Catheter ablation is an accepted therapeutic option for paroxysmal atrial fibrillation (AF), but its role is less certain in patients with persistent AF.1 The difference in response to pulmonary vein (PV) isolation (PVI) between paroxysmal and persistent forms of AF may arise because of triggers from non-PV sites or alterations in atrial substrate favoring maintenance of AF that are unaffected by PVI alone.2 In support of this statement, adjunctive ablation of certain sites (including the superior vena cava, ligament of Marshall [LOM], crista terminalis, coronary sinus [CS], posterior wall of the left atrium [LA], and left atrial appendage [LAA]) as well as more widespread ablation aimed at modifying substrate has been shown to improve the success of catheter ablation of persistent AF.

In the case of the LAA, the BELIEF study (Effect of Empirical Left Atrial Appendage Isolation on Long-term Procedure Outcome in Patients With Persistent or Long-standing Persistent Atrial Fibrillation Undergoing Catheter Ablation)3 recently showed that in patients with long-standing persistent AF, empirical electrical isolation of the LAA together with extensive atrial ablation markedly improved freedom from AF at 1 year compared to an extensive atrial ablation strategy alone. However, electrical isolation of the LAA can be challenging and is sometimes impossible to achieve. This may be partly because the electrical connections of the LAA are not completely understood.

Here we report 2 patients showing that the CS can be an important electrical conduit to the LAA.