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31 Cards in this Set

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  • Back
What is the normal variation of voltages measured in the standard 3 Bipolar limb leads?
(from Peak of R to bottom of S)
Between .5 - 2.0 mV
Which leads generally measure the highest or lowest voltages?
Highest = Lead II

Lowest = Lead III
What defines a "High-Voltage EKG" in a patient?
A sum of all voltages in the QRS complex greater than 4 mV.
Most common cause of a HIGH voltage QRS complex:
Hypertrophy of the muscle - most commonly left hypertrophy due to hypertension.
What causes right ventricle hypertrophy?
1. Lean tall person
2. Standing up
3. Pulmonary valve stenosis
What causes left ventricle hypertrophy?
1. Short fat person
2. Lying down
3. Aortic valve stenosis
Why does hypertrophy cause increased voltage in the EKG?
B/c the increased muscle mass generates increased electricity around the heart.
What generally causes DECREASED voltage in the EKG leads?
Cardiac myopathy
What is a common cause of cardiac myopathy?
Old Myocardial Artery infarcts with resulting diminished muscle mass.
How exactly does cardiac myopathy alter the EKG (2 ways)?
1. Prolonged QRS complex
2. Decreased voltage
What conditions surrounding the heart can cause decreased voltage on the EKG?
1.Effusion- Fluid in pericardium
2. Pleural effusion
3. Pulmonary emphysema
How does Effusion cause decreased voltage?
Fluid short-circuits the potentials generated by the heart b/c it is a great conductor and charge flows to the fluid instead of heart.
How does Pulmonary Emphysema decrease EKG voltage?
-Excess air in lungs
-Decreased current thru lungs
-Chest cavity enlarges - lungs wrap around heart and insulate
-Decreases spread of voltage in heart
3 Things that PROLONG the QRS complex:
-Purkinje system blocks
Length (time) of QRS complex:
Normal = 0.06 - 0.08

Prolonged = 0.09 - 0.12
What happens to impulse conduction when Purkinje fibers are blocked? How does that affect the EKG?
The ventricle muscle has to conduct it instead. Much slower, so QRS wave is prolonged.
What is the usual QRS duration in a purkinje complex block?
0.14 sec or longer
What 2 Conditions most frequently cause Bizarre QRS complex patterns?
1. Scar tissue from Cardiac muscle destructn in ventricles.
2. Multiple local conduction blocks in the purkinje system.
When current flows between pathologically depolarized and normally polarized areas - EVEN BETWEEN HEARTBEATS
What causes a Current of Injury?
Damage to the heart muscle that makes a part remain partially or fully depolarized ALL THE TIME.
What is the electrical state of the injured area in current of injury?
NEGATIVE - depolarized so surface is negative.
List 3 abnormalities that can cause current of injury:
1. Mechanical trauma
2. Infection
3. Ischemia
Which is the most common cause of current of injury?
How does an injury to the base of the left ventricle alter the EKG?
-Never completely repolarized, so current ALWAYS recorded.
-Lead I is always negative b/c vector points away from injury
-Leads II/III are still pos
Does the voltage ever record as zero in a current of injury?
Yes - when the heart is completely depolarized.
Since current is never NOT flowing in the resting heart with a current of injury, how is the baseline of zero determined?
By using the J point as a reference.
What is the J point?
The point right after ventricular depolarization when the complete heart is depolarized and Voltage is 0
How does the Current of injury vector relate to the area of heart muscle injured?
The NEGATIVE end of the vector points toward the permanently depolarized muscle section.
What are the 3 reasons for why Ischemia depresses the metabolism of muscle?
1. Lack of oxygen
2. Accumulation of CO2
3. Lack of sufficient nutrients
What is the consequence of severe ischemia in the heart?
Repolarization of the membrane cannot occur.
In what condition is Current of Injury an extremely important diagnostic feature?
Coronary occlusion - causing acute ischemia