Narrow & Regular tachycardia dDx

1. Sinus Tachycardia

• One P-wave for every QRS

• Upright P-waves in limb leads (I, II, III, aVF), inverted P-wave in aVR, biphasic P-wave in V₁

• Maximum sinus node rate is ~ (220 bpm – Age)

• Do not cardiovert, treat the underlying cause

2. Supraventricular Tachycardia (SVT)

• No distinct P-waves. May be hidden or may follow the QRS complex (“retrograde atrial activity”)

• Different types (AV Nodal re-entry, Non-paroxysmal junctional, etc.) but generally same treatment and management approach for emergency physicians

• SVT can commonly cause rate dependent ST-segment changes that are benign as long as 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

• Most commonly missed atrial tachycardia

• Always consider when rate is 150 ± 20 bpm

• The Bix rule, described by cardiologist Harold Bix, states that if a P-wave is located halfway between two QRS complexes, there is a good chance that P-waves are also buried inside the QRS complexes, think flutter!