Heart Attack Basics
What is a Heart Attack?
A heart attack occurs when the muscle of the heart is damaged. The medical term for a heart attack is a myocardial infarction.
All muscles in the human body require oxygen to function. A heart attack/myocardial infarction occurs when the heart muscle does not get enough oxygen.
The coronary arteries are responsible for the delivery of oxygen-containing blood to the heart muscle. When these arteries become severely blocked or narrowed, they restrict the flow of oxygen to the heart. The result may be a heart attack.
The symptoms of a heart attack vary, but are most commonly described as a squeezing, burning, tightness, fullness, or pressure across the chest. This discomfort may radiate to the shoulder, arms (especially the left), neck, jaw, teeth, earlobes, as well as the upper back between the shoulder blades. Numbness or tingling in the arms or hands may occur. Other symptoms include nausea and vomiting, sweating, palpitations, dizziness, and perhaps loss of consciousness. Some patients, particularly diabetics, might sustain a "silent" myocardial infarction, which occurs without any symptoms at all.
There are two main causes of clogged coronary arteries: Coronary Artery Disease and Coronary Thrombosis.
Coronary Artery Disease:
|TOP: Healthy artery with adequate blood flow
BOTTOM: Plaque build up restricts blood flow
also referred to as atherosclerosis, is a gradual process in which fatty layers (plaque) build up on the inside of the arterial walls. As the plaque continues to build up and the artery narrows, there is less room for adequate blood flow (see diagram).
is a blood clot that lodges inside a coronary artery and prevents the flow of blood.
Angina vs. Heart Attack
Angina (chest pain) is not a heart attack, but may be a warning of an impending heart attack.
Angina also occurs when the heart muscle is not receiving enough oxygen. With angina, however, no permanent damage is done to the heart muscle.
Angina is most commonly experienced with physical activity such as shoveling snow, raking leaves, or walking upstairs or uphill. It can also be associated with a stressful event or consuming a large meal.
The symptoms of angina are similar to those of a heart attack. They are most commonly described as a squeezing, burning, tightness, fullness, or pressure across the chest. This discomfort may radiate to the shoulder, arms (especially the left), neck, jaw, teeth, earlobes, as well as the upper back between the shoulder blades. Numbness or tingling in the arms or hands may occur. Angina can be mistaken for indigestion.
Unlike a heart attack, angina may be relieved by rest and/or nitroglycerin within 15 minutes.
How a Heart Attack is Diagnosed
Your physician has several tests at his/her disposal when determining whether or not you have had a heart attack.
Medical History and Physician Exam
Your physician will need to obtain your medical history and perform a complete physical examination. There will be questions asked regarding your present state of health, including specific symptoms you are experiencing. Questions concerning your lifestyle also need to be answered, i.e. dietary habits, exercise routine, stress, smoking history, alcohol consumption, and medications. It is important for your physician to know your family's medical history as well.
12 Lead Electrocardiogram (EKG)
An electrocardiogram records the electrical activity of your heart. A series of EKGs are taken during your hospitalization to observe the gradual changes which are indicative of a heart attack.
Cardiac enzymes are normally stored in the cells of the heart muscle. When the heart is injured, cardiac enzymes are released into the blood stream. A series of blood tests are drawn in order to observe changes of each specific enzyme.
Common Cardiac Tests and Procedures
An echocardiograrn is a non-invasive procedure using ultrasound waves to visualize the structures of the heart on the screen with the use of a probe. The handheld probe is moved across the chest to visualize the movements of the heart's valves and chambers.
A transesophageal echocardiogram is the same as a standard echocardiogram, except a miniature transducer (the probe) is passed down the esophagus by means of a flexible scope to visualize the heart. This procedure provides the physician with more information than a standard echocardiogram.
Exercise Stress Test:
An exercise stress test involves exercising on a treadmill or bike at increased degrees of difficulty while the heart's response is recorded on an electrocardiogram (EKG). The level of exercise tolerance is measured by changes on the EKG, reported symptoms, as well as blood pressure and heart rate response. It also allows the physician to evaluate the effectiveness of your medical treatment. Patients recovering from a heart attack are usually given a low level exercise stress test prior to discharge.
Persantine Stress Test:
A persantine stress test is similar to the graded exercise stress test except that a medication called persantine is used to elevate the heart rate instead of exercise.
Thallium Stress Test:
A thallium stress test may be done at rest, or follow the same procedure as a graded exercise test. It involves an intravenous administration of a low dose of radioactive material. A scan of the heart is then performed which can visualize areas of the heart that do not receive sufficient blood supply.
MUGA Scan: A MUGA scan uses low dose radioactive material given intravenously to visualize the heart's pumping action (ejection fraction).
Stress Echocardiogram: A stress echocardiogram is similar to a graded exercise stress test, except that an echocardiogram is performed prior to the stress test and immediately following the stress test. A stress echocardiogram allows the physician to visualize changes in the pumping action of the heart between rest and exercise.
24 Hour Holter Monitor: With a 24 hour Holter monitor, electrodes are placed on the chest wall and connected to a small tape recorder which records the heart rhythm for a 24 hour period. The patient resumes his/her normal lifestyle while being monitored. The patient maintains a log of activity and symptom over the same time period. The physician then correlates the activities and symptoms to any changes in the heart rhythm.
|Figure 1: Cath film showing coronary arteries
(coronary angiography): A cardiac catheterization is an invasive procedure performed in a special lab under a local anesthetic and sterile conditions. A catheter is introduced into the heart via an artery and/or vein located in the groin or arm. Dye is injected through the catheter into the coronary arteries and/or heart's chambers, while an x-ray is taken and recorded on film (see Figure 1). This procedure allows the physician to visualize the coronary arteries, as well as the function of the heart and its valves.
Thrombolytic therapy involves the administration of medication intravenously to dissolve the blood clot causing the heart attack. Once the blood clot is dissolved, blood flow can be restored to the affected area of the heart. Activase (t-PA) or Streptokinase are the most common medications used for dissolving a blood clot.
|| Figure 2: PTCA procedure
Angioplasty is a procedure performed on patients with blocked or clogged coronary arteries. The technique is similar to a catheterization except that a special catheter with a small balloon is inserted into the blockage and inflated in order to compress the plaque and open the artery (see Figure 2). A balloon catheter is advanced to the area of the blockage. The balloon is then inflated and deflated several times, until the blockage is compressed and the artery is widened.
Directional Coronary Atherectomy (DCA):
A directional coronary atherectomy is similar to an angioplasty except that the blockage is decreased by mechanically removing the plaque.
Coronary Artery Stenting:
|Figure 3: Stent procedure
Stenting is an adjunct to angioplasty. It involves the insertion of a wire tube (stent) into the coronary artery that was successfully opened with a balloon (see Figure 3). The stent will help keep the coronary artery open and will remain permanently in place.
Coronary Artery Bypass Grafting (CABG):
A CABG is an operation that involves surgically bypassing blood around the blockages in coronary arteries. Portions of vein from the leg or arteries from behind the breastbone are used to create "bypass grafts" that re-route the blood around the blocked coronary arteries.