Coronary steal syndrome

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Introduction0:00–0:31

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.

Physiology0:31–0:58

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.

Pathology0:58–4:44

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.

Symptoms4:44–5:11

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.

Diagnosis5:11–5:31

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.

Treatment5:31–6:00

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.

Review6:00–6:53

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.