Phys ECG Flashcards
Why is there a slow rate of rise in the SA node AP?
No Na channels
The basis for pacemaker function is ___
Funny channels cause sow, spontaneous DD
During the relative refractory period ___ are closed and ___ are open
All m gates are closed
Some h gates are open
___ is the neurotransmitter responsible for a negative chronotropic effect
___ is the neurotransmitter responsible for a positive inotropic effect.
ACh
NE
3 conditions for reentry
- Closed loop
- Unidirectional block
- Transit time > refractory period
The enzyme associated with overdrive suppression is ___
Na-K ATPase
Spontaneous DD in the SA node is due to:
- Funny channels
2. Na entry through Na-Ca antiporter
The mechanism for overdrive suppression is ___
Hyperpolarization due to increased Na efflux
Refractory period plasticity is related to changes in ___
Phosphorylation of K channels and increased K efflux
Decremental conduction refers to ___
Tendency for AP amplitude and conduction velocity to decrease
Circus movements progress to fibrillation when ___
Impulses divide and propagate
After a heart transplant what happens to heart rate?
It increases slowly because autonomic regulation is missing due to cut nerves during a heart transplant
*epinephrine and NE from the adrenal gland allows it to still increase
Conduction velocity of a Purkinje fiber
2-4 m/sec
P wave represents ___
Atrial depolarization
T wave represents
Ventricular repolarization
U wave represents
Purkinje fiber repolarization
*usually only seen in extremely low HRs
There is no dipole in which segments on an ECG?
ST and TP (flat lines)
Frontal plane leads
Standard limb leads (I, II, III)
*bipolar
Augmented limb leads (aVF, aVL, aVR)
*unipolar
Horizontal plane leads
Precotdial or chest leads (V1-6)
*unipolar
Frontal plane leads placement
I: + left arm, - right arm
II: + left leg, - right arm
III: + left leg, - left arm
Augmented limb leads placement
- aVF: + left leg (w/points on each arm)
- aVL: + left arm (points on left leg and right arm)
- aVR: + right arm (points on left leg and left arm)
Einthovens rule
The magnitude of lead II typically equals I + III at the QRS complexity
Precotdial chest leads placement
V1: 4th intercostal space right of sternum
V2: 4th intercostal space left of sternum
V4: 5th intercostal space, left mid-clavicular line
V3: between V2 and V4
V6: left midaxillary line, level with V4
V5: level with V4, left of anterior axillary line
Leads with negative deflections
V1
aVR
The T wave in the ventricles is ___ because ____.
The t wave in the atria is ___ because ___
Positive, it repolarizes in the opposite direction
Negative, same direction
