Heart failure is quite a complex issue, which needs to be simplified to make it more understandable. The heart failure is a condition where the heart becomes unable to deliver enough blood with oxygen and nutrients to the peripheral tissues. This definition is not completely accurate, but it is sufficient for basic understanding.
First, it is necessary to know some basic information about the heart and its circulation. The blood flows in our body through hollow tubes known as blood vessels. The heart works as a mechanic pump, which pushes certain volumes of the blood into the peripheral circulation. The blood circulation can be divided into the systemic and pulmonary circulation.
The blood flows from the left side of the heart from the left atrium to the left ventricle. Out of there it gets through the aorta into practically all smaller arteries that branch into the smallest blood capillaries located in peripheral tissues. The capillaries allow the exchange of breathing gases, nutrients and waste products. The oxygen and nutrients enter the tissues and carbon dioxide with waste products return to the capillaries. The blood is then taken by small veins that bring the blood to the vena cava, which leads to the right heart atrium. From there, the blood enters the pulmonary circulation.
The pulmonary circulation starts in the right atrium. From there, the deoxygenated blood enters the right ventricle and it is expelled into the pulmonary artery. The artery branches into smaller vessels. The smallest branches are in close contact with lung alveoli, where the exchange of respiratory gases takes place. Oxygen enters the blood vessels and carbon dioxide gets into the alveoli to be later exhaled. The oxygenated blood is then taken by pulmonary veins to the left heart atrium into the systemic circulation (see above).
As you can see, both circuits are continuously connected to each other and the amount of blood ejected into the systemic circulation must be the same as the amount of blood ejected into the pulmonary circulation. Given that the systemic circulation is formed by almost all blood vessels in the body, and the pulmonary circulation is formed “only” by vessels of one organ, the left ventricle must work against a much higher resistance. Therefore, it must have a larger muscle that is able to generate greater compression pressures.
Why the heart pump sometimes fails? There are many possible causes and I shall mention only those most common and clinically important.
Damage to the heart muscle
The heart muscle drives the pump. When the “motor” is damage, the pump does not work correctly. This can happen in myocardial infarction, myocarditis (inflammation of the heart muscle) and cardiomyopathy (hypertrophic cardiomyopathy, dilated cardiomyopathy, etc.).
The synchronized activity of the four heart valves enables one-direction flow of the blood. Opened valves enable the blood to flow into the both circulations and closed valves prevent the backflow of the blood. The valves may be narrowed by congenital defects, calcifications and degenerations occurring with increasing age and by bacterial vegetations in infective endocarditis. The opposite problem is when the valves do not close properly allowing the backflow of blood. This can happen in some congenital defects, by destruction of valves in rheumatic fever and by infective endocarditis.
High blood pressure in systemic circulation
This is the blood pressure, which can be measured by a classic manometer. Long-term hypertension forces the left ventricle to produce larger pressure to expel the blood. This may cause its overload and the heart failure.
Increased blood pressure in pulmonary circulation
The pulmonary hypertension increases the overload of the right ventricle. It may be a primary disease or it may accompany lung diseases and pulmonary embolism.
Under certain circumstances, abnormal heart rhythm may lead to heart failure. Normal speed heart rate is between 60-90 beats per minute. If the heart rate is much slower (bradycardia), the heart is unable to deliver sufficient amount of blood to the tissues. Accelerated heart rate causes similar problem as the quickly contracting ventricles are unable to fill with the desired volume of blood.
This life-threatening situation occurs when the pericardial space is filled with a fluid. It can follow a direct injury (blood within the pericardial space) or pericarditis. The signs of heart failure may occur suddenly and the condition may kill the patient within minutes. More can be read in the related article.
This is an extremely rare cause compared to other causes. Some tumors of the heart may grow into the heart cavities and cause obstruction for the blood flow causing the symptoms of heart failure.
The manifestations of heart failure are highly variable and occur with different severity depending on the extent and current subtype of the heart failure (right-sided, left-sided, both).
The symptoms can be easily derived from the mechanical point of view. We have a device pumping fluid. What happens when the pump gets broken? First, the first fluid is not pumped, where needed and in addition, the fluid accumulates in front of the pump.
And that is all. Now, let’s use the above- mentioned facts to describe the symptoms of failure of particular parts of the heart.
Symptoms of left-sided heart failure
The left ventricle is less capable of pumping the oxygenated blood into the systemic circulation. We must add, however, that this ability of the heart is quite well maintained in chronic heart failure and symptoms of the low cardiac output occur in the most advanced stage of the disease. In acute left-sided heart failure, on the contrary, the inadequate cardiac output causes decrease of the blood pressure and impaired oxygen delivery to tissue including the brain may cause sudden unconsciousness and death.
In chronic left-side heart failure, the blood accumulates in front of the left part of the heart, which means within the pulmonary circulation. The blood accumulates in the pulmonary arteries disrupting the exchange of breathing gases causing shortness of breath and bouts of cough. When the pulmonary blood pressure is too high due to the accumulated blood, the blood fluid may leak into the lungs causing the pulmonary edema. The fluid may begin to filter even into the space around the lungs, creating a so-called pleural effusion (“water on the lungs”).
Symptoms of left-sided heart failure
The right half of the heart is unable to pump the deoxygenated blood into the pulmonary circulation. For a progressive failure, this is again not a major problem, because the heart adapts to ensure at least partially effective blood output. Serious symptoms may follow an acute right-sided heart failure, which may occur due to a massive pulmonary embolism. In such case, the hear side of the heart is unable to get enough blood to the lungs meaning that the left side of the heart does not get enough oxygenated blood to deliver to the peripheral tissues. The situation is in the end similar to the acute left-sided heart failure and the condition results in unconsciousness and death.
In chronic right-side heart failure, the fluid accumulates in front of the right half of the heart. And what is in front of the right half of the heart? There is the vena cava and other major veins of the body. The blood accumulates in the veins causing their dilation. The most visible this is in neck veins. Dilated liver veins cause enlargement of the liver, which may be accompanied with abdominal pain. Long-lasting liver congestion may elevate the liver tests and even cause liver cirrhosis. Congestion of venous system of the lower extremities causes typical swelling of both legs. Another typical symptom of advanced right heart failure is frequent nighttime urination (nocturia). In horizontal position, the accumulated blood flows into the abdominal veins including renal veins. This leads to both the increase in blood pressure in kidneys and to the urine filtration.
I should emphasize that the above symptoms of right and left cardiac failure are mentioned separately just to make the issue easier to understand. In reality, they are present together, some of them dominant.