High-output heart failure

The BHF describes heart failure as a condition where the heart cannot pump blood around the body as well as it should, and classifies most cases by ejection fraction, the proportion of blood expelled with each beat. In typical systolic failure the muscle is weak and ejection fraction is low. In high-output heart failure, cardiac output is higher than normal but the body's needs, or the leakiness of the circulation, are greater still. Blood vessels are widened or short-circuited, pressure inside them falls, and the body responds by retaining salt and water, producing congestion.

Because ejection fraction is normal or high, high-output failure can slip through a quick glance at an echocardiogram. Clinicians usually suspect it when someone has typical heart failure symptoms, a normal-looking pumping function and a clue in the history or examination pointing to an underlying driver.

The BHF lists thyroid disorders among causes of heart failure, and an overactive thyroid raises heart rate and cardiac output continuously. The NHS notes that anaemia can contribute to heart failure, because severe anaemia forces the heart to compensate for reduced oxygen-carrying capacity. Other causes include arteriovenous fistulas, which are abnormal or surgically created connections between artery and vein, such as those used for dialysis access, advanced liver disease with widened blood vessels, Paget's disease of bone, and rarely nutritional deficiency states such as thiamine deficiency, or conditions such as obesity.

• Severe or long-standing anaemia.

• Overactive thyroid (thyrotoxicosis).

• Large arteriovenous fistula or shunt.

• Cirrhosis with systemic vasodilation.

• Paget's disease of bone and some other rarer conditions.

The NHS lists breathlessness during everyday activities, tiredness, light-headedness, swollen ankles and sudden weight gain as heart failure symptoms. In high-output states, hands and feet are often warm rather than cool, the pulse may feel bounding and a wide pulse pressure may be measured. There may also be signs of the cause, such as tremor, weight loss and heat intolerance in thyrotoxicosis, pallor in anaemia, or a thrill over a fistula.

Standard heart failure tests apply: blood tests including natriuretic peptide, ECG, chest X-ray and echocardiogram, as described by the NHS. To find the cause, doctors check haemoglobin and iron studies, thyroid function, liver tests and may examine dialysis access or imaging for shunts. Some specialist centres measure cardiac output through right-heart catheterisation when the diagnosis remains uncertain.

Treatment has two strands. Relieving congestion with diuretics provides symptom relief, but the key is to correct the driver. Anaemia is treated according to its cause, for example iron replacement or treating bleeding. Thyrotoxicosis is treated with antithyroid medicine, radioactive iodine or surgery, and beta-blockers may settle the heart rate. A large dialysis fistula may be reduced or closed, and shunts may be repaired. Where cirrhosis is the driver, care is led by liver specialists.

Heart failure medicines that suit weak-muscle disease may not be right here, so management should be led by someone who recognises the cause. Prolonged high-output states can eventually weaken the heart, which is another reason to treat early.

Outlook depends mainly on the underlying condition and how fully it can be treated. Many people improve markedly when anaemia or thyroid disease is corrected. The NHS advises seeing a GP if you suspect heart failure symptoms, using NHS 111 or a same-day GP appointment for breathlessness when lying down, pink frothy cough or rapid weight gain, and calling 999 for severe breathing difficulty, pale or blue lips or loss of consciousness.