22. Electrocardiography Flashcards
What type of electrocardiographic leads are used in clinical practice
Bipolar
Unipolar
Precordial leads by Wilson
What are bipolar leads
- Consists of a positive and negative electrode
- 1 (left arm right arm),11 (left leg right arm),111 (left leg left arm) standard leads by EInthoven
- They are suitable in determining the electrical axis of the heart
Why are bipolar leads not suitable in determing an electrical process in the heart
Because these leads measure the
potential difference between two
points, but not the potential changes
for each of the points,
What are unipolar leads
- Also called Goldberger leads
- the positive electrodes are attached to the right arm
(aVR), left arm (aVL), and left leg (aVF)
*The potential differences between these points and the reference electrode (zero point) are measured and recorded
*
Why are unipolar leads more advantageous
They are better in determining localization of the electrical process as each lead provides info abt the electrical changes ocurring in the area where active electrode placed
What are the axels of the peripheral leads ( Einthoven and goldberger)
frontal plane
What are precordial leads
- These are: V1, V2, V3, V4, V5, and V6.
- These leads are also unipolar
- V1, V2 register electrical potentials right side of hear, the rest for the left side
- The axels of these leads are in the horizontal plane
What is the result when the wave front of depolarization travels to the postive electrode/negative electrode
a positive-going deflection in ECG
vice versa
What is mean electrical axis of the heart
It is the summated vector of potential differences during ventricular depolarization
It shows the dominant direction of the
propagation of excitatory process.
Normally its 60 degrees
Depending on the angle size btw mean eelctrical axis and horizontal line, what can be the postions of the heart
+30-+60 = neutral position
+ 60- +110 = Right position (upper limit typical for tall skinny people)
-30-+30 = Left position ( lower limit typical for short fat people and pregannt women)
Which factors determine the direction of mean electrical axis
Anatomical position of the heart in the chest.
Body structure.
The relative thickness of the heart ventricles.
The sequence of ventricles activation.
Components of an ECG
P wave
QRS wave
T wave
What do P waves show
Depolarization of the atria
PQ interval reflects the
conduction of excitatory
process from the SAN
through AVN to the
ventricles.
What does the QRS complex show
Ventricular depolarization
What does the ST degemnt show
Time between end of QRS and start of T wave
Time of complete ventricular depolarization
Along with the QRS complex,
during this period the
ventricles are in the absolute
refractory period.
