Bachmann's bundle and upper septal inter-atrial connections as key paths for a biatrial macro re-entrant circle: a case report

Abstract

Background: The Bachmann's bundle has been described as a key route for re-entrant circuits in biatrial tachycardias. Septal inter-atrial muscular connections were discovered a while ago, but evidence on their potential role in re-entrant tachycardias is lacking.

Case summary: We describe an atrial macro re-entrant circuit presented as a wide complex tachycardia that utilized the Bachmann's bundle, septal inter-atrial connections, and a limited area of the anterior left atrial myocardium in a patient with previous multiple atrial fibrillation ablation procedures. This tachycardia was diagnosed by using a combination of electrophysiological visualization modalities and was terminated by a single radiofrequency application.

Discussion: The inter-atrial muscular connections can pose a major contribution to the mechanism of biatrial tachycardias, especially in patients after extensive left atrial ablation. Thorough mapping modalities, including entrainment stimulation, facilitate a correct diagnosis. Understanding inter-atrial connection anatomy is crucial for the detection and successful ablation of such tachycardia.

Keywords: Atrial tachycardia; Bachmann’s bundle; Biatrial flutter; Case report; Catheter ablation.

Figure 1

Electrocardiogram during tachycardia with wide QRS complexes. The blue arrows indicate the visible F waves of the atypical atrial flutter; the red arrows indicate QRS complexes with a gradual increase in RR intervals, followed by the loss of the next QRS and transient restoration of conduction through the left bundle branch (narrow QRS). Then, the atrioventricular conduction 1:1 is restored, and left bundle branch block appears again.

Figure 2

Electrocardiogram and intra-cardiac recordings demonstrating the same cycle length (365 ms—three first atrial deflections); radiofrequency ablation was started just before the first atrial deflection on this tracing; the cycle length was prolonged for one beat (the fourth atrial spike), and the tachycardia was terminated. I, II, III—electrocardiogram tracings; ABL d, the ablation catheter is placed at the anteroseptal aspect of the left atrium; Penta, electrograms from the Pentaray catheter; CS, electrograms recorded from the decapolar catheter placed in the coronary sinus.

Figure 3

Three-dimensional electroanatomic reconstruction of the right (A) and left (B) atria (CARTO 3, coherent module). The arrows indicate the course of electrical activation of the re-entry circle. The coherent mapping module indicates the direction of electrical activations between acquired points. Yellow points indicate a good post-pacing interval during entrainment stimulation (equivalent to the tachycardia cycle length). SVC, superior vena cava; RAA, atrial appendage; TA, tricuspid annulus; RSPV, right superior pulmonary vein; LSPV, left superior pulmonary vein; LAA, left atrial appendage; MA, mitral annulus; FO, fossa ovalis.

Figure 4

Three-dimensional anatomic reconstruction of the right and the left atria [(A) activation map; (B) bipolar map]. Left anterior oblique projection. (A) The isochronal map represents electrical impulse propagation (from red to magenta). (B) Red colour represents low-voltage areas (<0.2 mV); magenta colour represents normal voltage (>0.5 mV). SVC, superior vena cava; IVC, inferior vena cava; RAA, atrial appendage; TA, tricuspid annulus; RSPV, right superior pulmonary vein; LSPV, left superior pulmonary vein; LAA, left atrial appendage; MA, mitral annulus.

Figure 5

(A) Preparation of the left and right atria with removed epicardium. The blue arrows indicate the muscle bundles connecting the myocardium of the right and left atrial septum. (B) Bachmann’s bundle (indicated by blue arrows) on the outer surface of the atria. LA, left atrium; RA, right atrium.