2. Basis of the ECG Flashcards
What do the 9 electrodes that give us 12 readings record?
Each records voltage difference between itself and another electrode on the torso
When theres a difference there is deflection, no difference =no deflection
ECG illustrates changes of electrical activity of cardiac muscle tissue; depolarization and repolarization. It measures the extracellular potential. What 2 things cause a deflection?
- Part of the cardiac excitable tissue is at a different membrane potential than the rest of the heart
- Current flow can occur between those regions
What regions can the electrodes report voltage differences?
Either the ventricles or atria, not both due to fibrous skeleton of the heart blocking transmission
Depolarization starts between leads and there will be a positive increase in defelction. What occurs during repolarization?
Once all cells are depolarized, will go back will plateau
When repolarization starts, the deflection will go in a negative direction (because K+ going out). Once all are repolarized, will go back to 0
How does current flow in the heart?
Negativity toward the base of the heart and positivity toward the apex
What wave is caused by SA nodes causing atria to depolarize from right to left?
P wave
What interval is where the AV node delays signaling?
PR interval
What section of the ECG is where ventricles depolarize from right to left, apex to base, from interior to exterior?
QRS complex
What segment is when the action potential of phase 2 delays repolarization of ventricles?
ST segment
What wave is cause by ventricles repolarizing, generally from left to right, base to apex?
T wave
What phase does the T wave represent of AP in ventricular muscle?
Phase 3 - repolarization
What are the possible clinical significances of the not oftenly seen U wave? (4)
- Delayed repolarization of Purkinje fibers
- Prolonged repolarization of mid-myocardial M cells
- After-potentials from mechanical forces in ventricular wall
- Repolarization of papillary muscle
What is the difference between segment and interval?
Segment represents duration of a single event on the ECG
Interval represents the duration of two or more events
The PR interval is from beginning of P wave until QRS complex. What is the normal length of this interval?
0.16ms
The QT interval is from beginning of QRS until end of the T wave and is usually how long?
0.35ms
What is a possible clinical significance of a long PR segment?
AV block meaning longer for AV to transmit signal
What does aVF/R/L stand for?
augmented vector foot/right arm/left arm
What are the normal deflections (negative or positive) for V1-6 (chest/precordial leads)?
V1/V2 negative
V3 isoelectric
V4/V5/V6 positive
Lead 1 goes from right arm to left arm, what does lead 2 and 3 go from and to?
lead 2 from right arm to left foot
lead 3 from left arm to left foot
Inferior region of the heart is best seen by using which leads? (3)
II, III, AVF
Anterior region of the heart is best seen by using which leads? (3)
V2, V3, V4
Septal region of the heart is best seen by using which leads? (2)
V1 & V2
Lateral region of the heart is best seen by using which leads? (4)
V5, V6, Lead 1, AVL
the lateral region of the heart is associated with which blood vessel?
lateral circumflex A
