Pathophysiology
Clinical meaning
Heart failure progresses through predictable stages defined by the ACC/AHA staging system: Stage A (at risk, no structural disease), Stage B (structural disease, no symptoms), Stage C (structural disease with current or prior symptoms), and Stage D (refractory HF requiring advanced therapies). This staging system is unidirectional — patients progress forward but do not regress to earlier stages, reflecting the irreversible nature of cardiac remodeling. The neurohormonal cascade in heart failure creates a vicious cycle: decreased cardiac output activates baroreceptors and the sympathetic nervous system, increasing heart rate and contractility through norepinephrine release. Reduced renal perfusion activates RAAS: angiotensin II causes arteriolar vasoconstriction (increasing afterload and myocardial oxygen demand), stimulates aldosterone release (causing sodium and water retention, increasing preload), and directly promotes myocardial fibrosis and hypertrophy. ADH release further increases water retention. Natriuretic peptides (ANP from atria, BNP from ventricles) attempt to counteract these effects through vasodilation and natriuresis but are overwhelmed in advanced HF. At the cellular level, chronic sympathetic activation causes beta-1 receptor downregulation (explaining why exogenous catecholamines become less effective), myocyte apoptosis, and calcium handling abnormalities. Myocardial...