Heart Failure - Disease Process and Prevention

Heart Failure - Disease Process and Prevention

Heart failure has been the leading cause of death in the United States since 1950. Right now, more than 6.5 million people have heart failure and it is only becoming more prevalent [1]. Furthermore, national spending on heart failure-related expenses is astronomical and only expected to increase. In this post, I want to address what heart failure is, how it develops, and lifestyle factors geared toward prevention.

Why is heart failure becoming more common, despite advances in medication and treatment? The other day, I was speaking with a cardiology resident and he told me that his opinion from observation, and I agree, is that heart failure has become more prevalent because medicine has gotten a lot better at treating acute, life-threatening issues like heart attacks. More people are surviving these events which exposes underlying diseases. The typical American diet and lifestyle are less than optimal, so chronic diseases like diabetes and cardiovascular disease worsen the quality of the years that we have added by life-saving procedures.

What is heart failure? 

First, here is some background information on the heart. The heart is a pump that functions to circulate blood throughout the body. Essentially, there are two separate systems through which blood is circulated. In the pulmonary circulation, blood is pumped to the lungs to acquire oxygen. Once the oxygenated blood returns to the heart, it is pumped to the rest of the body through the systemic circulation. The rest of the tissues in the body depend on the heart to maintain a steady flow of essential oxygen.

Heart failure occurs when the heart is unable to maintain what is called cardiac output. This means that the heart is not able to pump enough blood out to the body. As a result, excess fluids from the blood can back up in the lungs or other tissues throughout the body. 

One of the defining characteristics of heart failure is the remodeling of the heart. When the heart is damaged or subjected to abnormal stresses, it adjusts and changes itself to try and maintain its cardiac output. There are two ways that the heart can remodel. 

1. Dilated cardiomyopathy occurs when the heart is stretched with each beat. This happens because excessive amounts of blood enter the left ventricle (the chamber of the heart that pumps blood to the rest of the body) before each contraction. Imagine it like a water balloon that filled up a little bit too much. Then, the water is squeezed out before the balloon is tied. Repeat this several times and the balloon will enlarge and stretch out. This is similar to the disease process of dilated cardiomyopathy.
2. Pathological hypertrophy (i.e. thickening of the muscle) of the heart occurs when the heart has to pump against higher resistance. In a healthy individual, the resistance the heart must pump against could be compared to inflating a pool flotation device. My two-year-old daughter has a small inflatable inner tube that I blow up every time we take her swimming. Using my lungs to inflate it is somewhat difficult but nothing I can’t handle. Going back to the heart, the term a doctor uses to describe the resistance the heart pumps against is afterload. In an individual with a high afterload, this could be compared to inflating an air mattress with your lungs. Doing this would take a tremendous amount of effort. Similarly, a heart that is pumping against a high afterload must exert enormous effort.

• Since afterload is synonymous with blood pressure, high blood pressure over long periods can lead to pathological (i.e. disease-causing) hypertrophy of the heart.

When I learned about pathological hypertrophy in response to high blood pressure, one of my questions was how it differed from hypertrophy of the heart after exercise. The simple answer is that with pathological hypertrophy, the heart enlarges inwards, reducing the volume of the left ventricle. You may think the heart is becoming stronger by becoming thicker, but it actually weakens in the long run. 

Exercise also causes the heart to hypertrophy. However, in this case, the heart enlarges outwards. The volume of the heart does not diminish, and the heart becomes stronger and more efficient with each beat. This is why a conditioned athlete will tend to have a lower resting heart rate. 

What causes heart failure?

• A myocardial infarction (i.e. heart attack) occurs when one of the arteries supplying blood to the heart muscle becomes blocked. Just like every other muscle in the body, the heart needs oxygen too. After a short amount of time being starved of oxygen, the heart muscle begins to die. 
• After a portion of the heart muscle dies, the muscle around it must compensate and beat harder to maintain cardiac output (i.e. keep pumping a sufficient amount of blood to the rest of the body).
• Eventually, the dead heart muscle will be replaced by fibrous tissue, similar to a scar, and some function will be restored. However, it will never be like it was before the heart attack. The degree of recovery depends on the severity of the initial damage and ranges from practically no recovery to nearly complete recovery.
• The extra strain on the surrounding heart muscle causes remodeling of the heart itself. As the heart strains to maintain its cardiac output, it will hypertrophy and/or dilate and eventually weaken. 
• As the heart weakens, fluid builds up in the lungs and peripheral tissues such as the legs. 
• Additionally, a weakened heart will struggle to supply oxygenated blood to the rest of the body. As the heart gets weaker and weaker, a condition called cardiogenic shock will develop, and once developed, death is likely not far away as the survival rate is less than 30%, even with proper medical care.

• Increased afterload from high blood pressure puts more strain on the heart. This causes pathological hypertrophy where the heart muscle enlarges in an inward direction. Less blood is able to enter the heart due to the decreased volume of the left ventricle, and therefore less blood is able to leave. The heart also weakens as it remodels, eventually leading to heart failure. 

• Heart valve issues can also lead to heart failure. The heart has four valves. The tricuspid and mitral valves guard the entrance to the right and left ventricles respectively. The pulmonary and aortic semilunar valves guard the outflow tracts to the lungs and systemic circulation respectively. 
• If a valve is stenosed, blood has a harder time flowing through it. If the aortic semilunar valve (guarding the outflow tract to the systemic circulation) has stenosis, this can mimic high afterload and cause pathologic cardiac hypertrophy. 
• If a valve is leaky, this is called regurgitation. Depending on which valve is leaking, blood can flow back into the heart chamber that it was just pumped out of eventually causing dilated cardiomyopathy. The heart muscle remodels by stretching out. This weakens the heart and ultimately reduces the amount of blood that can be pumped out. 

Symptoms of Heart Failure

• Shortness of breath: It is most common for the left side of the heart to fail first. Because the left side of the heart receives oxygenated blood from the lungs and pumps it out to the rest of the body, when the left side of the heart can’t pump out enough blood, it begins to back up into the lungs. When the pressure of blood in the capillaries of the lungs becomes too high, it starts leaking into the tiny air-filled sacs called alveoli, making it much more difficult to breathe. This is called pulmonary edema. In fact, if left-sided heart failure occurs acutely, death from pulmonary edema and subsequent suffocation can occur in as short as 20-30 minutes. With chronic (i.e. long-term) heart failure, pulmonary edema develops much slower but can still be deadly if not treated. 
• Exercise intolerance and fatigue: When we exercise, the heart must ramp up its output to meet the body’s increased oxygen needs. A healthy heart can raise cardiac output to 300-400% during exercise and a well-trained athlete can go as high as 500-600%. This is called cardiac reserve. In heart failure, cardiac reserve drops precipitously so that even mild activity becomes very difficult since the heart is not able to increase cardiac output to meet the body’s needs.  
• Peripheral edema (i.e. swelling in the legs, ankles, and feet): As cardiac output falls, the kidneys respond by releasing chemicals that make the body retain fluids. The kidneys make urine, so this basically means that you urinate less than you would normally. The extra fluid boosts the total volume of blood in the body. Initially, this increases cardiac output but eventually, it will cause the heart to dilate and weaken further. Eventually, fluid blood backs up capillaries throughout the body causing peripheral edema. An individual with progressing heart failure is often prescribed diuretics to decrease the fluid retained by their body and lessen the strain on the heart.
• Fluid can also back up into the abdomen causing swelling of the belly. 
• Individuals with heart failure can gain weight rapidly from retained fluids. 
• Chest pain: if heart failure is caused by a heart attack, symptoms like chest pain and pressure, radiating pain down the left arm, nausea, shortness of breath, jaw and back pain, and other symptoms typical of a heart attack would be expected to be present. 

Prevention-oriented Lifestyle Factors

• Don’t smoke, vape, or use tobacco:. Chemicals in tobacco and smoking-related products (not just limited to cigarettes but vaping and smoking marijuana as well) include oxidizing agents and reactive oxygen species. These create inflammation on the inner lining of blood vessels (referred to as the endothelium) which has two effects. First, it reduces the amount of nitric oxide produced. Nitric oxide is a potent vasodilator, so less of it leads to vasoconstriction and higher blood pressure. Second, it causes oxidation of cholesterol and activation of macrophages. This is a perfect recipe for the development of atherosclerosis (see my earlier post on cholesterol for a more detailed description of this process) which leads to cardiovascular disease and is ultimately a huge predisposing factor for heart failure [2]. 
• Exercise: Both resistance training and aerobic exercise strengthen the heart muscle, improving its function, lowering cholesterol, and lowering blood pressure. Exercise is a great way to lower the risk of adverse cardiovascular events like a heart attack and recover function in an already weakened heart. Optimal recommendations are to aim for 30 to 60 minutes of daily activity. One caveat is that if you already have some degree of heart damage or injury, your exercise plan should be closely monitored by a doctor to ensure that your heart can tolerate it.
• A heart-healthy diet: Generally speaking, foods that fall under the umbrella of a Mediterranean diet are good for your heart. Foods typical of the American diet that are highly processed, high in sugar and refined carbohydrates, and foods that are digested rapidly and lead to a spike in blood sugar and insulin are not good for your heart. One of the reasons for this is that chronic high blood sugar, as seen in someone with poorly controlled diabetes or prediabetes, leads to endothelial damage (the endothelium is the inner lining of the blood vessels). This creates an environment that is ideal for atherosclerosis and high blood pressure.  
• Lower salt intake: Less salt (sodium) in the diet is also important for heart health. According to the US Department of Health and Human Services, Nine out of ten Americans have too much sodium in their diet. Most of the salt in our diet comes from highly processed foods such as canned foods, processed meats, and flavored rice and noodles. Too much sodium can lead to higher blood pressure because it encourages more fluid to be retained in circulation. For adults and teens age 14 and older, the recommended daily intake should be less than 2300 mg of sodium [3]. 
• Get good sleep: Poor sleep amount and quality is associated with diabetes, obesity, impaired glucose tolerance, cardiovascular disease, hypertension, anxiety, and depression [4].
• Screening tests: Regularly check your cholesterol levels, blood pressure, and hemoglobin A1C. Cholesterol levels (specifically elevated LDL) and high blood pressure can be an early warning sign of developing heart disease. An elevated hemoglobin A1C indicates the development of type II diabetes, which correlates with cardiovascular disease.

The bottom line

The heart’s essential role is to pump oxygenated blood throughout the body. When it fails, fluid from the blood will either back up in the lungs or peripheral tissues like the feet and ankles. Heart failure will also eventually lead to inadequate delivery of oxygen and nutrients to tissues throughout the body. The end result of this is cardiogenic shock, which often leads to death. 

Heart failure often occurs in response to some kind of damage or a new type of stress placed on the heart. The heart will respond by remodeling itself to maintain its output, however, this generally results in a weaker heart in the long run. 

Taking active steps can help stave off cardiovascular disease and ultimately heart failure. While there are many factors such as genetics that are outside of one's control, making investments in long-term health will pay dividends later on. Personally, I exercise, strive to eat and sleep better, and monitor my health now so that my 80-year-old self will be less likely to be hindered by disease. Taking stewardship of my health will enable me to be a more effective instrument in the Lord's hands, and it is a powerful way to show my gratitude for the body God has blessed me with.

Sources

1. Heart Failure Society of America. (n.d.). Heart failure facts & information. HFSA. Retrieved June 1, 2024, from https://hfsa.org/patient-hub/heart-failure-facts-information
2. Messner, B., & Bernhard, D. (2014). Smoking and Cardiovascular Disease Mechanisms of Endothelial Dysfunction and Early Atherogenesis. Arteriosclerosis, Thrombosis, and Vascular Biology., 34(3). https://www.ahajournals.org/doi/10.1161/ATVBAHA.113.300156
3. Eat less sodium: Quick tips. Eat Less Sodium: Quick Tips - MyHealthfinder. (n.d.). https://health.gov/myhealthfinder/health-conditions/heart-health/eat-less-sodium-quick-tips#:~:text=Nine%20out%20of%2010%20Americans,and%20keep%20your%20heart%20healthy. 
4. Hanson JA, Huecker MR. Sleep Deprivation. [Updated 2023 Jun 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547676/