ST-elevation myocardial infarction

Introduction

ST-elevation myocardial infarction (STEMI) is a type of myocardial infarction (heart attack) characterized by a significant elevation in the ST segment on an electrocardiogram (ECG). This condition is a medical emergency that requires immediate intervention to restore blood flow to the affected part of the heart and minimize damage to the myocardium.

Pathophysiology

STEMI occurs when there is a complete and prolonged blockage of a coronary artery, leading to ischemia and necrosis of the heart muscle. The most common cause is the rupture of an atherosclerotic plaque, which triggers the formation of a thrombus that occludes the artery. The resulting lack of oxygen and nutrients causes the affected myocardial cells to die, leading to the characteristic ST-segment elevation on the ECG.

Atherosclerosis

Atherosclerosis is the underlying condition in most cases of STEMI. It involves the buildup of fatty deposits, or plaques, within the walls of the coronary arteries. These plaques can become unstable and rupture, leading to the formation of a blood clot that can completely block the artery.

Coronary Artery Occlusion

The occlusion of a coronary artery in STEMI is typically due to a thrombus that forms at the site of a ruptured plaque. This thrombus can rapidly grow and completely obstruct the flow of blood, causing ischemia and infarction of the downstream myocardial tissue.

Clinical Presentation

Patients with STEMI typically present with sudden onset of severe chest pain, often described as a crushing or squeezing sensation. The pain may radiate to the left arm, neck, jaw, or back. Other symptoms can include shortness of breath, diaphoresis (sweating), nausea, vomiting, and lightheadedness.

Diagnostic Criteria

The diagnosis of STEMI is primarily based on the presence of characteristic changes on the ECG, including ST-segment elevation in two or more contiguous leads. Additional diagnostic tools include blood tests for cardiac biomarkers such as troponin and creatine kinase-MB (CK-MB), which indicate myocardial injury.

Management

The primary goal in the management of STEMI is to restore blood flow to the affected area of the heart as quickly as possible. This is typically achieved through reperfusion therapy, which can be accomplished via thrombolytic therapy or percutaneous coronary intervention (PCI).

Thrombolytic Therapy

Thrombolytic therapy involves the administration of drugs that dissolve the blood clot blocking the coronary artery. Commonly used thrombolytic agents include tissue plasminogen activator (tPA), streptokinase, and tenecteplase. This therapy is most effective when administered within the first few hours of symptom onset.

Percutaneous Coronary Intervention

Percutaneous coronary intervention (PCI) is a procedure in which a catheter is inserted into the blocked coronary artery and a balloon is inflated to open the artery. A stent is often placed to keep the artery open. PCI is the preferred method of reperfusion therapy when it can be performed promptly.

Complications

STEMI can lead to a number of serious complications, including heart failure, arrhythmias, cardiogenic shock, and ventricular rupture. Early and effective treatment is crucial to minimize the risk of these complications.

Heart Failure

Heart failure can occur when the damage to the myocardium impairs the heart's ability to pump blood effectively. This can lead to symptoms such as shortness of breath, fatigue, and fluid retention.

Arrhythmias

Arrhythmias, or abnormal heart rhythms, are common following STEMI. These can range from benign premature ventricular contractions to life-threatening conditions such as ventricular fibrillation and ventricular tachycardia.

Cardiogenic Shock

Cardiogenic shock is a severe condition in which the heart is unable to pump enough blood to meet the body's needs. It is characterized by low blood pressure, reduced urine output, and altered mental status. This condition requires immediate medical intervention.

Ventricular Rupture

Ventricular rupture is a rare but catastrophic complication of STEMI. It involves a tear in the wall of the heart, which can lead to rapid blood loss and cardiac tamponade. This condition is often fatal without prompt surgical intervention.

Prognosis

The prognosis for patients with STEMI depends on the extent of myocardial damage, the timeliness and effectiveness of treatment, and the presence of any complications. Early reperfusion therapy significantly improves outcomes, reducing the risk of death and long-term disability.

Prevention

Preventing STEMI involves addressing the risk factors for coronary artery disease. This includes lifestyle modifications such as smoking cessation, regular exercise, a healthy diet, and weight management. Medical management of conditions such as hypertension, diabetes, and hyperlipidemia is also important.

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