Heart Failure Pathophysiology

Definition & Classification - Heart's Big Struggle

• Heart Failure (HF): Myocardial dysfunction leading to inadequate tissue perfusion or doing so only with ↑ filling pressures. A clinical syndrome.
• Key Types by Left Ventricular Ejection Fraction (LVEF):
  • HFrEF (Systolic HF): LVEF ≤ 40%
  • HFmrEF (Mildly Reduced EF): LVEF 41-49%
  • HFpEF (Diastolic HF): LVEF ≥ 50%
• NYHA Functional Classes (Symptoms):
  • I: No limits.
  • II: Slight limit, ordinary activity.
  • III: Marked limit, < ordinary activity.
  • IV: Symptoms at rest.
• ACC/AHA Stages (Progression):
  • A: High risk for HF.
  • B: Structural heart dz, no symptoms.
  • C: Structural heart dz + symptoms.
  • D: Refractory HF.
• Other Classifications:
  • Onset: Acute vs. Chronic
  • Side: Left (LVF), Right (RVF), Biventricular
  • Output: Low-output (common) vs. High-output (e.g., severe anemia, thyrotoxicosis)

⭐ Most common cause of right-sided heart failure (RVF) is left-sided heart failure (LVF).

Etiology & Precipitants - HF's Usual Suspects

• Underlying Causes (Chronic HF):

  • IHD/CAD: Most common cause.
  • Hypertension (HTN): Chronic ↑afterload.
  • Valvular Disease: e.g., Aortic Stenosis (AS), Mitral Regurgitation (MR).
  • Cardiomyopathies: Dilated (DCM), Hypertrophic (HCM), Restrictive (RCM).
  • Arrhythmias (Chronic): Atrial Fibrillation (AF), Tachycardiomyopathy.
  • High-Output States: Severe anemia, thyrotoxicosis.
  • Others: Myocarditis, Pericardial disease (constriction), Toxins (alcohol, doxorubicin).

• Precipitants (Acute Decompensation):

  • 📌 FAILURE Mnemonic:
    • Forgot meds / Fluid overload / Food (↑salt).
    • Arrhythmia (new AF) / Anemia.
    • Ischemia / Infarction / Infection (e.g., pneumonia).
    • Lifestyle (excess fluid/alcohol).
    • Uncontrolled HTN / Uremia.
    • Renal dysfunction.
    • Embolism (Pulmonary Embolism - PE) / Endocrine (thyroid disorders).
  • Drugs: NSAIDs, steroids, some Calcium Channel Blockers (CCBs), rapid β-blocker changes.

⭐ The most common cause of Right Heart Failure (RHF) is Left Heart Failure (LHF).

Neurohormonal Mechanisms - Body's Vicious Cycle

Heart failure (HF) triggers detrimental neurohormonal responses, forming a vicious cycle.

• Key Systems (Activated by ↓ Cardiac Output):
  • RAAS (Renin-Angiotensin-Aldosterone System): ↓ Renal perfusion → Renin → Angiotensin II (Ang II) → Aldosterone.
    • Ang II: Vasoconstriction (↑ afterload), aldosterone (Na⁺/H₂O retention → ↑ preload), cardiac remodeling (fibrosis, hypertrophy).
  • SNS (Sympathetic Nervous System): Baroreflex → ↑ Norepinephrine.
    • Effects: ↑ Heart rate, ↑ contractility, vasoconstriction. Chronic: β-receptor downregulation, myocyte toxicity, arrhythmogenic.
  • AVP (Arginine Vasopressin/ADH): From ↓ CO & Ang II.
    • Effects: Vasoconstriction, water reabsorption.
• Counter-Regulatory (Often Overwhelmed):
  • Natriuretic Peptides (ANP, BNP): From stretched atria/ventricles.
    • Actions: Vasodilation, natriuresis, diuresis; inhibit RAAS & SNS.

    ⭐ BNP levels are crucial for HF diagnosis, severity assessment, and prognosis.

Myocardial Remodeling & Progression - Heart's Slow Change

• Persistent cardiac injury (e.g., MI, chronic overload) triggers sustained neurohormonal (RAAS, SNS) & cytokine (TNF-α, IL-6) activation.
• Drives maladaptive changes in ventricular geometry, mass, & cellular composition:
  • Myocyte hypertrophy (later detrimental), dysfunction, apoptosis/necrosis.
  • Fibroblast activation → excessive collagen deposition → interstitial/perivascular fibrosis, ↑stiffness.
  • Altered ECM turnover: ↑Matrix Metalloproteinase (MMP) activity.
• Results in: Ventricular dilation (eccentric hypertrophy), increased sphericity, impaired pump mechanics.
• Functional impact: ↑Wall stress, ↓systolic/diastolic function, arrhythmogenicity, worsening HF.

⭐ Key drugs (ACEi, ARBs, β-blockers, MRAs) can attenuate/reverse adverse remodeling, improving prognosis in HF.

High‑Yield Points - ⚡ Biggest Takeaways

• Heart failure is the inability to meet metabolic demands or doing so only at ↑ filling pressures.
• Systolic dysfunction (HFrEF) features impaired contractility and ↓ ejection fraction (typically < 40%).
• Diastolic dysfunction (HFpEF) involves impaired ventricular relaxation and filling with a preserved ejection fraction (typically ≥ 50%).
• Key neurohormonal activation includes RAAS and SNS, leading to maladaptive cardiac remodeling.
• BNP (B-type Natriuretic Peptide) is elevated due to ventricular stretch, serving as a crucial diagnostic/prognostic marker.
• Left-sided HF leads to pulmonary congestion (dyspnea, orthopnea); Right-sided HF causes systemic venous congestion (edema, JVD).
• The Frank-Starling mechanism is an initial compensatory response, but becomes detrimental long-term.