Pathophysiology of Heart Failure

Heart failure pathophysiology involves four interconnected systems: the heart, vasculature, kidneys, and neurohumoral regulatory circuits. Myocardial overload or valvular defects reduce cardiac output, triggering compensatory hypertrophy and fibrosis. Vascular stiffness increases afterload, while kidneys dysregulate sodium and water levels. Together, these systems create a vicious cycle worsening heart failure progression.

Cardiac remodeling involves myocyte hypertrophy, increased fibroblast proliferation, and extracellular collagen deposition. These compensatory changes disrupt cardiomyocyte communication and trigger cell death through apoptosis or necrosis. While initially attempting to maintain cardiac output, prolonged remodeling worsens heart function and accelerates disease progression.

Vascular stiffness stems from impaired endothelial function and disrupted crosstalk between endothelial and smooth muscle cells. This imbalance increases vasoconstricting reactive oxygen species relative to vasodilating nitric oxide, elevating afterload. Age-related or disease-related vascular stiffness significantly worsens hemodynamic burden on the failing heart.

The sympathetic nervous system and renin-angiotensin-aldosterone system activate to compensate for reduced cardiac output. However, prolonged activation of these neurohumoral mechanisms increases cardiac workload through vasoconstriction, volume overload, and tachycardia. This creates a vicious cycle of worsening cardiac remodeling and progressive heart failure deterioration.

Systolic heart failure (HFrEF) involves reduced ejection fraction, indicating impaired cardiac pumping ability. Diastolic heart failure (HFpEF) preserves ejection fraction but involves stiffened ventricles unable to relax and fill properly. HFpEF is increasingly prevalent and often related to aging and hypertension.

Kidneys regulate sodium and water levels through autoregulatory and neurohumoral mechanisms. Heart failure dysregulates these processes, causing sodium and water retention that increases intravascular volume and cardiac workload. Impaired kidney function perpetuates the compensatory activation of neurohumoral systems, worsening heart failure progression.

Common symptoms include tachycardia, decreased exercise tolerance, shortness of breath, maldigestion, ascites, and peripheral or pulmonary edema. Heart failure ranges from Class I to IV based on symptom severity. The AHA and ACC classification extends this with stages A through D, from preventable risk factors to end-stage requiring transplantation.