Interplay Between Heart Disease & Neurodegenerative Diseases: Implications for Clinical Management

Abstract

Heart disease, also known as cardiovascular disease, encompasses a range of conditions affecting the heart or blood vessels. It is a significant health concern that cuts across race, gender and nationality. Various types of heart disease exist, including coronary artery disease, heart failure, arrhythmias, and valvular heart disease, each with its own set of symptoms and risk factors such as diet and genetics. Similarly, neurodegenerative diseases like Alzheimer’s, Parkinson’s, and Huntington’s disease pose challenges to cognitive and motor function, with Alzheimer’s being the most common form of dementia. These diseases affect individuals of different ethnic backgrounds and genders, with African Americans having a higher prevalence of Alzheimer’s.

The connection between heart disease and neurodegenerative diseases is substantial, with inflammation, oxidative stress, vascular dysfunction, hypertension, and dyslipidemia playing significant roles in both disease groups. Lifestyle factors such as diet and physical activity contribute to the development of these diseases. The heart-brain axis underscores the interplay between cardiovascular and brain health, with cardiovascular diseases influencing brain function and vice versa. Sleep apnea, often associated with heart failure, can exacerbate cognitive impairments due to its impact on oxygen flow to the brain.

Understanding the complex relationship between heart disease and neurodegenerative diseases is crucial for developing effective prevention and treatment strategies. Addressing common risk factors and promoting a healthy lifestyle may mitigate the burden of these diseases on individuals and healthcare systems. Further research into the mechanisms underlying their connection is warranted to advance clinical management and improve patient outcomes.

Keywords: cardiovascular, coronary, neurodegenerative, heart-brain, Alzheimer, Parkinsons

Introduction

Background Information

Heart disease, also known as cardiovascular disease, refers to a class of diseases that involve the heart or blood vessels. It is a broad term that encompasses various conditions, each affecting different parts of the cardiovascular system. In regard to ethnicity, the majority of people who die due to heart disease are African American. Asian people take up 18.6%, black people take up 22.6%, white people take up 8%, and hispanic people take up 11.6%. (1) In regard to sex, there are more male cases of heart disease compared to women. According to the american heart association, 52.9% were men and 47.1% were women in 2016 and this trend continues strongly and has been seen even in the many years after that. (2)

Types of heart disease

There are many different types of heart diseases. A few examples include coronary artery disease, heart failure, arrhythmias, and valvular heart disease. Coronary artery disease is the most common type and occurs when the blood vessels supplying the heart muscle become narrowed or blocked. (5) It can lead to chest pain, also known as angina, or a heart attack. It is generally due to the buildup of plaque which blocks the body’s blood supply and increases the strain on the heart.

Plaque buildup causes the arteries to narrow over time which is a process known as atherosclerosis. The most common cause of coronary artery disease is heart failure due to the weakening of the heart over time. Heart Failure occurs when the heart can’t pump blood effectively, leading to insufficient blood flow to meet the body’s needs. This can happen if the heart can’t fill up with enough blood or when the heart is too weak to pump blood properly. As the heart loses the ability to pump blood, blood backs up into other parts of the body; for example, it can back up into the lungs and cause shortness of breath.

Arrhythmias are irregular heartbeats. They can either be too fast, a condition known as tachycardia, too slow (bradycardia) or irregular. Arrhythmias can affect the heart’s ability to pump blood effectively when the electrical signals that tell the heart to beat don’t work properly. Valvular Heart Disease involves damage to or defects in the heart valves, impairing the flow of blood through the heart. The heart can’t pump blood effectively and has to work harder to pump, while the blood can be leaking back into the chamber or a narrow opening. This can also lead to heart failure since the heart can’t pump a sufficient amount of blood for the whole body. (6) There are many causes for heart disease, one leading factor being diet. Sodium intake plays a major role. The average American consumes about 3,400 mg of sodium each day, which is well over the recommended 2,300 mg. Eating too much sodium can lead to high blood pressure. Having a high blood pressure damages the lining of the arteries making them more susceptible to the buildup of plaque and narrowing of the arteries. (7) Congenital heart disease is a heart problem a baby has at birth. In most cases, congenital heart disease has no known reason, but it can be due to family history and chromosomal abnormalities (both genetic factors), or due to maternal factors (including medications or substances the mother comes in contact with while pregnant). (8)

Neurodegenerative diseases

Neurodegenerative diseases are a group of disorders characterized by the progressive degeneration of the structure and function of the nervous system. These conditions primarily affect neurons, the building blocks of the nervous system, leading to a decline in cognitive function and, in some cases, motor function. These diseases are generally characterized by neuron loss. A few examples of these kinds of diseases are Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis. (9) Going more in depth, Alzheimer’s Disease affects memory, thinking, and behavior. It is the most common cause of dementia. The brain itself shrinks causing brain cell connections and the cells themselves degenerate and die, causing the loss of memory. This disease mainly involves the parts of the brain that controls thought, memory, and language. (10) Parkinson’s Disease involves the degeneration of dopamine-producing neurons, leading to tremors, stiffness, and difficulty with balance and coordination. Nerve cell damage in the brain can cause the dopamine levels to drop. It affects the nervous system and parts of the body controlled by nerves. (11) Huntington’s Disease causes the progressive breakdown of nerve cells in the brain which can lead to the development of many different neurodegenerative diseases like Parkinson’s. A genetic mutation in the HTT gene causes Huntington’s disease. The HTT gene makes a protein known as huntingtin. This protein helps the neurons function. If the body is unable to make this protein, it can cause the development of this disease. (12) Amyotrophic Lateral Sclerosis affects motor neurons, leading to muscle weakness and atrophy. It is the progressive degeneration of nerve cells in the spinal cord and brain. As the motor neurons, which are the neurons that control the voluntary muscles decline, it stops being able to send signals to the muscles. There are 2 types of motor neurons: upper motor neurons and lower motor neurons. The upper controls the brain and spinal cord and its role is to control the lower motor neurons. The lower consists of cells in the brian stem which is the lower part of the brain. They first receive instructions from the upper neurons then send messages that tell the muscles in the body to move. Multiple Sclerosis is due to nerve damage disrupting the communication between the brain and the body. The immune system attacks the protective sheet, myelin, that protects and covers nerve fibers which cause communication problems between the brain and the rest of the body. The disease can cause permanent damage and deterioration to the nerve fibers.

For Alzheimer’s disease, African Americans still have the highest percentage of cases, which is 13.8%. Hispanic people have 12.2%, white people have 10.3%, and American Indian and Alaska Native individuals have 9.1% of the cases. (3) In this case, women are more likely to develop a neurodegenerative disease compared to men (3:1 ratio). (4)

Cerebral ischemia and ischemic strokes

A failing heart cannot pump a sufficient amount of blood to the body when it’s at rest or during physical activity. This can lead to a risk of the brain not getting enough blood, a condition known as cerebral ischemia. Atherosclerosis can lead to both cerebral ischemia and an ischemic stroke, the most common type of stroke. (13) An ischemic stroke occurs when the blood supply to part of the brain is blocked or reduced. Plaque buildup can reduce the blood flow to one part of the brain but it can also lead to blood clots which can completely block the flow. When a plaque formation becomes inflamed, it can rupture, causing the formation of a blood clot. This can prevent the brain cells from getting nutrients and oxygen it needs, causing them to die very quickly. (14) Once neurons start dying at a fast rate, people can start developing many different neurodegenerative diseases such as Alzheimers and Parkinsons. During the development of Alzheimer’s disease the brain starts shrinking and since neurons are dying, many connections in the brain are also lost. In the case of Parkinson’s disease, dopamine producing neurons start to degenerate. These neurons are only in specific parts of the brain, such as the prefrontal cortex, so blockages in the arteries near these parts of the brain can lead to the development of Parkinson’s.

Body

Mutual Influence of heart disease and neurodegenerative diseases:

Links between heart disease and neurodegenerative diseases

It is undeniable that there are some links that can affect both heart disease and neurodegenerative disease. Some autopsy studies show that as many as 80% of individuals with Alzheimer’s disease also have cardiovascular disease. This is very important because it shows a major correlation between the two seemingly distinct diseases. They can be linked together through a variety of ways that will further be looked into. (15) One main link is inflammation. In heart disease, inflammation contributes to the development and progression of atherosclerosis by promoting the accumulation of inflammatory cells in arterial walls, leading to plaque formation and increasing the risk of cardiovascular diseases.

In neurodegenerative diseases, inflammation contributes to neuronal damage; activated immune cells release pro-inflammatory molecules, starting the degeneration of neurons and contributing to the progression of conditions like Alzheimer’s, Parkinson’s, and Amyotrophic Lateral Sclerosis (ALS). Another link is oxidative stress. In heart disease, oxidative stress plays a role in the progression of atherosclerosis and cardiovascular events by causing damage to lipids, proteins, and DNA, contributing to inflammation. In neurodegenerative diseases, oxidative stress is implicated in the pathogenesis (development/ progress) as it leads to the accumulation of cellular damage in neurons, exacerbating inflammation, and contributing to the degeneration of nerve cells in conditions like Alzheimer’s, Parkinson’s, and ALS.

Vascular dysfunction also has a link between both diseases. In heart disease, vascular dysfunction impairs blood vessel function, leading to reduced blood flow, compromised oxygen delivery, and an increased risk of conditions like atherosclerosis. In neurodegenerative diseases, vascular dysfunction can contribute to reduced cerebral blood flow, impacting nutrient delivery to the brain and potentially showing cognitive decline in conditions like Alzheimer’s.

In heart disease, hypertension strains the heart and arteries, promoting vascular dysfunction and increasing the risk of coronary artery disease, heart failure, and stroke. In Neurodegenerative Disease, hypertension is a risk factor for small vessel disease and may contribute to cognitive impairment and an increased risk of neurodegenerative conditions. (16)

In Heart Diseases, dyslipidemia (elevated cholesterol levels), contributes to atherosclerosis, leading to vascular dysfunction and an increased risk of heart attacks and strokes. In Neurodegenerative Diseases, dyslipidemia may contribute to the development of vascular-related neurodegenerative disorders by affecting blood flow to the brain and promoting inflammation.

And of course, lifestyle is a key factor to living a good and healthy life. An unhealthy lifestyle, with factors such as poor diet and physical inactivity, contribute to vascular dysfunction, fostering conditions conducive to the development of heart disease and neurodegenerative diseases. (17)

Heart brain axis

It is believed that cardiovascular diseases can affect brain function and many brain diseases are associated with heart dysfunction which is the heart-brain axis. The brain is the one in charge of regulating the function of the heart and impaired brain function can lead to the development of cardiovascular diseases. Similarly, cardiovascular diseases can reduce the amount of blood flow sent to the brain which can lead to the development of various brain diseases. (18) Firstly, how do brain diseases contribute to the development of cardiovascular diseases? Cardiac rhythm changes, also known as arrhythmia, can reflect abnormal brain function and be biomarkers for different brain diseases. The autonomic nervous system (ANS) is in control of the body’s involuntary muscles such as the heart and lungs. The brain is in control of the ANS. When the body has a seizure, the brain’s electrical activity is disturbed and those changes can lead to a disruption in the ANS, also leading to arrhythmias.

Next, how do cardiovascular diseases contribute to brain diseases? Diseases such as heart failure and atrial fibrillation are risk factors to many different brain diseases such as dementia or Alzheimer’s disease. Cardiac rhythms and electroencephalograms are also found to be highly synchronized, which is another link between the brain and heart. Electroencephalography is the measurement of electric activity in different parts of the brain. This means the electrical rhythms of the heart and brain are very synchronized further confirming the idea of the heart-brain axis.

Sleep apnea

Heart failure can influence sleep apnea. One way in which this works is through the accumulation of fluids. Heart failure often leads to fluid buildup in the lungs and other tissues, which can block the airways. This makes it more challenging for the air to flow easily during breathing. The heightened resistance contributes to obstructive sleep apnea. Sleep apnea has a lot of effects. The first one being memory loss. Due to the lack of sleep, people can start to develop short term or long term memory loss. Another effect is brain damage due to the lack of oxygen going to the brain. By starving the brain of oxygen, the development of cerebral hypoxia can occur. Since brain cells are very sensitive to lack of oxygen, they can start dying rapidly especially as more and more oxygen is getting cut off.

Preventative measures for developing heart or neurodegenerative diseases

There isn’t a specific way to cure heart or neurodegenerative diseases so the important thing in these cases is prevention, with lifestyle and environmental factors being key. It’s important to focus on getting enough rest at night and staying regular with working out. Eating a healthy diet and cutting back on foods that have high sodium, cause high blood pressure and cholesterol is extremely important. The best thing you can do for your body and health is eat healthy, exercise regularly, and get enough sleep. Learning new things everyday can create new connections in the brain which delay the onset of diseases like Alzheimer’s or makes it less damaging for the brain. It’s simple to do this, start by learning a new language or picking up a new hobby. These small changes in your life can create a significant difference in the outcome of your health. That being said, since there’s no cure for Alzheimer’s, protecting your heart’s health can be key to delaying the onset of or reducing the effects of these neurodegenerative diseases.

Summary

Our research explores the relationship between heart disease and neurodegenerative disorders, emphasizing the impact of cardiovascular health on brain function. Our research has highlighted the significance of a healthy lifestyle in mitigating the risk of diseases like Alzheimer’s and Parkinson’s. We believe our findings can contribute to the field of cardiovascular and neurodegenerative diseases, offering fresh insights into prevention and treatment strategies. We thus conclude that understanding the interplay between heart and brain conditions is crucial for patient care and hope that our research could prompt further study and innovation in this area.

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