Cardiovascular Diseases / / August 12, 2017
Etiology and pathogenesis
Myocardial infarction - an acute disease caused by the occurrence of one or more foci of ischemic necrosis of the heart muscle due to absolute or relative failure of the coronary circulation.The most frequent cause of disturbances in coronary blood flow is atherosclerosis of the coronary arteries.On the intima of blood vessels are formed atherosclerotic plaques protruding into the lumen.Grow to a considerable size, plaques cause narrowing of the vessel lumen.Naturally, the myocardium portion that receives blood through the vessel - ishemiziruetsya.When fully closed lumen blood flow to the corresponding section of the myocardium stops - develops necrosis (infarction) of the myocardium.It should be noted that the coronary artery lumen could be obturated both the atherosclerotic plaque and thrombus formed on the surface of the vessel ulcerated plaque.
Myocardial infarction in a small percentage of cases may be associated with functional impairment, accompanied by spasm of the
cause of myocardial infarction may be some diseases, such as bacterial endocarditis, in which the possible closure of embolism and coronary artery lumen thrombotic masses;systemic vascular lesions involving the arteries of the heart in the process and some other diseases.
Depending on the size of necrosis distinguish melkoochagovyj macrofocal and myocardial infarction.In necrosis prevalence of heart muscle depth are the following forms of myocardial infarction: subendocardial (necrosis in the bed of the myocardium, adjacent to endocarditis), subepicardial (defeat layers myocardium adjacent to the epicardium), intramural (necrosis develops inside the walls before reaching the endocardial and epicardial) andtransmural (damage extends throughout the thickness of the myocardium).
most striking and constant symptom of acute myocardial infarction is an attack of intense pain.Most often, pain is localized behind the breastbone in the heart and may radiate to the left arm, shoulder, neck and lower jaw, in the back (in interscapulum).Pain in the retrosternal region often observed in myocardial anterior wall;localization of pain in the epigastric region more often observed in myocardial infarction of the rear wall.However, the precise localization of a heart attack can be determined only on the basis of ECG data as a clear correlation between the localization of pain and no necrosis.
pain is squeezing, crushing or bursting with character.The duration of pain attack in acute myocardial infarction from 20-30 minutes to several hours.The duration of pain attack and the lack of effect of nitroglycerin distinguish acute myocardial infarction from angina.Intensity of pain is not always corresponds to the amount of myocardial lesions, but in most cases a long and intense pain attack observed infarct myocardium.
pain is often accompanied by a sense of fear of death, lack of air.Patients with excited, restless, groaning in pain.In the future, usually develops severe weakness.
There are atypical forms of myocardial infarction, first described Strazhesko and VP Obraztsov.Along with the classical authors have identified a form of the disease manifests itself in early abdominal pain and dyspnea or shortness of breath.For these forms is characterized by the absence of typical myocardial infarction pain in the heart.Diagnosis of myocardial infarction, it is very difficult.For example, abdominal pain, vomiting, dyspepsia, often regarded as a food intoxication.Naturally, gastric lavage in this case will only aggravate the severity of the patient's condition.A crucial role in the diagnosis of myocardial infarction in this case, play the ECG data.Pain is the main but not the only characteristic symptom of myocardial infarction.There are several clinical and laboratory signs of the disease.Thus, as a rule, the body temperature rises to 38-38,5 ° C.Appears leukocytosis, marked shift in leukocyte formula to the left, later increased ESR.Increasing the activity of several enzymes - lactate dehydrogenase and its enzymes, creatine kinase, aspartate aminotransferase.All the above features are associated with the processes of absorption and necrotic masses aseptic inflammation in the tissues adjacent to the necrotic zone.
most important method for diagnosing myocardial infarction is electrocardiography. electrocardiographic signs of myocardial infarction are ST-segment changes, Q-wave and T-wave segment ST Shifting up and down from the isoelectric line appears in the very first hours of myocardial infarction.It should be noted discordance displacement of ST - segment elevation in leads placed over the area of infarction, and reduced this segment in leads, reflecting the activity of the healthy myocardium.
appearance of deep and wide Q wave is a sign of myocardial necrosis.Q wave is considered to be deep, if the amplitude of more than 25% of the Q wave amplitude in leads III and avF and over 15% of the amplitude of the wave R - in the left chest leads.
In the first hours and days of myocardial infarction may be observed an increase in the T wave, which merges with the raised interval S - T. Then, as you get closer to the ST segment contours, the height of the T wave is reduced and it turns from positive to negative."Coronary tooth" T may persist for many months or even years.
for myocardial anterior wall of the left ventricle is characterized by changes in the I, II and chest leads (Y2-Y4).
ECG in myocardial infarction.
and - infarction left ventricular posterior wall;B - front left ventricular myocardial wall.
Myocardial infarction left ventricular posterior wall of the main changes occur in leads II, III and aVF.
Complications of acute myocardial infarction
severity of myocardial infarction is largely determined by the complications that can occur in the first hours and days of illness.Complications developed in the first 3-5 days of myocardial infarction in 80% of cases are fatal.The most common cause of death after myocardial infarction - cardiogenic shock.When 'true' cardiogenic shock mortality rate is 80-90%.It usually develops in the first hours of myocardial infarction, often against a background of strong pain attack, but can also occur when a painless manner.
clinical picture of cardiogenic shock has several characteristic features:
1. On examination, the patient marked pointed facial features, pale skin, cold clammy sweat.Consciousness confused, lethargic patient, the surrounding barely reacts.
2. Pulse frequent, thready.Blood pressure is reduced.However, in some cases, shock may occur under normal systolic blood pressure of 100-120 mmHg figures.Art.(For example, in patients with baseline hypertension).Typically a decrease in pulse pressure (the difference between systolic and diastolic blood pressure).Typically, pulse pressure - less than 30 mm Hg.Art.
3. Heavy prognostic symptom is anuria or oliguria.Urine output is less than 20 ml / h.
4) true cardiogenic shock - is caused by a sharp decline in contractility of the left ventricle due to extensive myocardial damage;in this case shows a therapy aimed at increasing myocardial contractility;
5) arrhythmic shock - is associated with the occurrence of arrhythmias;most often it is a complete transverse blockade or ventricular paroxysmal tachycardia.This form of shock has a favorable prognosis;shock symptoms usually disappear after recovery of heart rate.
most frequent complication of myocardial infarction - a violation of cardiac rhythm and conduction. These disorders occur in almost all patients with myocardial macrofocal in the 1st day of the disease, and more than half of the patients - on the 2nd day.
In patients with myocardial infarction develop arrhythmias: Atrial premature beats, paroxysmal atrial tachycardia, atrial fibrillation, atrial flutter, ventricular premature beats, ventricular tachycardia, ventricular fibrillation.conduction disorders can manifest varying degrees of atrioventricular block.
90% of patients experiencing ventricular arrythmia.Ventricular premature beats often a harbinger of more severe arrhythmias - ventricular tachycardia and ventricular fibrillation.Particularly poor prognosis with frequent (more than 10 per minute) beats.For ventricular arrhythmia characteristic.
arrhythmia in myocardial infarction (ECG)
1) the occurrence of premature QRS complex, which broadened and deformed as compared with the QRS complexes in normal cycles;
2) the absence of P wave before the QRS complex;
3) T wave is directed to the opposite side of the QRS;
4) after the beats there is a "compensatory" pause, a longer than normal after complex.
Ventricular tachycardia - is rhythmic and very frequent (140 to 300) contraction of the ventricles.Clear distinction between the group of ventricular premature beats and paroxysmal ventricular tachycardia not.Regardless of the duration of the paroxysm of ventricular tachycardia prognosis is very unfavorable, since both the long and short paroxysms can go into ventricular fibrillation.
arrhythmia in myocardial infarction (ECG)
Ventricular fibrillation - the most common immediate cause of death in patients with myocardial infarction.
Among other complications of myocardial infarction occur: pulmonary edema, cardiac aneurysm, thrombosis in various organs, pericarditis, pleurisy.
General principles of treatment of patients with acute myocardial infarction
1. The primary objective of intensive therapy in acute myocardial infarction is the relief of equity attack.One of the oldest means of combating pain are opioids - morphine or omnopon (1-2 ml of 1% solution).However, these agents can cause adverse side effects - depression of the respiratory center, vomiting, paresis of the stomach and intestines.
2. Myocardial infarction complicated by cardiogenic shock, shows the introduction of sympathomimetic.
3. In order to prevent the formation and growth of intracoronary thrombus, as well as for the prevention of thromboembolic complications administered fibrinolytic and anticoagulant agents.At the same time injected intravenously with 10 000 IU of heparin, heparin, and then begin to introduce drip.