Sudden cardiac death due to ventricular tachycardia (VT) is a major health issue worldwide. Efforts to identify patients at risk, determine VT mechanisms, and effectively prevent and treat VT with a mechanism-based approach would benefit from continuous noninvasive imaging of the arrhythmia over the entire heart. This paper presents the first noninvasive images of human ventricular arrhythmias using electrocardiographic imaging (ECGI), highlighting the large diversity of human VT in terms of activation patterns, mechanisms, and sites of initiation. Based on comparison with catheter mapping, ECGI provided high spatial resolution; a property that overcomes a limitation of the body surface electrocardiogram, which provides only global information. The spatial resolution and ability to image the activation sequences over the entire ventricular surfaces in a single beat allowed us to make observations regarding VT initiation and continuation, and regarding relationships to ventricular substrates, including anatomical scars and abnormal electrophysiological substrate. The ability of ECGI to provide patient-specific physiologic insights, to map the VT activation sequence and to identify the location and depth of VT origin from a single beat has important clinical implications in treating patients with ventricular arrhythmias.
Aerosol-generating procedures in the office represent a major concern for health care–associated infection of patients and health care providers by SARS-CoV-2, the causative agent for coronavirus disease 2019 (COVID-19). Although the Centers for Disease Control and Prevention has not yet provided any recommendations for the use of portable air purifiers, air purifiers with high-efficiency particulate air (HEPA) filters have been discussed as an adjunctive means for decontamination of SARS-CoV-2 aerosols in health care settings. This commentary discusses HEPA filter mechanisms of action, decontamination time based on efficiency and flow rate, theoretical application to SARS-CoV-2, and limitations. HEPA filter functionality and prior guidance from the Centers for Disease Control and Prevention for SARS-CoV-1 suggest theoretical efficacy for HEPA filters to decontaminate airborne SARS-CoV-2, although direct studies for SARS-CoV-2 have not been performed. Any portable HEPA purifier utilization for SARS-CoV-2 should be considered an adjunctive infection control measure and undertaken with knowledge of HEPA filter functionality and limitations in mind.
Objectives To noninvasively image the electophysiologic substrate of human ventricles after myocardial infarction and define its characteristics. Background Ventricular infarct border zone is characterized by abnormal cellular electrophsyiology and altered structural architecture and is a key contributor to arrhythmogenesis. The ability to noninvasively image its electrical characteristics could contribute to understanding of mechanisms and to risk-stratification for ventricular arrhythmia. Methods Electrocardiographic Imaging (ECGI), a noninvasive functional electrophysiologic imaging modality, was performed during sinus rhythm in 24 subjects with infarct-related myocardial scar. The abnormal electrophysiologic substrate on the epicardial aspect of the scar was identified and its location, size, and morphology were compared to the anatomic scar imaged by other noninvasive modalities. Results ECGI constructs epicardial electrograms which have characteristics of reduced amplitude (low voltage) and fractionation. ECGI co-localizes the epicardial electrical scar to the anatomic scar with a high degree of accuracy (sensitivity 89%, specificity 85%). In nearly all subjects, sinus rhythm activation patterns were affected by the presence of myocardial scar. Late potentials could be identified and were almost always within ventricular scar. Conclusions ECGI accurately identifies areas of anatomic scar and complements standard anatomic imaging by providing scar - related electrophysiologic characteristics of low voltages, altered sinus rhythm activation, electrogram fragmentation and presence of late potentials.
Background Phase analysis of cardiac arrhythmias, particularly atrial fibrillation (AF), has gained interest due to the ability to detect organized stable drivers (rotors) and target them for therapy. However, the lack of methodology details in publications on the topic has resulted in ongoing debate over the phase mapping technique. By comparing phase maps and activation maps we examined advantages and limitations of phase mapping. Methods and Results 7 subjects were enrolled. We generated phase maps and activation maps from ECGI-reconstructed epicardial unipolar electrograms (EGMs). For ventricular signals, phase was computed with: i) pseudo-empirical mode decomposition (pEMD) detrending, and ii) a novel Moving Average (MVG) detrending approach. For AF signals, MVG was modified to incorporate cycle length (CL) changes (MVG-DCL). Phase maps were visually analyzed to study phase singularity points and rotors. Results show that phase is sensitive to CL choice, a limitation that was addressed by the MVG-DCL algorithm. MVG-DCL was optimal for AF analysis. Phase maps helped to highlight high-curvature wavefronts and rotors. However, for some activation patterns phase generated non-rotational singularity points and false rotors. Conclusions Phase mapping computes singularity points and visually highlights rotors. As such, it can help to provide a clearer picture of the spatiotemporal activation characteristics during AF. However, it is advisable to incorporate EGM characteristics and the time-domain AT sequence in the analysis, to prevent misinterpretation and false rotor detection. Therefore, for mapping complex arrhythmias, a combined time-domain activation and phase mapping with variable CL appears to be the most reliable method.
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