Coronary steal syndrome – causes, symptoms, diagnosis, treatment, pathology


Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
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much more. Try it free today! Coronary steal syndrome is a condition that
occurs due to dilation of coronary arteries in the presence of coronary artery disease,
which is when there’s a partial or complete blockage in the lumen of another coronary
artery. The result is a redirection of blood flow
from heart muscle supplied by the blocked artery, to other regions of the heart. Coronary steal syndrome is a finding observed
during a pharmacological cardiac stress test, which is used to diagnose coronary artery
disease. Now, the heart pumps out blood for all of
our organs and tissues to use – but the heart also needs blood. So it also pumps blood to itself, through
the coronary arteries on the outside of the heart. And coronary arteries are linked to one another
through teeny tiny blood vessels called collateral vessels, which are normally in an inactive
state, meaning blood doesn’t flow through them. Now, with coronary artery disease, there’s
ischemia, or reduced blood flow to the region of myocardium supplied by that artery. In this context, collateral circulation may
become active. For example, let’s say two coronary arteries,
A and B, are linked by a collateral vessel, and coronary artery B has developed a block. As a result of ischemia, in the myocardium
supplied by coronary artery B, the myocardial cells don’t receive enough oxygen, which
is called hypoxia. In response to hypoxia, myocardial cells release
signalling molecules called cytokines, which cause dilation of the segment of coronary
artery B beyond the blockage. This slightly improves the blood flow and
ameliorates hypoxia. But at the end of the day, blood flow within
coronary artery B is still decreased, while blood flow in coronary artery A remains the
same. This creates a pressure gradient across the
collateral vessel, which pulls blood from the region of higher pressure, of coronary
artery A, through the collateral vessel, and into the region of lower pressure, or the
dilated segment of coronary artery B. In other words, the low-pressure region acts like a
vacuum! Now, the sudden gush of blood through the
collateral vessel stretches its walls and deforms the endothelial cells, which stimulates
the production of growth factors like the vascular endothelial growth factor, or VEGF,
from the vessel wall. These growth factors act on the collateral
vessel wall and bring about two changes. First, they cause vasodilation, which allows
more blood to flow through the collateral vessel. Second, they promote the proliferation of
the smooth muscle cells in the vessel wall, which makes the vessel wall thicker and stronger. Over time, this results in maximal vasodilation
beyond the obstruction, and it helps the collateral vessel redivert blood to the ischemic myocardium. But when a vasodilating medication like dipyridamole
is given to an individual with coronary artery disease, coronary steal syndrome may occur. Dipyridamole is usually given intravenously
for a pharmacological cardiac stress test, and the heart’s response is observed on
an electrocardiogram, or ECG, to diagnose cardiac ischemia. When the test is done in an individual with
coronary artery disease, it results in vasodilation of all coronary arteries, except the ones
which are obstructed – because beyond the obstruction, the coronary artery is already
maximally dilated. Dilation of the non-obstructed coronary arteries
decreases the pressure within them, so if we look at coronary arteries A and B again,
now a low pressure region is formed at both ends of the collateral vessel, one by the
already dilated coronary artery B and the other by the newly dilated coronary artery
A. So, the pressure gradient across the collateral vessel vanishes, resulting in diminished collateral
circulation. The end result is that blood is diverted,
or stolen, away from the ischemic myocardium to non-ischemic areas, which further worsens
the ischemia. In severe cases, blood flow can been completely
cut off, which results in myocardial infarction, or the necrosis of a portion of myocardium. This typically happens if blood flow has been
cut off for more than 20 minutes. Symptoms of coronary steal syndrome mimic
that of a myocardial infarction, and include a typical type chest pain, which is described
as a squeezing pain or pressure that might radiate up to the left arm, jaw, shoulders,
or back. It’s often accompanied by other symptoms,
such as shortness of breath, diaphoresis, or sweating; nausea; and fatigue. Coronary steal syndrome is diagnosed when
the electrocardiogram shows an ST-segment depression during a pharmacological cardiac
stress test. A coronary angiography can be done to look
for coronary artery obstruction and collateral vessel formation. Treatment of coronary steal syndrome involves
opening up the obstructed coronary artery. A balloon angioplasty might be done, which
is a minimally invasive endovascular procedure where a deflated balloon is inserted into
the blockage then inflated to open the artery up. Another procedure is a percutaneous coronary
intervention, where a tiny catheter is used to place a stent in the coronary artery to
physically open up a blood vessel. All right, as a quick recap… Coronary steal syndrome is a condition where
there’s a fall in blood flow to a certain section of the heart in favour of another
during coronary vasodilation, typically caused by the use of vasodilators like dipyridamole
in individuals with coronary artery disease. Common symptoms include typical type chest
pain, which is described as a squeezing pain or pressure that might radiate up to the left
arm, jaw, shoulders, or back; shortness of breath, diaphoresis, or sweating; nausea;
and fatigue. Coronary steal syndrome is diagnosed with
the help of an ECG, which shows an ST-segment depression, and coronary angiography; and
treated using a balloon angioplasty or percutaneous coronary intervention.

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