WASHINGTON – Don't exclude a diagnosis of myocardial infarction unless you have done objective testing first, Dr. Corey M. Slovis said at the annual meeting of the American College of Emergency Physicians.
A missed diagnosis of myocardial infarction (MI) is a leading cause of emergency department malpractice awards in the United States, noted Dr. Slovis, chairman of the emergency medicine department at Vanderbilt University, Nashville, Tenn. Even though chest pain is a hallmark of acute MI, this pain may be absent or fleeting, and it may not be substernal. In fact, chest pain may be stabbing, pleuritic, or palpable.
“My goal is for you to accept that in some cases, testing is better than clinical judgment,” Dr. Slovis said. “There are times when an objective test is better than no test.”
Enzymes can be helpful tools in diagnosing acute myocardial infarction, but they should not be used in isolation. “One set of negative enzymes does not mean the absence of acute coronary syndrome,” Dr. Slovis said. He cited a 2001 metaanalysis of 22 years' worth of studies, which showed that a single set of enzymes missed 51%-63% of all acute MIs.
Myoglobin, creatine kinase, and troponin can serve as markers of acute coronary syndrome, but troponin is usually the most sensitive. Even so, troponin is not 100% sensitive, nor does it reliably pick up unstable angina, Dr. Slovis said.
He emphasized several enzyme caveats:
▸ Enzymes are rarely positive early in an acute myocardial infarction.
▸ Enzymes are almost never initially positive in patients with nondiagnostic ECGs.
▸ Delta values are more accurate than single values.
▸ Enzymes are not reliable for ruling out unstable angina.
In the area of ECGs, Dr. Slovis explained how to avoid mistakes. (See box.) “Remember that one ECG begets another,” he said. He cited data from several studies between 1977 and 2001 in which an average of 4%-5% of patients with documented MIs presented with normal ECGs.
Objective tests that can help diagnose ischemia are exercise tolerance tests, nuclear studies, stress echoes, or perhaps even CT coronary angiograms.
If you can't get an objective test on very low-risk patients–specifically young, healthy people you are ready to send home after you have decided there is “no chance” that it is a heart problem–have them run in place at the bedside. Calculate the patient's maximum heart rate (220 minus their age), then get their heart rate up to about 75% of maximum, and if they have chest pain or ST-segment changes, admit them. “It's not as good as a really expensive treadmill, but it is so much better than nothing,” Dr. Slovis said.
In addition to ischemia, doctors need to be on the lookout for aortic dissection, he said. They are required to ask three questions of patients with chest pain to be sure they don't miss that condition; unfortunately, many physicians ask only one or none of them:
▸ Did the pain start as a tearing or ripping sensation?
▸ Did the pain start at maximum intensity rather than building in intensity?
▸ Did the pain radiate to the back, abdomen, or legs?
Document as many variables as possible for two reasons: You are less likely to miss things, and you can code the patient's visit at a more appropriate higher level.
If you determine that a patient needs a cardiologist, call one. Document the exact time that you turned the patient over to a cardiologist–it can come back to haunt you in a lawsuit.
Atypical is typical, Dr. Slovis emphasized. Doctors are much more likely to miss acute MI in patients who present with a lack of typical symptoms. A diagnosis of acute myocardial ischemia is too important ever to miss, yet mistakes in MI diagnosis are made all the time.
“One missed MI can change your life, and that of your family and patients, forever,” he said. “When you miss an MI and get sued, you aren't notified on Monday and settle by Friday; it is 2-4 years of depositions, fact-finding, and interrogatories.”
Five Simple Rules for Catching MIs
Atypical is typical. No one is absolutely typical. Don't waste time trying to find that one thing that will let you avoid doing a full work-up.
Older patients are different. The elderly present with different symptoms than younger patients. The only symptoms an older patient may have are shortness of breath, weakness, syncope or near-syncope, diaphoresis, and nausea or vomiting. Older patients are often misdiagnosed because they don't present with “classic” MI symptoms.