A recoil coincidence technique has been applied to measure the α-decay branching ratios of nearthreshold states in 19 Ne. Populating these states using the (p, t) reaction in inverse kinematics, we detected the recoils and their decay products with 100% geometric efficiency using a magnetic spectrometer. Combining our branching ratio measurements with independent determinations of the radiative widths of these states, we calculate the astrophysical rate of 15 O(α, γ) 19 Ne. Using this reaction rate, we perform hydrodynamic calculations of nova outbursts and conclude that no significant breakout from the hot CNO cycles into the rp process occurs in novae via 15 O(α, γ) 19 Ne.