ECG I Flashcards
What is an electrocardiogram?
Recording of electrical potential changes at the skin surface that result from the depolarization and repolarization of heart muscle
A wave of depolarization traveling toward a positive electrode results in what?
Positive deflection
Traveling away results in a negative deflection
A wave of repolarization traveling toward a positive electrode results in what?
Negative deflection
Traveling away causes a positive deflection
What is the cardiac dipole?
At any instant during the spread of excitation through the heart there is a resting zone and an excited zone
The difference between these two areas can be represented by a single charge at the center, creating the cardiac dipole
Why is the cardiac dipole a vector quantity?
Direction - from negative to positive
Magnitude - voltage
What is the mean electrical vector?
The sum of the individual instantaneous vectors (electrical waves traveling throughout the heart)
How does the ECG record the mean electrical vector?
Records time-dependent changes in the mean electrical vector
The instantaneous amplitude of the measured potentials on the ECG depends on the angle of the recording leads
What are the locations of V1 and V2?
Both at the 4th ICS
V1 is 2cm right of sternum
V2 is 2cm left of sternum
What are the locations of V4-6?
All in the 5th ICS
V4 - left midclavicular line
V5 - left anterior axallary line
V6 - left midaxillary line
What is the location of V3?
Midway between V2 and V4
What are the bipolar limb leads?
Lead I, II, and III on each arm and the left leg
Each of these leads has a distinct positive and negative pole, so they are considered bipolar
Forms a triangle with the heart at the center
What are the augmented unipolar limb leads?
aVR, aVL, and aVF
Two limbs are connected simultaneously to the negative terminal of the ECG, producing an averaged signal located mid-chest
The third limb is connected to the positive terminal
What is the axial reference system?
Created by combining the limb leads
The direction from the negative electrode to the positive electrode is the “axis” of the lead
What is represented by the P wave?
Atrial depolarization
What does the QRS complex represent?
Ventricular depolarization
