MI (Myocardial Infarction) – Top USMLE Diseases

Congestive heart failure (CHF) is a progressive syndrome characterized by the failure of the heart to maintain the metabolic demands of the body either due to systolic or diastolic dysfunction. Treatment of CHF is centered around lifestyle modifications (salt and fluid restriction, smoking cessation, and weight loss) and pharmacologic management. Acute worsening of heart failure is often secondary to other medical conditions and is managed with aggressive diuresis and interventions to support cardiac and ventilatory functions. Angina is defined as chest pain or discomfort resulting from myocardial ischemia. Therapy for angina is targeted at limiting platelet aggregation and adhesion (with antiplatelet agents), reducing O2 demand (with beta-blockers), reducing preload (with nitrates), and preventing the progression of atherosclerotic disease (using statin therapy), along with the management of comorbidities.

The heart is a 4-chambered muscular pump made primarily of cardiac muscle tissue. The heart is divided into 4 chambers: 2 upper chambers for receiving blood from the great vessels, known as the right and left atria, and 2 stronger lower chambers, known as the right and left ventricles, which pump blood throughout the body. Blood flows through the heart in 1 direction, moving from the right side of the heart, through the lungs, and then returning to the left side of the heart, where it is pumped out to the rest of the body. As blood moves through the heart, 4 important valves prevent backflow. The heart muscle itself is supplied by the coronary arteries. The heart also has its own conduction system, triggering its own rhythmic contractions.

An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Electrocardiograms are simple, inexpensive, noninvasive, and readily obtained. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. In the healthy state, an ECG records predictable, reproducible waves and complexes, which correspond to electromechanically coupled physiologic events in the heart. Under pathologic conditions, the ECG can detect arrhythmias, ischemia, inflammation, and more.

Stable and unstable angina are considered an important symptom of coronary heart disease (CHD) and present with chest pain due to transient myocardial ischemia. These disorders can be a warning sign for the risk of heart attack (MI) in the future. Clinically, stable and unstable angina are differentiated by exacerbating factors, duration of symptoms, and response to rest and medications. Diagnosis is by history and examination, ECG, stress testing with possible additional nuclear medicine imaging, echocardiography, or coronary angiography. Management with lifestyle modifications and aggressive risk factor reduction (of hypertension, diabetes, and hyperlipidemia) is indicated to prevent the risk of progression to MI and death.

MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Diagnosis is by clinical history, ECG changes, an increase in cardiac enzymes, and evidence of wall motion abnormalities on imaging. Management depends on the timing of the presentation and local resources with regard to thrombolytic therapy versus percutaneous intervention. All patients receive nitrates, pain control, aspirin, anticoagulation, and beta-blockers (unless contraindicated).

Coronary heart disease (CHD), or ischemic heart disease, describes a situation in which an inadequate supply of blood to the myocardium exists due to a stenosis of the coronary arteries, typically from atherosclerosis. The myocardium becomes ischemic when oxygen supply does not meet oxygen demand. Diagnosis is based on history and ECG findings; cardiac stress tests and catheterizations may also be needed. Treatment is primarily based on reducing the heart's oxygen demand and increasing the delivery of oxygen.