The heart muscle needs a constant supply of oxygen-rich blood. The coronary arteries Blood Supply of the Heart The heart and blood vessels constitute the cardiovascular (circulatory) system. The heart pumps the blood to the lungs so it can pick up oxygen and then pumps oxygen-rich blood to the body.... read more , which branch off the aorta just after it leaves the heart, deliver this blood. An acute coronary syndrome Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount... read more occurs when a sudden blockage in a coronary artery greatly reduces or cuts off the blood supply to an area of the heart muscle (myocardium). The lack of blood supply to any tissue is termed ischemia. If the supply is greatly reduced or cut off for more than a few minutes, heart tissue dies. A heart attack, also termed myocardial infarction (MI), is death of heart tissue due to ischemia. (See also Overview of Coronary Artery Disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more .)
The complications of acute coronary syndromes depend on how much of the heart muscle is damaged, which is a direct result of where a coronary artery was blocked and how long this artery was blocked. If the blockage affects a large amount of heart muscle, the heart will not pump effectively. If the blockage shuts off blood flow to the electrical system of the heart, the heart rhythm may be affected.
In a heart attack, part of the heart muscle dies. Unlike muscle, dead tissue, and the scar tissue that eventually replaces it, does not contract. The scar tissue sometimes even expands or bulges when the rest of the heart contracts. Consequently, there is less muscle to pump blood. If enough muscle dies, the heart’s pumping ability may be so reduced that the heart cannot meet the body’s need for blood and oxygen. Heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , low blood pressure Low Blood Pressure Low blood pressure is blood pressure low enough to cause symptoms such as dizziness and fainting. Very low blood pressure can cause damage to organs, a process called shock. Various drugs and... read more (hypotension), and/or shock Cardiogenic shock Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death. Blood pressure is usually low... read more develop. If more than half of the heart tissue is damaged or dies, the heart generally cannot function, and severe disability or death is likely.
Drugs such as beta-blockers and especially angiotensin-converting enzyme (ACE) inhibitors can reduce the extent of the abnormal areas by reducing the workload of and the stress on the heart (see table Drugs Used to Treat Coronary Artery Disease Drugs Used to Treat Coronary Artery Disease* ). Thus, these drugs help the heart maintain its shape and function more normally.
The damaged heart may enlarge, partly to compensate for the decrease in pumping ability (up to a point, a larger heart beats more forcefully). Enlargement of the heart makes abnormal heart rhythms more likely.
Abnormal heart rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more (arrhythmias) occur in more than 90% of people who have had a heart attack. These abnormal rhythms may occur because the heart attack damaged part of the heart’s electrical system. Sometimes there is a problem with the part of the heart that triggers the heartbeat, so heart rate may be too slow (bradycardia). Other problems can cause the heart to beat rapidly or irregularly (for example, atrial fibrillation Atrial Fibrillation and Atrial Flutter Atrial fibrillation and atrial flutter are very fast electrical discharge patterns that make the atria (upper chambers of the heart) contract very rapidly, with some of the electrical impulses... read more ). Sometimes the signal to beat is not conducted from one part of the heart to the other, and the heartbeat may slow or stop (heart block Overview of Heart Block Heart block is a delay in the conduction of electrical current as it passes through the conduction system of the heart, including the atrioventricular node, bundle of His, or both bundle branches... read more ).
In addition, areas of heart muscle that have poor blood flow but that have not died can be very irritable. This irritability can cause heart rhythm problems, such as ventricular tachycardia Ventricular Tachycardia Ventricular tachycardia is a heart rhythm that originates in the ventricles (lower chambers of the heart) and produces a heart rate of at least 120 beats per minute (the normal heart rate is... read more or ventricular fibrillation Ventricular Fibrillation Ventricular fibrillation is a potentially fatal, uncoordinated series of very rapid, ineffective contractions of the ventricles (lower chambers of the heart) caused by many chaotic electrical... read more . These rhythm problems greatly interfere with the heart’s pumping ability and may cause the heart to stop beating (cardiac arrest Cardiac Arrest and CPR Cardiac arrest is when the heart stops pumping blood and oxygen to the brain and other organs and tissues. Sometimes a person can be revived after cardiac arrest, particularly if treatment is... read more ). A loss of consciousness or death can result. These rhythm disturbances are a particular problem in people who have an imbalance in blood chemicals, such as a low potassium level Hypokalemia (Low Level of Potassium in the Blood) In hypokalemia, the level of potassium in blood is too low. A low potassium level has many causes but usually results from vomiting, diarrhea, adrenal gland disorders, or use of diuretics. A... read more .
Pericarditis Acute Pericarditis Acute pericarditis is inflammation of the pericardium (the flexible two-layered sac that envelops the heart) that begins suddenly, is often painful, and causes fluid and blood components such... read more (inflammation of the two-layered sac that envelops the heart) may develop in the first day or two after a heart attack. Pericarditis is more common in people who have not had the blocked artery opened by percutaneous coronary intervention Percutaneous Coronary Intervention Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more (PCI) or coronary artery bypass grafting Coronary Artery Bypass Grafting Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more (CABG). People seldom notice symptoms of early developing pericarditis because their heart attack symptoms are more prominent. However, pericarditis produces a scratchy rhythmic sound that can sometimes be heard through a stethoscope 2 to 3 days after a heart attack. Sometimes, the inflammation causes a small amount of fluid to collect in the space between the two layers of the pericardium (pericardial effusion).
Post-myocardial infarction (Dressler) syndrome is pericarditis that develops 10 days to 2 months after a heart attack. This syndrome causes fever, pericardial effusion (extra fluid in the space surrounding the heart), inflammation of the membranes covering the lungs, pleural effusion (extra fluid in the space between the two layers of the pleura), and joint pain. Diagnosis is based on the symptoms it causes and on the time it occurs.
People who develop pericarditis are usually given a nonsteroidal anti-inflammatory drug. Colchicine is often rapidly effective. Even with treatment, the syndrome can recur. If post-myocardial infarction syndrome is severe, a corticosteroid or a different nonsteroidal anti-inflammatory drug may be needed for a short time.
Rarely, the heart muscle ruptures under the pressure of the heart’s pumping action because the damaged heart muscle is weak. Rupture usually occurs 1 to 10 days after a heart attack and is more common among women. The wall separating the two ventricles (septum), the external heart wall, and the muscles that open and close the mitral valve are particularly susceptible to rupture during or after a heart attack.
Rupture of the septum results in too much blood being diverted to the lungs, causing accumulation of fluid (pulmonary edema). A rupture of the septum can sometimes be repaired surgically.
Rupture of the external wall almost always causes rapid death. Doctors rarely have time to attempt surgery, and even then, surgery is rarely successful.
If the mitral valve muscles rupture, the valve cannot function—the result is sudden and severe heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more . Doctors can sometimes repair the damage surgically.
The damaged muscle may form a thin bulge (aneurysm) on the wall of the ventricle. Doctors may suspect an aneurysm based on abnormal results of electrocardiography (ECG), but echocardiography is done to be sure. These aneurysms may cause episodes of abnormal heart rhythms and may reduce the heart’s pumping ability. Because blood flows more slowly through aneurysms, blood clots can form in the heart’s chambers. If heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more or abnormal heart rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more develop, the aneurysm may be removed surgically.
Historically, about 20% of people who have had a heart attack form clots inside the heart, over the area of dead heart muscle. More recently, clot formation is less common. In about 10% of these people, parts of the clots break off, travel through the bloodstream, and lodge in smaller blood vessels throughout the body. They may block the blood supply to part of the brain (causing a stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more ) or to other organs.
Echocardiography may be done to detect clots forming in the heart or to determine whether a person has factors that make clots more likely to form. For example, an area of the left ventricle may not be beating as well as it should.
For people who have clots, doctors often prescribe anticoagulants (sometimes called blood thinners) such as heparin and warfarin. Heparin is given intravenously in the hospital for at least 2 days. Then, warfarin is given by mouth for 3 to 6 months. Aspirin also is taken indefinitely.
Other complications after a heart attack include leakage of the mitral valve (mitral valve regurgitation Mitral Regurgitation Mitral regurgitation is leakage of blood backward through the mitral valve each time the left ventricle contracts. Genetic weakness of the mitral valve tissue (myxomatous degeneration) and heart... read more ).
Nervousness and depression are common after a heart attack. Depression Depression A short discussion of prolonged grief disorder. Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to... read more after a heart attack may be significant and may persist.
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