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How to Perform Ethanol Ablation of the Vein of Marshall
Miguel Valderrábano, MD
Introduction
The ligament of Marshall (LOM) is an embryological remnant of the left superior vena cava1 that has been shown to harbor pro-arrhythmogenic substrates that may play a role in atrial fibrillation (AF). As early as 1972, Scherlag et al. demonstrated that atrial tachycardia would originate from the LOM after stimulation of the extracardiac left sympathetic nerves.2 Later on, adrenergic atrial tachycardia after catecholamine stimulation was shown to arise from the LOM.3 Abundant sympathetic4 and parasympathetic5 innervation was shown to present in the LOM. The LOM can be patent as a vein of Marshall (VOM), which connects to the coronary sinus (CS) and can be cannulated in humans.6 High-frequency stimulation of the LOM during atrial refractoriness can trigger atrial and ventricular arrhythmias in animals,7 and AF in humans.8 For these mechanistic reasons, the VOM is a reasonable therapeutic target in the treatment in AF.9 Additionally, the VOM sits in the posterior mitral isthmus, in part of the reentrant circuit of perimitral flutter.10 We have shown that the VOM can be cannulated from the CS and that it is a vascular route to deliver ablative ethanol to the underlying myocardium and nerve contents of the VOM, with utility for AF,11,12 atrial tachycardias,13 and perimitral flutter.10 Herein follows a brief description of the technical steps required for this procedure.
Procedure
Ethanol injection in the VOM requires a blend of procedural skills belonging to both interventional cardiology and electrophysiology, which may intimidate the neophyte. However, it only requires a minor adaptation of workflow and tools commonly used for left ventricular lead delivery. Arguably, the biggest challenge is to understand the fluoroscopic anatomy of the VOM and its variants. It is critical however, to have some familiarity with the tools to be used. Figure 20.1 shows the materials required for a VOM ethanol infusion. Figure 20.2 shows the operator workspace. Figure 20.3 and 
Video 20.1 show an example of each of the procedural steps required. Carefully following these steps can lead to a success rate of up to 89%, and failures can be consistently attributed to anatomical absence of the VOM.
Figure 20.1 Tools required for VOM ethanol infusion. Panel A: Coronary sinus sheath, designed to be inserted from an access point cephalad to the CS—either right internal jugular vein or left subclavian vein. Panels B and C: Subselector catheters used to engage the VOM ostium, including the left internal mammary artery (LIMA) angioplasty guide (Panel B) and the acute subselector left ventricular lead placement catheter (Panel C). Panel D: Angioplasty wire. Panel E: Angioplasty balloon–typically 1.5–2 mm x 6 mm. Panel F: Tuohy valve. Panel E: Balloon inflator.
Figure 20.2 Operator workspace. Panel A: View of the patient’s neck from the right side. A 9-Fr sheath is inserted in the right internal jugular vein and sutured to the skin. Panel B: Magnified view. Inside the 9-Fr sheath is a CS sheath. Once it is engaged securely in the CS, it can be bent towards the operator’s workspace and attached to the drapes with a towel clip. This way, the operator can complete the procedure standing from the usual ablation workspace.
Figure 20.3 Procedural steps. Panel A: CS venogram. From the internal jugular venous access, the CS is engaged with a sheath. Inside the CS sheath, a subselector LIMA guide catheter is inserted and contrast is injected with the LIMA catheter tip pointing superiorly. In this LAO projection, the VOM is not visible due to overlap with the CS. Panel B: In a shallow (10° to 30°) RAO projection, contrast injection, the VOM is clearly visible via a nonselective injection through the LIMA. Panel C: The preloaded angioplasty wire and balloon are advanced into the VOM. Once the wire is securely engaged in the VOM, the balloon is advanced as distal as possible in the VOM. Panels D through G: Balloon locations for the first (Panel D), second (Panel E), third (Panel F), and fourth (Panel G) injection of ethanol in the VOM. Some myocardial staining occurs (Panel G) when contrast is injected after ethanol.
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