Basic ECG Interpretation Flashcards
What is cardiac conduction based on?
Automaticity
What is automaticity?
The ability of heart cells to spontaneously generate an action potential.
What is conductivity?
The ability for cardiac cells to transmit action potential from one cell to another.
What is rhythmicity?
The ability for cardiac cells to spontaneously generate an action potential at a regular rate.
What are the three inherent rates?
The SA node, the AV node, and purkinje fibers.
What is the inherent rate of the SA node?
60-100 beats/min
What is the inherent rate of the AV node?
40-60 beats/min
What is the inherent rate of the purkinje fibers?
15-40 beats/min
When does atrial depolarization happen?
The P wave.
When does ventricular depolarization happen?
The QRS complex.
When does ventricular repolarization happen?
The T wave.
When does atrial contraction happen?
The P wave.
What happens during the PR interval?
Time (in seconds) from onset of atrial depolarization to the onset of ventricular depolarization (impulse travels from the SA node to the AV node with a brief delay to allow the atria to empty).
What is the QRS interval?
The time it takes for the impulse to travel through the bundle branches and purkinje fibers.
What is the J point?
The point at which the QRS returns to the isoelectric line.
What is the ST segment?
From the end of QRS to the beginning of T wave, when normal it is flat and the same level as the isoelectric baseline.
What might the ST segment indicate?
Myocardial ischemia.
What is the QT interval?
The time (in seconds) from the beginning of ventricular depolarization to the end of ventricular repolarization.
What is the small block method?
Counting the number of small blocks between complexes and dividing 1500 by that number.
How do you measure regularity?
- Check the consistency of distance between R to R interval.
- Check the consistency of distance between P to P interval.
- Is it the same distance or does it vary?
How can you calculate rhythm?
- Is R-R interval regular or irregular?
- Is P-P interval regular or irregular?
- Is rate within normal range (60-100)?
- Are the intervals normal, shortened, or prolonged?
- Are the intervals consistent or do they vary?
What is the normal interval of PR?
0.12-0.20 seconds (3-5 little boxes)
What is the normal QRS interval?
<0.12 seconds (less than 3 little boxes)
What is the normal interval for QT?
Most accurate: “normal” determined according to the heart rate. Should be less than half of the R-R interval.
When is the PR interval considered prolonged?
Longer than 0.20. This means that it is taking too long for the electrical impulse to leave the AV node.
What is a prolonged PR interval called?
A first-degree AV block.
When is the QRS interval considered prolonged?
> or equal to 0.12. This means that it is taking too long for the electrical impulse to travel down the bundle branches.
What is a prolonged QRS interval called?
Bundle Branch Block (BBB)
What is normal sinus rhythm?
The normal rhythm of the heart. The impulse is initiated at the sinus node. A “P” wave appears before each QRS complex. PR interval is within 0.12-0.20 seconds, and QRS is narrow (<0.12 seconds).
What is bradycardia?
Slow heartrate.
How can we treat bradycardia?
Digitalis, beta-blockers, calcium channel blockers.
What might bradycardia be associated with?
Sleep, severe pain, inferior wall myocardial ischemia, and spinal cord injuries.
What specific medication can we use to treat bradycardia?
Atropine 1.0 mg IV - if symptomatic every 3-5 minutes (3mg MAX)
What if atropine is ineffective for bradycardia?
Transcutaneous pacing, dopamine or epinephrine infusion may be used.
What is sinus tachycardia?
Fast heart rate.
What are causes for sinus tachycardia?
Stress, exercise, and stimulants (coffee and nicotine).
What clinical problems is sinus tachycardia associated with?
Fever, anemia, hyperthyroidism, hypoxemia, heart failure, and shock.
What medications can we use to treat sinus tachycardia?
Beta-blockers or calcium channel blockers can be used to decrease the heart rate.
When is sinus dysrhythmia present?
If the RR intervals are irregular by more than 0.12 seconds on the ECG. The rate gradually increases with inspiration and gradually decreases with expiration.
Does sinus dysrhythmia require treatment?
Generally no, unless there are long pauses.
