Non-ST-Segment Elevation Myocardial Infarction (NSTEMI)

Introduction

Non-ST-segment elevation myocardial infarction (NSTEMI) is a type of acute coronary syndrome characterized by myocardial necrosis, documented by elevated cardiac biomarkers, but without persistent ST-segment elevation on the electrocardiogram. Coronary occlusion is usually partial or transient, leading to less extensive ischemia compared to STEMI. However, NSTEMI carries a high risk of adverse events, requiring timely management.

Pathogenesis and Pathophysiology

NSTEMI is primarily caused by a partial or intermittent occlusion of a coronary artery, often due to the rupture of an atherosclerotic plaque with the formation of a non-occlusive thrombus. Unlike STEMI, where ischemia is transmural, in NSTEMI, ischemia is subendocardial and, if left untreated, can progress to a more extensive infarction.

The main pathophysiological mechanisms of NSTEMI include:

• Rupture or erosion of an atherosclerotic plaque with partial thrombus formation.
• Imbalance between myocardial oxygen demand and supply, as seen in stress-induced ischemia or severe anemia.
• Coronary vasospasm or endothelial dysfunction.

The extent of myocardial necrosis depends on the duration of ischemia and the presence of collateral coronary circulation.

Clinical Presentation

Patients with NSTEMI typically present with prolonged chest pain, similar to that seen in STEMI, but often less intense and less associated with shock symptoms. The pain may be oppressive, retrosternal, and radiating to the left arm, jaw, or back, lasting more than 20 minutes.

Other associated symptoms may include:

• Dyspnea, sweating, and pallor.
• Nausea and vomiting, more common in elderly and diabetic patients.
• Dizziness and hypotension in patients with left ventricular dysfunction.

Diagnosis

The diagnosis of NSTEMI is based on three main elements:

1. Electrocardiogram (ECG)

   In NSTEMI, ECG may show changes such as ST-segment depression, T-wave inversion, or nonspecific abnormalities. However, a normal ECG does not rule out NSTEMI, making cardiac biomarker assessment essential.

2. Cardiac Biomarkers

   High-sensitivity troponins are crucial for confirming myocardial necrosis. A progressive increase in troponins differentiates NSTEMI from unstable angina, in which biomarkers remain normal.

3. Cardiac Imaging

   Echocardiography helps identify wall motion abnormalities indicative of ischemia and excludes other causes of chest pain, such as aortic dissection.

Risk Stratification

Risk assessment in NSTEMI patients is crucial for determining the therapeutic approach. Scores such as the GRACE score help identify high-risk patients who require early invasive management.

Treatment

The treatment of NSTEMI aims to reduce ischemic burden, prevent further coronary occlusion, and improve long-term prognosis.

1. Anti-Ischemic Therapy

Patients with NSTEMI should receive beta-blockers to reduce myocardial oxygen demand and nitrates to relieve chest pain.

2. Antithrombotic Therapy

Antithrombotic therapy includes:

• Antiplatelet agents: aspirin combined with a P2Y12 inhibitor.
• Anticoagulants: unfractionated heparin, enoxaparin, or fondaparinux.

3. Revascularization Strategies

Coronary angiography is performed early in high-risk patients to evaluate the need for percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG).

Complications

Complications of NSTEMI may include:

• Progression to STEMI.
• Acute heart failure.
• Ventricular arrhythmias.
• Myocardial rupture or ventricular thrombosis.

Prognosis

The prognosis of NSTEMI depends on the timeliness of treatment and the severity of underlying coronary artery disease. In-hospital mortality is lower than in STEMI but remains significant, especially in patients with comorbidities or delayed diagnosis. Secondary prevention, focusing on cardiovascular risk factor control and adherence to medical therapy, is essential to reduce recurrence risk.

Bibliografia
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