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How to Perform a Hybrid Endocardial / Epicardial Mapping and Ablation for IST/POTS
Inappropriate sinus tachycardia (IST) is defined as a sinus HR >100 bpm at rest (with a mean 24-hour HR > 90 bpm not due to primary causes) and is associated with distressing symptoms of palpitations, fatigue and exercise intolerance. Postural tachycardia syndrome (POTS) is a systemic disease, with postural tachycardia being one of several underlying criteria. It is usually characterized by frequent symptoms that occur with standing, such as light-headedness, palpitations, tremor, generalized weakness, blurred vision, exercise intolerance, and fatigue.
Medical treatment as well as endocardial or epicardial ablation of IST or POTS have shown suboptimal results. We describe a combined single-step electrophysiological (EP) and surgical approach, where the endocardial part primarily maps the sinoatrial node and the area of earliest activation and the epicardial part primarily performs the sinus node sparing ablation of the venae cavae and crista terminalis. This procedure should preferably be performed in a hybrid suite.
The electrophysiologist cannulates the groin and utilizes a multipolar mapping catheter to localize the sinus node. A baseline EP study is performed to exclude any other mechanisms of supraventricular tachycardia. Bipolar activation mapping is done to identify the earliest site of activation referenced to both an endocardial fiducial point (e.g., coronary sinus electrogram) and the surface P wave. After the mapping the EPs shows the sinus node with the tip of the EP catheter on the videoscopic view of the surgeon who can use methylene blue on a 5-mm endoscopic Kittner or a surgical marker to stain the sinus node area. The SVC and right atrium has to be free of electrodes and of the central venous line to avoid damage during clamping and ablation.
Epicardial ablation is performed on the beating heart under general anaesthesia with left-sided selective lung ventilation. The right hemithorax is entered with three 5mm working ports. A camera port in the fifth intercostal space at the mid-axillary line, and two working ports for instruments (in the third and seventh intercostal space at the anterior axillary line). After placement of the camera port, CO2 insufflation is started at a pressure of 8 mmHg to increase the working space. The anatomical structures relevant to the epicardial treatment are: the sinoatrial node (SAN), the right phrenic nerve, the crista terminalis and the venae cavae, the right-sided pulmonary veins (RPVs), the right atrium (RA), the ganglionated plexi (GPs), the pericardial space and the pericardial sinuses (sinus tranversus and sinus obliquus). The right phrenic nerve passes along the pericardium lateral to the superior vena cava (SVC), superior to the antrum of the right superior PV (RSPV), the crista terminalis, and the inferior vena cava (IVC). The pericardium is opened with endoscopic scissors longitudinally, 2 cm anterior to the phrenic nerve, towards the SVC and IVC. To protect the nerve, improve visibility and facilitate the dissection of the pericardial reflection to gain access to the oblique sinus, the posterior part of the pericardium is retracted with 2 sutures that are pulled outside the chest posteriorly to the camera port. Since opening the pericardial reflection between the right pulmonary artery, the SVC, and the RSPV also dissects the right superior GP, and therefore increases the heart rate by decreasing the suppression of the vagal response, access to transverse sinus should be avoided. The pericardial reflection adjacent to the right inferior PV (RIPV) and the IVC is bluntly dissected until access to the oblique sinus is achieved. The lesion set performed with a bipolar clamp consists of a crista terminalis ablation together with SVC and IVC isolation. To facilitate the crista ablation, the lower jaw of the clamp can be positioned behind the RPVs and the upper on the crista thereby obtaining a stable grip. To achieve a safe passage of the bipolar clamp, a lighted tip dissector with gliding path is carefully placed under the RIPV towards the area between the right pulmonary artery (RPA) and the RSPV posteriorly. The gliding path is connected to the bipolar clamp, (Synergy, AtriCure Inc., Cincinnati, OH, USA) which is then safely put around the antral area of the right PVs. First, ablation of the right PV antrum is performed, then the upper jaw is placed over the crista terminalis taking into consideration the sinus node location. Ablation is performed similar to an intercaval line. IVC ablation is performed and the line is connecting to the lower part of the crista line. SVC ablation is performed, also connecting to the upper crista line. The endpoint of the lesion set is a rate reduction of 30% or the appearance of a junctional rhythm. The pericardium is closed.
Post ablation endocardial procedure
Post ablation mapping and identification of the sinus node is done using the same mapping catheter. The right atrium, SVC, and IVC are mapped. The point of earliest activation of the SAN is identified. A voltage or scar map is typically used to confirm SVC, IVC isolation and the crista terminalis lesion that connects to the IVC and SVC. If there is a gap, the EP can close this gap using an irrigated ablation catheter.
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