Diagnostic Electrophysiology & Ablation
Evolution of Force Sensing Technologies Dipen Shah Division of Cardiology, Hospital Cantonal de Genève, Switzerland
Abstract In order to improve the procedural success and long-term outcomes of catheter ablation techniques for atrial fibrillation (AF), an important unfulfilled requirement is to create durable electrophysiologically complete lesions. Measurement of contact force (CF) between the catheter tip and the target tissue can guide physicians to optimise both mapping and ablation procedures. Contact force can affect lesion size and clinical outcomes following catheter ablation of AF. Force sensing technologies have matured since their advent several years ago, and now allow the direct measurement of CF between the catheter tip and the target myocardium in real time. In order to obtain complete durable lesions, catheter tip spatial stability and stable contact force are important. Suboptimal energy delivery, lesion density/ contiguity and/or excessive wall thickness of the pulmonary vein-left atrial (PV-LA) junction may result in conduction recovery at these sites. Lesion assessment tools may help predict and localise electrical weak points resulting in conduction recovery during and after ablation. There is increasing clinical evidence to show that optimal use of CF sensing during ablation can reduce acute PV re-conduction, although prospective randomised studies are desirable to confirm long-term favourable clinical outcomes. In combination with optimised lesion assessment tools, contact force sensing technology has the potential to become the standard of care for all patients undergoing AF catheter ablation.
Keywords Catheter ablation, contact force Disclosure: Professor Shah has received grant support from Biosense Webster, Boston Scientific and St Jude; advisory board and/or consultancy fees: Biosense Webster, Boston Scientific, St Jude, EP Technologies. Acknowledgement: Katrina Mountfort of Medical Media Communications (Scientific) Ltd provided medical writing and editing support to the author, funded by Biosense Webster. Received: 27 April 2017 Accepted: 2 June 2017 Citation: Arrhythmia & Electrophysiology Review 2017;6(2):75–9. DOI: 10.15420/aer.2017:8:2 Correspondence: Prof. Dipen Shah, Cardiology Division, University Hospital Geneva, Rue Gabrielle-Perret-Gentil 4, 1205 Geneva, Switzerland. E: dipen.shah@hcuge.ch
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, is associated with increased risk of stroke and heart failure and is a significant global health challenge.1 Pharmacological treatments to restore sinus rhythm in patients with AF are associated with a considerable relapse rate,2,3 whereas nonpharmacological interventions, such as catheter ablation procedures, which isolate the pulmonary veins (PV) from the left atrium and prevent AF initiation, are associated with long-term (≥3 years after ablation) success rates of up to 80 % with multiple procedures.4 Rates of ablation procedures have been steadily increasing over the last decade,5 but in order for catheter ablation to become first-line treatment for AF patients, there is a need for higher and reproducible single-procedure success rates with a substantially reduced procedure time. In order to achieve this, durable transmural and contiguous radiofrequency (RF) lesions are required in concert with standardisation of the ablation strategy. An important part of the challenge is determining whether sufficient RF energy has been delivered to the appropriate local tissue site: the most common cause of failure of catheter ablation or arrhythmia recurrence is electrical reconnection of the PVs following suboptimal energy delivery,6 while excessive energy can result in overheating, local injury, perforation, fistulae, steam pops and char.7,8 Contact force (CF) between the ablation catheter tip and the target tissue is a key determinant of the locally delivered RF energy. Although applicable to other arrhythmia substrates as well, this review will mainly consider the impact of CF on procedural success of AF ablation.
© RADCLIFFE CARDIOLOGY 2017
Effect of Contact Force on Lesion Size A number of in vitro studies have shown that CF affects lesion size in RF catheter ablation.9,10 We described the first results of in vitro ablation with an optical fibre based real-time CF sensor equipped RF irrigation catheter showing that increased CF was associated with larger and deeper lesions despite fixed RF power.11 In 2008, a thigh muscle study confirmed that the underlying mechanism was related to increased tissue heating (see Figure 1): at high CF there was an increased incidence of steam pop, and thrombus.12 A 2010 in vitro study found that integrating CF information over time (for the first 40–60 seconds) provided a direct correlation with lesion size, again in the setting of stable fixed RF powers.13
Effect of Contact Force on Clinical Outcomes Technologies are now clinically available that allow the direct measurement of CF between the catheter tip and the target myocardium in real-time, and two CF sensing catheters have received approval by the US Food and Drug Administration for use in AF ablation. The first catheter approved was the ThermoCool® SmartTouch (Biosense Webster) irrigated tip ablation catheter (February 2014) followed by the TactiCath Quartz (St. Jude Medical) CF ablation catheter (October 2014). A growing body of clinical data, both observational and larger studies, supports their use.
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