Heart Failure: Systolic and Diastolic Dysfunction

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Core Idea

Heart failure is impaired myocardial contractility (systolic dysfunction) or relaxation (diastolic dysfunction) causing inadequate cardiac output. Neurohormonal compensation—sympathetic activation, RAAS, natriuretic peptides—initially maintains perfusion but eventually worsens remodeling.

How It's Best Learned

Use ejection fraction (EF) to classify: reduced EF (HFrEF, EF <40%), mildly reduced (HFmrEF, EF 40-49%), preserved (HFpEF, EF ≥50%). Understand diastolic dysfunction as impaired filling despite normal contractility.

Common Misconceptions

Low ejection fraction does not always cause symptoms—many patients are asymptomatic. HFpEF is not simply 'diastolic heart failure'; it involves complex interplay of stiffness, chronotropic incompetence, and vascular dysfunction.

Explainer

Heart failure is best understood by returning to the fundamentals of cardiac output you studied as a prerequisite. Cardiac output equals stroke volume times heart rate. Stroke volume itself depends on three variables: preload (ventricular filling), afterload (resistance the ventricle pumps against), and contractility (the intrinsic force of myocardial contraction). Heart failure occurs when these variables are so disrupted that the heart cannot maintain output sufficient for metabolic demands—or can only do so at the cost of abnormally elevated filling pressures.

Systolic dysfunction (HFrEF) is the classic picture: the ventricle contracts weakly, ejection fraction falls below 40%, and stroke volume drops. This follows directly from your study of myocardial infarction—dead myocardium cannot contract, so ischemic cardiomyopathy is a leading cause. The body's initial compensation is neurohormonal: the sympathetic nervous system increases heart rate and contractility, and the renin-angiotensin-aldosterone system (RAAS) promotes sodium and water retention to increase preload. In the short term, these Frank-Starling compensations maintain output. Over time, however, chronically elevated sympathetic tone causes maladaptive remodeling—the ventricle dilates and becomes more spherical, wall stress increases (by the law of LaPlace, tension = pressure × radius / 2 × wall thickness), and the dilated geometry further impairs ejection efficiency. Compensation becomes the disease.

Diastolic dysfunction (HFpEF) is mechanistically distinct: the ventricle contracts normally (EF ≥ 50%) but is abnormally stiff and cannot relax adequately during diastole. Think of the difference between squeezing a water balloon (systolic) and filling a stiff rubber ball (diastolic). In HFpEF, impaired relaxation means the ventricle requires elevated filling pressures to accept the same stroke volume—those elevated pressures back up into the pulmonary circulation, causing exertional dyspnea and pulmonary edema even with preserved contractility. Hypertension, diabetes, and obesity are major drivers because they all cause concentric left ventricular hypertrophy and increased myocardial stiffness.

The neurohormonal response is a unifying theme across both types. Natriuretic peptides (BNP, NT-proBNP) are secreted by stretched ventricular myocytes as a counter-regulatory signal—they promote vasodilation and natriuresis. Clinically, elevated BNP is the biochemical signature of heart failure regardless of type. The treatment logic for HFrEF follows directly from pathophysiology: ACE inhibitors/ARBs reduce afterload and blunt RAAS; beta-blockers counteract maladaptive sympathetic activation; aldosterone antagonists reduce fibrosis and fluid retention. The remarkable finding is that these agents reduce mortality not just by relieving symptoms but by partially reversing remodeling. For HFpEF, no therapy has yet demonstrated comparable mortality benefit—a reflection of our still-incomplete understanding of its heterogeneous pathophysiology.

Practice Questions 5 questions

Prerequisite Chain

Counting to 10 → Counting to 20 → Understanding Zero → The Number Zero → Counting to Five → One-to-One Correspondence → Combining Small Groups Within 5 → Addition Within 10 → Addition Within 20 → Two-Digit Addition Without Regrouping → Two-Digit Addition with Regrouping → Addition Within 100 → Repeated Addition as Multiplication → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Two-Digit by One-Digit Division → Division with Remainders → Remainders and Quotients in Division → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Reading and Writing Decimals → Comparing and Ordering Decimals → Adding and Subtracting Decimals → Multiplying Decimals → Dividing Decimals → Dividing Fractions → Mixed Number Arithmetic → Order of Operations → Integer Order of Operations → Variable Expressions → Combining Like Terms → One-Step Equations → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Iterated Integrals and Fubini's Theorem → Double Integrals in Cartesian Coordinates → Double Integrals over Rectangular Regions → Double Integrals in Polar Coordinates → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Green's Theorem → Surface Integrals and Flux of Vector Fields → Surface Integrals and Flux of Vector Fields → Divergence Theorem: Flux and Outflow → Divergence Theorem → Electric Flux → Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → The Electromagnetic Spectrum → Blackbody Radiation and Planck's Law → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → Heisenberg Uncertainty Principle → Wavefunction and the Born Rule → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → Quantum Entanglement → Bell Theorem and Bell Inequalities → Postulates of Quantum Mechanics → Scattering Theory → Introduction to Scattering Theory → Partial Wave Analysis in Scattering → Spin Angular Momentum → Electron Spin and Intrinsic Magnetic Moment → Stern-Gerlach Experiment: Spin Quantization and Measurement → Electron Diffraction and Matter Wave Properties → Davisson-Germer Experiment: Crystal Diffraction of Electrons → Electron Diffraction and Matter Wave Interference → Wavefunctions and Probability Density Interpretation → Quantum Superposition and Linear Combinations of States → Quantum Operators and Observables → Canonical Commutation Relations and Uncertainty → Heisenberg Uncertainty Principle and Measurement Limits → Time-Independent Schrödinger Equation and Eigenvalues → Hydrogen Atom in Quantum Mechanics → Spectral Lines and Energy Transitions → Selection Rules for Atomic Transitions → LS and jj Coupling Schemes in Multi-Electron Atoms → Pauli Exclusion Principle and Antisymmetric Wavefunctions → Electron Configuration and the Aufbau Principle → The Periodic Table and Atomic Electronic Structure → The Periodic Table → Electron Configuration → Periodic Trends → Ionization Energy → Ionic Bonding → Lewis Structures → Resonance Structures and Delocalized Electrons → Resonance and Formal Charge → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Acid-Base Chemistry → Organic Reaction Mechanisms and Arrow Pushing → Electrophilic Addition to Alkenes → Aromaticity and Benzene → DNA Structure → Central Dogma of Molecular Biology → The Genetic Code → DNA Mutations → DNA Repair Mechanisms → Cell Cycle Checkpoints and Cancer Prevention → Mitotic Spindle Checkpoint and Chromosome Segregation → Kinetochore Structure and Function → Mitochondria: Structure and Function → Cellular Respiration Overview → Glycolysis → Glycolysis: Mechanism and Regulation → Pentose Phosphate Pathway → Fatty Acid Synthesis and Regulation → Cholesterol Synthesis and Regulation → Membrane Lipids and Lipoproteins → Lipid Bilayer Structure and Amphipathic Molecules → The Cell Membrane: Fluid Mosaic Model → Cell Junctions: Adhesion and Communication → Epithelial and Connective Tissue Types → Bone Structure, Composition, and Remodeling → Skeletal Joints and Movement Mechanics → Skeletal Muscle Anatomy and Contraction → Cardiac Muscle Anatomy and Properties → Heart Chambers, Septa, and Valves → Blood Vessel Structure and Types → Hemodynamics: Pressure, Volume, and Flow Relationships → Vascular Physiology and Hemodynamics → Coronary Circulation Physiology → Myocardial Infarction and Ischemia-Reperfusion Injury → Heart Failure: Systolic and Diastolic Dysfunction

Longest path: 200 steps · 1020 total prerequisite topics

Prerequisites (4)

Cardiac Cycle and Heart Functionhard Cardiac Output and Stroke Volume Regulationhard Myocardial Infarction and Ischemia-Reperfusion Injurysoft Cardiac Output Control and Regulationsoft

Leads To (5)

Atrial Fibrillation: Atrial Remodeling, Substrate Formation, and Arrhythmia Progressionsoft Cardiogenic Pulmonary Edema: Elevated Hydrostatic Pressure, Fluid Accumulation, and Hypoxemiahard Mitral Regurgitation: Volume Overload, Chamber Remodeling, and Functional Declinesoft Pulmonary Edema: Pathophysiology and Mechanismssoft Right Heart Failure and Cor Pulmonalehard