Welcome back to Vascular Medicine - The Advanced
We are going to discuss today venous diseases.
We’ve been talking a lot about arterial
diseases up to this point. Now we’re going
to look at the second component of the cardiovascular
system: the venous diseases.
We’re going to start with a definition of
the various kinds of venous diseases. It turns
out that, just as in the arterial disease,
thrombosis – or the development of a blood
clot –can develop in patients in the veins
just as they can in the artery. And just as
in the artery, pieces of the blood clot can
break off and go elsewhere in the circulation
and cause mischief. The same thing can happen
in the venous system.
In the venous system, when a blood clot forms
and breaks off it goes to the lung and is
known as pulmonary embolism.
What often leads to clot in the veins is an
inflammatory process called deep venous thrombosis
or DVT. And that inflammation in the wall
of the vein – and we’ll talk about the
reasons why that can happen – results in
a blood clot forming. The blood clot can get
bigger and bigger and bigger, pieces can embolize
and result in pulmonary embolism. If enough
blood clot gets into the lung, you can have
enough obstruction of blood flow through the
lung that the patient may develop shock – the
subject of the last lecture.
So, often this disease is called venous thromboembolism
because there’s clots in the leg and there’s
clots embolising to the lung. And that’s
often abbreviated as VTE.
Remember what a thrombus is. A thrombus is
a solid mass of platelets and / or fibrin
that has formed locally in a vessel. It’s
a blood clot. And it forms when the clotting
mechanism is activated.
Thrombosis is actually obstruction of a blood
vessel by a thrombus. And, of course, when
that happens in the arterial system, nourishing
blood fails to get to a blood vessel. In the
venous system, that doesn’t happen because
we have so many reserve veins. Blood usually
goes around the area where there’s a thrombus
or thrombosis. However, when pieces break
off and embolize to the lung, that causes
The most common form of embolism, much more
common than arterial embolism, is venous thromboembolism.
And the commonest form of venous thromboembolism
results from deep venous thrombosis.
And there’s a whole variety of illnesses
that increase people’s risk for developing
thrombosis in the veins. For example, long
periods of bed rest; or long periods of travel
in an aeroplane where you’re seated with
your legs down; or cancer increases the clotting
ability of the blood and can result in that;
pregnancy. A whole variety of conditions can
lead to either increased clotting tendency
or injury to the vein. For example, a fracture,
a trauma can injure the vein and lead to deep
venous thrombosis. And, again, a piece of
the clot breaks off, goes up to the lung and
that can cause lots of trouble.
Occasionally, for example in some forms of
trauma, you can have fat or air that embolizes
or even little bits of an atherosclerotic
plaque that can embolize. But in fact the
vast majority of embolism on the venous side
is blood clot. And it’s a blood clot that
results from deep venous thrombosis.
When the embolus lodges downstream, it often
lodges in the narrowest area. And so in the
lung the thrombus will travel until it finds
a small enough blood vessel that it gets stuck
and then, of course, it causes obstruction
of blood flow through that area of the lung.
Let’s just review the venous-side events
that relate to thrombosis once more.
Deep venous thrombosis is due to a thrombus
– a blood clot – that forms within a deep
vein. We can also have superficial venous
thrombosis but that’s usually just a transient
irritation and not as serious as the deep
Deep venous thrombosis often involves a substantial
amount of clot so that, when it embolizes,
it causes significant obstruction in the lung
The source of these emboli in the legs – we’re
going to talk about some more subsequently
in this talk – but it usually starts in
the veins of the calf and then extends up
into the veins of the thigh.
When the blood clot breaks off and travels
to the lung as pulmonary embolism, if it blocks
a major artery of the lung, that can cause
immediate shock or decreased blood pressure
in the patient.
But often these clots are small. They get
out into the periphery and it’s only with
repeated episodes of embolisation of clot
to the lung that significant obstruction of
the pulmonary circuit occurs.
The condition with deep venous thrombosis
plus pulmonary embolism is often called venous
thromboembolism or VTE. And it’s obstruction
in the vein caused by a thrombus. But then
pieces break free and are carried away with
the blood flow into the lung. And if there’s
enough of the pulmonary circulation that’s
obstructed, as I said the patient can develop
very serious illness including shock and this
can be fatal.
Just to compare a little bit about what happens
with thrombosis in the arterial and the venous
Deep venous thrombosis can be asymptomatic.
It can resolve without any problems but, when
a blood clot breaks off and travels to the
lung as pulmonary embolism then, as I’ve
said, the patient can have a very serious
On the arterial side, the major problems relating
to thrombosis are either myocardial infarction
or unstable angina.
With myocardial infarction, the thrombosis
completely occludes the artery and cuts off
blood flow beyond.
With unstable angina, often the atherosclerotic
plaque plus some overlying thrombus doesn’t
completely occlude the artery so the patient
has chest pain at rest that comes and goes
or pain that’s easily provoked when they
do the most minimal exertion.
Again just to show you the difference between
what happens when there’s a clot on the
venous side versus a clot on the arterial
Venous side: DVT, pulmonary embolism, arterial-side
myocardial infarction, unstable angina.
Now it turns out that, as in hypertension,
DVT is often silent. And even pulmonary embolism
can be silent. In fact, as you can see from
this pyramid, the vast majority of patients
have silent DVT or silent PE. And often it
resolves without any therapy.
In a smaller percentage of patients, the DVT
and the pulmonary embolism can be symptomatic.
And in a very small amount, it’s fatal.
So of course what we would like to do is identify
the DVT or the PE when it’s silent and when
the amount of pulmonary embolism has been
very small so that we can prevent progression
up the pyramid to the point where the obstruction
causes symptoms or even is potentially fatal.
I mentioned before, where does deep venous
thrombosis commonly develop?
It commonly develops in the popliteal or superficial
femoral veins – that is just below the knee
and just above the knee. And that clot there,
particularly the ones in the popliteal veins,
can be quite small and may never embolize
or, if they embolize, they may not cause much
trouble. But as the clot develops – and
what happens is it can of course continue
to build – it may extend up into the common
femoral vein and even into the iliac vein.
At that point, we’re dealing with a large
volume of blood clot. If that large amount
of clot breaks off and goes to the lung, we
could see either fatal pulmonary embolism
You’ll notice that only a small percentage
of clots are found in the popliteal vein alone,
more in the superficial femoral vein. 42%
in popliteal vein, both veins. Again only
a small percentage in the common femoral but
a substantial number get into the iliac and
inferior vena cava – 35%. And those are
the most dangerous ones.
We would like to discover the clots when they’re
just down in the popliteal vein or in the
superficial femoral, not when they develop
in large volume up in the inferior vena cava
or the iliac vein where, if they embolise,
could be fatal.
Again, the consequences of venous thromboembolism
are clear. There can be fatality if the pulmonary
circulation is markedly occluded. This can
happen suddenly. There can be acute mortality.
There can be recurrence. So the patient may
have an episode of pulmonary embolism. He’s
sick, gets better, goes home from the hospital.
Once they’ve had one episode, they’re
at high risk for another episode. And often
that’s because they develop recurrent thrombophlebitis.
They have a tendency to develop this inflammatory
clotting disorder in the veins and then, of
course, for pieces of it to break off.
Sometimes the veins get completely occluded
with the clot and then they can cause something
I will talk about later called post-thrombotic
syndrome in which the patient experiences
chronic swelling of the leg. And even ulcers
and really a very, very unpleasant sequence
of events can occur with a lot of clotting
in the venous system.
The definition of thrombophlebitis is of course
the presence of thrombus in a vein. It’s
almost always accompanied by an inflammatory
process in the vein wall. As I’ve said before,
it can affect superficial veins when it’s
usually not very serious and often as a result
of some minor trauma. And it can be treated
with just some local heat and maybe some aspirin
or ibuprofen. When it gets in the deep veins,
that’s when there’s a much greater potential
for pulmonary embolism. As we said, pulmonary
embolism can be fatal. And there are a whole
variety of risk factors for developing thrombophlebitis:
long periods of bed rest, long airplane trips,
cancer, heart failure, severe lung disease…
A lot of these place patients at higher risk
for developing thrombophlebitis and pulmonary
I mentioned before the post-thrombotic syndrome.
This is a very serious complication of venous
thrombosis. It’s a long-term complication
of deep venous thrombosis. What happens is
you occlude enough of the veins in the lower
leg so that it is difficult for blood arriving
in the muscles and skin of the leg to get
out of the leg. So you have pooling of blood
there, you have increased pressure from standing,
from gravity. This results in much more fluid
getting out of the capillaries that can be
resorbed. So you have swelling. And then with
all of this swelling, it actually impairs
arterial flow from getting into the tissues
and you may have necrosis – or death of
tissues – and development of an ulcer as
you can see from the picture here.
A number of symptoms are related to the post-thrombotic
syndrome: there can be pain or heaviness in
the leg; itching or tingling; as I’ve already
mentioned, edema swelling; development of
severe varicose veins; brownish or reddish
skin discoloration from red blood cells being
deposited in the skin. And, of course, the
worst complication is ulcers. And even, occasionally,
the ulcer gets infected and this could lead
to amputation. So the post-thrombotic syndrome
can be very, very severe.
So, in summary, in this first lecture on the
venous system, we’ve talked about the most
common and potentially serious illness from
the venous system, which is that which occurs
when a thrombus or blood clot – a solid
mass of platelets and fibrin – forms locally
in the vein and often is associated with activation
of a clotting mechanism that increases the
size of the blood clot.
It’s not uncommon for these clots to form
in the veins of the legs, much more common
than in the arms, where they block blood flow.
Pieces of these clots can break off and travel
to the lung circulation where they cut off
blood flow to a portion of the lung – that’s
pulmonary embolism. We’re already talked
about it. Patients can be very sick with pulmonary
embolism or it can even be fatal. And we’ll
be talking more about therapy as we go along
and talk more about pulmonary embolism in
a subsequent lecture. The therapy is, of course,
blood thinners or blood-clot dissolvers to
help resolve the clots that are already in