Fig. 3

Changes in systemic and cardiac variables in the time before arrhythmia onset. Changes in HR over time while dead space (DS) had been in place until arrhythmia onset are shown in (a). This was preceded immediately by a baseline (BL) measurement. HR was measured for overlapping groups of animals entering VF (red/circle), non-sinus bradycardia (blue/square), and sinus bradycardia (black/triangle). Measurements were made over normalized time, i.e., at time intervals relative to the dead space placement and arrhythmia onset (VF, sinus/non-sinus bradycardia). These were generally about 1–3 min in duration. b shows the change in BP over the same time scale, where the BP in the non-sinus bradycardia group decreases significantly compared to the other two groups (p = 0.004 at last time point). c shows oxygen saturation at this time scale, and a measurement from one animal with sinus bradycardia is shown for reference. d1–d3 show echocardiographic measurements of end systolic diameter (ESD), end diastolic diameter (EDD), and ejection fraction (EF) along the same time scale as (a–c). No appreciable differences could be seen between VF and non-sinus bradycardia, except for a shift in EF in the VF group (arrow). This was observed as a change in systolic function, as can be seen in the drastic shift in ESD (d2). While the shifts are suggestive, the data do not show statistical significance (color figure online)