Techniques for preventing inadvertent detection of AT termination may involve predicting potential undersensing of atrial events, and delaying detection of AT termination when undersensing of atrial events is predicted. For example, an implantable medical device may measure ventricular-atrial (VA) intervals of a heart rhythm using tracked atrial and ventricular events. The device calculates a slope of the series of the VA intervals, and estimates a prospective VA interval using the calculated slope and the most recently measured VA interval. The device determines whether the estimated VA interval is within a threshold range. When the estimated VA interval is outside of the threshold range, the device predicts possible undersensing of atrial events and delays detection of the AT episode termination. The delay detection of AT episode termination improves the accuracy of information collected by event counters.