Do we need intracardiac echo to guide ablation of ventricular arrhythmias from the papillary muscles?

This editorial refers to ‘Intracardiac echo-facilitated 3D electroanatomical mapping of ventricular arrhythmias from the papillary muscles: assessing the “fourth dimension” during ablation’ by R. Proietti et al., on pages 21–28. Catheter ablation of ventricular arrhythmias is an increasingly performed procedure with high success rates in experienced hands.1 However, catheter ablation of arrhythmias originating from endocavitary structures might be challenging due to anatomical complexity with consecutive difficulties to ensure catheter stability and manipulation.2 An origin of arrhythmias located relatively deep beneath the endocardium might further aggravate successful ablation.3 According to recent reports, almost 10% of ventricular tachycardias (VTs) are suggested to involve endocavitary structures.2 In this context, ventricular arrhythmias from the left ventricular anterior and posterior papillary muscles have been described as a relatively novel entity in patients with and without structural heart disease.4–6 Actually, difficulties in fluoroscopic visualization of these structures might have led to prior underestimation of these arrhythmias emphasizing the value of additional imaging strategies.2,7 In this issue of EP-Europace, Proietti et al.8 assessed the value of an intracardiac echocardiography (ICE)-facilitated three-dimensional electro-anatomical mapping approach for ablation of ventricular arrhythmias from the papillary muscles. The authors retrospectively studied ablation procedures for ventricular arrhythmias (ventricular tachycardia and/or premature ventricular contractions) from the papillary muscles at two centres. A total of 16 patients (mean age 67 ± 6; 11 men; mean left ventricular ejection fraction 40.1 ± 11%) with and without structural heart disease underwent 24 ablation procedures. A three-dimensional electro-anatomical mapping system was used in all procedures, with additional integration of three-dimensional ICE in 15 of the 24 procedures. Consistent with earlier reports,3,5 the posteromedial papillary muscle was the most frequent origin of the clinical arrhythmia, with the body of the papillary muscle being the most successful site for ablation. Freedom from clinical arrhythmia was achieved in 62.5% (10 of 16) patients after the first procedure with a higher success rate in patients whose first procedure was performed with vs. without ICE [88.8% (8/9) vs. 28.5% (2/7), P = 0.0035]. After a mean follow-up of 10.5 ± 7 months, 13 patients remained arrhythmia free following a repeat ablation procedure with none of the patients showing new mitral insufficiency detected by transthoracic echo, also in accordance with others.3 The authors conclude that routine adoption of ICE-facilitated three-dimensional electro-anatomic mapping might result in improved success rates of arrhythmias from the papillary muscles due to real-time creation of precise geometries of cardiac chambers and endocavitary structures. The utility of an ICE-guided approach has also been described by others.3,9–11 However, this is the largest case series of patients undergoing ablation of papillary muscle ventricular arrhythmias with the described approach (15 of 24 procedures) and the rarity of these arrhythmias makes the performance of randomized studies difficult. Nevertheless, the final conclusions on the value of ICE-guided papillary muscle VT ablation cannot be drawn from this case series due to the following limitations: (i) relatively small sample size of a heterogeneous patient cohort with mixed ischaemic and non-ischaemic cardiomyopathies and preserved as well as reduced ejection fraction; (ii) varying access approaches (9 transseptal with a steerable sheeth, 15 retrograde aortic); (iii) non-randomized study design with a potential learning curve influencing the results (ICE was not available from the beginning in one centre); (iv) non-standardized follow-up according to the centres preference; (v) use of contact force-guided (n = 20) and non-contact force-guided ablation catheters (n = 4) with contact force-guided ablation potentially resulting in better outcome. Interestingly, in contrast to previous reports3,5 that describe difficulties in achieving successful ablation at the site of best pace-map, the authors observed good correlation of the best pace-map with the earliest site on the activation map. It remains to be determined whether this is really a matter of better imaging of the papillary muscles with consecutive better catheter stability as suggested by the authors or for instance a patient selection bias. In fact, stable catheter contact at the target location may still be challenging despite intensive monitoring with ICE because of the vigorous motion associated with normal papillary muscle contraction. Contact force data to further support this theory would be helpful. In addition in a case series, approximately 50% of patients with ventricular arrhythmias originating from the papillary muscle a variable QRS morphologies was noted either spontaneously, after the initial ablation lesions, or both.3 The authors postulated that this change in QRS morphology might be caused by a single origin with preferential conduction resulting from the complex structure of the papillary muscle. Our experience is in line with Yamada et al.3 that this change in QRS morphology is very typical and common in those patients and very useful to differentiate these ventricular arrhythmias from fascicular arrhythmias. Owing to the supposed deep intramural substrate with different exit sites or multifocal localization3 alternative ablation techniques like cryoablation12 potentially going along with more stable tissue contact or isolation of ventricular prepotentials11 have been described and might be helpful, but final conclusions on their value compared with the standard use of irrigated radiofrequency ablation catheters with high power settings cannot be drawn due to small case series. In the future, real-time magnetic resonance imaging-guided ablation might present the ideal imaging methodology for this arrhythmia due to real-time three-dimensional visualization not only of the underlying anatomy and substrate, but also of the exact catheter position in relation to these with the potential of immediate lesion detection.13 Until this methodology is mature for clinical use, the ICE-guided approach currently is the only real-time imaging method facilitating direct visualization of such complex three-dimensional endocavitary structures like the papillary muscles with simultaneous monitoring of catheter contact at the desired target location. The authors therefore have to be thanked for the straightforward description of this useful approach demonstrating the importance of precise understanding of the complex left ventricular anatomy and for bringing in mind this rather rare arrhythmia with its associated challenges. Conflict of interest: R.R.T. received travel grants from St Jude Medical, Topera, and Biosense Webster, and Medtronic and also received speaker's bureau/proctor honoraria from Biosense Webster, Topera, and Medtronic. C.E. received travel grants from St Jude Medical, Biosense Webster, and Medtronic and also received speaker's honoraria from St Jude Medical, Medtronic, and AstraZeneca.