Expert Commentary: Intra-Atrial Re-entrant Tachycardia Substrate Mapping Using the Ensite NavX™ Navigation and Visualization Technology in Post-surgical Congenital Heart Disease Patients
DOI: 10.19102/icrm.2012.031208
George M. McDaniel, MD, MS
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Intra-Atrial Re-entrant Tachycardia Substrate Mapping Using the Ensite NavX™ Navigation and Visualization Technology in Post-surgical Congenital Heart Disease Patients: Assessment of Automated Voltage Maps
Ablation of intra-atrial re-entry tachycardia (IART) in postoperative congenital heart disease patients is often a challenge at multiple levels. As a result of prior, often multiple, procedures requiring vascular access, vessels may no longer be patent. Access to the chamber of interest may be limited by the native anatomy and/or surgical interventions, further inhibiting catheter deployment. Lastly, limiting long-term success, the atria in these patients have multiple areas of scarring which allows for multiple tachycardia circuits. Finding an area where a line of block can be created that completely interrupts the tachycardia circuits can be a challenge. Any tool that potentially improves the long-term success or safety of these procedures is worthy of study. The institutional experience with one such tool, the Ensite NavX three-dimensional (3D) electroanatomic mapping system, is reported by Patel and Shah.
As noted by the authors, acute success rates in prior studies approached 90%, with a near 20% recurrence rate in a year. Authors have postulated that this was due in part to incomplete identification of potential circuits within the atrium. This concept underlies the approach used by Mavroudis et al1 in the surgical ablation of atrial dysrhythmia in patients with complex congenital heart disease. Surgical ablation of common potential circuits is achieved by creating multiple lines of block between anatomic boundaries for potential circuits intraoperatively, with reasonable long-term success. By combining careful 3D mapping with entrainment of the circuit from the putative ablation site, Patel and Shah report only one recurrence, with a mean follow-up of almost 3 years. While a larger sized, multicenter population is needed to define clinical efficacy, this trend is quite promising, particularly for a catheter-based approach.
The use of 0.5 mV as a threshold to define conducting tissue was based on reports using this threshold with a competing 3D technology. This chosen threshold allowed for the identification of the conduction pathways within the atrium of seven of the nine patients in this study. So, in 22% of the patients, this threshold failed to identify enough of the conduction pathways in these patients to have allowed for successful ablation by voltage mapping alone. By successively lowering the voltage threshold, maps of multiple potential circuits, as is often seen in these patients, could be described in the region where successful ablation had been performed. Again, long-term success was associated with combining 3D mapping, entrainment mapping, and loss of inducibility of the dysrhythmia.
As this was a post hoc analysis of known circuits, it is interesting to speculate about the complexity of mapping that would be needed to ablate tachycardia with a low-voltage threshold set at the start of the case. In this study, there was a wide range of mapping points taken. Certainly, with more potential zones of slow conduction, one could envision the need for very detailed mapping of scar borders. This could be a fairly time-consuming process, but, as the authors note, that time could be offset by the ability of the newer Ensite system to perform simultaneous acquisition of positional, voltage, and activation timing data. Further investigation is required to evaluate the net effect on time if lower voltage thresholds are routinely used.
Lastly, in their discussion, the authors note that a perceived advantage of the Ensite system is that it allows for the use of non-proprietary cryocatheters for mapping circuits close to critical conduction structures. The location of these structures is often altered by the underlying structural disease or by the surgical changes in the anatomy. Additionally, dysfunction of the conduction tissues may be a sequela of necessary surgical intervention(s). The necessity of careful delineation of the location of these structures cannot be overstated.
From this study, we are reminded that while being a promising tool, the use of a 3D mapping system alone is not sufficient to ensure success and safety of ablation in these complex patients. However, the combination of a 3D mapping system and commonly used pacing techniques can produce a successful outcome. As the capabilities of these systems and our capabilities to maximize their use develop, perhaps ablation in these patients can be performed faster, safer, and with improved long-term success. However, as my mentors have taught me, an intimate knowledge of the surgical anatomy along with the potential altercations of the location of nearby structures is necessary for success and safety in these complex patients.
George M. McDaniel, MD, MS
GMM4D@hscmail.mcc.virginia.edu
Division of Pediatric Cardiology
Department of Pediatrics
University of Virginia
Charlottesville, VA
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