Electroanatomic Determinants of Atrial Flutter Circuits
Type I (Counterclockwise, Common) Atrial Flutter (after a sketch for Dr. Gregory K. Feld, University of California - San Diego, CA)
Counterclockwise Atrial Flutter
Atrial flutter is a stable monomorphic intra-atrial macroreentrant tachycardia which has been described in all ages but most commonly occurs in patients with ischemia or pressure/volume overload. In a substantial majority of cases the substrate for generalization to atrial fibrillation is already present and hence a majority of atrial flutters eventually transition to fibrillation. As a rule atrial flutters depend on a protected isthmus to provide critical spatial and temporal delay in maintaining a large, stable circuit. Ablation of this isthmus destroys the circuit. The most common circuit in humans is a counterclockwise loop down the trabeculated side of the crista terminalis and up the septum through an isthmus between IVC, TA, and CS (type I flutter). Cartoon of tricuspid annulus shown as hatched band.(Figure after Greg K. Feld MD, UCSD Electrophysiology, San Diego, CA.)
Crista Terminalis "Hard" Boundary to Electrical Activity?
Left. This open right atrium (from a fluoro spot shot) shows the relative positions of specialized mapping catheters and a 10-mHz intracardiac ultrasound catheter used to define the anatomic landmarks and barriers to type 1 atrial flutter.
Atypical Atrial Flutters
Atrial flutter circuits may encompass any part of the two atria, including left atrial structures, so long as conditions for reentry are met. As the wave of depolarization meanders around electrical barriers (scars, vessels, valves, suture lines) through narrow areas with impaired conduction, it eventually returns to its region of origin which has since repolarized, giving rise to the endless loop. Thus right or left atrial incisions, including atrial septum repairs, transplant anastomoses, and valve repairs, can give rise to reentrant atrial tachycardias and flutters of bizarre morphology requiring detailed, simultaneous 3-D mapping of both atria to identify appropriate ablation sites. Coming soon: An example of atypical atrial flutter in the setting of old atrial incisions.
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All images, text, and captions ©2000 - 2003 Starr Kaplan.