Techniques for determining whether a patient will respond to cardiac resynchronization therapy (CRT) include identifying a plurality of consecutive cardiac beats within a cardiac electrogram of the patient and, for each of the consecutive cardiac beats, measuring a repolarization interval. The techniques also include determining a variability of the measured repolarization intervals. The variability of the measured repolarization intervals indicates whether the patient will respond to CRT. For example, a variability lower than a predetermined threshold may indicate that the patient is a CRT responder, while a variability greater than the predetermined threshold may indicate that the patient is a CRT non-responder.