Single high-intensity premature stimuli when applied to the ventricles during ventricular drive of an ectopic site, as in Winfree's "pinwheel experiment," usually induce reentry arrhythmias in the normal heart, while single low-intensity stimuli barely do. Yet ventricular arrhythmia vulnerability during normal sinus rhythm remains largely unexplored. With a view to define the role of anisotropy on ventricular vulnerability to unidirectional conduction block and reentry, we revisited the pinwheel experiment with reduced constraints in the in situ rat heart. New features included single premature stimulation during normal sinus rhythm, stimulation and unipolar potential mapping from the same high-resolution epicardial electrode array, and progressive increase in stimulation strength and prematurity from diastolic threshold until arrhythmia induction. Measurements were performed with 1-ms cathodal stimuli at multiple test sites ( = 26) in seven rats. Stimulus-induced virtual electrode polarization during sinus beat recovery phase influenced premature ventricular responses. Specifically, gradual increase in stimulus strength and prematurity progressively induced make, break, and graded-response stimulation mechanisms. Hence unidirectional conduction block occurred as follows: ) along fiber direction, on right and left ventricular free walls ( = 23), initiating figure-eight reentry ( = 17) and tachycardia ( = 12), and ) across fiber direction, on lower interventricular septum ( = 3), initiating spiral wave reentry ( = 2) and tachycardia ( = 1). Critical time window (55.1 ± 4.7 ms, 68.2 ± 6.0 ms) and stimulus strength lower limit (4.9 ± 0.6 mA) defined vulnerability to reentry. A novel finding of this study was that ventricular tachycardia evolves and is maintained by episodes of scroll-like wave and focal activation couplets. We also found that single low-intensity premature stimuli can induce repetitive ventricular response ( = 13) characterized by focal activations. We performed ventricular cathodal point stimulation during sinus rhythm by progressively increasing stimulus strength and prematurity. Virtual electrode polarization and recovery gradient progressively induced make, break, and graded-response stimulation mechanisms. Unidirectional conduction block occurred along or across fiber direction, initiating figure-eight or spiral wave reentry, respectively, and tachycardia sustained by scroll wave and focal activations.
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http://dx.doi.org/10.1152/ajpheart.00366.2016 | DOI Listing |
Indian Pacing Electrophysiol J
January 2025
Department of Cardiology, Tosei General Hospital, Seto, Aichi, Japan.
Introduction: Three-dimensional (3D) maps are useful for premature ventricular contraction (PVC) ablation. However, positional information changes compared with sinus rhythm when PVCs appear, rendering ablation difficult. We aimed to understand the spatial displacement characteristics of PVC ablation in 3D maps and the therapeutic effect after correction using the LAT-Hybrid function.
View Article and Find Full Text PDFInt J Cardiovasc Imaging
January 2025
Department of Cardiology and Nephrology, Mie University Graduate School of Medicine, 2-174, Edobashi, Tsu, Mie, 514-8507, Japan.
Myocardial extracellular volume fraction (ECV) measured via MRI serves as a quantitative indicator of myocardial fibrosis. However, accurate measurement of ECV using MRI in the presence of AF is challenging. Meanwhile, CT could be a promising alternative tool for measuring ECV regardless of sinus rhythm or AF.
View Article and Find Full Text PDFJ Clin Monit Comput
January 2025
Department of Electrical Engineering, Eindhoven University of Technology, Groene Loper 3, 5612 AZ, Eindhoven, the Netherlands.
Unobtrusive pulse rate monitoring by continuous video recording, based on remote photoplethysmography (rPPG), might enable early detection of perioperative arrhythmias in general ward patients. However, the accuracy of an rPPG-based machine learning model to monitor the pulse rate during sinus rhythm and arrhythmias is unknown. We conducted a prospective, observational diagnostic study in a cohort with a high prevalence of arrhythmias (patients undergoing elective electrical cardioversion).
View Article and Find Full Text PDFArq Bras Cardiol
January 2025
Cardiovascular Medicine Department, Faculty of Medicine, Tanta University, Tanta - Egito.
Background: There is still a significant population of patients with embolic stroke of Undetermined Source (ESUS) whose specific attributable cause of the stroke remains unknown.
Objectives: Our research aimed to assess clinical, electrocardiogram, laboratory, and echocardiographic parameters that may predict the propensity of paroxysmal atrial fibrillation (PAF).
Methods: We enrolled seventy-five ESUS patients who were in sinus rhythm at the time of stroke diagnosis to undergo in-hospital 7-day Holter monitoring, testing for Pro-BNP, and a standard echocardiographic examination.
Arrhythm Electrophysiol Rev
December 2024
Heart Rhythm Research Group, Division of Biomedical Sciences, Warwick Medical School, Clinical Sciences Research Laboratory Coventry, UK.
Functional substrate mapping has emerged as an essential tool for electrophysiologists, overcoming many limitations of conventional mapping techniques and demonstrating favourable long-term outcomes in clinical studies. However, a consensus on the definition of 'functional substrate' mapping remains elusive, hindering a structured approach to research in the field. In this review, we highlight the differences between 'functional mapping' techniques (which assess tissue response to the 'electrophysiological stress' using short coupled extrastimuli) and those highlighting regions of slow conduction during sinus rhythm.
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