**3.2 Tissue Ablation by VOM-ETHO**

Ethanol infusion in the VOM leads to generation of a new low-voltage area posterior and superior to the coronary sinus, encompassing variable extents of the posterior left atrial wall and the anterior aspect of the left inferior pulmonary vein. The area of the scarring depends on the size of the VOM. Valderrabano et al. reported that the area of scar (bipolar voltage amplitude <0.5 mV) was 10.2 + − 5.7 cm2 (range, 3.3 to 15.3 cm2 ) in the first human experience.17 On large population of over 700 patients, the Bordeaux group reported a scarring area of 10.2 + −5.3 cm2 [10, 17]. In this experience factors contributing to reduction of VOM-ETHO effectiveness in lesion formation were: VOM dissection (10.7%), iodine leakage (3.0%), and VOM morphology without visible branches (3.0%). Ethanol infusion in a wrong vein was associated with less mitral line block (72.7% versus 95.8%, P = 0.012).

*Vein of Marshall Ethanol Infusion in Setting of Atrial Fibrillation Ablation DOI: http://dx.doi.org/10.5772/intechopen.105593*

**Figure 3.**

*Step-by-step actions for VOM cannulation and ethanol delivery (right panels). Left panels: Pre and post-VOM-ETHO bipolar maps indicating typical location and shaping of scarring formation. From: Kitamura et al. [17].*

#### **3.3 Technical issues and considerations**

VOM-ETHO is highly feasible with a success rate of 91% from latest data on a population of over 700 patients [10]. Factors associated to procedural failure were: nonidentification of VOM (6.2%), noncannulation (1.5%) or ethanol infusion in the wrong vein (1.7%). The Vieussens valve was a helpful landmark and was visible in 63.2% of cases. Remarkably, previous ablation inside the coronary sinus was strictly associated to VOM nonidentification. The success rate of VOM-ETHO procedures increases with the experience of operators.

#### **3.4 Complications**

Complications related to VOM-ETHO procedures are reported in **Table 1**. Acute and delayed pericardial effusion represented the most described complications. During the procedure, pericardial tamponade was generally due to inadvertent CS perforation during VOM cannulation maneuvers or steam pops occurred during ablation. After the procedure, subacute pericardial effusion requiring pericardiocentesis was related to inflammatory reaction after alcohol delivery. The higher rate of delayed cardiac effusion or tamponade observed in patients with VOM perforation advocates a causal relationship between the inflammatory reaction and the inadvertent drainage of ethanol in the pericardial space. LAA isolation occurring after VOM-ETHO procedures may be observed in patients with previous extensive ablation settings involving septal and anterior scarring.

## **4. Role of VOM Bundle in atrial tachycardias**

Atrial tachycardias (ATs) are often seen in the context of atrial fibrillation ablation implicating macroreentrant or scar-related mechanisms [19, 20].


#### **Table 1.**

*Complications rate during VOM-ETHO procedures.*

Radiofrequency catheter ablation is an effective therapy for patients with AF but perimitral ATs and localized reentry circuits commonly appear after pulmonary vein isolation or additional linear lesion in the left atrium [21]. Patients having connections between Marshall bundle and the myocardium of coronary sinus, left atrium or pulmonary veins, may develop the anatomical substrate to generate localized reentry circuits or macroreentrant ATs around the mitral isthmus, using the epicardial Marshall bundle [22]. Vlachos et al. [23], considering a population of 140 patients previously underwent a pulmonary vein isolation procedure, reported that the Marshall bundle is involved in a higher proportion of post-AF ablation ATs (30.2%), being 51.7% macroreentrant ATs and 48.3% localized reentry. Marshall bundle-dependent ATs can be terminated with RF ablation, either endocardial via Marshall-bundle-left atrium connection, or epicardially via Marshall bundle-CS connections, and with ethanol infusion inside the VOM being the Marshall bundle an electrically protected, isolated anatomical structure, difficult to target with RF ablation (**Figures 4** and **5**) [24].

Endocardial ablation from within the left atrium may not successfully ablate the Marshall bundle, owing to the distance from endocardium to the critical site. As RF ablation induces a tissue heating by mostly resistive mechanism, the difficult to reach the epicardial Marshall bundle may explain the high failure rate of mitral isthmus block in published studies [25, 26]. For these reasons ethanol infusion inside the VOM *Vein of Marshall Ethanol Infusion in Setting of Atrial Fibrillation Ablation DOI: http://dx.doi.org/10.5772/intechopen.105593*

#### **Figure 4.**

*The bipolar EGMs recorded in MB-LA connections and MB-CS connections have a characteristic electrophysiological pattern: high-frequency long-duration amplitude multicomponent (multiphasic) EGMs. From Vlachos et al. [2].*

#### **Figure 5.**

*Example of Marshall Bundle-related perimitral circuit in a patient with previous pulmonary vein isolation and linear lesions in the left atrium (mitral line and roofline). Note that part of the circuit is lacking during endocardial mapping on the LAT Histogram (CARTO7 module). Circuit mapping is completed by annotating signals recorded on Vision-Wire (red arrow) in the VOM. Diastolic signal recorded on the mapping wire placed in the VOM appears fragmented and of long duration.*

may represent an adjunctive standalone strategy in patients with refractory Marshall bundle-related perimitral ATs or localized reentry circuits [14, 27, 28]. The additional use of VOM-ETHO strategy seems to improve ablation rates when compared with RF ablation alone [25, 26].
