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
