Mitral isthmus block and atrial tachycardia

SAN DIEGO, CALIFORNIA. Pulmonary vein isolation (PVI) is now the standard procedure for dealing with paroxysmal and persistent AF. In many cases, a PVI by itself is enough to eliminate AF in paroxysmal patients but in persistent afibbers it is often necessary to include additional lesions in order to achieve success. There are currently two major variants of the PVI procedure.

  • Pulmonary vein antrum isolation (PVAI or Haissaguerre/Natale procedure) – This procedure involves locating aberrant pathways through electrophysiological mapping (using a multipolar Lasso catheter) and ablating these pathways guided by an ultrasound (ICE) catheter. The ablation is performed as close as possible to the outside edge (antrum) of the junction between the pulmonary veins and the atrial wall. All four pulmonary veins as well as the superior vena cava (if indicated) are isolated during the procedure.
  • Circumferential anatomical pulmonary vein isolation (CAPVI or Pappone procedure) – In this procedure anatomical mapping (CARTO) is used to establish the exact location of the pulmonary veins. Two rings of lesions are then created in the left atrium - one completely encircling the left pulmonary veins and another completely encircling the right pulmonary veins; the two rings are usually joined by a linear lesion.

The PVAI yields superior results if performed by an experienced EP, while the CAPVI may enable less experienced EPs to achieve acceptable success rates. However, in order to achieve success with the anatomically-guided procedure in the case of persistent AF, it is necessary to create additional linear lesions in the left atrium. This, in turn, results in a high incidence (up to 30%) of post-procedure symptomatic, sustained atrial tachycardia (AT). Electrophysiologists at the University of California in San Diego now report that the AT is often due to incomplete mitral isthmus ablation. Their study included 35 paroxysmal and 25 persistent afibbers. Seventy percent of participants had lone AF, 77% were men, and 23% women with an average age of 60 years. All patients underwent a CAPVI using either the CARTO or NavX mapping system, ICE guidance for transseptal puncture, and an 8-mm non-irrigated catheter. Additional left atrial linear lesions were created in the left atrium roof and between the left inferior pulmonary vein and the edge of the mitral valve opening (annulus).

During an average 18 months of follow-up, AT occurred in 25% of the patients. The incidence of AT was 60% in the case of those where complete mitral isthmus block (electrical isolation) had not been demonstrated at completion of the procedure as compared to only 18% (9 patients) among the 50 patients whose mitral isthmus block was documented. Of these 9 patients, 7 underwent a repeat ablation and 2 were able to control the AT with amiodarone or sotalol. Post-procedure electrophysiology studies identified 5 ATs originating from the ridge between the left atrial appendage and the upper left pulmonary vein, 4 originating from the mitral isthmus, and 3 originating from the left atrial roof.

Also during the 18 months of follow-up, 12 patients (20%) had recurrence of AF after a 90-day blanking period. Seven of these underwent a repeat ablation. Complete success P> rate after an average 1.4 procedures (40% repeat rate) was 85% and partial success rate (sinus rhythm maintained with the help of antiarrhythmic drugs) was 2%.

The authors conclude that failure to achieve bidirectional mitral isthmus block during a CAPVI procedure increases the risk of subsequently developing atrial tachycardia by a factor of 4.

Anousheh, R, et al. Effect of mitral isthmus block on development of atrial tachycardia following ablation for atrial fibrillation.PACE, Vol. 33, April 2010, pp. 460-68,

Editor’s comment: This study clearly shows that the circumferential, anatomically-guided PVI procedure is associated with a substantial risk of post-procedure atrial tachycardia which may need a repeat ablation to fix.