indicated in patients with recurrent chest pain at rest or mild exertion or severe ischemia on stress testing.
While a timely primary PCI is favored over fibrinolysis in all STEMI patients, it is more heavily favored in the following circumstances, where the efficacy of fibrinolysis is reduced:
Cardiogenic shock or severe HF attributed to STEMI should undergo emergent PCI regardless of the delay to presentation (even if >24 hours). Fibrinolytics should not be a standalone therapy for cardiogenic shock but may be used en route to PCI in early presenters, when delays are expected.
Late presenters, 3–12 hours.
Age >75 years.
History of CABG with suspicion of SVG thrombosis. Both PCI and fibrinolytics have reduced efficacy in this high-risk subset, but PCI remains more effective than fibrinolytics. PCI re-establishes TIMI 3 flow in 50–70% of SVG MIs, vs. 25–50% with fibrinolytics.
ECG is not definite for STEMI (e.g., LBBB without ST concordance) or time of onset of symptoms is unclear (may be >12 hours).
Myocardial effect of reperfusion therapy:
In the first 2–3 hours, reperfusion prevents myocardial necrosis.
Between 3 (or 6) and 12 hours, reperfusion may not prevent further necrosis, but treats peri-infarct ischemia, prevents deleterious remodeling, improves scar turgor, and decreases mortality (absolute mortality reduction >2%).
III. ECG phases of STEMI (Figure 2.1)
Figure 2.1 Phases of STEMI.
Phase 3 does not imply that MI has already been too prolonged to benefit from PCI; some patients with phase 3 morphology have had only a brief period of ischemia.
ST elevation may persist for days, weeks, or chronically >3 weeks in patients with a dyskinetic or aneurysmal myocardium. In this case, the age of the infarct is implied clinically. Let’s take the case of a patient who had chest discomfort several days previously and currently has HF without angina; if his ECG shows Q waves and ST elevation, his STEMI is likely >24 hours old and the persistent ST elevation likely reflects dyskinesia. An echocardiogram showing a dilated LV with a truly thin wall in diastole confirms this suspicion.
The inverted T waves may persist for days, weeks, months, or even years. Patients with LV dyskinesia and persistent ST-segment elevation may have chronic T-wave inversion as well.
IV. STEMI diagnostic tips and clinical vignettes
1. A patient presents with one episode of chest pain that lasted 10 minutes. He does not have any pain currently. He reports a prior history of a large MI 2 years previously. His ECG shows 1.5 mm ST elevation in the anterior leads with Q waves and T-wave inversion. Should he undergo emergent reperfusion?
Emergent reperfusion is probably not warranted. It is important to seek old ECGs and urgently obtain an echocardiogram. In fact, ST elevation may represent an old STEMI with a chronic dyskinetic myocardium and a chronic, persistent ST elevation with Q waves; T waves may be inverted or upright, but not ample. A history of an old MI, an old ECG (if available), or a quick bedside echocardiogram may allow the diagnosis. Echocardiography shows a myocardium that is thin, not just in systole but in diastole, bright (scarred) and possibly aneurysmal in case of an old infarct, whereas in acute STEMI the myocardium is neither thin nor scarred yet. If the patient does not report a history of MI, if T wave is ample, or if he had a typical angina within the last 24 hours, ST elevation is generally considered acute STEMI.
2. A patient presents with ongoing chest pain for the last 8 hours. His ECG shows inferior ST elevation of 1 mm with deep Q waves. Should he undergo emergent reperfusion?
Q waves often develop at 1–14 hours after STEMI onset, while the ST segment is still elevated. While Q waves are associated with a more delayed presentation, larger MI, less myocardial salvage, and worse short-term prognosis, they are not synonymous with irreversible myocardial damage and do not preclude reperfusion therapy; significant myocardial salvage is achieved in the overwhelming majority of those patients (>70%).5-7 Persistent Q waves at >1 month have a stronger prognostic value than acute Q waves.
3. A patient presents with intermittent chest pain for the last 3 days. He had an episode of pain 2 hours previously but is currently free of any pain. His ECG shows anterolateral ST elevation. Should he undergo emergent reperfusion?
Some patients have episodes of unstable angina for hours or days before STEMI. Presume that the onset of STEMI is the onset of the last episode of prolonged chest pain. Thus, this patient qualifies for emergent reperfusion.
4. A patient presents with chest pain that started 4 hours previously and inferior ST elevation. His pain has just resolved with aspirin and nitroglycerin, but ST elevation is persistent. Should he undergo emergent reperfusion?
Some patients have resolution of chest pain with nitroglycerin or antithrombotic therapies but ST elevation persists. These patients should still undergo emergent reperfusion therapy, as long as they present within 24 hours of pain onset.
5. A patient presents with chest pain that started 4 hours previously and inferior ST elevation. Both his pain and ST elevation resolve after aspirin and nitroglycerin administration. Should he undergo emergent reperfusion?
Figure 2.2 The patient presents with chest discomfort that has lasted 3 hours and resolved 2 hours ago. Subtle ST elevation is seen in leads II and aVF, and in leads V5 and V6, with subtle ST depression in V1–V2. Three features suggest that this mild ST elevation is actually STEMI: (i) Q waves; (ii) ST depression in reciprocal leads (V1–V2); (iii) wide T-wave morphology and fused ST-T segments in leads I, II, V5, and V6 (arrows). This patient qualifies for emergent catheterization since his discomfort occurred in the last 24 hours. He is found to have an acutely occluded large obtuse marginal branch.
Chest pain and ST elevation may both resolve spontaneously or with the acute therapies. This often indicates spontaneous thrombolysis and occurs in ~15% of STEMIs, leading to a much lower mortality and a smaller infarct size.8,9 Occasionally, this may represent resolution
of a coronary spasm. Coronary angiography may be performed emergently, but this is not mandatory: delayed angiography (mean 23 hours) was associated with a similarly low event rate and infarct size in TRANSIENT-STEMI trial.9 Full ACS therapy and early coronary angiography, within the next day, are indicated.
6. A patient presents with chest pain that lasted 2–3 hours earlier today and has now resolved. His ECG shows subtle ST elevation (<1 mm) in leads II, aVF, V5, and V6 (Figure 2.2). Should he undergo emergent reperfusion?
Yes, he should. This patient has mild ST elevation (<1 mm) with a morphology that is, nonetheless, consistent with STEMI. Q waves are
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