Lithium toxicity, coumadin & delirium

Can chronic prescribed use of lithium carbonate in an 85 year old elderly patient (taking for over 5 years) coupled with recent prescription of coumadin (within the past 2 months) cause lithium toxicity manifested by delirium symptoms in the elderly patient, as well as very low heart rate? Delirium in this instance manifested as inability to communicate -with patient just muttering and moaning, with quick onset during a week's time after previously being able to effectively communicate with caretakers by talking.