Recognize the types of ECG recordings
Leads
-
-
The word “lead” is used to mean both a physical object, that is, the lead wire and
electrode that is attached to the patient and also to indicate a specific recording of
electrical currents between one positive pole and one negative pole, or two electrodes
A lead is like an eye of a camera, it has a narrow peripheral field of vision, looking only
at the electrical activity directly in front of it.
(SOURCE: EKG’s for nursing demystified, page 79)
This picture of electrical activity of the myocytes will correspond to the largest mass of activity
-
(SOURCE: EKG’s for nursing demystified, page 79)
This picture is the correlation of waveforms and flow of currents.
 Current flowing in the direction of the positive electrode will create a positive
deflection.
 Current flowing in the direction of the negative electrode will create a negative
deflection.
 Current flowing perpendicular to the line of current will create a biphasic
deflection.
FRONTAL PLANE
The six vertical or frontal plane leads are also known as the limb leads and consist of
three bipolar and three unipolar leads. The three bipolar leads form a triangle around
the heart to show a frontal plane view
Einthoven’s Triangle is used as a guide for the 6 vertical or limbs leads. [Elsevier’s ECGs Made Easy (2011)
by Barbana Aehlert]
This triangle is historically known as Einthoven’s triangle. Einthoven’s triangle is formed by the
axes of the first three limb leads with the heart at the epicenter. The axis of the lead is the
imaginary connection between the positive and negative electrodes of a lead
Bipolar Leads
A bipolar lead has both a positive and a negative electrode that records the electrical
potential difference between the two electrodes. The bipolar leads (also called the standard
limb leads) are leads I, II, and III
Lead I
-
The positive electrode for this lead is placed on the patient’s left arm or on the left side
of the chest while the negative electrode is placed on the right arm.
because current flows from negative to positive and this allows the EKG to show current
moving from right to left.
Lead II
-
The positive electrode is placed on the patient’s left leg while the negative electrode is
placed on the right arm. The current travels down to the left in this lead and produces a
positive deflection that causes tall P, R, and T waves.
Sinus node and atrial arrhythmias are monitored using this lead
Lead III
-
The positive electrode is placed on the left leg while the negative electrode is placed on
the left arm.
This lead produces a positive deflection and is used with lead II to view inferior myocardial
infarctions
Unipolar lead
-
has a single positive electrode and a relative negative “electrode” which is the heart itself.
The unipolar leads (also called unipolar limb leads or augmented limb leads) are
 aVR or “augmented vector right”
 aVL or “augmented vector left”
 aVF or “augmented foot”
if nakabantay mo small letter ang mga “a” because it is used in reference with these leads
means that they are “augmented” or enhanced because of their normal small amplitude.
While The “R”, “L”, and “F” refers to the location of the positive electrode, and kaning
positive electrode is naka placed sa right arm sa VR, on the left arm in aVL, and on the left
foot (or leg) kay sa VF
The “V” stands for vector since each one is looking at the direction of the electrical current
from that particular view
 aVR – is augmented vector right. The positive electrode is placed on the right arm and
normally produces a negative deflection since the heart’s electrical activity moves away
from the lead
This lead provides views of the atria and great vessels but no view of the heart’s walls.
 aVL – is augmented vector left. The positive electrode is placed on the left arm and
produces a positive deflection
This lead shows electrical activity coming from the lateral wall of the left ventricle.
 aVF – is augmented vector foot. The positive electrode is placed on the left leg and
produces a positive deflection.
This lead shows activity coming from the heart’s inferior wall
HORIZONTAL PLANE
The chest leads provide information about the heart’s horizontal plane and are placed in
chronological order across the patient’s chest. These are listed in order as: V1, V2, V3, V4, V5, and
V6
these leads are also unipolar with the center of the heart, as calculated by the EKG machine,
serving as the opposing pole for these leads
(SOURCE: EKG’s for nursing demystified, page 84)
A 12-lead ECG reflects the electrical activity primarily in the left ventricle. Placement of
additional electrodes for other leads may be needed to obtain more complete information
(Source: Brunner & Suddarth’s Textbook 14th.pdf page 1960)
ECG electrode placement:
Left precordial leads:
 V1 – fourth intercostal
space, right sternal
border
 V2 – fourth intercostal
space, left sternal
border
 V3 – between V2 and
V4
 V4 – fifth intercostal
space, mid clavicular
line
 V5 – same level as V4,
anterior axillary line
 V6 – (not illustrated)
same level as V4 and
V5
Right precordial leads:
placed across the right side of
the chest, are the mirror
opposite of the left leads




RA – right arm
LA – left arm
RL – right leg
LL – left leg
(Source: Brunner & Suddarth’s Textbook 14th.pdf page 1959)
Components of ECG Complexes
The ECG waveform reflects the function of the heart’s conduction system in relation to the
specific lead. ECG waveforms are printed on graph paper that is divided by vertical and horizontal
lines at standard intervals. Remember that the
 Time and rate – measured on the horizontal axis of the graft and the
 Amplitude or voltage – measured on the vertical axis of the graft
Positive deflection – When an ECG waveform moves toward the top of the paper
Negative deflection – When it moves toward the bottom of the paper
The P wave
-
The P wave is the first element of the ECG waveform. Or the first deflection noted on the
ecg waveform
the part of an ECG that reflects conduction of an electrical impulse through the atrium;
atrial depolarization. This represents depolarization of the atria
The beginning upstroke of this wave corresponds to the right atrial activity and the
downstroke denotes left atrial activity.
In lead II this is characterized by a positive deflection meaning that the wave will be above
the isoelectric line
P wave can be clearly defined, smaller than others or have a biphasic configuration,
The P wave should have a smooth, round appearance.
normal width for a P wave is 0.12 seconds or less or 3 small boxes on the ECG paper
normal amplitude or height of a P wave is about 0.5 to 2.5 mm depending on the view
P waves can also originate from different locations of the atria.
The term used to describe these pacemaker sites is Ectopic.
This ectopic impulse can come from different parts of the atria or from the atrioventricular (AV) junction. And this Ectopic waveform may appear as smaller than
normal, as a wavy line, or may have a sawtooth pattern.
P waves that originate from the AV junction will have negative deflections
The QRS Complex
-
-
the part of an ECG that reflects conduction of an electrical impulse through the ventricles;
ventricular depolarization
When the ventricles depolarize, the QRS complex is generated. It is much larger than the
P wave because the ventricles have a much larger muscle mass. Three separate wave
deflections comprise this complex known as the QRS
Q and the S wave — smaller negative deflections
R wave – larger positive deflections sometimes called inflections when it is positive, and
it is present between the Q and S wave
Normal duration of the QRS is 0.06 to 0.10 seconds
Other leads in which the R wave is positive are:
Positive leads
 Lead I
is positive electrode sya kay naka placed man sya sa patient’s left arm or left
side of the chest
 Lead II
is a good view of the QRS complex because the R wave is represented as a
strong positive deflection
 aVL
in the lead aVL the left arm electrode is exploring and the lead view from the
heart is -30o
 aVF
the electrode is placed on the left leg, so, this lead observes the heart directly
from the south
 V4
 V5
 V6
Negative R waves are seen in leads
Negative leads




aVR
V1
V2
V3
So, e differentiates nato ang meaning sa QRS
 The Q wave is always the first negative deflection.
 The R wave is considered to be the first positive deflection and
 The S wave is the final negative deflection.
The normal QRS complex
(SOURCE: EKG’s for nursing demystified, page 97)
The T wave
-
the part of an ECG that reflects repolarization of the ventricles
Ventricular repolarization is noted on the ECG as the T wave.
The normal T wave is approximately 0.5 mm in height in leads I, II, and III
These waves are normally smooth and rounded but are slightly asymmetric as they have
an upward slope to the top of the wave and then returns to the baseline or isoelectric line
(SOURCE: EKG’s for nursing demystified, page 104)
(SOURCE: EKG’s for nursing demystified, page 104)
The U wave
-
the part of an ECG that may reflect Purkinje fiber repolarization; usually, it is not seen
unless a patient’s serum potassium level is low
The U wave is not always seen and its presence is not necessarily an indicator of disease
or wellness
Normally these are small (<1.5 mm high).
It is best seen in slower heart rates
(SOURCE: EKG’s for nursing demystified, page 106)
These straight lines are called segments and are associated with the wave or complex that
precedes it. These segments follow the isoelectric line that is the baseline for the rhythm and
represent different periods of time in the cardiac cycle



PR segment
- The PR segment is the straight line from the end of the P wave to the beginning of
the QRS complex
ST segment
- begins at the end of the QRS complex and completes at the beginning of the T
wave
- This “end” of the QRS complex is still named ST whether an S wave is present or
not
TP segment
- begins at the end of the T wave and continues to the beginning of the next cardiac
cycle or P wave
The J point occurs in this segment and is the point at which the QRS complex itself joins to the
ST segment
(SOURCE: EKG’s for nursing demystified, page 107)
Two important intervals exist in the ECG tracing. These are the PR interval and the QT interval.


PR Interval or (PRI)
- This is measured from the beginning of the P wave to the beginning of the QRS
complex and includes the PR segment.
- Normal length for this interval is 0.12 to 0.20 seconds (3-5 small boxes on the EKG
graph paper)
(Source: EKG’s for nursing demystified, page 109)
QT Interval
- The QT interval starts at the beginning of the QRS complex and ends at the
conclusion of the T wave. This is representative of activity within the ventricles
inclusive of both ventricular depolarization and repolarization
(Source: EKG’s for nursing demystified, page 109)
SYSTEMATIC INTERPRETATION
All waves, complexes, straight lines, and intervals are labeled in a typical electrocardiogram
tracing of one heart beat or cardiac cycle.
(Source: EKG’s for nursing demystified, page 112)
(Source: Brunner & Suddarth’s Textbook 14th.pdf page 1963)
A. Ventricular and atrial heart rate determination with a regular rhythm:
1,500 divided by the number of small boxes between two P waves (atrial rate) or between two R
waves (ventricular rate). In this example, there are 25 small boxes between both the R waves and
the P waves, so the heart rate is 60 bpm
B. Heart rate determination if the rhythm is irregular.
There are approximately 7 RR intervals in 6 seconds, so there are about 70 RR intervals in 60
seconds (7 × 10 = 70). The ventricular heart rate is 70 bpm.
(Source: Brunner & Suddarth’s Textbook 14th.pdf page 1963)
Regular – same intervals or if the difference between the intervals is less than 0.8 seconds
throughout the strip
Irregular – different intervals
(Source: Brunner & Suddarth’s Textbook 14th.pdf page 1964)
Count the Rate
This can be accomplished using several different methods. Each of these methods will work
with either R waves (ventricular rate) or P waves (atrial rate)
(Source: EKG’s for nursing demystified, page 115)


Counting R waves
- simplest and fastest way to count heart rate is to determine the number of
complete QRS complexes (some professionals prefer to use the number of QRS
intervals) on a 6-second strip
- Multiply the number of QRS complexes in a 6-second strip by 10 to obtain an
estimation of the heart rate.
(Source: EKG’s for nursing demystified, page 114)
Large box method
- A more accurate way to determine rate is to count the number of large boxes
between two R waves that fall closest to a heavy line denoting a large box and
then divide that number into 300. So, if there are 5 large boxes in between two R
waves, 300 divided by 5 equals a heart rate of 60
(Source: EKG’s for nursing demystified, page 115)

Small box method
- count the number of small boxes between two R waves and divide into 1500. One
small box is equal to 0.04 seconds which would then be equal to 1 minute of time
per 1500 small squares. If the number of small squares between the R waves is 15,
1500 divided by 15 shows a heart rate of 100 beats per minute
(Source: EKG’s for nursing demystified, page 115)

Sequence method:
- When utilizing the sequence method, find an R wave (or P wave if atrial rate is
desired) that occurs on a heavy black line on the graph paper. Then label the next
six heavy black lines with a number from the following sequence starting with the
largest number first— 300, 150, 100, 75, 60, 50. The rate is then estimated by
finding the point at which the next R wave (or P wave) falls and determining where
it lies in relation to the marked dark lines
(Source: EKG’s for nursing demystified, page 115)