1. A system for managing care of a person, the system comprising: an external defibrillator, configured to monitor electrocardiogram (ECG) data from a person receiving emergency cardiac assistance, the ECG data defining a vector from multiple ECG signals; and one or more processors configured to perform operations comprising: performing a vectorized mathematical transform of the ECG data that defines the vector from a time domain to a frequency domain using a window in the time domain, determining a likelihood of future defibrillation shock success using at least the mathematical transformation, and affecting control of the external defibrillator based on an identification of whether a present defibrillation shock will likely be effective.