Heart Failure Chapter 19

Heart Failure Overview

• Heart failure occurs when cardiac output is insufficient to meet the body's oxygen needs.
• It is a progressive condition, characterized by gradual cardiac performance decline and episodes of acute decompensation, often requiring hospitalization.
• Major causes include coronary artery disease and hypertension.

Types of Heart Failure

• Systolic Failure
  • Involves reduced mechanical pumping action and decreased ejection fraction.
• Diastolic Failure
  • Characterized by stiffening and inadequate relaxation, leading to reduced filling and cardiac output.
  • Ejection fraction may be normal, although stroke volume is significantly decreased.

Symptoms of Heart Failure

• Common symptoms include tachycardia, decreased exercise tolerance, shortness of breath, peripheral and pulmonary edema, and cardiomegaly.

High-Output Heart Failure

• Rare form where the body's demands exceed even increased cardiac output.
• Associated conditions include hyperthyroidism, beriberi, anemia, and arteriovenous shunts.

Compensatory Responses

• Increased sympathetic activity and activation of the Renin-Angiotensin-Aldosterone System (RAAS) occur.
• Myocardial hypertrophy is a critical intrinsic mechanism to maintain cardiac performance despite potential adverse effects.

Myocardial Hypertrophy

• Signifies increased muscle mass, aiding cardiac performance but may lead to ischemic changes and impaired diastolic filling.

Remodeling

• Refers to dilation and structural changes in the stressed myocardium, occurring over time due to heart failure.

Cardiac Performance Factors

• Preload
  • Generally increased due to higher blood volume and venous tone, defined as initial stretching of cardiac myocytes prior to contraction.
• Afterload
  • Resistance the heart faces when pumping blood, represented by aortic impedance and systemic vascular resistance.
• Contractility
  • Patients exhibit reduced intrinsic contractility, but can still respond positively to inotropic drugs.
• Heart Rate
  • An essential determinant of cardiac output and the first compensatory mechanism, typically increased via sympathetic activation.

Pharmacology in Heart Failure

• Digitalis
  • A cardiac glycoside obtained from plants such as Digitalis lanata, used to treat heart failure.
• Digoxin (Lanoxin®)
  • Inhibits Na+/K+ ATPase, increasing calcium availability in the heart muscle, thereby enhancing contractility (inotropic effect).

Clinical Effects of Digoxin

• Increases cardiac contractility and has a parasympathomimetic effect, slowing heart rate and conduction.

Digoxin Toxicity

• Symptoms include nausea, vomiting, diarrhea, cardiac arrhythmias, disorientation, visual disturbances, and gynecomastia.
• Interactions with potassium, calcium, and magnesium can influence digoxin's effects, emphasizing the importance of electrolyte balance.

Other Inotropic Drugs

• Istaroxime
  • Investigational drug that enhances contractility by Na+/K+ ATPase inhibition and facilitates calcium sequestration in the sarcoplasmic reticulum.
• Levosimendan
  • Sensitizes the troponin system to calcium, with potential positive inotropic effects.