EKG Flashcards
Automaticity
any cells in the heart can initiate an impulse
Contractility
ability to respond mechanically
Conductivity
ability to transmit an impulse
Excitability
ability to be electrical stimulated
Electricity in resting state
cardiac cells are negative on inside and positive on outside
Depolarization
When cells are stimulated by pacemaker and Na moves rapidly to the inside of the cells and K moves to the outside leading to adjacent cells depolarizing
Does electrical activity mean that the heart is mechanically pumping?
Hopefully, but not always. EKG looks at electrical conduction but that does not mean the heart is pumping
Why is it important that depolarization is transmitted in a coordinated fashion?
Its important that there is contraction at the atrium then contraction and the ventricle to maintain CO and organization
Where does depolarization start?
SA node AKA pacemaker
What happens if the SA node fails?
The AV node is the backup pacemaker
How fast can the AV node discharge firing?
40-60 beats per minute
Where is the SA node located?
right atrium
Electrical impulse pathway
SA node –> AV node –> bundle of his –> right and left branches –> purkinje fibers
Repolarization
Muscles cells will recover and restore electrical charge
Absolute refectory period
Period where cardiac muscles cannot be stimulated by any stimuli
Protective mechanism
What is the absolute refractory period on the ECG?
beginning of QRS to peak of T wave
Relative refractory period
Period where cardiac muscle will respond to a STRONG stimuli
Very vulnerable period
If you shock someone during this phase, you can send them into a lethal rhythm
What is the absolute refractory phase as long as?
As long as the contraction phase
Where is the relative refractory phase on an ECG?
Peak to the end of the T wave
A change in a waveform is due to
change in electrical current or change in a lead
What is an ECG used to evaluate?
Heart function, heart rate, ischemia, infarction, chest pain, pacemaker function and medications
Left to right markings represent…
time
Verticle marking represent…
voltage or energy
Small boxes represent
0.04 seconds
Large boxes represent
0.20 seconds
Line/dashes at the top of the paper represent
3 seconds
An ECG waveform is
group of waves that record the electrical signal as it depolarizes that heart muscle cells
P wave represents and looks like
arterial depolarization
Small, rounds and before QRS
PR interval is from the.. to the..
beginning of P wave to beginning of QRS
Normal PR interval time is
0.12 - 0.20
PR interval represents
time it takes for the original impulse to leave the SA node and travel through the AV node
Time required for partial depolarization
How well AV node is functioning
What is the atrial kick?
the brief delay at AV node that allows atria to empty and contract and it a contributor to the CO
What does the AV node do?
it acts as the gatekeeper to limit the ventricular rate
QRS interval is from the.. to the..
Beginning of the Q wave to the end of the S wave
Normal QRS time is
less that 0.12 seconds
What does the QRS represent?
ventricular contraction
ST segment is the
time between completion of ventricular contraction and beginning of repolarization
What is the ST segment measured by?
Normal = isometric
Elevation due to myocardial injury/infarction (irreversible)
Depressed due to myocardial ischemia (reversible)
T wave represents
ventricular repolarization
What does an inverted T wave mean?
any condition that interferes with normal repolarization such as ischemia or injury
QT interval is from the .. to the ..
beginning of QRS to end of T wave
QT interval represents
the total ventricular depolarization and repolarization
QT interval time is
0.34-0.43 seconds
What is the isoelectric line?
baseline, flat, straight line that connects all the curves
Regular rhythm
distance between two QRS complexes does not vary by more than 3 small boxes
Regular irregular rhythm
patten is recognized and predicted
Irregular irregular
no pattern and no periods of regularity
Steps to read ECG
- determine if its regular
- Calculate HR
- Examine P waves
- measure PR interval
- Measure QRS interval
how to do you calculate the HR by looking at ECG?
count number of QRS intervals and multiple by 10
Examine P waves include..
Is there any P waves absent or present
Are P waves all the same shape
Is there one P wave for every QRS?
Normal sinus rhythm interpretation
Atrial/Ventricular rate: 60-100 bpm Rhythm: regular P wave: 1:1 PR interval: normal, .12-.20 seconds QRS complex: normal, less than 0.12 seconds