PMC5412606_01
Figure showing electrocardiogram in sinus rhythm (both preablation and postablation), left posterior fascicular idiopathic left ventricular tachycardia (LPF ILVT) and upper septal idiopathic left ventricular tachycardia (US ILVT). The preablation 12-lead electrocardiogram is within normal limits.
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ECGs recorded during these episodes demonstrated a wide complex tachycardia with a QRS width of 130 milliseconds and RBBB with a left-axis deviation pattern (Figure 1). The narrow complex tachycardia showed the following ECG characteristics: a right-axis deviation (>90  during tachycardia vs 60  during sinus rhythm), poor progression of R waves, lack of precordial transition, lack of R wave in lead V1 and an RS ration in lead V6 consistent with VT (Figure 1).
A: An illustration of the currently postulated mechanism of left posterior fascicular idiopathic left ventricular tachycardia. B: An illustration of the possible mechanism of transformation of the left posterior fascicular variant to the upper septal idiopathic left ventricular tachycardia variant. C: A view of the interventricular septal aspect of the left ventricle showing the ablation lesion set (blue arrow; maroon dots), the location of the atrioventricular node, the proximal left bundle, and the anterior and posterior fascicles (white arrows; green dots). The ablation line extends along the entire width of the interventricular septum and was created in the midportion to avoid the proximal left bundle and atrioventricular node.
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The location of the AV node and the course of the His bundle and the posterior and anterior fascicles of the left bundle were identified and marked on the electroanatomic map (Figure 2). Purkinje potentials in the region of the left posterior fascicle were identified on the ablation catheter (Thermocool SMARTTOUCH, Biosense Webster) and the octapolar recording catheter. Presystolic Purkinje potentials were noted 28 milliseconds ahead of the earliest surface QRS complexes in the distal third of the left posterior apical septum (Figure 2A). Radiofrequency (RF) energy (power of 30-35 W; 60-120 second duration) was applied to create a linear lesion set transecting the posterior region of the IVS at the intersection of the mid- and apical segments of the LV (Figure 2). RF ablation was continued along the previous linear ablation set to transect the entire IVS in its midsegment, so as to avoid damage to the main left bundle and AV node (Figure 2).
A: This illustration shows the transition of the left posterior fascicular variant of idiopathic left ventricular tachycardia (ILVT) to upper septal ILVT during catheter ablation. The transition point has been marked with a blue dot. B: This illustration shows the octapolar catheter recording (labeled LIVS 1-8 in pairs) during upper septal ILVT. The octapolar catheter has been positioned along the left ventricular aspect of the interventricular septum (LIVS). The distal-most electrodes (LIVS 1,2) are positioned at the apex, and the proximal-most electrodes (LIVS 7,8) are at the level of the proximal left bundle. The Purkinje potential to the earliest surface QRS interval was 21 milliseconds (compared with 42 milliseconds during sinus rhythm) Purkinje potentials are indicated by the blue arrows.
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During delivery of RF energy in the region of the LPF, the wide complex tachycardia (QRS width 135 milliseconds; CL -299 milliseconds) abruptly transitioned to a narrow complex tachycardia (QRS width 85 milliseconds; CL -281 milliseconds) (Figure 3A). The HV interval during the narrow complex tachycardia of 21 milliseconds was significantly shorter than that of the HV interval of 42 milliseconds during sinus rhythm (Figures 3A and 3B).