What is High-Output Cardiac Failure?
High-output cardiac failure is a less common type of heart failure. Although it might seem confusing, it essentially means that the heart can’t pump enough blood to meet the body’s needs, even though it may be functioning normally in other ways. Most people with heart failure have a problem with their heart contracting (systolic dysfunction) or relaxing (diastolic dysfunction), which increases the resistance to blood flow in their body. However, those with high-output cardiac failure have normal heart function but decreased resistance to blood flow. This can be because the small arteries throughout the body are too open (dilated) or there could be a bypass of these arteries and tiny blood vessels, leading to activation of certain hormones in the body.
The real issue with high-output cardiac failure is that the body’s demand for blood flow (perfusion) is higher than what the heart can provide, even though the heart’s function may be normal. In terms of heart performance, a high-output state is defined as a resting heart pumping over 8 liters of blood per minute or a blood flow rate greater than 4.0 per minute per square meter of body size. However, heart failure occurs when this output isn’t enough to meet the body’s demands.
High-output cardiac failure is often a result of an underlying disease. The symptoms, examination, and treatment largely depend on the cause of this type of heart failure.
What Causes High-Output Cardiac Failure?
High-output cardiac failure can essentially be caused by two main situations: (1) the body needs more blood due to increased metabolism, or (2) blood is bypassing smaller blood vessels, causing a lack of resistance, and increasing flow into the veins. This leads to higher oxygen use and reduced resistance in the overall circulatory system. These situations can produce an increase in the amount of blood the heart pumps, either by changing the heart’s structure or creating a rapid heartbeat and chronic blood overload.
Certain conditions may cause high-output cardiac failure, for example, obesity (31%), liver disease (23%), abnormal connections between arteries and veins known as arteriovenous shunts (23%), lung disease (16%), and myeloproliferative disorders (diseases that lead to the excess production of blood cells) (8%).
Some metabolic conditions increase the body’s metabolic demand, causing the heart to pump more blood. An example is hyperthyroidism, where the thyroid gland produces too much thyroid hormone, which can speed up your heart rate, and increase body metabolism, creating more waste at the cellular level. The consequent reduction in blood vessel resistance and the high heart rate could lead to heart muscle disease and growth.
Myeloproliferative disorders have also been associated with high-output cardiac failure. They are linked to increased cellular metabolism and high cell turnover, causing an over-need for metabolism and reduced resistance in blood vessels, leading to high-output heart failure.
Several conditions that directly affect the heart also generally involve both metabolic and vascular effects. For instance, hyperthyroidism has a global impact including a direct impact on heart tissue.
Sepsis, a severe inflammatory response to an infection, can cause a variety of changes in the blood flow throughout the body. Patients with sepsis usually need volume resuscitation to cope with reduced blood volume, but later they enter a phase of high cardiac output and low systemic vascular resistance which can lead to high-output cardiac failure.
Thiamine, a vitamin used in energy metabolism, can lead to a disease called beriberi when deficient. Beriberi can result in dilated blood vessels, leading to high cardiac output and eventually heart muscle disease. If left untreated, symptoms of heart failure suggesting a worsened state become evident.
Chronic lung disease is associated with high-output heart failure, mainly resulting in right-sided heart failure. Chronic lack of oxygen and too much carbon dioxide in the blood reduce systemic arterial resistance, leading to chronic blood volume overload. At the same time, pulmonary vascular constriction causes increased right-sided heart growth. However, the left side of the heart remains largely functional and produces a high cardiac output.
In the systemic vascular system, most resistance is in the small blood vessels (arterioles). If these small blood vessels are bypassed, blood flow increases into the venous circulation, causing an increased return of blood to the heart, eventually leading to cardiac volume overload.
Arteriovenous fistulas (AVF), where an artery is directly connected to a vein and bypasses the arterioles, can increase blood flow to the heart and lead to high-output cardiac failure. These can be congenital or acquired due to certain reasons such as physical trauma, medical procedures, or skeletal disorders involving bone turnover.
Liver cirrhosis is associated with arteriovenous shunts and decreased systemic vascular resistance. The decrease in systemic vascular resistance due to liver cirrhosis can be so severe that the heart cannot compensate, leading to decompensated high-output cardiac failure.
The link between obesity and high-output cardiac is not well defined but is thought to be associated with excessive dilatation of blood vessels. Obesity can also directly affect cardiac function by altering the metabolism in the heart due to increased resistance to insulin.
Other less clear causes of high-output heart failure include erythroderma, carcinoid syndrome, mitochondrial diseases, acromegaly, and Paget’s disease of bone. Although stress, exercise, fever, and pregnancy can all contribute to high-output cardiac failure, they are not direct causes of the condition.
Risk Factors and Frequency for High-Output Cardiac Failure
Heart failure is a prevalent health problem that leads to millions of doctor’s visits each year and is the most common reason for patient hospitalizations. In the United States, over 500,000 new cases are diagnosed yearly, making the total number of people with heart failure around 5 million. This includes all types of heart failure, such as systolic and diastolic dysfunction, as well as high-output cardiac failure.
However, high-output cardiac failure – a specific type of heart failure – is less common, and it’s unclear how often it occurs. This could be because it mostly happens as a result of other underlying health problems and might not always get properly identified. Moreover, the likelihood of having high-output cardiac failure has a lot to do with the presence of conditions that lead to a high-output state – where the heart needs to work harder than usual.
Signs and Symptoms of High-Output Cardiac Failure
High-output cardiac failure is a serious medical condition that requires an in-depth history check and physical examination. Patients often report symptoms similar to other types of heart failure, including fatigue, swelling, and shortness of breath that worsens in a lying down position. Some patients may also experience heart palpitations. During a physical exam, doctors may notice signs such as a rapid heartbeat, swelling in the lungs and extremities, distended neck veins, warm extremities, and a wide pulse-pressure, which are unique to high-output cardiac failure.
Furthermore, ailments related to the underlying cause of heart failure often present themselves. For example:
- In patients with hyperthyroidism, they may experience a fast heart rate, shortness of breath, visible changes in the eyes, hyperactivity, and an enlarged thyroid gland.
- Patients with myeloproliferative disorders can experience symptoms like fever, tiredness, difficulty breathing, increased episodes of bleeding, and an enlarged spleen.
- Sepsis presents varying symptoms, ranging from fever, rapid heartbeat, fast breathing, and warm limbs to mental changes and even a coma, due to severe body-wide inflammation.
- Beriberi often affects malnourished or alcoholic patients, causing symptoms such as difficulty breathing, heart palpitations, swelling, muscle weakness, and difficulty walking due to nerve damage.
- Patients with chronic lung disease may initially report difficulty breathing, coughing, and wheezing, eventually resulting in right-sided heart failure due to increased blood pressure in the lungs.
- Arteriovenous fistulas (AVF), either congenital or acquired, often cause difficulty breathing, heart palpitations, and swelling, in addition to heart failure. Patients with AVFs may also present with visible blood vessels and associated bleeding episodes.
- Patients with liver cirrhosis can show various symptoms such as general discomfort, increased swelling, yellowing of skin and eyes, confusion, internal bleeding and even heart failure.
- Obese patients, with a high body mass index (BMI greater than or equal to 30 kg/m2), may display signs of heart failure including a rapid heart rate, typically noticed during a physical exam.
It’s essential to understand that these symptoms can often be related to the underlying condition causing high-output heart failure, and not exclusively to the heart failure itself.
Testing for High-Output Cardiac Failure
Detecting high-output cardiac failure, a type of heart failure where the heart is working harder than normal, involves a few steps. But, the most important thing is to find out what’s causing it. Cardiac failure is a condition where the heart is unable to pump enough blood to meet the body’s needs. So, how do doctors pinpoint this condition?
Firstly, your doctor will listen to your medical history and perform a physical exam. This can give them a general idea about whether you might have heart failure or not.
Next, they’ll likely order some initial lab tests and imaging scans to help confirm the diagnosis. One valuable test looks at natriuretic peptide levels in your blood. Natriuretic peptides are substances made by the heart and blood vessels that help reduce blood pressure. If these levels are high, it can indicate heart failure.
Your doctor may also order an electrocardiogram, a test that measures the heart’s electrical activity. It can help doctors find out if the heart is beating normally or if there is any damage to the heart muscle.
Another important imaging test is a transthoracic echocardiogram. This uses ultrasound technology to create images of the heart, allowing doctors to see its size, shape and if it’s pumping effectively.
If these tests suggest that your heart is working harder than it should be (a high cardiac output) and also show signs of heart failure, your doctor may diagnose you with high-output cardiac failure.
With this diagnosis, the focus becomes to find out what’s causing this. This largely depends on what your doctor learns from your medical history and physical exam. Based on these, they’ll decide what other tests are necessary. Each individual’s situation can be different, so the testing can change based on your specific symptoms or concerns.
Treatment Options for High-Output Cardiac Failure
Treatment for heart failure typically starts with acute intervention, tailored according to how severe the condition is. Initial treatment can include measures such as intermittently-administered water pills and oxygen, or continuous use of water pills and either non-invasive positive pressure ventilation (a breathing aid to increase air pressure in your lungs, helping to keep your airways open) or the placement of a tube into the windpipe through the mouth or nose, especially if there’s difficulty breathing from fluid overload, or low blood pressure. If signs of abnormally low blood pressure and poor blood flow to organs are present, drugs known as inotropic medications are used to help the heart pump blood more efficiently. After a patient has been stabilized and isn’t in a critical condition anymore, doctors can then focus on treating the root cause of the heart failure.
Treatment for hyperthyroidism, an overactive thyroid, aims to reduce excess thyroid hormone levels in the body by using medications, radiotherapy, or surgery if necessary. Myeloproliferative disorders, conditions that cause your body to produce too many blood cells, are treated based on the specific type and severity of the disorder, and may involve transplanting cells in your blood and bone marrow. Treatment for sepsis, a serious infection that can cause tissue damage and organ failure, follows guidelines established by the Surviving Sepsis Campaign, an international initiative to reduce deaths from sepsis. This usually includes quickly identifying the condition, replacing lost fluids intravenously, and starting antibiotic therapy to get rid of the infection.
Beriberi, a disease caused by thiamine (vitamin B1) deficiency, is treated with thiamine supplements for at least 2 weeks. Chronic lung disease treatment focuses on addressing low blood oxygen levels and excessive carbon dioxide in the blood. The treatment is designed to alleviate symptoms and slow the progression of the underlying lung disease. Arteriovenous fistulas, abnormal connections between arteries and veins, may be treated with a closing procedure or by reducing blood flow through them. It’s especially relevant for people on dialysis who need access to their blood system. If the fistula is causing heart failure due to the high blood flow through it, it may need to be closed, and an alternative access site to the blood system might need to be found. Treating liver cirrhosis that has advanced to cause high output heart failure mainly involves liver transplantation. Water pills and drugs that block the body’s production of a hormone called aldosterone can help to manage blood volume and limit blood flow through shunts, abnormal passages or connections between two arteries.
What else can High-Output Cardiac Failure be?
Heart failure is diagnosed based on a patient’s medical history and an initial physical check-up. Patients with different types of heart failure often have similar symptoms. These general symptoms include:
- Fluid overload (hypervolemia)
- Shortness of breath at rest or during activity (dyspnea)
- Difficulty breathing while lying flat (orthopnea)
- Fatigue
Different types of heart failure include ‘heart failure with reduced ejection fraction’ and ‘heart failure with preserved ejection fraction’. It’s also possible to have a high-output cardiac failure. To tell the difference between these types, doctors check the heart’s output and/or cardiac index and monitor for low resistance in the body’s blood vessels.
What to expect with High-Output Cardiac Failure
The outlook for people with a condition called high-output cardiac failure depends on what caused the condition in the first place. Cardiac failure refers to the heart’s inability to pump enough blood to meet the body’s needs. High-output cardiac failure means the heart is working overtime, but it’s still not enough.
According to a study by a researcher named Reddy, people with high-output cardiac failure are more likely to pass away within three years compared to those without heart problems. This was clearly shown by a hazard ratio of 3.4 (1.6 to 7.6) – a hazard ratio is a measure used in health studies to compare the risk of a certain event (like passing away) happening in one group compared to another.
The study also mentioned that among patients with high-output cardiac failure, individuals where the cause was linked to obesity had the lowest chance of passing away within 5 years – at 19%. This compared to liver disease at 58%, and heart failure associated with ‘shunt formation’ – which is when the blood bypasses the normal flow route in the body – at 59%. These two carried the highest 5-year mortality according to the study.