electrocardiography Flashcards
what does hypokalemia and hyperkalemia do to nodal tissue
hyperkalemia- increase the time between beats via hyperpolarization
hypokalemia- will depolarize the heart and decrease the time between beats (increase HR) via hyperpolarization
what does hypokalemia do to myocytes? hyperkalemia?
- hypokalemia- hyperpolarizes the membrane bring it further away from threshold
- hyperkalemia will depolarize the membrane bringing it closer to threshold
electrocardiogram
-summation of all depolarizations and repolarizations occurring in cardiac cells
what’s a P wave?
how long should it be?
- summation of depolarizations of atrial myocytes
- positive charge moving towards electrode causes upward deflection
- 0.06 - 0.11 sec (1-2) small boxes
QRS complex? how long?
- summation of lots of ventricular myocytes depolarizing
- entire time ventricles are contracting
- 0.03-0.12 sec (<1-3 small boxes)
what does the PR interval represent? length?
- 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)
Q
- slight negative deflection -pos ions moving away from the electrode
- corresponds to septal depolarization
R
-pos upward reflection (ventricular muscle depolarization moving toward the electrode)
S
-negative downward deflection- ventricular muscle depolarization spreading away from the electrode
T wave
summation of ventricular cells Repolarizing
reversal of charge movement makes direction of QRS and T waves similar
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?
- between s and t line (s-t segment) -plateau for ventricular myocytes
- shifts if there is probs with ventricular myocytes
where would the SA node show if it could? AV? atrial repolarize?
SA- before P
AV- before Q
atrial repol- in the middle of R wave
Describe the values of an electrocardiogram graph
-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
what does QT interval show us?
it show us all of the ventricular activity
how long is the S-T segment? what does it tell us?
- variable but usually half the R-R interval
- shows plateau phase of ventricular action potential and if there is something wrong with the ventricles
how long is the QT interval? what does it tell us?
- variable with HR
- ventricular action potential duration
what type of leads does a frontal plane ecg use?
Horizontal?
frontal uses- standard bipolar limb leads and augmented unipolar limb leads (aVR, aVL. aVF)
where are the leads placed in a frontal plane ecg
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)
where are the chest leads placed?
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
How do you determine heart rate from an ecg?
- 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
what’s considered bradycardia and tachycardia?
tachycardia >100, bradycardia <60
