CASE PRESENTATION

A 23-year-old female patient with Ebstein’s anomaly presented with a history of palpitations since the age of 10, which have increased in frequency over the past two years. She has not responded to beta-blocker therapy. The 12-lead electrocardiogram predicted the origin of the accessory pathway in the free wall of the tricuspid annulus (Figure 1). The echocardiogram showed apical implantation of the septal leaflet of the tricuspid valve with a 41.6 mm distance to the mitral valve insertion. It also indicated severe regurgitation with an eccentric jet along the lateral right atrial wall to the atrial roof, a vena contracta of 7mm, a gradient of 15mmHg, and a pulmonary artery systolic pressure (PASP) of 20mmHg. The left atrium measured 16cm² and was non-dilated. The left ventricle had normal diameters, wall thickness, and systolic function with an ejection fraction of 55%. The right atrium measured 18cm² plus an arterialized portion of the right ventricle 18 cm². The right ventricle was functional, with an area of 5cm² and systolic function at the lower limit of normal. Electrophysiological study induced a narrow QRS tachycardia with a 330ms cycle and a VA interval of 194ms (Figure 2). In sinus rhythm, the accessory pathway's effective refractory period was 190ms, indicating a high risk for sudden cardiac death.

Radiofrequency ablation was conducted utilizing the ENSITE PRECISION system with 3D mapping, under the guidance of intracardiac echocardiography. Using a high-density HD Grid catheter with the Open Window technique, an activation map in sinus rhythm was created, revealing the accessory pathway (Figure 1). Intracardiac echocardiography with the Abbott Viewflex Xtra probe provided clear images of the tricuspid annulus, regurgitant jet, and catheter position (Figure 3). A deflectable sheath supported the ablation catheter and contact force measurement confirmed its placement. The pathway's location in the activation map was confirmed using the electrogram fused with the ablation catheter. The accessory pathway was successfully ablated through two 60-second applications of radiofrequency at 40 watts and 45°C.

DISCUSSION

Ebstein's anomaly is a rare developmental disorder, it represents less than 1% of all congenital malformations and is associated with Wolff-Parkinson-White syndrome in 10 to 30% of cases [3,4]. It consists of a malformation of the tricuspid valve in which displacement of the septal and posterior leaflet towards the ventricular cavity occurs; The anterior leaflet is generally dysplastic and has variable mobility depending on the degree of adherence to the free wall of the right ventricle. The orifice of the tricuspid valve located abnormally generates a portion of the right ventricle between the atrioventricular annulus and the origin of the valve, continuing with the right atrial cavity (arterialized ventricular portion), leaving a remaining ventricle of variable size with an always dilated atrium. The functional right ventricle presents variable degrees of fibrosis that in severe cases also involves the left ventricle, the Koch triangle is smaller, the ostium of the coronary sinus is larger, the bundle of His usually begins before the vertex of the Koch triangle with a shorter length. In the electrocardiogram, the P wave shows right atrial growth in 75% of cases, the PR interval is prolonged in 15% of patients due to delayed atrial conduction, and there may be a normal PR even with pre-excitation. The QRS complex presents right bundle branch block (RBBB) (75 to 90%) due to abnormal development of the septal leaflet and the middle papillary muscle [3]; The absence of RBBB in patients with Ebstein's anomaly and recurrent supraventricular tachycardias has 98% sensitivity and 92% specificity for the diagnosis of associated Wolff-Parkinson-White syndrome [4]. The association between intraventricular conduction disorders and Ebstein's anomaly was described in 1955 and confirmed by Schiebler et al. in 1958, particularly with type B ventricular preexcitation. In 1959, Schiebler et al found that 24 (29%) of 83 cases, reported with WPW syndrome and associated congenital heart disease, had Ebstein's anomaly.

WPW syndrome is considered type B when the pre-excitation zone is located in right ventricular structures: septal or paraseptal, anterior or posterior regions and also in right lateral parietal areas. Thus, anomalous activation fronts are created that are directed from the right ventricular myocardium to the left [5]. In symptomatic cases with tachyarrhythmias such as Wolff-Parkinson-White syndrome, surgical ablation or transcatheter radiofrequency is recommended [6]. The recurrence of arrhythmias after catheter ablation remains high despite current technological advances. Intracardiac echocardiography (ICE) is increasingly used during ablation of ventricular arrhythmias to characterize the substrate. It can help characterize the true tricuspid annulus and facilitate mapping efforts in the true AV annulus instead of the arterialized RV [3]. In a case series report (6 patients) carried out by Tapias et al., of patients undergoing accessory ablation using ICE to delineate the true tricuspid annulus, it was found that the duration of the procedure was 253.33 ± 60, 92 minutes, with an immediate 100% success. After a mean follow-up of 16.16 ± 7.7 months, no recurrences of tachycardia were documented and all patients were free of antiarrhythmic medications. Therefore, they concluded that the use of images (intraprocedural ICE) is useful to delineate the true tricuspid annulus that contains the accessory pathway, facilitating mapping and ablation [7]. Data compatible with that described by Vukmirović M [8] and Cismaru [9] who were the first to describe the use of ICE for this type of ablations.

CONCLUSION

Imaging integration in accessory pathway ablation for patients with Ebstein’s anomaly significantly boosts procedural success compared to conventional fluoroscopy-guided ablation and reduces the likelihood of complications during the procedure.