Acute Myocardial Infarction (MI),احتشاء عضله القلب

 Acute Myocardial Infarction (MI)

introduction:

Most myocardial infarctions are caused by a disruption in the vascular endothelium associated with an unstable atherosclerotic plaque that stimulates the formation of an intracoronary thrombus, which results in coronary artery blood flow occlusion. If such an occlusion persists for more than 20 minutes, irreversible myocardial cell damage and cell death will occur.

The death of myocardial cells first occurs in the area of myocardium most distal to the arterial blood supply: the endocardium. As the duration of the occlusion increases, the area of myocardial cell death enlarges, extending from the endocardium to the myocardium and ultimately to the epicardium. The area of myocardial cell death then spreads laterally to areas of watershed or collateral perfusion. Generally, after a 6- to 8-hour period of coronary occlusion, most of the distal myocardium has died. The extent of myocardial cell death defines the magnitude of the MI. If blood flow can be restored to atrisk myocardium, more heart muscle can be saved from irreversible damage or death.

The severity of an MI depends on three factors: the level of the occlusion in the coronary artery, the length of time of the occlusion, and the presence or absence of collateral circulation. Generally, the more proximal the coronary occlusion, the more extensive the amount of myocardium that will be at risk of necrosis. The larger the myocardial infarction, the greater the chance of death because of a mechanical complication or pump failure. The longer the period of vessel occlusion, the greater the chances of irreversible myocardial damage distal to the occlusion.

Definition:

Myocardial Infarction is a life threatening condition characterized by the formation of localized necrotic area within the myocardium. MI usually follows the sudden occlusion of coronary artery, stop of blood and oxygen flow to the heart muscle.

Or

It is the irreversible death (necrosis) of heart muscle secondary to prolonged lack of oxygen supply (ischemia). Myocardial Infarction = Heart attack = coronary occlusion.

Risk factors:

• As In coronary artery disease the causes is Atherosclerosis and block of artery by thrombi and blood supply to the heart is abrupt, also coronary artery spasm and hemorrhage may lead to MI.

• Six primary risk factors have been associated with the development of atherosclerotic coronary artery disease and MI:

1.  hyperlipidemia
2.  diabetes mellitus
3.  hypertension
4.  tobacco use
5.  male gender
6.  family history of atherosclerotic arterial disease

Chest pain in acute MI has the following characteristics:

•  Chest pain described as asubsternal pressure sensation, fullness, squeezing, aching, burning, or even sharp in the mid portion of the thorax.

•  Intense and unremitting for 30-60 minutes

•  Radiation of chest pain into the jaw or teeth, shoulder, arm, and/or back.

•  Associated dyspnea or shortness of breath.

•  In some patients, associated epigastric discomfort with a feeling of indigestion or fullness and gas with or without nausea and vomiting.

•  Associated diaphoresis or sweating.

•  Syncope or near syncope without other cause.

•  Impairment of cognitive function without other cause.

This table show comparison between heartburn for patient with heart attack and gastrointestinal disorder:

Diagnostic Tests:

•  ECG

•  MRI.

•  Echocardiograph.

•  Cardiac enzymes

Treatment :

The goals of medical management are to minimize myocardial damage, preserve myocardial function, and prevent complications.

• Morphine administered in IV boluses is used for MI to reduce pain and anxiety.

•  ACE Inhibitors. ACE inhibitors prevent the conversion of angiotensin I to angiotensin Il to decrease blood pressure and for the kidneys to secrete sodium and fluid, decreasing the oxygen demand of the heart.

•  Thrombolytics. Thrombolytic dissolve the thrombus in the coronary artery, allowing blood to flow through the coronary artery again, minimizing the size of the infarction and preserving ventricular function.

• Emergent Percutaneous Coronary Intervention

•  PCI may also be indicated in patients with unstable angina and NSTEMI for patients who are at high risk due to persistent ischemia.