Electrophysiological characteristics of the Marshall bundle in humans

Abstract

Background: Marshall bundles (MBs) are the muscle bundles within the ligament of Marshall.

Objective: This trial sought to the electrophysiological characteristics of the MB and the anatomical connections between MB and left atrium (LA) in patients with persistent atrial fibrillation (AF).

Methods: We enrolled 72 patients (male:female 59:13, age 59.9 +/- 9.4 years) who underwent MB mapping and ablation for AF. MB mapping was done via an endocardial or epicardial approach during sinus rhythm and AF.

Results: Recordings were successful in 64 of 72 patients (89%). A single connection was noted in 11 of 64 patients between the MB and the coronary sinus (CS) muscle sleeves. The MB recordings showed distinct MB potentials with a proximal-to-distal activation pattern during sinus rhythm. During AF, organized passive activations and dissociated slow MB ectopic activities were commonly observed in this type of connection. Double connections to both CS and LA around left pulmonary veins were noted in 23 of 64 patients (36%). After the ablation of the distal connection, MB recording showed typical double potentials as in single connection. Multiple connections were noted in 30 of 64 patients (47%). During sinus rhythm, the earliest activation was in the middle of the MB. The activation patterns were irregular and variable in each patient. During AF, rapid and fractionated complex activations were noted in all patients of this group.

Conclusion: We documented 3 different types of MB-LA connections. Rapid and fractionated activations were most commonly observed in the MB that had multiple LA connections.

Figure 1

Simultaneous endocardial and epicardial mapping of the MB. A: Sinus rhythm and MB ectopic activity. The thin arrows point to VOM, and Epi channels were MB potentials during sinus rhythm. Ectopic beats from the MB (thick arrows) were recorded on both VOM-d and on Epi-d at the same time, indicating that the deflection on Epi-d is the VOM activation. B, C: Fluoroscopic images show that the Cardima catheter (filled arrow) within the VOM and the duodecapolar catheter (unfilled arrow) used for epicardial mapping. These 2 were close to each other. CS = coronary sinus; d = distal; Epi = epicardial; His = His bundle; HRA = high right atrium; MB = Marshall bundle; p = proximal; VOM = vein of Marshall.

Figure 2

Electrogram characteristics of single MB-CS connection. A: Sinus rhythm. The second potentials in LOM channel, which were recorded by a duode-capolar catheter placed epicardially on the LOM, were MB potentials. The earliest activation site was the proximal site near the coronary sinus. The activation propagated to the distal MB (arrow). B: MB recordings of a single connection type during AF. The electrical activities of the MB (marked as LOM) were regular and organized without chaotic fibrillatory activities. Independent of passive activities of MB, ectopic beats (arrow) from the distal MB were observed. C: The MB is activated from proximal to distal (dashed arrow) during persistent AF, but the MB ectopy activated in a distal to proximal direction (arrow). AF = atrial fibrillation; LOM = ligament of Marshall; other abbreviations as in Figure 1.

Figure 3

Electrogram characteristics of double-MB connections (to CS and to LA–PVs). A: Sinus rhythm. The MB electrogram (arrow) and the local LA electrogram were close to each other. Therefore, distinct MB potentials were not seen in most recordings. B: A premature beat from the LSPV (dashed arrow) propagated first into the distal MB and then activated the MB in a distal-to-proximal direction (solid arrow). C: A recording from a double-connection type after the ablation of the distal connection between the MB and LSPV. During sinus rhythm, the MB activation was consistent with a single-connection type (proximal-to-distal activation pattern, solid arrow). Note that there was dissociated PV potential (dashed arrow). D: Fluoroscopic image in the left anterior oblique projection. A circular mapping catheter was located in the LSPV, and a duodecapolar catheter was placed epicardially on the LOM. LA = left atrium; LSPV = left superior pulmonary vein; PV = pulmonary vein; other abbreviations as in Figure 2.

Figure 4

Example of differential pacing to map the MP potentials. A: Intracardiac recordings during sinus rhythm. B: Activation during CS pacing. The earliest activation was in CS, followed by proximal-to-distal propagation within the VOM. These VOM potentials (arrows) clearly preceded the onset of PV and HRA potentials. C: Pacing from distal pole of the ablation catheter located within the LAA. The potentials recorded by the VOM catheter (arrows) are completely separated from atrial and PV potentials. D: Pacing from left PV separated the VOM potentials (arrows) from the PV potentials. E: Pacing from the distal VOM showed that the proximal VOM potential (arrow) preceded the PV potential, indicating that these potentials are not from the PVs. F and G: Fluoroscopic images during differential pacing. Abl = ablation; HRA = high right atrium; LAA = left atrial appendage; LAO = left anterior oblique; LPV = left pulmonary vein; RAO = right anterior oblique; other abbreviations as in Figure 3.

Figure 5

Electrogram characteristics of MB pacing. A: Pacing at the LOM with 1.1 mA output resulted in simultaneous LA and MB capture. B: When the pacing output was decreased to 0.3 mA, the stimulus selectively captured MB without capturing the LA. Therefore, the interval between stimulus and the earliest CS activation was 44 ms, which is 10 ms longer than that in A. C: MB pacing after ablation of the MB–LA junction showed loss of MB capture with the same pacing output as pre-ablation. This finding is one of the end points of MB ablation. Abl = ablation catheter; Stim = stimulus, other abbreviations as in Figure 3.

Figure 6

MB potentials before and after radiofrequency catheter ablation in a patient with multiple MB connections. A: Recording during AF. The MB activity demonstrated sustained complex fractionated activations. B: Recording after isolation and during infusion of 1 μg/ml isoproterenol. The MB recording showed fast but organized tachycardia (arrows), which was dissociated with the rest of the LA. Abbreviations as in Figure 3.

Figure 7

Electrogram characteristics of multiple connections. A, B: MB recordings during sinus rhythm. The earliest breakthrough was in the middle of the MB. The MB potentials were typically small (arrows), and the activation sequence of the MB was irregular and did not show either a distal or a proximal activation pattern. C: During premature complex from the MB (thin arrow), the earliest atrial breakthrough site (thick arrow) was not at either end but was in the middle. SVC = superior vena cava; other abbreviations as in Figure 3.