Transcript lecture 4 A 12-lead electrocardiogram (ECG)

A 12-lead electrocardiogram
By
Dr Abdul-Monim Batiha
Dr Ibrahim Bashayreh
A 12-lead electrocardiogram
(ECG)
ECG is a graphic record of
electric
currents
that
are
generated by the heart muscles.
Electrical impulses are picked up
by the surface electrode which
are placed at various points on
the body and connect the ECG
machine to the body.
Objectives
 To
diagnose the presence of MI.
 To diagnose the presence of cardiac
dysrrhythmias.
 To diagnose the presence of cardiac
enlargement and size of cardiac
champers.
 To
detect
the
electrolyte
abnormalities especially K and Ca.
 To
evaluate the effect of
therapeutic interventions on the
heart ( e.g. drugs, fluid, and
mechanical support)
 The
12-lead ECG provides “views”
of cardiac electrical activity from
12 different vantage points on the
body surface.
ASSESSMENT
1.
Assess age, gender, and current
medication history for any
medications with possible cardiac
or hemodynamic effects. Gather
other data that may be required by
unit/institution protocol (height,
weight, recent blood pressure,
operator identification).
A 15-lead ECG adds 3 additional chest
leads across the right precordium and
is a valuable tool for the early diagnosis
of right ventricular and posterior left
ventricular infarction. The 18-lead
ECG adds 3 posterior leads to the 15lead ECG and is very useful for early
detection of myocardial ischemia and
injury
Determine that the client is able to tolerate
a supine position and that adequate
exposure of chest and limbs is possible for
electrode placement. Correct sitting of
electrodes
is
enhanced
by
comfortable, stable position.
Determine presence of neck, arm, jaw, or
other pain with possible cardiac origin.
Chest or other pain may provide
additional information useful in serial
comparison of ECGs.
Assess client need for information about the
procedure purpose and requirements and
ability to cooperate: that client should lie
still and refrain from talking, electrode
attachment, procedure lasts only a few
minutes and is painless. Anxiety may be
relieved by simple explanation of
intent, duration, and purpose.
Equipment Needed
• Twelve-lead ECG machine with charged battery,
cables and leads, graph paper
• Disposable electrodes (12)
• Electrode paste or gel
• Alcohol wipes
• Pillows
• Sheet or drape
• Towel and washcloth
• Disposable razor
Each of the 12 leads represents a particular
orientation in space, as indicated below (RA =
right arm; LA = left arm, LF = left foot):
 Bipolar limb leads (frontal plane):
Lead I: RA (-) to LA (+) (Right Left, or lateral)

Lead II: RA (-) to LF (+) (Superior Inferior)
Lead III: LA (-) to LF (+) (Superior Inferior)
Continuous Electrocardiographic
Monitoring
 Continuous
ECG monitoring is
standard for patients who are at
high risk for dysrhythmias.
Two continuous ECG monitoring
techniques
hardwire monitoring, found in critical care
units and specialty step-down units, and
 telemetry, found in specialty step-down
units and general nursing care units.

Patients who are receiving
continuous ECG monitoring
need to be informed of its
purpose and cautioned that
this monitoring method will not
detect symptoms such as
dyspnea
or
chest
pain.
Therefore, patients need to be
advised to report symptoms to
the nurse whenever they
occur.
HARDWIRE CARDIAC MONITORING
 The
patient’s ECG can be
continuously
observed
for
dysrhythmias and conduction
disorders on an oscilloscope at
the bedside or at a central
monitoring station by a hardwire
monitoring system.
Objectives of cardiac monitor
•
Monitor
more
than
one
lead
simultaneously
• Monitor ST segments (ST-segment
depression is a marker of myocardial
ischemia; ST-segment elevation provides
evidence of an evolving MI)
• Provide graded visual and audible alarms
(based on priority, asystole would be
highest)
 • Computerize rhythm monitoring
(dysrhythmias are interpreted and stored
in memory)
 • Print a rhythm strip
 • Record a 12-lead ECG

commonly used for
continuous monitoring are leads
II and V1 or a modification of V1
Lead II provides the best
visualization
of
atrial
depolarization (represented by
the P wave). Leads V1 and II best
visualize the ventricle responsible
for
ectopic
or
abnormal
ventricular beats.
Two
leads
Following the guidelines for electrode
placement
will
ensure
good
•conduction and a clear picture of the
patient’s rhythm on the monitor:
Clean the skin surface with soap
and water and dry well (or as
recommended
by
the
manufacturer) before applying
the electrodes. If the patient has
much hair where the electrodes
need to be placed, shave or clip
the hair.
 Apply
a small amount of benzoin
to the skin if the patient is
diaphoretic (sweaty) and the
electrodes do not adhere well.
PULSE OXIMETRY
 Is
a
noninvasive
method
of
continuously monitoring the oxygen
saturation of hemoglobin (SpO2 or
SaO2). Although pulse oximetry does
not replace arterial blood gas
measurement, it is an effective tool to
monitor for subtle or sudden changes
in oxygen saturation.

It is used in all settings where oxygen
saturation monitoring is needed, such as
the home, clinics, ambulatory surgical
settings, and hospitals.

It is used in all settings where oxygen
saturation monitoring is needed, such as
the home, clinics, ambulatory surgical
settings, and hospitals.

A probe or sensor is attached to the
fingertip, forehead, earlobe, or bridge of
the nose. The sensor detects changes in
oxygen saturation levels by monitoring
light signals generated by the oximeter
and reflected by blood pulsing through the
tissue at the probe.
naloxone :a drug resembling morphine, used in the diagnosis of narcotics
addiction and to reverse the effects of narcotics poisoning
Physiologic Limitations.
Elevated levels of abnormal hemoglobins,
 Presence of vascular dyes,
 Poor tissue perfusion. The pulse oximeter
cannot differentiate between normal and
abnormal hemoglobin.

 Elevated
levels
of
abnormal
hemoglobin falsely elevate the Spo2.
 Vascular dyes such as methylene
blue, indigo also interfere with pulse
oximetry and can lead to falsely low
readings.
 Poor tissue perfusion to the area with
the probe leads to loss of pulsatile
flow and signal failure.
Technical Limitations.
 Technical
limitations include
 Bright lights,
 Excessive motion,
 Incorrect placement of the probe.
Bright lights may interfere with
the photodetector and cause
inaccurate results. The probe
must be covered to limit optical
interference.
 Excessive
motion can mimic
arterial pulsations and can lead to
false
readings.
Incorrect
placement of the probe can lead
to inaccurate results, because
part of the light can reach the
photodetector without having
passed through blood (optical
shunting).
Interventions to limit these
problems include
Using the proper probe in the appropriate
spot (e.g., not using a finger probe on the
ear),
 Applying the probe according to the
directions, and ensuring that the area
being monitored has adequate perfusion.

Equipment
Pulse oximeter
 Sensor (permanent or disposable)
 Alcohol wipe(s)
 Nail polish remover, if indicated

Assessment
Signs and symptoms of hypoxemia
(restlessness; confusion; dusky skin,
nailbeds, or mucous membranes)
 Quality of pulse and capillary refill
proximal to potential sensor application
site
 Respiratory rate and character
 Previous pulse oximetry readings
 Amount and type of oxygen
administration, if applicable
 Arterial blood gases, if available

Capnography
Is the measurement of exhaled carbon
dioxide gas and can be used to
monitor a patient's ventilatory status.
A capnograph is also known as an
end-tidal CO2 monitor, because the
CO2 is measured near the end of the
exhalation.
 Most
often, the gas sample is
analyzed
through
infrared
gas
analysis. Frequently the CO2 is
measured via the exhalation port of
the ventilator tubing; as the gas
passes through the sensor, the data
are transferred to the display unit. A
display unit produces a waveform,
called a capnogram
and a numeric recording approximating
the Paco2.
 The
ability of the capnograph to
approximate arterial Paco2 is altered with
abnormal cardiopulmonary function

Clinical application of
capnography
can provide information in a number of
areas including:
 Estimation of Paco2 levels,
 Assessment of dead space (increased
V/Q),
 Assessment of pulmonary blood flow, and
endotracheal tube placement.

Normally alveolar and arterial CO2
concentrations are equal in the presence
of
normal
ventilation/perfusion
relationships. In a patient who is
hemodynamically stable, the end-tidal CO2
(Petco2) can be used to estimate the
Paco2, with the Petco2 levels 1 to 5 mm
Hg less than Paco2 levels.The practitioner
must determine first that a normal V/Q
relationship exists before correlation of the
Petco2 and the Paco2 can be assumed.
 Assessment
of
changes
in
physiologic dead space can be
carried out with end-tidal CO2
monitoring, based on the degree
of difference between the Paco2
and the Petco2. As the severity of
pulmonary impairment increases,
so does the disparity between the
Paco2 and the Petco2, as
indicated
by
an
increased
gradient.

A gradient of greater than 5 mm Hg can
be seen with underperfused alveolarcapillary units (dead space–producing
situations) and nonperfused alveolarcapillary units (alveolar dead space).
Increased dead space ventilation is a
result of decreased pulmonary blood flow
or cardiac output and lung disease. This
leads to an abnormality in the transfer of
CO2 from the blood to the lung.
 The
result is a Petco2 level that is
lower than the Paco2 because of
the mixing of carbon dioxide
between
perfused
and
nonperfused units. The end result
is an increased or widened Paco2to-Petco2 gradient.
The noninvasive measurement of
Petco2 Allows for :
 The
assessment of adequacy of
cardiopulmonary resuscitation and
endotracheal tube placement.
 Decreased pulmonary blood flow is
associated with lower Petco2 values,
reflected clinically by decreased
cardiac output, as in the case of
cardiopulmonary resuscitation.
 During
endotracheal intubation, a low
Petco2 reading would indicate that
the tube is positioned in the stomach,
because the amount of carbon
dioxide in the esophagus is expected
to be low.
Sublingual Capnometry
 Sublingual
carbon dioxide (PSLco2)
measurement is a new noninvasive
technology available for monitoring
patients at risk for hypoperfusion.
Unrelieved hypoperfusion has been
closely linked with development of
multisystem
organ
dysfunction
syndrome (MODS).