ST Segment Elevation Myocardial Infarction

Published on 17/05/2015 by admin

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Chapter 18

St Segment Elevation Myocardial Infarction

1. What are the electrocardiograph (ECG) criteria for the diagnosis of ST segment elevation myocardial infarction (STEMI)?

    Criteria for the diagnosis of STEMI can derive from criteria established for the administration of thrombolytic therapy, which evolved in the late 1980s and 1990s. ECG criteria for suspected coronary artery occlusion include:

image American College of Cardiology Foundation/American Heart Association (ACCF/AHA) criteria for STEMI consist of ST segment elevation greater than 0.1 mV (one small box) in at least two contiguous leads (e.g., leads III and aVF, or leads V2 and V3). The European Society of Cardiology (ESC) STEMI guidelines require 0.2 mV or greater ST elevation when analyzing leads V1 through V3 (but similarly, 0.1 mV elevation for other leads and/or territories). Figure 18.1 demonstrates the ECG finding of ST elevation in a patient with acute myocardial infarction.

image New or presumably new left bundle branch block (LBBB)

2. Is intracoronary thrombus common in STEMI?

    Yes. The majority of STEMI is due to plaque rupture, fissure, or disruption, leading to superimposed thrombus formation and vessel occlusion. Angioscopy demonstrates coronary thrombus in more than 90% of patients with STEMI (as opposed to 35% to 75% of patients with non–ST segment elevation acute coronary syndrome [NSTE-ACS] and 1% of patients with stable angina).

3. What is primary PCI?

    Primary percutaneous coronary intervention (PCI) refers to the strategy of taking a patient who presents with STEMI directly to the cardiac catheterization laboratory to undergo mechanical revascularization using balloon angioplasty, coronary stents, aspiration thrombectomy, and other measures. Patients are not treated with thrombolytic therapy in the emergency room (or ambulance) but preferentially taken directly to the cardiac catheterization laboratory for primary PCI. Studies have demonstrated that primary PCI is superior to thrombolytic therapy when it can be performed in a timely manner by a skilled interventional cardiologist with a skilled and experienced catheterization laboratory team.

4. What are considered to be contraindications to thrombolytic therapy?

    Several absolute contraindications to thrombolytic therapy and several relative contraindications (or cautions) must be considered in deciding whether to treat a patient with lytic agents. As would be expected, these are based on the risks and consequences of bleeding resulting from thrombolytic therapy. These contraindications and cautions are given in Box 18-1.

Modified from Antman EM, Anbe DT, Armstrong PW, et al: ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction. J Am Coll Cardiol 44:E1-E211, 2004, and from Van de Werf F, Ardissino D, Betriu A, et al: Management of acute myocardial infarction in patients presenting with ST-segment elevation. The Task Force on the Management of Acute Myocardial Infarction of the European Society of Cardiology. Eur Heart J 24:28-66, 2003.

5. What is door-to-balloon time?

    Door-to-balloon time is a phrase that denotes the time it takes from when a patient with STEMI sets foot in the emergency room until the time that a balloon is inflated in the occluded, culprit coronary artery. More recently, the concept of medical contact-to-balloon time has been emphasized, given that STEMI may first be diagnosed in the transporting ambulance in some cases. Because balloon angioplasty is no longer always the first intervention performed on an occluded artery, the term has further evolved to medical contact-to-device time. The generally accepted medical contact-to-device time goal is 90 minutes or less in cases in which the patient presents or is taken directly to a hospital that performs PCI. In cases in which the patient must be transferred from a hospital that does not perform PCI to a hospital that does perform PCI, the goal is a medical contact-to-device time of no more than 120 minutes.

6. What is door-to-needle time?

    Door-to-needle time is a phrase that denotes the time it takes from when a patient with STEMI sets foot in the emergency room until the beginning of thrombolytic therapy administration. The generally accepted goal for door-to-needle time is 30 minutes or less.

7. In patients treated with thrombolytic therapy, how long should antithrombin therapy be continued?

    Patients who are treated with unfractionated heparin (UFH) should be treated for 48 hours. Studies of low-molecular-weight heparins (EXTRACT, CREATE) and of direct thrombin inhibitors (OASIS-6) have suggested that patients treated with these agents should be treated throughout their hospitalizations, up to 8 days maximum. Guidelines for adjunctive antiplatelet and antithrombin therapy in patients treated with thrombolytic therapy are given in Table 18-1.

8. Which patients with STEMI should undergo cardiac catheterization?

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