Etiology

Pathophysiology

Narrow complex tachycardia
Regular atrial activity at ~300 bpm
Loss of the isoelectric baseline
“Saw-tooth” pattern of inverted flutter waves in leads II, III, aVF
- Anticlockwise Reentry: Commonest form of atrial flutter (90% of cases). Retrograde atrial conduction produces
  - Inverted flutter waves in leads II,III, aVF
  - Positive flutter waves in V1 — may resemble upright P waves
Upright flutter waves in V1 that may resemble P waves
Ventricular rate depends on AV conduction ratio (see below)

Narrow complex tachycardia at 150 bpm (range 130-170)? Yes → Suspect flutter!
Turn the ECG upside down and closely examine the inferior leads (II, III + aVF) for flutter waves

Atrial flutter will not usually cardiovert with these techniques (unlike AVNRT), although typically there will be a transient period of increased AV block during which flutter waves may be unmasked

In atrial flutter with variable block the R-R intervals will be multiples of the P-P interval — e.g. assuming an atrial rate of 300bpm (P-P interval of 200 ms), the R-R interval would be 400 ms with 2:1 block, 600 ms with 3:1 block, and 800 ms with 4:1 block
Look for identical R-R intervals occurring sporadically along the rhythm strip; then look to see whether there is a mathematical relationship between the various R-R intervals on the ECG
In contrast, atrial fibrillation will be completely irregular, with no patterns to be discerned within the R-R intervals