HARD QUIZ PATHOPHYS OF HF

Pathophysiology of Heart Failure

• Heart failure is the inability of the heart to deliver adequate blood flow and oxygen to organs, possibly only at elevated filling pressures.
• Two major categories of heart failure:
  • Heart Failure with Reduced Ejection Fraction (HFrEF):
    • Systolic dysfunction characterized by a loss of the heart's ability to contract.
    • Leads to reduced ejection fraction (EF) below 40%.
    • Common causes include ischemic heart disease, dilated cardiomyopathies, myocarditis, persistent tachycardia, chronic volume overload, valve disease, chronic hypertension, congenital cardiac defects, and pregnancy.
  • Heart Failure with Preserved Ejection Fraction (HFpEF):
    • Diastolic dysfunction characterized by impaired ventricular filling with elevated filling pressures.
    • Preserved ejection fraction (EF) of 50% or higher.
    • Common causes include chronic hypertension, aortic valve stenosis, genetic defects (hypertrophic cardiomyopathy), restrictive cardiomyopathy, cardiac tamponade, and impaired relaxation (e.g., ischemia).

Learning Objectives

• Define heart failure and list major causes.
• Differentiate between systolic (HFrEF) and diastolic dysfunction (HFpEF).
• Explain how systolic dysfunction affects Frank-Starling curves, pressure-volume loops (EDV, ESV, EF), and ventricular compliance.
• Explain how diastolic dysfunction affects ventricular compliance and pressure-volume loops (EDV, ESV, EF).
• Describe the beneficial and deleterious effects of neurohumoral compensatory responses to heart failure.
• Describe how heart failure impairs the cardiovascular responses to exercise.

Neurohumoral Compensation

• The body activates sympathetic nerves and catecholamine release in response to heart failure.
• This response is initially beneficial to maintain cardiac output and blood pressure in acute failure.
  • Baroreceptor reflex
  • Cardiac stretch receptors
  • Chronic central sympathetic activation
  • Increased circulating angiotensin II
  • RAAS activated by reduced renal perfusion
  • Increased sympathetic activity
  • Enhanced release of vasopressin and ANP (antidiuretic hormone, and atrial natriuretic peptide)
• However, chronic activation of these compensatory mechanisms leads to detrimental effects, including:
  • Increased blood volume.
  • Increased venous pressures.
  • Pulmonary and systemic edema.
  • Increased afterload impairing ventricular ejection.
  • Cardiac remodeling.
  • Arrhythmias.

Heart Failure Signs and Symptoms

• Exertional dyspnea (shortness of breath during exertion).
• Exercise intolerance.
• Cognitive deficits and fatigue.
• Cough or wheezing.
• Swelling in the legs or abdomen.
• Arrhythmias.
• Cardiac murmurs.

Systolic Dysfunction

• Acute systolic dysfunction results in a loss of intrinsic inotropy that leads to decreased stroke volume (SV) and ejection fraction (EF) at a given preload.
• Compensatory responses include ventricular dilation (not initially remodeling, then it becomes permanent), increased heart rate (HR), and increased end-diastolic volume (EDV) and end-diastolic pressure (EDP).
• Chronic systolic dysfunction, characterized by dilation and remodeling, results in reduced ventricular compliance, increased end-systolic volume (ESV), lower ejection fraction, and increased end-diastolic pressure.

Diastolic Dysfunction

• Diastolic dysfunction results from decreased ventricular compliance ("stiffness").
• The pressure-volume relationship curve shifts to the left, but the stroke volume is normal at a given EDV.
• This leads to higher filling pressures (increased EDV/P) for the same stroke volume, which contributes to pulmonary congestion and edema

HFrEF, HFpEF, and Combined Dysfunction

• HFrEF (reduced ejection fraction): Reduced stroke volume and ejection fraction, with compensatory mechanisms that lead to cardiac dilation.
• HFpEF (preserved ejection fraction): Normal ejection fraction, but increased filling pressures due to stiff ventricles.
• Combined dysfunction: Both systolic and diastolic dysfunction coexist, resulting in decreased stroke volume and increased filling pressures.

Impaired Exercise Responses in Heart Failure

• Patients with heart failure exhibit reduced maximal cardiac output, limited by dyspnea, fatigue and impaired inotropic responses, typically affecting primarily HFrEF disease states.
• Endurance to exercise is also reduced due to impaired gas exchange and inadequate perfusion to the exercising muscles.

Key Terms and Abbreviations

• EDV (End-Diastolic Volume): Volume of blood in the ventricle at the end of diastole.
• ESV (End-Systolic Volume): Volume of blood in the ventricle at the end of systole.
• EF (Ejection Fraction): Percentage of blood ejected from the ventricle per beat.
• SV (Stroke Volume): Volume of blood ejected from the ventricle per beat.
• HR (Heart Rate): Number of heartbeats per minute.
• MAP (Mean Arterial Pressure): Average blood pressure over a cardiac cycle.
• CO (Cardiac Output): Volume of blood pumped by the heart per minute.
• PCWP (Pulmonary Capillary Wedge Pressure): Pressure in the pulmonary capillaries; it correlates with left ventricular filling pressure.
• SVR (Systemic Vascular Resistance): Resistance encountered by blood flow in the systemic circulation.
• RAAS (Renin-Angiotensin-Aldosterone System): A system that regulates blood pressure and fluid balance.
• ANP (Atrial Natriuretic Peptide): Hormone that opposes the RAAS system
• ADH (Antidiuretic Hormone): Hormone that promotes water reabsorption in the kidneys.
• HFrEF (Heart Failure with Reduced Ejection Fraction): A type of heart failure characterized by reduced ejection fraction (EF).
• HFpEF (Heart Failure with Preserved Ejection Fraction): A type of heart failure characterized by preserved ejection fraction (EF).