Enfermeria

TORAX

the posterior boundaries of the reentry circuit, while the tricuspid annulus forms the
anterior boundary [39-44]. Thus, type 1 AFL is due to reentry around anatomically
determinedobstacles in the right atrium.
Type 2 AFL is characterized by an atypical F wave pattern on ECG, with
atrial rates greater than 350 beats per minutes [45-46]. Type 2 AFL appears to be
due to reentry aroundfunctionally determined lines of block. Such reentry circuits
typically have only a partially excitable gap and may not be stable, thus accounting
for the variability in F wave morphology of type 2AFL between patients, or even
between episodes in the same patient. As originally described by Waldo, et.al. in
post-operative cardiac surgery patients, type 2 atrial flutter cannot be terminatedby
rapid overdrive atrial pacing [45]. Furthermore, since the arrhythmia circuit is
functionally determined, localized catheter ablation is not an effective treatment for
type 2 AFL.
Atrialtachycardias are rapid regular arrhythmias, characterized by discrete
P waves with a distinct diastolic interval on ECG, at rates up to 240 beats per
minute. Atrial tachycardias are due to reentry in manycases. In the post-operative
cardiac surgery patient reentry may occur around a surgically created anatomical
obstacle including an atriotomy scar or synthetic patch material [7-8]. Atrialtachycardia in the post-operative cardiac surgery patient, commonly called "scar
tachycardia", usually involves a large reentry circuit with a fully excitable gap.
Classical criteria for entrainment canusually be demonstrated during such AT.
Double-potential electrograms may be recorded along an atriotomy scar identifying
it as an anatomical obstacle. Typically, there will be a narrow isthmus oftissue
between a scar or patch material, and an anatomical structure such as an AV valve
annulus, vena cava or puhnonary vein, in which conduction velocity is slower than
normal, and from which...