An implantable medical device includes a tachyarrhythmia detection and classification system that classifies tachyarrhythmias based on a morphological analysis of template and arrhythmic waveforms. The morphological analysis takes effect of heart rate on the morphological characteristics of the template and arrhythmic waveforms into consideration. Correlation between morphological features of the template waveform and corresponding morphological features of an arrhythmic waveform provides for the basis for classifying the tachyarrhythmia. In one embodiment, corresponding morphological features are extracted from the template and arrhythmic waveforms at locations determined by the heart rate associated with a detected arrhythmia episode. In another embodiment, weighting factors each being a function of the heart rate are applied to the template and arrhythmic morphological features before a correlation coefficient is calculated.
