Body Systems and Disease
Richard Barber
Myocardial Infarction Myocardial infarction or acute myocardial infarction, commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing cells to die. This is most commonly due to occlusion of a coronary artery following the rupture of a vulnerable atherosclerotic plaque, which is an unstable collection of lipids and white blood cells in the wall of the artery. The resulting ischemia (restriction in blood supply) and ensuing oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death (infarction) of heart muscle tissue. Typical symptoms of acute myocardial infarction include sudden chest pain, typically radiating to the left arm or left side of the neck, shortness of breath, nausea, vomiting, palpitations, sweating, and anxiety. Women may experience fewer typical symptoms than men, most commonly shortness of breath, weakness, a feeling of indigestion, and fatigue. A sizeable proportion of myocardial infarctions, 22-64%, are “silent”, that is without chest pain or other symptoms. Among the diagnostic tests available to detect heart muscle damage are an electrocardiogram (ECG), echocardiography, cardiac MRI and various blood tests. The most often used blood markers are the creatine kinase-MB fraction and the troponin levels. Immediate treatment for suspected acute myocardial infarction includes oxygen, aspirin, and nitroglycerin. Most cases of myocardial infarction with ST elevation on ECG are treated with reperfusion therapy, such as percutaneous coronary intervention or thrombolysis. Non-ST elevation myocardial infarction may be managed with medication, although PCI may be required if the patient’s risk warrants it. People, who have multiple blockages of their coronary arteries, particularly if they also have diabetes mellitus, may benefit from bypass surgery.
There are two basic types of acute myocardial infarction based on pathology: * Transmural: associated with atherosclerosis involving a major coronary artery. It can be subclassified into anterior, posterior, inferior, lateral or septal. Transmural infarcts extend through the whole thickness of the heart muscle and are usually a result of complete occlusion of the area’s blood supply. * Subendocardial: involving a small area in the subendocardial wall of the left ventricle, ventricular septum, or papillary muscles. The subendocardial area is particularly susceptible to ischemia.
The phrase heart attack is sometimes used incorrectly to describe sudden cardiac death, which may or may not be the result of myocardial infarction. A heart attack is different from, but can be the cause of cardiac arrest, which is the stopping of the heartbeat, and cardiac arrhythmia, an abnormal heartbeat. It is also distinct from heart failure, in which the pumping of the heart is impaired; however severe myocardial infarction may lead to heart failure.
A 2007 consensus document classifies myocardial infarction into five main types: * Type 1-Spontaneous myocardial infarction related to ischemia due to a primary coronary event such as plaque erosion and/or rupture, fissuring, or dissection. * Type 2-Myocardial infarction secondary to ischemia due to increased oxygen demand or decreased supply, coronary artery spasm, coronary embolism, anaemia, arrhythmias, hypertension, or hypotension. * Type 3-Sudden unexpected cardiac death, including cardiac arrest, often with symptoms suggestive of myocardial ischaemia, accompanied by new ST elevation, or evidence of fresh thrombus in a coronary artery by angiography and/or at autopsy, but death occurring before blood samples could be obtained, or at a time before the appearance of cardiac biomarkers in the blood. * Type 4-Associated with coronary angioplasty or stents: * Type 4a-Myocardial infarction associated with PCI * Type 4b-Myocardial infarction associated with stent thrombosis with