Myocardial infarction

The myocardial infarction ( IDM being a current abbreviation) is a Nécrose (death of cells) of part of the cardiac muscle . In current language, one generally calls it a heart attack . It occurs when one or more coronary arteries is stopped, the cells of the Myocarde (the muscle constituting the heart) irrigated by this (or these) artery (S) then are not oxygenated more, which causes their suffering (felt pain) and can lead to their Mort (scar of the infarction which will usually persist). The zone " infarcie" will not contract correctly any more.

Anatomy and terminology

There exist three essential coronary arteries (Inter-Ventricular former, Circonflexe and Coronary Right-hand side), which give all of the branches of unequal importance. These arteries irrigate (bring blood - Oxygen) each zone different from the heart. One can thus observe several Infarctions, according to (or of) artery (S) touched (S) and of the importance of the suffering of the muscular cells of the heart (myocardium).

According to topography

According to the anatomical extension, one distinguished the trans-mural infarctions classically , i.e. interesting the totality thickness of the cardiac muscle (myocardium), of the nontrans-mural , the latter being separate in rudimentary and under-endocardiques (interesting the internal part of the myocardium, in contact with the blood of the cavities). This distinction was put in correspondence with the various types of presentation on the electrocardiogram (ECG):

the infarction transmural corresponding to the presence of a wave Q broad and deep,
infarction under-endocardique correspondent with under shift of the segment ST,
rudimentary infarction corresponding to a negative wave T.

This anatomo-electrocardiographic correspondence, sails very about it in the years 1970-80, proved to be very often erroneous and is hardly any more used in the international publications.

In the same way, one distinguished the former infarctions or antéro-septal , the postéro-diaphragmatic , the inféro-basal on only electrocardiographic criteria by calculating a bijective correspondence with the injured artery. This relation is however law to be absolute and this terminology is also gradually abandoned.

Currently, the classification of the infarctions rests only on electrocardiographic criteria without prejudging anatomical real attack. One distinguishes as follows:

infarctions with wave Q;
infarctions without wave Q.

The territory of the infarction is named according to the topography of the electrocardiographic signs: a former infarction corresponds to an infarction whose wave Q visible in derivations is located “ahead” (V1-V2-V3) and not to an infarction interesting the former part of the myocardium (even if it is often the case).

One distinguishes as follows:

former infarctions (in V1-V2-V3 on the ECG);
lower infarctions (in D2, D3 and VF);
posterior infarctions (in V7-V8-V9);
apical infarctions (V4, V5 and V6);
side infarctions (D1, VL).

According to time

an acute infarction arrives at the hospital before the twelfth hour of the beginning of the pain: the essential problem is then to emerge the coronary artery to safeguard the maximum of muscle cardiac.
a subacute infarction or semi-recent arrives beyond the twelfth hour. The problem is not any more the removal of obstructions from the responsible artery, the essence of the damage being already made, but to avoid the complications.

The most frequent risk factors are: - lack of physical-activity - arterial hypertension - heredity - hyperlipidemy - tobacco - diabetes - obesity - the hypothyroïdie - stress

Mechanisms of occlusion

The Obliteration of a coronary Artère obeys, schematically, with two mechanisms:

formation of a thrombus, formation of a " caillot" of blood by the plates which are incorporated, released from the substances thrombogenes and start chain reactions, generally on the level of plate (S) of athérome preexistent (S) - the Athérome being a deposit which " encrasse" arterial walls - as the tartar which stops the drains -.
the coronary spasm, brutal reduction of the arterial light related to the vasomotricity of the Arteries, as in a crisis of Asthma where gauge of the bronchi car-tiny room spontaneously.

The two mechanisms join and car-discuss - each one reinforcing the activity of the other. Form most usual of coronary occlusion.

But there exist forms " pures" , spastic, more " classique" being the Prinz Metal , characteristic know-shift of ST on the electrocardiogram (ECG), on the condition of being able to record ECG at the good place, the good moment. The recording continuous ECG (Holter ECG) is an invaluable tool here, always provided that the spasm occurs during the examination.

Concurrently to this described in the past affection, exist perfectly authenticated infarctions, not being accompanied by the well-known know-shift. Infarction with coronary normals, healthy in Coronarographie (radiographies of the coronary arteries) or by endoscopy intracoronaire, less usual technique which consists in assembling a " caméra" - an apparatus with ultrasounds - microphone Echograph - as the echo of a fetus during the pregnancy, inside the coronary arteries.

These two forms require different treatments (not to say opposite). In all the cases, an occlusion of the coronary Artère occurs then, more or less supplements and, especially, more or less prolonged, causing an ischaemia (a lack of oxygen) of the territory myocardic. Beyond of a time evaluated at four hours, the death of the muscular cells of the heart will occur. The more the Ischémie persists, the more necroses it will extend and the more the zone infarcie will extend. It is to underline the factor time in the management of this medical emergency and the peremptory necessity for a meticulous, fastidious analysis of the examination of reference: the Electrocardiogram (ECG) including/understanding at least 12 derivations (12 " angles of vision" activity - electric - heart), whose recording must be of excellent quality (sometimes obstructed by the anguish, quite legitimate, of a person suffering and distressed) to affirm the myocardic Ischémie, if possible before the constitution of the Nécrose, to recognize of it the mechanism on which will depend the therapeutic attitude.

Risk factors

In half of the cases, it occurs without no risk factor being detected.

" Factors of risque" essential recognized today:

the tobacco
the Cholesterol
excess the age
the sex (male)
lack of
physical-activities the diabetes
the stress (infarctions recognized like occupational disease)
the blood hyper pressure
heredity (infarction in the family)

the list is unfortunately not exhaustive ........

It was observed that the daily catch in very minor amount of Aspirine, which supports the fluidity of the measurable blood of way (plate action anti-aggrégante - AAP-), clearly reduced the risks of infarction. The amount necessary however, is considered negligible at 84mg for an individual of average stoutness, which represents hardly the third of an amount for child as used in the preceding analgesics applications of aspirine. For the little story, the results of the study were if Nets as of the beginning which the conclusions could be about it drawn before even the completion date planned for the countryside from experiment (see Experimental design).

Diagnosis with the acute phase

Symptoms

The principal symptom is the thoracic pain. The pain relates to the area " retro-sternale" (behind of the Sternum). It is violent, usually intense (feeling of vice " crushing the cage thoracique"), prolonged and not (or little) sensitive to the Trinitrine (the trinitrine relieves the pains of Angina pectoris). It is known as " side-radiante" , irradiant in the back, the jaw, the shoulders, the arm, the left hand, the épigastre (stomach). It is distressing, oppressive (difficulties of breathing).

This description corresponds to the form " idéale" (if one can employ this word here). It is quasi-caricatural, book. It is B + has = BA.

In practice, all the variations exist, until the asymptomatic infarction (without pain, respiratory embarrassment, anguish, faintness, ANYTHING). The myocardial infarction can be discovered at the time of a Electro-Cardiogramme (ECG) " systématique" , for example at the time of a checkup. Still is necessary it to be able to recognize it (the analyzes automated according to various software placed at the disposal of the medical personnel providing of not very reliable information. Their interest is to draw the attention, if the program makes it possible to detect a " ECG anormal")

On the symptomatic level, the authors described forms known as " more trompeuses" , pains limited to one (or with) irradiation (S), forms " particulières" , " digestives" with type of epigastric pains (area of the stomach), abdominal high, forms where prevail such or such demonstration (for example " vagale" with sweats, faintness, feeling of heat, éructations), forms limited to a distressing oppression, of the forms dominated by a complication; faintnesses, sudden death, pulmonary edema (unexplained acute breathlessness), shock cardiogenic (impregnable pulses and tension), tamponnade (compression of the heart by one épanchement), disorders of the rate/rhythm (palpitations, faintness), of the psychiatric forms (brutal confusion), of the unapparent forms (without any symptom).

And there exists about it well of different .....

The essential problem is practically this one: to carry out a Electrocardiogram (ECG) in front of any demonstration which one does not have the certainty of the diagnosis and/or at people " exposées" (cf Risk factors) ....... And to analyze it correctly (cf supra), by being fully aware that to err is human ........

Physical signs

The clinical examination of the noncomplicated infarction is disappointing:
no the objective sign: the thoracic pains rétrosternales (bars sternale and/or dorsal), irradiant towards the arms or the top of the Thorax, the bottom of the Mâchoire, etc Essoufflement, feeling of tiredness, are elements brought by the interrogation which must be a quasi-police officer.
Only count: the credit that one brings there, " a dye gris" (with the dires of the close relations), the observation of frontal sudation, a Dyspnea, some small ants in the fingers and grouillements (?) thoracic (as after an intense meeting of muscu…). One can perceive, with the cardiac sounding, a noise known as of " galop" (disorder of the filling of the ventricle), a friction translating épanchement pericardial (tunic which entourre the heart). But it is not a usual Péricardite (ignition in viral rule and bégnine of the Péricarde, structure which entourre the heart and enables him to have movements of contraction).

Signs of gravity

One can classify them in several categories:

Bound to the " terrain" :

the age
the diabetes (increased risk of shock cardiogenic)
associated grave disease

Bound to the cardiac dysfonction:

wide infarction (electric diagnosis - on the Electrocardiogram)
cardiac failure
pulmonary edema
shock cardiogenic

Dependant on mechanical complications of the infarction:

tamponnade (compression of the heart by one épanchement)
communication inter ventricular
rupture of wall (side or different)
acute valvular insufficiency (mitral insufficiency by dysfonction or rupture of pillar)

Dependant on a disorder of the rate/rhythm (Ventricular Tachycardia) or conduction (auriculo-ventricular blocks).

Complementary examinations

Electrocardiogram with At least 12 derivations

The interpretation of a electrocardiogram (ECG) is not easy matter to achieve (cf remarks on the automated analyzes) One endeavors to study the whole of ECG and to seek, within 12 minimal derivations of the concordant signs of myocardic Ischémie.

Concordant wants to say: signs concerning, according to 12 minimal derivations - " angles of vue" electric operation of the heart - one (or several) territory (S) of very the paroie irrigated by a coronary Artery.

Extremely fortunately, the infarction touches only exceptionally the whole of the heart (infarction circonférenciels): the person, if she did not die, is on the way to die, in a table of Choc cardiogenic - not of pulse, not of tension -. The problem is then the vital reanimation aiming at restoring a effective Hémodynamique is an acceptable blood circulation. The forecast is appalling, short-term. But there are sometimes the divine ones surprised!

Twelve minimal derivations - these " angles of vue" - explore different zones of the heart: former wall, Septum interVentriculaire, wall side, wall lower (or inféro-basal), Ventricle Right. These twelve derivations are " regroupées" , several derivations (2 or 3) exploring, in manner a a little different (the visual angle is not completely the same one) wall of the heart.

If it ya ischaemia, it must exist one (or of) zone (S) - " topographiques" - which suffers. L" electric aspect of these ischémiées zones CONSTRASTE with the aspect of the zones remained healthy, nonconcerned by the process, because irrigated by another artery or irrigated by branches of the injured artery, these branches being born upstream from coronary occlusion. This souffrace concordant, is found in part of twelve derivations.

The diagnosis of ECG is thus a topographic diagnosis. It is a question of authenticating the zone (zones) ischémiée (S). This ischaemia is present only in derivations exploring (in a a little different way) the same territory. It is this agreement of the signs, according to derivations, different but " regroupée" , which signs myocardic ischaemia and makes it possible to locate the wall reached. This aspect contrasts with that of the territories remained unscathed.

But the correspondence ECG - anatomical lesion is far from being constant.

In practice, there is a " center" (zone where ischaemia is deepest) and of the " adjacent zones of extension" , known, according to the anatomy of the Ventricles (Left Venticule in rule, because it is subjected to pressures 10 times higher than those of the Ventricle Right and thus much more " vulnérable") and anatomy of the coronary arteries.

Electric descriptions " classiques" pursue the study themselves

of complexes QRS (corresponding to the contraction of Venticules)
of the repolarization (corresponding to relieving (" repos") ventricles, during which they fill " passivement"): segment ST, wave T.

Schematically: the modifications induced by the Ischémie relate to the repolarization: " disorders of the repolarization"

Know-shift of the segment ST,
Under-shift of the segment ST, inversion or excessive positivation of the wave T

The modifications induced by necroses relate to complexes QRS:

Wave Q (larger than a third of another QRS and than 1mm

Attention, the wave Q can be the result of an old infarction or reflect the activity of important Inter-Ventricular Septum (or hypertrophied).

Proportioning of the cardiac Enzyme S

Troponine I or T
CPK-MB, fraction MB of the Creatin phosphokinase

Appearance of these " enzymes cardiaques" in blood (with significant concentrations) is a marker of necroses (death) cells of the myocardium, which revêt a diagnostic interest (infarction without significant ElectroCardioGraphique modification) and prognostic. The importance of enzymatic rise is proportional to the importance of the infarction (one speaks about infarction with " peak of TROPONINE" to 10, for example. Proportionings thus should BE REPEATED, to follow the evolution of it.

SGOT
alphahydroxybutyrate déshydrogénase (HBDH)

myocardic Scintiscanning

Scintiscanning with the ²⁰¹ Thallium in time of effort and rest.
Scintiscanning with ²⁰¹thallium associated with vector MIBI (Cardiolite^ʀ).

Assumption of responsibility of the infarction

First aid

The diagnosis of myocardial infarction is of a medical nature. This one thus escapes in theory competence from the first-aid worker or the witness rescuer, from whom it will seem either a faintness, or like an cardiac arrest (sudden death). In the case of a faintness, one should not be ventured with a pseudo-diagnosis: a person can have a myocardial infarction without feeling the typical signs (neither thoracic pain, nor pain in the radiant jaw in the left arm), and contrary, a person can feel her signs without it making a myocardial infarction. In all the cases, any faintness must be regarded as being able to evolve to a vital urgency and requires a making of contact with a doctor, who will establish a diagnosis.

For a Malayan:

one puts the person at rest in the position where it feels best, one proposes in this case the position semi-base (lengthened legs, tilted raised bust);
one questions it on what it feels, the circumstances of occurred of faintness (in particular since how long), the antecedents (this is the first time that it feels this faintness, takes it drugs, it was hospitalized)
one prevents the medical Régulation (“112” in the European Union, the “15” in France, “144” in Switzerland, “100” in Belgium, “911” Quebec, to see emergency Call number ) by transmitting the maximum of information,
one returns to supervise the victim and one applies the councils given by the medical regulation;
within the framework of the Prompt help: setting under inhalation of Dioxygène with a flow of 15 L/min.

For a cardiac arrest:

one protects so necessary,
one prevents immediately the helps (like above);
one practices the cardiopulmonary Réanimation while waiting for the helps;
use of a automatic Défibrillateur so available.

Hospital treatment

It is about a SERIOUS medical emergency : it is shown that the earlier the removal of obstructions from the responsible coronary artery is, the less there will be after-effects. This removal of obstructions will have to be made before the twelfth hour, and if possible, before the first hours. Any suspicion of infarction (in practice prolonged thoracic pain) must lead to the call of the medical Régulation (see emergency Call number ).

The diagnosis must be certain.

In addition to the assumption of responsibility of the pain and possible complications, the crucial problem is as soon as possible to emerge (at best in the first four hours) to it (or them) artery (S) coronary (S) concerned (S):

Is by a " treatment; médical" , using products which aim at destroying (" lyser") the thrombus (blood clot) obtruant the artery; it is the " THROMBOLYSE - FIBRINOLYSE" (injection by simple intravenous way - as at the time of a blood test - of a drug which will dissolve the clot in the artery.
Is removal of obstructions " instrumentale" , while introducing, aucours of a CORONAROGRAPHIE (radiographies of the coronary arteries) a microphone catheter in the artery to dilate the lesion (lesions) responsible (S); it is the ANGIOPLASTIE (dilation of the injured zone), often associated with the installation of a STENT (arises), in a specialized center.

It will always be necessary to make sure of the success of the désobtruction:

disappearance of the symptoms (pain primarily), standardization of the electrocardiogram (ECG) in the event of fibrinolyse;
checking of the permeability of the artery dilated in the event of angioplastie;
standardization of the rate of the " enzymes cardiaques" in all the cases.

Sometimes, these measurements can prove indeed partially even completely ineffective (multiplicity of the coronary arteries concerned, extended from the obstructions, insuperable complete obstruction, particular seat and/or anatomical character of the lesions). The treatment is then medical " classique" and must allow TO LIMIT the size of the INFARCTION, to ensure the good comfort of the patient (often painful and distressed), to prevent occurred of complications, to ensure of the satisfactory hemodynamic conditions by maintaining (or while restoring) the capacities of the heart (which ensures the flow of blood in the whole of the organization - brain, kidneys, lungs heart itself…). Once a " cap" crucial last, a specialized surgeon will carry out one (or more often of) Aorto-Coronary Bridgings (PAC). Défibrillation, Thrombolyse/Fibrinolyse, Angioplastie, poses of a Stent, aorto-coronary Pontage

Complications

The Troubles of the cardiac rhythm are a frequent complication.

See too

External bonds

Dealt with of the acute coronary syndrome (SCA) (@ Urgencies Online 2006)
acute coronary Syndromes, the intervention of the general practitioner, the General practitioner n°2275, January 30th 2004
conceptual Chart presenting the factors being able to lead to the their relation and myocardial infarction (in English)

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