Chapters Archive – Page 20 of 23 – The Cardiovascular

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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Figure 1. Acute myocardial infarction is usually initiated by rupture or erosion of a vulnerable (unstable) atherosclerotic coronary plaque.

Diagnostic Criteria for Acute Myocardial Infarction: Cardiac troponins, ECG & Symptoms

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Figure 1. Myocardial cells require continues oxygen supply in order to maintain normal metabolism. If oxygen supply is less than oxygen demand, ischemia developes. Myocardial cells can switch to anaerobic metabolism and discontinue contractions in order to alleviate the ischemia. This enables the cell to endure up to 30 minutes of severe ischemia. If blood flow is not restored before 30 minutes, the cell will die. Death of myocardial cells is referred to as myocardial infarction.

Myocardial Ischemia & infarction: Cellular changes, ECG and symptoms

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Figure 1. Flow-chart showing the natural course of coronary artery disease and classification of acute coronary syndromes into STEMI, NSTEMI and unstable angina using ECG criteria.

Classification of Acute Coronary Syndromes (ACS) & Acute Myocardial Infarction (AMI)

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