Physiological Basis Of ECG Flashcards
How is an Electrocardiogram set up?
9 electrodes (12 readings) placed on skin surface at various location on torso
What does the ECG record?
Voltage difference b/w itself and another electrode
(Differences in region of either the ventricles or the atria)
Measures EXTRA-cellular potential
What does the ECG illustrate?
Changes in electrical activity of the cardiac msucle tissue
When will deflection occur on the ECG trace?
When
- Part of cardiac excitable tissue is at different membrane potential than rest of heart
- Current flow can occur b/w those regions
What are the standard limb leads?
1-3
Where is lead 1?
RA to LA
Looks at heart from L to R
Where is lead 2?
RA to LL
Where is lead 3?
La to LL
Where is aVF?
At foot
(RA + LA) to LL
Where is aVR?
Right arm
(LL + LA) to RA
Where is aVL?
left arm
(LL+RA) to LA
What does a positive tracing deflection show?
Depolarization going toward apex
What does a negative tracing deflection show?
Depolarization going toward base
What phase does the P wave coordinate w/ ?
Phase 0 in atrial muscle (depolarization of atria)
What phase does the QRS complex coordinate w/?
Phase 0 (depolarization) in ventricular muscle
What does an elevation in the ST segment show?
Injury, infarction
What does a depression in ST segment show?
Ischemia
What does the ST segment represent?
All cells are depolarized
Time b/w Ventricular DEpolarization and REpolarization
What phase does the T-wave coordinate w/ ?
Phase 3 (repolarization) in Ventricular m.
What does the QT segment represent?
When all Ventricular myocytes are depolarized
What is a “segment” on an ECG?
Duration of a single event
What is an “interval” on the ECG?
Duration of 2 or more events
What do 5 large boxes horizontally on the ECG represent?
1 sec
What do 2 large boxes VERTICALLY on the ECG represent?
1.0 mV
What is the usual length of the PR interval?
Usually 0.16 sec
What are the chest/precordial leads assigned to?
Are they positive or negative?
Assigned to regions of the heart
Positive electrodes
What are the leads in the Inferior regions?
2, 3, aVF
What are the leads in the Septal region?
V1 & V2
What are the leads in the anterior region ?
V2, V3, V4
What are the leads in the Lateral region?
V4, V5, V6, 1 and aVL
What does a prolonged PR interval indicate?
First degree AV block
How long is a normal QT interval?
0.35 ms
What is the Mean electrical axis showing?
Average direction of spreading AP in ventricles
How do you estimate the Mean Electrical axis?
Uses average amplitude of QRS in leads 1 and aVF
What can shift the mean electric Le axis?
Hypertrophy
MI
Physical heart placement
Bundle branch blocks
What does a RIght Axis Deviation indicate?
Right ventricle hypertrophy
What does a LEft Axis Deviation indicate?
Left ventricle hypertrophy
What does the PR interval represent?
AV node delayed signal from SA
