Heart attack – What causes myocardial infarction & what’s next?
Heart attack and its synonym myocardial infarction describe a vascular disease of the heart. The heart, the most important human organ, is integrated into two of the body’s bloodstreams.
On the one hand, it pumps blood into the large circulation, which supplies the organs and extremities with oxygen-rich blood.
On the other hand, the heart operates a small circulation with the lungs, in which the oxygen-poor blood is again enriched with oxygen, and then brought back into the large circulation to be fed.
In addition, the heart has its own blood supply. The vessels are also called coronary vessels because they wrap around the heart like a wreath. They arise from the ascending main artery, the aorta (just behind the aortic valve) and are supplied with oxygen-rich blood by this.
The main vessels are called the left (arteria coronaria sinistra) and right (arteria coronaria dexter) coronary artery and have several secondary and lateral branches.
If you want to name the position of the heart in the body, this is always done from the patient’s perspective. The heart basically consists of a right and a left half of the heart. These are separated from one another by a partition (septum).
The anatomy of the heart
The respective half of the heart is in turn divided into an atrium (atrium) and a chamber (ventricle). In between are the so-called leaflet valves (mitral and tricuspid valves). The oxygen-poor blood from the circulatory system flows from the right atrium via the tricuspid valve into the right chamber and from there via the pulmonary valve into the lungs (small circulation).
The oxygen-rich blood from the lungs reaches the left ventricle via the left atrium through the mitral valve and from there via the aortic valve back into the great circulation. The heart muscle needs an adequate blood supply for this process.
Roughly speaking, the left coronary artery supplies more to the left and the right coronary artery more to the right half of the heart (including pacemaker centers such as sinus nodes or AV nodes).
If this happens in equal proportions, one speaks of a normal provider type (70 percent of people). If the blood flow predominates in an artery, one speaks accordingly of a left-supply type or right-supply type.
The impact of chronic diseases
Chronic diseases such as arteriosclerosis (hardening of the arteries) can lead to pathological changes in the heart vessels and lead to coronary artery disease (CHD).
If the changes affect the inner wall of the vessels and there build an increased deposit of fats and lime, this can lead to a narrowing or even a complete closure of the vessels.
So it happens that certain areas of the heart are no longer adequately supplied with blood (reduced perfusion) and one then speaks of ischemia or, in the case of a complete vascular occlusion, of a myocardial infarction.
In this way, the heart tissue is irreversibly damaged and dies (necrosis). As a result, functional disorders of the muscles occur, which can lead to cardiac insufficiency and even death. Cardiac arrhythmias are also dangerous consequences of a heart attack.
Since obesity and nicotine consumption increase the risk of heart attack enormously, it is no wonder that heart attacks are one of the most common causes of death in society today.
Causes of Heart Attack
The most important cause of a heart attack is a blood clot (thrombosis) in 80 percent of cases. This can form due to calcification of the vascular wall (arteriosclerosis) and clogs the vessel. An embolus (also a blood clot) can lead to a vascular blockage.
Unlike the thrombus, this does not form locally, but is transported with the bloodstream, for example from the left atrium, into one of the coronary arteries.
The obstruction of the vessels leads to a reduced blood flow to the heart tissue. If the lack of oxygen persists for several hours, the damage is irreversible. This leads to death (necrosis) and scarring of the affected area.
Even in the case of aortic valve insufficiency, there is a reduced blood flow to the heart tissue. The aortic valve does not close properly and so oxygen-rich blood flows back into the left ventricle and increases the stroke volume (normally 70 ml) of the heart. This leads to an overload of the left ventricle and less blood reaches the coronary vessels via the aorta.
A sharp drop in blood pressure (hypotension) due to large blood loss also leads to reduced blood flow. The regular blood supply through the coronary vessels is from the outside in (epicardium, myocardium, endocardium) and so the inner layer, the endocardium, is the first layer affected by ischemia. Usually the infarct is in the anterior wall of the left ventricle.
Depending on how many large vessels are affected, one speaks of a 1-vessel, 2-vessel or 3-vessel disease (GE). One of the chronic signs of an insufficient supply of oxygen-rich blood is fatty heart.
Symptoms of myocardial infarction
In most cases, those affected by a heart attach already have symptoms in advance, as the vascular occlusion (stenosis) in most cases develops over a longer period of time (chronically) due to arteriosclerosis.
The disease only becomes noticeable when the blood vessels are constricted by more than 70 percent. Symptoms can include general weakness, a feeling of pressure over the heart and tightness of the chest (angina pectoris).
The angina pectoris symptoms are triggered or exacerbated by:
Psychological or physical stress
If a sudden acute heart attack occurs, the sick often suffer from “annihilation pain”, sudden shortness of breath, great fear (cold sweat), paleness, nausea and anxiety. The heart pain then usually radiates into the left arm.
In a diabetic, the damage to the nerves (polyneuropathy) can mean that the myocardial infarction is not even noticed because the pain stimuli can no longer be perceived.
The diagnosis of a heart attack is relatively easy because of the acute symptoms. It is based on the one hand on a detailed questioning of the patient (anamnesis) and relatives (external anamnesis) and on the other hand on a physical and laboratory examination.
The current medical history includes questions about the type and location of the symptoms. Risk factors such as smoking, high blood pressure, diabetes, a lipid metabolism disorder or an increased incidence of coronary heart disease in the family should also be inquired about.
During the physical examination, special attention should be paid to pulse and blood pressure measurements. Then an EKG (electrocardiogram) should be performed at rest; it registers the heart’s action.
Physical examination methods
The ECG can be abnormal and show changes such as an ST segment elevation (in most cases all layers of the heart are affected). The heart attack is known as a STEMI infarction. If not all layers of the heart muscles are affected, the ST segment elevation may not occur.
Such a myocardial infarction is known as an NSTEMI infarction. The localization of it can be determined on the basis of the various recordings (chest wall or extremities). An echocardiography or ultrasound examination of the heart shows possible wall or valve damage.
Myocardial scintigraphy with a radioactive contrast medium allows conclusions to be drawn about the blood flow to the heart muscle. A cardio MRI (magnetic resonance imaging of the heart) shows destroyed tissue.
More examination opportunities
In addition, laboratory parameters such as myoglobin (protein component of muscles, indicates damage), the total CK (creatine kinase, is an enzyme in the muscle’s energy cycle) and the heart muscle-specific CK-MB as well as the troponin T and troponin I (heart muscle proteins) can be determined.
The BNP (brain natriuretic peptide), which is formed in the heart chamber when there is an increased volume load, can also be determined and in this way, in the event of dyspnea, it is possible to find out whether this is caused by the heart (cardiac) or the lungs (pulmonary) .
In addition to these examinations, a cardiac catheter is indicated in the event of an acute heart attack. The catheter itself is a thin plastic tube through which contrast agents can be injected.
It is advanced either through the great artery of the leg or over the arm to the heart and placed at the entrance to the coronary arteries in the aorta.
If the catheter is filled with a radiopaque contrast medium, the vessels can be shown very precisely during fluoroscopy with X-rays. This is how you can find any tight spots.
Before the diagnosis of “myocardial infarction” is made, diseases that lead to similar symptoms should be excluded: a pulmonary embolism (blood clot closes a pulmonary vessel), pericarditis (inflammation of the pericardium), a ruptured aortic aneurysm (a bulging of the main artery with a possible tear), a spinal disease or nerve irritation, gallstone disease or inflammation of the pancreas. Heartburn (increased acid production in the stomach) can also mimic a heart attack.
Immediate measures in the event of an acute heart attack include a comfortable position for the patient (upper body usually elevated), administration of oxygen, adequate medication calming (sedation), administration of painkillers (e.g. morphine) and administration of an anti-nausea agent.
It is important that no injection is made into a muscle (intramuscularly) because this would falsify important laboratory parameters (e.g. CK-MB).
In addition, there could be a major bleeding into the muscle if anticoagulant substances (such as heparin) are absolutely necessary to treat the heart attack.
In the acute phase, nitroglycerin is regularly used because it relieves the load on the heart via venous vasodilation. It also has a direct widening effect on the coronary arteries.
It is also possible to differentiate between angina pectoris and a heart attack. If the patient responds to nitroglycerin, then it is more likely that angina pectoris is suspected.
About Thrombolytic therapy and Bypass
Thrombolytic therapy (dissolution of the thrombus) with fibrinolytics can be carried out within six hours after the myocardial infarction. The possibility of a cardiac catheter examination should be used.
If narrow narrow areas are found, these are widened with a balloon and a short, stable tube (stent) is placed to keep the vessel open.
Bypasses can be an option if large stretches of the blood vessel are affected. In this case, a vein is removed from the affected person’s leg.
This is supposed to bridge the narrow area, with one end being sewn into the main artery (aorta) and the other end being sewn onto the coronary artery below the stenosis. This is the only way to ensure optimal supply of the target area.
Heart transplants are sometimes necessary
If too large an area of the heart is damaged or destroyed by the myocardial infarction and the heart can no longer provide the necessary performance, a heart transplant must be considered. In this case, the sick person receives a donor heart.
At the moment there are a lot of people who need a new heart and too few organ donations. In order to avoid a heart attack or a repeated heart attack (re-infarction) in the long term, patients at risk should consider to optimally adjust their blood pressure either with ß-blockers or an ACE inhibitor, their cholesterol level (with a cholesterol synthesis inhibitor) and their blood sugar (with an antidiabetic or anti-diabetic drug, such as insulin).
Regular intake of aspirin (acetylsalicylic acid) inhibits blood platelets (thrombocytes) and prevents clots from forming. In addition, attending a coronary sports group under the supervision of a doctor is advised and a smoking ban is issued.
The complications of a heart attack include ventricular fibrillation and ventricular flutter (heart rates> 200 / min). Half of the infarct patients do not survive this derailment of the heartbeat.
Further complications of a heart attack are a pulmonary embolism, damage to the leaflet valves, cardiac arrhythmias, a heart wall sac (aneurysm) and, in an emergency, a heart wall rupture (tear in the heart wall), which leads to immediate death.
It is gratifying that in more than 60 percent of patients the clot in a coronary artery dissolves again within the first 24 hours and the coronary artery is again adequately supplied with blood.
Instructions for the patient
The risk factors for myocardial infarction correspond to those of arteriosclerosis. The risk factors are divided into those that have arisen in the body itself (endogenous) and into substances that have an external effect on the body (exogenous).
Endogenous factors include
- High blood pressure (hypertension, stresses the vascular wall)
Fat metabolism disorder (hyperlipoproteinemia, increased fat transport proteins)
Diabetes (diabetes mellitus)
Increased concentration of homocysteine (hyperhomocysteinemia, damages the endothelium)
Heightened level of fibrinogen in the blood (one of the coagulation factors)
Genetic causes are also discussed.
As exogenous factors, smoking (nicotine damages the endothelium and promotes coagulation) and lack of exercise are the most important points to be considered in prevention. Further explanations for the development of arteriosclerosis are:
- Chronic infections
Medicines, such as birth control pills that contain estrogens
Increased number of cells in the blood (an increased hematocrit level)
Here we can see clearly that a lot of external factors can contribute to heart disease. This is actually a good thing, as we can control and, thus, manage our risks. The best way to do this is to eat a healthy and balanced diet, exercise regularly, keep stress and anxiety away with meditation and yoga, for example, and to not indulge in luxury items.
The peak frequency of a heart attack is around the age of 60 in men and around the age of 70 in women (previously protected against estrogen).
In America, 1.5 million of people suffer a heart attack every year and over the half of those affected (800,000) die within the first few hours of the consequences of a myocardial infarction. Given this number it is definitely worth to be more mindful of our health.
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