Cardiac Electrophysiology

SA Node

Natural pacemaker of heart, determines heart rate

AV Node

Electrical gateway to ventricles, ensure atria eject all blood to ventricles

Bundle of His

Right and left bundle branches conduct impulses toward apex of heart

Purkinje Fibers

Signals from Bundle of His spread through ventricles

Via this

Conducting cells

SA node, AV node, His-Purkinje fibers

Contractile cells

Atrial and ventricular cardiac muscle

Pacemaker, AV, SA

SA and AV nodes have __ action potentials

• Although the __ node is slower than the __ node

HCN, If

1 - __ channels open (I_)

T-type Ca2+, ICaT

2 - __ __ channels open (I_)

L-type Ca2+, ICaL

3 - __ __ channels open (I_)

Voltage-gated K+, L-type, Ik

4 - __-__ __ channels open and _-__ channels inactivate (I_)

Gradual, funny

HCN channels move to a __ depolarization of SA node

• As they do not follow the rules of action potentials, they are nicknamed “__ current”

Na+

__ channels do NOT contribute to pacemaker action potentials in SA node

automaticity, resting MP

SA node has “__” with pacemaker potential and NO true __ __ __

Long-lasting (L-type)

After reaching threshold, SA node has more gradual phase 0 from __-__ Ca2+ DHPR channels opening

Hyperpolarization, cAMP, depolarization, Na+

HCN channels

• Open in response to __ (super negative MP)

• Regulated by __ (2nd messenger) for opening channels

• When HCN channels are open, Na+ moves into cell and K+ moves out

  • Net effect = Gradual __ by increasing __ (ion) percent of the vote at a slowed rate

60-100, 40-60

SA node firing rate is at __-__ bpm

Whereas AV node + Bundle of His firing rate are at __-__ bpm

AV, atria, ventricles, decrease

What would happen if SA node is ablated/destroyed?

• __ node would take over as the pacemaker

• However depolarization of __ and __ at the same time → Not very conducive

• __ (increase/decrease) HR

Ventricles, depolarization, firing

What would happen if AV node is ablated/destroyed?

• Destroys main communicator to the heart’s __ (atria/ventricles)

• Uncontrolled __ of myocytes with no supervisor node

• Means discoordinated __

Chronotropy, HCN, L

__ (autonomic) affects impulse rate (time)

• Via influence on opening of __ channels and _-type Ca2+ channels (more cAMP)

Dromotropy, AV

__ (autonomic) affects conduction speed

• Important in __ node

Ionotropy, DHPR, RyR

__ (autonomic) affects myocyte contractility

• Via influence on __s (Receptor) and __s (Receptor)

• Increase cytosolic Ca2+

Lusitropy, SERCA, NCX

__ (autonomic) affects myocyte relaxation

• Via influence on __ and __ for reuptake

• Decrease cytosolic Ca2+

M2, HCN, decrease, increase, hyper, pacemaker

Parasympathetic influence on chronotropy

• ACh effects via __ receptors

  • Decrease in __ channel opening due to __ in cAMP

  • __ in K+ permeability (Vm more negative)

    • __polarization leads to a decrease in heart rate

  • Slower rise in __ potential (cardiac)

0.5 m/s

Atrial muscle and ventricular muscle conduction velocity

(Same for both)

0.05 m/s

AV node conduction velocity

2 m/s

Bundle of His conduction velocity

Atrial, conduction, ventricles, bundles, Purkinje fibers, ventricular

Cardiac Electric Cycle

• Depolarization of the SA node spreads rapidly thru __ muscle

• AV node slows impulse __ to allow complete systole of atria and filling of all __ before they depolarize

• Impulse travels down __ and up from apex thru __ __

• Depolarization then spreads rapidly thru __ muscle

external, current, all, APs

Electrocardiogram (EKG) is a __ (internal/external) recording of summed net __ towards or away from a sensor/lead

• Summed electrical activity of __ heart cells and NOT individual __ __

Mass, lead

Amplitude of a deflection on EKG recording depends on:

•  __ of tissue involved

•  Direction of electrical activity relative to the __