Further evidence for the "muscle bundle" hypothesis of cavotricuspid isthmus conduction: physiological proof, with clinical implications for ablation.
BACKGROUND
It has been suggested that the cavotricuspid isthmus (CTI) is composed of discrete muscle bundles with preferred paths of conduction. An ablation technique targeting high-voltage local electrograms (maximum voltage guided or MVG technique) has been described with the aim of preferentially targeting the muscle bundles. We hypothesized that the MVG technique could provide isthmus block even if the high voltage targets were clearly separated on different ablation lines. In contrast, conduction over a continuous sheet of muscle would require a single continuous ablation line.


METHODS
Twenty-two consecutive patients (mean age 65 ± 11.7, 5 females) underwent ablation using the MVG technique on 2 noncontiguous lines in the CTI. Ablation lesions were first applied at the septal aspect of the CTI, targeting only the ventricular (anterior) aspect of the annulus. A line distinctly lateral and noncontiguous to the first was then chosen to target high voltage potentials on the atrial (posterior) aspect of the CTI.


RESULTS
Complete CTI block was achieved in all study patients without complication. A mean of 7.8 ± 3.7 ablation lesions were required. Mean ablation time was 401.0 ± 414.5 seconds.


CONCLUSIONS
Two nonoverlapping incomplete lines of ablation in the CTI consistently lead to bidirectional conduction block. This further supports the hypothesis that conduction over the CTI occurs over discrete muscle bundles. These bundles can be targeted individually for ablation without the need to ablate a continuous line over the CTI.
University of Western Ontario, Division of Cardiology, London, Ontario, Canada.
Alexis
A
Mechulan
Lorne J
LJ
Gula
George J
GJ
Klein
Peter
P
Leong-Sit
Manoj
M
Obeyesekere
Andrew D
AD
Krahn
Raymond
R
Yee
Allan C
AC
Skanes
D000368:Aged; D001282:Atrial Flutter / Q000503:physiopathology* / Q000601:surgery*; D019317:Evidence-Based Medicine; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008297:Male; D009431:Neural Conduction; D016896:Treatment Outcome; D014261:Tricuspid Valve / Q000503:physiopathology* / Q000601:surgery*