Guyton Kap.11- The Normal Ekg

Front 1

Repolarization of atria:

Back 1

0.15- 0.20 sec after termination of P wave (usually where QRS complex starts)

Front 2

Contraction relative to EKG:

Back 2

Contraction of ventricles starts in the beginning of QRS complex and ends at the ends in the end of the T wave

Front 3

P-R interval (P-Q segment):

Back 3

0.16 sec (4 small boxes)

Front 4

Q-T intervall:

Back 4

0.35 s

Front 5

R-R intervall:

Back 5

0.83 sec

Front 6

Calculating of heart rate:

Back 6

60 /R-R intervall

60/ 0.83= 72 beats/ min

Front 7

Lead I:

Back 7

Negative electrode on right arm, positive electrode on the left arm. Records positively. +0 degrees

Front 8

Lead II:

Back 8

Negative electrode on right arm, positive electrode on left leg. Records positively. +60 degrees

Front 9

Lead III:

Back 9

Negative electrode on left arm, positive on left leg. Records positively. +120 degrees

Front 10

Einthoven`s Law:

Back 10

If the electrical potential of any two of the three bipolar limb leads is know, the third one can be calculated.

Front 11

Which lead can be used to diagnose cardiac arrhythmia's:

Back 11

Any of the bipolar limb lead, because diagnosis of arrhythmia`s depend mainly on the time relations between the different waves of the cardiac cycle.

Front 12

Electric current flow during the cardiac cycle:

Back 12

When a cell is depolarized it is positive on the inside and negative on the outside. These negative charges on the outside move as electrical current towards the positive charges in the polarized (not yet depolarized) areas of the heart.

Thus, in normal heart ventricles, current flows from negative to positive primarily in the direction from base (where depolarization starts) towards the apex.

Except in the end of depolarization because the last area to be depolarized is the outer area of the ventricles in the area of the base of the heart. Then currents will flow with a vector from the apex to the base of the heart, and give negative recording. Repolarization starts in epicardium of apex and move towards the base, giving a positive deflection on the EKG (if it moves away from the positive electrode)

Front 13

aVL

Back 13

Positive electrode on left arm. Records positively. + 30 degrees

Front 14

aVR

Back 14

Positive electrode on right arm. Records NEGATIVELY. - 150 degrees

Front 15

aVF

Back 15

Positive electrode on left leg. Records positively. +90 degrees

Front 16

Inferior wall leads:

Back 16

II, II and aVF

Front 17

Anterior wall leads:

Back 17

V2, V3, V4

Front 18

Left lateral wall leads:

Back 18

I, aVL, V5, V6

Front 19

Right ventricle leads:

Back 19

aVR, V1

Front 20

Vector:

Back 20

Is precisely what an EKG electrode record when measuring electrical flow within the heart. The vector`s angle of orientation represents the average direction of current flow, and its length represents its voltage.

Front 21

General statement about repolarization:

Back 21

In the normal heart, repolarization usually begins in the last area of the heart to be depolarized and then travels backwards in a direction opposite that of the wave of depolarization.

Front 22

Repolarization recorded on EKG:

Back 22

Repolarization moving away from a positive electrode is recorded as a positive deflection on EKG (opposite of depolarization). This means that the leads having positive R waves will also have positive T waves and visa versa. Amplitude is usually two thirds that of the corresponding R wave.

Front 23

Resting cardiac cells are:

Back 23

Polarized, meaning that they are positive on the outside relative to the negative inside

Front 24

Depolarized cells:

Back 24

Have lost their negative charge on the inside and is positive instead. The outside is negative relative to the inside.

Front 25

Connection between poles of electrodes and recording:

Back 25

Negative electrode on area of depolarization and positive electrode on polarized area, gives a positive recording and visa versa with opposite electrode placement.