Myocardial infarction (or heart attack), is produced by blocking one or more of the coronary arteries. Coronary arteries supply oxygenated blood to the heart. Artery blockage occurs when an atheromatous plaque within artery ruptures and forms a thrombus (blood clot) around it.
The atheromatous plaque and thrombus will obstruct the blood flow to the myocardial cells, thus depriving them of oxygen and nutrients. Without blood supply, the heart muscle cells die. If during myocardial infarction a large area of myocardium is affected, this may cause death. Myocardial infarction requires emergency therapy to restore blood flow.
Angina pectoris represents a kind of chest pain that occurs when the myocardial blood flow is not sufficient, most commonly occurs when the size of the blood vessels (coronary arteries) are reduced. Stable angina occurs after a particular exercise or physical activity.
Unstable angina occurs as:
- A change in the manifestation of stable angina;
- A chest pain occurring at rest or during minor exercise; chest pain may be more severe and last longer or does not respond to administration of nitroglycerin;
Chest pain is not present in all cases. In a recent study of 700 patients treated for myocardial infarction, 47% presented to the emergency room for other symptoms. These symptoms are dyspnea (altered breathing, air hunger), dizziness, fatigue, weakness and abdominal pain. Women, diabetics or older people have retrosternal pain in a smaller percentage and more frequently they have other symptoms.
Protocol in Myocardial Infarction
If a person suspects a myocardial infarction and was prescribed nitroglycerin, it is advisable to administer a nitroglycerin pill. After 5 minutes, if the pain does not respond or worsens, calling the emergency services is indicated.
If it implies a myocardial infarction or unstable angina and no prescribed nitroglycerin, is indicated for the patient to go to the emergency room or call an ambulance. It is important to start the treatment as soon as possible.
If you cannot call an ambulance, presenting to the emergency room is indicated. It is not advisable to drive the car in this state, except where no other alternative. Do not wait to see if the symptoms will pass, as they does, this may be fatal.
Every year, about 40% of the myocardial infarctions are fatal, and more than half of the deaths occur in the emergency room or before reaching hospital.
After calling an ambulance, they will recommend chewing an aspirin.
Unstable angina can lead to myocardial infarction or cardiac arrest (heart stopping). In case of suspected unstable angina, the same measures as in the case of myocardial infarction are recommended.
Causes of Myocardial infarction
The main cause of both unstable angina and myocardial infarction is coronary artery disease. Coronary heart disease occurs when the atheromatous plaques occur along the internal walls of the coronary arteries and thus reduce blood flow to the heart. In most people, coronary heart disease begins in adolescence and grows over the years.
High cholesterol, high blood pressure and smoking damages the arteries and contribute to plaque buildup. The process of forming plaques is called atherosclerosis. Atheromatous plaques are deposits of cholesterol, calcium and other substances covered by a fibrous capsule.
In case of plaque rupture the organism will try to repair the tear or crack in the same way that a skin lesion is repaired by forming a thrombus on the surface of the capsule. The formed thrombus may completely obstruct the artery, blocking the blood flow to the heart muscle and thus produce infarction. Newly formed atheromatous plaque has the highest risk of rupture. The fibrous capsule of a newly formed atheromatous plaque has a more pronounced tendency to break or crack (it is more unstable) than the thicker capsule of old atheromatous plaques.
Atheromatous plaques are not always the cause of myocardial infarction. In some cases, quite rare, coronary spasm and contracture can completely obstruct the blood flow and cause myocardial infarction. Most often in these cases the atherosclerosis is also involved, but there are cases where other factors produce spasm. Cocaine, cold weather, emotional stress can cause episodes of arterial spasm. In many cases we do not know the cause of these spasms.
The thrombus formed on a ruptured or fissured atheromatous plaque, may not be large enough to block the artery completely, but can decrease the blood flow in the vascular territory of the artery, causing unstable angina. Unstable angina may be the sign that would follow a myocardial infarction, because thrombus may grow in size and completely obstruct the artery. If the thrombus is dissolved, infarction will be immediately prevented, but the body will try, over time, to repair the damaged capsule of atheromatous plaque buildup. Also, a newly repaired plaque can be unstable. The probability of repeated rupture is high, making it a risk factor for a new myocardial infarction.
Precipitating factors for Myocardial infarction
In many cases we do not know for sure the cause of a myocardial infarction. Sometimes, the body releases adrenaline and other hormones into the bloodstream in response to some intense emotions like anger or fear.
Strenuous exercise, emotional stress, lack of sleep, and overeating can also be precipitating factors. Adrenaline increases blood pressure and heart rate and can cause coronary artery spasm, things that can cause rupture of unstable atheromatous plaques.
Cocaine and nicotine, which are found in tobacco products, can produce similar effects.
Symptoms of Myocardial infarction
In some cases, myocardial infarction occurs silently, without symptoms, but this is rare.
Most people with myocardial infarction have retrosternal pain and at least one of the following symptoms:
- Suffocation, foreign body sensation in the throat and the permanent need to swallow;
- Cold sweats;
- Sensation of imminent death;
- Difficulty in breathing or inability to breathe;
- Palpitations or feeling that the heart beats quickly and irregularly (palpitations can be common symptoms in healthy people);
- Numbness or discomfort in the hand or arm.
People who have had a myocardial infarction described chest pain in several ways.
The pain may be described in the following forms:
- Feeling pressure, weight, squeezing, discomfort, burning, sharp pain (less common); people usually put the fist on chest when are asked to describe it;
- The pain may radiate from the chest in the left shoulder and left hand (the most common site of irradiation) or in other regions, including the back, upper abdomen and right hand;
- It can be diffused, the exact location of the pain is usually doable;
- Does not improve after a forced inspiration or chest press;
- Usually begins with low intensity and increases in intensity over several minutes to a maximum. Discomfort may be intermittent. Chest pain that reaches maximum intensity within seconds can be a sign of another disease (aortic dissection).
It indicated to call the emergency service when:
- Chest pain gets worse or does not go away over 5 minutes, especially if associated with breathing difficulty, nausea or disturbance of consciousness;
- Chest pain does not improve or worsens within 5 minutes after administration of nitroglycerin.
The difference between unstable angina and myocardial infarction may not be always easy to make. Most of the symptoms are often similar. Both conditions require emergency treatment.
People who have had unstable angina described pain with the following characteristics:
- The onset in the past two months and worsening in time;
- The frequency of the pain is 3 or more times per day;
- Suddenly increasing in intensity, becomes more frequent, lasts longer and is caused more easily;
- Appears at rest, without being precipitated by exercise or stress; can awaken a person from sleep;
- Does not respond to nitroglycerin.
Stable angina symptoms are different from unstable angina. Stable angina occurs in a predictable time after a certain effort or a particular activity and can have the same character over a long period of time, even years. Pain is relieved at rest or after nitroglycerin administration and lasts less than 20 minutes.
Risk factors for Myocardial infarction
Coronary heart disease is the leading cause of myocardial infarction in almost all cases. Therefore, the higher the risk factors for coronary heart disease, the greater will be the risk of unstable angina or myocardial infarction. Smoking, diabetes, high cholesterol, high blood pressure and a family history of heart disease are important factors for coronary artery disease.
In order to reduce the risk:
- Stop smoking: smoking cessation is probably the most important step to decrease the risk of a myocardial infarction;
- Reduction of serum cholesterol: hypercholesterolemia can cause cholesterol plaques inside the arteries;
- Lower the blood pressure: Hypertension damages the coronary arteries and increases cardiac labor so it will increase the need for blood of the heart and the arteries already damaged cannot provide this supply;
- Treatment of diabetes: diabetic persons develop a thickening and a decrease in the size of arteries more frequently and at a younger age than those who do not have diabetes; maintaining blood sugar (blood glucose values) in normal range slows these processes;
- Maintaining an optimal weight: weight loss improves blood pressure and serum cholesterol levels and may also help to control diabetes;
- Regular physical activity: Regular exercises reduce the risk of myocardial infarction by helping to control the serum levels of cholesterol, blood pressure, regulates blood sugar levels (important for people with diabetes) and aids weight loss;
- treatment of depression and emotional control: treatment of depression and emotional disorders are important steps in improving cardiac function and quality of life;
- Reducing stress: stressful periods increase blood pressure and increase the heart rate, which may cause narrowing of the arterial caliber;
- Assessment of the effects of birth control pills and hormone therapy: hormone replacement therapy (estrogen and progestin) increase the risk of heart disease; birth control pills increase the risk of heart disease if the woman is over age 35 and is a smoker;
- Daily administration of aspirin (is indicated to ask your doctor before starting aspirin administration).
Some risk factors that cannot be controlled:
- Family history for heart disease, especially if the disease occurred in men younger than 55 years and women under 65;
- Age and sex: the number of people affected by heart disease is higher with age, after 45 years in men and 55 years in women; Women and men also have different risk factors.
Levels of homocysteine and mutation of a specific gene can also increase the risk of myocardial infarction, although more studies are needed to fully understand the role of these factors in heart disease. Some tests to highlight these risk factors may be necessary for some people, especially those who have had a myocardial infarction at a young age.
Increased levels of C-reactive protein, a substance found in the blood that indicates inflammation, may have a higher predictive value for myocardial infarction than cholesterol. Two studies based on C-reactive protein level and statin therapy have shown that C-reactive protein levels may predict the risk of myocardial infarction even when the person has normal or low levels of LDL-cholesterol.
In the ambulance, the doctor or nurse will assess the heart rate, blood pressure, respiratory rate and will place electrodes on the chest to perform an ECG (electrocardiogram). The ECG is a graphic record of the electrical activity of the heart.
After you arrive at the emergency room, the doctor will perform an anamnesis, a physical exam and will make another ECG. The ECG can detect cardiac abnormalities, signs of circulatory failure, heart muscle damages, abnormal heart beats.
A nurse will take blood samples and tests will be performed for cardiac enzymes that are released into the bloodstream when heart cells are injured. Troponin enzyme present in the blood usually demonstrates a cardiac lesion.
The test results will be available quickly. If the tests indicate a myocardial infarction or a stroke in evolution, they will transfer you at a cardiac catheterization laboratory.
Cardiac catheterization involves inserting a thin tube along an artery (radial or femoral artery) up to the heart. Then iodine substance is injected which will make it possible to visualize the coronary arteries (Read more about coronary arteries) on a screen. The doctor will see if the arteries are blocked and how the heart works.
If an artery appears to be blocked, an angioplasty with stent implantation will be performed, a procedure which unblocks the culprit artery. In some cases CABG (Coronary artery bypass graft surgery) may be indicated.
Read more about heart catheterization and coronary angiography.
If the tests do not clearly indicate a myocardial infarction or an unstable angina and other indicators of risk are not present (such as another myocardial infarction in the past), another investigation will be performed – myocardial perfusion scan (SPECT). SPECT is a noninvasive imaging investigation and can be performed in the emergency room, to evaluate whether the risk of myocardial infarction is high. If the SPECT test is abnormal, the patient will be considered at high-risk and heart catheterization is required.
If the test does not indicate a myocardial infarction, but the doctor thinks it is an unstable angina, the patient will be hospitalized for monitoring.
Investigations made after myocardial infarction
After 2-3 days of myocardial infarction or hospitalization for unstable angina, further investigations will be conducted to assess how is the heart and to determine if the affected heart areas are perfused properly.
These investigations include:
- Cardiac ultrasound: This is an ultrasound investigation that evaluates the size, thickness, shape and heart muscle movements; it also evaluates the flow of blood and heart valves;
- ECG at stress: a stress test will compare the ECG at rest during the period after stressing the heart, either by physical activity (cycling or climbing stairs) or by the use of drugs; a stress test to detect ischemia, which translates as a reduced blood flow to the myocardium tissue; Read more about cardiovascular exercise testing.
- Stress echocardiogram: it determines if there is a reduced blood flow to the heart;
- Cardiac perfusion scanning: scanning with thallium or technetium is used to estimate the amount of blood reaching the myocardium at rest and after exercise;
- Angiogram: This test involves injecting a contrast agent to evaluate the coronary heart and coronary arteries. Indications for angiography.