What causes a heart attack?
A heart attack results when blood supply to the heart is cut off or reduced. (Read about "The Heart & Cardiovascular System") This limits the supply of oxygen to the heart, resulting in potential damage to the heart muscle. The heart's blood supply can be cut off as a result of atherosclerosis, in which fatty deposits build up on the lining of the artery walls until a blockage occurs. Although heart attacks can strike without warning, an attack may also be preceded by periodic spells of
chest pain called angina. While the symptoms of angina may seem to mimic those of a heart attack, the National Heart, Lung, and Blood Institute (NHLBI) says angina is more often triggered by physical exertion, whereas a heart attack can occur at any time, even during rest. Although angina is not the same as a heart attack, it does indicate the presence of coronary artery disease and should not be ignored.
The underlying mechanism of a heart attack is the destruction of heart muscle cells due to a lack of oxygen. If these cells are not supplied with sufficient oxygen by the coronary arteries to meet their metabolic demands, they die by a process called infarction. The decrease in blood supply has the following consequences: Heart muscle which has lost blood flow long enough, e.g. 10-15 minutes, ends up dying (necrosis) and does not grow back. Thus the heart ends up permanently weaker as a pump for the remainder of the individual's life; Injured, but still living, heart muscle conducts the electrical impulses which initiate each heart beat much more slowly. The speed can end up so slow that the spreading impulse is preserved long enough for the uninjured muscle to complete contraction; now the slowed electrical signal, still traveling within the injured area, can re-enter and trigger the healthy muscle (termed re-entry) to beat again too soon for the heart to relax long enough and receive any blood return from the veins. If this re-entry process results in sustained heart rates in the >200 to over 400 beats per minute range (called ventricular tachycardia (V-Tach) or ventricular fibrillation (V-Fib), then the rapid heart rate effectively stops heart pumping. Heart output and blood pressure falls to near zero and the individual quickly dies. This is the most common mechanism of the sudden death that can result from a myocardial infarction. The cardiac defibrillator device was specifically designed for stopping these too rapid heart rates. If used properly, it stimulates the entire heart muscle to contract all at once, in synchrony; hopefully stopping continuation of the re-entry process. If used within one minute of onset of V-Tach or V-Fib, the defibrillator has a high success rate in stopping these often fatal arrhythmias allowing a functional heart rhythm to return.
The most common cause of heart attack by far is atherosclerosis, a gradual buildup of fat-containing substances in plaques in the arterial wall. Placques can become unstable, rupture, and form a thrombus (blood clot) that occludes the artery. When this process happens in the coronary vasculature, it leads to necrosis of downstream myocardium. All risk factors for atherosclerosis are also (modifiable) risk factors for ischemic heart disease: older age, smoking, hypercholesterolemia, diabetes (or insulin resistance) and obesity. The blood flow problem is nearly always a result of exposure of atheroma tissue within the wall of the artery to the blood flow inside the artery, atheroma being the primary lesion of the atherosclerotic process. The many blood stream column irregularities, visible in the single frame angiogram image to the right, reflects artery lumen changes as a result of decades of advancing atherosclerosis.
Heart attacks can also infrequently occur if the work load of the heart suddenly rises and the necessary oxygen cannot be supplied quickly enough. This is why extreme stress or physical exertion can result in heart attacks. Sudden contraction of coronary arteries in cocaine abuse can also precipitate myocardial infarction.
More information on heart attack (myocardial infarction)
What's a heart attack (myocardial infarction)? - A heart attack (myocardial infarction) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot.
What're the signs and symptoms of a heart attack? - Symptoms of a heart attack include pain and pressure in the chest, which often spread to the shoulder, arm, and neck.
What're the women's heart attack symptoms? - A woman's heart attack has more varied symptoms than a man's. Women are more likely to have nausea and pain high in the abdomen.
What're the warning signs of a heart attack? - Warning signs of a heart attack include uncomfortable pressure, fullness, squeezing, or pain in the center of the chest, cold sweat or paleness.
What causes a heart attack? - Heart attack is caused by a lack of blood supply to the heart for an extended time period. The most common cause of heart attack is atherosclerosis.
What're the complications of a heart attack? - Complications of a heart attack include ventricular tachycardia, ventricular fibrillation, cardiogenic shock, arrhythmias, heart failure.
What're the risk factors for heart attack? - Heart attack risk factors can be devided into two groups: Inherited (or genetic) risk factors and acquired risk factors.
How is a heart attack diagnosed? - The most important factor in diagnosing and treating a heart attack is prompt medical attention. For a complete diagnosis, the medical history is vital.
What're the treatments for heart attack? - The goal of treatment for heart attack is to quickly open the blocked artery and restore blood flow to the heart muscle, a process called reperfusion.
What drugs are used to cure heart attack? - Medications used to treat heart attacks include blood vessel dilators, clot busters, beta blockers, antiarrhythmic drugs, pain relievers.
What surgeries treat heart attacks? - Surgeries to treat heart attacks include coronary angioplasty, coronary artery bypass surgery, transmyocardial revascularization, and atherectomy.
Aspirin and heart attacks - Aspirin is taken daily following a heart attack to reduce the risk of another heart attack. Aspirin reduces heart attacks and improve survival in the patients.
How to survive a heart attack? - In wilderness first aid, a possible heart attack justifies medical evacuation by the fastest available means. Heart attacks are survivable.
How to prevent a heart attack? - Heart attack can be prevented with a healthy liestyle. Daily aspirin therapy or other medical treatment help prevent heart disease and heart attack.
How to recover after a heart attack? - Following discharge from the hospital, patients continue their recovery at home. Lowering cholesterol can reduce the risk for another heart attack.