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    • In this study the distribution of LPs was also analyzed

    2019-04-17

    In this study, the distribution of LPs was also analyzed. Similar to previously published data, there was a tendency that vLPs were more frequently observed in patients with ICM than in patients with NICM. However, the total number of those abnormal ventricular electrograms was less documented than previously published data [10]. Furthermore, the surface areas of low-voltage regions including DS and BZ, especially in patients with ICM, were also smaller than in previous data [9,10]. These discrepancies may be due to the differences in the electrophysiological substrate of the ventricular scar or to the differences in the studied populations. Precise prospective studies are required to elucidate these findings. A recent study showed that in post-myocardial infarction (MI) patients with frequent PVCs, the PVCs originated from sites with a low voltage corresponding to the infarct location in approximately 85% of patients, similar to patients with post-MI VT [14]. In this cohort, both endocardial and epicardial origins of the PVCs that matched the targeted VT morphology were successfully identified during mapping with the multipolar catheter in two patients. Furthermore, ablation of frequent PVCs rendered the targeted VT noninducible in those patients. This finding suggests that in patients with frequent PVCs and scar-related VT, those arrhythmias share an anatomically preformed reentrant circuit or at least a common exit site. Thus, mapping the PVCs with multipolar catheters can be a helpful additional technique for identifying critical areas, especially exit sites, in scar-related VT; however, a prospective study is necessary to confirm this hypothesis. The NavX system registers the electrode impedance in relation to myeloperoxidase patches that apply a low-level electrical current [15]. The nonlinearity of the LV geometry that occurs as a result of local changes in the impedance fields may also affect that error; however, the field-scaling algorithm adjusts the geometry for this adverse effect, on the basis of the measured interelectrode spacing for all locations. In this study, a distinct geometric distortion of the endocardial LV occurred in two cases (12.5%), even after using the field-scaling algorithm. One plausible explanation for this distortion was due to the inhomogeneous dispersion of the impedance field within the endocardial LV. Another possible explanation was that an unexpected retraction of the proximal electrodes of the multipolar catheter into the sheath during the mapping may have occurred, which caused a partial impedance dispersion. Fortunately, that distortion was considerably modified by dividing the LV geometry into two portions. This inventive method may minimize that adverse impact and may facilitate the accuracy of the NavX fusion technique for ventricular chambers [16]; however, further studies are warranted.
    Conclusions
    Disclosures and funding sources
    Conflict of interest
    Introduction In patients with ischemic cardiomyopathy, ventricular tachycardia (VT) predominantly arises via a reentrant mechanism involving areas of slow and anisotropic conduction. Delayed local activation can be identified by late potentials (LPs) recorded during electroanatomical mapping, and ablation strategies based on targeting LPs have been shown to be effective [1–4]. We describe a patient with ischemic cardiomyopathy in whom successful radiofrequency (RF) ablation of LPs within a scar resulted in the dissociation of the LPs.
    Case report A 72-year-old man had a history of ischemic heart disease. Seven months prior, he received an implantable cardioverter-defibrillator (ICD) because of ventricular tachycardia (VT). His echocardiogram revealed poor left ventricular function (EF=30%) with inferior-lateral and septal wall hypokinesis. On admission, he underwent radiofrequency catheter ablation for VT despite tolerating maximal dose levels of antiarrhythmic drugs. A sustained monomorphic VT with a right bundle branch block and superior axis morphology was reproducibly inducible (Fig. 1A). Because the VT was poorly tolerated hemodynamically, a substrate-based voltage map of the left ventricular endocardium during sinus rhythm was constructed under the guidance of a NavX mapping system (NavX Velocity, St. Jude Medical Inc., St. Paul, MN, USA). The map revealed the presence of a low-voltage area (defined by a voltage <1.5mV) in the inferior-lateral and septal walls of the left ventricle (LV). LV mapping using a duodecapolar catheter allowed us to delineate scar heterogeneity [5]. Late potentials (LPs) were constantly recorded during sinus rhythm using a 4-mm tip electrode ablation catheter (Safire Blu, St. Jude Medical, St. Paul, MN) adjacent to the surviving tissue islets within the scar (Fig. 1B, white circles). Pacing at that site demonstrated a 12-lead QRS morphology similar to that of the clinical VT with a long stimulus-to-QRS duration (Fig. 1A). Delivery of 4 radiofrequency (RF) lesions targeting areas exhibiting LPs and areas with pace-mapping consistent with the putative isthmus rendered the targeted VT noninducible. After RF delivery, dissociation of the LPs with an interval of 3140ms was documented during sinus rhythm (Fig. 2).