electrocardiography

Question 1

what does hypokalemia and hyperkalemia do to nodal tissue

Answer 1

hyperkalemia- increase the time between beats via hyperpolarization
hypokalemia- will depolarize the heart and decrease the time between beats (increase HR) via hyperpolarization

Question 2

what does hypokalemia do to myocytes? hyperkalemia?

Answer 2

• hypokalemia- hyperpolarizes the membrane bring it further away from threshold
• hyperkalemia will depolarize the membrane bringing it closer to threshold

Question 3

electrocardiogram

Answer 3

-summation of all depolarizations and repolarizations occurring in cardiac cells

Question 4

what’s a P wave?

how long should it be?

Answer 4

• summation of depolarizations of atrial myocytes
• positive charge moving towards electrode causes upward deflection
• 0.06 - 0.11 sec (1-2) small boxes

Question 5

QRS complex? how long?

Answer 5

• summation of lots of ventricular myocytes depolarizing
• entire time ventricles are contracting
• 0.03-0.12 sec (<1-3 small boxes)

Question 6

what does the PR interval represent? length?

Answer 6

• it is the plateau phase (phase 2) for cardiac myocytes and it is maintained by continuous, slow Ca++ influx into the cell and K+ efflux out of the cell
• initiation of atrial depolarization to initiation of ventricular depolarization
• 0.12 - 0.2 sec (3-5 boxes)

Question 7

Q

Answer 7

• slight negative deflection -pos ions moving away from the electrode
• corresponds to septal depolarization

Question 8

R

Answer 8

-pos upward reflection (ventricular muscle depolarization moving toward the electrode)

Question 9

S

Answer 9

-negative downward deflection- ventricular muscle depolarization spreading away from the electrode

Question 10

T wave

Answer 10

summation of ventricular cells Repolarizing

reversal of charge movement makes direction of QRS and T waves similar

Question 11

if there were a problem with ventricular myocytes not being able to sustain the current or are too excited, etc where would we see it?

Answer 11

• between s and t line (s-t segment) -plateau for ventricular myocytes
• shifts if there is probs with ventricular myocytes

Question 12

where would the SA node show if it could? AV? atrial repolarize?

Answer 12

SA- before P
AV- before Q
atrial repol- in the middle of R wave

Question 13

Describe the values of an electrocardiogram graph

Answer 13

-voltage against time
-paper moving at 25 mm/sec
-each small box = 0.04 sec or 1mm
-each large box = 0.2 sec or 5 mm
10mm (10 small boxes) = 1.0 mV

Question 14

what does QT interval show us?

Answer 14

it show us all of the ventricular activity

Question 15

how long is the S-T segment? what does it tell us?

Answer 15

• variable but usually half the R-R interval

- shows plateau phase of ventricular action potential and if there is something wrong with the ventricles

Question 16

how long is the QT interval? what does it tell us?

Answer 16

• variable with HR

- ventricular action potential duration

Question 17

what type of leads does a frontal plane ecg use?

Horizontal?

Answer 17

frontal uses- standard bipolar limb leads and augmented unipolar limb leads (aVR, aVL. aVF)

Question 18

where are the leads placed in a frontal plane ecg

Answer 18

lead I- neg on right arm to positive on left
II- neg on right arm, positive on left foot
III- neg on left arm, positive on left foot
aVR- ground to positive charges moving toward right arm
aVL- looking at pos charges going to left arm
aVF- looking at pos charges going to the right foot straight down (lead one is grounding lead)

Question 19

where are the chest leads placed?

Answer 19

V1- 4th intercostal space-right sternal border
V2-4th intercostal space- left sternal border
V4- 5th LEFT intercostal space in midclavicular line
V3-between V2 and V4
V5- in line with V4 in ant axillary line
V6-in line with v 4 and 5 down from mid arm pit mid axillary line MOST IMP

Question 20

How do you determine heart rate from an ecg?

Answer 20

• look at R-R interval
• count how many large boxes are between each R and use that number to divide 300
  ex) 4 boxes= 300/4 = 75 BPM

Question 21

what’s considered bradycardia and tachycardia?

Answer 21

tachycardia >100, bradycardia <60