1 AFib reduces the ability of the atria to pump blood into the ventricles, and usually causes the heart to beat too rapidly. 2  One-half million new cases of atrial fibrillation are diagnosed every year in the U.S., and billions of dollars are spent annually on its diagnosis and treatment.
noun, (used with a singular verb) 1. the branch of mechanics that deals with the motion of air and other gases and with the effects of such motion on bodies in the medium. Compare aerostatics (def 1). Origin of aerodynamics.
envelope - a curve that is tangent to each of a family of curves. curve, curved shape - the trace of a point whose direction of motion changes. 4. envelope - a natural covering (as by a fluid); the spacecraft detected an envelope of gas around the comet covering, natural covering, cover - a natural object that covers or envelops; under a covering of dust; the fox was flushed from its cover