Burning bridges: Ablation of a Bi-atrial macro-reentrant tachycardia conducting via Bachman's bundle and the Marshall bundle complex

A 62-year-old woman with prior pulmonary vein isolation and lateral mitral isthmus (LMI) ablation presented with recurrent atrial tachycardia (AT1). Two additional tachycardias (AT2 and AT3) were induced in the laboratory (see Fig. 1).

Fig. 1.

Electroanatomic maps for atrial tachycardia (AT) 1–3 generated using the Coherent feature from the Carto (Biosense Webster) system with corresponding local activation time (LAT) histograms and intracardiac electrograms.

With entrainment of AT1, a post pacing interval minus tachycardia cycle length (PPI-TCL) of <30 ms was observed from the coronary sinus (CS), interatrial septum, and anterior left atrial (LA) wall adjacent to the LA appendage base and left pulmonary veins. The PPI-TCL was >30 ms from the right atrium (RA). Activation was consistent with a macro-reentrant circuit revolving counter-clockwise around the mitral annulus utilizing the Marshall bundle (MB) to bridge the existing LMI line. Ablation within the vein of Marshall (VOM) was unsuccessful. The insertion of Bachman's bundle (BB) was mapped in sinus rhythm after cardioversion of AT1 and a septal mitral isthmus (SMI) line was created septal to the BB insertion to avoid significant interatrial delay or isolation of the LA appendage. AT1 was not inducible after this.

AT2 was induced with burst pacing. A PPI-TCL>30 ms was observed with entrainment from the CS. A PPI-TCL<30 ms was observed with entrainment from the LA roof. Activation was consistent with roof dependent circuit with the MB bridging the existing LMI line. The CS was passively activated presumably via the VOM. A roof line was created resulting in a change in cycle length (CL) which represented development of a new tachycardia (AT3).

With entrainment of AT3, a PPI-TCL<30 ms from the BB insertion on the anterior LA, CS, and RA septum. Both the SMI and LMI lines appeared to be intact. Activation was consistent with a clockwise bi-atrial flutter traveling up the RA septum from the CS and utilizing BB to access the anterior LA and MB complex. The CS was likely activated via the VOM and the posterior LA was passively activated via an insertion of the MB. The patient was cardioverted to sinus rhythm. A plan was made for VOM ethanol infusion if AFL3 recurred clinically.

Bi-atrial flutter often occurs in the presence of anteroseptal conduction anomalies resulting from prior ablation, such as the SMI line in the present case [1]. Ablation of bi-atrial flutter conducting via BB can be achieved with a SMI line lateral to the BB insertion or by targeting the BB insertion site on the LA. Unfortunately, burning this bridge can result in interatrial conduction delay/block and isolation of the LA appendage if a LMI line is present [2]. LMI ablation can be challenging due to the presence epicardial fibers including those from the MB complex, which can have discrete connections to the CS and posterior LA. Fortunately, while recurrence of MB-related tachycardias is high after attempted ablation of MB connections, VOM ethanol infusion has shown promise [3].

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tobias Ahnert reports a relationship with Biosense Webster Inc that includes: employment.