When should someone stop consuming alcohol before cardiac catheterization?

Long before. Alcohol is a toxin to the heart and more than two drinks a day has been associated with arrhythmias and heavy drinking can lead to weakening of the heart. Alcohol in moderation is good for the heart up to 2 glasses of red wine daily. Since, alcohol can interact with medications, one should not consume alcohol for at least 24 hours prior to angiography. Chronic drinkers, are a risk for withdrawl.
Alcohol cardiac. Alcohol directly damages the heart muscle and its conduction system with time, besides making the blood coagulate more slowly ( or much more slowly) then normal. Card cath uses a big needle on the femoral artery which is very large and can cause bleeding that would not stop even with precautions to put powerful pressures on the artery after the cath. Your doc may not even cath you.