Characteristics of Macroreentries Using an Epicardial Bypass:
Pseudo-Focal Atrial Tachycardia Case Series
Abstract
Introduction: Human atria comprise distinct epicardial layers, which can
bypass endocardial layers and lead to downstream centrifugal propagation
at the “epi-endo” connection. We sought to characterize anatomical
substrates, electrophysiological properties, and ablation outcomes of
“pseudo-focal” atrial tachycardias (ATs), defined as macroreentrant
ATs mimicking focal ATs. Methods and Results: We retrospectively
analyzed ATs showing centrifugal propagation with post-pacing intervals
(PPIs) after entrainment pacing suggestive of a macroreentry. A total of
26 patients had pseudo-focal ATs consisting of 15 perimitral, 7
roof-dependent, and 5 cavotricuspid isthmus (CTI)-dependent flutters. A
low-voltage area was consistently found at the collision site and
co-localized with epicardial layers like the: (1) coronary sinus-great
cardiac vein bundle (22%); (2) vein of Marshall bundle (15%); (3)
Bachmann bundle (22%); (4) septopulmonary bundle (15%); (5) fossa
ovalis (7%); and (6) low right atrium (19%). The mean missing
tachycardia cycle length (TCL) was 67 ± 29 ms (22%) on the endocardial
activation map. PPI was 9 [0-15] ms and 10 [0-20] ms longer than
TCL at the breakthrough site and the opposite site, respectively. While
feasible in 25 pseudo-focal ATs (93%), termination was better achieved
by blocking the anatomical isthmus than ablating the breakthrough site
[24/26 (92%) vs. 1/6 (17%); p < 0.001]. Conclusion:
Perimitral, roof-dependent, and CTI-dependent flutters with centrifugal
propagation are favored by a low-voltage area located at well-identified
epicardial bundles. Comprehensive entrainment pacing maneuvers are
crucial to distinguish pseudo-focal ATs from true focal ATs. Blocking
the anatomical isthmus is a better therapeutic option than ablating the
breakthrough site.