  We consider the at-the-money strike derivative of implied volatility as the
maturity tends to zero. Our main results quantify the behavior of the slope for
infinite activity exponential L\'evy models including a Brownian component. As
auxiliary results, we obtain asymptotic expansions of short maturity
at-the-money digital call options, using Mellin transform asymptotics. Finally,
we discuss when the at-the-money slope is consistent with the steepness of the
smile wings, as given by Lee's moment formula.
