ECG1 Flashcards
What is the SA node’s intrinsic rate?
60 to 100 bpm
Define Bachman’s bundle.
The anterior tract that divides and extends into the LA.
What is considered the primary pacemaker of the heart?
SA node
Where is the SA node located?
In the superior right atrium at the entrance to the superior vena cava
Where is the triangle of Koch located?
In the floor of the right atrium superior to the septal leaflet of the tricuspid valve.
What is the only pathway to the ventricles called (in a normal person)?
Triangle of Koch
What is the AV nodes intrinsic rate?
40 to 60 bpm
What node is considered the secondary pacemaker?
The AV node.
Why is the AV node delayed?
- to allow for atrial contraction (increase preload and subsequent contraction due to Frank-Starling mechanism)
- protects the ventricles from inappropriate high atrial rates (ie atrial fibrillation and flutter)
Is the refractory period longer for the SA or the AV node?
The AV node refractory period is longer.
Why is Ca++ important for electrical conduction in the heart?
Calcium is the major ion responsible for the action potential.
What is the most proximal portion of the ventricular conduction system called?
Bundle of His
What is the terminal end of the electrical conduction system called?
Purkinje Fibers
What is the intrinsic rate of the Purkinje Fibers?
20 to 40 bpm
Define automaticity
Self-excitation
(accomplished by P cells which are located in the SA node, atrial tissue, AV node, and ventricular tissue —they have different rates bc different refractory periods)
What maintains the negative resting potential?
The sodium-potassium ATPase pump
How does the ATPase pump reset the membrane to pre-depolarizing electrolyte levels?
It exchanges 3 Na+ ions OUT of the cell for
2 K+ ions INTO the cell
Using the sodium-potassium ATPase pump is an active process. What does it require?
Magnesium and ATP(energy)
Which phase of the action potential plot corresponds with the resting membrane potential?
Phase 4
Describe phase 4 of the action potential
resting membrane potential (-80 to -90mV)
negativity maintained by the sodium/potassium pump
sodium out/potassium in
(corresponds with the baseline between the T and P wave)
Where happens during phase 0 of the action potential?
Rapid depolarization of the cell (stimulus applied)
Sodium rushes out of the cell making it less negative
(Potassium leaks out of the cell)
In what phase do the drugs lidocaine and procainamide work?
Phase 0
Describe phase 1 of the action potential.
(Brief rapid initiation of repolarization)
(closure of the sodium channels)
Chloride ions enter the cell (makes it more negative)
What effect does sympathetic innervation have on electrical conduction?
Increases SA nodal chronotropy, increases AV nodal dromotropy and increases myocardial iontopy
Describe Phase 2 of the action potential.
“Plateau” phase
Slowing of repolarization
Calcium enters the cell, leading to contraction of the muscle in a sustained, slower manner
Which class of antiarrhythmics work at phase 2 of the action potential?
Class IV antiarrhythmics (calcium channel blockers)
Verapamil, Diltiazem
Describe Phase 3 of the action potential.
Sudden acceleration in the rate of repolarization.
Potassium movement into the cell causes this rapid return in intracellular negativity
Sodium-potassium pump operates at this phase
What class of antiarrhythmics work in phase 3?
Class III
Amiodarone, sotalol (by prolonging the return to a resting potential)
What do funny (If) channels do?
Define chronotropy.
Effects that change the HR
Positive chronotropes increase HR
Negative chronotropes decrease the HR
Define dromotropy
Effects the conduction speed of the AV node
What effect does parasympathetic innervation have on electrical conduction?
Decreases the SA nodal chronotropy and decreases the AV nodal dromotropy
