Myocardial Infarction: Definition, Causes, Characteristics, Diagnosis, Course

Myocardial infarction is one of the most common causes of death in Germany. The definition of a heart attack is: death of a part of the heart muscle of varying size due to lack of oxygen with complications, some of which are life-threatening. Here you can learn how and why a heart attack occurs, how to recognize it and what to do if you suspect a heart attack.

How does a heart attack develop?

As the engine of the circulatory system, the heart represents the driving force of all blood flow processes in the organism. Of course, the heart muscle also requires an adequate supply of oxygen for its continuous, highly energy-consuming pumping activity. The blood supply to the heart muscle is ensured by the coronary vessels, which originate directly at the outlet of the aorta and fan out on the surface of the heart like the branches of a tree crown. The heart muscle reacts very sensitively to circulatory disturbances lasting only seconds, whereas the human arms or legs, for example, can tolerate a loss of blood flow, sometimes for several hours, without significant damage. Myocardial infarction occurs when blood flow to the heart muscle via the coronary arteries is acutely restricted to such an extent that part of the heart muscle dies.

Causes of a heart attack

In the vast majority of cases, such a heart attack is caused by chronic calcification of the coronary vessels, which is promoted by high blood pressure, diabetes, dyslipidemia, gout, obesity, smoking and genetic factors. Like calcium deposits in the pipes of a washing machine, narrowing of the coronary arteries occurs over the course of decades. When an important vessel is completely blocked – usually by an additional small blood clot – a heart attack occurs. However, heart attack mechanisms are also conceivable in which the coronary vessels are healthy. This would be the case, for example, if a blood clot from the heart itself is carried along with the blood flow, enters the coronary vessels, clogs a healthy vessel there and triggers the heart attack. In very rare cases, acute thrombosis of a primarily healthy coronary vessel or even vascular spasm can also be considered as triggers of a heart attack. The possible causes of a myocardial infarction once again at a glance:

General information about heart attacks

Myocardial infarction is the most serious complication of coronary artery disease. In Western industrialized nations, it ranks high in the cause of death statistics. On average, approximately 300 to 400 of every 100,000 35- to 64-year-old men die as a result of a heart attack. Between the ages of 45 and 50, heart attacks occur significantly more frequently in men than in women. In older people, these differences level out again. In addition, it can be observed that the incidence of both coronary heart disease and heart attacks has increased significantly in women over the last few decades – most likely as a result of nicotine consumption and use of the contraceptive pill. Arteriosclerosis of the coronary arteries can take on very different individual forms and can also lead to a wide variety of symptoms. If there is only a slight narrowing of the coronary vessels – usually less than 70 percent of the vessel diameter – no symptoms need occur at all. The extreme form would be the complete occlusion of a coronary vessel with a heart attack. In between, there are fluid transitions between angina pectoris symptoms during intense physical exertion (exertional angina) to angina pectoris at rest (resting angina), which can already be a harbinger of a heart attack. In addition, the severity of a patient’s symptoms in the presence of coronary artery calcification also depends on his or her physical training status and possible concomitant diseases, such as diabetes.

Characteristics and symptoms

Regular physical training improves blood flow to the heart muscle, which is accordingly better equipped to protect against a heart attack. The heart attack in some cases can be the first and at the same time the most dramatic manifestation of the atherosclerosis on the coronary arteries.Thus, a seemingly healthy person may experience a fatal heart attack out of the blue. However, the heart attack can also be at the end of a long-term increase in angina pectoris symptoms. In a classic heart attack, the following symptoms exist:

  • Strong, pressing chest pain in part with radiation into the left arm (“as if an iron ring tightens around the chest”).
  • Cold sweating
  • Shortness of breath
  • Paleness
  • Flat, rapid pulse
  • Feelings of anxiety

However, a heart attack can also hide behind far less typical symptoms such as jaw pain, abdominal pain, back pain, nausea, vomiting, shortness of breath, fainting spells or cardiac arrhythmias. In individual cases, one also speaks of silent heart attacks, which are usually diagnosed by chance in an electrocardiogram (ECG) years later.

Rapid action required

If a heart attack is suspected, the highest level of alert is required. Even of those patients who can still be brought to the hospital in this life-threatening emergency situation, 15 to 30 percent die in the hours that follow. If the heart attack is survived, three percent of patients still die each year from complications such as malignant cardiac arrhythmias, recurrent heart attack or heart failure. Lay people in particular like to speculate about the specific causes of a heart attack in individual cases. Contrary to popular belief, experience has shown that it is much more often rest and relaxation situations than stress situations in which heart attacks occur.

Diagnosis by ECG and blood tests

Diagnosis can only be made with certainty by means of an ECG and certain blood tests if the symptoms are appropriate, since the transitions between circulatory disturbances in angina pectoris and a real heart attack are fluid. In the ECG, the physician sees typical changes that indicate a heart attack: in addition, the region of the heart – anterior wall, posterior wall or lateral wall – that is affected by the infarction can already be determined. The blood tests, in turn, provide information about the extent and stage of the heart attack. Indeed, it is crucial for treatment to know the exact stage and ideally to initiate initial measures at the earliest possible stage of the heart attack.

Progression in myocardial infarction

If the onset of the heart attack was already more than four to six hours ago when the diagnosis was made, major irreversible damage to the heart muscle must already be expected. The dead part of the heart muscle is normally replaced by the body within 10 to 14 days by a connective tissue scar like after a burn of the skin. This scar material, of course, does not have the efficiency of the formerly intact heart muscle, so heart muscle weakness to the point of heart failure often persists after a heart attack.

When a definitive diagnosis is not possible

Sometimes the diagnosis cannot be made unequivocally-especially in small infarcts. However, when in doubt, a patient is treated as if he or she had a real infarction for safety reasons. In addition to indirect methods such as blood tests and ECG, the changes in the coronary arteries themselves can only be seen directly by cardiac catheterization. In this procedure, the coronary vessels are visited via long plastic tubes that are advanced to the heart through the inguinal vessels and visualized with X-ray contrast medium. Classically, an occluded infarct vessel is found in acute myocardial infarction. In addition, a reduced contractile force can be detected in the region of the heart muscle that was previously supplied with blood by the infarct vessel. Even years after a heart attack, the regionally reduced contractility of the heart muscle persists and can be diagnosed by cardiac catheterization or – far less complex – by ultrasound examination of the heart. However, if the coronary vessels are unremarkable on cardiac catheterization in acute infarction, embolic infarction (with self-dissolution of the blood clot) or, rarely, vasospastic infarction is suspected.