Utilizing Advanced EP Techniques and Technologies in the Treatment of Supraventricular Tachycardias: Experience Using the EnSite

Martin Lowe, MD, Director of Cardiac Electrophysiology, The Heart Hospital, University College of London, London, United Kingdom

Martin Lowe, MD, Director of Cardiac Electrophysiology, The Heart Hospital, University College of London, London, United Kingdom

Atrioventricular Nodal Reentrant Tachycardia (AVNRT) Recently, a female patient was referred for treatment of AVNRT. She had been experiencing heart palpitations for approximately two years despite medication and was highly symptomatic, suffering episodes once per week. After an EP study was performed, it was determined she had atypical AVNRT. In order to gain a better understanding of the patient's individual anatomy and location of critical cardiac structures, the EnSite® System (St. Jude Medical, St. Paul, Minnesota) was used to build a three-dimensional (3-D) model of cardiac structures in her heart. Using the system's multi-surface tool capabilities, individual surfaces were created beginning with the coronary sinus, followed by the superior vena cava (SVC), the inferior vena cava (IVC) and finally the body of the right atrium. These surfaces were then linked together automatically by the system to create an incredibly detailed representation of the cardiac anatomy. Creation of the geometry with the ablation catheter took approximately 10 minutes. The Respiration Compensation was utilized in order to ensure accurate navigation and visualization of the ablation catheter. This feature subtracts movement due to changes in impedance and cardiac motion to provide an accurate representation of catheter position. This is very helpful when creating lesions in the vicinity of the AV node. Once the geometry was created, the critical areas were labeled, including locations where slow pathway potentials (SPP) were noted as well as the His region. It is the hospital's general practice during AVNRT procedures to begin ablation at the SPP farthest from the AV node, then to draw the catheter tip up towards the region of the AV node. This method ensures that a minimal amount of ablation occurs near the His region and prevents any unnecessary risk to the AV node. In this case, a Safire Bi-directional Ablation Catheter (St. Jude Medical) was utilized. The bi-directionality of the catheter is incredibly useful in maneuvering quickly throughout the cardiac chamber. In addition, the catheter offers highly precise, smooth movement and excellent stability when positioned against the cardiac wall. The handle and steering mechanism are designed so that a simple thumb movement is all that is needed to manipulate the distal end of the catheter. It is very sensitive, so a light touch is all that is required. Most importantly, the catheter provides automatic steering lock. This actuator mechanism provides great confidence that the tip will not spring upward or recoil unexpectedly. For procedures such as AVNRT, where lesions are being created in such close proximity to the AV node, this is especially important. During the procedure, the catheter tip was moved upward along the annulus in very small increments using the EnSite geometry as a guide. Having plotted the slow and fast pathways, it was clear where RF energy could and could not be applied. The primary slow pathway was found to be only one or two centimeters away from the AV node, but was clearly a safe distance away from the node. In addition to the certainty provided by this detailed visualization, use of the EnSite System also contributed to a reduction in fluoroscopy time for the procedure. Atrial Flutter Similarly, these techniques have proven quite useful in the treatment of atrial flutter. Recently, a male patient who had been suffering palpitations due to atrial flutter for some time was admitted for catheter ablation. Upon examination, it was determined to be an atypical flutter, and once again, the EnSite System and Safire Catheter were employed. As it is standard to have a multi-pole mapping catheter in the right atrium for these procedures, the Livewire Duo-Deca Steerable Diagnostic Catheter (St. Jude Medical) was used to create the EnSite chamber model. Because the system is able to gather data points from all 20 electrodes on the catheter simultaneously, a highly detailed multi-surface geometry including the coronary sinus, SVC, IVC and right atrium was created in under 10 minutes. Ablation was commenced, and a set of lesions was placed very closely to the annulus using the Safire catheter. Again the precise steering, bi-directionality and automatic lock proved to be very helpful in creating a complete lesion to block the circuit. Upon pacing to confirm the block, though, it was determined that another circuit was present and was perpetuating the arrhythmia. Using the 3-D geometry, it was quite straightforward to determine where the second circuit might exist. This location was quickly confirmed, and a second set of lesions was created to block the additional circuit. Testing was conducted to ensure that flutter could not be sustained, and the procedure was complete. The benefits of using advanced mapping and a premium ablation catheter were once again evident in this case, through enhanced understanding of the patient anatomy and precise, intuitive movement of the catheter within the chamber. In addition, it is quite likely that had the EnSite System not been in use during this procedure the patient would have been forced to return for a second procedure to eliminate the second circuit. Ideal Applications for Advanced Technology The benefits of using advanced technology in the management of AF are extensive. Three-dimensional mapping enables us to document the exact location of the pulmonary veins (PVs) and visualize the catheters within the geometry. It is quite useful to see both the PV mapping catheter and the ablation catheter in the anatomy during the case. In addition, an esophageal temperature sensor has recently been put into service at the Heart Hospital. By locating and navigating a distal and proximal electrode on the esophageal probe, we can now allow the esophagus to be mapped and visualized on the EnSite System geometry. This is one additional piece of information we have that provides a greater level of confidence when creating lesions in the vicinity of the posterior wall and esophagus. It has also become evident that these technologies have a place in the treatment of less complex arrhythmias as well. Often a SVT is more complex than it initially appears, and in these cases, 3-D visualization and an intuitive, bi-directional ablation catheter can provide reduced fluoroscopy time and improved confidence when ablating near critical cardiac structures. In fact, using these technologies together is advantageous for a variety of SVT cases, including: Abnormal anatomy Congenital heart disease Dilated right atrium Any chamber where it is difficult to maneuver a catheter Slow pathways situated close to the AV node In any of these situations, there is clinical benefit to utilizing advanced techniques and technologies, ensuring the utmost level of confidence during and after an EP lab procedure.