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Definition
| Depolarization of the atria, represents the depolarization of the SA node down to the AV node. Once the wave of depolarization hits the AV node, they are retained for a short period before traveling down the bundle of His (shown by the flat part of the wave immediately before the QRS complex). |
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| Represents summed repolarization of the subendocardium and subepicardium. |
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Definition
| Generated by the Bundle of His, represents summed depolarization of the subendocardium and subepicardium. |
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Definition
| In some cases, the ECG will show an afterwave of repolarization after T wave, may be pathological. |
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Term
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Definition
Allows for determination of the direction of electrical impulses.
Head=-90 degrees
Left arm= 0 degrees
Feet= 90 degrees
Right arm= 180 degrees
Normal direction of electrical impulses should be from the head to the feet and from the right arm to the left arm. Impulses should be 0 |
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Term
| Locations where electrical potential is measured |
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Definition
| At right arm (VR), left arm (VL), and left foot (VF). The right leg is used for grounding. |
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Definition
VR+VL+VF=0
0 represents the eolectrical center of the heart.
Also
Voltage of Lead I (VL-VR) + Voltage of Lead III (VF-VL)= Voltage of Lead II (VF-VR) |
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Term
| Components of the hexaxial system |
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Definition
Leads I (important),II, and II with AVR, AVL, and AVF (important)
Makes up frontal plane of the heart |
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Term
| Normal QRS and T wave orientation |
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Definition
| Should be on the positive sides of both Lead I (right to left) and AVF (head to feet). Vectors should be located between 0 and 90 degrees. T wave should also be positive. |
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Term
| Horizontal orientation of QRS wave |
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Definition
| Lead I is positive (normal), while AVF is isoelectric (direction of impulse is perpendicular to frontal plane). This causes an unopposed Lead I vector in the frontal plane going from right to left. |
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Term
| LAD (left axis deviation) orientation of QRS wave |
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Definition
| Lead I is positive (normal), while AVF is negative (abnormal, goes from feet to head). Causes an upward deviation of the vector (between 0 and -90 degrees). |
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Term
| Vertical orientation of QRS complex |
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Definition
| Lead I is isoelectric, while AVF is normal, causes downward QRS vector. |
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Term
| RAD (right axis deviation) orientation of the QRS complex |
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Definition
| Lead I is negative (from left to right), while AVF is positive. Most likely caused by right ventricular hypertrophy. |
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Term
| RAD (right axis deviation) extreme orientation of QRS wave |
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Definition
| Occurs when both Lead I and AVF travel in opposite directions (left to right and feet to head respectively). Common cause are congenital heart defects. |
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Term
| Pattern analysis of T axis |
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Definition
A wide angle between the ARS and T vectors (>60 degrees) is ventricular strain. A negative T vector with a positive QRS vector is also indicative of strain.
Newborns typically have right axis deviation and right ventricular strain that normalizes with development. |
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Definition
| Occurs when T axis is in right lower quadrant and QRS is in left quadrant. In horizontal plane, transitional lead starts sooner and V1 starts showing isoelectricity. Signals left ventricle enlargement. |
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Term
| Causes of ventricular strain |
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Definition
1. Hypertrophy of ventricle
2. Bundle branch block
3. Ischemia
4. Digitalis
5. Epinephrine
6. Metabolic disturbances |
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Term
| Horizontal/transverse plane leads |
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Definition
| Consists of anterior leads (V1, V2, V3) and lateral leads (V4, V5, V6) |
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Term
| Analysis of QRS axis in horizontal plane |
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Definition
| Horizontal plane designates where QRS depolarization starts. Any lead above the line should be negative, and any lead below should be positive. Leads V1 and V2 are above the line (negative). Lead 3 is on the line (isoelectric), also called the transitional lead. Leads V4-6 are below the line and should be positive. |
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Definition
| Occurs when QRS is in right quadrant and T vector is in left quadrant. Results in positive V1 and negative V6 in horizontal plane. |
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Term
| Left Ventricular Hypertrophy |
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Definition
| Causes increase in magnitude in QRS vector and shift in orientation upwards (AVF deviation). Has lefwards deviation and left ventricular strain. In horizontal plane, large voltages are evident and transitional lead occurs later than normal (line more to the left). |
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Term
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Definition
| Similar ECG to left ventricle hypertrophy (left ventricular divation and strain), but with less voltage. Also has slow generation of QRS complex (dead giveaway).Block also moves back the transitional lead in the horizontal plane (V6 is transitional lead). |
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Term
| 3 pathologies of myocardial infarction |
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Definition
From innermost layer to outermost layer
1. Death zone, results in Q wave
2. Injury zone, causes marked elevation of the ST segment (time between QRS and T wave)
3. Ischemia (low blood flow, causes negative T wave and ventricular strain). |
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