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K is higher in or out of the cell?
In
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Na is higher in or out of the cell?
Out
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Ca is higher in or out of the cell?
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Define the equilibrium potential:
membrane potential that will exactly balance the diffusion gradient
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What is the Nernst equation?
- EX = 61/Z log[Xo]/[Xi]
- EX= equil. Pot. for ion in mV, Xo = conc. outside cell, Xi = conc. inside the cell, Z = valence of ion
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Ex in the Nernst equation has what meaning?
Membrane potential of Ex inside the cell is required to balance the ion gradient
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What is the relevance of the membrane potential equaling the Nernst potential for an ion?
No net flux of the ion
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How do Em and Ek relate during hyperkalemia?
Em is more negative than Ek, causing K influx into the cell, leading to depolarization
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How do Em and Ek relate during hypokalemia?
Em is more positive than Ek, causing K outflow from the cell, leading to hyperpolarization
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When the equilibrium potential for an ion differs from the membrane potential, that ion will tend to____________________________ for the purpose of __________________.
- Flow across membrane
- for the purpose of correcting the difference.
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___________ dependent conformational changes determine current flow through Na+ channels.
Voltage
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What do waves moving through the SA node look like?
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What do waves moving through the Heart’s Atrium look like?
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What do waves moving through the AV node look like?
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What do waves moving through the Heart’s Ventricle look like?
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What is the effective refractory period?
 - Period of time that a new action potential cannot be initiated
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What is the Relative Refractory Period?
 - Period shortly after the firing of a nerve fiber when partial repolarization has occurred and a GREATER THAN NORMAL STIMULUS can cause a second response
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What is the Relative Refractory Period?
 - Decreased phase 4 slope, causing delayed action potential and reducing spontaneous automaticity
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Describe the effects of Na and Ca Channel blockers on the action potential:
 - Increased Threshold, causing delayed action potential and reducing spontaneous automaticity
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Describe the effects of Adenosine and Aceylcholine on the action potential:
 - Increased Maximum diastolic potential, causing delayed action potential and reducing spontaneous automaticity
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Describe the effects of K channel blockers on the action potential:
 - Increased duration of action potential, causing delayed action potential and reducing spontaneous automaticity
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What does DAD stand for?
Delayed afterdepolarizations
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What does EAD stand for?
Early afterdepolarizations
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What can cause EADs?
Hypokalemia, Congenital long QT syndrome, Drug induced increases in action potential
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What can causes DADs?
Ca overload caused by: MI, Adrenergic stress, Digoxin, HF
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What are the three major mechanisms of Cardiac arrhythmias?
Enhanced automaticity, Afterpolarizations, Reentry
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What is Reentry?
Wave of excitation transverses the heart muscle in a circuitous pathway and returns to the point of origin
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What cardiac physiology must be present for Reentry to occur?
Shortened Refractory Period and reduced Conduction velocity
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What ways do drugs suppress reentry?
- Depress the conduction to produce a bidirectional block
- Lengthen the refractory period
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What is the Vaughn-Williams Classification?
Antiarrhythmatic drug classification used to classified based on ability to block ionic currents and beta adrenergic receptors
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What are the advantages of the Vaughn-Williams Classification?
Physiologically based and Highlights benefits and deleterious effects of specific drugs
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What is a Vaughn-Williams Class I drug?
Na channel blocker
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What is a Vaughn-Williams Class II drug?
Sympatholytic agent
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What is a Vaughn-Williams Class III drug?
Prolongs repolarization
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What is a Vaughn-Williams Class IV drug?
Ca Channel blocker
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Vaughn-Williams Class I – Subgroup IA has what characteristics?
 - Moderate reduction in Phase 0 slope, ↑ ERP and AP duration, Medium duration of blockade
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What drugs are classified as Vaughn-Williams Class I – Subgroup IA?
Quinidine, Procainamide and Disopyramide
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What basic characteristics does Disopyramide have?
Only treating ventricular arrhythmias, extended DOA
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What basic characteristics does Procainamide have?
↑ RP but has substantial side effects
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What basic characteristics does Quinidine have?
- 1st Antiarrhythmic drug
- Used for atrial and ventricular arrhythmias
- ↑ RP
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Vaughn-Williams Class I – Subgroup IB has what characteristics?
 - Small ↓ in Phase 0 slope
- may ↓ ERP and AP duration
- Brief duration of blockade
- preferential interaction with inactivated Na channels
- negligible interaction with Na channels
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What drugs are classified as Vaughn-Williams Class I – Subgroup IB?
Lidocaine and Mexiletine
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What are the basic characteristics of Lidocaine?
Blocks Na channels mostly in ventricular myocytes
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What are the basic characteristics of Mexiletine?
Oral lidocaine derivative, Blocks Na channels mostly in ventricular myocytes
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Vaughn-Williams Class I – Subgroup IC has what characteristics?
 - Pronounced ↓ in Phase 0 slope
- ↓ conduction
- little effect on AP duration and ERP
- LONG duration of blockade
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What drugs are classified as Vaughn-Williams Class I – Subgroup IC?
Flecainide and Propafenone
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What are the basic characteristics of Flecainide?
Slows conduction all of heart, inhibits abnormal automaticity, local anesthetic
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What are the basic characteristics of Propafenone?
↓ Conduction, Ca channel blockade, Weak B-blocker
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Describe the changes in action potential, ERP and Na channel blockade expected with a Class IA drug:
- Moderate Na channel blockade, Increased ERP
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Describe the changes in action potential, ERP and Na channel blockade expected with a Class IB drug:
- Weak Na channel blockade, Decreased ERP
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Describe the changes in action potential, ERP and Na channel blockade expected with a Class IC drug:
- Strong Na channel blockade, no effect on ERP
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