Amal Mattu’s ECG Case of the Week – July 19, 2021

ECG findings in Hypothermia

Onset of ECG findings can vary, but resolve with warming

• Early sinus tachycardia
• Shivering artifact
• Bradycardia: sinus, junctional rhythms, slow atrial fibrillation
• J-waves/Osborn waves (positive deflections at the J-point)
  • Can cause pseudo-ST segment elevation or depression
• Prolongation of all intervals
  • Long QT due to lengthening of the ST segment
• Ventricular fibrillation
• Asystole

Narrow-Complex & Regular Tachycardia Differential

1. Sinus Tachycardia

• One P-wave for every QRS
• Upright P-waves in limb leads (I, II, III, aVF) & inverted P-wave in aVR
• Maximum sinus node rate is generally ~ (220 bpm – Age)
  • Maximum sinus rate can sometimes exceed this in cases of thyrotoxicosis, sympathomimetic toxicity, well-conditioned athletes, etc.

2. Supraventricular Tachycardia (SVT)

• No distinct P-waves. May be hidden or may follow the QRS complex (“retrograde atrial activity”)
• Different types (AVNRT, AVRT, atrial tachycardia, etc.) but generally same treatment and management approach for emergency physicians
• SVT can commonly cause rate dependent ST-segment changes that are benign if it goes away when sinus rhythm is restored
• SVT can also cause electrical alternans that disappears when sinus rhythm is restored

3. Atrial flutter with 2:1 Conduction

• 2 atrial beats for every QRS
• Saw tooth pattern, flipping the ECG upside down and paying attention to all 12 leads will help you identify subtle flutter waves
• The most commonly missed atrial tachycardia
• Always consider when rate is 150 ± 20 bpm

To differentiate…always look at what the atrium is doing
(V₁ typically best lead to look for atrial activity)