Transcript Slide 1

Chapter 14
Heart: Cardiovascular Physiology
Part 3
Exam 3 will be on Monday November 21
Will cover chapters 11, 12, 13, 14
May cover more, depends on how far we get
Bring Scantron, #2 pencils
Electrocardiogram (ECG or EKG)
Recordings of the electrical activity of the heart
First ECG: 1887
Walter Einthoven, a Dutch physiologist figured all of
this out and named everything
He also came up with Einthoven's Triangle (next slide)
– Hypothetical triangle – leads are placed on both
arms and the left leg
Figure 14-19
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Figure 14-22
An ECG is not
the same as an
Action Potential
(from a single cell)
ECG is the sum
of electrical
activity from all
cells
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Electrocardiogram (ECG or EKG)
An ECG is recorded from one lead at a time
One electrode acts as the positive and the other as the
negative
In lead I, left arm electrode is positive, right arm
electrode is negative
Figure 14-19
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Electrocardiogram (ECG or EKG)
An ECG tracing shows the summed electrical
potentials generated by the heart cells
Atrial and ventricular depolarization and repolarization
(electrical events) are shown on the ECG
Because depolarization initiates muscle contraction,
the electrical events of the heart can be associated
with the mechanical events (contraction/relaxation) of
the heart
Electrocardiogram (ECG or EKG)
Cardiac Cycle
A single contraction-relaxation cycle of the heart
Major components to an ECG
– Waves
• Deflections above or below the baseline
– Segments
• Sections of baseline between two waves
– Intervals
• Combinations of waves and segments
Figure 14-20
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Electrocardiogram (ECG or EKG)
P wave
– Depolarization of the atria
QRS complex
– The progressive wave of ventricular depolarization
T wave
– Repolarization of the ventricles
Note: Atrial repolarization isn't shown as a separate
wave – It is part of the QRS complex
Figure 14-20
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ECG (fig. 14-21, p. 493)
Mechanical events lag slightly behind electrical events
P wave
– Atrial contraction begins during latter part of P
wave, continues during PR segment
QRS complex
– Ventricular contraction begins just after the Q
wave, continues through the T wave
Figure 14-21, overview
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ECG is a good diagnostic tool:
– Quick, painless, non-invasive
But interpretation of results can be quite complicated
Interpretation of results:
1. Heart rate
• Timed from beginning of one P wave to
beginning of next P wave
• Normal resting heart rate: 60-100 beats/min
• Often slower in trained athletes
Heart rate
– Tachycardia: faster than normal
– Bradycardia: slower than normal
2. Heart Rhythm
– Regular (occurs at regular intervals)
– Irregular or Arrhythmia
• Can range from a benign extra beat to fibrillation
• “dropped beats” caused by ventricles not getting
their signal to contract
• Premature ventricular contractions (PVCs)
–A pacemaker other than the SA node jumps in
and fires out of sequence
3. Are all normal waves present and recognizable?
– See examples in fig. 14-23, p. 495
4. Does a QRS complex follow each P wave; is the PR segment constant in length?
– If not, then a problem with signal conduction
through the AV node may be present
5. Look for subtle changes:
– For example: Alterations in shape or duration of
waves or segments
Long QT syndrome (LQTS):
Results from structural abnormalities in the potassium
channels of the heart,
Predisposes affected persons to an accelerated heart
rhythm (arrhythmia)
Can lead to sudden loss of consciousness and may
cause sudden cardiac death in teenagers and young
adults who are faced with stressors ranging from
exercise to loud sounds.
Normal ECG
Long QT syndrome (LQTS)
With training and experience, it becomes possible to
see, in the ECG, heart conditions such as:
– Enlargement of the heart
– Tissue damage from ischemia (lack of adequate
blood flow and oxygen to a tissue)
– Changes in conduction velocity
– Etc.
Figure 14-23
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Cardiac Cycle
(fig. 14-24, p. 496)
Cardiac cycle has 2 phases:
Systole and Diastole
Systole
– Time interval during which cardiac muscle
contracts
Diastole
– Time interval during which cardiac muscle relaxes
Figure 14-24, overview
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Cardiac Cycle
(fig. 14-24, p. 496)
1. Heart at rest: atrial and ventricular diastole
– Both atria and ventricles are relaxed
– Atria are filling with blood from veins
– Ventricles have just completed a contraction
– As ventricles relax, the AV valves open
– Blood flows by gravity from atria to ventricles
Cardiac Cycle
(fig. 14-24, p. 496)
2. Completion of ventricular filling: atrial systole
– Most blood flows to the ventricles via gravity
– The last 20% is squeezed down into ventricles
when the atria contract (normal person at rest)
– During exercise, atrial contraction can play a
bigger role in ventricular filling
– Atrial contraction (systole) begins after the
depolarization wave has swept across the atria
Cardiac Cycle
(fig. 14-24, p. 496)
2. Completion of ventricular filling: atrial systole (con't)
During atrial contraction, a small amount of blood is
forced back into the veins since they don't have oneway valves
This backward flow can be felt as a pulse in the jugular
vein (normal person, lying with head and chest
elevated about 30 degrees)
Cardiac Cycle
(fig. 14-24, p. 496)
3. Early ventricular contraction and first heart sound
Ventricular contraction begins as the spiral bands of
muscle squeeze the blood upward, from apex towards
the base of the heart
AV valves are forced closed by blood pushing up
against them
First heart sound (S1 or “lub”) comes from vibrations
after AV valves have closed
Cardiac Cycle
(fig. 14-24, p. 496)
Isovolumic ventricular contraction
Similar to an isometric contraction (like squeezing a
water balloon)
Both AV and semilunar valves are closed during this
part—blood has nowhere to go
At the same time, the atria are repolarizing and
relaxing
Cardiac Cycle
(fig. 14-24, p. 496)
4. Ventricular ejection
As the ventricles continue to contract (from part 3),
they soon generate enough pressure to open the
semilunar valves and push blood into the arteries
The pressure generated by ventricular contraction
b4comes the driving force for blood flow
At the same time, AV valves remain closed, atria are
filling
5. Ventricular relaxation and the second heart sound
At the end of ventricular ejection, Ventricles begin to
repolarize and relax
Ventricular pressure decreases
Once it falls below the pressure in the arteries, blood
begins to flow backward into the heart
The backflow fills the cusps of the semilunar valves
and forces them closed
Second heart sound (S2 or “dup”)
Heart sound: lub-dup
Isovolumic ventricular relaxation
Semilunar valves close, ventricles become sealed
chambers again
AV valves are still closed also
When ventricular relaxation causes ventricular
pressure to fall below atrial pressure, the AV valves
open
Blood rushes into the ventricles and the cycle starts
over again
Figure 14-24, overview
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Figure 14-25
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Figure 14-26, overview
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Figure 14-27
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Figure 14-28
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Figure 14-29
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Figure 14-30
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Figure 14-31
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