Determination by termination: Use of termination of atrial fibrillation to determine comparability of methods to detect focal fibrillation sources

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Validity (does a test or technique correctly measure or achieve outcomes as it purports?) and reproducibility (can the same results be replicated by repeating the test or technique, especially by other investigators?) are 2 pillars of scientific investigation. Both of these are important and should be satisfied before a new test or technique is generally accepted. Since the initial description of focal sources of atrial fibrillation (AF) in man using focal impulse and rotor modulation (FIRM)1 as well as other techniques, the validity and reproducibility of these techniques have been challenged. Opinions among some investigators are sharply divided as to the role of focal sources in AF—if they even exist.2 The techniques and mathematical formulations used to detect focal AF sources are complex and not easily accessible to most electrophysiologists (who generally prefer to understand what they are doing and know “what's under the hood”). The proprietary algorithm used in FIRM further complicates validation and reproducibility. Some users of FIRM technology have, however, provided some validation, finding that (1) persistent AF can be terminated (to sinus rhythm or an organized atrial tachycardia or flutter when ablating at sites indicated by FIRM); (2) AF inducibility is eliminated acutely, when easily induced prior to ablation at FIRM‐guided sites (since the trigger has been provided both before and after ablation, but presumably substrate has been eliminated after ablation, thus AF cannot be initiated); and, most importantly, (3) patients have improved long‐term freedom from recurrent AF.4 These would not be expected outcomes if one ablated randomly in the atrium (i.e., FIRM had no capacity to correctly designate focal sources of AF).
Termination of an arrhythmia by ablation based on intentional targeting of selection tissue is a powerful tool for validation of the targeting strategy.5 In the study by Alhusseini et al.,6 the authors used their own data from procedures in which FIRM‐guided ablation resulted in AF termination, and analyzed those recordings using a different method (that of Kuklik et al.7). With this, they found very good concordance of detection of focal AF sources (mainly rotors). Their criteria for a “match” were rather strict, and readers blinded to outcome agreed on mapped locations. Thus, termination of AF was used as a validating endpoint by which a determination could be made as to reproducibility of techniques of at least finding focal sources (albeit with a slightly different analytical algorithm).
Determining reproducibility of FIRM results will of course take more than the present study by Alhusseini and colleagues, or others using the same technology at multiple centers; necessary randomized trials are already in progress. Electrophysiology has seen new techniques to generate considerable enthusiasm based on initial reports, only to falter when others are unable to replicate the initial results. Examples include ablation of complex fractionated atrial electrograms (“CAFEs”) and ganglionated plexi. Each of these has good conceptual underpinnings as well as reasonable bodies of data supporting their clinical application. However, since many other investigators failed to replicate the initial encouraging results, these earlier techniques have been rarely used. The question always arises, however: are those who are trying to replicate the initial results really using the same techniques as the original investigators? CAFEs, and to an extent, identification of sites of ganglionated plexi and their ablation, are at least somewhat subjective and if electrophysiologists who wished to replicate initial results did not use the same techniques the original investigators did, why should the same results be expected? As a trivial example, I remember the first few cases of pulmonary vein (PV) isolation I attempted, with dismal intraprocedural results; I concluded the technique was neither valid nor reproducible.
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