CLEVELAND, OHIO. By far the majority of atrial fibrillation triggers are located in or around the pulmonary veins making pulmonary vein isolation (PVI) and pulmonary vein antrum isolation (PVAI) highly successful techniques for eliminating afib. Nevertheless, the procedures are not always successful with one of the reasons being that some triggers are located outside the ablation rings formed around the pulmonary veins.
EPs at the Cleveland Clinic estimate that the superior vena cava (large vein that carries the de-oxygenated blood from the upper half of the body to the right atrium) harbors about 6-8% of these extraneous (to the pulmonary veins) triggers. In a recent clinical trial they investigated the feasibility and safety of adding isolation of the superior vena cava (SVC) to the standard PVAI procedure as a means of improving overall success rate. The trial involved 407 afibbers with an average age of 55 years of which 51% had the paroxysmal variety, 39% were in permanent afib, and the remaining 10% had persistent afib.
The participants were divided into two groups – Group I consisting of 190 patients who had undergone an initial PVAI followed by a search for triggers in the SVC, a nd Group II who underwent a PVAI followed by empirical SVC isolation. Twenty-four patients (12%) in Group I exhibited triggers in the SVC (accompanied by triggers in the right superior pulmonary vein) that were successfully isolated leaving all 24 patients arrhythmia free for an average of 450 days post-procedure. Among the 217 Group II patients, 208 (96%) exhibited SVC potentials. These were successfully isolated by segmental ablation (approximately 50%) of the SVC circumference in 59% of patients. Complete ablation of the circumference was necessary in 19% of patients, and in 18% of patients complete isolation was not possible owing to excessive phrenic nerve stimulation.
During follow-up, 16% of all patients experienced afib recurrence. Six percent underwent successful PVAI or SVC touch-up procedures bringing the overall total success rate to 90%. The remaining 10% achieved satisfactory control of their afib through the use of previously ineffective antiarrhythmic drugs.
The Cleveland researchers conclude that the SVC harbors the majority of afib triggers outside the pulmonary veins, and that SVC isolation is feasible and safe and should be considered as a standard adjunct to a regular PVAI. They found no evidence of SVC stenosis, but warn that SVC isolation may not be possible in all patients due to the danger of phrenic nerve injury.
Arruda, M, et al. Electrical isolation of the superior vena cava. Journal of Cardiovascular Electrophysiology, Vol. 18, December 2007, pp. 1261-66