February is American Heart Month, a time to raise awareness about heart disease, the leading cause of death among adults in the United States. Heart disease, sometimes called coronary heart disease or coronary artery disease, is responsible for nearly 375,000 deaths each year, mostly from heart attacks. Over 13 million adults have been diagnosed with heart disease and, if other cardiovascular diseases like high blood pressure, heart failure, and stroke are included, that number jumps to 80 million. (more statistics are available from the American Heart Association)
The process that leads to heart disease is called atherosclerosis and is characterized by the accumulation of cholesterol-containing plaques in the coronary arteries, the vessels that supply blood to the heart. These plaques narrow the vessels and reduce the amount blood delivered to the heart. The heart requires a constant supply of oxygen to beat and any narrowing in the vessels reduces blood flow and interferes with normal heart function. A decrease in oxygen delivery can cause chest pain (angina pectoris), especially during activity or exertion. It is usually relieved with rest, but can limit normal activities. A complete blockage in blood flow causes a heart attack, also called a myocardial infarction or MI, in which the heart muscle is damaged, sometimes permanently. Many MIs lead to death because dangerous arrhythmias—abnormal heart rhythms—develop that lead to cardiac arrest.
The traditional view of heart disease holds that the cholesterol plaques progressively narrow the arteries until they close completely, a process similar to a blockage in a pipe in your house. It turns out that the process of atherosclerosis is more complex. In fact, most heart attacks occur because of vessels that are around 50% blocked.
Current evidence shows that inflammation plays an important role in the accumulation of plaque in the vessel walls. Additionally, inflammation plays a role in making the plaques unstable and prone to rupture, resulting in a blood clot in the artery which completely blocks the flow of blood leading to a heart attack. This makes more sense if you think of the inside of a blood vessel like your skin. A cut on your finger results in inflammation and the formation of a blood clot which stops blood flow. A similar process occurs inside the coronary arteries to lead to an MI.
The process that occurs in coronary arteries also takes place in other vessels. A blood clot that forms in a vessel in the brain can cause a stroke, sometimes called a “brain attack” because the process is similar to a heart attack. Narrowed vessels that reduce blood flow to the brain can cause a reversible condition called a transient ischemic attack (TIA) or mini-stroke. Narrowed arteries in the legs can cause muscle pain during exercise or activity.
Atherosclerosis is a process that starts when we are young and progresses as we age. It generally doesn’t cause symptoms like chest pain until the arteries are at least 70% narrowed, so most people are unaware that it is happening. The process is accelerated by conditions like obesity, diabetes, high cholesterol, and high blood pressure as well as risk factors like a high fat diet, lack of exercise, and smoking.
Genetics play a role, too, but since you can’t change your genes, the emphasis is placed on factors that you can control. It turns out that making lifestyle changes can greatly reduce your risk of heart attack, and may even reverse the process that causes heart disease.
I will continue to celebrate Heart Month with more information about how to assess your risk for heart disease and what you can do to prevent and treat heart disease.