Do you know the new definition of MI?

Do you know the definition of a myocardial infarction (MI)? You may be surprised to find out what new guidelines from the Dallas-based American Heart Association have to say.1

The new definition actually describes MI as including a typical rise and gradual fall of cardiac troponin I or T, or a more rapid rise and fall of CK-MB, explains Katherine Littrell, RN, PhD, of the cardiovascular center of medical affairs for Genentech, based in South San Francisco, CA.

In addition, you also need one of the following to diagnose MI, says Littrell:

• ischemic symptoms;

• development of pathological Q-waves from the ECG;

• ECG changes indicative of ischemia;

• coronary intervention such as angioplasty.

An MI is both myocardial cell death and ischemia, says Littrell. "Before this change in definition, there was a lot of confusion about the newer cardiac marker troponin," she adds. "Troponin will elevate any time there is myocardial cell death, but it was not reaching what we called the acute MI level."

There was misunderstanding about whether these patients had an MI, she explains. "Actually, these patients did have myocardial cell death," she says. "So while they had a smaller MI, they still had an MI."

This new definition moved all patients who had elevated cardiac troponin and ischemic symptoms into the non-ST-segment elevation MI group, she explains. "Once the patient is determined to have a myocardial infarction or unstable angina, this will help guide the therapies," says Littrell.

The new definition of an MI now rules in many patients previously diagnosed with severe, stable or unstable angina, explains Julie Bracken, RN, MS, CEN, director of nursing education for the ED at Cook County Hospital in Chicago and the Des Plaines, IL-based Emergency Nurses Association representative to the National Heart Attack Alert Program. "The new diagnosis is a "small MI,’" she says.

This changes the way you’ll treat these patients, says Littrell. "Maybe this patient had a positive troponin level and also ST-segment depression," she says. "So the patient would be considered high risk."

This means many more patients should be placed on the acute MI pathway or protocol for treatment, says Bracken. "ED nurses must be prepared to initiate ordered treatment to a larger number of patients," she says.

According to Littrell, you should consider administering aspirin, heparin (either unfractionated heparin or low molecular weight heparin), a GP IIb/IIIa inhibitor, a beta-blocker, and nitroglycerin IV. "For continuing or recurrent ischemia, the patient may be considered for coronary catheterization or revascularization," she says.

Reference

1. Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2000; 102(suppl 1):I-172-175.

Sources

For more information on the new definition of myocardial infarction, contact:

Julie Bracken, RN, MS, CEN, Cook County Hospital, 1835 W. Harrison St., Chicago, IL 60612. Telephone: (312) 633-7683. Fax: (312) 633-8539. E-mail: juliebracken@msn.com.

Katherine Littrell, RN, PhD, Genentech, Cardiovascular Center of Medical Affairs, Room 24333, 1600 Grandview Blvd., South San Francisco, CA 94080. Telephone: (650) 225-8610. E-mail: littrell@gene.com.