Basics of ECG Interpretation Flashcards
How many steps are in the systematic analysis of ECG Interpretation?
Nine
What are the 9 steps of ECG analysis?
- determine atrial and ventricular rates
- assess rhythm. Regular or Irregular?
- identify and examine the p-waves
- examine and measure the PR interval
- identify, examine and measure the QRS complex
- locate and examine the ST segment
- locate and examine the T-wave
- locate and measure the QT interval
- interpretation
Describe the 6 second method in calculating heart rate. Pros and Cons?
Count the number of QRS complexes in a 6 scedon period, and multiply x10 to get number of complexes in one minute
Pro: quick and easy
Con: least accurate method
Describe the Sequence method in calculating heart rate.
What is the numerical sequence?
300-150-100-75-60-50
Locate R-wave that falls on a dark line. Starting on the NEXT dark line, number them with the sequence above. Note where the next R-wave falls between 2 dark lines. Calculate the HR.
Describe the ruler method in calculating HR.
be sure to follow instruction on ruler
place arrow along ECG strip at QRS complex. Count the 3rd QRS complex (sometimes 2nd) and locate rate on ruler. Indicates ventricular rate - can be done with P-P interval as well to calculate atrial rate
What is the MOST accurate method of calculating HR from the rhythm strip?
Small Square Method
What is the LEAST accurate method of calculating HR from the rhythm strip?
Six Second Method
Describe the Large Square Method in calculating HR.
Count number of large squares between 2 consecutive R-waves. Divide number INTO 300
ex. 5 large squares. 300/5 = 60 bpm
Describe the Small Square Method in calculating HR.
Count number of small squares between 2 consecutive R-waves. Divide number INTO 1500
ex. 23 small squares. 1500/23 = 65 bpm
How many methods are there for calculating heart rate? List them
5 methods.
- 6 second method
- sequence method
- ruler method
- large square method
- small square method
What step takes place after calculating heart rate? Describe this step
Next step: Assess the Rhythm. Is it Regular or Irregular?
Use caliper, measure distance between R-R interval. ‘Walk’ caliper to determine if complex occurs at regular intervals
After assessing rhythm, what comes next?
Identify and Examine P-wave
What do you ask yourself when locating P-waves?
- Is it smooth and rounded?
- Is it upright or inverted? (originates in SA node or other focus)
- Does a p-wave precede each QRS complex? (sinus origin)
What are normal p-wave characteristics?
Location, Amplitude, Duration, Configuration, Deflection
Location - precedes QRS complex Amplitude - 2-3mm high Duration - 0.06-0.12 seconds Configuration - rounded and upright Deflection - positive/upright in Lead II
What does the PR Interval represent?
The time for the electrical impulse to leave the SA node, depolarize the atria and pass through the AV junction
What are the normal PR Interval characteristics?
Location and Duration
Location - from beginning of P-wave to beginning of QRS complex
Duration - 0.12-0.20 seconds
PR Interval Facts
- interval ends when ventricular depolarization begins
- should be consistent throughout rhythm strip
- tells you if the beat is transmitted to the ventricle in a normal manner
What does it mean when it’s said that the PR Interval is rate-related in duration?
If HR is faster = PR interval is shorter
If HR is slower = PR interval is longer
What does the QRS complex represent?
Ventricular depolarization
What is the normal duration of the QRS Complex? What is the max duration before it is considered abnormal?
Normal duration - 0.10 sec
A QRS complex greater than 0.12s in duration is abnormal
What does a widened QRS complex indicate?
a delay in ventricular depolarization
What is happening during a ‘normal’ QRS complex?
Represents the wave of electrical activity that proceeds in a normal, orderly fashion from the junction, through the remainder of the conduction system (Bundle of His, RBB, LBB, fasicles and Purkinje fibers), and over the left and right ventricles
What does the ST Segment represent?
the time when ventricles are completely depolarized and repolarization begins
What are you looking for with regards to the ST segment?
NOT length/duration
Looking at it’s relationship/orientation to the isoelectric line (PR segment)
ST segment ABOVE iso line = elevated
ST segment BELOW iso line = depressed
What measurement is considered significant when determining ST elevation or depression?
> 1 mm
What does the T-wave represent?
Ventricular repolarization
What are the typical t-wave characteristics?
Positive/upright deflection.
Same direction as QRS complex
Gently sloping, asymmetrical shape (symmetrical wave can indicate pathology)
What can impact interpretation of T-wave? What steps to take to determine start?
ST elevation/depression can make it difficult to determine start of T-wave. Look at ST segment for point where wave abruptly gets steep.
If no ST segment seen - T wave begins at end of QRS
What does the QT Interval represent? How do you measure it?
Total ventricular activity. Measured from start of QRS complex to end of T-wave
Most common concern with prolonged QT interval
life threatening arrhythmias
QT interval varies with HR. True/False?
TRUE
QT Interval (Normal: Range) HR: 40 HR: 60 HR: 80 HR: 100
QT length (Normal: Range) in seconds HR: 40 -- 0.46: 0.41-0.51 HR: 60 -- 0.39: 0.35-0.43 HR: 80 -- 0.35: 0.32-0.39 HR: 100 -- 0.31: 0.28-0.34
QT Interval (Normal: Range)
HR: 120
HR: 150
HR: 180
QT length (Normal: Range) in seconds
HR: 120 – 0.29: 0.26-0.32
HR: 150 – 0.25: 0.23-0.28
HR: 180 – 0.23: 0.21-0.25
Describe a quick method to determine if the QT interval is prolonged
Measure R-R interval. If QT interval > 50% of interval then it is considered prolonged
