Theoretical considerations for mapping activation in human cardiac fibrillation

Abstract

Defining mechanisms for cardiac fibrillation is challenging because, in contrast to other arrhythmias, fibrillation exhibits complex non-repeatability in spatiotemporal activation but paradoxically exhibits conserved spatial gradients in rate, dominant frequency, and electrical propagation. Unlike animal models, in which fibrillation can be mapped at high spatial and temporal resolution using optical dyes or arrays of contact electrodes, mapping of cardiac fibrillation in patients is constrained practically to lower resolutions or smaller fields-of-view. In many animal models, atrial fibrillation is maintained by localized electrical rotors and focal sources. However, until recently, few studies had revealed localized sources in human fibrillation, so that the impact of mapping constraints on the ability to identify rotors or focal sources in humans was not described. Here, we determine the minimum spatial and temporal resolutions theoretically required to detect rigidly rotating spiral waves and focal sources, then extend these requirements for spiral waves in computer simulations. Finally, we apply our results to clinical data acquired during human atrial fibrillation using a novel technique termed focal impulse and rotor mapping (FIRM). Our results provide theoretical justification and clinical demonstration that FIRM meets the spatio-temporal resolution requirements to reliably identify rotors and focal sources for human atrial fibrillation. Atrial fibrillation (AF) is the most common heart rhythm disorder (cardiac arrhythmia) in the United States that may cause substantial morbidity and mortality. However, the precise mechanisms causing AF are still not well understood, partly due to difficulties in reliably mapping electrical activity during the spatio-temporal variations of AF in patients. In this article, we determine the minimal spatial and temporal resolution required to accurately map in humans the electrical rotors and focal sources shown to sustain AF in various model systems. We first test these requirements in computer simulations. We then validate that a recently developed mapping technique which employs bi-atrial multielectrode contact arrays is able to capture localized rotors and focal sources for human AF.

2012 HRS/EHRA/ECAS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation: Recommendations for Patient Selection, Procedural Techniques, Patient Management and Follow-up, Definitions, Endpoints, and Research Trial Design

“…After considerable processing and interpolation, evidence was found for rotational activity in patients with paroxysmal, persistent, and long-standing persistent AF. 564 MAPs established the minimum repolarization interval and provided physiologically feasible sequential activation paths. Movies of activation patterns and isochronal maps from individual cycles showed circulating activity around a center of rotation that was identified as rotational activity.…”

“…Movies of activation patterns and isochronal maps from individual cycles showed circulating activity around a center of rotation that was identified as rotational activity. 564 Focal (centrifugal) activations were also identified. Both were considered drivers only if they sustained for ≥50 rotations or focal discharges.…”

“…Further research is clearly needed. 223,564,566,569 At the present time, several prospective, randomized clinical trials are underway to evaluate the long-term safety and efficacy of this approach.…”

Role of Rotors in the Ablative Therapy of Persistent Atrial Fibrillation

“…This is theoretically sufficient to map re-entry circuits in human atria whose minimum wavelength is ~4-5 cm. 22 Direct electrode contact baskets overcome many limitations inherent to other mapping methods, such as potentially unreliable signals in AF from the inverse solution, limited mapping areas by surgical plaques, and toxicity from voltage-sensitive dyes. Nevertheless, improved basket resolution and compliance characteristics would further enhance mapping.…”

Ablation of Atrial Fibrillation

“…There has been much debate over lines -in terms of their function, where they should be placed, and if they should be created at all. Mechanistically, lines were designed to 'constrain' wavelets in human AF, but whether this is feasible is debated 75 and it has been shown that lines may interrupt localized sources 59 . A full discussion is outside the scope of this review, but since lines may be difficult to complete and incomplete lines may cause iatrogenic atrial tachycardias 12 , there is a perceptible trend towards reduced creation of lines (particularly the mitral).…”