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SF3 - Test 1 > 3 - Cardiac Excitation (Kim) > Flashcards

3 - Cardiac Excitation (Kim) Flashcards

1
Q

Why do the Atria and Ventricles not contract simultaneously?

What is automaticity?

What is Rhymicity?

A

To allow atria to empty prior to ventricle contraction

Automaticity = Ability to initiate own beat

Rhyhmicity = Regularity of pacemaking activity

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2
Q

**What is the conduction pathway and the major players in the heart?**

A

Start: Sinoatrial (SA) Node - “Pacemaker”

I

Atrioventricular (AV) Node - “Relay”

I

Bundle of His - “Tunnel”

I

Bundle Branches (R/L)

I

End: Purkinje Fibers - “Fastest!”

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3
Q

What is the only electrical conduction between the atria and ventricles?

A

AV Node

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4
Q

How do depolarizations spread in the heart?

A

Cell to Cell

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5
Q

What is the purpose of the Anterior and Middle Tracts?

What is the purpose of the Brachmann Bundle?

A

Connect SA to AV Node

Connects the Right and Left Atria

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6
Q

Bundle of His

A

Continuous with AV node; gives off left bundle branch at top of interventircular septum and continues as right bundle branch

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7
Q

Left and Right Bundle Branches

A

Contact Purkinje System, whose fibers spread to all parts of ventricular myocardium

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8
Q

Purkinje Fibers

A

Transmits electrical impulses through ventricular system

Fastest signal transduction, synchronized contraction of both ventricles

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9
Q

What ais the fastest and slowest signal transduction in the cardiac conduction system?

A

Fastest = Purkinje Fibers

Slowest = AV Node

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10
Q

Within the cardiac tissue, how does the conduction spread in the heart?

A

Depolarizations spread from Endocardium to Epicardium

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11
Q

Sympathetic Control of Heart

A

Increased activity Raises heart rate

NT: Norepinephrine stimulates B-1 Adrenergic Receptors

Inreases rate of Phase 4 Depolarizations

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12
Q

Parasympathetic Control of Heart

A

Increased parasympathetic activity diminishes heart rate

NT: Acetylcholine (ACh) activates Muscarinic (M2) receptors in SA node.

Decrease in rate of Phase 4 Depolarizations

Increases OUTWARD K+ current; hyperpolarizing maximum diastolic potential (makes it harder to fire Action Potentials)

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13
Q

Temperature influence on SA Node?

A

Increase rate with increase in temperature

Tachycardia associated with fever

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14
Q

Digitalis (drug) influed on SA node?

A

Strengthen contractility; increase AV node conduction velocity

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15
Q

Latent Pacemakers

A

AV Node / Bundle of His and Purkinje Cells exhibit automaticity less than SA Node

Blocked by Overdrive Supression

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16
Q

Overdrive Suppression

A

SA Node initiates 70-80 BPM; which is faster than Latent Pacemakers (AV Node/Bundle of His/Purkinje); thus supressing their firing rate

- - -

If SA Node (or downstream) get’s broke, it can dork this up

17
Q

Mechanisms of Tachyarrythmias (increased firing rate)

A

Increased Automaticity of SA Node (pacemaker)

Increased Autmaticity of Latent Pacemakers (AV/Bundle of His/Purkinje)

Abnormal Automaticity (disease state)

Triggered Activity

Unidirectional Block and Reentry

18
Q

Mechanisms of Bradyarrhythmias (decreased firing rate)

A

Altered Impulse Formation: Decrease Automaticity of SA Node (pacemaker)

Altered Impulse Conduction: Conduction Block

19
Q

How can Sinus Node Automaticity be altered?

A

Increase: Increase Sympathetic Activity (normal during exercise)

Decease: Increas Parasympathetics, or Decrease Sympathetic

B-Blockers slow heart rate

20
Q

Escape Rhythms

Escape Beat

A

If SA Node becomes too suppressed, Latent Pacemakers may take over (overdrive supression lost)

Continued series of escape beats = Escape Rhythm

Escape Beat = impulse initiated by latent pacemaker

21
Q

Junctional Escape

A

Escape beats arise from AV Node or proximal Bundle of His

Moderate Parasympathetic Stimulation slows the SA Rate, and allows pacemaker to shift to the AV Node

22
Q

Ventricular Escape

A

Beats arise from distal end of conduction system

Very strong Parasympathetic stimulation suppresses both SA and AV Nodes

Usually 15-40 BPM

23
Q

What can enhance automaticity of latent pacemakers?

(Ectopic Beat, Rhythm)

A

High Catecholamine Concentrations

Hypoxemia, Ischemia, Electrolyte Disturbances

Certain drug toxicities

24
Q

How may myocytes play a role in Ectopic Beat or Ryhthm formation?

A

When myocytes become injured (ischemia, etc), their membranes become leaky

Unable to maintain gradients, become easily depolarize

25
Q

What can Trigger Activity and result in Extra Heart Beats or Rapid Arrhythmias?

A

When first action potential leads to oscillation of membrane voltage - afterdepolarizations

26
Q

Early vs Delayed Afterdepolarizations

A

Early - Changes of the membrane potential in the positive direction that interupt normal repolarization

More likely in conditions that prolong action potential duration (Inherited Long-QT Syndromes)

Tachyarryhthmia

- - -

Delayed - Appear shortly after repolarization is complete; mostly develop in states of high intracellular calcium (digitalis intoxication)

Tachyarryhthmia

27
Q

Altered Impulse Conduction - Conduction Block

A

Propagating impulse i blocked when it encounters region of hart electrically unexcitable; can be transient or pemanent

Cause: Ischemia, Fibrosis, Inflammation, Drugs

Block within AV Node, or His-Purkinje System prevents normal propagation of the cardiac impulse from the sinus node to more distal sites

28
Q

Unidirectional Block and Reentry

A

Occurs when a conduction pathway is stimulated prematurely by a previously conduction action potential, leading to rapid cyclical reactivtion

29
Q

Anatomical Reentry

A

Reentry occuring over anatomically fixed path

AV Nodal Reentrant Tachycardia (AVNRT)

Atioventricular Reentran Tachycardias (AVRT)

Atrial Flutter

ECG - monomorphic tachycardia

30
Q

Functional Reentry

A

Reentry does not require a fixed path

Can occur in electrically geterogeneous myocardium

Examples:

Polymorphic Ventricular Tachycardia

Atrial Fibrillation

Ventricular Fibrillation

31
Q

Clinical: Atripventricular Reentran Tachycardias (AVRT)

A

Presency of abnormal pathway creates conduction for rrentry due to altered refractory period from AV Node

32
Q
A

SF3 - Test 1 (28 decks)

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