Understanding atrial arrhythmia mechanisms by mapping and ablation

strate for the arrhythmia. It is perhaps pertinent to note the limitations of the electrocardiogram diagnosis. The term ‘flutter’ is used to describe rapid atrial tachycardias (AT) with an undulating waveform without isoelectric baseline; however, this has been overlooked by many groups reporting left AT that, as in Coffey’s paper, show rather long cycle lengths, around 300 ms, and longer isoelectric baselines between P-waves. Since the term ‘flutter’ is so closely related to typical flutter, depending on the cavotricuspid isthmus, it tends to suggest a macroreentrant mechanism, and the term ‘atrial tachycardia’ would appear more appropriate, as it does not pre-judge the mechanism. 2 In fact, around one-third of the mechanisms described in this study were focal discharges. The mapping technique, leading to ablation of the critical isthmus or the focus responsible for the arrhythmia, is remarkable because it creates excellent activation maps on the virtual atrial anatomy and allows, with some limitations, better understanding of the arrhythmia mechanism. Reduction of pacing manoeuvres to the minimum necessary to confirm the role of critical areas of the circuit minimizes the chances of altering activation sequences, a significant concern in left atrial macroreentrant AT, in which complex combinations of anatomic and functional obstacles can support multiple reentrant circuits and/or focal mechanisms. The average number of AT mechanisms encountered was 1.9 per patient, and 21 patients had three or more AT mechanisms, underlining the importance of this method. Another point of interest is the extremely low voltage recorded at some of the critical isthmuses that would suggest that activation could course over thin epicardial layers of atrial myocardium over endocardial scars. The interpretation of these local electrograms would be very difficult in the absence of the full activation maps supported with critical entrainment runs to confirm participation of adjacent areas in the circuit. The complexity and low amplitude of the electrograms would make quite impossible to reliably measure local post-pacing intervals at these critical isthmuses. Atrial tachycardia mechanisms were based in both atria and one-third were called septal. Two-thirds of the AT had a macroreentrant mechanism, and about one-third were focal. It is not clear from the paper if combinations of focal and macroreentrant mechanisms were found in the same patient and if more than one AT could be localized at distant sites in the same patient, but the report does give the general impression of dealing with severely diseased (remodelled? injured?) atria. The worse performance with ‘septal’ AT raises questions about the ability to precisely locate foci or critical isthmuses in this anatomically complex area. This seems particularly relevant because fragmented electrograms are often recorded from the septal atrial walls 3 and this