Myocardial infarction, commonly referred to as heart attack, is the sudden death of part of the heart muscle (the myocardium) due to loss of blood flow (ischemia). This occurs when one of the coronary arteries – the arteries that supply blood to the heart – is blocked.
Fig. 1: Coronary arteries supply blood to the heart. They branch out from the first part of the aorta. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
The blockage is commonly due to atherosclerosis – cholesterol plaques/fat deposits on the wall of blood vessels. As the plaque builds up, the vessel becomes narrow restricting blood flow. Under stress, the plaque may rupture. This triggers formation of blood clot on top of the plaque leading to complete blockage of blood flow. When this happens in a coronary artery, the downstream patch of the myocardium dies from lack of oxygen (Fig. 2). Weaken heart muscle may disrupt electrical activity of the heart and cause fibrillation with subsequent cardiac arrest.
Fig. 2: Anatomy of a heart attack due to atherosclerotic plaque. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
Click here to see an animation of heart attack on Alila Medical Media website where the video is also available for licensing.
Signs and symptoms
The most common symptom is described as a heavy pressure and squeezing pain inside the chest which often radiates to the shoulder and left arm. Other symptoms include shortness of breath, sweating, weakness, nausea and vomiting.
In a number of cases, especially in elderly and people with diabetes, no chest pain or other symptoms are reported. These are called silent myocardial infarction. In such a case, myocardial infarction is diagnosed later with electrocardiograms (ECG), blood enzyme tests or an autopsy.
Risk factors and Causes
Heart attack is caused by build-up of atherosclerotic plaques. Risk factors include smoking, alcohol consumption, obesity, sedentary lifestyle, stress. Incidence increases with age, also, men are more at risk than women.
Onset of acute myocardial infarction is commonly associated with physical and/or psychological exertion. When the body is under physical or emotional stress, blood flow is increased. This leads to stretching of the wall of blood vessels and potentially rupture of plaques.
Below is a narrated animation about myocardial infarction, cardiac catheterization and coronary angioplasty. Click here to license this video and/or other cardiovascular related videos on Alila Medical Media website.
Treatments
Immediate treatments for suspected heart attack include blood thinners such as aspirin. Blood thinners are drugs that prevent further blood clotting. If this doesn’t help, another class of drugs called thrombolytic may be used. Thrombolytic drugs act to dissolve blood clots. This process is called thrombolysis.
Severe cases will require interventional therapy such as angioplasty where the blocked blood vessel is forced to open wider with a balloon and possibly a stent.
People with multiple sites of blockage may require heart bypass surgery. In this surgical procedure, a piece of healthy artery or vein taken from elsewhere in the body is used as a graft to “bypass” the blocked part of coronary artery.
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