EKG: Section C - 2

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MI's; Hypertrophy; Intraventricular conduction delays and axis deviation

Describe Myocardial Ischemia:

narrowing of coronary arteries reduces blood flow to myocardium; transient oxygen deficiency

what does the pt often feel with myocardial ischemia?

chest pain during exertion

What is most affected with myocardial ischemia?

left ventricle

What is the EKG criteria for Myocardial ischemia?

ST segment depression = or greater than 1mm at 0.08 sec; ST segment may be upsloping, downsloping or horizontal and T waves may be flattened or inverted

Describe what myocardial injury is:

stage beyond ischemia; transient, usually no permanent damage; vasoplastic angina(coronary artery spasm) can cause temporary ST segment elevation

What is a myocardial infarction also known as?

heart attack

2 types of myocardial infarction:

Transmural and Subendocardial MI

Transmural MI affects what?

all layers of the heart wall - endocardial, myocardial and epicardial layers of the heart wall

Subendocardial MI affects what?

only affects the endocardium of the heart

EKG changes due to MI include:

ischemia is normally displayed as ST Segment depression; old MIs show prominent Q waves that never resolve

When are serum enzymes secreted?

After an MI only when cardiac muscle tissue is damaged

Measuring serum enzymes is the primary diagnostic too for determining what?

the severity and age of infarction

What are the serum enzymes measured to determine MIs?

Creatine phosphokinase (CPK) -sometimes shortened to creatine kinase (CK); Glutamic Oxoloacetic transaminase (SGOT); Lactic dehydrogenase (LDH) and Troponin I

How long after MI does CPK elevate?

in first few hours

How long after MI does CPK peak?

in 24 hours

After MI how long does it take for CPK levels to return to normal?

3 -4 days

How long after MI does it take SGOT levels to elevate?

several hours after infarction

When does SGOT peak after MI?

in 1 1/2 to 3 days

When does SGOT levels return to normal after MI?

4 -5 days

How long after MI does it take LDH levels to elevate?

48 hours after infarction

When do LDH levels peak after MI?

4 to 7 days

How long does it take LDH levels to return back to normal?

2 weeks

When do Troponin I levels begin to rise?

4 -6 hours after injury

When do Troponin I levels peak?

12 - 16 hours

5 examples of the different causes of death resulting from complications of MI (sometimes years later)

Cardiac arrest; ventricular aneurysm rupture (necrotic muscle wall becomes thin and bulges outwardly until it cracks; CHF (impaired pumping action of the heart) and R-side HF due to L-Side HF which occurs more frequently

What is the Hallmark of Left sided heart failure?

Elevated pressure and congestion in systemic veins and capillaries

What is the Hallmarke of Right sides heart failure?

elevated pressure and congestion in the pulmonary veins and capillaries

What does left sided heart failure cause?

systemic edema (peripheral)

What does right sided heart failure cause?

pulmonary edema

What does CHF signify and what is it known as?

Signifies the terminal period of other diseases and is known as "end stage cardiac disease"

CHF may result in what?

an embolism (thrombus)

What is a thrombus?

an embolism which is blood clot that can occlude any vessel

CHF causes what?

total or near total, lack of perfusion to tissue

EKG criteria for Q waves for MI

may appear immediately or in several days; 1/3 height of R wave; 0.04 sec wide (if neither criteria is met, Q waves are not diagnostic)

EKG criteria for T waves for MI:

prolonged; increased in magnitude; upright; inverted

EKG criteria for ST segment for MI:

elevation in leads facing injured area; depression in leads opposite injured area; when elevation occurs damage is often progressive and severe

Initial EKG tests is DIAGNOSTIC of acute MI in what percent of patients?

60%

Initial EKG tests is INCONCLUSIVE of acute MI in what percent of patients?

25%

Initial EKG tests is INACCURATE of acute MI in what percent of patients?

15%

What is necessary for accurate diagnosis?

successive tracings

A definitive diagnosis for determining an old infarction depends on what?

presence of Q waves; (abnormal Q waves may be absent in transmural MI and nearly half of Q waves in anterior and inferior leads are false positive)

To determine the location of an MI you have to have what?

Significant Q waves in at least 2 leads

Significant Q waves for Anterior Infarction would be in what leads?

(AWMI) VI - V4

Significant Q waves for Lateral Infarction would be in what leads?

(LWMI) I, AVL, V5 and V6

Significant Q waves for Inferior Infarction would be in what leads?

(IWMI) II, III, AVF

Criteria for Posterior Infarction:

(PWMI) tall R wave in V1 and V2; AVF at least 25% of amplitude of R wave; serum levels very critical to obtain ( esophageal leads make accurate)

To make an accurate diagnosis of hypertrophy what procedures comes first, second and third?

echocardiography, angiography and then EKG to determine hypertrophy

In hypertrophied areas what is the signifying markings on the EKG?

large voltages are recorded in the leads over hypertrophied areas

Criteria for LEFT ATRIAL HYPERTROPHY:

Lead VI- diaphasic Pwave with terminal portion bigger; Lead I - Pwave is greater than 2.5 mm in hieght

Criteria for RIGHT ATRIAL HYPERTROPHY:

Lead II, III, AVF - Pwave hight is 2.5mm or greater; Lead V1 - diaphasic P wave with initial portion bigger

Criteria for LEFT VENTRICULAR HYPERTROPHY:

AVL will measure greater than 11mm; R wave in V5 and the S wave in V1 will be greater than 35 mm; V5 or V6 is greater than 27 mm high; repolarization changes may show ST depression and asymmetrical T wave inversion

Criteria for RIGHT VENTRICULAR HYPERTROPHY:

V1 - R wave is taller than S wave; Inverted R wave progression; Repolarization changes with St depression and asymmetrical T wave inversion in VI and V2

What are Intraventricular Conduction Delays?

abnormal conduction of impulse in one or more of conduction pathways below the Bundle of His

Intraventricular conduction delays include what 4 arrythmias?

Right /Left Bundle Branch blocks; and Left Anterior/Posterior Fascicular Blocks

The impulse pathway of a RBBB:

normal impulse reaches RBBB and advances to LBB and depolarizes left ventricle; impulse then travels through the intraventricular septum and intiates right ventricular depolarization

EKG Criteria for RBBB:

QRS greater than 0.10 sec; QRS positive in V1; repolarization changes in V1 and V2 and QRS has a RSR wave appearance in V1 and V2

The impulse pathway of a LBBB:

Cardiac impulse travels to LBB, deflects to RBB and depolarizes through IV septum to depolarize LV

EKG criteria for LBBB:

QRS greater than 0.10sec; QRS negative in V1; repolarization changes in I, AVL, V5 and V6; QRS has an RR wave appearance in V5,V6

The impulse pathway of a Left Anterior Fascicular Block:

impulses reaches LBB, is delayed at anterior fascicle and travels down posterior fascicle; LV depolarized through connection of Purkinje Fibers

EKG Criteria for Left anterior Fascicular Block:

QRS axis -30 degrees or greater with small Q wave in lead I

The impulse pathway of a Left Posterior Fascicular Block:

impulse travels down anterior fascicle through connection of Purkinje fibers and depolarizes LB

EKG criteria for Left Posterior Fascicular Block:

QRS axis shifts right to +110 degrees or greater with small Q waves in lead III

For Quick Look Method for axis deviation what 2 leads do you use?

Lead I and AVF

Both Lead I and AVF positive =

Normal Axis Deviation

Lead I Negative and AVF Positive =

Right Axis Deviation

Leave I Positive and AVF Negative =

Left Axis Deviation

Both Lead I and AVF Negative =

Extreme Right Axis Deviation

If Lead II is positive it is:

truly normal

If Leave II is negative it is:

truly Left Axis

3 Causes of Axis Deviation:

Hypertrophy (towards the affected side); myocardial infarction (away from the affected side) and anatomical position of the heart

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