• Atrial flutter (AFL) or macro-reentrant atrial tachycardia arises from macro-reentrant circuit.
• The resulting P waves have a distinctive “saw-tooth” appearance, conducted at a regular and very fast rate ranging from 250 to 350 bpm.
• Because some but not all impulses reach the ventricles (no conduction takes place when AV node is in refractory period), there is often an increased P:QRS ratio.
• Vagal maneuver, which triggers parasympathetic response and prolongs AV refractory period, can be used to slow down flutter rhythm and increase P:QRS ratios making it easier to detect flutter.
• Atrial flutter can be further classified into “typical” and “atypical” flutter, depending on whether it involves the cavotricuspid isthmus (CTI) or not:
Typical: involves the CTI (CTI-dependent flutter)
Atypical: does not involve the CTI (non-CTI-dependent flutter, also referred to as intraatrial reentry tachycardia)
• AFL can co-exist and be triggered by atrial fibrillation and tachycardia.
• Typical atrial flutter arises when the macro-reentrant circuit conducts around the cavotricuspid isthmus (CTI) in right atrium (CTI-dependent flutter).
• This results in a series of flutter (saw-tooth appearing) P waves conducting at a very fast rate and regular rhythm.
• Every once a while, the depolarization is successfully conducted through AV node to the ventricles, resulting in narrow QRS complexes (example below is flutter with 3:1 AV block).
• Typical atrial flutter is further classified into “common or counterclockwise” and “uncommon or clockwise or reverse typical” flutter depending on the direction of conduction of the reentry loop. These can be differentiated based on the deflection of P waves in V1 and inferior leads (II, III, aVF).
• Counterclockwise direction
• Conduction wave moves towards V1 (upright Ps in V1) and away from inferior leads (inverted Ps in II, III, aVF)
• Clockwise direction
• Conduction wave moves away from V1 (inverted Ps in V1) and towards inferior leads (upright Ps in II, III, aVF)
• In most cases, atrial flutter is accompanied by AV block (AV node in refractory period) with either variable or fixed block.
• This results in either fixed or variable P: QRS ratios (higher ratio ~ higher degree of AV block which can be induced by increased PANS stimulation such as vagal maneuver-- recall that PANS specifically innervates the SA and AV node).
• This rhythm is often seen in digitalis toxicity.
• Atypical atrial flutter (also referred to as "intraatrial reentry tachycardia") arises when the macro-reentrant circuit does not conduct around the cavotricuspid isthmus (CTI) (non-CTI-dependent flutter).
• Atypical AFL involves either regions around the mitral annulus, left atrial roof, or any scarring within the left or right atria.
• A common example is left atrial flutter with counterclockwise conduction that moves towards V1 (upright Ps in V1), towards inferior leads (upright but low amplitude Ps in II, III, aVF), and away from lateral leads (inverted Ps in I, aVL).
