Single-shot time-resolved resistance measurements have been used to determine the magnetization reversal mechanisms of orthogonal spin transfer magnetic random access memory (OST-MRAM) devices at nanosecond time scales. There is a strong asymmetry between antiparallel (AP) to parallel (P) and P to AP transitions under the same pulse conditions. P to AP transitions are shown to occur by precession of the free layer magnetization, while the AP to P transition is typically direct, occurring in less than 200 ps. We associate the asymmetry with spin torques perpendicular to the plane of the free layer, an important characteristic of OST-MRAM bit cells that can be used to optimize device performance.