CHAPTER 14 ARRYTHMIAS Flashcards
What is a Block?
Conduction in the heart where transmission is not in the correct order. Deviations from the SA node, AV node, Bundle Branch, Purkinje Fibers.
Describe the conduction system of the heart?
SA node - left and right atrium will contract at same time
AV node - has own pacemaker in case SA node takes a dump
Atrioventricular Bundle/ Bundle of His
Bundle Branches
Purkinje Fibers- has own automaticity can also fire on their own
At resting sodium channels are ________.
What is the concentration and charge of Na+ outside?
What is the concentration and charge of Na+ inside?
Closed
Outside concentration and charge: 140 mmol/L and 0 mV
Inside concentration and charge: 10-14 mmol/L and -90 mV
At resting potassium channels are ________.
What is the concentration and charge of K+ outside?
What is the concentration and charge of K+ inside?
Open
Outside concentration and charge: 4 mmol/L and 0 mV
Inside concentration and charge: 140 mmol/L and -90 mV
What is the activation gate on the sodium channel?
What is the inactivation gate of the sodium channel?
M-gate (activation gate)
H-gate (inactivation gate)
What establishes the charge gradient and rectifying current inside the cell membrane?
The potassium channel staying open at rest
Where is our pacemaker cells?
SA Node
Site of spontaneous depolarization that occurs during diastole.
Pacemaker cells have their own automaticity.
Describe the action potential of a pacemaker cell.
- Vrm is -60mV, during prepotential phase there is a slow influx of Na+
- Threshold is reached at -40mV
- During depolarization, rapid influx of Ca2+
- During repolarization, outflux of K+
- Na/K/ATPase will re-establish gradient of the membrane
Describe the action potential of the atria, ventricular, and purkinje fiber cells.
- Vrm is -100 mV, once threshold potential is met there is an action potential upstroke (phase 0) dependent on sodium current. Massive influx of Na+ (m-gate open).
- Phase 1, H-gate inactivates sodium channel, providing the overshoot. K+ channels open and will provide the phase1 slope.
- Phase 2, plateau period d/t K+ being up and Ca2+ channels opening. Ca2+ and K+ balanced.
- Phase 3, Ca2+ channels have shut off. K+ is still leaving the cell.
- Before phase 4, N/K Pump is re-establishing the gradient.
- Phase 4 slow depolarization for the next action potential
What are the three states of sodium channels?
Resting - m-gate closed/ h-gate open
Activated - m-gate open/ h-gate open, massive Na+ influx
Inactivated- m-gate open/ h-gate closed
How does the sodium channel recovery to resting state?
During Effective Refractory Period:
m-gate close first
h-gate opens second
What is the Effective Recovery Period?
Sodium channels are inactivated and not able to fire another AP, until sodium returns to resting state. m-gate closed, h-gate open.
Genetic defects or medications can cause clusters of sodium channels to recovery faster, this can result in arrhythmias.
What are the two main classification of arrhythmias?
Disturbances in Impulse Formation
Disturbances in Impuse Conductance
What is Disturbances in Impulse Formation
Formation is where the current starts. SA/AV node abnormalities.
Ion Changes
SNS Stimulation
This will increase or decrease the pacemaker rate
What is Disturbances in Impulse Conduction
Typically we talk about blocks in the heart. Interruption in transmission.
Reentry is a type of block with one way current (circus movement)
Give examples of disturbance in impulse formation.
Vagal Discharge will slow pacemaker rate and cause a reduction in the phase 4 slope.
Acceleration of pacemaker maker rate will increase phase 4 slope (beta agonist, fiber stretch, acidosis)