| Part I:Comparison of the Bipolar Voltage, Percentage of Activation Time and Conduction Velocity in Different Regions along the Mitral Annulus among Different Peri-matiral Atrial FluttersBackground:Mitral isthmus (MI) ablation is conventionally employed for peri-mitral atrial flutter (PMAFL) patients. However, the PMAFL’s proarrhythmic substrate is less known. The aim of this study was to investigate the underlying substrate promoting PMAFLs.Methods:Thirty-six consecutive PMAFL patients (mean age:63.8±11.3,23 males) underwent detailed three-dimensional electroanatomic mapping in left atrium (LA). The LA was divided into septal-anterior wall (SAW), posterior-inferior wall (PIW) and MI region, respectively. The bipolar voltage, percentage of activation time and conduction velocity (CV) in these regions were determined.Result:10 cases were classified into iatrogenic (I-PMAFL),17 spontaneous (S-PMAFL), and 9 no substrate (N-PMAFL) PMAFL group. No LVZ around the PMFAL reentrant circuit was observed in the N-PMAFL group. The distribution of LVZ was located at the regions of SAW (5/10), PIW (0/10), and MI area (9/10), respectively, in the I-PMAFL group; while 17/17,2/17 and 0/17 in the S-PMAFL group. Of note, the electrograms within or surrounding LVZ were more complex (voltage diminishing, splitting, double potentials or fractionating). The overall mean bipolar voltage of the PMAFL circuit was significantly reduced in the I-PMAFL and S-PMAFL group when compared with the N-PMAFL group (1.03 ± 0.59,0.93 ± 0.48 vs.1.61 ± 0.45 mV, P= 0.009). The average voltage in the SAW region was significantly lower in I-PMAFL and S-PMAFL patients than that in the N-PMAFL patients (1.07 ± 0.66 mV,0.65 ± 0.44 mV vs.1.60 ± 0.53 mV, P<0.001). The mean voltage of MI in I-PMAFL was more diminished than that in the S-PMAFL and N-PMAFL groups (0.51 ± 0.23 mV vs.1.55±0.78 mV,1.61±0.56 mV, P<0.001). The activation time over the SAW region took a much higher percentage of the total tachycardia cycle length in the S-PMAFL group (I-PMAFL:45.7±11.0% vs. S-PMAFL:55.3±9.1% vs. N-PMAFL:45.9±6.6%, P<0.014). Among three groups, the slowest CV of the SAW region was found in S-PMAFL (I-PMAFL:0.60 ±0.24 m/s vs. S-PMAFL:0.55±0.13 m/s vs. N-PMAFL:0.77±0.16 m/s, P< 0.015); but in I-PMAFL group in MI area (I-PMAFL:0.60±0.20 m/s vs. S-PMAFL: 0.84±0.17 m/s vs. N-PMAFL:0.75±0.16 m/s, P= 0.005).Conclusions:Left atrial anterior wall and prior linear ablation lesions were the critical electrophysiological substrates for developing PMAFL. PMAFL with relative short cycle length (<200 ms) and no eletrophysiological substrate is supposed to be electrical remodeling induced and does not need ablation.Part Ⅱ:Evaluation of the Individualized Ablation Strategy for the Treatment of Peri-mitral atrial flutterBackground:Linear mitral isthmus (MI) ablation was often implemented indiscriminately once the diagnosis of PMAFL was made, regardless of its complex milieu. In the current study, we hypothesized that ablation strategy to eliminate PMAFL should be based on the characteristics of the different arrhythmogenic substrates in the left atrium (LA). The aim of this study was to determine the individualized ablation strategy per the different substrate.Methods:Twenty-seven PMAFL patients (mean age:66.6 ± 10.5,14 males) were ablated based on different arrhythmogenic substrates. Linear lesions were then devised to traverse the LVZs and close potential channels, and extend to the conduction barriers (electrical silent zones such as dense scar or CPVI lines and/or MA). Ablation was delivered to the arrhythmogenic substrates until an absolute amplitude of electrogram<0.1 mV was achieved in order to homogenize the arrhythmogenic substrates (LVZs and/or slow conduction areas). For S-PMAFL cases, if the LVZs were located in SAW but spared the Bachmann’s bundle (BB) region, a new modified septal-anterior ablation line (MSAL) was performed by connecting the right anterior carina region to the anterior MA and traversing the LVZ to avoid injuring the BB. Considering the inter-atrial myocardial connections of the atrial septum, if the sufficient septal-anterior lesions at LA could not achieve bidirectional conduction block, adjunctive ablation would be conducted at the corresponding sites on the right atrial side, If the LVZs extended to the BB region, linear ablation was created by connecting the right superior vein roof junction or the roof line, across the LVZs, to the anterior MA. In I-PMAFL group, lesion placement was reinforced in the initial ablation areas to eliminate residual conduction across the gaps along the linear ablation line or among the defragmentation areas. Once the PMAFL was terminated by MSAL and/or anterior ablation line and bidirectional conduction block was verified, the ablation catheter or the circular mapping catheter was placed in LAA during sinus rhythm to measure the interval between the onset of P wave in lead V1 and the earliest LAA potential (P-LAA interval).Result:The MSAL was performed in 10 patients with S-PMAFL whose LVZs were not covering the BB region. Complete linear block of this line was confirmed in 9 (90%,9/10) patients and 6 of them (66.7%,6/9) were supplemented by right atrial side (superior and posterior right atrial wall corresponding to the right anterior PV carina area) ablation in order to achieve bidirectional conduction block. The P-LAA interval was 78.1±13.7 ms (58-96 ms) after creation of this linear block. The rest 7 S-PMAFL cases, with LVZs extended to the BB region, had linear ablation connecting right PV roof or the LA roof line to MA, traversing and homogenizing the LVZs with consequently longer P-LAA interval of 162.4 ± 27.8 ms (116-185 ms) in 6 successful ablation cases (vs. MSAL successful cases:P< 0.001). In the failed 2 cases, MI linear ablation was performed and achieved success via endo/epicardial ablation. In the I-PMAFL group, anterior wall or MI LVZs were reinforced to eliminate the residual "gap" conduction of the linear lesion areas. I-PMAFLs were terminated in 8 cases by the "gap" closure ablation with confirmed bidirectional conduction block. In the remaining 2 cases who were resistant to MI ablation, MSAL was supplemented and achieved success in one, and the other was finally restored to sinus rhythm by electrical conversion. No complications occurred during the procedures. After a median follow-up of 12 (7-39) months,2 S-PMAFL patients received redo procedures for recurrence due to "gap" conduction.Conclusions:Personalized arrhythmogenic substrate-guided linear ablation in PMAFL patients was effective in eliminating PMAFL. The MSAL, which connected right anterior carina to the MA and traversed the LVZs can avoid injuring the BB. This line could be intensified on the corresponding right side to achieve bidirectional conduction block. |
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