Unstable Angina

Introduction

Unstable angina is an acute coronary syndrome characterized by myocardial ischemia without necrosis. Unlike myocardial infarction (STEMI and NSTEMI), unstable angina does not present an increase in cardiac biomarkers but is distinguished by worsening symptoms compared to stable angina.

This condition is considered an intermediate stage between stable angina and acute myocardial infarction. It is a medical emergency due to the high risk of progressing to a full-blown infarction.

Pathogenesis and Pathophysiology

The pathogenesis of unstable angina is related to a critical reduction in coronary blood flow, mainly caused by:

• Partial rupture or erosion of an atherosclerotic plaque, leading to the formation of a non-occlusive thrombus.
• Coronary vasospasm, transiently reducing blood flow.
• Coronary microembolization, due to dislodged thrombotic material.
• Imbalance between oxygen demand and supply, typical in patients with tachycardia, hypertension, or severe anemia.

The result is acute myocardial ischemia, which may remain transient or progress to necrosis.

Clinical Presentation

Patients with unstable angina report episodes of worsening chest pain, with characteristics that differentiate it from stable angina:

• Pain at rest, without the need for physical exertion.
• Increased frequency and duration of episodes, with more intense and prolonged symptoms than before.
• Resistance to nitrate therapy, with a poor response to sublingual nitroglycerin.
• Typical radiation to the left arm, jaw, and back.

In elderly and diabetic patients, symptoms may be atypical, with predominant dyspnea, nausea, and profuse sweating.

Diagnosis

The diagnosis of unstable angina is based on:

1. Electrocardiogram (ECG)

   May show ST-segment depression or T-wave inversion, although it may also be normal in many cases.

2. Cardiac Biomarkers

   High-sensitivity troponins are not elevated, helping to distinguish unstable angina from NSTEMI.

3. Functional Tests and Imaging

   To assess residual ischemia, the following tests may be performed:

   • Stress echocardiography: useful for detecting myocardial contractility abnormalities.
   • Myocardial scintigraphy: identifies silent ischemia.
   • Coronary angiography: indicated in high-risk patients to assess the need for revascularization.

Risk Stratification

Risk stratification tools such as the GRACE score are used to guide treatment strategies and identify patients at higher risk of progressing to myocardial infarction.

The GRACE score (Global Registry of Acute Coronary Events) is a prognostic tool used to assess the risk of adverse events in patients with unstable angina and NSTEMI. It considers various clinical and laboratory parameters and categorizes patients into three risk levels:

• Low risk: mortality below 3% at six months.
• Intermediate risk: mortality between 3% and 8% at six months.
• High risk: mortality above 8% at six months.

The parameters included in the GRACE score calculation are:

• Patient's age.
• Systolic blood pressure.
• Heart rate.
• Serum creatinine levels.
• Killip classification for heart failure.
• ECG changes (ST-segment depression or bundle branch block).
• Elevation of cardiac biomarkers.
• Cardiac arrest at admission.

The final score helps guide therapeutic decisions, identifying patients who may benefit from an early invasive approach with coronary angiography and potential revascularization.

Treatment

The goal of treatment is to reduce ischemia and prevent progression to myocardial infarction.

1. Pharmacological Therapy

Includes:

• Antiplatelet agents: aspirin and P2Y12 inhibitors to reduce thrombotic risk.
• Anticoagulants: low-molecular-weight heparin or fondaparinux.
• Beta-blockers: reduce heart rate and oxygen consumption.
• Nitrates: alleviate symptoms by decreasing cardiac workload.

2. Invasive Strategy

In high-risk patients, an early coronary angiography is indicated, followed by angioplasty with stent placement or coronary artery bypass grafting if necessary.

Complications

If left untreated, unstable angina may progress to:

• Acute myocardial infarction, with documented myocardial necrosis.
• Acute heart failure, in patients with prolonged ischemia.
• Ventricular arrhythmias, due to the electrical instability of ischemic myocardium.

Prognosis

Prognosis depends on the timeliness of intervention and the extent of underlying coronary artery disease. Patients treated early with medical therapy and/or revascularization have a lower risk of progressing to myocardial infarction. Secondary prevention, through cardiovascular risk factor management, is essential to reduce recurrence.

Bibliografia
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