On the surface ECG, RMVT from the ASC has a QRS morphology similar to that of RVOT arrhythmias. The indexes of R-wave duration and R/S-wave amplitude can be used to differentiate between the two origins. Radiofrequency ablation can be safely performed within the left ASC with a catheter cannulating the LMCA.

(1) Defibrillation outcome cannot be determined during the first postshock cycle. (2) At least three rapid successive cycles with overlap of cycles 2 and 3 are present in all failed and in no successful episodes. (3) The overlapping index is a marker to predict defibrillation outcome.

Background-An abnormal potential (retroPP) from the left posterior Purkinje network has been demonstrated during sinus rhythm (SR) in some patients with idiopathic left ventricular tachycardia (ILVT). We hypothesized that this potential can specifically be identified and be a critical substrate for ILVT. Methods and Results-In 9 patients with ILVT and 6 control patients who underwent mapping of the left ventricle during SR using 3-dimensional electroanatomic mapping, an area with retroPP was found within the posterior Purkinje fiber network only in patients with ILVT. The earliest and latest retroPP was 185.4Ϯ57.4 and 465.2Ϯ37.3 ms after Purkinje potential; in the other patient with ILVT, an entire left ventricle mapping demonstrated a slow conduction area and passive retrograde activation along the posterior fascicle during ILVT. ILVT was noninducible in 3 patients after SR mapping. Diastolic potentials critical for ILVT during ILVT coincided with the earliest retroPP during SR in 7 patients. Mechanical termination of ILVT occurred in 5 patients. A single radiofrequency pulse was applied at the site with mechanical translation in 5 patients and the site with diastolic potential in 2 patients, and 3 radiofrequency pulses were delivered to the site with the earliest retroPP in the other 3 patients without inducible ILVT after SR mapping. No ILVT was inducible during control stimulation, and none recurred during follow-up of 9.1Ϯ5.1 months. Conclusion-In patients with ILVT, abnormal retroPP within the posterior Purkinje fiber network is a common finding.The earliest retroPP critical for ILVT substrate can be used for guiding successful ablation.

Following near-DFT50 shocks, the first postshock cycles did not arise by macroreentry. Instead, they originated from a true focus or microreentry, most commonly near the epicardium.

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