Myocardial Infarction: Difference between revisions

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Myocardial Infarction (view source)

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The localisation of the occlusion can be adequately visualized using a coronary angiogram (CAG). On the CAG report,  the place of the occlusion is often graded with a number (for example LAD(7)) using the classification of the American Heart Association.<cite>AHACAG</cite>
The localisation of the occlusion can be adequately visualized using a coronary angiogram (CAG). On the CAG report,  the place of the occlusion is often graded with a number (for example LAD(7)) using the classification of the American Heart Association.<cite>AHACAG</cite>


===Anterior wall===
ECG-characteristics:<cite>Wung</cite>
ST-elevation in leads V1-V6, I and aVL. Maximum elevation in V3, maximal depression in III
later: pathological Q-wave in the precordial leads V2 to V4-V5.
[[Image:AMI_anterior.png|thumb| A typical example of an acute anterior wall infarction. ST elevation in leads I, AVL and V2-V5. Reciprocal depressions in the inferior leads (II,III,AVF)]]
[[Image:heart_with_AL_infarct.png|thumb|Anterolateral infarct caused by occlusion of the LAD.]]
[[Image:ECG_VWI_2wk.jpg|thumb| A 2 weeks old anterior infarction with Q waves in V2-V4 and persisting ST elevation, a sign of formation of a [[Ischemia#Cardiac_aneurysm|cardiac aneurysm]].]]
Encomprises the anterior part of the heart and a part of the ventricular septum. Is supplied by blood by the LAD.
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===Septal===
QS in V1 and V2. Later the septum-Q in V5 and V6 disappears.
Encomprises the ventricular septum which is supplied of blood by the septal branches of the LAD.
===Lateral===
ST elevation in I, aVL, V5 and V6
Encomprises the lateral side of the left ventricle. This is supplied with blood by the RCX or the MO. The MO, the '''marginalis obtusis''' is a sidebranch between the LAD and the RCX. In case of a lateral infarct, the maximal ST elevation is in lead V7 and the maximal depression in V2. <cite>Wung</cite>
===Antero-lateral===
[[Image:AMI_Anterolateral.png|thumb]]
ST-elevation in the precordial leads V2-V6
Later, negative T waves and Q-waves have developed in I, aVL, V5 en V6.
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===Inferior wall===
ST elevation in II, III and aVF
This part of the heart muscle lies on the diaphragm and is supplied of blood bij the right coronary artery (RCA) in 8% of patients. In the remaing 20% the inferior wall is supplied by the ramus circumflexus(RCX).
[[Image:AMI_inferior.jpg|thumb| An example of an inferior waal infarction.]]
An occlusion of the RCA can be distinguished of a RCX occulsuion on the ECG: in a RCA occlusion, there is ST depression in I and AvL and the ST-elevation is higher in III than in II. If the elevation is higher in II, suspect a RCX occlusion.
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===Posterior wall===
High R-waves with ST-depression in V1-V3.
[[Image:Heart_with_P_infarct.png|thumb|Posteriorinfarction caused by occlusion of the RCA]]
The posterior wall is usually supplied of blood by the RCA. Because no leads "look" at the posterior wall in the normal ECG, no leads show ST-elevation in case of a posterior wall infarction. The ST depressions in V1-V3 that can be observed in case of a posterior wall infarction are in fact mirrored ST elevations and the high R-waves are the Q-waves of the infarct. To be able to confirm a posterior-infarct, leads V7, V8 and V9 may be helpfull. These leads are horizontally placed from V6 to the back and do show the ST elevations of the posterior wall.
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===Right ventricle===
ST-elevation >1 mm in lead V4 right
ST elevation in lead V1
Can be seen after a proximal occlusion of the RCA.
'''V4 right''' is located at the same place as lead V4, but is placed on the right side of the patient. This means it is placed under the right nipple instead of the left. This increases the sensitivity of detecting right ventricle infarcts.
===Atrial infarct===
In approximately 10% of the infractpatients, atrial infarct is suspected. An atrial infarct can manifest itself in atrial rhytmdisturbances: atrial fibrillation / atrial rhythm. Because the atria are hemodynamically of minor importance, the consequences of an atrial infarct are limited (and therfore often missed!).
On the ECG, an atrial infarct manifests by rhythmchanges and/or chnage of the P-Ta segment (sometimes calledPTA (''P'' - ''a''triale ''T'') segment or PR or PQ or PTp (''P'' - ''T'' wave of ''P'' wave) segment)<cite>Abildskov</cite>. This is the part between the P wave and the Q. The ST segment indicates an infarct in the ventricle, the P-Ta segment indicates an infarct in the atria.
Diagnostic criteria for an atrial infarct <cite>Liu</cite>:
* P-Ta elevation >0.5mm in V5 and V6 with reciprocal depression in V1 and V2
* P-Ta elevation >0.5mm in I and depression in II and III
* >1.5mm P-Ta depression in precordial leads
* >1.2mm P-Ta depression in I,II or III in combination with atrial arrhytmias
Several diagnostic criteria are in use, and this is just an example of one. An important differential diagnosis of PTa segment elevation or depression is pericarditis.
==Infarct diagnosis in LBBB==
In case of a left bundelbranch block (LBBB), infarct diagnostics based on the ECG is difficult. The ST segments are always abnormal in a LBBB, so new ischemia can not be detected. A new LBBB is always pathologocal and can be a sign of myocardial  infarction. The criteria (Sgarbossa <cite>LBTB</cite>) that can be used in case of a LBBB and suspicion of infarction are:
*ST elevation > 1mm in leads with a positive QRS complex (concordance in ST deviation) (score 5)
*ST depression > 1 mm in V1-V3 (discordance in ST deviation) (score 3)
*ST elevation > 5 mm in leads with a negative QRS complex (discordance in ST deviation) (score 2)
At a score-sum of 3, these criteria have a specificity of 90% for detecting a myocardial infarction.
==Cardiac aneurysm==
A large mostly anterior myocardial infarction without adequate and timely reperfusion therapy can lead to extensive loss of myocardial tissue. As this weakens the anterior ventrical wall, this can result in local bulging of the anterior wall. If profound this is called a cardiac aneurysm.
Cardiac aneurysms often have typical ECG characteristics: anterior Q waves and persistent ST elevation.
Patients with cardiac aneurysms have a bad prognosis due to the severely reduced ejection fraction, they often have heart failure and risk sudden death due to [[Arrhythmias#Ventricular fibrillation|ventricular fibrillation]].
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==References==
==References==
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