Typical (Right Atrial Isthmus Dependant) Flutter
• Typical atrial flutter is right atrial isthmus dependant.
• Typical flutter is usually counterclockwise in rotation when viewed in the LAO projection.
• There is clockwise typical flutter that utilizes the same circuit as the counterclockwise version, only in a reverse direction. For this reason, both the clockwise and the more common counterclockwise atrial flutters are grouped as Typical Atrial Flutter.
By far the most common type of atrial flutter is the right atrial isthmus dependant flutter. The arrhythmia utilizes a circuit that can be mapped entirley within the right atrium with the right atrial isthmus acting as the zone of slow conduction. This isthmus is the tissue that lies between the Inferior Vena Cava(IVC) and the Tricuspid Valve(TV) annulus. The circuit usually runs in a counterclockwise fasion as described below. The clockwise varient uses the exact same tissue yet conducts in a reverse circuit. Both of these flutters can be ablated by creating a lesion line that extends from around 6 oclock on the TV annulus and extends to the IVC.
Counterclockwise Flutter
The counterclockwise flutter circuit exits the right atrial isthmus on the septal side and moves from low to high posteriorly up the septal wall. It transitions across the superior aspect of the posterior wall and then high to low down the lateral wall where it reenters the isthmus. As this is a continuous circuit, there is no real defined starting point or early activation. It is often easier to describe a reentry circuit of this nature based upon some alternate reference. When documenting flutter circuits, the reference most commonly used is the proximal CS electrode pair.
Clockwise Flutter
The clockwise flutter circuit exits the right atrial isthmus on the lateral side and moves from low to high posteriorly up the lateral wall. It transitions across the superior aspect of the posterior wall and then high to low down the septal wall where it reenters the isthmus.
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