Extended Data Figure 6 : Characteristics of epicardial electrical and mechanical phase singularities during ventricular fibrillation in pig and rabbit hearts.

From: Electromechanical vortex filaments during cardiac fibrillation

Extended Data Figure 6

a, b, Mean number of electrical (green) and mechanical (red) phase singularities (PS) during ventricular fibrillation imaged on the epicardial ventricular surface of isolated Langendorff-perfused pig hearts (a; four measurements from n = 3 hearts) and rabbit hearts (b; three measurements from n = 3 hearts). The number of phase singularities fluctuates strongly over time (error bars indicate the standard deviation; see also Fig. 4g). Both the electrical and mechanical average numbers of phase singularities similarly reflect different regimes of ventricular fibrillation (b). We consistently observed a slightly larger number of mechanical phase singularities (factor 1.2 ± 0.1). The average numbers of phase singularities were computed from 10-s long (500 frames per second) or 20-s long (250 frames per second) recordings with 5,000 video images, including >10,000 measurements of phase singularities, the recordings were more than 100 times longer than the average period or lifetime of a rotor. c, Ratio of the mean number of electrical and mechanical phase singularities (ratio = number mechanical PS/number electrical PS) during ventricular fibrillation on epicardial ventricular surface of isolated Langendorff-perfused pig hearts (four measurements from n = 3 hearts) and rabbit hearts (three measurements from n = 3 hearts). The ratio is close to 1 (1.2 ± 0.1) and consistently larger than 1, indicating that more mechanical than electrical phase singularities appear on the surface during ventricular fibrillation. Error bars are large as the number of phase singularities fluctuates strongly (from 0 to approximately 10) over long times (Fig. 4g). Error bars were computed as the standard deviation of the fluctuations of number of phase singularities over time (>1,000 samples or time-steps). The ratio (or centre of the plot) was computed from the simple average of the number of phase singularities (>1,000 samples or time-steps). d, Co-localization factor sigma indicating the precision, with which a mechanical phase singularity describes on average the position of a nearby electrical phase singularity. For large phase singularity numbers (nPS = 6–10; right) the precision is about 0.2 or 1/5 of the average rotor distance (of 1). In this regime, two phase singularities can clearly be separated from each other (Fig. 4a). For the computation of sigma, the average rotor distances and co-localization distances from the distributions as shown in Fig. 3g and Fig. 4awere used. For smaller phase singularity numbers (nPS = 1–3; left) sigma increases, indicating that the precision with which a mechanical phase singularity predicts the location of an electrical phase singularity decreases. The two data points (on the left) describe dynamical regimes with few strongly meandering rotors with linear cores and larger overall deformations of the cardiac muscle (also data point 5 in c) during ventricular fibrillation in rabbit hearts (Fig. 3). However, lower sigmas were observed in both pig and rabbit hearts. Lower sigmas or a higher precision is obtained during ventricular fibrillation with a larger number of smaller rotors and a weaker overall deformation of the cardiac muscle. e, Trajectories of mechanical phase singularities during ventricular fibrillation on the surface of the rabbit heart. Mechanical phase singularities (red dots) computed individually from voltage-sensitive (top) and calcium-sensitive (bottom) imaging data during multimodal fluorescence imaging (voltage, calcium and strain) with interleaved acquisition of the two channels (250 frames per second per channel = 500 frames per second). The plots show the accumulated mechanical phase singularities during a 400-ms long time interval at 2 s (left), 4 s (centre) and 8 s (right) of a 20-s long recording. The positions and trajectories of the mechanical phase singularities computed from the voltage or the calcium data are identical or at least almost identical throughout time. The corresponding strain rate patterns, from which the phase singularities were computed, are also almost identical or highly similar in each frame over time. The positions and trajectories of the mechanical phase singularities and strain rate patterns are also identical or at least almost identical when only one dye is used and one of the channels does not contain a fluorescent signal. The data demonstrate that the optically derived strain rate patterns are robust, that is, independent of fluorescence-induced image intensity fluctuations.