Possible Re-entry Circuits for Atrial Flutter

Atrial flutter is a classical macroreentrant arrhythmia with a large re-entrant circuit within the atria. That is why it is the arrhythmia which is most sensitive to electrical cardioversion, unlike atrial fibrillation which has multiple tiny wavefronts which require a larger energy level for termination by electrical cardioversion. Majority of the atrial flutter occur as a re-entry involving the cavotricuspid isthmus as the zone of slow conduction. Some others occur around an atrial scar. Here are some of the possible re-entry circuits in atrial flutter:

1. Typical and reverse typical atrial flutter involving cavotricuspid isthmus
2. Upper loop re-entry around the superior vena cava
3. Lower loop re-entry around the inferior vena cava
4. Re-entry around an atriotomy scar
5. Re-entry around the foramen ovale
6. Re-entry circuits involving one or two pulmonary vein ostia on each side
7. Re-entry in the region of the mitral annulus