What Happens to Preload and Afterload in Heart Failure?

In heart failure, preload and afterload can change depending on how the heart fills and pumps blood. Preload describes the stretch of the heart muscle at the end of filling, while afterload describes the load the heart must overcome to pump blood out. Both can be affected by changes in blood volume, filling pressure, blood pressure and the condition of the heart muscle.

You might notice that a flight of stairs leaves you more breathless than it used to. Then your echocardiogram shows a normal ejection fraction, and you wonder how your symptoms and the report fit together. This article explains preload and afterload in heart failure, why the heart can fill under higher pressure even when its pumping percentage looks normal, and what changes in your symptoms to bring up with your doctor. 

What is Preload and Afterload in the Heart?

With every heartbeat, the heart’s lower chambers, called ventricles, fill with blood and then squeeze to pump it out. The StatPearls review of cardiac preload describes preload as the stretch in the heart muscle at the end of filling, just before the squeeze. Its review of afterload explains afterload as the load the heart works against as it ejects blood.

An easy way to remember preload and afterload is stretch before the squeeze, load during the squeeze. An easy way to remember preload and afterload is stretch before the squeeze, load during the squeeze,

Why Can Filling Pressure Rise in Heart Failure?

The ejection fraction, or EF, is the percentage of blood the left ventricle pumps out with each beat. The 2022 AHA guideline  explains that pressure can build up as the heart fills, whether your ejection fraction is low or normal. That pressure can leave you short of breath. 

• Heart failure with reduced ejection fraction (HFrEF). The left ventricle squeezes less effectively, so more blood can remain after a beat. If the body also retains salt and water, the chamber may fill with more blood and the pressure inside it can rise. 
• Heart failure with preserved ejection fraction (HFpEF). The left ventricle still pumps out a usual percentage of the blood it holds. If the chamber is stiff or relaxes poorly, however, pressure can rise even when it fills with a usual amount of blood. That is why a preserved EF can coexist with breathlessness from heart failure. 

Think of trying to fill a firm balloon. It takes more pressure to get the same amount in. A stiff ventricle can behave in a similar way. As pressure builds on the left side of the heart, it can back up towards the lungs and contribute to breathlessness. This is one way congestion develops in heart failure. 

In a 2010 study published in Circulation: Heart Failure, Borlaug and colleagues found that 32 of 55 patients who had unexplained breathlessness during activity and normal heart filling pressures at rest met the study’s criteria for heart failure with preserved ejection fraction (HFpEF) during exercise testing. 

Some people can therefore have normal filling pressures at rest and develop abnormally high pressures when they exert themselves. 

Does Afterload Always Increase in Heart Failure?

No. Heart failure can occur even when afterload isn’t high. Afterload is how hard the heart has to push to get blood out. As the StatPearls review on afterload explains, when pressure in the arteries rises, the left side of the heart has to push harder to send blood to the body. That’s an increase in afterload.

The heart can also struggle for other reasons. Its muscle may be too weak to pump enough blood, or it may be too stiff to fill without a rise in pressure. 

Afterload describes how hard it is to push blood out. Filling pressure describes the pressure inside the heart as blood comes in.

For example, high blood pressure can increase the load on the left ventricle, while increased pressure in the pulmonary arteries can increase the load on the right ventricle. However, heart failure can also occur due to weakened or stiff heart muscle without persistently elevated afterload. 

How do Doctors Find the Cause of Your Symptoms?

• Ask about your symptoms. Your doctor asks when you feel breathless and checks for signs of fluid build-up, such as swollen ankles.
• Do a heart ultrasound. If heart failure is suspected, the AHA/ACC/HFSA guideline recommends an echocardiogram. It shows how well your heart pumps and gives clues about the pressure inside it as it fills.

This scan helps your doctor assess:

• How well your heart pumps. It measures your ejection fraction, the percentage of blood the main pumping chamber pushes out with each beat.
• The size of your heart chambers and the thickness of their walls.
• How well your heart valves work. It can show whether a valve has narrowed or allows blood to leak backwards.
• How your heart fills. Doppler ultrasound tracks how blood moves through the heart. These measurements can help estimate the pressure inside the heart as it fills.

• Order other tests if needed. Blood tests can help with the assessment. If you mainly get breathless during activity, your doctor may suggest testing while you exercise.

How doctors treat what they find

• If extra fluid is causing symptoms, water tablets (diuretics) help your body get rid of extra salt and water.
• If high blood pressure is making your heart work harder, your doctor may recommend treatment to bring it down.

Other treatments may be recommended depending on the type of heart failure, ejection fraction (EF), underlying cause and associated conditions. 

These may include specific heart failure medicines, treatment of valve disease or management of coronary artery disease. Treatment decisions should be made by a qualified cardiologist. 

When Is It an Emergency? 

The American Heart Association recommends telling your care team promptly if you notice any new or worsening signs of heart failure, such as:

• You need more pillows to breathe comfortably at night.
• Your ankles or feet are more swollen than usual.
• Your weight goes up quickly.

Tell your care team when the changes started. If you weigh yourself daily, ask how much weight gain should prompt a call.

Contact emergency services right away if you suddenly struggle to breathe, have new chest pain or pressure, or someone collapses and doesn’t respond. Severe breathlessness with a cough that brings up pink, foamy mucus is also an emergency.

Conclusion

Preload and afterload describe two parts of every heartbeat: how much the heart muscle stretches as it fills and what it pumps against. If everyday activities leave you more breathless than usual, tell your doctor, even if your echo shows a normal ejection fraction.

For a review of your symptoms and reports, book a consultation with SAAOL Heartcare Delhi.

FAQs

Q1. Can dehydration lower preload in someone with heart failure?

Yes. Preload depends partly on how much blood returns to the heart. Fluid loss from vomiting or diarrhoea can reduce that return. If you have heart failure and cannot keep fluids down, contact your care team for advice about fluids and medicines. 

Q2. Can high pressure in the lungs increase afterload on the right side of the heart?

Yes. When pressure in the lung arteries rises, the right ventricle has to work harder to pump blood through them. This is called pulmonary hypertension. The ESC heart failure guideline discusses assessing the underlying cause, since that helps guide treatment. 

Q3. Does a BNP blood test measure preload?

No. BNP measures a hormone the heart releases in response to strain. The AHA/ACC/HFSA guideline recommends using it to help evaluate suspected heart failure in people with breathlessness. A clinician interprets the result alongside symptoms, examination findings and other tests. 

Q4. Can a narrowed aortic valve increase afterload?

Yes. The StatPearls review identifies aortic stenosis, or narrowing of the valve through which blood leaves the left ventricle, as a cause of increased afterload. The chamber has to generate extra pressure to move blood through the narrowed opening.

Q5. Should everyone with heart failure limit how much they drink?

No. Some people with heart failure may need to limit fluids, for example, if they have fluid build-up or low sodium levels in their blood. Ask your doctor whether you need a daily limit and, if so, how much you can drink.

Q6. Is a low ejection fraction always caused by blocked arteries?

No. A low ejection fraction means the heart’s main pumping chamber pushes out a smaller share of the blood it holds with each beat. Blocked arteries are one possible cause. Heart valve problems, inflammation of the heart muscle or inherited conditions can also affect how well the heart pumps. Your doctor can review your medical history and test results to find the cause.

Disclaimer: This article is for general education. A qualified clinician can assess your symptoms, interpret your results and advise you on treatment or changes to medicines, salt or fluid intake.