Question Raised About False-positive Cardiac Cathetorization

(Ivanhoe Newswire) –Restoring blood flow (reperfusion) in heart attack victims with a blocked artery is a race against time. To get reperfusion quickly current emergency guidelines recommend that when someone is suspected of having a blocked artery heart attack (STEMI), emergency doctors immediately activate a cardiac catheterization laboratory and get the patient an angioplasty or a stent as soon as possible. The immediate activation is necessary so that laboratory personal can be in place before the doctor makes the decision about the need for a procedure rather than waiting until they see the results to call the catheterization team in.

But a new study done by David M. Larson of the Minneapolis Heart Institute Foundation at Abbott Northwestern Hospital, says that the speed of the protocol can also lead to false alarms and unnecessary procedures. The study is appearing in the Dec. 19, 2007 edition of JAMA

STEMI (segment elevation myocardial infarction) is the medical term for a heart attack caused by a prolonged period of blocked blood supply. It affects a large area of the heart and causes changes on the ECG (electro enceplogram) as well as in blood levels of key chemical markers. According to background information in the article, emergency physicians have to make a decision about reperfusion therapy within 10 to 20 minutes of seeing the ECG, many times without having a previous ECG to compare it to. The article also states that other serious condition can cause an ST (segment elevation) and in the short time doctors have to make a decision the possibility of a false alarm needs to be considered.

The study Larson and his colleagues conducted involved 1,335 patients between March 2003 and November 2006. Each of them was part of a registry from a regional system that included transfer of patients with STEMI from 30 community and rural hospitals with pre-transfer catheterization labs activated and ready to perform angioplasty or stent procedures. All of the patients had angiography. They found that 14% (187) of the patients with suspected STEMI did not have a clear culprit blocked artery that could be identified as the cause. 9.5% (127) had no significant coronary artery disease.
Of the 14% with no clear culprit artery, 4.8% (64) had positive and negative biomarkers.
They also found that out that out of entire the patient pool, cardiac biomarker results were negative in 11.2% (149) of the patients. The rate of death after 30 days was 2.7% without a culprit artery and 4.6% with one.

Concerning their findings, the authors of the study write “The issue of false-positive catheterization laboratory activation remains a significant concern because unnecessary emergency coronary angiography is not without risk to the patient and may impose a burden on limited human resources. This critical decision process must balance the risk of a false positive alarm with the consequences of delaying myocardial reperfusion.”

This article was reported by Ivanhoe.com, which offers Medical Alerts by e-mail every day of the week. To subscribe, click on: http://www.ivanhoe.com/newsalert/.

SOURCE: JAMA, Dec. 19, 2007