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.