorphic.

• Wide Irregular Tachycardias:

  • Torsades de Pointes: Polymorphic ventricular tachycardia with prolonged QT interval.
  • Ventricular Fibrillation: Ineffectual, irregular rhythms.

Bradycardic Rhythms

• Sinus Bradycardia: Normal PR interval, every P-wave followed by a QRS complex.
• First Degree AV Block: Prolonged PR interval without dropped beats.
• Second Degree AV Block (Mobitz I): Progressive PR prolongation followed by a dropped beat.
• Second Degree AV Block (Mobitz II): Constant prolonged PR interval with dropped beats.
• Third Degree AV Block: No relationship between P-waves and QRS complexes.

Axis Analysis

• Normal Axis: Lead I and AVF are both positive.
• Left Axis Deviation: Lead I is positive, AVF is negative, and Lead II is negative or isoelectric.
• Right Axis Deviation: Lead I is negative, AVF is positive.
• Extreme Right Axis Deviation: Both Lead I and AVF are negative.

PR and QT Intervals

• Prolonged PR Interval: Can indicate AV blocks.
• Short PR Interval: Associated with Wolf Parkinson White Syndrome (Delta wave, wide QRS).
• Prolonged QT Interval: Increases risk for Torsades de Pointes; caused by drugs, electrolyte imbalances.

Atrial Enlargement

• Left Atrial Enlargement (P mitrale): Bifid P-waves in Lead II; terminal portion larger in V1.
• Right Atrial Enlargement (P pulmonale): Peaked P-waves in Lead II; initial portion larger in V1.

Ventricular Hypertrophy

• Left Ventricular Hypertrophy: Deep S-waves in V1/V2, large R-waves in V5/V6 (Sum >35 mm).
• Right Ventricular Hypertrophy: Tall R-waves in V1/V2, large S-waves in V5/V6.

Bundle Branch Blocks

• Left Bundle Branch Block: Deep S-waves in V1/V2, notched R-waves in V5/V6.
• Right Bundle Branch Block: RSR’ pattern in V1/V2, wide S-wave in V5/V6.

ST Segment and T-wave Analysis

• ST Depression: Horizontal or down-sloping indicates myocardial ischemia; check contiguous leads.
• ST Elevation: Assess in contiguous leads; determines location of myocardial infarction (MI).
  • Anterior MI: ST elevation in V1-V4, reciprocal changes in II, III, AVF.
  • Inferior MI: ST elevation in II, III, AVF, reciprocal changes in I, AVL.
  • Lateral MI: ST elevation in I, AVL, V5, V6, reciprocal changes in II, III, AVF.
  • Posterior MI: Look for ST depression in V1-V3, confirm with posterior leads (V7-V9).

Differential Diagnoses for ST Changes

• Pericarditis: Diffuse ST elevation with concave morphology, PR depression.
• Hyperkalemia: Peaked T-waves, can cause ST changes.

Conclusion

• Systematic approach to EKG interpretation aids in identifying arrhythmias, AV blocks, hypertrophy, and ischemia.
• Essential to evaluate rate, rhythm, axis, intervals, p-waves, QRS complexes, ST segments, and T-waves.