What
is an EKG?
An EKG machine is a voltmeter. In other words, it reads electrical
energy from the body. The heart uses electrical energy to cause
muscle cells to contract. By reading the electrical energy of the
heart, the nurse can tell if it is generated and conducted correctly.
An EKG
is obtained by placing electrical sensors (leads) on the patient’s
chest. Usually 12 leads are used to look at the heart from many
angles. The EKG machine doesn’t look at all 12 leads at once;
instead it chooses one at a time to view, and each view we call
a lead on the resulting tracing.
What
does it measure?
Electrical impulses are transferred to paper by the EKG machine.
Two components of the tracing are especially useful: time and amplitude.
Time is measured horizontally across the EKG strip. Amplitude is
measured by the height of the tracing, which corresponds to the
strength of the electrical impulse.
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EKG
paper is divided into small squares and larger squares. Small
squares are 1mm high and 0.04 seconds long. Large squares are
five small squares high (5mm) and five small squares long (0.20
seconds). |
The
EKG Complex
Depolarization:
Impulses begin at the Sinoatrial (SA) node, generating a P-wave.
The impulse travels through the electrical pathways to the Atrio-Ventricular
(AV) node. The AV node delays the impulse, so that the atria and
ventricles don’t fire at the same time. The delay is seen
on the EKG as the P-R interval. As the impulse travels down the
perkinje fibers in the ventricles, it generates the QRS complex.
Repolarization:
In order for the heart to fire again, it needs to re-load. Electrical
re-loading of the heart is called repolarization and is represented
by the T-wave on the EKG.
Using
the 5-step method
The EKG site uses a 5-step method to recognizing normal and abnormal
EKG rhythms (see level 1). The five steps
are listed below:
Step
1. Is the speed of the rhythm between 60-100?
Step 2. Is it regular?
Step 3. Is the complex narrow?
Step 4. Is it preceded by a P-wave?
Step 5. Do all the complexes look the same?
Step
1 evaluates the speed of the rhythm to determine if it is normal,
too slow or too fast. A speed between 60-100 maintains the best
hemodynamic stability. Rates less than 60 or greater than 100, can
lead to hemodynamic instability and become symptomatic.
Step
2 asks if the rhythm is regular. Rhythms originating from the normal
pacemakers in the heart will be regular. Irregular rhythms indicate
extra beats or abnormal rhythms.
Step
3 assesses the shape of the complex. A narrow complex is normal.
A wide complex indicates conduction abnormalities.
Step
4 asks if a P-wave precedes the QRS complex. This represents normal
conduction from the atria to the ventricles. If the P-wave is absent,
the impulse is being generated from elsewhere in the heart.
Step
5 assesses whether all the complexes look the same. Normal conduction
follows the same pathway with each beat. Different looking complexes
indicate the some impulses are following
alternative or aberrant pathways.
Regular
Sinus Rhythm
A heart rhythm that originates in the sinoatrial node and is normally
conducted is called a Normal Sinus Rhythm (NSR). The characteristics
of a normal sinus rhythm are a regular rate between 60-100 beats
per minute, a narrow complex, preceded by a P-wave where all the
complexes look the same.
Normal
conduction indicates that the myocardium is not irritable or injured.
The real test to determine whether a patient is hemodynamically
stable is to check his blood pressure. So, vital signs should be
taken.
Use the 5-Step approach to identify the rhythm:
Step 1. Rate: 60-100
Step 2. Regular
Step 3. P-wave precedes QRS (PR interval 0.16 sec)
Step 4. Narrow complex (QRS duration 0.06 seconds)
Step 5. All complexes look the same
All
five questions were answered with a “yes”; therefore
this is a normal sinus rhythm. A normal sinus rhythm is usually
associated with normal hemodynamics, but the blood pressure should
be taken to validate stability. There is no treatment necessary
if the patient’s blood pressure is normal.
Practice
and work with abnormal rhythms
Level 1 uses the “5-Steps to Rhythm Strip Interpretation”
to identify sinus rhythm and recognize abnormal rhythms. If you
would like to be able to easily interpret rhythm strips and implement
appropriate treatment for your patients, check out the Level
1 program.
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