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Introduction: His bundle pacing (HBP) is the most physiological pacing. The standard technique based on fluoroscopic approach might be challenging and fluoro consuming. Targeting the His guided exclusively by the electrical signals could enable a precise lead implant, thus reducing fluoroscopy time (FT) and X‐ray dose, desirable both for patients and operators. The aim of the study is to evaluate the feasibility, efficacy, and safety both acutely and at 30 days of the electrogram (EGM)‐guided HBP with minimal or no fluoroscopy. Methods and Results: Between October and December 2018, 41 consecutive patients underwent EGM‐guided HBP. Successful HBP was obtained in 39 (95%) patients, (30 males, 78 ± 10 years). Selective HBP (S‐HBP) was achieved in 23 (59%), nonselective HBP (NS‐HBP) in 16 (41%) patients. The final HBP lead position was reached in 31 (79.4%) patients without fluoroscopy, only guided by electrical signals. In eight patients a minimal fluoroscopy (mean, 8 seconds) has been required. The sheath's cutting and the slack of the lead were routinely performed under fluoroscopy. No difference was observed in FT for HBP lead placement in S‐HBP and NS‐HBP (mean, 8.1 ± 25 vs 7.5 ± 20 seconds, P =.8; median value 0 vs 0 seconds). No differences were observed in FT for the entire procedure, total dose area product and total procedural time in S‐HBP and NS‐HBP. Lead dislodgement occurred in one (2.6%) patient 1 day after the procedure. Conclusions: HBP could be performed safely and efficiently using the EGMs, with minimal or no fluoroscopy. Fluoroscopy was required during sheath removal and atrial lead placement. [ABSTRACT FROM AUTHOR]

Orthotropic Intramural Spread of LV Electrical Potentials Introduction Extracellular potentials measured on the heart surfaces are used to infer events that originate deep within the heart wall. We have reconstructed intramural potentials in three dimensions for the first time, and compare these with epicardial and endocardial surface potentials and cardiac microstructure. Methods and Results Extracellular potentials from intramural point stimulation were measured from a high density 3-D electrode array in the in vivo pig LV. MR and extended volume imaging were used to register electrode locations and characterize fiber and laminar orientations throughout the recording volume. Measured potentials were compared with predictions of tissue-specific bidomain computer activation models. Positive potentials recorded in the LV wall preceded the depolarization wavefront as it spread in the fiber direction. Transverse to this, passive and active potentials spread preferentially in the laminar direction (anisotropy ratio ∼1.6:1). Epicardial surface potentials reflect initial intramural propagation at the stimulus location, but endocardial potentials do not, particularly adjacent to papillary muscles. Measured 3-D potentials were consistently better captured by computer models that incorporate three distinct conductivities aligned with local microstructural axes, but the preferential spread of potentials in the laminar direction was not fully predicted. Conclusions This study provides evidence for preferential transmural conduction and raises questions about the extent to which intramural electrical events can be inferred from endocardial potentials. [ABSTRACT FROM AUTHOR]

An editorial is presented on the importance of electrical mapping of ventricular tachycardia (VT) in the approaching era of clinical imaging. Topics include the approach to the VT ablation has changed significantly, the initial efforts began in the 1980s has consisted of intra‐operative, and mapping has performed during cardiac surgery with 20‐electrode arrays has placed by hand on the endo‐epicardial surface.

Introduction: Cultured neonatal rat ventricular myocytes (NRVM) reestablish gap junctions as they form synchronously and spontaneously beating monolayers, thus providing a useful model for studying activation and repolarization. Methods and Results: We used the multielectrode array data acquisition system with 60 unipolar electrodes to investigate the functional organization of cultured NRVM, by determining propagation and repolarization patterns. Activation maps were constructed from the local activation times at each electrode. During days 3 to 8 in culture, QRS amplitude and dV/dtmax increased with age. Concomitantly, with the culture maturation, QT interval (representing action potential duration) decreased, and T wave amplitude and slopes of the T wave ascending and descending limbs progressively increased. The changes in conduction velocity were different than those of the electrogram properties, slightly increasing during the first 3 to 5 days and gradually declining toward day 8 in culture. Conclusion: Establishment of uniform activation patterns in spontaneously firing or driven myocytes in monolayer cultures is accompanied by organization of activation and repolarization whose evolution appears in concert with that of a mature connexin43 staining pattern. The experimental techniques developed in this study provide useful tools to investigate the complex relations among gap junctions, conduction velocity, and propagation patterns, as well as a means to learn how gap junctional remodeling under pathophysiologic conditions predisposes the myocardium to arrhythmias. [ABSTRACT FROM AUTHOR]

Introduction: Unsuccessful defibrillation shocks may reinitiate fibrillation by causing postshock reentry. Methods and Results: To better understand why some waveforms are more efficacious for defibrillation, reentry was induced in six dogs with 1-, 2-, 4-, 8-, and 16-msec monophasic and 1/1- (both phases 1 msec) 2/2-, 4/4-, and 8/8-msec biphasic shocks. Reentry was initiated by 141 ± 15 V shocks delivered from a defibrillator with a 150-μF capacitance during the vulnerable period of paced rhythm (183 ± 12 msec after the last pacing stimulus). The shock potential gradient field was orthogonal to the dispersion of refractoriness. Activation was mapped with 121 electrodes covering 4 İ 4 cm of the right ventricular epicardium, and potential gradient and degree of recovery of excitability were estimated at the sites of reentry. Defibrillation thresholds (DFTs) were estimated by an up-down protocol for the same nine waveforms in eight dogs internally and in nine other dogs externally. DFT voltages for the different waveforms were positively correlated with the magnitude of shock potential gradient and negatively correlated with the recovery interval at the site at which reentry was induced by the waveform during paced rhythm for both internal (DFT = 1719 + 64.5∇V - 11.1RI; R² = 0.93) and external defibrillation (DFT = 3445 + 150∇V - 22RI; R² = 0.93). Conclusion: The defibrillation waveforms with the lowest DFTs were those that induced reentry at sites of low shock potential gradient, indicating efficacious stimulation of myocardium. Additionally, the site of reentry induced by waveforms with the lowest DFTs was in myocardium that was more highly recovered just before the shock, perhaps because this high degree of recovery seldom occurs during defibrillation due to the rapid activation rate during fibrillation. [ABSTRACT FROM AUTHOR]