977-72 Irregular Atrial Tachycardias in the Canine Sterile Pericarditis Model: Epicardial Activation Pattern

Besides atrial flutter (AF) and atrial fibrillation (AFib), irregular atrial tachycardias (AT) demonstrating irregular “P”-waves on surface-ECG are also inducible in dogs with sterile pericarditis. Afib is due to multiple, variable, simultaneously activated wavelets, whereas a single, stable reentrant circuit is continuously activated in AF. To determine the epicardial activation pattern during irregular AT, 128 bipolar right and left atrial electrograms (electrode distance 3–8mm) were simultaneously recorded in 6 dogs after induction of the arrhythmia. Irregular ATs were always non-sustained, with the longest episode lasting for 70 consecutive beats. Mean cycle length was 125±32 s, and the mean number of consecutive beats was 36±28. Circus movement reentry around pure functional or functional-anatomical obstacles was the mechanism underlying AT in all dogs. Functional obstacles were formed by long arcs of conduction block, and anatomical obstacles were provided by the orifices of the atrial vessels. As in AF, only one reentrant circuit was active during AT. However, similar to Afib, the central obstacle differed in size and location from beat-to-beat. A marked area of slow conduction was not evident. Spontaneous termination of AT was typically associated with reentry around a small central obstacle. This resulted in a relatively short revolution time of the circulating impulse, which then encountered refractory tissue.ConclusionsLinking the single, stationary circuits in AF and the multiple, variable circuits in AFib, irregular ATs are due to single but variable reentrant circuits. The instability of this type of reentry may be contributed to the lack of a marked area of slow conduction and/or the absence of long arcs of functional conduction block