Natural selection, which includes sexual selection, is the fact that some traits make it more likely for an organism to survive and reproduce. Population genetics describes natural selection by defining fitness as a propensity or probability of survival and reproduction in a particular environment. The fitness is normally given by the symbol w=1-s where s is the selection coefficient.
Atrial fibrillation with RVR (Rapid Ventricular Response) is a heart condition caused by irregular electrical activity that results in irregular contractions of the heart walls and its chambers. The heart (atrium), shakes with a rapid tremulous movement or makes fine irregular twitching movements, generally referred to as fibrillating.
Persistent Afib is a sustained pattern of atrial fibrillation that does not return to normal by itself. A person is usually said to have persistent atrial fibrillation if their heart rate does not return to normal sinus rhythm within 7 days when not treated. Persistent afib is a when the abnormal heartbeat continues until it is returned to normal by some form of treatment. In a lot of patients the Atrial Fibrillation will progress further to the point of Permanent Atrial Fibrillation. This type of afib is now mostly refereed to as Longstanding Persistent Atrial Fibrillation as most patients can now be cured by the newer anti-arrhythmic drugs, or catheter or surgical ablation.