High Output Heart Failure

High output heart failure is heart failure in the presence of a persistently raised cardiac output, with low systemic vascular resistance or raised metabolic demand. A cardiac index over 4.0 L/min/m2 at rest, or a cardiac output over 8 L/min, defines it.

It is uncommon and often missed. Warm peripheries, a wide pulse pressure and congestion in a patient with a normal or only mildly reduced ejection fraction are the clue.

Causes are severe anaemia, thyrotoxicosis, arteriovenous fistula (dialysis access, traumatic, congenital, hereditary haemorrhagic telangiectasia), obesity, cirrhosis, sepsis, wet beriberi, Paget disease of bone, pregnancy, chronic lung disease, myeloproliferative disease and carcinoid.

In sub-Saharan Africa, severe anaemia (malaria, hookworm, sickle cell disease, nutritional deficiency) and beriberi are important causes.

Pathophysiology. Low systemic vascular resistance causes arterial underfilling, which activates the renin angiotensin, sympathetic and vasopressin systems. Sodium and water retention expands blood volume and preload.

Chronic volume overload causes dilatation and eccentric hypertrophy, and in time systolic failure and right sided failure. Pulmonary hypertension can develop.

• Dyspnoea, orthopnoea, fatigue, oedema and palpitations.
• Warm peripheries, bounding pulse, wide pulse pressure, tachycardia, hyperdynamic apex, third heart sound and flow murmurs.
• Features of the cause: pallor, goitre and tremor, bruit or thrill over a fistula, spider naevi and ascites, neuropathy in beriberi, obesity, bone pain and deformity in Paget disease, fever in sepsis.
• Nicoladoni-Branham sign: slowing of the pulse on compressing an arteriovenous fistula.

Red flags.

• Shock with warm peripheries
• Haemoglobin under 70 g/L
• Pulmonary oedema or ejection fraction falling under 40%
• Access flow over 2 L/min, or over 30% of cardiac output, with heart failure
• Lactic acidosis, confusion or ophthalmoplegia (beriberi, Wernicke encephalopathy)
• Fever, suspected sepsis or thyroid storm

• Echocardiography. Dilated chambers, ejection fraction often normal or mildly reduced, raised left ventricular outflow velocity time integral (over 22 cm suggests high output), pulmonary pressure, right ventricle.
• Right heart catheterisation. Cardiac index over 4.0 L/min/m2, systemic vascular resistance under 800 dyn·s/cm5, raised wedge pressure, and mixed venous saturation often over 75%.
• Laboratory. Haemoglobin, film, ferritin, B12, folate, TSH, free T4, liver function, albumin, alkaline phosphatase, lactate, blood cultures, malaria test in endemic regions, stool for ova, and transketolase or thiamine level where available.
• Cause specific imaging. Doppler of dialysis access with flow measurement, CT angiography for fistula, liver imaging, bone imaging for Paget disease.

Differential diagnosis.

• Low output heart failure (cold peripheries, narrow pulse pressure)
• Sepsis and other distributive shock
• Constrictive pericarditis and restrictive cardiomyopathy
• Primary pulmonary hypertension and right heart failure
• Nephrotic syndrome and cirrhosis with oedema alone
• Hypertrophic cardiomyopathy
• Tachycardia induced cardiomyopathy
• Obesity related heart failure with preserved ejection fraction

Treat the cause first. Inotropes and vasodilators do not help, and neurohormonal drugs are unproven.

• Congestion. Furosemide 40 to 80 mg intravenously for pulmonary oedema, doubled after 1 to 2 hours if the response is inadequate (maximum single dose 200 mg). Oral furosemide 40 mg once daily in the morning, increased to 80 to 120 mg daily as needed (higher doses in renal impairment under specialist care). Sodium restriction. Monitor sodium, potassium and creatinine.
• Hypotension or shock. Noradrenaline 0.05 microgram/kg/min intravenously, titrated to a mean pressure of 65 mm Hg, usual maximum 0.5 microgram/kg/min, to restore vascular tone. Avoid inotropes and vasodilators. Beta blockers are used only when thyrotoxicosis or a non-compensatory tachycardia is present.
• Anaemia.
  • Transfuse packed red cells for haemoglobin under 70 g/L (under 80 g/L with cardiac disease): one unit over 3 to 4 hours with furosemide 20 to 40 mg intravenously before or between units, reassessing after each unit.
  • Iron deficiency: ferrous sulphate 200 mg (65 mg elemental iron) orally once daily or on alternate days, once deficiency is shown.
  • Hookworm: albendazole 400 mg orally as a single dose, repeated after 2 weeks in heavy infection, avoided in the first trimester. Treat malaria with an artemisinin based combination at the labelled dose. Give folic acid 5 mg orally once daily in haemolysis.
• Thyrotoxicosis. Propranolol 20 to 40 mg orally every 6 to 8 hours, to a heart rate under 90/min, maximum 320 mg daily, with carbimazole 15 to 40 mg orally once daily, maximum 60 mg daily. Contraindicated in asthma, severe bradycardia and high grade atrioventricular block. Stop carbimazole and check the white count at once for sore throat or fever.
• Wet beriberi. Thiamine 500 mg intravenously over 30 minutes three times daily for 2 to 3 days, then 250 mg once daily for 3 to 5 days, then 100 mg orally once daily. Give before any glucose containing fluid. Improvement is often rapid.
• Arteriovenous fistula. Reduce flow when access flow is over 2 L/min or over 30% of cardiac output with heart failure: banding, revision using distal inflow, or ligation with conversion to a catheter or transplantation.
• Obesity. Weight reduction by diet, exercise, drug therapy or bariatric surgery. Dapagliflozin 10 mg orally once daily (start at eGFR 25 mL/min/1.73 m2 or more; contraindicated in type 1 diabetes; withhold during acute illness with poor oral intake).
• Paget disease. Zoledronic acid 5 mg intravenously as a single infusion over at least 15 minutes, after correcting calcium and vitamin D. Avoid at creatinine clearance under 35 mL/min.
• Sepsis. Early antibiotics after blood cultures, intravenous fluid, and noradrenaline 0.05 microgram/kg/min intravenously titrated to a mean pressure of 65 mm Hg (usual maximum 0.5 microgram/kg/min).
• Cirrhosis and hereditary haemorrhagic telangiectasia. Specialist liver and vascular care, with transplantation considered for refractory disease.
• Avoid anti-inflammatory drugs and excess salt.

Special groups. Pregnancy is a physiological high output state. Heart failure in pregnancy needs an obstetric and cardiology review for anaemia, thyroid disease and peripartum cardiomyopathy.

Monitoring. Haemoglobin, thyroid function and electrolytes during treatment. Echocardiography at 3 months once the cause is corrected. Access flow every 3 to 6 months in patients with a high flow fistula.

Referral and escalation. Refer to cardiology and the specialist for the cause. Urgent for shock, pulmonary oedema, haemoglobin under 70 g/L or suspected thyroid storm.