{'fraction_non_alphanumeric': 0.03270042194092827, 'fraction_numerical': 0.011603375527426161, 'mean_word_length': 5.083333333333333, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Careful Observation of Changes in Cycle Length in the Evaluation of Atrial Tachycardia Mechanism

A 79-year-old gentleman with known ischemic cardiomyopathy and a 6-month history of lethargy on exertion was referred for catheter ablation. His 12-lead electrocardiograph suggested an atypical atrial flutter morphology with positive flutter waves in the inferior and right precordial leads. During the procedure, informed by a distal (d) to proximal (p) coronary sinus (CS) activation pattern, a 4 mm irrigated tip ablation catheter was advanced into the left atrium. Initial activation mapping started at the antero-septal left atrium at approximately a 9 o’clock position (Fig. 1A) relative to the mitral annulus, and then moved a 10 o’clock position (Fig. 1B). Based on just these initial mapping findings, what tachycardia mechanism is ruled out? What window of interest would you set, relative to CSp, if you were to perform activation mapping?