Having 8.8 level of Coumadin (warfarin) in the system could cause internal bleeding and cardiac arrest?

Supratherapeutic INR. When you are on coumadin, (warfarin) in general your goal for the inr will be between 2-3. The higher the number the higher your risk for bleeding. Bleeding can occur anywhere in the body- including intraabdominal bleeding, bleed in the brain etc. So, you need to make sure you follow up with your doctor regularly , make sure you be careful with your diet and other medication.
Yes. Inr therapeutic for dvt, mechanical valves etc is 2.5 -3.5 higher inr may be associated sometimes with spontaneous, or post traumatic bleeding. Enough bleeding can cause shock and even cardiac arrest on occasion. Needs treatment to get to correct range. Carefully, to avoid precipitating clotting.