ECK shows ischemia and palpitations....how reliable is ECG in detecting ischemia

My husband (49 years old) was told by our family doc that his baseline ECG showed ischemia and palpitations.  We are scheduled for a Stress test later this week. My question is...how sure can we be there is a problem from the ECG?  My husband is also a lifelong functional alcoholic (10/12 beers daily, all after work)  For the last several months he has cut down to 4-5 per day during the week, resuming his bad (worse?) habits during the weekend.   He has been completely alcohol free for the last 6 days.  How will that affect Ischemic Cardiomyopathy, if that is in fact what we're facing?   P. S. He'snot overwiegt (6'7" 230lbs) and no family history of heart disease.