High-Output Heart Failure

• Chronotropic and inotropic insufficiency with excessive peripheral demands: The failing ventricle cannot generate sufficient cardiac output to meet elevated metabolic requirements. In sepsis, profound systemic vasodilation reduces peripheral vascular resistance (SVR <800 dyne·s·cm⁻⁵), necessitating compensatory increases in heart rate and contractility. Similarly, arteriovenous fistulas create obligatory left-to-right shunting (effective circulating volume depletion with reflex tachycardia and increased contractility), while thyrotoxicosis increases cellular oxygen consumption by 30-50%, demanding sustained elevation in cardiac index. The myocardium, already compromised by underlying disease or chronic volume overload, cannot sustain the necessary inotropic escalation without decompensation. Activation of the sympathetic nervous system and renin-angiotensin-aldosterone system (RAAS) initially compensate through increased heart rate, contractility, and vasoconstriction, but these mechanisms become maladaptive, increasing afterload and myocardial oxygen demand.

• Eccentric LV remodeling with chamber dilation and elevated ventricular compliance: Chronic volume overload (anemia, hyperthyroidism, pregnancy) induces eccentric hypertrophy where sarcomere addition occurs in series, elongating myocytes and increasing chamber size disproportionately to wall thickness. This remodeling increases end-diastolic volume (EDV) and end-diastolic pressure (EDP), causing functional mitral regurgitation and pulmonary congestion despite preserved or elevated ejection fraction initially. As remodeling progresses, wall stress increases according to the Laplace law (stress = PR/2h), further compromising systolic function. The dilated LV becomes spherical rather than ellipsoid, unfavorably altering the geometry-contractility relationship and reducing ejection fraction from initially preserved values (<40% in advanced cases).

• Pulmonary and systemic congestion from elevated LV filling pressures: Despite elevated cardiac output, pulmonary capillary wedge pressure (PCWP) rises due to increased EDV and reduced myocardial compliance. The combination of elevated output with congestion is pathognomonic: patients develop dyspnea, orthopnea, and peripheral edema despite hyperdynamic circulation with warm extremities and wide pulse pressures. Hepatic congestion occurs from elevated right atrial pressures, causing hepatic synthetic dysfunction, portal hypertension, and potential ascites. The PCWP elevation is often disproportionate to output, reflecting severe myocardial dysfunction underlying the high-output state.

• Hyperthyroidism and thyroid storm: Thyroid hormone increases β-adrenergic receptor expression, enhances mitochondrial oxidative metabolism, and increases myosin ATPase activity, producing a hypermetabolic state with persistent tachycardia (resting HR often 100-120 bpm), systolic hypertension, and wide pulse pressure. In thyrotoxic cardiomyopathy, chronic excess hormone causes myocyte apoptosis and fibrosis, transitioning high-output to dilated physiology. TSH suppression and elevated free T3/T4 confirm diagnosis.

• Severe anemia (hemoglobin <7 g/dL): Reduced oxygen-carrying capacity necessitates increased cardiac output to maintain oxygen delivery (DO₂ = CO × CaO₂). Chronic anemia triggers LV dilation and eccentric remodeling. Acute hemorrhage causes immediate reflex tachycardia and increased contractility; chronic anemia causes gradual myocardial adaptation with potential progression to cardiomyopathy if prolonged.

• Arteriovenous fistulas and malformations: Congenital or acquired AV communications (hemodialysis grafts, traumatic fistulas, Osler-Weber-Rendu syndrome with pulmonary AV malformations) create low-resistance shunts returning deoxygenated blood directly to the left atrium, bypassing the lungs. This reduces systemic vascular resistance and effective circulating volume, triggering reflex tachycardia and increased contractility. Pulmonary AV malformations also cause right-to-left shunting with hypoxemia.

• Chronic obstructive pulmonary disease (COPD) and pulmonary hypertension: Hypoxemia, hypercapnia, and pulmonary vascular remodeling increase right ventricular (RV) afterload. RV dilatation compounds the problem by rightward septal bowing, reducing LV cavity size and impairing LV filling (ventricular interdependence). Cor pulmonale results, though this is technically right-sided failure with elevated output secondary to compensation.

• Pregnancy and peripartum cardiomyopathy: Plasma volume expands 40-50% by third trimester; systemic vascular resistance decreases 15-20%; cardiac output increases 30-40%. In peripartum cardiomyopathy, an unexplained dilated cardiomyopathy develops in the last trimester or within 5 months postpartum, possibly from myocarditis, immune activation, or stress-activated kinase signaling. Presentation combines physiologic high output of pregnancy with the myocardial dysfunction of cardiomyopathy.

• Paget's disease of bone and other hypermetabolic states: Increased osteoblastic activity and bone blood flow dramatically increase systemic metabolism. Cardiac output may increase 5-15% proportional to disease burden. Other metabolic states include beriberi (thiamine deficiency with vasodilation and polyneuropathy), hyperbilirubinemia, and malignancy with hypermetabolism.

• Sepsis and systemic inflammatory response syndrome (SIRS): Inflammatory cytokines (TNF-α, IL-1, IL-6) and bacterial lipopolysaccharides trigger profound vasodilation via inducible nitric oxide synthase (iNOS), reducing SVR to <600 dyne·s·cm⁻⁵ and increasing cardiac output 5-10 fold. Myocardial depression (decreased contractility and prolonged systolic/diastolic times) develops despite elevated output, creating a unique "septic cardiomyopathy" pattern. Lactate elevation and tissue hypoxia persist despite adequate cardiac output (distributive shock).

• Hypoxemia from any cause: Chronic hypoxemia (altitude, chronic lung disease, cyanotic heart disease) triggers increased erythropoietin production and compensatory polycythemia, increasing blood viscosity and cardiac workload. Paradoxically, chronic hypoxemia also causes pulmonary vascular remodeling and cor pulmonale.

• Valvular regurgitation (acute, severe): Acute mitral or aortic regurgitation dramatically increases cardiac output as the heart must eject both systemic flow and regurgitant volume. Acute aortic regurgitation causes wide pulse pressure, bounding carotid pulses, and hyperdynamic precordium with rapid diastolic decompression.

• Intracardiac and extracardiac shunts: Persistent patent ductus arteriosus (PDA), atrial septal defect (ASD), or ventricular septal defect (VSD) cause left-to-right shunting with effective circulating volume depletion and compensatory output increase. Shunt magnitude (Qp:Qs ratio) determines severity.

• Cirrhosis and portal hypertension: Splanchnic vasodilation reduces systemic vascular resistance; ascites further depletes effective circulating volume. High-output renal failure can develop with oliguria despite elevated systemic cardiac output (hepatorenal syndrome type 1).

• Dyspnea and orthopnea: Paroxysmal nocturnal dyspnea (PND) reflects elevated pulmonary capillary wedge pressure causing nocturnal pulmonary edema. Exertional dyspnea may be disproportionate to output, indicating severe myocardial dysfunction. Patients often report better dyspnea tolerance when upright due to improved ventricular geometry.

• Fatigue and reduced exercise tolerance: Despite elevated cardiac output, tissue oxygen delivery may be inadequate due to abnormal oxygen extraction (sepsis, mitochondrial dysfunction) or shunting past tissue beds. Patients paradoxically fatigue easily despite hyperdynamic appearance.

• Edema (peripheral, sacral, pulmonary): Bilateral lower extremity edema, sacral edema in bedridden patients, and rales on lung auscultation reflect systemic and pulmonary venous hypertension. Hepatic congestion causes right upper quadrant pain and hepatomegaly with pulsatile hepatic vein distention.

• Palpitations and arrhythmias: Sustained tachycardia (often 100-120 bpm at rest) and compensatory arrhythmias (atrial fibrillation, premature ventricular contractions) are common, particularly with hyperthyroidism or sepsis. Rapid ventricular response in atrial fibrillation further deteriorates hemodynamics.

• Hyperdynamic precordium: Vigorous apical impulse displaced laterally beyond the midclavicular line; brisk carotid upstroke with wide pulse pressure; prominent right ventricular heave if RV involvement; pulsatile hepatomegaly from elevated JVP.

• Physical exam findings specific to underlying cause:
• Thyrotoxicosis: Fine tremor, warm moist skin, proximal weakness, lid lag/stare, tachycardia out of proportion to fever
• Anemia: Pallor, tachycardia, systolic flow murmur (anemia-related functional systolic murmur at left sternal border)
• AV fistula: Palpable thrill and continuous "machinery" murmur over the fistula; unilateral edema if extremity fistula
• Sepsis: Fever or hypothermia, hypotension, altered mental status, skin mottling in severe cases
• Peripartum cardiomyopathy: Third-trimester or early postpartum presentation; may have preceding preeclampsia signs (hypertension, proteinuria)

• Wide pulse pressure and bounding pulses: The combination of increased cardiac output and reduced systemic vascular resistance produces augmented systolic pressure with rapid diastolic runoff, widening pulse pressure (difference between systolic and diastolic BP often >50 mmHg).

• Hepatomegaly and ascites: Hepatic congestion from elevated right atrial pressure; ascites develops with chronic right-sided pressure elevation or underlying cirrhosis. Hepatic synthetic dysfunction may produce jaundice and coagulopathy.

• Cool extremities paradoxically coexist with warm core: In decompensated HOHF with cardiogenic shock features, vasoconstriction in peripheral vascular beds produces cool, clammy skin despite elevated core temperature and hyperdynamic precordium (mixed high-output and low-output physiology).

• Echocardiography (TTE or TEE):
• Left ventricular size and function: Increased left ventricular end-diastolic dimension (LVEDD) (>55 mm), eccentric LV hypertrophy with wall thickness-to-radius ratio <0.9, reduced ejection fraction (EF) from baseline (may be preserved initially but declines with progression). Systolic dysfunction contrasts with the expected preserved EF of isolated high-output physiology, indicating underlying myocardial disease.
• Mitral regurgitation: Functional (secondary) mitral regurgitation from annular dilation and papillary muscle displacement; regurgitant jet area and effective regurgitant orifice quantify severity.
• Doppler findings: Increased stroke volume by pulsed-wave Doppler; reduced deceleration time of mitral E wave (<160 ms) indicating elevated LV filling pressures; elevated early mitral annular velocity (E') <8 cm/s suggesting diastolic dysfunction.
• RV assessment: RV dilation, reduced tricuspid annular plane systolic excursion (TAPSE), elevated tricuspid regurgitation velocity estimating RV systolic pressure.
• Specific findings:
• Sepsis: Global hypokinesis with reduced ejection fraction despite high output initially; may show enhanced contractility with catecholamine use
• Pregnancy: Mild eccentric hypertrophy; generally preserved EF unless peripartum cardiomyopathy develops
• Severe valve disease: Specific chamber changes (AV regurgitation dilates receiving chamber)

• Cardiac catheterization and hemodynamic measurements:
• Essential for diagnosis when high-output state is suspected: Demonstrates elevated cardiac index (CI) >2.5 L/min/m² (often >3.5-4.0 in HOHF) with elevated pulmonary capillary wedge pressure (PCWP) >18 mmHg and elevated right atrial pressure (RAP) >8 mmHg, confirming congestion despite high output.
• Reduced systemic vascular resistance (SVR) <800 dyne·s·cm⁻⁵ in vasodilatory states (sepsis, AV fistula, cirrhosis)
• Elevated mixed venous oxygen saturation (SvO₂) >75% (normal <75%) may occur with AV shunting or sepsis with maldistribution of flow
• Oxygen consumption (VO₂) elevated proportional to metabolic state (thyrotoxicosis, sepsis, malignancy); Thermodilution CO measurement provides accurate output assessment
• Allows identification of intracardiac shunts via oxygen step-up (left-to-right shunting in ASD/VSD)

• Laboratory evaluation:
• Natriuretic peptides (BNP, NT-proBNP): Usually elevated (BNP >400 pg/mL or NT-proBNP >900 pg/mL) reflecting ventricular wall stress and diastolic dysfunction, but may be lower in acute high-output states before LV remodeling occurs. Serial measurement tracks progression.
• Thyroid function tests (TSH, free T3, free T4): Low TSH with elevated free T4 and/or T3 confirms hyperthyroidism. TSI (thyroid-stimulating immunoglobulin) and TRAB (TSH receptor antibodies) identify Graves' disease. Essential in any young patient with HOHF and tachycardia.
• Complete blood count: Hemoglobin <7 g/dL confirms anemia; high reticulocyte count indicates compensatory erythropoiesis; iron studies assess iron-deficiency anemia.
• Liver function tests and synthetic function: Elevated bilirubin, INR, and low albumin indicate hepatic congestion with synthetic dysfunction (passive hepatic congestion from cor pulmonale or sepsis). Aspartate aminotransferase (AST) >alanine aminotransferase (ALT) pattern favors congestion over primary hepatitis.
• Lactate level: Elevated lactate (>2 mmol/L) despite adequate or elevated cardiac output indicates sepsis-related tissue hypoxia, microvascular maldistribution, or mitochondrial dysfunction.
• Procalcitonin and inflammatory markers (CRP, IL-6): Markedly elevated in sepsis (procalcitonin >2 ng/mL). Moderate elevation in other inflammatory conditions.
• Troponin and myoglobin: Elevated troponin (high-sensitivity assay) indicates myocardial injury from sep

Immediate stabilisation (congestion first, cause simultaneously)

• Loop diuretic: IV furosemide. The ACC/AHA/HFSA 2022 Heart Failure Guideline recommends IV loop diuretics for volume overload in acute decompensated HF; this relieves elevated PCWP without lowering the cardiac output the tissues currently require.
• Non-invasive positive-pressure ventilation for frank pulmonary edema: raises intrathoracic pressure, reduces preload and LV transmural wall stress.
• Correct the driver, not the number: cardiac output is high because of a peripheral demand or shunt; congestion recurs until that is addressed.

Cause-directed first-line therapy

• Thyrotoxicosis: per the American Thyroid Association, a beta blocker (propranolol, which also blunts peripheral T4→T3 conversion) plus a thionamide (methimazole; propylthiouracil preferred in storm and first trimester), with iodine (SSKI) given at least an hour after the thionamide, and glucocorticoid (hydrocortisone) in storm.
• Severe anemia: red cell transfusion using the AABB restrictive strategy, plus iron repletion for iron deficiency; avoid rapid large-volume transfusion in a congested patient.
• Beriberi: thiamine IV before any glucose load; hemodynamic reversal can be dramatic.
• Sepsis: Surviving Sepsis Campaign bundle — early broad-spectrum antibiotics, source control, balanced crystalloid, norepinephrine as first-line vasopressor for persistent hypotension.
• Paget disease: bisphosphonate (zoledronic acid) to reduce bone blood flow.

Definitive / procedural

• Access-related HOHF: surgical flow reduction (banding), revision, or ligation of a high-flow hemodialysis fistula or traumatic AV fistula; endovascular embolization for AVMs, including pulmonary AVMs in hereditary hemorrhagic telangiectasia.
• Definitive thyroid therapy (radioiodine or thyroidectomy) once euthyroid; shunt or valve repair for anatomic lesions.
• If EF remains reduced after the cause is corrected, full ACC/AHA GDMT applies: ARNI (or ACEI/ARB), beta blocker, MRA, and SGLT2 inhibitor.

Avoid

• ACE inhibitors, ARBs, ARNI in pregnancy — fetotoxic in all trimesters (captopril included; its short half-life does not make it safe).
• Reflex beta blockade or aggressive vasodilation when tachycardia and low SVR are compensatory (sepsis, profound anemia) — output falls and shock ensues.

Disease-related

• Acute pulmonary edema / cardiogenic-congestive crisis — emergency: rising PCWP in a non-compliant dilated LV; signalled by orthopnea, diffuse rales, hypoxemia, and radiographic vascular redistribution.
• Thyroid storm — emergency: uncompensated thyrotoxicosis with fever, delirium, and tachyarrhythmia out of proportion to fever; a high Burch–Wartofsky score prompts treatment before labs return.
• Atrial fibrillation with rapid ventricular response: atrial stretch plus adrenergic/thyroid hormone drive; loss of atrial kick collapses filling in a stiff dilated ventricle, and stasis brings thromboembolic stroke risk.
• Cardiorenal syndrome: elevated right atrial pressure raises renal venous pressure and lowers transrenal perfusion gradient; rising creatinine with low urine sodium despite a hyperdynamic circulation.
• Congestive hepatopathy → cardiac cirrhosis: chronic hepatic venous congestion; pulsatile hepatomegaly, AST/ALT elevation with disproportionate bilirubin and INR rise.
• Pulmonary hypertension and RV failure: chronic high transpulmonary flow plus elevated left-sided pressures; JVD, ascites, TR murmur, falling TAPSE.
• Progression to a low-output dilated cardiomyopathy: sustained eccentric remodeling and wall stress; the giveaway is a normalizing cardiac output in a patient who is getting worse.

Treatment-related

• Over-diuresis: hypotension, prerenal azotemia, contraction alkalosis, hypokalemia and hypomagnesemia — the latter precipitating ventricular arrhythmia.
• Transfusion-associated circulatory overload (TACO): acute dyspnea and hypertension during or shortly after transfusion in an already volume-overloaded patient.
• Thionamide agranulocytosis — emergency: fever and sore throat mandate stopping the drug and obtaining a CBC with differential; propylthiouracil hepatotoxicity is the other class toxicity.
• Beta blocker–precipitated decompensation: removing compensatory chronotropy in sepsis, severe anemia, or thyrotoxic cardiomyopathy drops output abruptly.
• Post-ligation/banding complications: loss of dialysis access, distal ischemic steal, and access thrombosis.
• Refeeding/glucose before thiamine in beriberi: precipitates Wernicke encephalopathy and worsens cardiac failure.

• The defining paradox: congestion (elevated PCWP, JVD, edema) with a high cardiac index, warm extremities, wide pulse pressure, and bounding pulses. Warm-and-wet with a hyperdynamic precordium is high-output failure until proven otherwise.
• Nicoladoni–Branham sign is the single most tested association: manual compression of a large AV fistula abruptly increases SVR and produces reflex bradycardia, confirming the fistula as the driver of failure.
• Best next step in a young patient with new HF, resting tachycardia, tremor, and wide pulse pressure: check TSH with free T4/T3 before escalating cardiac therapy — thyrotoxicosis is the classic reversible cause.
• Buzzword set worth memorizing: wet beriberi (thiamine deficiency, high output plus peripheral neuropathy, alcohol use or bariatric surgery), machinery murmur with a palpable thrill over a dialysis access, warm bone/skull enlargement with high alkaline phosphatase in Paget disease.
• Mixed venous oxygen saturation is high, not low — the opposite of low-output HF. An elevated SvO₂ with congestion points to shunting (AV fistula, cirrhosis) or impaired extraction (sepsis).
• Give thiamine before glucose in suspected beriberi; a dextrose-containing fluid first can precipitate Wernicke encephalopathy and acute decompensation.
• Common distractor — reflex GDMT: starting a beta blocker or ACE inhibitor as the "answer" for any heart failure stem. In sepsis or profound anemia the tachycardia is compensatory, and ACE inhibitors (including captopril) are contraindicated in pregnancy. Per the ACC/AHA/HFSA 2022 guideline, the four-pillar regimen — ARNI (or ACEI/ARB), beta blocker, MRA, SGLT2 inhibitor — belongs to persistent HFrEF, not to the reversible high-output state itself.
• Second distractor: labeling a preserved-EF high-output patient as HFpEF. The diagnosis hinges on the measured cardiac index and the identified peripheral cause, not on the ejection fraction.