In a “normal” electrocardiogram (ECG), the transition of the QRS axis in the precordial leads occurs between leads V 3 and V 4 (i.e., there is a dominant S in V 3 and a dominant R in V 4).
Our planet may have had a recent change of heart. Earth’s inner core may have temporarily stopped rotating relative to the mantle and surface, researchers report in the January 23 Nature Geoscience.