Transcript ischemia

ISCHEMIA
Continuing Education
March, 2001
GOALS:
Upon completion of this offering, the
participant will be able to:
• define ischemia
• discuss its significance, and
• recognize major S-T segment changes in
the ECG
Lesson Outline (Objectives):
• Review of coronary circulation
• Review of ECG components
• Definition of ischemia
• Causes of ischemia
• Corresponding ECG changes with coronary ischemia
S-T segment elevation
S-T segment depression
Examples of ST changes
• Diagnosis of ischemia
• Study questions
Review of Coronary Artery Circulation
The heart is a muscular organ
composed of four chambers:
the two upper (smaller)
chambers are called atria and
the two lower (larger) are
known as ventricles. The four
chambers work together to
pump blood throughout the
body, bringing oxygenated
blood to the cells. Since the
heart is a muscle, it too must
have oxygen and nutrients to
do its job.
NOTE: Aorta tell you that although the heart
pumps blood to the body during ventricular
contraction (systole), the blood to its own
arteries is circulated during rest (diastole)
The heart’s blood supply comes
from its own arteries, the
coronary arteries, which form
a network over the surface of
the heart much like the
branches or roots of a tree.
Review of Coronary Artery Circulation
The coronary circulation is provided by two
arteries that branch off from an area close
to where the aorta leaves the heart. They
are known as the right and left coronary
arteries. Although each person has his or
her own unique pattern of circulation, for
most persons the arteries supply the heart
in the following manner:
The LEFT CORONARY ARTERY divides into
the left anterior descending (LAD) and the
circumflex arteries. The LAD provides
oxygen and nutrients down the front of the
heart, to both (but primarily the left)
ventricles. The circumflex branch winds
around the back (posterior) part of the
heart.
The RIGHT CORONARY ARTERY (RCA) is the conduit for blood
flow to the right heart, inferior (lower) portion of the ventricle
and a portion of the left lateral wall of the ventricle.
Both arteries continue to branch out into many “limbs” to supply
the heart muscle with oxygen and nutrients.
Review of ECG Components
Correlation between ECG components and heart activity: the P-R
interval represents atrial activity, the QRS represents systole
(contraction), and ST repolarization (diastole or rest).
Review of ECG Components
ECG components are measured in time and distance. Each small horizontal square equals
0.04 seconds. Each small vertical square is the equivalent of 0.1 millivolt, or more
commonly, 1 mm. The above diagram shows the electrical activity in one heart beat. (More
on this in next month’s lesson.)
What is Ischemia?
Ischemia is the result of loss or
decrease of blood supply to a tissue
or organ, particularly the heart
muscle. Untreated, ischemia will
lead to death of the muscle or organ
tissue.
Heart or myocardial ischemia occurs when the demand for
oxygen by the heart is not met, or when the work of the
heart muscle (myocardium) exceeds available oxygen.
Pain that is the result of diminished blood supply is
referred to as “angina”. If the lack of oxygen continues,
the heart muscle will die and the patient will suffer a
myocardial infarction (death of myocardium).
What causes Ischemia?
BLOCKAGE Any process that impedes the
circulation of heart arteries can cause ischemia.
Impaired flow of blood and oxygen to heart muscle
is usually due to a blockage in one of the arteries
that serve the heart itself. A blockage can be
composed of substances such as lipids (blood fats),
tar and nicotine from cigarette smoking, or blood
components such as sticky platelets or red blood
cells.
CONSTRICTION The arteries themselves may be
narrowed because of spasm or constriction, which in
turn lessens blood flow and oxygen.
BLOOD DEFICIENCY Low blood volumes, such as a
person suffering from massive bleeding or severe
anemia, can lead to ischemia because of the lack of
sufficient blood to carry oxygen to the myocardium,
resulting in ischemia.
ST Segment Changes with Ischemia
Electrical conduction going through the heart muscle that is
ischemic is altered: if the normal pathway for electrical
conduction is affected, the electrical impulse will go around
the area, with corresponding changes on the ECG.
The new pathway will result in either ST segment depression
or elevation. Generally, four millimeters (four small vertical
blocks on the ECG) of depression or elevation indicate
ischemia. Normally, ST segments are in the isoelectric line
or no more than 1 mm (one small block) above or below it. ST
segment changes are the earliest indication on the ECG of
myocardial ischemia or impending damage.
Isoelectric line
Note how the electrical
conduction circumvents the
area of ischemia, resulting in
ST segment elevation on the
ECG (normal ECG in green)
Examples of Abnormal ST Segment Changes
The green line represents the isoelectric, or base,
line
Coronary Arteries and Related ECG
Changes
Ischemia, injury or death involving the right
coronary artery (RCA) most often result in
changes in the inferior surface of the heart:
Leads II, III, AVF
Obstruction of blood flow in the
circumflex artery is associated with
lateral changes from ischemia or
infarction: Leads I, AVL, V5, V6
Left anterior descending branch (LAD) of
the left coronary artery (LCA) flow
obstructions are associated with anterior
wall and/or septal changes: Leads V1 and
V2 (septal)…Leads 2,3,4 (anterior wall)
Diagnosing Ischemia
Cardiac ischemia must be verified by
a 12 lead ECG. A rhythm strip or
one lead will show only a single view
of the heart, and as was seen in the
preceding slide, different blockages
will affect different areas of the
heart and thus different areas of
the ECG.
Cardiac angiography (dye
inserted into the arteries of
the heart via leg vein) can
pinpoint anatomical areas of
blockage. See Fig. 4
Fig. 4 The above picture represents a
blockage in the left anterior descending
artery as seen via angiography. This is not
a good situation for the patient.
Stress testing via treadmill or bike may demonstrate ischemic
changes. Laboratory blood tests can also determine whether
heart muscle has been affected. Cardiac enzymes, myoglobin
and troponin if present can help pinpoint diagnosis of ischemia in
the emergency room.
Treatment
Treatment of ischemia/angina is dependent upon the underlying cause.
For a narrowing or blockage in a coronary artery, surgery can bypass the
blockage by implanting a blood vessel to go around the affected area
(coronary artery bypass graft - CABG)
An angioplasty (informally called a Roto Rooter) allows the surgeon to
remove some of the material blocking the inside of the artery to improve
blood flow. A small wire frame can also be placed inside an artery to keep
the vessel from re-occluding (stenting).
Medical treatment can include various medications or combinations thereof,
such as nitrates, which dilate the arteries and reduce work of the heart.
This group of medication includes nitroglycerin, which patients put under
their tongues to relieve angina from ischemia.
Aspirin should be given immediately when ischemia is suspected.
Supplemental oxygen is also frequently given. Other groups of medications
such as calcium channel blockers or beta blockers may be prescribed as
well. Cholesterol lowering medication can help prevent further blockages. If
the ischemia is due to low blood volume, replacement of blood can relieve
the lack of oxygen.
REMEMBER……
Untreated myocardial ischemia
can lead to a heart attack and
death. Ischemia is reversible.
Study Questions
1. Ischemia is defined as
a. Heart attack b. Blockage in an artery
d. Rapid heart rate
c. Lack of oxygen to heart muscle
2. ST segment changes of ischemia should be at least _______ mm from the
isoelectric (base) line.
a. One
b. Two
c. Three
d. Four
3. The CardGuard products that can be used in detection of ischemia are:
a. Rhythm check
e. A and D
b. CG 6560 disclosure
f. B and C
c. Micro12 ECG
d. King of Hearts
4. Persons experiencing signs of ischemia or heart attack should immediately take:
a. red wine
b. aspirin
c. strong coffee
d. ibuprofen
Study Questions
5. Indicate whether the ST segments in the following ECG
demonstrate
a. Elevation
Extra
Credit:
What part of
the heart is
depicted
here?
b. Depression
c. Horizontal
d. Normal
Study Questions
6. The main arteries of the heart are:
a. Top and bottom coronary arteries
b. Right and left coronary arteries
and back coronary arteries
d. Interior and exterior coronary arteries
c. Front
7. The number of ECG leads needed to diagnose heart attack or ischemia are:
a. Six
b. Twelve
c. Four
d.
Eight
7. Nitroglycerine is used by patients to
a. Alleviate headache b. Constrict the arteries of the heart
d. Blow up the back yard
c. Relieve angina
9. When the electrical activity of the heart travels over damaged heart tissue, the
electrical impulse will
a. Go through it at a rapid rate
d. Return to its point of origin
b. Stop completely c. Go around the area
Study Questions
10. Chuck, an avid golfer aged 55, had been experiencing
intermittent pressure between his shoulder blades for several weeks.
At first he dismissed it as a muscle strain, but the fact that he had a
history of high cholesterol and cigarette smoking compelled him to
visit a cardiologist. He did not experience any pressure on the
treadmill stress test nor did it show any abnormalities; however, the
pressure continued to present itself on and off, particularly when he
walked up the steep eighteenth fairway at his home club. What
device(s) in your bag of products would you recommend that the
cardiologist try with Chuck?
a. King of Hearts
b. MicroER
c. Rhythm Check
d. Micro 12 ECG
e. CG 6550 Disclosure