Patients with two-zone devices received more shocks without any mortality benefit.

AV node reentry, catheter ablation, double response, slow pathway Case PresentationA 58-year-old man with diabetes mellitus, hypertension, and hyperlipidemia presented with a 42-year history of discrete episodes of palpitation of sudden onset and associated with dizziness. A 12-lead electrocardiogram (ECG) showed a regular tachycardia with a QRS duration of 104 ms, a right bundle branch block pattern and a frontal plane QRS axis of -60 ( Fig. 1). The tachycardia terminated spontaneously, whereafter the ECG in sinus rhythm was normal. Routine laboratory tests were unremarkable and a transthoracic echocardiogram demonstrated a structurally normal heart.At electrophysiology study, the baseline atrio-His interval was 98 ms and the His-ventricular interval was 58 ms. Steady-state pacing from the right ventricular apex at 600 ms Figure 1. Twelve-lead ECG during tachycardia at presentation. Paper speed 25 mm/s.with progressively shorter single extrastimuli demonstrated decremental ventriculo-atrial (VA) conduction, a concentric atrial activation sequence and VA jump. Anterograde conduction was decremental with no AH interval jump. Dual atrial extrastimuli, however, evoked a reproducible response of 2 ventricular complexes (Fig. 2). Following isoproterenol, dual atrial extrastimuli reproducibly induced clinical tachycardia (Fig. 3). What is the mechanism of the dual ventricular response? What is the mechanism of the tachycardia? CommentaryThe 12-lead ECG during tachycardia (Fig. 1) demonstrates a regular tachycardia at a rate of 150 bpm, with a right bundle branch block/left axis deviation morphology. P waves are visible in leads V2 and V3 with an RP interval of approximately 160 ms. In this clinical context, the differential diagnosis includes a supraventricular tachycardia with bifascicular conduction delay (or block) with preferential anterograde conduction over the left posterior fascicle, or left posterior fascicular ventricular tachycardia (VT) with retrograde VA conduction.The 2 for 1 response, observed during both sensed atrial extrastimuli and during programmed atrial stimulation was consistent and reproducible. The differential diagnosis of 2 ventricular impulses for a single atrial extrastimulus

Aims Our study analyzed cardiac electrograms (EGMs) to identify characteristics for detecting cathodal, anodal, or cathodal‐anodal (simultaneous) capture in left ventricular (LV) quadripolar pacing leads of cardiac resynchronization therapy (CRT) patients. The relationship between these EGM characteristics and the electrocardiogram (ECG) was also examined. Methods We performed a retrospective analysis of 54 bipolar pacing configurations across nine patients with implanted CRT devices and quadripolar leads who had undergone a 12 lead ECG optimization. Three pacing tests (cathode unipolar, anode unipolar, and bipolar) per bipolar pair were performed, examining ECG and EGM morphology changes accompanying each test and any transitions of morphology or amplitude during voltage stepdown. Results During the cathode and anode unipolar pacing tests, the EGM was biphasic (negative/positive) or monophasic (positive) in 52/53 (98%), and biphasic (positive/negative) or monophasic (negative) in 50/51 (98%), respectively. During bipolar LV capture threshold testing, 30 bipolar pairs displayed a sudden increase in EGM amplitude (median 9.4 mV, interquartile range [7–14 mV]) when transitioning from cathodal‐anodal capture to cathodal or anodal capture. Ninety percent of these EGM transitions had a corresponding simultaneous change in ECG, while 10% had no ECG changes. Two patients demonstrated “quad‐site” capture on their quadripolar lead with multipoint pacing enabled and cathodal‐anodal capture from each stimulus. Conclusion EGM characteristics during LV pacing tests can reliably detect cathodal, anodal, or cathodal‐anodal capture, with greater sensitivity than 12 lead ECG changes. Integration of EGM analysis into routine CRT device follow up can be performed easily and may have implications for CRT efficacy.