Cardiovascular Function and Health

Heart disease is a top killer worldwide. Learn about how the cardiovascular system works, what can go wrong with it, and how to keep it healthy.

By Mark D. Harris

Pastors and physicians are never off duty. I have the obligation, and the privilege, to educate family, friends, and acquaintances in spiritual and physical matters. One gentleman at church has an abnormal heart rhythm (dysrhythmia or arrhythmia). Another has cardiac manifestations of sarcoidosis. Still other church members have hardening of the arteries (atherosclerosis) or heart failure. The article summarizes basic information on cardiovascular disease in a way, I hope, that will best meet their needs.

The Blood

Blood brings oxygen and nutrients to every cell in the body and removes harmful gases and waste products. Blood is composed of oxygen-carrying cells (red blood cells), infection-fighting cells (white blood cells), proteins, water, and an array of elements such as glucose (sugar), sodium (salt), and potassium. Blood is created in the bone marrow within long bones. The spleen filters solid elements (like aged red cells or sickle cells) from the blood. The kidneys filter chemicals from the blood, thus maintaining the proper chemical balance.

Blood is required for life. Leviticus 17:11 states that the life of the flesh is in the blood. In many other verses, the Bible equates life with blood (Genesis 9:4). If the blood is not replenished or does not circulate, the person or animal dies.

The Vascular System

The heart is the pump that pushes blood throughout the body. Arteries, veins, and capillaries are the plumbing that carry the blood to its destination. Arteries are muscular tubes that can increase or decrease in diameter to carry fresh blood away from the heart and lungs. Veins are thin-walled tubes with one-way valves that carry blood back to the heart and lungs. Capillaries are tiny, thin-walled tubes that carry blood to the smallest areas and connect the arteries and the veins.

Arteries can spasm too tightly, as in drug use. They can relax too much, as occurs in sepsis (a serious infection in which bacterial toxins invade the bloodstream). Arteries can also be blocked by plaque. Veins cannot spasm, but the valves therein can fail. Blood clots more easily in veins. Being thin-walled, veins can more easily be compressed by surrounding structures, thus compromising flow.

Hardening of the arteries due to plaque in one area is a clue that such hardening due to plaque is present throughout the body. Atherosclerosis (vessel hardening) in the abdominal aorta, for example, tells the doctor to look for it in the heart (coronary arteries) and neck (carotid arteries). Male erectile dysfunction can be an early sign of atherosclerosis.

The Heart

The heart itself is divided into four chambers.[1] The two upper chambers are the thinly muscled atria. The two lower chambers are the thickly muscled ventricles. The right atrium accepts dark venous blood from elsewhere in the body – the brain, bowels, arms, and legs via the inferior and superior vena cava (veins) – and pumps it through the tricuspid valve into the right ventricle. The right ventricle pushes blood into the lungs via the pulmonary valve and artery so that oxygen can be replenished and toxic chemicals such as carbon dioxide can be released. Oxygenated blood goes from the lungs to the left atrium via the pulmonary veins. The left atrium then pumps the blood through the mitral valve into the left ventricle. Very thickly walled, the left ventricle pumps the blood throughout the body through the aortic valve and aorta (artery). The total human blood volume is five liters (1.3 gallons). The heart beats 60-100 times per minute over a 70-year lifespan. Like the rest of the body, the human heart is fearfully and wonderfully made (Psalm 139:14).

The heart has an electrical system to make each chamber contract and relax at exactly the right time to receive blood and then to push the blood where it needs to go. The initial electrical impulse starts at the sino-atrial (SA) node in the right atrium.[2] That impulse travels across the right and left atria to trigger the muscle to contract. The impulse also travels to the atrioventricular (AV) node via internodal pathways. The AV node delays the electrical impulse so that the atria can finish their contraction and begin to relax before the ventricles contract. The electrical impulse travels from the AV node to the middle muscle mass of the heart, the intraventricular septum, through specialized pathways called bundle branches.[3] Finally, the electrical impulse triggers the right and left ventricles to contract. Moments later, the cycle restarts.

Problems in the Heart

As robust as a normal human heart is, malfunctions happen. Direct blunt injury such as a car accident or penetrating injury such as a stab wound can obviously disrupt function. Cancer, autoimmune diseases, infection, and toxins (like alcohol) injure the heart. Three areas demand special attention: ischemia, arrhythmia, and failure.

Ischemic Heart Injury

Like all tissues, the heart needs blood to carry oxygen and nutrients to itself, and to eliminate waste such as lactic acid.[4] With every beat, less than 5% of the total blood pumped goes to the heart muscle through the coronary arteries.[5]

• The left coronary artery delivers blood to the left side of your heart, including your left atrium and ventricle and the septum between the ventricles.
• The circumflex artery branches off from the left coronary artery to supply blood to part of the left ventricle.
• The left anterior descending artery also branches from the left coronary artery and provides blood to parts of both the right and left ventricles.
• The right coronary artery provides blood to the right atrium and parts of both ventricles.
• The marginal arteries branch from the right coronary artery and provide blood to the surface of the right atrium.
• The posterior descending artery also branches from the right coronary artery and provides blood to the bottom of both ventricles.

These arteries can be blocked with atherosclerotic plaque made up of fat, platelets, and calcium (hardening of the arteries). Over the decades, this plaque builds up and slowly blocks the artery, decreasing its ability to carry blood to the heart muscle. If the blood vessel gets too small, the muscle cell cannot get enough blood to survive. Pain, called angina[6], and even cell death results.

A speedier process occurs when a piece of a plaque (embolus) in a large portion of a coronary artery breaks off and flows downstream into a smaller area. The piece completely occludes the smaller part of the vessel and the heart muscle cells served by that vessel begin to die. This sequence is what usually occurs in a myocardial infarction (heart attack).

An even faster but less common process resulting in a lack of blood to the heart muscle is a spasm of the coronary arteries. Under the influence of drugs like cocaine, the muscles in the arterial walls clamp down, severely restricting the flow of blood to the heart muscle itself. Heart attacks in young and otherwise healthy people more commonly have this cause.

Abnormal Heart Rhythms

The electrical system plays a crucial role in normal heart function. It can be disrupted by aging, heart disease, infection, cancer, and genetics. Damage to the SA node can cause the node to slow its impulse so much that another location, typically in the atria, provides the electrical stimulus. The current is conducted abnormally across the atria. This causes the atrial muscle to contract in a disorganized fashion. If the AV node is functioning normally and there are no accessory pathways from the atria to the ventricles, the electrical activity slows as it passes to the ventricles and the ventricles continue to contract at a normal or slow rate. Atrial tachyarrhythmias (AKA supraventricular tachycardia) like multifocal atrial tachycardia, atrial flutter, and atrial fibrillation result.[7]

Atrial fibrillation (AFib) is the most common abnormal heart rhythm above the ventricles. When in AFib, the atria quiver, unable to coordinate muscular contractions with enough force to pump blood. Symptoms include chest palpitations, shortness of breath, a sensation of the heart beating too hard, chest pain, and lightheadedness. AFib is paradoxical, in which episodes occur with varying frequency and duration but resolve on their own within seven days.[8] AFib can also be persistent. Causes of AFib include heart disease, alcohol use, hyperthyroidism, drugs that stimulate the heart, lung disease, obesity, diabetes, chronic kidney disease, and sleep apnea. Atrial flutter, the second most common abnormal supraventricular (atrial) heart rhythm, has similar symptoms. Later signs of heart failure include difficulty breathing at night, leg swelling, and the inability to lie flat.

Patients face three primary complications when they have abnormal heart rhythms. First, if the ventricles try to keep up with the atria, problems develop. A rapid ventricular response to an abnormal atrial rhythm can cause heart rates from 150 to 300. The ventricles cannot sustain such rapid contractions, and the ventricle begins to tire and die. Ventricular tachycardia, ventricular fibrillation, and sudden cardiac death can follow. Second, since the blood in the atria is not moving, blood clots can develop. These clots can travel anywhere in the body, blocking blood flow to affected areas. For example, a blood clot that travels to the brain can cause a stroke (cerebrovascular accident). Third, abnormal atrial rhythms in people with abnormal electrical pathways in their hearts can cause sudden cardiac death.

 

Heart failure

As the heart muscle wears out, either from injury (solitary or repeated), abnormal rhythms, or the wear and tear of life, the heart becomes less able to pump blood to the whole body, especially during physical exertion. Alcohol, drugs (stimulants), and medications (such as anticancer and mental health) cause direct toxic injury to the heart muscle. New heart muscle cells do not arise to replace dead muscle cells, but scars develop. Scars impair heart function and can themselves contribute to abnormal rhythms.

Heart failure is commonly evaluated with an ultrasound examination that reveals the ejection fraction (EF). The EF is the percentage of blood that is ejected from the left ventricle into the body with each beat of the heart. Mathematically, the EF = amount of blood pumped out divided by the amount of blood in the chamber. A healthy heart will eject 50-70% of the blood in the left ventricle with every contraction. A heart with mildly impaired function will eject 41-49% and a diseased heart will eject 40% or less.

The New York Heart Association (NYHA) developed a widely used classification system for heart failure.[9]

• Class I – People in this class have no limitations during ordinary physical activity, meaning that ordinary activities do not cause fatigue or shortness of breath. Activities that can be performed in Class I include jogging or walking at 5 mph, engaging in recreational activities like baseball, and performing outdoor activities like shoveling.
• Class II – This class describes people who have slight symptoms such as fatigue and shortness of breath during moderate physical activity, yet show no symptoms at rest. People in Class II can typically walk at 4 mph, have intercourse without needing to stop, and garden.
• Class III – People who have symptoms while performing some activity of daily living, yet who are comfortable at rest, fall into this class. Activities that can still be performed include dressing and/or showering without pausing, making the bed, and walking at 2.5 mph.
• Class IV – This is the most severe classification. People in Class IV cannot perform any physical activities without experiencing discomfort.

Patients with class IV heart failure often require skilled nursing care.

Diagnosis and Treatment of Heart Problems

Ischemic Heart Injury

Heart injury caused by a lack of blood flow to an area is called ischemic injury. Patients with acute ischemic injury (like a heart attack) often present for care with chest pain (typically crushing), shortness of breath, pain radiating to the jaw or right arm, nausea, flushing, and a feeling of impending doom. Emergency medical staff will use an electrocardiogram (ECG) and blood tests such as CK-MB and troponin to look for signs of cell death. A chest x-ray will demonstrate the condition and size of the heart and lungs. An echocardiogram (heart ultrasound) will show how the heart is moving, if any valves are leaking, and other key information. Cardiac computed tomography (CT) or magnetic resonance imaging (MRI) evaluates the extent of heart damage.

Heart muscle dies in just a few hours after losing blood, so rapid treatment is essential.[10] Treatment includes:

• Medications such as aspirin to reduce blood clotting.
• Surgical and other procedures such as clot-dissolving drugs, balloon angioplasty, surgery or a combination of treatments to restore blood flow to part of the heart muscle damaged during a heart attack.
• Cardiac rehabilitation, a personalized exercise and education program that teaches ways to improve heart health after heart surgery.
• Dual antiplatelet therapy (DAPT) for some patients who have heart attacks, that have stents placed in their coronary arteries, or undergo coronary artery bypass graft surgery (CABG) to prevent blood clotting.

Treatment for less acute chest pain, like angina pectoris, includes aspirin, nitroglycerin, beta-blockers, and statins to lower cholesterol. Lifestyle modifications including exercise and a healthy diet are indispensable.

Abnormal Heart Rhythms

Life-threatening rhythms like ventricular fibrillation and tachycardia must be treated immediately, usually with drugs and electrical cardioversion. For non-life-threatening rhythms like A Fib and A Flutter, the first priority is to treat the ventricular response. This prevents abnormal ventricular rhythms from developing and is usually done with medications called beta blockers, including atenolol and metoprolol. Once the ventricular rates have fallen to less than 110, medical staff try to prevent blood clots and treat the atrial rhythm. Presenting symptoms for aberrant atrial (supraventricular) rhythms including palpitations, chest pain, shortness of breath, and those noted above.

Adenosine is the first drug to treat abnormal atrial rhythms. Given intravenously in a rapid push, the success or failure of adenosine treatment is quickly apparent. If adenosine fails, antiarrhythmic drugs such as amiodarone can be effective. Other antiarrhythmic drugs include flecainide, propafenone, sotalol, and dofetilide. All antiarrhythmics have significant side effects.

AFib and A Flutter cause stasis of the blood in the atria and can propagate blood clots. Anticoagulants should be used for four weeks between diagnosis and treatment (cardioversion) and then six months or more afterward.  Exercise and good hydration minimize the chance of blood clots, improve overall function, and are associated with good outcomes.

Heart Failure

In addition to the symptoms noted above, patients with heart failure can have swelling of the feet and ankles, enlarged neck veins, inability to lie flat on a bed (orthopnea), and difficulty breathing when lying flat (paradoxical nocturnal dyspnea). Exercise intolerance is common later in the disease course, but exercise remains important to slow disease progression and improve quality of life.

Medications such as beta blockers can decrease pressure in the vascular system (by arterial vasodilation) and thus make it easier for the heart to pump. Treating ischemic injury and abnormal rhythms can also improve heart failure. Limiting sodium intake and other dietary changes will minimize symptoms. Diuretics such as Lasix, hydrochlorothiazide, and spironolactone help remove extra water from the system and can decrease swelling. An ejection fraction of less than 20% is not long compatible with life. Hearts that are so severely diseased should be replaced when possible.

Prevention of Heart Problems

Healthy living, including regular exercise, a vegetable and whole grain diet, avoidance of alcohol and illegal drugs, and adequate sleep form the foundation of good heart health. Eschewing sugary drinks, minimizing highly processed food, and maintaining a body mass index between 20 and 25 will help. Getting immunizations recommended by the US Centers for Disease Control and Prevention will limit the infectious component of heart troubles. Poor mental health powerfully contributes to heart disease. Poor dental health does the same. Therefore, strive to improve your mental and dental health.

Specific actions to prevent heart problems are sprinkled throughout this article. Taking the right medications as directed is a start. Formal rehabilitation after heart or lung disease is associated with longer, happier living. If symptoms appear or worsen, get help promptly, not slowly. This is especially true for emergency symptoms.

Conclusion

This article was written for family, friends and acquaintances, especially in church, and patients around the world.  Cardiovascular disease is the number one killer in many nations. Ischemia, arrhythmia, and failure are the most common categories of heart disease. Knowing about heart disease is the first step in minimizing sickness (morbidity) and death (mortality). Living healthy lives in accordance with God’s word will help us as individuals, families, and communities. When someone does fall sick, knowing what to do and doing it will make things better.

 

[1] Please see accompanying diagrams.

[2] Every place in the entire heart can provide electrical impulses but the SA node is fastest and thus takes the lead. If the SA node is damaged, another area takes the lead and conduction becomes aberrant.

[3] If the intraventicular septum is too thick, as in hypertrophic cardiomyopathy, the septum may not get enough blood.

[4] Coronary arteries, https://youtu.be/QmxZcEHs7HA.

[5] Supplying oxygen to the heart’s muscle, https://www.nhlbi.nih.gov/health/heart/blood-flow.

[6] Angina means pain and angina pectoris means chest pain.

[7] Tachycardia is a fast heart rate (over 100 beats per minute). Bradycardia is a slow heart rate (under 60 beats per minute).

[8] https://www.uptodate.com/contents/atrial-fibrillation-beyond-the-basics.

[9] https://heart-failure.net/living/nyha-classification.

[10] Heart attack, https://www.mayoclinic.org/diseases-conditions/heart-attack/diagnosis-treatment/drc-20373112.