Normal ECGs DSA Flashcards
What causes the heart to beat?
rhythmic discharge of electrical stimuli
What is an EKG?
records the electrical activity of the heart, provides a record of cardiac electrical activity, & info about heart function/structure
What does the EKG record?
electrical activity of contraction of heart muscle (myocardium)
How does the depolarization move throughout the heart?
cell to cell conduction of depolarization is carried by fast-moving Na+ ions
Where can you detect the heart’s electrical activity?
from the skin surface using electrodes
What does an upward wave indicate on an EKG?
depolarization wave moving toward positive electrode
What is the SA node?
in upper posterior wall of RA & is the heart’s dominant pacemaker
What is automaticity?
ability of SA node to generate pacemaking stimuli
What does the P wave represent?
contraction of BOTH atria
What happens to depolarization when it reaches the AV node?
depolarization slows down to allow time for blood in atria to enter the ventricles (b/c carried by slow moving Ca2+ ions)
What happens when depolarization reaches the ventricular conduction system?
depolarization rapidly shoots through the His bundle & the L/R bundles branches
(purkinje fibers)
What are Purkinje fibers?
rapidly conducting cells that use fast moving Na+ ions for conduction of depolarization to ventricular myocytes
What is the QRS complex on the EKG?
depolarization of the entire ventricular myocardium
How does ventricular depolarization spread?
from terminal filaments of Purkinje fibers beneath endocardium that proceeds outward to epicardium of ventricles
What does the ST segment represent?
ventricular repolarization
What does an abnormal ST segment indicate?
sign of serious pathology (if elevated or depressed beyond normal baseline level)
What is the T wave?
rapid phase of ventricular repolarization (K+ leaving the myocytes)
What does ventricular systole include?
begins w/ QRS & persists until end of T wave
What is a long QT interval syndrome?
pts vulnerable to dangerous rapid ventricular rhythms
What ions are used in cell to cell conduction in myocardium?
by Na+ ions
What ions are used in AV node conduction?
slow movement of Ca2+ ions
Where would you place electrodes?
on R & L arms, L leg
What are the lateral leads?
Leads I & AVL b/c each has a positive electrode positioned laterally on the L arm
What are the inferior leads?
leads II, III & AVF b/c each of these leads has a positive electrode positioned inferiorly on the L foot
What is at the center of leads V1 to V6?
AV node
What are leads V3 & V4 over?
oriented over the interventricular septum (V3 near RV & V4 near LV)
What are bipolar limb leads?
pair of electrodes on each limb that has 1 positive & 1 negative
What direction is lead I in?
horizontal (L arm is + & R arm is -)
What is + & - in lead III?
L arm is negative & L leg is positivve
What is the AVF lead?
uses L foot electrode as positive & both arm electrodes as negative
What is the AVR lead?
R arm is positive & others are negative
What is the AVL lead?
L arm is positive & others are negative
How is the rate of an EKG read?
cycles per minute
What is the most common cause of sinus tachycardia?
sympathetic stimulation of SA node via exercise
automaticity of atria
60 to 80 beats per minute
automaticity of AV junction
40 to 60 beats per minuate
automaticity of venticles
20 to 40 beats per minute
What happens if AV junction is blocked?
automaticity focus in Purkinje fibers of ventricles will act
What is the importance of overdrive suppression?
provides emergency backup pacing @ 3 separate levels
What should you first use to calculate the rate?
R wave
What are the next 3 thick lines following R wave?
300, 150, 100
then 75, 60, 50
How do you determine rate?
start with 1 R wave & where next R wave falls gives you the rate
If rate is 60 beats per minute & due to rhythm from automaticity focus, which one is producing the rate?
pacemaker in the AV junction
would also not see any P waves on that ECG
What is the proper term for slow heart rate?
bradycardia
How does bradycardia show on an ECG?
few cycles per 6 second strip
(10 of 6 second strips gives 1 minute & #of cycles per min is rate…so cycles per 6 second strip is multiplied by 10)
What does the vector on an EKG represent?
general direction of depolarization in the heart
What is the mean QRS vector?
represents general direction of ventricular depolarization (tail is the AV node) & points more toward L
What happen if heart is rotated toward R side?
mean QRS vector moves toward R
common in tall & slender pts
What direction is heart rotated in obese people?
toward L side of pt
What is a myocardial infarction?
when 1 branch of coronary arteries is occluded (that area of heart becomes electrically dead)
What direction does mean QRS vector point in MI?
points away from infarction
What is the normal mean QRS vector?
points down & to L side of pt (in 0-90 degree range)
Describe normal position of mean QRS vector
points toward ventricular hypertrophy & away from MI
What does lead I pass through?
AV node (R arm is - & left arm is +)
What does a positive QRS complex in lead I indicate?
mean QRS vector is pointing to pt L half
What does lead I detect?
right axis deviation
What does a positive QRS complex in lead AVF indicate?
downward pointing mean QRS vector
What does you want to see for lead I & lead AVF in normal pt?
lead I should point left & lead AVF should point down (in normal quadrant!)
indicates ventricular depolarization moving down & left
What is left axis deviation?
lead I & lead AVF point upward & to left
When do you see left axis deviation?
lead I QRS is positive & lead AVF QRS is negative
What should lead V2 always be?
positive (just anterior to AV node)
How does lead V2 split the body?
front half is positive & back half is negative (center of sphere is still the AV node)
Why is QRS lead in V2 negative usually?
mean QRS vector should point backward b/c of general posterior position of thick L ventricle
