Aggressive new guidelines published Monday call for quick treatment of a common form of heart attack marked by chest pain and shortness of breath.

The American Heart Association and American College of Cardiology issued the joint guidelines for treating ST elevation myocardial infarction or STEMI, a severe heart attack in which an artery is completely blocked.

While heart attack patients may be unsure about their symptoms and wait to call an ambulance, every minute counts in this form of heart attack, said Dr. Elliott Antman of Harvard Medical School and Brigham and Women’s Hospital in Boston, who helped write the new guidelines.

“It is not unusual for patients to wait two hours or longer before seeking treatment, when they should get help as quickly as possible to minimize damage to their hearts,” Antman said in a statement.

The Heart Association said an estimated 500,000 Americans have a STEMI every year.

“Treating this type of heart attack requires fast action, because if blood flow is not restored to the heart within 20 minutes, permanent damage will occur,” Antman said.

“Speedy treatment not only means the difference between life and death, but also between disability and a return to an active lifestyle after a heart attack.”

Antman said earlier guidelines were not always helpful to doctors trying to make fast decisions about treatment.

One crucial decision is whether to open the blocked artery with a clot-busting drug or by using tiny flexible tubes called stents that prop open blocked arteries.

The new guidelines, published in the journal Circulation and the Journal of the American College of Cardiology, distill this decision to four issues:

# How much time has passed since the onset of symptoms?

# How great is the risk of death?

# How great is the risk of bleeding in the brain if clot-busting drugs are used?

# How long will it take to get the patient into a cardiac catheterization lab for stenting?

The guidelines, found on the Internet at http:// [url=http://www.americanheart.org]http://www.americanheart.org[/url] and http://www.acc.org/, also recommend that patients take aspirin and drugs called beta-blockers after a heart attack.

“We also strongly endorse the use of angiotensin-converting enzyme (ACE) inhibitors for all patients to improve heart function,” Antman said.

And all patients with low-density lipoprotein cholesterol or LDL of 100 or more should get cholesterol-lowering statin drugs, the guidelines say.