Something similar to (and better than) the free PulsePoint app that allows emergency dispatch personnel to mass-communicate a cardiac arrest or medical emergency to a wide network of volunteers. 
More on Pulse Point here: URL via AP

With 5G network speeds, a similar app can not only help call/dispatch good samaritans and volunteers, the app can also load and play instructions and videos to coach the samaritan to render effective aid until trained personnel arrive. For example, when CPR is performed, the app can provide clear instructions and set a pace for the required 100 compressions per minute. Similarly, if a defibrillator is needed, not only can the app show the location of the nearest defibrillator, but it can also load video/audio step-by-step instructions for the use of the defibrillator - which ensures the safety of the patient as well as that of the samaritan(s). 

By providing clear step-by-step instructions for CPR, we have a greater likelihood that people shall render effective assistance, even if they learned CPR but have not practiced it in real life emergencies before.