Author + information
- Mathew D. Hutchinson, MD∗ ()
- Division of Cardiology, Department of Medicine, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania
- ↵∗Reprint requests and correspondence:
Dr. Mathew D. Hutchinson, Department of Medicine, Hospital of the University of Pennsylvania, 3400 Spruce Street, 9 Founders Pavilion, Philadelphia, Pennsylvania 19104.
- catheter ablation
- premature ventricular complexes
- pulmonary artery
- right ventricular outflow tract
- ventricular tachycardia
Unbridled enthusiasm for catheter ablation of idiopathic outflow tract ventricular arrhythmias (VA) is tempered by suboptimal long-term procedural success. A recent multicenter report of outcomes after ablation of idiopathic premature ventricular contractions found 71% success (defined as a >80% reduction in premature ventricular contractions burden off antiarrhythmic agents) at a mean 20-month follow-up (1). Patients with right ventricular outflow tract (RVOT) ectopy fared best; however, the recurrence rate in these patients was a surprising 18%. In light of this experience, it is appropriate that we revisit RVOT ablation conceptually in an effort to improve both ablation efficiency and efficacy.
The classical electrophysiological description of the RVOT with opposing planar septal and free wall surfaces provides an excellent construct for predicting geographical regions subtending VA origin; however, the 3-dimensional relationships of the great vessels are more complex, with ablation targets often not directly accessible from the endocardium. It is also useful to differentiate the “site of origin” from “site of successful ablation” for the VA; these sites are often spatially distinct with the former inaccessible to direct catheter mapping. Well known to cardiac anatomists, the presence of ventricular myocardial extensions beyond the pulmonic ventriculo-arterial junction were documented by Gami et al. in 74% of 602 autopsy specimens (2). They found both the prevalence and the length of these extensions above each of the pulmonic cusps were similar (anterior: 45%, 3.7 ± 2.2 mm; left: 52%, 3.6 ± 2.1 mm; and right: 60%, 4.0 ± 2.5 mm). Intercuspal myocardial extensions beyond the echocardiographic PV annulus were also present in 73% of hearts.
Several reports have described mapping and ablation of VA within the pulmonary artery (PA) (3–5). Each of these used anterograde mapping of the PA, often at or above the level of the sinotubular junction. No consistent electrocardiographic signature for the VA in the PA is discernable from these studies; however, all reported a distinct electrophysiological hallmark: a sharp, delayed potential on the bipolar electrogram within the PA during sinus rhythm that reversed, becoming presystolic during the VA.
The current approach to left ventricular (LV) outflow tract mapping of VA has occurred contemporaneously; numerous reports have described ablation within the aortic cusps to approach regions less readily accessible from the LV outflow tract. In light of the similar anatomical configurations of the great vessels, the potential value of ablation within the pulmonic cusps is self-evident.
The report by Liao et al. (6) in this issue of the Journal provides detailed information regarding the anatomic, electrocardiographic, and electrophysiological characteristics of VA successfully eliminated with ablation from the pulmonary cusps. Their cohort of 24 patients was taken from a larger series of 244 patients presenting with idiopathic left bundle inferior axis VA referred for catheter ablation at their center. All 24 patients underwent mapping of the RVOT and PA, with the PA sites boasting activation times 8.3 ms earlier than the nearest RVOT site (mean: 4.1 mm distant). Similar to previous reports, the investigators noted a multicomponent bipolar electrogram in sinus rhythm (rounded or “far-field” early, followed by sharp or “near-field” late) that reversed during the VA in every case. Irrigated ablation within the PV cusp conferred durable arrhythmia suppression in all patients at a mean follow-up of 9 months.
The most important contribution of the report by Liao et al. (6) is the methodical demonstration of a new technique of RVOT mapping. The PV cusps were engaged retrogradely by passing the ablation catheter through the pulmonic valve and withdrawing the D-curved loop into the respective pulmonic cusps. This specific catheter maneuver resonates with operators, as it represents a mirror image of the retrograde aortic approach to the LV outflow tract. Formation of this reverse curve appeared to be fairly straightforward and safe, although a long sheath was necessary to stabilize the catheter shaft. The inclusion of representative orthogonal fluoroscopic projections, as well as tomographic reconstructions, allows the reader not only to understand the mechanics of their manipulations, but also to compare the anatomical relationships of the pulmonic and aortic roots.
The investigators also demonstrate the use of pulmonary arterial angiography as an important adjunctive tool to guide catheter positioning when real-time modalities such as intracardiac echocardiography are not available. Similar to published experience in the aortic root, the investigators underscore the limitations of pace mapping within the pulmonic cusps; they consider that only one-half of the patients had a >10 of 12 pace map match from the successful cusp ablation site.
The study has several other findings that warrant further discussion. First, the paper presumes a clear evolution in the investigators’ approach to RVOT VA. Whereas the initial 7 patients in the cohort had ablation in the RVOT prior to cusp mapping, the subsequent 17 underwent both RVOT and cusp mapping prior to energy application. Despite the procedural success achieved from the cusps, it is noteworthy that relatively extensive ablation was required to eliminate the VA (mean: 6.2 lesions). Although the investigators presupposed that their VA were likely of RVOT origin, there are striking similarities between the typical left and right pulmonic cusp morphologies presented with those often localized to the respective aortic cusps. Moreover, the degree of electrogram prematurity at successful sites was fairly modest (mean: 29 ms) when compared with studies reporting successful activation times from the LV ostium and LV summit (7,8). Given the direct continuity of the myocardium adjacent to the aortic and pulmonic cusps at the level of the septum, it would be interesting to know the relative activation times within the closest LV structure at each successful pulmonic cusp site (9,10).
Despite the high prevalence of supravalvular myocardial extensions, direct extensions within the pulmonic leaflets are rare (2). Thus, one must presume that ablation in these cases was directed rather at the myocardium at the ventriculo-arterial junction or within the crest of the RVOT. An unfortunate reality, well known to ablationists, is that the most common sites of RVOT VA origin (i.e., immediately beneath the pulmonic valve circumference) are also the most challenging upon which to achieve catheter stability. In this regard, it is likely that pulmonic cusp ablation may provide a novel method of ablating (indirectly) the apex of the RVOT with greater efficiency, rather than eliminating an arrhythmic source within the cusp per se.
Lastly, although not specifically addressed in the paper, operators should be mindful of the close anatomical relationship between the PA and the left main coronary artery. One study found that the left main coronary artery coursed within 2 mm of the left pulmonic cusp in 43% of cases (11). The optimal power delivery and minimal safe distance in such cases are unknown; thus, consideration should be given to coronary angiography prior to energy application within the pulmonic cusps.
In summary, Liao et al. (6) provide an important new technique to facilitate catheter mapping of the RVOT-PA junction. Future studies with combined RV and LV mapping may provide greater precision in localizing nonendocardial VA origin, thereby enhancing ablation efficiency.
↵∗ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
Dr. Hutchinson has reported that he has no relationships relevant to the contents of this paper to disclose.
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