Intro to EKG and interpretation Flashcards
Automaticity
produce impulse without outside stimulation
excitability
ability to respond to an electrical stimulus
conductivity
ability to transmit electrical signal from cell to cell
pacemaker cells
- SA node/ R atrium
- normal electrical power source
- automaticity
- 60-100 bpm
electrical conduction cells
- hardwiring of the heart
- excitability and conductivity
- AV node, HIS branch, LBB/RBB, anterior and post fascicles, purkinge fibers
myocardial cells
- contractile machinery of heart
- excitability and conductivity
what determines HR?
- innate electrical characteristics of the cell
- external neurohormonal input
factors that influence rate of pacemaker cell discharge
- catecholamines (increase HR)
- acetylcholine (decrease HR)
what does the P wave represent?
- atrial depolarization
- Should proceed each QRS complex
what does the QRS complex represent?
ventricular depolarization
what does the T wave represent?
ventricular repolarization
Lead I
- L arm is positive
- R arm is negative
Lead II
- leg positive
- R arm negative
Lead III
- leg positive
- L arm negative
AVL
- L arm positive
- other limbs negative (-30)
AVR
- R arm positive
- other limbs negative ( -150)
AVF
- Leg positive
- other limbs negative (+90)
what are the standard limb leads?
I, II, III
what are the augmented limb leads?
AVR, AVL, AVF
inferior leads
II, III, AVF
left lateral leads
- I, AVL
- V5, V5
Right leads
- AVR
- V1
Anterior leads
V2, V3, V4
how many seconds is one small square?
0.04 seconds
how many seconds is one large square?
0.2 seconds
in what leads is there a positively deflected P wave?
- I, II
- AVL, AVF
- V5, V6
in what leads is there a biphasic P wave?
III and V1
in what leads is there a negatively deflected P wave?
AVR
in what leads is the P wave variable?
V2, V3 and V4
what is a normal P wave amplitude and duration?
- amplitude= 0.5-2.5 mm
- duration= 0.06-0.10 seconds
right atrial enlargement
- taller than 2.5 mm
- initial component of biphasic P wave is taller in V1
- normal duration
left atrial enlargement
- wide, often notched
- wide biphase wave in V1
- amplitude is normal or increased
what does the PR interval represent?
- the time from the start of atrial depolarization to start of ventricular depolarization
- is the distance from beginning of P wave to beginning of Q wave
what is a normal PR interval?
- 0.12- 0.2 seconds or up to one big box
- larger than one box means heart block
what does the PR segment represent?
- time from end of atrial depolarization to beginning of ventricular depolarization
- from end of P wave to beginning of Q wave
what does the Q wave represent?
- septal depolarization
- negative deflection at start of QRS complex
what is a pathologic Q wave?
- abnormally large Q wave
- generally indicates previous MI and irreversible damage
- occurs hours to days after MI
- can have simultaneous loss of R wave
what are the criteria to be considered a pathologic Q wave?
- duration greater than 0.04 seconds
- depth > 1/3 the height of the R wave
what is the average vector of current flow?
0 degrees to +90 degrees
what is R wave progression?
- R wave progressively increases in amplitude moving L to R in precordial leads
- usually largest in V5 at apex of the heart
what is considered a normal QRS complex duration?
- 0.06- 0.1 seconds
- should not be larger than 3 small boxes
why would someone have a wide QRS complex?
- impulse generated in ventricle
- impulse takes an aberrant pathway through the ventricle
what does the ST segment represent?
- time from end of ventricular depolarization to start of ventricular repolarization
what does ST segment elevation represent?
MI
what does ST segment depression represent?
ischemia
what is the J point
termination of QRS complex at start of ST segment
what are the criteria to be considered a STEMI
- 1 mm in heigh in limb leads
- 2 mm in height in precordial leads
- has non-concave shape
what does J point elevation look like?
concave in appearance
what does the T wave represent?
- ventricular repolarization/ relaxation
- variable in appearance
what does the QT interval represent?
- from beginning of ventricular depolarization to end of ventricular repolarization
- inversely proportionate to HR
- normally 40% of cardiac cycle
what is an easy way to check the QT interval?
should be less than half way between the two QRS complexes
AV Node pacemaker rate
40-60 bpm
ventricular pacemaker rate
20-40 bpm
methods for determining HR
- 300, 150, 100, 75, 60, 60
- count QRS in 6 sec interval then multiply by 10
common reasons for cardiac hypertrophy
- chronic HTN
- congenital
- more common in ventricles
common reasons for cardiac enlargement
- volume overload
- more common in atria
mean axis
- summation of all vectors in the heart
- normally falls between 0-90 degrees
- positive QRS in leads I and aVF
right axis deviation
- QRS negative in lead I
- QRS positive in aVF
left axis deviation
- QRS positive in lead I
- QRS negative in aVF
extreme right axis deviation
- QRS negative in lead I
- WRS negative in aVF
characteristics of right axis deviation
- poor R wave progression
characteristics of left ventricular hypertrophy
- left axis deviation (sometimes)
- increased R wave amplitude in leads over L ventricle
- increased S wave amplitude in leads over R ventricle
- down sloping ST segment
- T wave inversion
criteria for dx of L ventricular hypertrophy
R wave amplitude in V5 or V6 plus S wave amplitude in V1 or V2 exceeds 35 mm/7 boxes