Learning Objectives
After reading this chapter you should be able to:
1. Describe the organization of the cardiovascular system.
2. Describe the sequence of events that occur during one cardiac cycle.
Explain how pressures and volumes within the heart chambers change.
3. Describe the pressure – volume loop.
4. List the approximate values for mean pressures found at various stages of
the cardiac cycle.
5. Explain how an increase in heart rate would affect various stages of the
cardiac cycle.
6. Describe and explain the atrial and central venous pressure waves.
7. Explain the ECG in terms of the cardiac cycle.
8. Describe and explain when sounds are heard during the cardiac cycle.
9. Explain why S2 is split.
10. List and explain the common types of heart murmurs.
Cardiac cycle describes the sequence of
electrical and mechanical events that occur in
the heart during one single beat
• The cycle is divided into two major phases, both named
for events in the ventricles: the period of ventricular
contraction and blood ejection, systole, followed by the
period of ventricular relaxation and blood filling,
diastole.
• At an average heart rate of 72 beats/min, each cardiac
cycle lasts approximately 0.8 s, with 0.3 s in systole and
0.5 s in diastole
Like a pump with a
reciprocating
piston, the heart
alternates
between a filling
phase and an
emptying phase.
To understand the
Mechanical event you must
recall:
Anatomy of the Heart
• The atrioventricular (AV)
valves prevent blood flow from
the ventricles back into the atria
• The pulmonary and aortic
valves prevent backflow from
the pulmonary trunk into the
right ventricle and from the
aorta into the left ventricle
respectively
Cardiac valves operation. They open when pressure gradient across the valves is
increasing in the direction that blood normally flows (forward pressure gradient)
(A). A reverse pressure gradient (B) will force the valve closed, which prevents
reverse blood flow in response to reverse pressure gradient that occur as a result of the
pumping action. (C). A forward pressure gradient forces the semilunar valve to open.
Darker colors correspond to higher pressure
Isovolumetric ventricular relaxation
/phase 4
ventricular
filling/phase 1
Diastole =
Iso-volumetric
ventricular contraction/phase 2
Systole =
Ventricular ejection/phase 3
Mechanical events of the cardiac cycle
1
START
5
4
Isovolumic ventricular
relaxation: as ventricles
relax, pressure in ventricles
falls, blood flows back into
cups of semilunar valves
and snaps them closed.
Ventricular ejection:
as ventricular pressure
rises and exceeds
pressure in the arteries,
the semilunar valves
open and blood is
ejected.
Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
Atrial systole: atrial contraction
forces a small amount of
additional blood into ventricles.
2
3
Isovolumic ventricular
contraction: first phase of
ventricular contraction pushes
AV valves closed but does not
create enough pressure to open
semilunar valves.
Mechanical Events
1
START
Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
1
START
Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
2
Atrial systole:
atrial contraction
forces a small amount
of additional blood into
ventricles.
1
START
Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
Atrial systole: atrial contraction
forces a small amount of
additional blood into ventricles.
2
Isovolumic ventricular
contraction: first phase of
ventricular contraction
pushes AV valves closed but
does not create enough
pressure to open
semilunar valves.
3
1
START
Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
Atrial systole: atrial contraction
forces a small amount of
additional blood into ventricles.
2
Ventricular ejection:
as ventricular pressure
rises and exceeds
pressure in the arteries,
the semilunar valves
open and blood is
ejected.
3
4
Isovolumic ventricular
contraction: first phase of
ventricular contraction pushes
AV valves closed but does not
create enough pressure to open
semilunar valves.
Isovolumic ventricular
relaxation: as ventricles
relax, pressure in ventricles
falls, blood flows back into
cups of semilunar valves
and snaps them closed.
5
Ventricular ejection:
4
as ventricular pressure
rises and exceeds
pressure in the arteries,
the semilunar valves
open and blood is
ejected.
START
1 Late diastole: both sets of
chambers are relaxed and
ventricles fill passively.
2 Atrial systole: atrial contraction
forces a small amount of
additional blood into ventricles.
3
Isovolumic ventricular
contraction: first phase of
ventricular contraction pushes
AV valves closed but does not
create enough pressure to open
semilunar valves.
http://library.med.utah.edu/kw/pharm/hyper_
heart1.html
The period lasting from the closure of the
atrioventricular (AV) valve to the opening of the aortic
valve is generally known as
A
B
C
D
E
Ventricular filling phase
Isovolumetric ventricular contraction
Ventricular ejection phase
Isovolumetric ventricular relaxation
Protodiastole period
The heart at rest:
atrial and ventricular
diastole.
The atria are filling with blood from
the veins, and the ventricles are
relaxing – the AV valves between the
atria and ventricles open. Blood is
flowing by gravity into the
ventricles. The relaxing ventricles
expand to accommodate the entering
blood. At this moment the ventricles
are ~ 80 – 90% filled with blood.
This is the section to the left of
atrial systole on the diagram.
1. Atrial systole and completion of
ventricular filling.
The generation of an action potential by the SA
node results in a wave of depolarization
spreading through the atria P wave on the
ECG.
Atrial muscle contracts (atrial systole)
and atrial pressure rises (a wave).
A little more blood (10 – 20%), sometimes
called the‘atrial kick’ is pushed into the almost
full ventricles. However, a small amount of
blood is forced backwards into the great veins
(there are no one way valves between the
veins and the atria) causing a similar a wave in
the central veins (vena cava). This wave can
be seen as a pulse in the jugular vein of a
person who is semirecumbent with the head
and chest elevated ~ 30 degrees .
If a pulse is seen higher up the jugular vein in a
person who is upright it indicates that the right
atrial pressure is higher than normal.
End Diastolic Volume, end-systolic volume and
stroke volume
• The amount of blood in the ventricles just before
systole is the end-diastolic volume. The volume
remaining after ejection is the end-systolic volume,
and the volume ejected is the stroke volume
•S4- caused by vibration of the ventricular wall during atrial
contraction. Generally, it is noted when the ventricle compliance is
reduced ("stiff" ventricle) as occurs in ventricular hypertrophy and in
many older individuals.
2. Ventricular systole
A. Isovolumetric Contraction
The wave of depolarization reaches
ventricles and we have the QRS complex
on the ECG, which denotes ventricular
depolarization.
Shortly thereafter the ventricles
contract and squeeze the blood upward
and towards the base. As soon as the
pressure in the ventricles rises above the
atrial pressure, the AV
valves close causing the first heart
sound.
Since the aortic and pulmonary valves are
already closed each ventricle is now a closed
chamber. They continue to contract and
because they are closed, the pressure within
them rises very steeply (more in the LV than
the RV). This is called the isovolumetric
contraction phase
-c wave in the RA pressure tracing.
• When Ventricular pressures
exceed aortic and pulmonary
trunk pressure, the aortic and
pulmonary valves open, and V
ejection of blood occurs
• When the ventricles relax at the
beginning of the diastole, the V
pressures fall significantly below
those in the aorta and pulmonary
trunk, and the aortic and
pulmonary valves close. Because
the AV valves are also still
closed, no change in V volume
occurs during this isovolumetric
ventricular relaxation
The vibrations due to closure of the semilunar
valves give rise to the second heart sound.
• When
ventricular
pressures fall below the
pressures in the right and
the left atria, the AV valves
open, and the ventricular
filling phase of diastole
begins
• Filling occurs very
rapidly at first so that atrial
contraction, which occurs
at the very end of diastole,
usually adds only a small
amount of additional blood
to the ventricles
Fig. 12. Cardiac cycle again
Angiography
Heart Sounds. The common heart sound
are:
• The first heart sound is due to the closing
of the AV valves
• The second heart sound is due to the
closing of the aortic and pulmonary valves
Heart Sounds
Sound Characteristics
Associated events
S1
First heart sound (sounds like “lub”)
Two bursts, a mitral M1 and a tricuspid T1
components
Closure of mitral &
tricuspid valves
S2
Second heart sound (sounds like “dub”)
An aortic A2 and a pulmonary P2 component
Closure of aortic and
pulmonary valves
OS
Opening Snap
Opening of a stenotic
mitral valve
S3
Third heard sound
Diastolic filling gallop or
V or protodiastolic gallop
S4
Fourth heart sound
Atrial sound that creates
an atrial or presystolic
gallop
Note that a physiological S3 sound is present in some normal individuals,
particularly children. Occurs in early diastole with rapid filling of the ventricles;
When present S4 coincides with atrial contraction but usually it is abnormal
Location of the sounds on the
chest
Each valve is best heard by a
stethoscope from 4 distinct areas:
Mitral valve: Mid clavicular line of
the 5th left intercostal space
Tricuspid valve: 5th interspace at the
left sternal edge
Aortic valve: 2nd interspace at the
right sternal edge
Pulmonary valve: 2nd interspace at
the left sternal edge
Heart Murmurs: Abnormal heart sounds heard on
auscultation which are due to faulty valves.
• Incompetence: Failure of the valve to seal properly
(valve may be torn, perforated, affected by rheumatic fever
or a failing heart may be enlarged) such that it becomes
leaky allowing blood to regurgitate through it
• Stenosis: The open valve is narrowed so that a higher
pressure gradient is needed to drive blood through
(cicatrization after rheumatic or other infection)
• Defective valves can be congenital or acquired. Abnormal valve
causes blood turbulence which sets up high frequency vibrations
which are heard as murmurs through the stetoscope
Rheumatic
heart disease
Heart Murmurs (cont.)
• Benign Systolic Murmur
• Aortic stenosis: Systolic
murmur. Due to narrowing
of the aortic valve when the
flow during ejection becomes
turbulent. Heard during
ejection (systolic murmur) as
ejection waxes and wanes (a
crescendo – decrescendo
murmur). Loudest over
aortic area
Aortic stenosis murmur
Mitral Stenosis
• left atrial pressure is elevated
with mitral stenosis  induce
hypertrophy of the left atrial
muscle.
• Elevated left atrial pressure
is reflected back into the
pulmonary bed and, if high
enough, causes pulmonary
congestion and "shortness of
breath.“
• A diastolic murmur
associated with turbulent flow
through the stenotic mitral
valve can often be heard.
If a murmur
heard
during
C and
increased
A. Thewas
aortic
valve
opens
at D2 which
and closes
at 7then
decreased in volume, which of the following valve defects is
Thetoaortic
valve opens at 3 and closes at 5
mostB.
likely
be present?
C. The
mitral valve opens at 2 and closes at 5
A) Aortic
incompetence
B) Aortic
stenosis
D. The
mitral valve closes at 3 and opens at 5
C) Mitral
stenosis
E. The
mitral valve closes at 3 and opens at 7.
D) Mitral incompetence
The Atrial and Central Venous Pressure (CVP) waves
• Since there are no valves between the jugular veins (JV), v. cavae
ant the RA, the right JV are communicated with the RA.
• Changes in pressure in the RA produces a series of pressure changes
which are reflected in the central veins and recorded from the JV: a, c
and v waves.
• CVP is the pressure in the vein at the entrance of the RA
• a wave is due to increase in pressure caused by atrial systole
• av descent (minimum) is due to relaxation of the right atrium and
closure of the tricuspid valve
• c wave is caused in the RA by the tricuspid valve bulging back into
the atrial chamber as it closes. In the internal JV the c wave (c =
carotid) is caused partly by expansions of the carotid artery
• X descent is a sharp fall in
the pressure caused by atrial
relaxation
• v wave. As the atria fill, A
pressure rises producing v
wave (v = ventricular systole
which is occurring at the same
time)
• Y descent is a fall in pressure
due to the rapid emptying of
the atria after the AV valve
opens
Fig. 13. Jugular venous pressure changes caused by cardiac cycle
Clinical examination of the JVP
• JP of the internal jugular vein can be assessed by expecting the
right side of the neck of a recumbent subject(45 degrees). Two
sudden venous collapses (the X and Y descent) should be seen
and measured externally on the right side of the neck- positive
JVP
• In right-side cardiac failure there is a positive JVP due to
accumulation of blood into the failing RV and RA
Summary of the Cardiac Cycle
Assessed at the bedside by noting:
• Peripheral pulse at radial artery (heart rate and force)
• Systolic and diastolic blood pressure (will be discussed later)
• Jugular venous pulse observation
• Apex beat (displacement on the left identifies left V hypertrophy)
• Heart sounds
When pathology is suspected more specialized tests are carried out:
• Echocardiography (non-invasive): Observing movement of the
valves and walls of the heart (valve lesions, myocardial infarction,
cardiac hypertrophy of different origin)
• Cardiac catheterization (invasive)
Hello Dr. Vishal,
My step 1 went well. I ended up with a score of 237.
Thanks to you and all the other teachers at Windsor for laying
a solid foundation in all the subjects, it made my preparation
much easier and a pleasant experience. Many of the concepts
we learned in school were tested on the exam so I felt
confident having that good foundation. I still remember all the
tips you used to give us in class about tackling the exam, they
helped a great deal.
Thank you again for all that you have done for us, I really
appreciate it.
Regards,