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.
That is why a patient with atrial fibrillation has an irregular and high pulse rate. Put simply-during atrial fibrillation the contractions of the two upper chambers of the heart are not synchronized with the contractions of the two lower chambers. Atrial fibrillation is a rapid and irregular heart rate. It frequently causes poor blood flow to the body.