Clinical meaning
Unlike A-fib's multiple chaotic circuits, atrial flutter involves a single macro-reentrant circuit, typically circling around the tricuspid valve annulus in the right atrium. This circuit fires at approximately 300 bpm, producing the characteristic sawtooth flutter waves on ECG. The AV node cannot conduct all 300 impulses, so it blocks in a fixed ratio — most commonly 2:1 (ventricular rate around 150), but also 3:1, 4:1, or variable. The regular sawtooth pattern and fixed conduction ratio distinguish flutter from fibrillation.
Exam relevance
Risk factors: - Heart failure - Chronic lung disease (COPD, pulmonary hypertension) - Mitral or tricuspid valve disease - Post-cardiac surgery (especially atrial surgery) - Hypertension - Thyrotoxicosis - Alcohol use - Obesity - Often coexists with or converts to atrial fibrillation
Diagnostics: - ECG: classic sawtooth flutter waves (F waves) best seen in leads II, III, aVF, and V1 - Atrial rate approximately 300 bpm - Ventricular rate depends on conduction ratio (typically 150 with 2:1 block) - Regular ventricular rhythm if fixed conduction ratio - Narrow QRS complexes (unless aberrant conduction) - Carotid massage or adenosine may temporarily increase AV block to reveal hidden flutter waves