Complex sentence: First, recording may be activated automatically according to heart rate ranges set on the device by the physician: if the heart rate drops below or rises above the set rates, the ILR will start to record without the patient's knowledge.
Split into simpler sentences: First, recording may be activated automatically according to heart rate ranges previously set in the device by the physician. If the heart rate drops below, or rises above, the set rates, the ILR will start to record without the patient's knowledge.