Extended Data Figure 7: Electromechanical dissociation and loss of contractility during very rapid (20 Hz) ventricular fibrillation in pig hearts.

a, Example traces of action potential wave activity measured on the left ventricular epicardial surface of a pig heart during ventricular fibrillation using multimodal optical mapping (voltage and contraction). Before the addition of the K_ATP channel opener cromakalim (baseline ventricular fibrillation, top), the ventricular muscle exhibits both fibrillatory electrical as well as contractile activity and associated deformations (see also Supplementary Video 12). Owing to the motion of the tissue, the optical traces are superimposed by motion artefacts, visible as modulations of the baseline of the signal. Motion stabilization and motion artefact removal retrieves the action potential wave activity (middle) with substantially reduced motion artefacts. The associated optical maps show spiral vortex wave patterns on the surface of the heart (see also Supplementary Video 12). The dominant frequency of the basal fibrillatory activity is 10.6 ± 1.5 Hz (b). After the addition of cromakalim, the dominant frequency of the electrical activity increases markedly (compared to ref. 40) to 20.5 ± 0.5 Hz, see b. At the same time, we measured that the heart does not exhibit any visible motion any longer (Supplementary Video 12). Because the contractions of the cardiac muscle vanish during very rapid ventricular fibrillation, optical maps and traces of the action potential wave activity can be retrieved without numerical motion tracking and motion stabilization (bottom). The modulations of the baseline of the signals, which can be seen during baseline ventricular fibrillation (10 Hz), do not appear at very rapid ventricular fibrillation (20 Hz), indicating that motion is not present (Supplementary Video 12). The data demonstrate a decoupling of the electromechanical wave dynamics during very rapid ventricular fibrillation induced by cromakalim. b, Loss of contractile activity during very rapid (20 Hz) ventricular fibrillation. Frequency spectra of electrical action potential wave pattern (green) and mechanical activity (red) measured during baseline ventricular fibrillation (top left, maxima at approximately 10 Hz) and very rapid ventricular fibrillation (bottom left, 20 Hz peak). The dominant frequency of the action potential wave activity approximately doubles from 10 Hz to 20 Hz after the addition of cromakalim, as previously described⁴⁰. At the same time, the contractile motion of the heart vanishes. Correspondingly, a frequency spectrum of the contractile or mechanical activity could not be computed during very rapid ventricular fibrillation. The histograms (middle) show large amplitudes of motion (1–3 pixels displacements of tissue segments within short time spans of 2–3 wave periods) during baseline ventricular fibrillation (top middle) and substantially reduced or vanishing amplitudes of motion (0–0.3 pixels displacements, Supplementary Video 12) during very rapid ventricular fibrillation (bottom middle). The amplitudes of motion were calculated from the displacement data obtained from the motion-tracking procedure. The corresponding maps (top right and bottom right) show the amplitudes of motion measured across the ventricular surface (yellow indicates 2–3 pixels displacement; blue indicates 0 pixels displacement).