Preventing Heart Attacks in Athletes
NatureMed Clinic Boulder, Colorado
Myth number one
The thought of having a sudden heart attack is so disturbing that many people don’t even consider that it could happen to them. I call this the “it can’t happen to me scenario”. Other people may say things like “my cholesterol is normal and I exercise, eat well and don’t have too much stress so I will not get a heart attack.” Well I’m here to tell you from personal experience that this is a very poor way to gauge your risk of an unexpected heart attack. I call this myth number one. While getting regular exercise and following a heart healthy diet reduce risk of heart disease these elements alone do not completely prevent it and if you have plaque, I assure you that diet and exercise are not enough to reverse it.
When I speak about unexpected heart attacks, I am referring to heart attacks in otherwise healthy people between 30 and 70. At over 70 years of age many of us already have extensive coronary plaque, and though still somewhat preventable, a heart attack would not be that unexpected. In clinical practice my focus on modifiable causes of heart attacks: arteriosclerosis, atherosclerosis and coronary heart disease. Many other non-reversible cardiac and vascular conditions exist (valve problems, aneurysms, conduction abnormalities), and these may need to be corrected with surgery.
In the Boulder area in particular there are people who get much more exercise than the average American. They think that because they train 6-12 hours a week their heart must be very healthy. This simply is not true. In fact, athletes may even be at increased risk for coronary artery disease. Here’s why. It’s because of phenomenon called shear stress. Shear stress is cause by a combination of pressure, velocity and high blood viscosity (thick blood). If your blood is very thick and the pressure is high stress on the wall of the artery is the highest. High pressure and thick blood can also occur separately. Shear stress causes damage to the blood vessel lining, causing the vessel wall to thicken, become stiffer and develop plaque.
Athletes, especially those who live at higher elevation, tend to have high red blood cell counts which are a major cause of thick blood. Also, the higher work demands that they put their vascular systems through can exacerbate this effect. I’m not saying exercise is bad, but if you have a high blood viscosity exercising at high intensity may be like taking three steps forward and two back. The incidence of sudden death during athletic activity is still very low, ranging from 1 per 13,000 man-hours of activity in cross-country skiing, to 1 in 396,000 man-hours of activity in jogging.
Blood viscosity
Blood is a non Newtonian fluid and behaves much like catsup coming out of a bottle. Once you get it moving is really moves fast. Non Newtonian fluids do not behave in a linear fashion. An example of a Newtonian fluid is water. Blood, on the other hand, moves sluggishly is low speeds and is more liquid at fast speeds. When the heart is resting between beats (called diastole) it becomes more viscous and then when the heart forces blood out (called systole) blood becomes less viscous. The main determinant of blood viscosity is red blood cell mass (also known as hematocrit). Though there are other factors that affect blood viscosity, they go beyond the scope of this discussion.
Why is blood viscosity important?
1) High blood viscosity increases the amount of work the heart must do to perfuse the tissues and deliver oxygen. This makes for an inefficient circulatory system and can cause the heart to enlarge to compensate for the extra work. An enlarged heart requires more oxygen and can lead to other problems. Enlarged hearts are common in athletes but become a health risk if the enlargement becomes too great.
An analogy is the car engine. Motor oil comes in different viscosities…thicker for summer and thinner for winter. High blood viscosity is analogous to putting summer oil in your car in the winter and the result is poor gas mileage as the engine’s efficiency is decreased.
1) A surplus of red blood cells (the most common cause of elevated blood viscosity) can cause damage to the inner lining of the blood vessel as they constantly bump against the surface
2) The damage eventually leads to plaque formation (also called a callus). This is an adaptive response to the injury and acts to protect the artery wall in the short term at the expense of long term function. An analogy here is the calluses we get in response to friction on the skin.
4) High blood viscosity also creates something called low shear stress. The easiest way to think about this is that in between heart beats the blood thickens and swirls around, causing eddies and turbulence. Turbulent blood flow also causes damage to the cells that line your arteries. A good analogy here is the sandbars that form in rivers and streams from eddies and back currents. Plaque tends to deposit most heavily in the low shear regions of arteries, like a sandbar. As plaque continues to deposit blood flow is further disturbed leading to more turbulence and plaque deposition.
5) High blood viscosity also contributes to something called injurious pulsatile blood flow. Think of this as a pressure wave with a high peak. Injurious pulsatile blood flow damages the lining of the blood vessel.
Why thinner blood might make you faster
As long ago as the early 1970 researchers began study the question of what is the hematocrit level that allows for optimal oxygen delivery to the body. Recently, in 2000 an Oxygen Delivery Index (ODI) was created by Kamenva et al. The highest oxygen delivery occurred in subjects with hematocrits between 25-30%. Higher hematocrits and elevated blood viscosity were also associated with higher risk of coronary artery disease in these studies.The workload of the heart is also reduced by having thinner blood. Also by donating blood younger red cell blood (RBCs) will predominate. Younger RBCs carry and deliver oxygen better than older cells.
How do you get tested?
I run this test though a special lab dedicated to blood viscosity testing. This is NOT a standard test any doctor can do.
What is the treatment for elevated blood viscosity?
Often the best treatment is to donate blood. Red blood cells are the main causeof thick blood and donating blood lowers your red blood cell count. In the Boulder/ Denver area I shoot for 40-45 in men and 35-40 in women. How often you should donate will depend on your profile. Some people should not donate at all. Occasionally there are other causes of elevated blood viscosity which I will test you for.
Why have you not heard of blood viscosity before?
The science of hemodynamics and blood rheology is not new, but the testing is, thus it has not entered the mainstream yet. Also since drugs do not treat this problem pharmaceutical companies are not interested.
Cholesterol and Lipoproteins
Where does cholesterol come in? Think of cholesterol as a mediator of plaque formation. Cholesterol has received overemphasis by the media and drug companies because there are profitable drugs to treat it but cholesterol by itself is not really the problem. We should be focusing on particles called lipoproteins. Cholesterol is packaged in a protein shell called a lipoprotein. It’s the nature of the lipoprotein that determines how damaging a given level of cholesterol is. Lipoproteins also affect blood viscosity.
Lipoproteins that are small and dense are more damaging than those that are large and non-dense. Some types of cholesterol are worse than others, and some types, such as large HDL are actually protective. Only treating cholesterol in a patient with evidence of coronary artery disease is like fighting forest fires but neglecting to deal with the problem of too much underbrush and dry wood in the forest. Cholesterol is an important risk factor but to get the best results it’s the lipoproteins we should be targeting, along with other risk factors.
Myth number two
Many of you reading this will have asked your doctor about heart disease. Most doctors respond by giving you an electrocardiogram (ECG) or a stress test (also known as a treadmill test). If you fail the treadmill test you will need further work up by your cardiologist (angiogram etc). But if you pass these tests, are you free of heart disease? The answer is no. You can have extensive plaque and still pass a treadmill test. There usually has to be blood flow limitation to the heart muscle to cause you to fail this test.
It’s a good idea to have an ECG to rule out an abnormal electrical heart pattern called "diffusely distributed and deeply inverted T waves." This pattern has been linked to sudden death in young athletes. But what about older athletes? In addition to plaque rupture chronic exercise conditioning may cause a condition called hypertropic cardiomyopathy. An echocardiogram can rule this out and I occasionally recommend these to older athletes. The main concerns in older athletes are plaque rupture.
The single best way to determine the level of plaque in your coronary arteries is to get a heart scan. Special low radiation CT scan machines can now accurately give you a “plaque score.” This score is based on the fact that 20% of well established hard plaque is calcium. The machine is able to detect this calcium and even show which arteries are affected. I recommend that everyone over 40 get this test. Occasionally I recommend it for people under 40 who have more risk factors. I can track plaque progression (or reversal) by repeating the heart scan every few years. This is one of the best anti-aging and heart disease prevention tools that we have. Blood viscosity testing coupled with plaque scoring, blood chemistries and lipoprotein analysis provides an unsurpassed method for preventing heart attacks.
