Myocardial infarction (MI), commonly referred to as a heart attack, is a critical cardiovascular event characterized by the interruption of blood supply to a portion of the heart muscle, leading to tissue death.

This condition is among the leading causes of morbidity and mortality worldwide and represents a significant burden on healthcare systems.

Pathophysiology and Mechanisms

The pathogenesis of myocardial infarction centers on the acute occlusion of one or more coronary arteries, most frequently due to thrombus formation atop a ruptured atherosclerotic plaque. Atherosclerosis is characterized by the deposition of lipids, inflammatory cells, and fibrous tissue within the arterial wall, progressively narrowing the lumen.

When a plaque ruptures or erodes, it exposes thrombogenic material, activating platelet aggregation and the coagulation cascade, resulting in clot formation that impedes blood flow.

Ischemia ensues when myocardium is deprived of oxygen and nutrients beyond a critical threshold, typically more than 20 to 40 minutes, triggering irreversible cellular injury. Key ultrastructural changes during ischemia include disruption of the sarcolemma, mitochondrial dysfunction, and myofibril relaxation.

Risk Factors and Causes

The bulk of myocardial infarctions stem from coronary artery atherosclerosis, linked to modifiable and non-modifiable risk factors. High blood pressure, diabetes mellitus, hyperlipidemia, sedentary lifestyle, obesity, and poor diet significantly contribute to the development and progression of coronary artery disease. Rarely, coronary spasms, embolism, trauma, or anomalies in coronary anatomy precipitate an infarction.

Clinical Presentation

Myocardial infarction typically manifests as retrosternal chest pain or discomfort, described as pressure, squeezing, or heaviness, which may radiate to the left shoulder, arm, neck, jaw, or back. The pain often lasts longer than 20 minutes and may not be relieved by rest or nitroglycerin. Associated symptoms include dyspnea (shortness of breath), nausea, vomiting, diaphoresis (cold sweats), lightheadedness, and palpitations.

Atypical presentations are especially common among women, elderly patients, and individuals with diabetes, who may experience non-classical symptoms such as fatigue, neck or jaw pain, or epigastric discomfort without overt chest pain. Silent myocardial infarctions, which show minimal or absent symptoms, contribute to delayed diagnosis and increased risk of adverse outcomes.

Diagnostic Evaluation

Prompt and accurate diagnosis relies on a combination of clinical assessment, electrocardiography (ECG), and cardiac biomarkers. ECG can reveal ST-segment elevation (STEMI), ST-segment depression, or new left bundle branch block, indicating myocardial injury or ischemia. Cardiac-specific enzymes such as troponin I or T are sensitive markers of myocardial cell death, with levels rising within hours of infarction onset.

Management and Treatment

Immediate management focuses on restoring coronary blood flow and minimizing myocardial damage. Reperfusion therapy through percutaneous coronary intervention (PCI), primarily angioplasty with stenting, is the gold standard when available and performed rapidly. Fibrinolytic therapy serves as an alternative when PCI is not feasible within recommended timeframes.

Complications and Prognosis

Complications of myocardial infarction range from arrhythmias, heart failure, cardiogenic shock, ventricular aneurysm, to mechanical rupture involving the papillary muscles or the interventricular septum. The extent of myocardial damage and timely intervention determine prognosis, with significant mortality risk in the acute phase.

Long-term prognosis improves with adherence to medical therapy and risk factor control, but survivors often face an increased risk of recurrent cardiovascular events.

Dr. Valentin Fuster, MD, PhD with Dr. Eric Topol discusses the pathophysiology of myocardial infarction, "Myocardial infarction (MI) is a clinical syndrome resulting from the rupture or erosion of an atherosclerotic plaque and the subsequent formation of a thrombus that occludes a coronary artery, leading to myocardial ischemia and necrosis."

Myocardial infarction is a life-threatening condition caused by coronary artery obstruction resulting in necrosis of heart muscle tissue. It presents with characteristic chest pain but can manifest atypically, particularly in vulnerable populations. Diagnosis hinges on clinical assessment, ECG, and biomarkers, while urgent reperfusion therapy is essential to salvage myocardium.

Comprehensive care entails managing complications, secondary prevention, and lifestyle adjustments. Advances in understanding and treatment have improved survival rates, highlighting the importance of early recognition and intervention in this critical cardiovascular emergency.