Anatomy Spotlight: Septopulmonary Bundle – Why Roof Lines Fail and PVs Reconnect

Key concept

• Endocardial & Epicardial activation can be electrically dissociated due to functional block from disparate endo-epi fibre orientation, sink source mismatch & intramural fibrosis & fat pads physically separating the layers. They are connected to one another through discrete endo-epi connections that allow epicardial conduction to bypass endocardial (non-transmural) ablation lines.

 

 

Anatomy of the Septopulmonary bundle?

• Septopulmonary bundle is a thick muscular band on the epicardial surface of the LA. It’s thick muscular fibres traverses & drapes over the epicardial aspect of the entire posterior wall and inserts into the antral posterior aspect of the RSPV & Right Carina.

 

• It often has endocardial connections to the endocardial LA posterior wall and right-sided veins and can sometimes require extensive endocardial ablation to isolate.

 

Sánchez-Quintana D, Doblado-Calatrava M, Cabrera JA, Macías Y, Saremi F. Biomed Res Int. 2015;2015:547364.
Sánchez-Quintana D, López-Mínguez JR, Macías Y, Cabrera JA, Saremi F. Cardiol Res Pract. 2014;2014:289720.
Garcia F, Enriquez A, Arroyo A, Supple G, Marchlinski F, Saenz L. J Cardiovasc Electrophysiol. 2019;30(7):1159–1163

 

Septopulmonary Ablation Challenges

• Thermal (and possibly PFA) ablation lesions often fail to permanently injure the SPB due to interposing intramural fat-pads (and fibrosis associated with atrial disease) which insulate the septopulmonary bundle from ablation.

 

Hasebe Y, Noda T, Nakano M, et al. Heart Rhythm O2. 2024;6(1):3–10.
Pambrun T, Duchateau J, Delgove A, et al.Heart Rhythm. 2021;18:349–357.

 

How does the Septopulmonary bundle contribute to recurrence?

Pulmonary vein reconnection

• 60% of PVI patients do not have isolated veins on remapping procedures. Yes, you read that right, 60% have at least 1 pulmonary vein reconnected.

 

• About 60% of the reconnections are located in the right sided veins. Mechanisms likely include SPB epicardial bridging and carina/ostial endocardial gaps.
  • (You may have noticed that right-carina gaps are common on remap – these are often caused by our old friend the SPB).

 

 

Roof & Posterior wall recurrence

• Case series suggest the majority of roof-line recurrences are due to epicardial bridging consistent with SPB conduction.

 

• In the Australian study CAPLA, 75% of Posterior walls had recovered in patients who re-presented for a redo procedure. This highlights the difficulty in achieving enduring posterior wall isolation and is often due to septopulmonary conduction.

 

• • This actually highlights a great discussion point when interpreting the results of CAPLA & the impact of Posterior Wall isolation. I have a deep dive into posterior wall isolation in a future BeatBox coming up.

 

 

 

 

 

 

 

Kobayashi A, Hasebe H, Yoshida K. J Arrhythm. 2024;40(3):624–628.

More Examples of Septopulmonary conduction

The below examples highlight three things:

1. Thermal ablation (and possibly PFA) may fail to durably injure epicardial structures such as the SPB.

2. Our mapping catheters only map the endocardial regions and are poor at detecting epicardial recovery or conduction.

3. The endocardium & epicardium are electrically dissociated and it is possible to have a  silent posterior wall with intact epicardial conduction contributing to arrhythmia recurrence.

 

Ishimura M, Yamamoto K, Yamamoto M, Himi T, Kobayashi Y. Ann Noninvasive Electrocardiol. 2023;28(1):e12997.

 

My two Cents

• The endocardium & epicardium can be electrically isolated with discrete focal locations of endo-epi connections.

 

• The septopulmonary bundle is a thick muscular band of fibres draping across the LA roof & posterior wall and is a major contributor to posterior wall and right carina/vein reconnection.

 

• The SPB may be transiently injured in the initial procedure, but recover conduction due to inadequate endocardial ablation penetrance due to tissue thickness & intramural fibrosis & fat pads insulating epicardial structures from ablation.

 

• Many posterior wall & right sided vein reconnections are due to endo-epi connections from the septopulmonary bundle, explaining why the earliest site may be remote from previous ablation lines.

 

• The septopulmonary bundle can participate in atypical flutters, even in the setting of enduring endocardial posterior wall isolation.

 

• Awareness of the septopulmonary bundle anatomy is critical in the setting of any PVI & posterior wall isolation procedure.

 

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

 

References:

• Kistler PM, Chieng D, Sugumar H, Ling LH, Segan L, Azzopardi S, et al. Effect of Catheter Ablation Using Pulmonary Vein Isolation With vs Without Posterior Left Atrial Wall Isolation on Atrial Arrhythmia Recurrence in Patients With Persistent Atrial Fibrillation: The CAPLA Randomized Clinical Trial. JAMA. 2023;329(2):127-135. doi:10.1001/jama.2022.23722.

 

• Ishimura M, Yamamoto K, Yamamoto M, Himi T, Kobayashi Y. Roof-dependent atrial flutter with epicardial conduction pathway masked by left atrium posterior wall debulking ablation. Ann Noninvasive Electrocardiol. 2023 Jan;28(1):e12997.

 

• Crawford TC. PVI With vs. Without Posterior Wall Isolation for Persistent AF. American College of Cardiology – Journal Scan. January 11, 2023.

 

• William J, Chieng D, Curtin AG, Sugumar H, Ling LH, Segan L, et al. Radiofrequency catheter ablation of persistent atrial fibrillation by pulmonary vein isolation with or without left atrial posterior wall isolation: long-term outcomes of the CAPLA trial. European Heart Journal. 2024;46(2):132-143. doi:10.1093/eurheartj/ehae580

 

• William J, Virk S, Kalman J, et al. Sustained Improvement in Quality of Life Following Catheter Ablation for Persistent AF Beyond 3 Years: That’s No Sham. JACC: Clinical Electrophysiology. Published online July 2, 2025. doi:10.1016/j.jacep.2025.05.010. (ACC Journal Scan coverage: July 2, 2025).

 

• Neale T. CAPLA: Adding Posterior Wall Isolation No Help in Ablation for Persistent AF. TCTMD. January 13, 2023.

 

• Hasebe Y, Noda T, Nakano M, Chiba T, Sato H, Yamamoto N, Ito T, Kumagai K, Yasuda S. Impact of fat on the left atrial roof identified using intracardiac echocardiography during pulmonary vein isolation procedures. Heart Rhythm O2. 2024 Nov 9;6(1):3-10.

 

• Kobayashi A, Hasebe H, Yoshida K. Uncoupling endocardial bundles coupled by an epicardial bundle in the left atrium and pulmonary veins. J Arrhythm. 2024 Apr 24;40(3):624-628.

 

• Sánchez-Quintana D, López-Mínguez JR, Macías Y, Cabrera JA, Saremi F. Left atrial anatomy relevant to catheter ablation. Cardiol Res Pract. 2014;2014:289720.

 

• van Campenhout MJ, Yaksh A, Kik C, de Jaegere PP, Ho SY, Allessie MA, de Groot NM. Bachmann’s bundle: a key player in the development of atrial fibrillation? Circ Arrhythm Electrophysiol. 2013 Oct;6(5):1041-6.

 

•  Pambrun T, Duchateau J, Delgove A, Denis A, Constantin M, Ramirez FD et al.  Epicardial course of the septopulmonary bundle: anatomical considerations and clinical implications for roof line completion. Heart Rhythm 2021;18:349–57

 

• Johanna Bérénice Tonko, John Silberbauer, Ian Mann, How to ablate the septo-pulmonary bundle: a case-based review of percutaneous ablation strategies to achieve roof line block, EP Europace, Volume 25, Issue 10, October 2023, euad283

 

• Mahajan R, Thiyagarajah A, Lau DH, Sanders P. Single ring isolation for atrial fibrillation ablation: How to do it and avoid the esophagus. HeartRhythm Case Rep. 2020 Apr 15;6(4):169-173.

 

• Soto N, Datino T, Gonzalez-Casal D, González-Panizo J, Sánchez-Quintana D, Macias Y, Cabrera JÁ. Anatomical knowledge for the ablation of left and right atrial flutter. Herzschrittmacherther Elektrophysiol. 2022 Jun;33(2):124-132. English.

 

• Sánchez-Quintana D, Doblado-Calatrava M, Cabrera JA, Macías Y, Saremi F. Anatomical Basis for the Cardiac Interventional Electrophysiologist. Biomed Res Int. 2015;2015:547364.

 

• Garcia F, Enriquez A, Arroyo A, Supple G, Marchlinski F, Saenz L. Roof-dependent atrial flutter with an epicardial component: Role of the septopulmonary bundle. J Cardiovasc Electrophysiol. 2019 Jul;30(7):1159-1163.

 

• Ali Gharaviri, Sander Verheule, Jens Eckstein, Mark Potse, Pawel Kuklik, Nico H.L. Kuijpers, Ulrich Schotten, How disruption of endo-epicardial electrical connections enhances endo-epicardial conduction during atrial fibrillation, EP Europace, Volume 19, Issue 2, 1 February 2017, Pages 308–318,