A medical system comprising: a plurality of electrodes configured to sense a cardiac electrogram of a patient; and processing circuitry (50, 80, 98) configured to: identify a plurality of ventricular depolarizations within the cardiac electrogram; for each of the plurality of ventricular depolarizations, identify a maximum slope point, a minimum slope point, and an interval from the maximum slope point to the minimum slope point; and for each of the plurality ventricular depolarizations as a current ventricular depolarization: determine that the intervals from the maximum slope point to the minimum slope point for the current ventricular depolarization, a preceding adjacent ventricular depolarization of the plurality of ventricular depolarizations, and a subsequent adjacent ventricular depolarization of the plurality of ventricular depolarizations satisfy one or more slope criteria; and determine that the current ventricular depolarization is a premature ventricular contraction depolarization based on the intervals from the maximum slope point to the minimum slope point satisfying the one or more slope criteria. a plurality of electrodes configured to sense a cardiac electrogram of a patient; and processing circuitry (50, 80, 98) configured to: identify a plurality of ventricular depolarizations within the cardiac electrogram; for each of the plurality of ventricular depolarizations, identify a maximum slope point, a minimum slope point, and an interval from the maximum slope point to the minimum slope point; and for each of the plurality ventricular depolarizations as a current ventricular depolarization: determine that the intervals from the maximum slope point to the minimum slope point for the current ventricular depolarization, a preceding adjacent ventricular depolarization of the plurality of ventricular depolarizations, and a subsequent adjacent ventricular depolarization of the plurality of ventricular depolarizations satisfy one or more slope criteria; and determine that the current ventricular depolarization is a premature ventricular contraction depolarization based on the intervals from the maximum slope point to the minimum slope point satisfying the one or more slope criteria. identify a plurality of ventricular depolarizations within the cardiac electrogram; for each of the plurality of ventricular depolarizations, identify a maximum slope point, a minimum slope point, and an interval from the maximum slope point to the minimum slope point; and for each of the plurality ventricular depolarizations as a current ventricular depolarization: determine that the intervals from the maximum slope point to the minimum slope point for the current ventricular depolarization, a preceding adjacent ventricular depolarization of the plurality of ventricular depolarizations, and a subsequent adjacent ventricular depolarization of the plurality of ventricular depolarizations satisfy one or more slope criteria; and determine that the current ventricular depolarization is a premature ventricular contraction depolarization based on the intervals from the maximum slope point to the minimum slope point satisfying the one or more slope criteria. determine that the intervals from the maximum slope point to the minimum slope point for the current ventricular depolarization, a preceding adjacent ventricular depolarization of the plurality of ventricular depolarizations, and a subsequent adjacent ventricular depolarization of the plurality of ventricular depolarizations satisfy one or more slope criteria; and determine that the current ventricular depolarization is a premature ventricular contraction depolarization based on the intervals from the maximum slope point to the minimum slope point satisfying the one or more slope criteria.