EKG Acute Myocardial Infarction - Studen

Acute Myocardial Infarction Student note set

Page 1 of 4 EKG Acute Myocardial Infarction - Student Note Set - Created by Greg Pato, PA-C - PA Program SP 2014. Revision 1.2

1. Introduction a. Acute Coronary Syndromes (ACS) are the result of a mismatch between the demand for myocardial

blood flow, and its supply. b. Myocardial ischemia is not a static event, but instead an evolution of biochemical and functional

changes. c. Accordingly, obtaining serial 12 lead EKGs and telemetry monitoring is a standard and important

practice in the treatment of ACS. d. Myocardial ischemia can be found on the EKG in three important patterns: Ischemia, Injury, and

Infarction. 2. EKG Manifestation of Myocardial Ischemia

a. Repolarization changes (ST segments and T waves) are the primary EKG manifestations of acute myocardial infarction.

b. Recall that the EKG records the same event from multiple vantage points (multiple leads). One can approximate location of an ischemic area by the group of contiguous EKG leads that are affected.

c. ACS related EKG changes occur in discrete regions of the heart because ischemia is most often the result of one artery or a segment of an artery being occluded. The tissue distal to the occlusion suffers ischemia as long as the event lasts, or until it becomes necrotic. As a result, EKG changes are seen in leads which are both contiguous and which relate to the particular artery involved. In order to reliably diagnose myocardial ischemia, one must see ST-T changes, typical of ACS, on two or more contiguous leads.

d. ST-T changes occurring in one isolated lead are typically benign. However, new changes on the EKG should always be investigated.

e. Depressed or Elevated ST segments which are flat or down-sloping, are suggestive of ischemia. f. Depressed ST segments which are up-sloping are much less suggestive of ischemia. The reason for this is

explained in the section on ST Segments and T waves, and relates to J-point depression during exercise. However, if the ST is downsloping from a normal or depressed J point, then this is much more consistent with true ST depression, which in turn is consistent with ischemia. Of course, this is a guideline which must be used in conjunction with good clinical judgment.

g. Elevated ST segments with a Concave down pattern especially when merged into the T wave are highly suggestive of Infarction or ventricular aneurism and are often referred to as Tombstone T Waves.



h. Patterns of ST changes in Ischemia

i. Reversible Myocardial Damage 1. Ischemia:

a. ST Depression b. Flat or Down sloping ST segments

2. Injury: a. ST Elevation b. Flat or concave down ST segment

ii. Irreversible Myocardial Damage: 1. Infarction:

a. Pathological Q Waves (deep and wide Q waves) b. A late manifestation of myocardial Infarction c. AMI can be classified as Q-wave or Non-Q-wave MI, which carries prognostic

significance and will not be discussed here.

i. Reciprocal changes i. ST-T wave changes occurring in one region can manifest themselves in opposite leads in

opposite ways. This means that ST elevation occurring in the lateral wall, for example, can show up as ST depression in the Septal wall.

ii. Typical Reciprocal Partners: 1. Lateral (V5,V6) Septal Wall (V1, V2) 2. Inferior (II, II, aVF) Lateral Wall (I, aVL) 3. Posterior Wall Septal (V1, V2)



4. Limb leads and precordial leads do not reciprocate to each other because the lie in different planes.

3. Remember: ACS typically has its root in Coronary Artery Disease (CAD) a. ST-T changes which are localized to a region on the EKG, effectively allow the approximation of the

coronary artery (arteries) with the problematic lesion. b. Briefly, the coronary arteries supply the following areas:

i. Left Coronary Artery 1. Anterior and Lateral Left Ventricle 2. Anterior 2/3 of Septum

ii. Right Coronary Artery 1. SA Node 2. AV Node 3. Posterior and Inferior Left and Right Ventricles

Hint: This summary of the coronary arteries is on the exam, not the entire chart.



References:

Garica, Holtz. 12-Lead ECG, The Art of Interpretation. Jones and Bartlet. Sudbury, MA.

Libby, Bonnow, Mann, Zipes. Brunwalds Heart Disease, A Textbook of Cardiovascular Medicine. 8th Edition. Saunders, Elsevier. Philadelphia, PA.

Lilly. Pathophysiology of Heart Disease. 4th Edition. Lippincott, Williams & Wilkins. Philadelphia, PA.

Surawicz, Knilans. Chous electrocardiography in Clinical Practice. 6th Edition. Saunders, Elsevier. Philadelphia, PA.

Widmaier, Raff, Strang. Vanders Human Physiology. 10th Edition. McGraw Hill. New York, NY.

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EKG Acute Myocardial Infarction - Studen