12-Lead 12-Lead ElectrocardiographyElectrocardiography

a comprehensive course

Adam Thompson, EMT-P, A.S.Adam Thompson, EMT-P, A.S.

Ischemia,

Injury, &

Infarct

(Part 2)

Evolution of MI

• Insufficient blood supply to the myocardium.– Ischemia, injury or infarction, or all three.

• The branches of coronary arteries arising from the aortic root are distributed on the epicardial surface of the heart.

• These in turn provide intramural branches that supply the cardiac muscle.

• Myocardial ischemia generally appears first.

Evolution of MI

InfarctionIschemia Injury

Needs O2 Damage from Irreversible lack of O2 damage

Ischemia

• Subendocardial ischemia– Ischemia in this area prolongs local recovery time.

Since repolarization normally proceeds in an epicardial-to-endocardial direction, delayed recovery in the subendocardial region due to ischemia does not reverse the direction of repolarization but merely lengthens it.

Ischemia

• Transmural ischemia

– is said to exist when ischemia extends subepicardially. This process has a more visible effect on recovery of subepicardial cells compared with subendocardial cells. Recovery is more delayed in the subepicardial layers, and the subendocardial muscle fibers seem to recover first.

Ischemia

• Hyperacute T-Waves– Results from subendocardial ischemia– Symmetrical & tall– Wide with blunt peak (unlike Hyperkalemia)– Present for about first 30 min. of AMI

• Inverted T-waves– Results from transmural ischemia

Ischemia

Asymmetrical

Symmetrical

Ischemia

Ischemia-Mimic

Peaked T-Waves

Inverted T-Waves

Hyperkalemia STE-Mimic

Injury

• Injury to the myocardial cells results when the ischemic process is more severe.

• In patients with coronary artery disease, ischemia, injury and myocardial infarction of different areas frequently coexist, producing mixed and complex ECG patterns.

Injury

• ST-Depression– Subendocardial

• ST-Elevation – Subepicardial– Transmural.

Injury

Injury

ST-Depression

ST-Elevation

Injury-Mimic

ST-Elevation

Hyperkalemia STE-Mimic

Infarct

• The term infarction describes necrosis or death of myocardial cells.

• Atherosclerotic heart disease is the most common underlying cause of myocardial infarction.

• The left ventricle is the predominant site for infarction; however, right ventricular infarction occasionally coexists with infarction of the inferior wall of the left ventricle.

Infarct

• During acute myocardial infarction, the central area of necrosis is generally surrounded by an area of injury, which in turn is surrounded by an area of ischemia.

• Various stages of myocardial damage can coexist.

• The distinction between ischemia and necrosis is whether the phenomenon is reversible.

Infarct

• Pathological Q-waves– Wider than 0.04sec / 40ms (1 small box)– Deeper than 25% the height of R-Wave

Part 2

• More up next…