Critical Care: Basics of EKGs

Interpretation:

  • 1 small square = 0.04 seconds horizontally and 0.1 mV vertically
  • 1 large square =  0.20 seconds horizontally and 0.5 mV vertically

To calculate heart rate (HR), there are 3 methods:

  • Count the number of R waves in a 6 second strip (30 large squares)
  • Count the number of large squares between two QRS complexes and divide into 300.
  • Count the number of small squares between two QRS complexes and divide into 1500

The process of interpreting a rhythm:

  1. Look for the P wave – is it upright or inverted? is there one for every QRS? are there flutter of fibrillatory waves present?
  2. Measure the PR interval – is it normal or prolonged?
  3. Measure duration of QRS complex – is it normal of prolonged?
  4. Assess the ST segment – is it flat, elevated or depressed?
  5. Note the T wave – is it upright or inverted?

Overall, you want to know: what is the dominant rhythm, what is the clinical significance and what is the appropriate treatment?

Normal EKG durations:

  • P wave = 0.06-0.12 seconds
  • P-R Interval = 0.12-0.20 seconds
  • QRS complex = 0.06-0.10 seconds
  • ST segment = 0.12 seconds
  • T wave = 0.16 seconds
  • QT interval = 0.34-0.43 seconds

Types of dysrhythmias (general names and classifications, more detail covered in your theory classes)

  • Sinus rhythms:
    Normal sinus rhythm
    Sinus tachycardia
    Sinus bradycardia
    Sinus arrhythmia
  • Atrial rhythms:
    Premature atrial contractions (PACs)
    Paroxysmal supraventricular tachycardia (P/SVT)
    Atrial flutter
    Atrial fibrillation
  • Heart blocks (the AV node is sick!):
    1st degree heart block
    2nd degree heart block, Type I (Wenckebach)
    2nd degree heart block, Type II
    3rd degree heart block or complete heart block
  • Ventricular rhythms:
    Premature ventricular contractions (PVCs)
    Ventricular tachycardia
    Ventricular fibrillation
    Asystole
    Pulseless electrical activity (PEA)

In studying for each of the dysrhythmias, you need to not only learn how to identify them, but also what to do next once you have identified the rhythm (treatment? monitor? IV? O2?)

Image Source: #1, #2.
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