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Myocardial Infarction

78 bytes added, 04:37, 18 January 2010
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Ischemia occurs when part of the heartmuscleheart muscle, the myocardium, is deprived from of oxygen and nutrients.
Common causes of ischemia are:
* Narrowing or obstruction of a coronary artery.
* A rapid arrhythmia, causing a disbalance an imbalance in supply and demand of for energy.
A short period of ischemia causes ''reversible'' effects: The heartcells heart cells will be able to recover. When the episode of ischemia lasts for a longer period of time, heartmuscle heart muscle cells will die. This is called a '''heart attack''' or '''myocardial infarction'''. That is why it is critical to recognize ischemia on the ECG in an early stage.
Severe ischemia results in ECG changes within minutes. While the ischemia lasts, several ECG changes will occur and disappear again. Therefore, it may be difficult to estimate the duration of the ischemia on the ECG, which is crucial for adequate treatment.
* Nausea
* Shock (manifesting as paleness, low blood pressure, fast weak pulse) shock
* Rhythm dysturbances disturbances (in particular , increasing prevalnce prevalence of ventricular ectopia, ventricular tachycardia, AV block)
===Risk assessment of Cardiovascular disease===
The narrowing Narrowing of the coronary artery , leading to a myocardial infarction, usually develops over several years. An increased risk of cardiovascular disease, which may lead to a myocardial infarction or strokecerebrovascular accident, can be estimated using [ SCORE system] which is developed by the European Society of cardiology (ESC).
As shown in the figure, the most important risk factors for myocardial infarction are:
*Male sex
===Risk assessment of ischemia===
An [[Exercise Testing|exercise test]] such as a bicycle or treadmilltesttreadmill test, may be usefull useful in detecting myocardial ischemia after exercise.<cite>accexercise</cite> In such a test, a continuous ECG registration monitoring is performed during exercise. The ST-segment, blood pressure asnd and clinical status of the patient (i.e. chest complaints) are monitorered monitored during and after the test.
An [[Exercise Testing|exercise test]] is positive for myocardial ischemia when the following criteria are met:
* Horizontal or downsloping ST-depression of > 1mm, 60 or 80ms after the J-point
* ST elevation of > 1.0 mm
* Elevated blood levels of cardiac enzymes ([[w:Creatine_kinase|CKMB]] or [[w:Troponin|Troponin T]]) AND
* One of the following criteria are met:
** The patient has typical complaints,** The ECG shows ST elevation or depression.
** [[Pathologic_Q_Waves|pathological Q waves]] develop on the ECG
** A coronary intervention had been performed (such as stent placement)
So detection of elevated serum heartenzymes is more important than ECG changes. However, the heartenzymes cardiac enzymes can only be detected in the serum 5-7 hours after the onset of the myocardial infarction. So , especially in the first few hours after the myocardial infarction , the ECG can be crucial.
ECG Manifestations of Acute Myocardial Ischaemia (in Absence of LVH and [[MI Diagnosis in LBBB|LBBB]])are <cite>Thygesen</cite>:
;ST elevation
:New ST elevation at the J-point in two contiguous leads with the cut-off points: ≥ 0≥0.2 mV in men or ≥ 0.15 mV in women in leads V2–V3 and/or ≥ 0.1 mV in other leads.;ST depression and T-wave changes.:New horizontal or down-sloping ST depression > 0.05 mV in two contiguous leads; and/or T inversion ≥ 0≥0.1 mVin two contiguous leads with prominent R-wave or R/S ratio ≥ 1
A study using MRI to diagnose myocardial infarction has shown that more emphasis on ST segment depression could greatly improve the yield of the ECG in the diagnosis of myocardial infarction (sensitivity increase from 50% to 84%).<cite>martin</cite>
Myocardial infarction diagnosis in left or right bundle branch block can be difficult, but it is explained in these seperate chapters:
*[[MI Diagnosis in LBBB]]
*[[MI Diagnosis in RBBB]]
<gallery perRow="2">
Image:coronary_anatomy.png| An overview of the coronary arteries. LM = 'Left Main' = mainstem; LAD = 'Left Anterior Descending' artery; RCX = Ramus Circumflexus; RCA = 'Right Coronary Artery'.
Image:lead_overview.png|Overview of the seperate separate ECG leads. The lead with ST segment elevation 'highlights' the infarct. An infarction of the inferior wall will result in ST segment elevation in leads II, III and AVF. A lateral wall infarct results in ST segment elevation in leads I and AVL. An Anterior wall infarct results in ST-segment elevation in the precordial leads.Image:MI_colours_en.png|The coloured figure shows contiguous leads in matching colourscolorsImage:MIregions.jpg|The ST segment elevation points at the infarct location. Inferior MI = ST segment elevation in red regions (lead II,III and AVF). Lateral MI = ST elevation in blue leads (lead I, AVL, V5-V6). Anterio MI: ST segment elevation in yellow region (V1-V4). Left main stenosis: ST elevation in gray area (AVR)
Image:conduction_blood_supply.png|The coronary blockade can cause conduction block, on AV nodal, His or bundle branch level.


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