A Step-by-Step Guide to reading an EKG

Interpreting EKGs (Electrocardiograms) is an essential skill for healthcare professionals. As with any complex ability, mastering it necessitates the cultivation of robust habits and consistent practice.

I fear not the man who has practiced 10,000 kicks once, but I fear the man who has practiced one kick 10,000 times.

– Bruce Lee

Bruce Lee’s wisdom extends to the interpretation of EKGs: the most proficient interpreters cultivate a systematic approach that they consistently apply until they attain mastery. Although the repetitive process may seem tedious and sluggish at first, with diligent practice, mastery is simply a matter of time.

This guide aims to simplify EKG interpretation by outlining a systematic approach that covers all the essential aspects. By establishing the right habits and recognizing normal patterns, identifying abnormalities becomes straightforward. Let’s delve into the steps to enhance your EKG reading skills.

Verifying the EKG

Before interpreting an EKG, always verify:

• Correct Patient Information: Ensure the EKG belongs to the right patient.
• Quality of the EKG: Check for artifacts and confirm that the EKG was performed correctly.
• Calibration: Confirm that the EKG is appropriately calibrated.
• Clinical Context: Understand the patient’s clinical history and current presentation.
• Comparison with Previous EKGs: If available, compare the current EKG with prior ones to identify new changes.

Four Steps to Reading Every EKG

Adopt these four essential steps when interpreting every EKG:

Step 1: Calculate the Rate

Determine the heart rate:

• Normal Rate: 60–100 beats per minute (bpm)
• Tachycardia: Heart rate > 100 bpm
• Bradycardia: Heart rate < 60 bpm

Step 2: Determine the Rhythm

Assess the heart rhythm by examining:

Regularity

Is the rhythm regular, regularly irregular, or irregularly irregular?

P-waves

• Are normal P waves present?
• Is the P wave morphology normal?

P:QRS Ratio

Is there a 1:1 ratio of P waves to QRS complexes?

QRS Complexes

• Are the QRS complexes narrow (< 100 ms) or wide (> 100 ms)?
• A narrow QRS suggests a supraventricular origin.

Step 3: Check the Axes

Determine the electrical axis of the heart:

P-wave axis

• Normal: 0° and +75°.

QRS axis

• Normal Axis: Between -30° and +90°
• Right Axis Deviation: Axis > +90°
• Left Axis Deviation: Axis < -30°
• Extreme Right Axis Deviation: -90° and +180°

Step 4: Examine Intervals and Morphology

Evaluate the intervals and waveform morphology:

• P-wave morphology
• PR Interval:
  • Normal: 120–200 ms (3–5 small squares)
  • Short PR Interval: May indicate pre-excitation syndromes.
  • Prolonged PR Interval: Suggests first-degree AV block.
• PR Segment:
  • Elevated?
  • Depressed?
• QRS Complex Morphology:
  • Check for normal morphology.
  • Assess for bundle branch blocks:
    • Right Bundle Branch Block (RBBB)
    • Left Bundle Branch Block (LBBB)
    • Left Anterior Fascicular Block (LAFB)
    • Left Posterior Fascicular Block (LPFB)
    • Non-Specific Intraventricular Conduction delay
• ST Segment:
  • Elevated?
  • Depressed?
• QT Interval: Use QTc and recognize that it’s use is limited if the heart rate is too high or too low or if there is a conduction defect.
  • Prolonged QTc: > 440 ms in men, > 460 ms in women.
  • Short QTc: < 350 ms.
  • Rule of Thumb: A normal QT interval is less than half the preceding RR interval.
• T-wave abnormalities
  • Too tall?
  • Inverted?
• U-waves
  • Are they prominent?

Applying Occam’s Razor in EKG Interpretation

When interpreting EKG findings, apply Occam’s Razor: choose the simplest diagnosis that accounts for all findings within the clinical context. If multiple abnormalities are present, consider whether they could be due to a single underlying cause rather than multiple unrelated issues.