Thursday, October 6, 2011

2 important points about treating ACS

I wanted to quickly review 2 issues that come up with regularity when a resident & I have a patient with ACS, either a STEMI or NSTEMI. Let me start with the conclusion first, and go from there.

1. Tachycardia is a reason not to give IV beta-blockers in the ED for NSTEMI or STEMI.
2. Heparin hasn't actually been shown to have much effect in NSTEMI.

Okay, first about the beta-blockers. There used to be a lot more enthusiasm for using IV metoprolol in the ED with a STEMI, and many clinicians still feel that they are obligated to give them. But a lot of that changed, first when the COMMIT trial came out, and then when the AHA modified their guidelines to reflect the new evidence. In that big trial, patients with a STEMI were given the IV metoprolol load in the ED, followed by PO. The kicker is that there was overall no difference in 28 day mortality, since for every person who apparently didn't have a reinfarct or fatal arrhythmia. there was an extra person who died of HF!

Make special note of the risk factors listed after the asterix, in small print, at the bottom: sinus tachycardia exceeding 110 bpm.

These considerations were extended to the NSTEMI guidelines as well, although the evidence base is not as direct or contemporary as it is for STEMI. The 2007 AHA UA/NSTEMI guidelines basically mirror those for STEMI with regard to PO beta-blockers (Class 1 in the first 24 hours) and IV beta-blockers (class 2a, with same contraindications as above).

As for heparin for NSTEMI, it is sort of absurd looking at the recommendations and the supporting evidence. The 2007 AHA UA/NSTEMI guidelines cite 2 studies in support of the use of UFH. The more recent, and larger, was  this paper , a meta-analysis of 6 studies that looked at the benefit of adding heparin to aspirin in UA/NSTEMI.
 Ok, look at the title. Seems like a pretty clear title - you know just what they found in their study, and you should expect to find at least statistical significance in the results, right?
Not really
Right there, first page - the RR for MI or death was not significantly reduced when heparin was added to aspirin. They include this helpful graph, which shows the results of 6 trials, and the summary estimate that they calculate.
In the last few sentences, the authors, note that "this meta-analysis of 6 randomized controlled trials demonstrated a strong trend toward reduction in risk of MI or death during randomized therapy in patients with unstable angina treated with aspirin plus heparin compared with those treated with aspirin alone." The phrase "strong trend" is not found in the conclusion of the abstract, but instead they highlight the "33% reduction" in outcomes. 

 Heparin probably has utility in the sicker subset of NSTEMI, the patients with positive enzymes, dynamic ECG changes, ongoing pain. But those are the kind of patients you're talking about with the cardiologist, calling CCU, and perhaps arranging same-day cath lab evaluation. But for the run o' the mill ACS patient, check out the evidence first.

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