Electrophysiology

Question 1

Depressed fast response

Answer 1

Action potentials in partially depolarized myocardial cells with take off potentials between -75 and -60 mV. Important in re-entrant arrhythmias. May cause conduction blocks.

Question 2

muscle artifact

Answer 2

1-35 Hz, amplitudes of 0.03 to 5 mV. worse with inspiration, decreases during expiration/periodic pattern.
Creates pseudo atrial dissociation. Eliminate- low pass filter, reposition leads, no standing, calm animal

Question 3

Breathing artifacts

Answer 3

low frequency artifacts (less than 0.5 Hz) rhythmic fluctuations.
Can be mitigated by activating the high-pass filter with cut off frequency of 0.5 Hz.

Question 4

Electrical artifacts

Answer 4

Interference originating from the alternating current power source generates regular sinusoidal waves with frequency 60 Hz (60 cycles) in the US and 50 Hz (50 cycles)
cause rapid regular and low voltage undulations of the isoelectric line and are associated with electromagnetic fields in the room.
Eliminated by- notch filter on, appropriate grounding, good skin contact, wear gloves

Question 5

Synchronous diaphragmatic flutter

Answer 5

Diaphragmatic contraction due to electrical or mechanical stimulation of phrenic nerves (arise from 5-7 sometimes 4 cervical nerves) by cardiac activity. Horse- lactation, stress or sweat provoking work (electrolyte or acid base disorders- hypocalcemia, hypokalemia, metabolic alkalosis); usually stops with rest “thumps”.

Question 6

U wave

Answer 6

Leads II, III, and aVF, positive deflection, 40 ms after T wave. Repolarization of M cells. Can see in systemic hypertension, anemia, myocardial ischemia, hypokalemia, hypomagnesemia, prolonged QT interval

Question 7

M cells

Answer 7

Hybrid between Purkinje and ventricular cells
like Purkinje- prominent APD prolongation and develop EAD with Ikr blockers, develop DAD with Ca load/overload
Have: smaller slowly activing delayed rectifier current Iks, larger late Na current (INa), larger Na-Ca exchange current (I na-ca)

Question 8

Supernormal excitability

Answer 8

short period after relative refractory period when subthreshold stimulus can elicit an AP. AP is unexpected bc same stimulus would fail to initiate an AP if delivered just before or just after the supernormal phase. Corresponds to the period when membrane potential is close to threshold potential as it returns to diastolic values

Question 9

K currents responsible for inc HR= shorter AP, slow HR= longer AP

Answer 9

Iks and Ito

Question 10

Overdrive suppression

Answer 10

Driven by Na/K ATPase. hyperpolarizes=increases time needed for cell to reach threshold

Question 11

Location of:
slow pathway
fast pathway
of AV node

Answer 11

slow- starts in postero-inferior region of RA by coronary sinus ostium. bordered by tendon of todaro and insertion of TV, travels. also called infero nodal. shorter refractory period
Fast- antero-superior RA region, travels anteriorly down IAS toward compact node. longer refractory period.

Question 12

Decremental conduction

Answer 12

occurs in: AV node, postero-septal AV acessory pathways and sinus node
progressive delay of impulse propagation across AV junction with increased HR. as rate increases, myocytes only have time for partial recovery so slope and prop of AP affected. can lead to block of pulse through AV junction
can limit ventricular response

Question 13

Concealed conduction

Answer 13

characteristics of ECG that reveal an alteration of properties of the AVN by a previous event that was hidden to the observer
unexplained PQ prolongation (node in state of partial refractoriness)- may see in sinus beat following a VPC due to retrograde AVN stimulation
BBB blocks?

Question 14

Concentric ventriculo-atrial conduction

Answer 14

Retrograde electrical impulses from ventricles to atria along AV conduction axis
occurs with vpcs, vtach, ventricular escape, junctional rhythms, pacemakers

Question 15

Eccentric ventriculo-atrial conduction

Answer 15

passage of impulses from ventricles to atria using atrioventricular accessory pathway
OAVRT, ventricular rhythms with retrograde conduction through accessory pathway

Question 16

Activation of muscarinic receptors

Answer 16

Increase in K conductance, decrease in IcaL, shift of If channel activation towards more negative values

Question 17

ECG characteristics of pre-excitation

Answer 17

Short PQ interval (<60 dog, <50 cat), delta wave, wide QRS complex (2 areas depolarizations), alterations of ventricular depolarization

Question 18

OAVRT ECG

Answer 18

Narrow QRS, rate 190-300 (dogs) >300 cats, regular R-R, QRS electrical alternans, 1:1 ventriculo-atrial conduction- eccentric, P’ inferior to superior, short R-P’