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Myocardial Infarction

Infart de miocardi

Acute myocardial infarction (AMI), commonly known as a heart attack, is the necrosis –the degeneration of tissues due to cell death– of a part of the heart, caused by an interruption in blood flow (ischaemia). The most common cause is the obstruction of a coronary artery (the arteries that supply blood to the heart itself) by a blood clot formed by the rupture or erosion of an atherosclerotic plaque. In the absence of atherosclerosis, there are other, less frequent mechanisms that can cause this condition, such as strokes, dissection, and coronary artery spasms. The main factor determining the prognosis and initial course of treatment is whether the obstruction of blood flow to the heart is total and persistent or not. The former case is a medical emergency, since the entire myocardial area irrigated by the obstructed artery will die if the blood flow is not quickly restored. The latter, without total and persistent blockage, constitutes a less severe heart attack and treatment is not as urgent. The clinical presentation, in which the symptoms and initial signs can be characterised, and, most importantly, the electrocardiogram (ECG) results, help distinguish between these two scenarios. AMI is one of the leading causes of death worldwide, since it goes hand-in-hand with a high risk of serious complications, such as malignant arrhythmias, especially in the first few hours following the heart attack. It is also a common cause of long-term disability. Even with the considerable therapeutic advances of the past few decades, it is still a serious condition. A timely diagnosis and treatment initiation is essential in improving the prognosis.

Description

The symptoms

The most common symptom is chest pain, usually described by patients as a kind of pressure in the middle of their chest, which often radiates to the arms, neck, jaw, or back; it starts off as mild pain and progressively increases in intensity. It is sometimes defined as a burning sensation, and it can occur in other parts of the body, such as the stomach area. 

Often, it is accompanied by a subjective feeling of weightiness, cold sweats, nausea, and vomiting. Sometimes, especially in the elderly, in women, and in diabetic patients or those with other chronic diseases, the pain is not as obvious or it is accompanied by other symptoms such as shortness of breath, fatigue, or feeling unsteady. 

AMI can occur suddenly, as the first sign of ischaemic heart disease, but often, patients have had prior, brief episodes of chest pain, usually upon physical exertion, which should serve as a warning that they may have an unstable coronary injury. Other associated symptoms, such as trouble breathing, fainting, confusion, drowsiness, or extreme weakness usually indicate the presence of serious complications of AMI such as heart failure, arrhythmia, or cardiogenic shock.

  

Who does it affect? 

Many people, since ischaemic heart disease is the leading cause of death worldwide. According to the WHO, in 2016, it caused close to 10% of deaths overall, surpassing strokes and chronic obstructive pulmonary disease. In Europe, the mortality rates due to ischaemic heart disease and cancer are quite similar. The prevalence of AMI and ischaemic heart disease in general is less in the Mediterranean countries than in the Northern or Eastern European countries. 

In Spain, there are some 100,000 cases of AMI per year, a third of which prove to be fatal before the patient reaches the hospital. The prognosis for hospitalised patients has improved greatly in the past few decades; the current hospital mortality rate here is close to 5%. 

The prevalence of AMI increases at advanced ages. Although it is commonly believed that AMI is a condition that affects mostly men, its prevalence is similar in both sexes. What happens is that men usually develop this condition starting in their forties, whereas women see an increased incidence of the disease 10-20 years later, almost always after menopause. However, young women can also have an AMI. 

Anyone can suffer an AMI, but there are risk factors that are closely associated with a higher risk. The most characteristic of these are those related to any kind of atherosclerosis, such as tobacco use, diabetes, hypertension, and high cholesterol. There are also genetic traits associated with an increased predisposition to the illness. 

Lastly, there are factors that can provoke a rupture in the atherosclerotic plaque or a thrombotic response and trigger an AMI, such as:

  • tobacco use¡
  • cocaine use
  • pollution
  • intense physical or mental stress

 

Diagnosis 

It is of the utmost importance to identify those patients with complete coronary artery blockage, and who therefore require urgent reperfusion treatment (which restores the blood flow to the blocked arteries), as soon as possible. Every minute counts when it comes to saving myocardial tissue. 

In most cases, this identification can be done by assessing the symptoms and analysing the ECG. Therefore, patients with chest pain or other symptoms consistent with an AMI should immediately seek medical attention, and medical staff should perform a clinical evaluation and ECG analysis without delay. 

The safest and most effective way to do this is to call 112, as the Spanish Medical Emergency System usually evaluates these patients faster than most accident and emergency departments at health centres and hospitals. In addition, when an AMI requiring immediate catheterisation is detected, the treatment process is initiated at the site where the patient first receives medical attention and they are transferred to a hospital that is equipped for the procedure they need. Moreover, the patient is received directly at the cardiac catheter laboratory, where a team will have already been alerted and will be waiting for them, without losing time having to first go through the emergency department.  

In Patients with an ECG that is normal or whose ECG shows ischaemic changes but in whom a complete coronary artery blockage is not suspected, do not require immediate catheterisation and can be evaluated with less urgency at an accident and emergency department. An AMI diagnosis is confirmed by the presence of elevated myocardial necrosis markers in the blood analysis. 

 

Typical treatment 

From the moment they are diagnosed, AMI patients' heart rate must be continuously monitored to detect and treat serious ventricular arrhythmias, in case they occur. They should be admitted to a cardiovascular intensive care unit or intermediate care unit, depending on their initial risk assessment, and once they are stabilised, they can be transferred to the general ward. The average length of hospital stay due to a non-complicated AMI is 4 to 5 days. 

            

AMI patients require antiplatelet drugs to combat thrombosis and a coronarography is also recommended in all cases. When an acute coronary occlusion is suspected, the coronarography must be performed quickly so than an angioplasty can be carried out to re-open the obstructed artery as soon as possible. Often, a coronary stent, a device that reduces the risk of reobstruction, is simultaneously implanted. If an urgent coronarography cannot be done, for example because the patient is located in an area very far away from a hospital equipped for this procedure, pharmaceuticals can be administered to dissolve the coronary thrombus. 

 

In all other AMI cases, the coronarography and revascularisation are carried out within the first few days of admission. Some patients may require coronary bypass surgery instead of percutaneous revascularisation and stenting, due to the characteristics of their cardiovascular injuries. Apart from this, all patients will receive pharmaceuticals to reduce their cholesterol, and those with severe heart attacks will require specific medications to improve their ventricular dysfunction and prognosis. Participating in cardiovascular rehabilitation programmes after discharge has been shown to improve the prognosis and fosters patient adherence to healthy lifestyle guidelines.

 

Some patients who experience complications may require implantable electronic devices such as pacemakers or defibrillators, and more severe cases may warrant aggressive interventions such as:

  • Respiratory support
  • Dialysis
  • Ventricular assist devices 
  • Heart transplants

 

Prevention

The risk of suffering an AMI can be reduced with preventative health measures, including controlling one's diet. Regular physical exercise and avoiding being overweight are very beneficial to this end. One's diet should be balanced, and following a Mediterranean diet rich in virgin olive oil, vegetables, fruits, legumes, and fish, supplemented with nuts and with a limited intake of red meat and sugar, is the healthiest option. Tobacco consumption should be completely eliminated, and it is wise to avoid heavy exposure to pollution, as well as strenuous activity and high-stress situations.

For patients with cardiovascular risk factors, medications to control cholesterol, hypertension, and diabetes are often recommended, and in very high-risk patients, prophylactic therapy with antiplatelet drugs may be warranted.

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