How the heart compensates for heart failure

Your heart's goal in compensating for heart failure is to maintain your cardiac output. Cardiac output is the amount of blood your heart is able to pump in 1 minute. The problem in heart failure is that the heart is not pumping out enough blood each time it beats (low stroke volume). To maintain your cardiac output, your heart can try to:

• Beat faster (increase your heart rate).
• Pump more blood with each beat (increase your stroke volume).

How does my heart know to beat faster? Your brain signals your heart to beat faster by sending messages to your heart's electrical system, which controls the timing of your heartbeat. When your cardiac output is low, your adrenal glands also release more norepinephrine (adrenaline), which travels in the bloodstream and stimulates your heart to beat faster. Although beating faster helps to maintain cardiac output as the stroke volume falls, a faster heart rate can be counterproductive because it allows less time for the ventricle to fill with blood after each heartbeat. Also, a very fast heart rate can itself weaken the heart muscle over time.

How does my heart increase its stroke volume? To increase its stroke volume, your heart can try to:

• Get more blood into your heart. If your left ventricle is not doing a good job pumping blood out, your heart can try to compensate by allowing more blood to fill the ventricle before it pumps by expanding its size (dilating) to increase its volume. This form of compensation may be helpful at first, but as the heart gets bigger and bigger, there is more and more tension on the walls of the heart to pump out the blood inside it. This increases the strain on the heart, making its function worse over time.
• Pump harder. Your heart can pump harder by developing stronger, thicker muscle. This thickening of your heart muscle is called hypertrophy, and it can help your heart pump more forcefully and increase your stroke volume. However, hypertrophy of the heart muscle increases the heart's need for oxygen and other nutrients. These requirements can eventually outstrip the blood supply to the heart, leading to further weakening of the heart muscle. In addition, hypertrophy of the walls of the heart can make diastolic function worse by impairing the ability of the heart to relax properly. This limits the heart's ability to fill with blood, which can also further lessen cardiac output.

How do other parts of my body compensate for heart failure? In addition to trying to increase your cardiac output, the rest of your body tries to compensate for heart failure in two main ways:

• By increasing the amount of blood in your circulatory system. Your kidneys remove excess fluid from your system. If your kidneys sense that there is not enough blood circulating in your system, they can cause your body to retain extra salt and water, which adds fluid to your circulatory system. This fluid becomes part of the blood circulating throughout your system. Having more blood in your circulatory system can help prevent a drop in blood pressure to your brain and other vital organs.
• By enabling more blood to reach your brain and other vital organs. Arteries are the blood vessels that circulate the blood pumped by your heart to the rest of your body. If your body senses that the brain and vital organs are not receiving enough blood, some arteries narrow to increase blood pressure and blood flow to the brain and other vital organs. At the same time, the arteries supplying the brain and vital organs widen to carry the increased blood flow.

How well does my body compensate for heart failure? Your body has a remarkable ability to compensate for heart failure. It may do such a good job compensating, in fact, that many people do not feel symptoms in the earlier stages of heart failure. It is only when your body is not able to compensate enough that you will begin to experience symptoms.

People who develop heart failure suddenly following a heart attack may not be able to compensate as well as people who develop heart failure gradually. Sudden heart failure can be a shock to your body, and without adequate compensation, it can cause more sudden and severe symptoms and a greater risk of complications.

What goes wrong with my body's efforts to compensate for heart failure? Unfortunately, your body's efforts to compensate for your failing heart only cause more problems and ultimately make your heart failure worse. Specifically, your body's efforts to compensate can:

• Damage your heart muscle further, which can lead to worsening heart failure, more compensation, and more heart muscle damage. The result is a vicious cycle that continues until the body can no longer compensate.
• Increase your risk of serious complications, such as an irregular heartbeat.

How does compensation for heart failure damage my heart? The table below explains why each of the ways that your body tries to compensate for heart failure can damage your heart and lead to heart failure that continues to get worse.

How the body compensates for heart failure

Compensation effort	Short-term benefit	Long-term complication(s)
Increase heart rate	Maintains cardiac output as stroke volume falls	Can directly weaken heart muscle Decreases the filling time of the heart
Get more blood into your heart	Increases cardiac output by stimulating the heart to beat more forcefully	Leads to dilation of the heart, which increases metabolic demand and further worsens systolic function
Increase muscle mass (hypertrophy) to pump harder	Increases cardiac output by increasing stroke volume	Increases metabolic requirement of the heart Decreases ability of the heart to fill with blood, leading to diastolic heart failure
Increase volume of blood	Maintains blood pressure to the vital organs	Can overload the heart Blood can back up into the lungs and other organs, causing congestive symptoms.
Divert blood to your brain and other vital organs	Maintains blood pressure to the vital organs	If the pressure in your arteries is higher, your heart has to work harder to pump against this pressure. Since your heart is already weak, it has to pump even harder and faster, which only weakens it more.

How does compensation increase my risk of arrhythmias? In addition to damaging your heart, your body's efforts to compensate for heart failure can also increase your risk for developing an abnormal heartbeat (arrhythmia).

When the brain senses that it is not getting enough blood, it sends signals to the heart telling it to beat faster and squeeze harder to increase cardiac output. Your brain sends these signals using a chemical messenger called norepinephrine (adrenaline). Your adrenal glands also secrete norepinephrine into the bloodstream to cause the heart to beat faster and more forcefully.

Unfortunately, these chemical messengers can also cause portions of the muscle to generate abnormal electrical signals that can disrupt the heart's orderly pumping action. The result is an irregular heartbeat.

High levels of norepinephrine increase your risk of developing an irregular heartbeat from damaged areas of the heart.

Certain types of arrhythmias can be life-threatening, such as ventricular tachycardia (VT) or ventricular fibrillation (V-fib, VF), which are abnormally fast heart rhythms that originate in the ventricles instead of in the sinus node in the right atrium, which is normal. VT or V-fib can cause a dangerous drop in cardiac output. This may prevent the brain and other organs from getting any blood and may result in fainting (syncope) or sudden death.

Your body's attempts to compensate for heart failure by increasing the blood volume and dilating the left ventricle can also lead to another abnormal rhythm called atrial fibrillation (A-fib, AF). Atrial fibrillation is a rapid, irregular beating of the atria that leads to ineffective atrial contractions. Stretching of the atria from the increased blood volume can cause atrial fibrillation, which is also more likely to occur when norepinephrine levels are high.

Atrial fibrillation is an important complication of heart failure because it can:

• Further lessen cardiac output. This is because filling of the left ventricle partially depends on having the left atrium contract effectively, which does not happen during atrial fibrillation.
• Cause blood to pool in the left atrium, which can lead to the formation of blood clots and increased risk of stroke.

What happens when my body can no longer compensate for my heart failure? At this point, you will begin to experience the usual symptoms of heart failure, which consist of two major types:

• Congestive symptoms, which are caused by the backup of blood into the lungs and the other organs of the body. These symptoms include shortness of breath and swelling in the ankles and abdomen.
• Low-output symptoms, which are caused by the inability of the heart to generate enough cardiac output, leading to reduced blood flow to the brain and other vital organs. These symptoms may include lightheadedness, fatigue, and low urine output. If the cardiac output is very low, this can damage organs, particularly the kidneys.

Why does uncompensated heart failure cause problems?

As your heart failure becomes worse and your body's ability to compensate declines, two major problems occur:

1. Blood backs up into the lungs and other organs.
2. The lungs and the rest of the organs do not get enough blood. This sets up a vicious cycle where worsening heart failure leads to more congestion and less cardiac output, both of which further worsen heart failure.

When your heart failure becomes very severe, your cardiac output is severely reduced along with the blood flow to the brain, kidneys, and other organs. This drop in blood pressure can cause more serious symptoms, such as a decrease in how often you urinate, mental confusion, and fainting. These symptoms are evidence of severe heart failure that is beyond the body's ability to compensate, a condition called decompensated heart failure. If your cardiac output drops too low, you may go into shock, which is a potentially life-threatening condition in which the blood supply to your brain and other vital organs becomes critically low.

How long does it take before my body stops compensating for heart failure? Your body can compensate for heart failure for a long time, often for many years. However, the duration of compensation can be extremely variable and depends on the cause of your heart failure and whether you have other medical problems. For example, if you have coronary artery disease in addition to mitral valve regurgitation, your heart may be less able to compensate for heart failure than the heart of someone with mitral valve regurgitation alone.

Severe heart failure can also develop suddenly, such as when a heart attack damages a significant portion of the heart muscle. In such cases, your body may not be able to compensate as well as it can when it has years to adjust. In some cases the body may not be able to compensate at all.

Doctors often refer to heart failure that develops over many years as gradual-onset heart failure. When heart failure develops suddenly, such as after a heart attack, it is often called acute-onset heart failure.