EKG 1

Question 1

Dipole

Answer 1

. Positive and negative charge separated by a small distance
. Can generate local current flow and small electrical field
. Magnitude of small electrical field generated by single dipole is too small to measure, but can be summated with other nearby dipoles

Question 2

Electrodes

Answer 2

. sensor
. Active (exploring): electrode that senses the electrical field
. Passive (indifferent): reference electrode not sensing the field that is considered to be at 0 mV

Question 3

Leads

Answer 3

. Combination of 2 electrodes
. Unipolar lead: combination of an active plus a passive electrode, measure voltage only at the active electrode
. Bipolar lead: combo of 2 active electrodes, measure voltage difference btw them (neg. electrode minus pos. Electrode)

Question 4

Dark lines on grid are ____ apart

Answer 4

0.2 sec

Question 5

Light lines on grid are ____ apart

Answer 5

. 0.04 sec

Question 6

Y axis on EKG recording

Answer 6

. Voltage gain = 1 mV/cm

Question 7

Vv;large polarity on EKG recording

Answer 7

. Up = pos.
. Down = neg.
. Baseline (0 mV) is isoelectric line

Question 8

Standard limb lead electrode arrangements

Answer 8

. Lead 1: RA (-). And LA (+)
. Lead 2: RA (-) and LL (+)
. Lead 3: LA (-) and LL (+)

Question 9

Augmented Limb Leads

Answer 9

. Unipolar limb leads
. Indifferent electrode consists of 2 or more electrodes connected via high resistance (5000 Ohms) to junction box, called central terminal
. Leads are at intermediate angles btw standard limb leads in spite of the fact that augmented limb leads use same electrodes as standard ones

Question 10

Precordial leads

Answer 10

. Unipolar chest leads
. 6 leads w/ 6 active electrodes position on chest
. Indifferent electrode is central terminal
. Leads positioned perpendicular to the plane of the limb leads
. Axes of leads in horizontal plane
. Goes from right of sternum to lat. chest in 5th ICS

Question 11

Assumptions made in surface recording of the EKG

Answer 11

. Body is uniform volume conductor
. Surface contacts btw all electrodes and body at of low and comparable resistances
. Signals detected at surface of body represent true changes in electrical activity w/in heart and not artifacts from other dipole sources

Question 12

What is measured w/in EKG trace?

Answer 12

. Rate
. Rhythm
. Amplitude (voltage)

Question 13

Amplitude in EKG is influenced by ___

Answer 13

. Mass of tissue involved
. Resistance
. Angle

Question 14

What an EKG trace can tell you

Answer 14

. Pattern and frequency of events (rate, rhythm, single or multiple waveforms)
. Conduction time ( intervals/segments btw waves, width of waveforms)
. Direction of depolarization/repolarization of cardiac structures (from angle btw electrical vectors i heart and recording electrodes at surface)