Going around phase defects: reliable phase mapping for realistic data

Phase mapping is a widespread method for identifying rotational electrical activity sustaining cardiac arrhythmias. However, conventional implementations assume that the cardiac phase map is continuous, leading to ill-defined phase indices in regions affected by functional conduction block, fibrosis, or anatomical boundaries. These regions of discontinuous or undefined phase, termed phase defects, lead to both false positive and false negative detections of rotational drivers. This work introduces an improved phase mapping implementation termed extended phase mapping that explicitly detects and accounts for phase defects, enabling robust calculation of the phase index around them. Extended phase mapping is applied to (1) simulated excitation patterns using the Fenton-Karma model, (2) experimental optical mapping data of rat ventricular fibrillation, and (3) a clinical CARTO activation map of atrial tachycardia. Across all datasets, the extended approach eliminates erroneous detections and resolves previously missed rotations. Our results demonstrate that proper treatment of phase defects yields a unified and physiologically consistent characterization of all rotational drivers including near-complete and anatomical reentries. Therefore, we propose replacing the classical notion of phase singularities with critical phase defects as the fundamental entities governing rotational dynamics in cardiac tissue. Author summaryDetecting rotating electrical activity in the heart is crucial for understanding and treating abnormal heart rhythms. A common method, phase mapping, assigns a timing phase to each region of the heart to identify these rotations. However, in regions affected by scars, blocked conduction, or anatomical boundaries, the phase can become undefined or discontinuous. These so-called phase defects make current methods unreliable, causing false detections or missed rotations. In this study, we introduce an extended method that explicitly identifies phase defects and calculates phase indices around them. We test this approach using computer simulations, experimental recordings from animal hearts, and clinical heart-mapping data. Across all datasets, it eliminates false detections and reveals previously overlooked rotational activity. By properly accounting for phase defects, the extended phase mapping method provides a more reliable and complete characterization of heart rhythms, offering a physiologically meaningful framework for studying electrical dynamics in cardiac tissue.