The human body is endlessly fascinating, isn’t it? Consider how humans get started in the first place – only after one tiny sperm, one of hundreds of millions, has somehow negotiated its way past the lethal acid coating the vagina and made its long journey up to the waiting egg. The odds are stupefyingly against that one brave little sperm.
And then, consider the heart.
Before my heart attack, I had never heard of the heart’s little collateral arteries. These are small, normally closed arteries that, in times of dire need (like a blocked coronary artery that leads to a heart attack) can wake up, open wide, and enlarge enough to form a kind of detour around the blockage, thus providing an alternate route of blood supply to feed the oxygen-starved heart muscle. Do-it-yourself bypass surgery!
Consider also the example of Juliet’s life-saving collateral arteries. At the age of 46, this young mother of two in London, England suffered a heart attack due to Spontaneous Coronary Artery Dissection (SCAD).
Like most SCAD patients, she had no cardiac risk factors, and was very healthy at the time. (Just the day before, she had gone on a 40-minute run). But her early heart attack symptoms were initially misdiagnosed, and she now suspects that the tear in her artery may have unravelled further by the time she underwent a diagnostic angiogram. Juliet ended up with five stainless steel stents implanted along the length of her torn Left Anterior Descending (LAD) coronary artery.
But then things went from bad to worse for Juliet, as over the next three months, her stents re-stenosed (blocked) due to scar tissue build-up. She explains:
“During the period of re-stenosis and for about a year after, I suffered angina pain on exertion and most particularly after eating. Unfortunately, the stents subsequently failed, and my LAD is now 100% occluded with scar tissue. But that part of my heart is now functioning on collateral circulation. The chest pain symptoms disappeared slowly as my collateral arteries developed.
“It was a happy surprise to discover how wonderfully a heart can adapt with collaterals, and although I would love to still have the use of my LAD, I am doing fine without it!
“My cardiologists said these collateral arteries would have started to develop as soon as my LAD started to re-stenose, especially as I went straight back to running, post-cardiac rehab. I am surprisingly well and happy to be alive.”
Drawing of the coronary artery circulation with (left panel) and without (right panel) collateral artery growth between the right coronary artery (these are the small red blood vessels in the left illustration) and the blocked artery. The grey area below the blockage shows the area of the heart muscle at risk in the absence of collaterals. (Illustration by Anne Wadmore, London, UK). From BMCMed.
Some researchers suggest that, because Juliet was already a physically active runner, her own collateral arteries may have already started this important process called arteriogenesis, which is defined as the transformation of pre-existing collateral artery pathways into conducting vessels.
In 2004, Swiss researchers, for example, found that enhanced physical exertion (like running) may indeed cause those tiny collaterals to kick into action.(1) Study authors explained in the journal, Heart:
“For the first time in a human being with entirely normal coronary arteries, we have shown evidence of enhanced coronary collateral flow in response to an endurance exercise programme.”
I’ve been told the same theory – that my 19 years of distance running contributed to that enhanced coronary collateral flow, which may have been the factor that helped to save me during my own heart attack, despite having a Left Anterior Descending coronary artery that was also fully occluded.
While every human has these amazing little sleeping arteries, not every collateral will work when it needs to – especially if you’re not training for a marathon. And not everybody has functional collateral arteries (a blood flow of 20% to 25% is generally considered sufficient to provide the required blood supply to the heart muscle at rest). One in three patients with coronary artery disease has sufficient collaterals.(2) We don’t know the reasons for this, but genetic factors are likely to play a role. Some factors that may influence whether patients with coronary artery disease develop collaterals include the severity of the coronary blockage(2), a longer duration of angina, and the location of the blockage.
Researchers at Tel Aviv University have developed a protein-based injection that, delivered straight to muscles in the body, may spark the regrowth of tiny new blood vessels, much like the body’s own collateral arteries. Their study was designed to discover a way to prevent leg amputations, but their preliminary tests may suggest potential value to future heart patients whose arteries are fully occluded.
Find out more about Spontaneous Coronary Artery Dissection (SCAD).