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Terms in this set (20)
What are the different components of the cardiac conduction pathway?
SA node conducted impulse to the atria to the AV node to bundle of his and then to the purkinje fibers of ventricles
Name the primary natural pacemaker for the heart.
Sinoatrial Node (SA)
What are the different phases of action potential and which ion is involved in each step and which drug could affect that phase of an action potential?
The most important phases are 0, 2, 3, these are the targets of the meds.
***0 - Depolarization: opening of Na+ channels
1- Repolarization: Inactivation of Na+ channels, Activation of K+ Channels
***2- Plateau phase: Slow inward current caused by Ca++ Channels (L-type)
***3- Repolarization: K+ exits the cell
4- Spontaneous depolarization to threshold where the critical voltage activates the Na+ channels
Define absolute refractory period in a myocyte.
from start of depolarization to the beginning of repolarization
if new depolarization the neuron will not fire no matter how big the stimulus is because it is already depolarized
Define relative refractory period in a myocyte.
Stronger than normal stimulus can induce depolarization
What is arrhythmia?
arrhythmia is an abnormal impulse generation or conduction
What could cause arrhythmias?
Myocardial damage (dead cells dont conduct so in MI sometimes pathways are cut short causing irregularities in the pathway
Abnormal Ionic environment (hypokalemia)
Explain what is meant by 're-entry' that leads to arrhythmia.
The action potential that bifurcates hits dead tissue on one path but the other path comes back around and gives the current from the back side causing a delay which leads to an arrhythmia. (bad at explaining it)
Explain what is meant by conduction block. What are the three types of AV block?
Abnormal conduction of AV node or Bundle of His branches
AV block: delay in AV node: three types
(1) 1st degree: slight delay, not serious (PR interval >.2 s)
(2) 2nd degree: intermittent block, some signals don't reach ventricle
(3) 3rd degree: complete block, serious esp if beat less than 40 bpm.
What is torsades de pointes? What causes it?
Potentially a fatal ventricular arrhythmia usually caused by drugs (that affect K channels) and is one of the most common reasons for removing a drug from the market.
QT interval increases due to prolongation of action potential during depolarization.
we don't need to know all the drugs but some examples are Antiarrhythmic drugs, Antihistamines, Anti-infectives, Psychiatric drugs, etc......
Identify some commonly used drugs, including antibacterials that could cause torsades?
List the different types of arrhythmia.
Heart rate abnormalities: tachycardia, bradycardia
Supraventricular arrhythmias: Originating above the ventricles (typically AV node)
1) supraventricular tachycardia
2) atrial fibrillation
3) atrial flutter
1) originating in the ventricles
2) ventricular tachycardia
3) ventricular fibrillation (the worst)
How does atrial fibrillation cause clot formation?
In fibrillation blood pools in the atria which can lead to thrombosis
What is the major consequence of clot formation in the left atrium?
Thrombosis in the Left atria will most likely travel to the brain causing stroke.
List the different classes of antiarrhythmic drugs (Vaughan Williams classification).
Class I: Sodium Channel Blockers
Class II: Beta Blockers
Class III: Potassium Channel Blockers
Class 4: Calcium Channel Blockers
Non specific agents (don't fall under this classification system) or Class V: digoxin, adenosine
Name the prototypical drugs for Class 1: Sodium Channel Blockers and explain the mechanism.
Quinidine- Class 1A Mechanism: Slows phase 0 depolarization
Lidocaine- Class 1B Mechanism: Decrease phase 0 upstroke, shorten phase 3 repolarization
Name the prototypical drugs for Class 2: Beta Blockers and explain the mechanism.
Mechanism: diminish phase 4 depolarization, thus depressing automaticity, prolonging AV conduction and decreasing heart rate and contractility
Name the prototypical drugs for Class 3: Potassium Channel Blockers and explain the mechanism.
Mechanism: Prolong the duration of action potential increase QT interval, block potassium channels and therefore diminish the outward current of potassium ion during repolarization of cardiac cells w/no effect on Na Channels
Name the prototypical drugs for Class 4: Calcium Channel Blockers and explain the mechanism.
Mechanism: Act by blocking the entry of calcium into the myocardial cell, resulting in decrease in the rate of phase 4 spontaneous depolarization, reduced conduction in tissues dependent on calcium currents and prolong PR interval
Which is the most fatal type of arrhythmia? Which drugs are usually used to treat it?
Ventricular fibrillation (V-Fib)
IV amiodarone and Epinephrine
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