Cardio: Electric

Front 1

wave of depolarization

Back 1

-SA triggers AP that runs through entire heart
- These factors vary continuously:
1. number of muscle fibers involved
2. direction of depolarization

Front 2

# of depolarizing cells and strength of signal

Back 2

strength of signal depends directly on # of depolarizing cells
- resulting potential increases until it reaches a maximum then heads back down to zero

Front 3

generated vs recorded potential

Back 3

1. recorded cannot exceed generated
2. recorded can however be much lower than generated, due to the direction of depolarization vs direction of measurement

Front 4

size of signal: factors

Back 4

1. side of measurement
2. view angle
3. location of signal in relation to electrodes

Front 5

vectors

Back 5

-line point from are depolarizing to non depolarized area
-if vector is 90 degrees to viewer, no potential is recorded

Front 6

Einthoven method

Back 6

-electrodes at each arm and one foot: in theory distance from each electrode to the heart is equivalent
-ground electrode on other foot

Front 7

plane

Back 7

- orientation of pair of electrodes in relation to the heart
1. horizontal: 1-2
2. angular: 1-2 and 1-3
-determines how much of cardiac vector is measured

Front 8

size of vector in each plane

Back 8

1. plane/lead 1 (1-2): horizontal
2. plane/lead 2 (1-3): recorded vector is smaller
3. plane/lead 3 (2-3): largest vector compared to the other leads

Front 9

electrode placement

Back 9

1. right TL
2. left TL
3. left PL

Front 10

lead 1

Back 10

right TL- left TL

Front 11

lead 2

Back 11

right TL- left PL

Front 12

lead 3

Back 12

left TL- left PL

Front 13

unipolar leads after Goldberger

Back 13

1. aVr: lead 1 + augmented LPL connected to left electrode
2. aVl: lead 1 + augmented LPL connected to right electrode
3. lead 3 + augmented RPL connected to right electrode

Front 14

Goldberger vs Einthoven

Back 14

-Goldberger provides stonger signals:
1. aVr> lead 1
2. aVf> lead 3

Front 15

Wilson

Back 15

-6 electrodes on chest close to heart record electrical events in more detail

Front 16

wave

Back 16

one positive or negative deflection

Front 17

segment

Back 17

distance/time between two waves

Front 18

interval

Back 18

one or more waves and segments

Front 19

P wave

Back 19

depolarization of atria:
begins with the first upward deflection from the baseline and end with return to the baseline

Front 20

PQ segment

Back 20

depolarization of AV node, bundle of His:
signal too small to generate a wave

Front 21

QRS interval

Back 21

Depolarization of the ventricle:
Q=septum, R= ventricular walls, S=final depolarization of L ventricular wall.
-Measured from 1st deflection of QRS from baseline (- or +) to eventual return to baseline

Front 22

PQ interval

Back 22

Time from beginning of atrial depolarization to the beginning of ventricular depolarization:
measured from the 1st upward deflection of P wave to the 1st deflection of the QRS complex. If no visible Q wave, called PR interval

Front 23

ST segment

Back 23

ventricle remains depolarized (contraction):
-measured from end of S wave to the start of the T wave

Front 24

T wave

Back 24

repolarization of the ventricle:
-T wave shows the wave of repolarization of the ventricle.
-Atria repolarize much earlier but the signal is too small to be recorded

Front 25

SA signal

Back 25

-depolarization begins
-signal too small to be recorded

Front 26

Atria, AV node signal

Back 26

P wave:
-depolarization of AV node begins

Front 27

AV node, Bundle of His signal

Back 27

PQ segment:
- often signal too small to be recorded, so -Q, PQ= PR segment

Front 28

septum signal

Back 28

Q wave:
can be missing

Front 29

ventricular muscle wall signal

Back 29

1. R wave: normally strongest signal
2. S wave: asymmetric as L ventricle depolarization completed later
-can be missing physiologically

Front 30

ventricles remaining depolarized signal

Back 30

ST segment:
no electrical change = no signal

Front 31

ventricular repolarization signal

Back 31

T wave:
only repolarization signal in physiological ECG

Front 32

atrial contraction in ECG

Back 32

PQ

Front 33

ventricular contraction in ECG

Back 33

ST

Front 34

relaxation in ECG

Back 34

PT

Front 35

amplification

Back 35

- needed to get comparable results
- standard: 5 or 10 mm/ mV

Front 36

low paper speed

Back 36

-better :
1. general idea of rhythmic events (HR)
2. easier to reveal random events, eg extra systoles

Front 37

higher paper speed

Back 37

shows more details, eg split R waves, etc

Front 38

standard paper speeds

Back 38

5, 10, 25, and 50 mm/sec

Front 39

ECG standards for waves and segments in dogs

Back 39

1. P wave: <0.06 sec
2. PR segment: < 0.13 sec
3. QRS interval: < 0.05 sec
4. QT interval: <0.19...0.23 sec

Front 40

Limitations of ECG

Back 40

1. deflections correspond to specific electrical events
2. timing and duration of deflections can be calculated and compared with standard values
3. provides partial information about mechanical events of the heart

Front 41

Einthoven ECG vectors

Back 41

-cannot record actual vectors, but its projections to the three planes
- vector can be reconstructed from its projections
-vector changes value and direction progressively during cardiac cycle

Front 42

Einthoven ECG and vector cardiogram

Back 42

-depolarization and repolarization begin and end at zero millivolts
- 3 loops of the vector cardiogram (P, QRS, T) that begin and end in the center of the lead 1, 2, 3 axis
- QRS strongest signal= QRS largest loop in vector cardiogram

Front 43

Making vectorcardiogram from ECG

Back 43

-actual vector can be obtained by drawing lines at the vector head perpendicular to the lead
-Interestion of the three lines marks the head of the actual vector
- any two leads are sufficient to construct actual vector

Front 44

VCG and ECG: resting state

Back 44

-no signal recorded during the resting state
- VCG shows just a dot in the center
-ECG shows baseline

Front 45

VCG: Atrial loop

Back 45

-atrial depolarization mirrored in VCG as a clockwise loop
- each dot in loop represents the value and direction at moments of atrial depolarizatin
-

Front 46

ECG: atrial depolarization

Back 46

-ECG shows wave
-unlike VCG it represents only 1 of the 3 leads and thus not the entire vector
-value of recorded potential represented by the vertical distance from the baseline as time progresses

Front 47

Ventricular depolarization loop

Back 47

- ventricles represent most of the cardiac muscle tissue
- generates largest loop in the VCG and the largest deflection in the ECG

Front 48

Ventricular repolarization loop

Back 48

- not just the reversal of the depolarization
- sequence and timing is slightly different resulting in a round shaped wave: not pointed as QRS wave and smaller
-timing results in smaller loop
-In ECG, T wave is not tipped and smaller

Front 49

Limitations of VCG

Back 49

-ECG segments PQ, ST, and TQ represent points where potential is 0: times of complete repol or depol
-VCG: these segments are dot in intersection point of leads
therefore duration of these 0 phases:
1. aren't shown
2. cannot be measured

Front 50

VCG examples of cow

Back 50

1. normal: VCG large diameter, ellipse almost vertical
2. abnormal: VCG large diameter, ellipse almost horizontal, Wolff-Parkinson- White Snydrome