Atrial flutter: mechanism, conduction and diagnosis
THE CONTEXT
Atrial flutter involves a large atrial re-entry circuit; atrioventricular conduction determines the resulting heart rate and can obscure its ECG appearance.
Mechanism and rates
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The macro re-entry circuit usually lies within the right atrium and encircles the tricuspid annulus.
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The atrial rate is approximately 300/min. Atrioventricular (AV) block of 2:1, 3:1 or 4:1 produces corresponding heart rates of 150, 100 or 75/min.
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Rarely, young patients conduct every flutter wave, producing a rate of 300/min with potential haemodynamic compromise.
ECG recognition
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The ECG shows saw-tooth flutter waves. With regular 2:1 AV block, these waves may be buried within QRS complexes and T waves.
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Atrial flutter should be suspected in a narrow-complex tachycardia at 150/min.
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Carotid sinus pressure or intravenous adenosine may temporarily increase AV block and reveal flutter waves, helping establish the diagnosis.