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.