Efficacy of functional substrate mapping to identify critical isthmus of atrial tachycardia

Left atrial tachycardia (AT) is often observed in patients who have undergone atrial fibrillation (AF) ablation.1 The main mechanisms of the ATs are macroreentry, such as peri-mitral flutter and roof-dependent AT.2 The use of ultra-high-density mapping with multielectrode catheters enables to delineate the ATs rapidly and precisely.3 However, due to the scar and low-voltage area (LVA), it can often be difficult to identify the circuit of AT exactly. A 74-year-old woman with hypertrophic cardiomyopathy was referred to our institution for catheter ablation of symptomatic drug-refractory persistent AF. After a pulmonary vein isolation, high-density 3D electroanatomical mapping of the left atrium (LA) was performed using a 1-mm spacing multielectrode mapping catheter (PentaRay) and CARTO3® system. The voltage map during right atrial pacing (pacing cycle length: 600 ms) revealed an extensive LVA throughout the left atrium, especially in the septum (LVA: <0.5 mV in Figure 1(A) and LVA: <0.3 mV in Figure 1(B)). Thereafter, an AT tachycardia cycle length (TCL):246 ms was induced by right atrial burst pacing (Figure 2). The local activation time (LAT) map during the AT displayed a macroreentrant tachycardia rotating in the LA septum, but LA activation map covered <90% of the TCL (Figure 3(A), supplemental movies 1, 2). Postpacing interval (PPI) at the LA septum near mitral valve was equal to the TCL with orthodromic capture of all atrial potentials (Figure 3(B)), while PPI at the right atrium and proximal coronary sinus was greater than TCL by +266 ms and + 132 ms, respectively. Therefore, the tachycardia was diagnosed as a macroreentrant tachycardia of the LA septum. However, many local potentials of LA septum were too tiny to be annotated on the map (Figure 3(A)). Recently, Aziz Z et al.4 demonstrated that slow conduction zones displayed by functional substrate mapping during sinus rhythm correspond to the critical isthmus of ventricular tachycardias. Based on the isochronal map during atrial pacing of 600 ms (Figure 4(A)), a radiofrequency application at the isochronal crowding site on the LA septum immediately terminated the AT. Although entrainment mapping is an effective method to understand the mechanism of the target AT, it has the potential to terminate the AT. Zhang X et al reported that AT ablation with 3-D electroanatomical mapping alone has similar outcomes compared with 3-D electroanatomical mapping combined with entrainment mapping.5 If the mechanism of AT circuit is fully understood by 3D electroanatomical mapping alone, entrainment mapping, which can terminate AT, would not necessarily be necessary. In mapping ventricular tachycardia, an approach that targets the deceleration zone during sinus rhythm has been shown to be effective in predicting critical isthmus.4 Recently, a functional substrate mapping during sinus rhythm to identify the conduction slowing zone was shown to be useful to identify critical isthmus also in AT cases.6, 7 The automatic annotation of LAT using the Wavefront with CARTO3® system map often fails to accurately annotate local potentials within a broad LVA during AT. However, LAT map at pacing rate lower than heart rate during AT allows for relatively more local potentials to be annotated on the 3D map (Figure 4(B)). Therefore, in AT cases whose LAT maps are difficult to interpret, isochronal map at a pacing rate lower than the heart rate during AT may provide useful information to identify the termination site of AT. None. N/A Approval was obtained from the local ethics committee. The patient provided written informed consent. N/A Supplemental movie 1. Video illustrates the LAT map during atrial tachycardia. LAT—local activation time. Supplemental movie 2. Video illustrates the Ripple map during atrial tachycardia. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.