Myocardial Bridge 101

Got home from the scan had a light dinner and went to bed. As suggested by the doc the next day I hung at home and relaxed reading up on bridges. For those that don't know much about Myocardial Bridges here is my best attempt at creating…

Myocardial Bridge 101:

First, as I write this in 2016 I have to say up front that Myocardial Bridges are actually a controversial thing. Pretty much from the day they were first discovered in the late 1700s up to about 2006 they were considered totally benign. Even today there really only seem to be two or three medical centers that consider them anything other than benign. 

The bottom line seems to be that unless you get "needle in a haystack" lucky any cardiologists not directly affiliated with the bridge program at one of the afore mentioned medical centers is going to be very skeptical that your bridge is anything other than an anatomical curiosity. So I feel extraordinarily lucky that I am with Stanford (which probably is the most advanced with bridge research in the world). 

Okay so what is a M-Bridge anyway?

A Myocardial Bridge is basically a construction anomaly when your heart is forming in utero. The arteries that supply blood to our hearts (there are four major ones) run along the outside of the heart itself. They then send little runners down into the heart every so often to supply blood to the muscle. In about ~25% (big debate on this number) of the population some of the heart muscle, instead of being under the artery, grows over the top of it. Thus when the heart beats and that muscle contracts it squeezes some of the blood out of the section of the artery it covers. 

For 95%+ of the people with bridges this is never a big deal. Lots of reasons but basically they seem to boil down to:

• Not much of the artery is covered so what is has little effect.
• The muscle over the artery just does not squeeze it very hard for mechanical reasons.
• Most of the blood flow to the heart actually happens when the heart is relaxed (in diastole) after having finished a beat (in systole) so it really does not limit that much flow in the first place.

But, for the remaining 2 - 5% of people with more severe bridges they do cause problems. This probably is because they either cover a significant portion of the artery (3 cm or more), really squeeze hard on what they cover,  or have a slight delay after systole before the artery can pop-open again to let blood through.

A very important little LAD:

While there are four major arteries in the heart one, nicknamed "the widow maker", is pretty significant as far as bridges (and other things go). The Left Anterior Descending artery supplies blood to the left portion the heart but does more than just send runners along, and into, the surface muscle. It also dives deep into the heart supplying a disproportionate (as compared to it's partners) amount of oxygen rich blood to the ventricles. Wikipedia says it best: "…if the artery gets abruptly and completely occluded it will cause a massive heart attack that will likely lead to a sudden death." So a bridge on this artery is probably more significant / impactful than a bridge on other arteries given its critical role.

Congenital means since birth right?

I find it really interesting that bridge problems don't usually show up until sometime in the late 30s or early 40s. As we age our hearts, lungs, etc. become less efficient at getting O2 into and out of the blood stream. So as younger people we can deal with a bridge better because we are just better at getting O2 where it needs to go.

Aside: I have always gotten really altitude sick and I kinda wonder if the decreased O2 at altitude plus the bridges was enough to tip my heart into a lower O2 zone with altitude sickness as the result. Regardless, altitude clearly played a role in my initial "wake up" attack in Sedona as I was exercising at 4,500 feet rather than basically at sea level where I normally live. And that decreased O2 was enough to turn a "sports injury" (rollerblading really can be a sport) into a full on episode. 

Links in a chain:

Lastly, are related issues that severe bridges can cause (or at least influence). There is much research and discussion around what are the complications that bridges cause or influence. Candidates range from Endothelial dysfunction to coronary artery disease. But, frankly due to personal relevancy (see next post), I dove deeply into CAD. 

Coronary artery disease (CAD) is the big source of heart attacks we hear about. It is where a plaque builds up on the walls of an artery in the heart and eventually blocks blood from getting to the muscle downstream causing all sort of Very Bad Things™. This of course absolutely does not need a bridge to happen. But, having a severe bridge seems to add extra layers of fun to the problem. 

There are two issues. The first one has to do with the nature of fluids. An artery under a severe bridge is filled with blood. When the heart beats and the bridge squeezes the artery that blood is forced out of the bridged section. Some of it goes with the typical flow (out the bottom so to speak) but some of it also squirts out the top. This runs directly into the flow of blood that is normally coming into the artery. Now if you have ever had a garden hose fight where you and your sister spray one hose stream into another you know that causes water to shoot in all directions. When blood does this in the arteries of the heart it does a bit of hydrostatic damage to the walls of the artery. (It actually even causes changes in the DNA of the cells of the arterial wall). This damage can greatly increase the probability of a plaque forming at the place where the streams collide. And, in people with severe bridges, that seems to be just about 20 mm from the entrance of the bridge.

So not only do bridges contribute to a plaque the location of the plaque to the bridge makes doing something about it very difficult. If you accept the premise that the bridge probably contributed to the formation of the plaque then so long as the bridge remains anything you do to treat the plaque will fail, or not work well, because the bridge will keep doing what it did. So following the line of reasoning to ground: in order to do something about the plaque you need to do something about the bridge. 

Aside: If you found this blog because you have a plaque, and it is near a bridge (<20mm), there are a number of studies covering what happens if you stent the plaque without treating the bridge. This apparently (which is frightening to me) still is typically done. I would strongly encourage you to get a second opinion from someone whom has knowledge of bridges (or the studies) before agreeing to this. 

What can you do about them?

There currently seem to be four options for treating a bridge:

1. Do nothing. For 95%+ of the population with bridges (which is only ~25% of the general population) this is totally fine as the bridge is not causing any problems. 
2. Medication: Different hospitals / doctors are experimenting with beta blockers or calcium channel blockers. The basic goal seems to be by keeping the heart rate from spiking you prevent the cascade that triggers an attack. At issue is that with a severe bridge the faster your heart beats the less oxygenated blood gets through because the stupid bridge keeps squirting some back out the top out or at least delaying the time before it flows freely through the artery. 
3. Stenting the bridge: Some cardiologists have placed a stent in the bridge itself. From
   
   everything I understand, that is a really really bad idea. Stents are mechanical things. They are not designed to be squeezed 40 - 160 times a minute forever and if they fail mechanically (think flexing a credit card 20 or 50 times until it breaks) you really don't want that debris in a line that supplies blood to your heart. Even stenting a plaque too close to a severe bridge (< 20mm) can cause mechanical problems. Seriously, get a second opinion from a cardiologist that understands bridges before agreeing to this.
4. Unroofing surgery: This is open heart surgery where the surgeon exposes the heart and cuts the muscle that is covering the bridged artery therefore preventing it from squeezing it anymore. It has been described to me by a surgeon that does it as like a bypass – just without the bypass. 

Obviously the best place to be would be option 1 which, again, for the majority of people is just fine. (I say that here for anyone that hit this page via a google search)

If symptoms of a bridge are affecting your quality of life but, you have no other complications, and you can tolerate the drugs (they make many people tired and sleepy) then option 2 might be enough. 

In my opinion option 3 is a non-starter. Period.

Option 4, the surgery comes with all of the risks and long and painful recovery that open heart surgery is known for. But, if nothing else works or you have potential complications caused by your bridge. Well, at least you get to have a cool scar for halloween and (more importantly) have the best chance of getting some relief.