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    • br Discussion The differential diagnosis

    2019-06-26


    Discussion The differential diagnosis of ATA with a constant CS activation sequence following PV isolation for AF includes (a) AF originating from a non-PV focus [1], (b) focal ATA, and (c) macro-reentrant AFL of LA or RA origin [2–4]. First, the proximal-to-distal CS activation sequence during tachycardia excluded focal ATA originating from left side of LA outside the PV, such as the ligament of Marshall or the posterior wall [1,2]. However, it did not exclude an ATA originating from a RA focus, such as the CS ostium, the interatrial septum, or the crista terminalis [1] or a focal ATA originating from right side of the LA outside the PV [2]. Although macroreentrant AFL is an unlikely mechanism for irregular tachycardia, it was not excluded [6]. Second, the electro-anatomical activation map of the LA during tachycardia showed no atrial activity preceding the proximal CS, excluding focal ATA or macroreentrant AFL originating from the LA outside the PV. Finally, to distinguish focal ATA from macroreentrant AFL originating from the RA, we performed entrainment pacing along the tricuspid annulus (TA) and electro-anatomical activation mapping of the RA, confirming the diagnosis of typical CCW AFL. Although spontaneous transition from AF to CTI-dependent typical AFL during and after LA ablation of AFL is often observed [3,4], irregular AFL is uncommon [5–7]. In this case, a fixed CS activation sequence revealed the diagnosis of AFL. Atypical flutter waves may result from abnormal LA activation [4]. Entrainment mapping at the CTI early in the procedure, even in absence of typical electrocardiographic characteristics, may prevent unnecessary LA mapping [4]. The oscillatory AFL Fmoc-Ala-OMe length is mediated by variations in conduction velocity and refractoriness among sites within the reentry circuit. It depends on the duration of the preceding diastolic interval and results in a complex oscillation of the cycle length, as demonstrated in animal models [8,9]. Albeit rare, cases of AFL exhibiting irregular atrial cycles have been described. Ibutilide increases the cycle length variability and diastolic interval of AFL perhaps by varying the beat-to-beat duration of action potential, refractoriness, and diastolic interval [5]. Alternating typical AFL and lower-loop reentry may cause cycle length oscillation [6]. The cycle-to-cycle length variability of non-isthmus-dependent AFL wavefronts may be greater than those of isthmus-dependent AFL [7]. In the present case, the variations in cycle length were possibly due to the atrial electrical and structural remodeling caused by long-standing AF, resulting in abnormally slow conduction and random functional block in the RA during ongoing typical AFL [10]. Unfortunately, we did not evaluate activation sequences along the tricuspid annulus with Halo catheter and could not determine whether the variation in cycle length depended on an oscillation in conductivity through the inferior vena cava (IVC)-TA isthmus, lateral RA, or transverse conductivity through the crista terminalis with conduction gap. Moreover, we did not evaluate the activation pattern in the RA during pacing from CS after restoring sinus rhythm.
    Conflict of interest
    Introduction Macroreentrant right AT occurs commonly after surgical correction of CHD [1–4]. The mechanism often suggested is a re-entry circuit around surgical scars and/or anatomic barriers [5]. Electroanatomical mapping with extensive reference to the spatial geometry of the mapped atrial chamber is useful in delineating the tachycardia isthmus of periatriotomy circuits [6,7]. For a patient with surgically corrected CHD, the anatomic position of the atriotomy scar as the arrhythmogenic substrate is commonly found in the free wall, and not in the septum [8]. The cause of this large area of low voltage (“atrial myopathy”) is still unclear, and is not always consistent with surgical trauma (incisions or cannulation sites) [8]. To identify the mechanism of the circuits of tachycardias, local electrograms must be carefully assessed in combination with conventional mapping techniques.