Download Canine and Feline Electrocardiography

Canine and Feline
Electrocardiography
VTHT 1491
Special Topics
Reading:
VTDRG: Pg: 338-345; 205-220
CTVT: Pg: 699-702; 1179-1182; 1306
All Handout
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A little history….
• In 1790, an audience of usually sedated scientists gasped in
disbelief as Luigi Galvani, with a flare of showmanship, made
a dead frog’s legs dance by electrical stimuli
• Galvani knew that completing a circuit connecting dissimilar
metals to the legs of a recently deceased frog would create a
stimulating electrical current
• The resulting current would stimulate the frog’s legs to jump,
and with repeated stimulation, he could make then dance
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History cont’d
• In 1855, Kollicker and Mueller discovered that when a
motor nerve to a frog’s leg was laid over its isolated,
beating heart, the leg kicked with each heartbeat
• Therefore, the same electrical stimulus that causes a frog’s
leg to kick must cause the heart to beat
• Logic dictated that the beating of the heart must be due to
a rhythmic discharge of electrical stimuli
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History cont’d
• 1880’s - Ludwig and Waller discovered that the
heart’s rhythmic electrical stimuli could be
monitored from a person’s skin
• 1887-Augustus Waller invented the electrode. This
device allowed the currents to be measured
through intact skin
• 1901 – Dr. William Einthoven invented the EKG
machine, the PQRST system and established the 3
points on the body where electrodes are placed
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History…
• Dr. Einthoven won the Nobel peace prize for his
invention
• Today, the ECG machine remains one of the single
most important tools in medicine used for
diagnosis, monitoring, and gauging response to
therapy
• We rely on ECGs daily in ambulances and
hospitals and by phone line to save the lives of
thousands
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Applications of the Electrocardiogram
•
•
•
•
Acute onset of dyspnea
Shock
Fainting or seizures
Monitoring during and after surgery
(monitors depth of anesthesia as
well as cardiac monitoring)
• All cardiac murmurs
• Cardiomegaly (enlarged heart) that is
found on thoracic radiographs
• Preoperatively
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Applications of ECG continued
• Cyanosis ( Blue or Purple coloration of the skin
or M Membranes)
• Evaluating effect of cardiac drugs
• Pericardiocentesis (fluid is aspirated
from the sac around the heart)
• Systemic diseases
– Examples?
• Electrolyte disturbances
– What electrolytes do you
think may be associated with ECG
abnormalities?
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Conduction System of the Heart
Review
• Electrical impulses are
transmitted through the heart
via specialized conduction
cells in a specific sequence:
–
–
–
–
–
Sinoatrial (SA) node
Atrioventricular (AV) node
Bundle of His
Left and right bundle branches
Purkinje fibers
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Remember Depolarization vs
Repolarization?
• Depolarization- heart muscle contraction in
response to electrical stimulus. (Squeeze)
– Occurs when electrolytes (Na, Ca, and K) move
across the cell membrane causing a contraction
• Repolarization- heart muscle relaxation occurs
when the electrolytes move back across the
cell membrane rendering the cell ready for the
next electrical impulse
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Five Physiologic Properties of Cardiac
Muscle
1. Automaticity
– SA node is the primary pacemaker of the heart, but any
cells of conduction system can initiate their own
impulses under right circumstances
– The further down in the conduction system, the slower
the rate of automaticity
2. Excitability
– Cardiac muscle is excited when the electrical stimulus
reduces the resting potential to the threshold potential
– The degree of the resting potential within the cell
determines its excitability and obeys the “all-or-none”
law.
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3. Refractoriness
– Heart muscle will not respond to external stimuli
during its period of contraction (Resting period in
between beats)
4. Conductivity
– Activation of an individual muscle cell produces activity
in the neighboring muscle cell
– Conduction velocity varies in the different portions of
the specialized conduction system and muscle fibers
– Velocity is greatest in the Purkinje Fibers and least in
the mid-portion of the AV node
– Activation sequence is so arranged that the maximum
mechanical efficiency is provided from each
corresponding contraction
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5. Contractility
– Occurs in response to electrical current
– The ECG only measures the stimulus for
contraction- not the actual contraction itself
*ECG is the tool of choice for measuring contractility
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Major Confusion!!!
• Reading an ECG and deciphering
what it is telling you can be
confusing
• ECGs provide a graphical
representation of the electrical
impulses of the heart
• Electrical impulses are what make
the heart contract
• This contraction is a result of
depolarization and repolarization
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Electrocardiogram
• Definition: Graphic recording of electrical
potentials produced by heart muscle during the
different phases of the cardiac cycle
• The information recorded on the EKG represents
the heart’s electrical activity
• Most of the information on the EKG represents
electrical activity of contraction of the
myocardium
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Electrocardiogram cont’d
– The voltage
variations are
produced by
depolarization and
repolarization of
individual muscle
cells
– Each portion of the
electrocardiogram
thus arises from a
specific anatomic or
physiologic area of
the heart
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A Little Vocabulary
• Artifact: A wave that arises from sources other than the heart
• Cardiac Arrhythmia: Any electrical activity of the heart that
differs from that of a healthy, awake patient. Can be
innocuous or life-threatening
• Deflection: Movement from one side to the other
• Ectopic: Occurring in an abnormal location/position
• Lead: A pair of electrodes, connected by an axis that provides
a particular view of the electrical activity of the heart
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Solid Ground
• Having the ECG machine well grounded is an
important factor for obtaining an accurate
reading
• Placing the patient on a rubber mat and ensuring
that the machine is plugged into a grounded
outlet as well as checking the ECG machine for
loose wires or cracked insulation on wires are
steps that can be taken for a good ground
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ECG CONNECTOR AND LEADS
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