Cardiology

ECG Basics: Analysis of Dysrhythmias

Rate

1. Ventricular rate:
   • Fast: > 100 beats/min
   • Slow: < 50-60 beats/min
   • Normal Sinus Rhythm: 60 - 100 beats/min
2. If the rhythm is irregular
   • Number of complexes x 6 (standard ECG displays 10 seconds)

Rhythm

1. Check ventricular rhythm first
   • Use ECG calipers and long rhythm strips (1 min) to demonstrate subtle variations
   • Normal (Regular) (View image)
2. Rhythm Changes
   • Completely irregular
     • AKA: chaotic rhythm
   • Irregularly irregular
     • Occasional irregularities
     • Grouped impulse

QRS Complex

1. **Note**: If ECG not available
   • Ask about # of small boxes QRS takes up (each small box = 0.04 sec)
   • Clinical queues
     • Is the QRS wide? (View image)
       • If so, examine the morphology to determine if there is LBBB/RBBB or pre-excitation present
     • Increased voltage may indicate left or right ventricular hypertrophy
     • Q waves may be suggestive of infarction
     • QRS notching could represent myocardial disease
2. Prolonged: > 0.12 sec
3. Borderline: 0.09 - 0.12 sec
4. Normal

P-wave and the QRS complex

1. "Map" p waves out
   • Can detect P-waves that are obscured by QRS complexes or T waves
   • This may require using calipers
2. Are P waves present?
   • Is a P wave before every QRS complex?
   • Is a QRS complex after every P wave?
   • Are P waves and QRS complexes regular?
3. Is the PR interval constant?

Technical points

1. Examine multiple leads
   • Chest leads
   • Consider esophageal leads
     • Especially if can't find P-wave
2. Make use of old ECGs
   • Compare current ECG with old tracings

Related Topics

• Intervals and Segments
• Abnormal ECG Complexes
• Tachycardia
• Bradycardia
• Atrial Fibrillation
• Ventricular Fibrillation

References

1. Yealy DM, Kosowsky JM. Dysrthythmias. In: Walls RM, Hockberger RS, et al; (eds). Rosen's Emergency Medicine: Concepts and Clinical Practice, 10th ed., Elsevier, 2023; Chapter 65
2. Arrhythmias. In: Crawford MH; (ed). Lange Cardiology: Current Diagnosis and Treatment, 5th ed., McGraw Hill Education, 2017; Section 3
3. In: Dubin D (ed). Rapid Interpretation of EKG's, 6th ed., COVER publishing company, Inc: Fort Myers, FL, 2000
4. Romito B, Meltzer JS. Tachycardia and Bradycardia. In: Vincent JL, Abraham E, et al; (eds). Textbook of Critical Care, 7th ed., Elsevier, 2017; Chapter 7

Contributor(s)

1. Ballarin, Daniel, MD
2. Ho, Nghia, MD

Updated/Reviewed: October 2022