Term
| the pathway of electrical conduction of the heart |
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Definition
| SA node--> depolarize the ventricles--> AV node--> through the AV bundle-->to the left and right bundle branches--> to the purkinje fibers-->to the cells of the ventricles |
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Term
| What occurs during the AV node bottleneck delay? |
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Definition
| the ventricles fill with blood |
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Term
| what physically causes the AV nodal delay? |
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Definition
| decreased numbers of gap junctions in the AV node, also the fibrous tissues between the atria and ventricles act as a insulator |
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Term
| Where is cardiac impulse conduction the fastest? |
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Definition
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Term
| the fast conduction of the purkinje fibers promotes what? |
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Definition
| coordinated ventricular contraction |
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Term
| Where the cardiac impulse is conducted the slowest? |
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Definition
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Term
| the ion that causes the plateau period during ventricular AP |
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Definition
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Term
| the ion that causes promotes repolarization during ventricular AP |
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Definition
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Term
| WHat cases the large spike during ventricluar AP |
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Definition
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Term
THese occur during which phase
Slow voltage-gated Ca++ channels (L-type) open Ca++ influx
Voltage-gated K+ channels close reduce K+ efflux,
however ungated K+ channels still open
Inward Ca++ current is balanced by outward K+ current
Ca++ influx contraction + release Ca++ from SR |
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Definition
| Phase 2 plateau period of ventricular contraction |
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Term
| What occurs during the Phase 1 dip of ventricular AP |
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Definition
Partial repolarization due to close Na+ channels and opens
of K+ channels |
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Term
| The conduction of the action potential through the heart is slowest in the |
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Definition
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Term
A patient received a heart transplant from a healthy donor and it is routine that
the surgeon leaves the transplanted heart unconnected to the
patient’s autonomic nervous system. What do you predict will be the
patient’s resting heart rate when fully recovered from the operation? |
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Definition
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Term
| What causes the phase 2 in ventricular action potenital |
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Definition
Slow voltage-gated Ca++ channels (L-type) open Ca++ influx
Voltage-gated K+ channels close reduce K+ efflux,
however ungated K+ channels still open
Inward Ca++ current is balanced by outward K+ current
Ca++ influx contraction + release Ca++ from SR |
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Term
| what causes phase 1 (dip) in ventricular AP |
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Definition
| partial repolariztion due to the closing of Na channels and the opening of K channels |
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Term
| Phase 3 repolarization of ventricular AP |
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Definition
Ca++ channels close stop Ca++ influx
Voltage-gated K+ open K+ efflux |
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Term
| Phase 4 AP is caused by (rest/ reload) |
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Definition
| Stable resting membrane potential due to high K+ permeability |
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Term
| why can't cardiac musle go into tetani |
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Definition
| because the absolute and the relative refractory preriod are almost as long as the AP |
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Term
| what is a common mechanism for arrhythmia |
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Definition
| abnormal waves of conduction through the heart |
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Term
| Long QT syndrome leads to |
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Definition
| ventricular tachycardia and sudden death |
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Term
| What can the physician do to prevent sudden death in these patients with Long QT syndrome ? |
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Definition
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Term
| What symptoms is a patient with ventricular tachycardia likely to experience? |
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Definition
| light headed, heart flutter, decreased pump efficiecny |
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Term
| for which part of the heart is the resting potential losest to threshold |
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Definition
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Term
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Definition
Phase 0: upstroke phase
Phase 3: repolarization
Phase 4: spontaneous depolariztion and pacemaker potential |
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Term
| what happens during phase 0 of SA node AP? |
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Definition
| slow voltage gated Ca channels T-type open and calcium enters the cell |
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Term
| what happens at phase 3 of SA node AP? |
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Definition
| voltage gated K channels open and K leaves the cell |
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Term
| what occurs during phase 4 of SA node AP |
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Definition
there are multiple mechanisms
1. FUnny sodium current
2. Calcium current
3. Potassium current |
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Term
| hyperpolarization-activated Na channels open causing Na to enter and is modulated by cAMP, ACH, and NE |
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Definition
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Term
| L-type and T-type channels cause an inward calcium current SR-mediated ----- channels |
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Definition
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Term
| decreased K conductance promotes depolarization |
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Definition
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Term
| If your patient does not have a normally functioning ‘funny’ (If) current (hyperpolarization-actived sodium channel); what do you expect the patient’s resting heart rate to be ? |
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Definition
| there would be a decreasein heart rate because less Na channels are available to cause depolarization |
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Term
| Why does the SA node set the pace or rate of electrical impulses through the heart ? |
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Definition
| because it has the most rapid phase 4 depolarization |
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Term
| Given the intrinsic rate of the SA node; what keeps the normal heart rate 60-90 bests/minute ? |
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Definition
| the vagus nerve of the parasympathetic autonomic nervous system |
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Term
An Atrial Tachycardia is causing too rapid a ventricular rate and causes fainting.
What site along the conduction pathway is the best target to slow the ventricular response? |
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Definition
| the best place to control is the AV node because there are multiple autorhymic sites in the atria |
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Term
| Based on your knowledge of the cellular physiology of SA and AV node Phase 4 depolarization ; what do you predict may happen to the patient’s A-V conduction when you administer a drug for an atrial tachyarrhythmia that: |
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Definition
blocks nodal L-type calcium channels ?
reduces nodal cAMP levels ? |
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Term
Patient symptomatic due to rapid ventricular response to atrial tachyarrhythmia.
Application of Physiology Principles
Therapy -- further delay A-V node conduction |
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Definition
the target would be the Phase 4 channels
Adenosine (reduces cAMP) this reduces Na influx frim the funny channels and enhances K efflux
Verapmil block L tpye calcium channels
reducing Ca influx |
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Term
| What is the mechanism underlying the effect of parasympathetic nerve activation and acetylcholine release on the SA node rate ? |
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Definition
Ach slows the heart rate by activating the G-protein coupled muscarinic receptor to modulate several pathways in the SA nodal cells:
Decreases Na+ influx via If ‘funny current’
(If current reduced by Ach-induced decrease in cAMP)
Decreases Ca + + influx
Increases K + efflux |
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