A general framework for vibrational autoionization in polyatomic molecules with nondegenerate ion cores is presented in terms of a nondiagonal quantum defect matrix. The expressions for the vibrational autoionization rate depend on two vibrational-mode-dependent factors; (1) a vibrational "zero-point amplitude" that describes the displacement along a given normal coordinate and (2) a quantum defect derivative that describes the effect of the vibration on the electronic degrees of freedom. The latter is closely related to the dipole moment derivative and thus to the infrared intensity of that mode. This connection provides insight into the recently observed mode dependence of the vibrational autoionization rates for NO2 and other small molecules.