Cardiac Excitation

Question 1

what determines rate of SA firing?

Answer 1

rate of phase 4 depol (decreases time)
max neg. diastolic potential (increases time)
threshold potential (less neg, dec time)

Question 2

how does SNS control excitation?

Answer 2

increases HR by increasing # of diastolic depol events
(B1 increases, increases Phase 4)
all of heart

Question 3

how does PNS control excitation

Answer 3

pacemaker cells

decreases HR by hyperpolarizing thru ACh and K efflux

Question 4

what is overdrive suppression

Answer 4

whatever pacemaker fires faster takes over as primary (usually SA)

Question 5

escape rhythm

Answer 5

impulse initiated by not SA

Question 6

Junctional escape

Answer 6

AV node or prox. bundle of His (40-60 bpm)

Question 7

Ventricular escape

Answer 7

purkinje fibers or RT/LT AV bundles

PNS 15-40 bpm

Question 8

Ectopic rhythm

Answer 8

premie beat from latents due to electrolyte change or drugs by increase in Catecholamine concentration

non pacemaker too

Question 9

early afterdepolarizations

Answer 9

phase 2&3–> torsades de pointes

prolonged action potential

Question 10

delayed afterdepolarizations

Answer 10

post repolarization; digitoxin, TACHY

Question 11

Conduction block

Answer 11

common in AV, induces escape rhythm

no excitability due to ischemia

Question 12

Reentry

Answer 12

due to unidirectional block, reexcites retropath

Question 13

anatomical reentry

Answer 13

AVNRT, WPW Syndrome, VT from MI, Atrial Flutter

monomorphic tachy on EKG

Question 14

functional reentry

Answer 14

no fixed path

*polymorphic tachy** the fibs