Download EKG Paper ECG tracings are recorded on grid paper. The horizontal

EKG Paper
ECG tracings are recorded on grid paper. The horizontal axis of the
EKG paper records time, with black marks at the top indicating 3 second intervals.
Each second is marked by 5 large grid blocks. Thus each large blocks equals 0.2 second. The vertical axis records
EKG amplitude (voltage). Two large blocks equal 1 millivolt (mV). Each small block equals 0.1 mV.
Within the large blocks are 5 small blocks, each representing 0.04 seconds.
EKG Nomenclature
Normal EKG tracings consist of waveform components which indicate electrical events during one heart beat.
These waveforms are labeled P, Q, R, S, T and U. The following descriptions are with respect to Lead II.
P wave is the first deflection and is normally a positive (upward) waveform. It indicates atrial depolarization.
QRS complex follows the P wave. It normally begins with a downward deflection, Q; a larger upwards deflection, R;
and then a downwards S wave. The QRS complex represents ventricular depolarization and contraction.
T wave is normally a modest upwards waveform, representing ventricular repolarization.
U wave indicates the recovery of the Purkinje conduction fibers. This wave component may not be observable.
Interpretation
EKG interpretation should be performed using a standard procedure. For this course, we are using an eight step
procedure:

Rhythm

PR Interval

QT Interval

Rate

QRS Interval

ST Segment

P Wave

T Wave
For ventricular rhythm, examine the R to R intervals on the EKG strip. Calipers or paper marks can be used to fix
the distance for one R-R interval and then this distance can be compared to other R-R pairs. Within this web site,
you will also be able to use virtual calipers.
Are they regular, meaning that each heart beat's R-R interval is equal? Small variations of up to 10% are considered
equal. Is the rhythm regularly irregular? For example is there a pattern, such as increasing R-R durations? Or
perhaps groups of similar intervals as illustrated on the right? Or are R-R intervals completely irregular?
For atrial rhythm, observe the P-P intervals. Are they regular (minor variations can be caused by the breath cycle)?
If P-P intervals are irregular, is there a pattern?
Heart Rate
There are several methods for determining heart rate. Our first method is simple. Count the number of QRS
complexes over a 6 second interval. Multiple by 10 to determine heart rate. This method works well for both
regular and irregular rhythms. In the first image, we can count 7 QRS complexes, so the heart rate is 70.
The second method uses small boxes. Count the number of small boxes for a typical R-R interval. Divide this
number into 1500 to determine heart rate. In the second image, the number of small boxes for the R-R interval is
22.5. The heart rate is 1500/21.5, which is 69.8.
P-wave
The P wave represents atrial depolarization. In normal EKGs, the P-wave preceeds the QRS complex. It looks like a
small bump upwards from the baseline. The amplitude is normally 0.05 to 0.25mV (0.5 to 2.5 small boxes). Normal
duration is 0.06-0.11 seconds (1.5 to 2.75 small boxes). The shape of a P-wave is usually smooth and rounded.
P-wave questions:

Are they present?

Do they occur regularly?

Is there one P-wave for each QRS complex?

Are the P-Waves smooth, rounded, and
upright?

Do all P-Waves have similar shapes?
PR Interval
The PR Interval indicates AV conduction time.
In this step you should measure the interval from where the P wave begins until the beginning of the QRS complex.
Calipers, marked paper or counting small boxes methods can be used to determine PR Intervals. Normally this
interval is 0.12 to 0.20 seconds (3 to 5 small boxes) in adults, longer in elderly people. This interval shortens with
increased heart rate.
Also evaluate if PR Intervals are constant or varying across the EKG strip. If they vary, determine if the variations
are a steady lengthening until the point where an expected QRS does not appear.
PR Interval questions to address:


Does the PR-Interval fall within the norm of 0.12-0.20 seconds?
Is the PR-Interval constant across the ECG tracing?
QRS Complex
The QRS complex indicates ventricular depolarization. Depolarization triggers contraction of the ventricules.
Because of the larger tissue mass, the QRS complex is larger than the P wave. While the prototypical QRS complex
consists of three wave components, one or two of these components may be missing.
In this step, measure the QRS interval from the end of the PR interval to the end of the S wave. Use calipers,
marking paper or by counting small boxes. Normally this interval is 0.06 to 0.12 seconds (1.5 to 3 boxes).
QRS questions:


Does the QRS interval fall within the range of 0.08-0.12 seconds?
Are the QRS complexes similar in appearance across the ECG tracing?
T-Wave
The T wave indicates the repolarization of the ventricules. It is a slightly asymmetrical waveform which follows
(after a pause), the QRS complex. Take note of T waves which have a downward (negative) deflection or of T waves
with tall, pointed peaks.
The U-wave is a small upright, rounded bump. When observed, it follows the T-wave.
QT Interval
The QT interval represents the time of ventricular activity including both depolarization and repolarization.
It is measured from the beginning of the QRS complex to the end of the T wave. Normally, the QT interval is 0.36 to
0.44 seconds (9-11 boxes). The QT interval will vary with patient gender, age and heart rate. Another guideline is
that normal QT Intervals is less than half of the R-R Interval for heart rates below 100 bpm.
ST Segment
The ST segment represents the early part of ventricular repolarization.
The ST segment is the line that from the end of the QRS complex to beginning of the T wave. Normally the ST
segment is flat, being neither positive or negative relative to the baseline.
Practice
What is the ventricular heart rate?
30 beats per minute
50 beats per minute
60 beats per minute
70 beats per minute
80 beats per minute
90 beats per minute
Evaluate the P Wave
Normal P Wave
Inverted P Wave
More P Waves than QRS complexes
P Wave shape varies
Absent P Wave
Evaluate the QRS Complex
Normal QRS Interval
Wide QRS Interval
Wide QRS, bizarre appearance
None
Evaluate the EKG rhythm (regularity)
Regular
Regular with block
Irregular - PVC couplets
Irregular - chaotic
Irregular independent ventricular & atrial rhythms
No rhythm - asystole
Evaluate the P-R Interval
Normal PR Interval
Long PR Interval
Short PR Interval
PR Interval lengthens
PR Interval varies
None
Evaluate the QT Interval
Normal QT Interval
Long QT Interval
Short QT Interval
QT Interval varies
Not measurable