Why would a patient with Congestive Heart Failure (CHF) but preserved Ejection Fraction (EF) be fluid overloaded?

Fluid Overload in Heart Failure with Preserved Ejection Fraction (HFpEF)

Patients with HFpEF experience fluid overload primarily due to diastolic dysfunction, which leads to elevated left ventricular filling pressures and subsequent pulmonary and systemic congestion despite normal ejection fraction. 1

Pathophysiology of Fluid Overload in HFpEF

• HFpEF is defined as heart failure with an ejection fraction ≥50%, representing approximately half of all heart failure cases 1
• Unlike heart failure with reduced ejection fraction (HFrEF), the primary issue in HFpEF is impaired ventricular filling rather than impaired ejection 1
• Diastolic dysfunction causes increased left ventricular stiffness and impaired relaxation, leading to elevated filling pressures even with normal contractility 1, 2
• These elevated filling pressures are transmitted backward to the pulmonary circulation, causing pulmonary congestion and dyspnea 1, 3

Key Mechanisms Contributing to Fluid Overload in HFpEF

1. Ventricular Remodeling and Stiffness

• Increased left ventricular wall thickness and reduced chamber compliance limit diastolic filling 1
• Structural abnormalities include left ventricular hypertrophy and increased extracellular matrix deposition 1
• These changes increase resistance to ventricular filling, requiring higher atrial pressures to maintain adequate filling volumes 1, 3

2. Neurohormonal Activation

• Activation of the renin-angiotensin-aldosterone system (RAAS) leads to sodium and water retention 1
• Increased sympathetic nervous system activity further contributes to fluid retention 1, 3
• Neurohormonal adaptations initially compensate for reduced cardiac output but ultimately worsen congestion 1, 4

3. Comorbidity Contributions

• Hypertension is a major contributor to ventricular stiffness and diastolic dysfunction 1, 2
• Renal dysfunction impairs sodium and fluid excretion, worsening volume overload 1, 5
• Obesity increases circulating blood volume and contributes to ventricular remodeling 1, 2
• Atrial fibrillation, common in HFpEF, can exacerbate symptoms through loss of atrial contraction and irregular filling 1

Clinical Manifestations of Fluid Overload in HFpEF

• Pulmonary congestion leading to dyspnea, orthopnea, and paroxysmal nocturnal dyspnea 1, 2
• Peripheral edema due to increased systemic venous pressure 1
• Elevated jugular venous pressure reflecting right-sided heart congestion 1
• Pleural effusions and ascites in advanced cases 1, 3

Diagnostic Evaluation

• Echocardiographic evidence of diastolic dysfunction with preserved ejection fraction (≥50%) 1
• Elevated E/e' ratio (>14) on echocardiography indicates increased left ventricular filling pressures 1
• Enlarged left atrium (increased left atrial volume index) reflecting chronic elevation of filling pressures 1
• Elevated natriuretic peptide levels (BNP >35 pg/mL or NT-proBNP >125 pg/mL) 1, 2
• In uncertain cases, invasive hemodynamic testing may confirm elevated filling pressures 1, 2

Management Considerations

• Diuretics remain the cornerstone of treatment for fluid overload in HFpEF 1, 2
• Sodium and fluid restriction can improve symptoms in patients with fluid retention 6, 3
• SGLT-2 inhibitors (dapagliflozin, empagliflozin) reduce heart failure hospitalizations in HFpEF 1, 2
• Treatment of contributing comorbidities (hypertension, diabetes, obesity, atrial fibrillation) is essential 1, 2
• In diuretic-resistant cases, sequential nephron blockade with addition of thiazide diuretics or acetazolamide may be effective 1, 3

Clinical Pitfalls and Caveats

• Not all dyspnea in patients with preserved EF is due to HFpEF; consider alternative diagnoses such as pulmonary disease, anemia, or deconditioning 1
• HFpEF is a diagnosis of exclusion; rule out specific cardiac causes like infiltrative cardiomyopathy, hypertrophic cardiomyopathy, or pericardial disease 1
• Volume assessment can be challenging in HFpEF as patients may have significant congestion with subtle clinical signs 1, 3
• Overdiuresis should be avoided as patients with HFpEF are preload-dependent and may experience hypotension or worsening renal function with excessive fluid removal 1, 3