Chapters Archive – Page 19 of 22 – The Cardiovascular

Figure 1. The coronary arteries and their relation to the ECG leads. Localization of myocardial infarction / ischemia is done by using ECG changes to determine the affected area and subsequently the occluded coronary artery (culprit).

ECG localization of myocardial infarction / ischemia and coronary artery occlusion (culprit)

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Figure 1. The component of the cardiac conduction system and the vascular supply. RCA = right coronary artery. LAD = Left anterior descending coronary artery. LCX = left circumflex coronary artery.

Supraventricular and intraventricular conduction defects in myocardial ischemia and infarction

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Figure 2. The electrocardiographic natural course in STEMI (ST elevation myocardial infarction).

The ECG in assessment of myocardial reperfusion

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Figure 1. Pathological R-wave progression is indicative of previous myocardial infarction.

Other ECG changes in ischemia and infarction

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Figure 1. Examples of STE-ACS (STEMI). Note that these patients presented with pathological Q-waves, which means that these ECGs were recorded several hours after symptom onset or those are signs of old infarction.

ECG signs of myocardial infarction: pathological Q-waves & pathological R-waves

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Figure 1. Posterolateral (posterior, inferobasal) transmural ischemia causes reciprocal ST-segment depressions in V1–V3 (ocasionally V4). Leads V7–V9 must be placed to reveal the ST-segment elevations.

ST elevation myocardial infarction (STEMI) without ST elevations on 12-lead ECG

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Figure 1. Types of ST segment elevations on ECG.

ST segment elevation in acute myocardial ischemia and differential diagnoses

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Figure 1. (A) The relation between the action potential and the ECG curve. Myocardial ischemia primarily affects the repolarization, which is reflected on ST-T changes on the ECG. (B) Note that the reference level for measuring deviation (elevation or depression) of the ST segment is the PR segment (the terminal portion of the PR interval). (C) and (D) Shows how to measure the magnitude of ST segment elevation and ST segment depression. The J 60 point is located 60 ms after the J point.

ECG in myocardial ischemia: ischemic changes in the ST segment & T-wave

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Figure 3. STE-ACS (STEMI) is caused by a complete occlusion, which means that there is no flow in the artery. The ischemia will affect all layers of the myocardium, from the endocardium to the epicardium (in the region supplied by the occluded artery). This type of ischemia, which affects all myocardial layers, is referred to as transmural ischemia.

Factors that modify the natural course in acute myocardial infarction (AMI)

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The right ventricle is supplied by the right marginal artery (r. marginalis dx), which originates from the right coronary artery (RCA). The RCA also supplies the inferior left ventricular wall in over 90% of all individuals. Hence, a proximal occlusion (in the RCA) which cuts off blood flow to the right ventricle, will also affect the inferior wall of the left ventricle in 90% of the cases.

The left ventricle in myocardial ischemia and infarction

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