First Evidence of Clinical Benefit of Robotically Driven Catheter Ablation or an Outlayer?

Results of catheter ablation of atrial fibrillation (AF) are far from optimal at the present time. Even in paroxysmal AF, where there is general agreement on the crucial role of the atrial muscle around the pulmonary vein ostial region in the genesis of AF,1 antral pulmonary vein isolation not infrequently fails in providing long-term AF free status. One of the possibilities to explain the failures is venoatrial conduction recovery. In fact, a universal finding when patients come back to the electrophysiology laboratory because of AF recurrence after a first ablation procedure is venoatrial electrical reconnection.2, 3 And just by reisolating the pulmonary veins the majority of patients obtain significant clinical benefit.2, 3 A likely hypothesis for such a clinical scenario is that the initial ablation is not “good enough,” i.e., the lesions acutely deteriorate electrical conduction to the point of conduction block (electrical isolation of the pulmonary veins) but somehow reduce in size during the healing process and conduction recovers. When discussing this phenomenon with my patients, I used to tell them “we are electro-physiologists; we know when we change the function of the conduction in your heart, but we do not see the lesions we are creating.” If we consider how we create lesions, with a catheter introduced and manipulated 70–80 cm away from the heart, the heart chamber beating and changing dimensions every second, and the thoracic volume changing every inspiratory excursion, it may even be surprising that we are able to create lesions at all. Several technological improvements have been developed in recent years in order to improve lesion creation. In particular, in relation to radiofrequency ablation, two of the most important developments are robotic catheter navigation and contact force measurement. Robotic navigation, either by “attracting” the tip of a catheter containing a magnetic sensor4 or by the use of a robotically controlled steerable sheath that contains and guides an otherwise regular catheter,5 has the final purpose of catheter stabilization to maintain the catheter at the same spot during the time of radiofrequency delivery. However, even if the purpose is obtained, catheter stability does not ensure by itself lesion formation. Catheter contact with the endocardium is another necessary requirement for lesion formation. It has been known for years in experimental settings that the contact force between the catheter and the heart is an important determinant of the size of the lesion that can be created in the heart wall.6, 7 In recent years, catheters have been developed that can measure, in clinical grounds, contact force between the catheter tip and the endocardium.8, 9 Initial results with the use of these catheters seem promising.10-18 Theoretically speaking, the association of the stability provided by a robotically driven catheter and the assurance of good contact force provided by catheters that measure contact force is probably the best combination to ensure the physical conditions that can produce an adequate lesion. In this context, the study by Ullah et al., in this issue of the Journal,19 could be particularly relevant. They compared four groups of 50 patients each that underwent catheter ablation of persistent AF at six hospitals from two countries. Two prospective groups, with either manual or robotically controlled steerable sheath navigation, included patients in whom the catheters used had contact force sensing technology. The two other groups were historic controls of patients with either manual or robotic (with the same system) navigation, but in whom the ablation catheter did not have contact force sensing technology. The ablation procedure included wide area circumferential ablation of the pulmonary veins with documentation of bidirectional electrical conduction block in all patients and a right atrial isthmus flutter line in the cases with common flutter documented. Other lines of block and ablation of areas with fractionated activity were left to the discretion of the operator. The main finding of the study is that with a single ablation procedure and after a 12-month follow-up period, a significantly higher proportion of patients in the robotic/contact force arm was free of AF recurrences as compared with both the manual/contact force arm and the robotic/no contact force arm. The crude numbers for the proportion of AF-free patients were 64% for the robotic/contact force arm, 36% for the manual/contact force arm, 36% for the robotic/no contact force arm, and 38% for manual/no contact force arm.19 What is the difference, then, between the study by Ullah et al.19 and all these other “negative” trials? There are three possibilities: (1) the authors have not been able to detect certain bias that make the groups not comparable; (2) the robotic system works better for the ablation of substrates other than the pulmonary vein antra, and since in the majority of the other trials most patients had paroxysmal AF and only the pulmonary veins were treated, the difference went unnoticed; and (3) the contact force sensing technology included in the catheter, in association with robotic navigation, makes the difference. At the present time, we cannot decide which of these possibilities is most likely. However, the third possibility merits special attention. The robotic system used in the study by Ullah et al.19 already incorporates contact force sensing technology that can be used with all catheters. However, this system reads the contact force from the robotic arm rather than from the catheter tip, as catheters with contact force sensing capabilities do, and it is conceivable that the latter is more precise. Could this make the difference to the point of decreasing the clinical arrhythmia recurrence rate by almost half? More studies are necessary to clarify the above issues, but certainly Ullah et al. should be congratulated for having detected a technological combination that could be clinically superior to what is at the present time the most frequently used technology for catheter ablation of AF, and also for being able to show clinical results that suggest a substantial benefit for the patients as a result of the use of this technology. I am sure that the issues presented in their manuscript will inspire important research in the coming years.