INTRODUCTION
Inappropriate sinus tachycardia (IST) is a common condition that causes an abnormally high resting heart rate (HR) with an exaggerated chronotropic response during exercise and/or stress, and is associated with debilitating symptoms, exercise intolerance, and near syncope1. Pharmacological treatment with B-blockers, calcium channel blockers and/ or Ivabradine are considered first-line therapies for symptomatic patients2. However, these medications are frequently not tolerated due to side effects or are ineffective in controlling patient’s symptoms3. Radiofrequency catheter ablation (RFA) aimed at sinus node modulation (SNM) has been proposed as an alternative therapy for refractory patients, with success rates varying between 23% and 85% in the published literature, and with a variable incidence of procedural related complications (9.5 to 50%) such as phrenic nerve (PN) injury, pericarditis, superior vena cava (SVC) stenosis, cardiac tamponade and iatrogenic sinus node (SN) dysfunction requiring pacemaker implantation4. The most common RFA approach for SNM is based on the identification of the upper part (“head”) of the SN complex that is activated during higher HR using 3D mapping and is expected to be localized at the lateral aspect of the SVC-right atrium (SVC-RA) junction, according to early anatomic descriptions of sinus node myoarchitecture5. In order to activate the higher hierarchy of the SN cells, high doses of isoproterenol are used to increase SN automaticity, and RFA is applied over the earliest activation site. In most cases, additional RFA includes an extension of the RF lesions towards the posteroinferior aspect of the SN complex (“tail”) located along the superior aspect of the Crista Terminalis (CT), to achieve clinically significant modulation of the SN activity (Fig. 1a and 1b). An extensive RFA from the “head” to the “tail” in this region could increase the risk for procedural complications from collateral injury of structures such as the PN.
We describe the systematic use of an anatomical approach for SNM to treat IST under intracardiac echography (ICE) guidance, aiming to identify and ablate the earliest activation sites at the arcuate ridge (AR) in the antero-superior SVC-RA junction, and extending the RFA lesion set towards its more septal aspect, at the level of the interatrial septum.
The presented approach is based on the following considerations: 1. ICE is the most accurate real-time imaging technology to delineate the SVC-RA junction6. 2. In redo procedures, the extension of ablation from the lateral SVC-RA junction to the AR was needed to obtain final control of HR, as previously reported (Fig. 1c and 1d)7. 3. The high doses of isoproterenol required to increase the HR during the procedure are usually poorly tolerated, affecting the accuracy of identifying the most anterosuperior and septal extension of the upper SN region, target for RFA.