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Acute Coronary Syndrome: A Concise Summary for the Non-cardiologist
By James E. McFeely, MD, Medical Director Critical Care Units, Alta Bates Summit Medical Center, Berkeley, CA, is Associate Editor for Critical Care Alert.
Patients with acute coronary syndrome present one of the most common admission diagnoses in the intensive care unit. For non-cardiology intensivists, the ever-evolving treatment algorithms present a challenging body of literature on which to remain current. Nevertheless, because of the frequent need to assist with the management of these patients, it behooves us to stay as current as possible with this literature. Fortunately, our cardiology colleagues have done an excellent job of designing large, well-controlled (and cleverly named) clinical trials that are published in readily accessible journals. In addition, they frequently update practice guidelines incorporating the most recent findings and recommendations.1,2
ST-Elevation Myocardial Infarction (STEMI)
The main goal of management of STEMI is localizing and then opening the occluded coronary artery as quickly as possible. The availability of 12-lead ECG recordings in the field has decreased the time from initial diagnosis to intervention by allowing earlier activation of the cardiac catheterization laboratory team and emergency room staff prior to patients' arrival. Any emergency management system without this capacity should be addressing this deficiency now.
Once the diagnosis of STEMI is made, percutaneous coronary intervention (PCI) remains the treatment of choice if it can be accomplished within 90 minutes (preferably significantly sooner) by a competent angiographer (level of evidence A, Class I recommendation).3 If patients present to a hospital without PCI capability and cannot be transferred to a PCI center within 90 minutes of first medical contact, they should be treated with fibrinolytic therapy within 30 minutes of hospital presentation (level of evidence B, Class I recommendation).
Other elements of acute medical management involve multidrug anticoagulant therapy, including enoxaparin or other heparin-like drug, as well as clopidogrel bisulfate (Plavix®) and potentially eptifibatide (Integrilin®) or tirofiban (Aggrastat®). All patients should receive aspirin unless there is a well-documented intolerance. The most recent guideline recommends coronary artery bypass grafting (CABG) only for patients who fail PCI or have unsuitable anatomy with ongoing pain or hemodynamic instability. Successful reperfusion is defined as at least a 50% reduction in ST- elevation in the lead initially showing the greatest elevation. The presence or absence of chest pain is unreliable for identifying failed reperfusion and should not be used as an indicator. Meta-analysis of rescue trials of PCI following failed thrombolytic therapy has shown a decrease in adverse clinical events compared with medical therapy alone.4
A strategy of planned immediate PCI following fibrinolytic therapy ("facilitated PCI") has been shown to result in worse outcomes than primary PCI alone. The mortality rate was significantly higher when there was a very short time between thrombolytic administration and PCI. This approach is now considered harmful.
The question of whether to invasively study patients who are successfully treated with fibrinolytic therapy remains in evolution. Angiography with possible revascularization is needed in the setting of symptoms of ischemia following STEMI. The question remains what to do with patients who have no ischemic symptoms. Two studies addressed this issue, randomizing patients to angiography or conservative management. A modest improvement in long-term survival was seen in patients who underwent routine angiography. Patients with an angiographically documented total occlusion of the STEMI artery should not have PCI of that lesion, as they had less favorable long-term outcomes with PCI than with treatment by medical management alone.5
Unstable Angina or Non-ST-Elevation Myocardial Infarction (UA/NSTEMI)
The first line of therapy for the other acute coronary syndrome, UA/NSTEMI, is anticoagulation.6 Without significant contraindications, all patients should be given aspirin, heparin, and potentially a glycoprotein IIb/IIIa receptor blocker, in anticipation that coronary revascularization will occur shortly thereafter. An analysis of 7 randomized trials found better long-term survival with routine early invasive strategy compared to a conservative medical approach. Currently, PCI strategies have a Class I recommendation for high-risk asymptomatic patients with a recent acute coronary syndrome and no serious comorbidities and amenable lesions. There are 11 risk factors that can identify the patient as high-risk, including abnormal troponin and/or new ST-segment depression. As these are part of the diagnosis of UA/NSTEMI, essentially all patients with this syndrome should undergo angiography. CABG is currently recommended for any left main coronary artery disease, three-vessel disease, or two-vessel disease with proximal left anterior descending (LAD) involvement. Two-vessel disease with a large area of myocardium at risk is also an indication for CABG. Over the last several years, PCI has been used with increasing frequency relative to CABG for UA/NSTEMI.
Remaining questions in the treatment of UA/NSTEMI include when to perform the angiography and how complete the revascularization should be. On the basis of 1 randomized trial, early revascularization within 6 hours would be optimal. Beyond that, outcomes show little change as the time to angiography lengthens.
In patients with UA/NSTEMI it can be difficult at angiography to identify the culprit lesion. This may result in the need to perform PCI on several lesions when there are multiple possible candidates. By contrast, in the case of STEMI it is recommended that elective PCI not be performed in a non-infarct-related artery at the time of the primary PCI.
Beyond the revascularization procedures, medical management of both groups of patients is similar. Beta blockade is strongly recommended within the first few hours (contraindications include signs of heart failure, high risk for cardiogenic shock, heart block, or active reactive airways disease). Early use of angiotensin-converting enzyme (ACE) inhibitors is recommended in patients with ejection fractions less than 40% in the absence of shock. In non-PCI patients, clopidogrel should be added to aspirin and administered for at least 1 month and preferably up to 1 year. PCI patients may need to take antiplatelet therapy much longer.
As intensivists, we frequently see bleeding complications related to antiplatelet therapy.7 With aspirin therapy there is a low but persistent and relatively constant rate of bleeding. When clopidogrel is added to aspirin, there is an increased risk of bleeding in the first 9-12 months, which then plateaus. Patients who have their clopidogrel stopped prior to 1 year, particularly patients with drug-eluting stents, are at significantly increased risk of late stent thrombosis.
In terms of general medical management, maintenance of normal potassium and magnesium levels is recommended. Maintenance of normal blood sugar may be beneficial, but hypoglycemia needs to be carefully avoided. Use of a proton pump inhibitor is recommended in hospitalized patients on dual antiplatelet therapy who are at high risk for gastrointestinal bleeding, such as those older than age 60 or with a previous history of bleeding, steroid use, or prolonged hospital or ICU stay.
The clearest trend to emerge from the literature on the management of acute coronary syndrome is improved outcomes with rapid revascularization and with prolonged use of anticoagulant and antiplatelet therapy. However, given the pace of change in treating this disorder, intensivists are well advised to review this literature annually.