Lecture 5: Physiologic Basis Of The ECG Flashcards
An electrocardiogram uses ______ electrodes placed on the skin surface at various locations on the torso generating ______ recordings
9;12
When does an ECG cause a deflection?
- Part of the cardiac excitable tissue is at a different membrane potential than the rest of the heart -> Current flow occurs between those regions
**Doesnt cause a deflection when only the atria and ventricles are of differing potentials
Electrodes of an ECG report voltage differences in regions of either the ventricles OR atria but not differences between the atria AND ventricles. Why?
Because of the fibrous cartilage that prevents current flow -> you can have atria at one voltage and the ventricles at another since you dont generate a voltage field between them
At rest what is the extracellular potential of the ventricles? A) 0mV B) -90mV C) +90mV D) -15 mV E) +15mV
C) +90mV -> extracellular potential is positive when the intracellular potential is negative
During phase 2 what is the extracellular potential of the ventricles? A) 0mV B) +90mV C) -90mV D) +15mV E) -15mV
E) -15mV -> inside is +15 during phase 2 SO extracellular potential is -15
SA node causes atria to depolarize from ______ (Right/left) to ________ (right/left)
Right to left
This is the P wave
Ventricles depolarize generally from ________ (right/left) to ________ (right/left) and from ________ (apex/base) to _________ (apex/base)
Right to left and from apex to base
- Depolarize from lower left to upper right
this is the QRS complex
Ventricles repolarize generally from _______ (right/left) to _________ (right/left) and ________ (base/apex) to __________(base/apex)
Left to right and base to apex
- repolarize from upper right to lower left
This is the T wave
The P wave represents phase ____ of the AP’s spreading through the atrial muscle
Phase 0
**Atria repolarizes during QRS so we dont see this because its burried in the depolarization of the ventricles
The T wave represents phase _____ or repolarization of ventricular muscle fibers spreading through the ventricles
Phase 3
What does a segment on an ECG represent?
The duration of a SINGLE event on the ECG
What does an interval on an ECG represent?
The duration of SEVERAL events
What does a changing PR interval on an ECG indicate?
Its the speed of the AV node that determines the PR interval so changes in the conduction rate through the node would change the PR interval
A long QT syndrome indicates that which phase of the AP is longer than normal and what ions account for this?
Phase 2 is longer than normal -> calcium and potassium determine the length of phase 2, so if these are messed up then you have a QT interval problem
What leads are best for viewing the inferior portion of the heart?
II, III, aVF
