Left Heart Failure: Pathophysiology (Neurohormonal Activation)
Frank Starling Mechanism • The Frank Starling mechanism of the heart represents the relationship between preload (EDV) and SV • As preload (EDV) increases, SV increases, because higher volumes of blood in the ventricles stretch the cardiac fibers and increases cardiac contraction during systole. However, volume overload causes reduced SV.
Myocardial Dysfunction: • Left ventricular Compensatory 4, SV 4A, CO 4 Mechanisms
4, BP
Important equations: • BP = CO x SVR • CO = SV x HR Cardiac hemodynamics: • Stroke volume is affected by three factors 1) Preload (end-diastolic volume (EDV)) 2) Afterload (resistance to LV ejection) 3) Contractility (inherent strength of contraction of LV myocytes) Definition of heart failure: • Myocardial dysfunction (systolic or diastolic) results in decreased CO, such that the heart cannot meet the body’s metabolic demands or can only do so at elevated filling pressures
Anti-diuretic hormone (ADH) activation: Arginine 4, BP 4 carotid sinus Vasopressin –• and aortic arch (V2) receptor baroceptors activation activation 4 I` ADH release
RAAS System: 4, BP 4 t release of renin from the juxtaglomerular kidney cells due to renal hypoperfusion
SNS System: In response to CO, 4 SNS t release of (catecholamines) norepinephrine and epinephrine
Adrenal Glands: Aldosterone release
Angiotensin II Type 1 receptor activation
al receptor activation
13, receptor activation
—•
Renal Collecting Ducts: t H2O retention
Renal Distal —• Tubules: t Na+ & H2O retention
Heart: Activation of fibroblasts 4 collagen synthesis and hypertrophy
Blood Vessels: Peripheral vasoconstriction 4 SVR
Heart: Chronic p, receptor activation 4 Ca2+ overload myocyte apoptosis
Heart: Increase HR to maintain normal CO
Maladaptive Response: t preload (EDV), —• volume overload
Abbreviations: • SV — Stroke volume • CO — Cardiac output • SVR — Systemic vascular resistance • BP — Blood pressure • RAAS — Renin-Angiotensin-Aldosterone System • SNS — Sympathetic nervous system
tin systemic and pulmonary congestion via the Frank-Starling Mechanism
Maladaptive 1` resistance Response: t BP, —• against LV afterload ejection 4 4, SV
Maladaptive Response: Adverse LV remodelling
Maladaptive Response: t myocardial oxygen demand and 4, diastolic time
4, contractility —• of the heart
4, coronary blood flow 4 myocardial ischemia
Physical signs and symptoms of congestive heart failure (see relevant slide)
Authors: Sunny Fong Reviewers: —• I Jack Fu Usama Malik Dr. Jason Waechter* *MD at time of publication