title: Demonstration of electrical and anatomic connections between Marshall bundles and left atrium in dogs: implications on the generation of P waves on surface electrocardiogram.
abstract: BACKGROUND
  The muscle bundles within the ligament of Marshall (LOM) are electrically active. The importance of these muscle bundles (Marshall bundle [MB]) to atrial activation and the generation of the ECG P wave is unclear.
  
  
  RESULTS
  We used optical mapping techniques to study epicardial activation patterns in isolated perfused left atrium in four dogs. In another seven dogs, P waves were studied before and after in vivo radiofrequency (RF) ablation of the connection between coronary sinus (CS) and the LOM. Computerized mapping was performed before and after RF ablation. Optical mapping studies showed that CS pacing resulted in broad wavefronts propagating from the middle and distal LOM directly to the adjacent left atrium (LA). Serial sections showed direct connection between MB and LA near the orifice of the left superior pulmonary vein in two dogs. In vivo studies showed that MB potentials were recorded in three dogs. After ablation, the duration of P waves remained unchanged. In the other four dogs, MB potentials were not recorded. Computerized mapping showed that LA wavefronts propagated to the MB region via LA-MB connection and then excited the CS. After ablation, the activation of CS muscle sleeves is delayed, and P wave duration increased from 65.3 +/- 14.9 msec to 70.5 +/- 17.2 msec (P = 0.025).
  
  
  CONCLUSIONS
  In about half of the normal dogs, MB provides an electrical conduit between LA free wall and CS. Severing MB alters the atrial activation and lengthens the P wave. MB contributes to generation of the P wave on surface ECG.
authors.affiliation: Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California 90048-1865, USA.
authors.forename: Chikaya
authors.initials: C
authors.lastname: Omichi
authors.forename: Chung-Chuan
authors.initials: CC
authors.lastname: Chou
authors.forename: Moon-Hyoung
authors.initials: MH
authors.lastname: Lee
authors.forename: Che-Ming
authors.initials: CM
authors.lastname: Chang
authors.forename: Angela C
authors.initials: AC
authors.lastname: Lai
authors.forename: Hideki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Shengmei
authors.initials: S
authors.lastname: Zhou
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Miyauchi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Okuyama
authors.forename: Akira
authors.initials: A
authors.lastname: Hamabe
authors.forename: Chun
authors.initials: C
authors.lastname: Hwang
authors.forename: Michael C
authors.initials: MC
authors.lastname: Fishbein
authors.forename: Shien-Fong
authors.initials: SF
authors.lastname: Lin
authors.forename: Hrayr S
authors.initials: HS
authors.lastname: Karagueuzian
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Chen
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial; D003326:Coronary Circulation / Q000502:physiology; D004285:Dogs; D004562:Electrocardiography; D004594:Electrophysiology; D006321:Heart / Q000033:anatomy & histology* / Q000502:physiology*; D006325:Heart Atria; D006801:Humans; D055095:Optics and Photonics; D014680:Veins