Unusual response to atrial entrainment pacing dependent on pacing
current strength: What is the mechanism?
Abstract
A 77-year-old woman with palpitations was referred for a second
radiofrequency ablation for persistent atrial tachycardia (AT). She
previously underwent pulmonary vein (PV) isolation for paroxysmal atrial
fibrillation, linear ablation between the 3’o clock position of the
mitral annulus (MA) and left PV from the endocardium, and ablation
inside the coronary sinus (CS) for perimitral atrial tachycardia (PMAT)
in the first procedure. A baseline 12-lead electrocardiogram in the
second procedure showed stable AT with a cycle length (CL) of 250 ms. No
PV reconnection was observed. The CS catheter was placed from 3:30 to
5:00 on the MA, and a proximal-to-distal pattern of CS activation during
AT was observed. Activation mapping in the left atrial (LA) endocardium
using a three-dimensional mapping system (CARTO3, Biosense Webster,
Diamond Bar, CA, USA) revealed a sequence of counterclockwise rotations
of the MA. Figures 1A and 1B show the intracardiac electrograms during
high-output (20 V) and low-output (5 V) atrial entrainment pacing at a
pacing CL of 240ms from CS 3,4, which corresponds to the 4’o clock
position of the MA. Dose residual conduction occur across the mitral
isthmus (MI) endocardium, epicardium, or both? What is the
electrophysiological mechanism during high- and low-output entrainment
pacing?