Introduction 

Heart failure describes a condition in which your heart is less able to pump blood and deliver oxygen around your body, leading to various symptoms. It may be caused by a problem in the structure (like valve defects) or the function of the heart (like arrhythmias, disorders of heart electrical activity and heart rhythm), or a combination of both.​¹​ 

High-output heart failure (HOHF) is a distinct and less common subtype of heart failure. Although it may seem paradoxical at first, the underlying concept of heart failure still applies: the heart remains unable to meet the oxygen needs of the body, despite the high output of blood. It results from multiple causes with varying severities. Understanding the basic principles of HOHF, its causes, and clinical features is essential for providing the appropriate management.​²​ 

What is high-output heart failure? 

Definition  

Unlike most cases of heart failure, in which the output of blood is limited as a result of heart weakness or damage, in HOHF the output is markedly raised; the problem lies in the increased requirement of oxygen even when the heart is pumping properly, although it may also be accompanied with an existing heart problem.​³​  

How does HOHF happen? 

• Reduced blood vessel resistance:  

One of the most prominent features of HOHF is reduced blood vessel resistance, which is caused by the increase in diameter of the vessel wall. Imagine a garden hose: if the nozzle is tight, the water will shoot out with force and travel far distances. However, if you open the nozzle widely, the water will flow more gently and will not reach distant areas. Similarly, if a vessel widens, the blood will be unable to reach the target organs unless the heart pumps more forcefully and more frequently.   

• Increased oxygen demand:  

Many conditions increase the body’s oxygen requirements, which causes the heart to have to pump much harder to deliver larger volumes.  

• Increased heart output: 

Eventually, both conditions lead to a rise in heart output of blood, because the heart is trying harder to compensate for changes brought by the causative factor.​²​ 

Causes 

Many conditions lead to high heart output, some of which are normal and represent the usual body response to certain events, like exercise or pregnancy. HOHF occurs when the heart is unable to keep up with the increased demand even with this high output.  

Chronic anaemia 

Anaemia happens due to low red blood cell count or haemoglobin, essential to provide your body cells with oxygen. Persistent anaemia forces the heart to pump extra hard to deliver more oxygen to your body.​⁴​   

Obesity 

Obesity is becoming increasingly common and can affect many aspects of our health, especially the heart. Obesity puts extra strain on the heart as a result of the increased body weight; it also reduces vascular resistance by the direct metabolic effect of fat tissue. Weight loss was proven to reduce heart work and stress and improve the high output.​⁵​ 

Hyperthyroidism 

An overactive thyroid also overstimulates the heart, leading to an elevated heart rate and increased contraction strength. If not treated properly, it may cause changes in the heart muscle that may further worsen the condition, and give rise to symptoms of heart failure. 

Arteriovenous fistulas 

An arteriovenous fistula is an abnormal connection between arteries or veins. One can either be born with it (congenital), or develop it later (acquired) due to injury or medical procedure like in the case of haemodialysis in kidney failure. The fistula causes the blood to shift rapidly to the low-resistance veins, which then deliver extra volumes of blood to the heart, putting it under more pressure to pump even harder.​³​   

Beriberi (thiamine deficiency) 

Beriberi describes a condition caused by a lack of vitamin B1 or thiamine, mostly seen in alcoholics and people with gut malabsorption. It affects how the heart muscles work and leads to heart failure with elevated output.​⁴​ 

Sepsis 

Sepsis is a severe form of infection characterised by the presence of widespread dilation of blood vessels and increased oxygen needs, it also has a direct damaging effect on the heart, all of which can result in heart failure. 

Liver disease  

Conditions like liver cirrhosis lead to the formation of arteriovenous shunts, mimicking the effects of arteriovenous fistulas.  

Lung disease  

Lung disorders lead to reduced oxygen levels with elevated carbon dioxide (CO₂) levels in the blood, both result in a drop in blood vessel resistance, an essential causative mechanism of HOHF. 

Blood cancers 

Some forms of blood cancers are linked to HOHF.​²​ 

Why does HOHF make the heart bigger? 

Heart overwork 

The uniform feature in all cases of HOHF is that there is overstimulation of the heart, through neuronal and hormonal signals, to adapt to the decreased supply of oxygen, leading to a rise in the output. This is achieved by increasing how fast (heart rate) and how strongly (heart contractility) the heart muscle contract; however, when this adaptation is prolonged, it becomes harmful to the heart by causing:  

• Heart chamber dilation 

Heart chamber dilation occurs when the heart is forced to pump extra volumes of blood for long periods, placing stress on its walls. The heart adjusts by stretching its muscular wall, causing the chambers to expand from the inside to accommodate the larger blood volumes. Over time, this dilation will increase to hold much larger volumes, exceeding the heart pumping abilities. 

• Thicker heart walls 

Just like how muscles grow thicker from heavy lifting, heart muscles thicken and become stronger in response to the extra workload, to maintain the high output of blood; eventually, this will lead to a stiffer and less efficient heart.​⁴​  

Heart enlargement 

Both remodelling processes- chamber dilation and wall thickening- cause heart enlargement (the whole heart becomes bigger), which can be assessed by the doctor through clinical examination or with the appropriate imaging technique. These changes are beneficial at first, but over time, the heart becomes weaker, and features of heart failure become evident with symptoms of generalised fluid buildup in the body.​²​ 

Symptoms and signs of HOHF 

The clinical features of HOHF are similar to other forms of heart failure, and can present as: 

• Shortness of breath that becomes worse on lying flat  
• Fast breathing  
• Easy fatigue and exercise intolerance 
• Leg and ankle swelling 
• The feeling of heart racing (palpitation) 
• Warm extremities, unlike other forms of heart failure⁴​ 

How is HOHF diagnosed? 

Talking to a doctor 

It is important to seek medical advice if you start to feel any of the symptoms of HOHF. Your care provider will take a history and perform a thorough clinical examination to confirm the presence of heart failure, search for possible causes, and then request the needed tests.   

Tests  

• Blood tests to check for blood oxygen and CO₂  levels, and conditions like anaemia, sepsis, and thyroid disease 
• Imaging to check the heart structure and functions, using techniques like chest X-ray (CXR), echocardiogram, and magnetic resonance imaging (MRI).⁴​ 

Treatment options 

Treating the root cause 

Treatment should always be targeted to correct the underlying cause in order to stop disease progression. This includes managing conditions such as anaemia, giving antithyroid drugs in cases of hyperthyroidism, antibiotics for sepsis and reducing BMI in cases of obesity.  

Medications 

Some drugs given for other forms of heart failure may aggravate the symptoms in HOHF; therefore, it is crucial to consult with a healthcare provider before taking any medication to provide you with the most appropriate medications. 

Examples of drugs that are used to control the symptoms are:  

• Diuretics to remove the excess salts and water to reduce the fluid buildup; you may be advised to reduce your dietary intake of water and salt as well 
• Inotropes like noradrenaline are given in cases of emergency⁴​ 

FAQs 

What is the prognosis for HOHF?  

The prognosis for HOHF is largely dependent on the cause. Less severe and curable causes have the best prognosis which may even be reversible. 

What lifestyle changes can help prevent HOHF?  

The risk for HOHF is reduced by eating a healthier diet to maintain your BMI within the normal limit, and by managing the probable causative risks like anaemia and hyperthyroidism. 

Summary  

High-output heart failure is a unique type of heart failure characterised by increased body demand for oxygen, in spite of the high blood output. It results from factors such as anaemia, obesity, arteriovenous fistula, and sepsis, leading to progressive heart weakness and enlargement which manifests with symptoms like shortness of breath, tiredness, and leg swelling. Treatment focuses on addressing the underlying cause along with the use of medications to control the symptoms and possibly reverse the damage.