case_images: PMC5420048_01
case_images: A: Twelve-lead ECG showing constant fusion during right ventricular apex (RVA) overdrive pacing (cycle length [CL] = 360 ms) of the ventricular tachycardia (VT; CL = 370 ms). B: ECG showing progressive fusion during RVA overdrive pacing (CL = 340 ms) of the VT.
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case_images: PMC5420048_01_gr1.jpg
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case_images: This was reflected in the constant fusion beats in the electrogram (Figures 1A and 1B). The degree of constant fusion differs between Figures 1A and 1B, and the morphology of fusion was more similar to that of the RVA pacing complexes when the pacing CL was decreased from 360 to 340 ms (progressive fusion is demonstrated).
case_images: A: Intracardiac electrogram showing overdrive pacing from the LCC/RCC commissure during ventricular tachycardia (cycle length = 360 ms) at a paced cycle length of 340 ms. B: Catheter position under fluoroscopy. C: Catheter position under intracardiac ultrasonography (Soundstar, Biosense Webster, Diamond Bar, CA). The tip of the ablation catheter is positioned in the LCC/RCC commissure. ABL = ablation catheter; CS = coronary sinus; HB = His bundle; LAO = left anterior oblique; LCC = left coronary cusp; NCC = noncoronary cusp; RCC = right coronary cusp; RVOT = right ventricular outflow tract; US = ultrasonography.
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case_images: Interestingly, it was terminated by overdrive pacing and a single extrastimulus from the left coronary cusp (LCC)/right coronary cusp (RCC) commissure (Figure 2, Figure 3).
case_images: Intracardiac electrogram showing that the single extrastimulus terminated the ventricular tachycardia (VT). A potential in the mid-diastolic phase during the VT is observed that persisted even after the VT terminated. However, this mid-diastolic potential more likely is a mechanical valve artifact as a result of a tiny potential, such as the mid-diastolic potential recorded, after the last QRS complex (asterisk).
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case_images: PMC5420048_01_gr3.jpg
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case_images: Interestingly, it was terminated by overdrive pacing and a single extrastimulus from the left coronary cusp (LCC)/right coronary cusp (RCC) commissure (Figure 2, Figure 3).