What does blockage of heart
arteries, or coronary artery disease mean?
The heart is a strong pump that
delivers fresh oxygenated blood to different organs
in the body with each heartbeat. The heart muscle
itself gets blood through arteries called coronary
arteries. These conduits called coronary arteries
run on the surface of the heart. The disease of
these arteries is called coronary artery disease.
Note the heart arteries (coronaries) running
on the surface of the heart.
Picture from
Cleveland Clinic Website
The blockage
of these arteries can cause lack of blood supply to
the heart muscle. The most dreaded consequence of
the blockage is heart attack, which can be a fatal
event. The blockages can also lead to heart failure,
chest pain etc.
How can I find out if my
heart arteries are blocked?
Coronary artery disease,
technically speaking, means any disease of these
arteries. The tests done in everyday cardiology
practice mostly check for the blockage in the heart
arteries that are bad enough to cause decreased
blood supply to the heart muscles.
There are two kinds of tests
for the diagnosis of coronary artery disease. One
group includes different kinds of stress tests and
the other one includes tests that actually look at
the anatomy of heart arteries. The later group
includes coronary angiogram, also known as heart
cath (short for catheterization) and CT angiogram.
The way to understand the
difference between these two modalities is the
following. Let us say you want to see if the
sprinkler system for the grass in your backyard is
working well. There are two ways to do that. You can
look at the grass in the back yard. If the grass on
the northwest corner of the yard appears unhealthy,
the sprinkler system to that area may not be working
well. The other possibility is to actually run an
instrument through the sprinkler pipes to see if
there are blockages. The stress test involves
looking at the ‘grass’ (heart muscle) and coronary
angiogram involves looking through the ‘pipes’
(heart arteries).
Which is better at
diagnosing coronary artery disease- stress tests or
coronary angiogram?
It really depends on the
situation. A heart cath, although a very safe test,
is an invasive procedure. A non-invasive test like a
stress test is usually preferable screening test.
However, there are several scenarios where a heart
cath is considered first choice for the diagnosis of
coronary artery disease.
Isn’t coronary angiogram a
gold standard?
The coronary angiogram gives us
an anatomical description of coronary arteries. The
anatomy, unlike biochemistry or physiology lends
itself to concrete mental grasp. It is also likely
to be interpreted in a somewhat similar fashion by
different observers.
Notice the tight spot marked by an arrow. The
extent of narrowing is estimated based on the
appearance of adjacent area.
Picture from texasheart.org
The coronary angiogram has
some shortcomings including:
-
The coronary angiogram is a two dimensional
picture. The inner lumen of the artery may be
significantly diseased without showing obvious
abnormalities on the two dimensional pictures.
-
Comparing a diseased segment to the adjacent
‘normal’ segment makes the diagnosis of disease or
blockage. If whole length of the artery is diseased,
the artery may be uniformly narrowed throughout its
length, and hence give the impression of a normal
artery.
-
The angiogram looks at the anatomical
characteristics of the vessels. While looking at
angiographic findings, we run the risk of presuming
that coronaries are just like water pipes. In fact,
coronaries are living structures that have their own
dynamic behavior unlike dead water pipes.
If coronary angiogram has
all these shortcomings and is invasive, why do it?
Coronary angiogram continues to
be a very important test for the diagnosis of
blockages of heart arteries. Two of the important
ways to deal with coronary artery disease are bypass
surgery and angioplasty/stent placement. An
angiogram is an indispensable step before either of
these two treatment options.
If I have a normal stress
test today, does that mean that I can rest
assured that I will not have a heart attack in the next 5, 10
or 15 years?
Unfortunately, a normal
angiogram or a stress test today does not guarantee
against a heart attack tomorrow. We have known this ever
since we learned about the phenomenon of plaque
rupture.
A
picture of plaque rupture which leads to something
like a numerous blood-cells-pile-up leading to a
heart attack
Slide from
escardio.org
Not too long ago, we used to
think that coronary artery blockage progressed in a
linear fashion. This meant 60% blockage will turn
into 70, then 80 and eventually 100%. The studies
have now shown that close to 70% of heart attacks
occur in the arteries that were less than 50%
blocked at the time of heart attack. Fifty percent
is the severity that can be easily missed on a
stress test or even on coronary angiogram. I am not
saying this to propagate a defeatist attitude, but
to make a stronger case for proactive approach
toward management of coronary artery disease. An
important part of proactive approach is management
of
risk factors.
What is the importance of
tests for diagnosis of coronary artery disease?
Various diagnostic tests help
with timely detection of coronary artery disease.
This can prevent many potentially fatal events. A
diagnostic test is very important if there are signs
and symptoms of disease of heart arteries or if
suspicion for blockages in heart arteries is high.
As an example, diabetics may have severe blockages
in the heart arteries despite the absence of
classical symptoms.
The information above is based
on actual questions that I have been asked. I hope
this gives you a good perspective on coronary artery
disease. Various tests for the diagnosis
remain an important part of management of heart
disease.
What are different types
of tests used to diagnose coronary artery disease or
blockage of heart arteries?
There are two kinds of tests:
Stress tests:
-
Exercise
treadmill test or stress test
-
Exercise nuclear
scan or nuclear stress test or Cardiolyte stress
test
-
Exercise stress
echo or echocardiogram -
Adenosine
nuclear stress test
-
Dobutamine
nuclear stress test
-
Dobutamine
stress echo The last three are also called as chemical stress
tests.
Tests looking at the
anatomy of coronary arteries:
Coronary angiogram or heart
catheterization
CT angiogram
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