Cardiac Glycosides and Therapy of Congestive Heart Failure

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Cardiac Glycosides and Therapy of Congestive
Heart Failure

• Philip Marcus, MD MPH

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Pathophysiology of Congestive Heart Failure

• Inability of the heart to pump blood in amounts
  sufficient to meet metabolic needs of the tissues
• Will result in
• Fatigue
• Decreased exercise tolerance
• Dyspnea
• Orthopnea
• Venous distention
• Edema
• Cardiomegaly
• Hepatomegaly
• Tachycardia

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Pathophysiology of Congestive Heart Failure

• Etiology of Congestive Heart Failure
• Hypertension
• Coronary artery disease
• Acute myocardial infarction
• Cardiomyopathy
• Primary defect in CHF (systolic dysfunction)
• Reduction in contractile force of cardiac muscle
• Decreased Cardiac Output (reduced ejection
  fraction)
• Diastolic Dysfunction
• Elevated end-diastolic pressure
• Normal-sized chamber (LV)
• Inability to fill and relax ventricle

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Physiologic Adaptations to Reduced Cardiac Output
(to improve perfusion)

• Cardiac Dilatation
• Increased sympathetic tone
• Increased heart rate
• Increased contractility
• Increase in venous tone
• Increase in preload
• Increase in arteriolar tone
• Increase in afterload

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Physiologic Adaptations to Reduced Cardiac Output
(to improve perfusion)

• Water retention and increase in blood volume
• Reduction in CO leads to decrease in RBF
• Reduced RBF leads to decrease in GFR
• Decrease in GFR leads to decreased urine
  production
• Decrease in RBF leads to increase in renin
  activity
• Increase in renin causes increase in aldosterone
• Increased aldosterone leads to sodium and water
  retention

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Determinants of Cardiac Performance

• Preload
• Measure of LV filling (stretch)
• Measure LVEDV, LVEDP
• In CHF, preload increases and cardiac performance
  (SV, Stroke work) decrease
• Increased preload secondary to
• Increase in blood volume
• Increase in venous tone
• Reduction of high filling pressure is goal of
  therapy

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Determinants of Cardiac Performance

• Afterload
• Resistance against which the heart must pump
  blood
• Represented by aortic impedance and systemic
  vascular resistance
• SVR increases in CHF secondary to
• Increased sympathetic outflow
• Increase in circulating catecholamines
• Activation of renin-angiotensin-aldosterone
  system
• Increase in SVR further reduces C.O.
• Reduction of SVR is one goal of treatment

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Determinants of Cardiac Performance

• Contractility
• Vigor of contraction of heart muscle
• As contractility decreases, velocity of muscle
  shortening and rate of intraventricular pressure
  development decrease (dP/dt)
• Goal of inotropic therapy is to increase
  contractility
• Heart Rate

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Left Ventricular Dysfunction
Remodeling
Arrhythmia
Low Ejection Fraction
Death
Pump Failure
Congestive Heart Failure Pathophysiology
Chronic Heart Failure
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Agents used to treat CHF

• Inotropic agents
• Diuretics
• Antialdosterone therapy
• Vasodilators
• b-blockers
• Salt restriction

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Diuretics in CHF

• Diuretic therapy results in
• Improvement in sodium excretion
• Improvement in symptoms of fluid overload
• Improvement in exercise tolerance
• Improvement of cardiac function
• Should not be prescribed as monotherapy
• Start for symptom control
• Titrate to avoid excess volume depletion
• Undertitration can diminish response to ACE
  inhibitors and increase frequency of adverse
  effects of treatment with b-blockers

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Possible means of increasing myocardial
contractility

• Increased intracellular Ca
• Increased cAMP
• Stimulation of b-receptors
• Stimulation of adenylate cyclase
• Inhibition of phosphodiesterase III
• cAMP independent mechanisms
• Membrane channels
• Activation of Ca and Na channels
• Inhibition of K channels
• Membrane pumps
• Inhibition of Na/ K ATPase
• Inhibition of Na/ Ca exchange
• Other mechanisms (stimulation of a receptors)
• Increased sensitivity of contractile proteins to
  Ca

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Inotropic agents

• Act on heart muscle to improve contractility and
  increase C.O.
• b1 adrenergic agonists
• Dopamine
• Dobutamine
• Bipyridine compounds
• Inamrinone
• Milrinone
• Cardiac (digitalis) glycosides
• Digoxin
• Digitoxin (discontinued Oct., 2000)

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Common Foxglove PlantD. Purpurea
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Cardiac Glycosides

• All compounds exert similar pharmacological
  effects
• Agents differ in pharmacokinetic characteristics
• Derived from naturally occurring compounds
  obtained from leaves of
• Digitalis purpurea (digitoxin)
• Digitalis lanata (digoxin)
• Known to ancient Egyptians
• Withering (1785) described effects of extract of
  Foxglove plant in patients with dropsy
• An Account of the Foxglove, and Some of Its
  Medical Uses With Practical Remarks on Dropsy
  and Other Diseases

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Cardiac Glycosides (Chemistry)

• Steroid nucleus combines with unsaturated
  5-member lactone ring at C17 position and series
  of sugars linked to C3 of the nucleus
• Lactone ring and steroid nucleus essential for
  activity (aglycone)
• Sugar moiety influences
• Absorption
• Half-life
• Metabolism

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Cardiac Glycosides Pharmacological effects

• Pharmacodynamics
• Mechanical effects
• Electrical effects
• Direct
• Indirect (involve reflex actions)
• Extracardiac effects
• Digitalis toxicity
• Pharmacokinetics
• Clinical use

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Mechanical Effects

• Acts on cardiac muscle to increase contractile
  force
• inotropic action
• Mechanism of inotropic action
• Inhibition of Na-K ATPase (sodium pump)
• Promotes Ca accumulation
• Increases force of contraction by facilitating
  interaction of myocardial contractile proteins
• Increases intensity of interaction of actin and
  myosin filaments of cardiac sarcomere
• Caused by increases in free Ca in vicinity of
  contractile proteins during systole

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Ion Fluxes across the Cardiac Cell Membrane
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Relationship of K to digitalis action

• Potassium competes with digitalis for binding to
  Na-K ATPase
• When Potassium levels low, digitalis binding
  increases
• Increased binding produces excess inhibition of
  Na-K ATPase with resultant toxicity
• K must be kept within normal range

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Digitalis Effects

• In patients with CHF
• Enhances contractility (inotropic)
• Reduces SVR (which occurred via compensatory
  processes)
• Heart size decreases
• C.O. increases
• As efficiency improves, MVO2 decreases
• In normal patients
• Increases SVR
• Increases peripheral vasoconstriction (direct)
• Increases central sympathetic outflow
• Increases contractility
• No change in C.O.

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Electrical Effects

• Therapeutic and Toxicological Importance
• Digitalis glycosides useful for treatment of
  arrhythmias
• Atrial fibrillation
• Atrial flutter
• May also cause arrhythmias
• Complex effects
• Direct effects
• Indirect effects

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Electrical Effects

• Digitalis alters electrical activity of
  non-contractile tissue
• S-A node
• A-V node
• Purkinje fibers
• Alters electrical activity of atrial and
  ventricular muscle
• Can alter
• Automaticity
• Refractoriness
• Impulse conduction

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Direct Electrical Effects

• Result from inhibition of Na-K ATPase
• Alters distribution of ions across cardiac cell
  membrane
• Alters electrical responsiveness of cells
• Direct effects heightened by hypokalemia

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Direct Electrical Actions

• Direct actions on membranes of cardiac cells
  follow well-defined progression
• Early, brief prolongation of action potential
• Protracted period of shortening of action
  potential, especially plateau
• ? Result of inc. K conductance
• Caused by inc. intracellular Ca
• Contributes to shortening of atrial and
  ventricular refractoriness
• Decreased conduction velocity through A-V node
  and in Purkinje system
• Increased refractory period in A-V node

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Direct Electrical Actions

• Automaticity increases, particularly in
  ventricular tissue
• Decreased activity of normal pacemaker tissue
• Decreased ventricular refractory period
• Increase A-V block
• Ectopic foci can therefore be generated,
  particularly in Purkinje system
• PVCs, bigeminy
• Ventricular tachycardia
• Ventricular fibrillation

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EKG Effects of Digitalis Glycosides

• P-R interval prolongation
• Prolonged A-V nodal conduction
• T-wave depression
• Increase in repolarization of subendocardial
  tissue
• ST depression
• QT interval shortening
• Decreased time for ventricular systole

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Indirect Electrical Effects

• Digitalis increases vagal influences
• Increased rate of vagal firing
• Slows spontaneous discharge of SA node
• Suppresses conduction through AV node
• Causes reflex reduction in sympathetic tone
• Increase in vagal firing and decrease in
  sympathetic tone causes
• Decrease in SA automaticity
• Decrease in AV conduction (A-V block)
• Actions are complimentary

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Digital Glycosides Specific Effects

• SA Node
• Slows pacemaker activity
• Increased vagal activity
• Decreased sympathetic activity
• AV Node
• Decreased conduction through AV node
• Increased refractoriness of AV node
• A-V block
• Purkinje Fibers
• Increased automaticity
• Ectopic foci
• Ventricular arrhythmias

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Cardiotoxicity of Digitalis

• Arrhythmia production
• Most serious adverse effect
• Secondary to alteration of electrical properties
• Assess all patients for alterations in rate and
  rhythm
• All arrhythmias seen
• Bradycardia
• A-V block, A-V junctional rhythm
• Ventricular tachycardia
• Ventricular fibrillation

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Cardiotoxicity of Digitalis

• Mechanism of arrhythmia generation
• Inc. automaticity of atrial and ventricular
  tissue
• ectopy
• Dec. conduction through A-V node
• A-V block
• Both factors due to Na-K ATPase inhibition
• Augmented by hypokalemia

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Cardiotoxicity of Digitalis

• Predisposing factors
• Hypokalemia
• Digitalis toxicity
• Myocarditis
• Hypercalcemia
• Hypomagnesemia
• Hypothyroidism
• Age
• Renal disease
• Hypoxemia

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Digitalis Toxicity

• Defined solely as elevation in serum digitalis
  level
• Digoxin gt 2.5 ng/ml
• Digitoxin gt35 ng/ml (of historical interest)
• Digoxin levels may rise secondary to use of
• Amiodarone
• Verapamil
• Diltiazem
• Quinidine

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Digitalis Toxicity Management

• Discontinue drug
• Correct hypokalemia
• Antiarrhythmics
• Lidocaine
• Phenytoin
• Pacemaker Insertion
• Digibind administration
• Digoxin-specific Fab fragments
• Prevents tissue binding of digoxin
• 30 minute onset of action
• Clearance within 3-4 days
• Digoxin Fab fragments in urine
• Dialysis ineffective

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Extracardiac Effects of Digitalis

• Gastrointestinal
• Anorexia
• Nausea
• Vomiting
• Central Nervous System
• Fatigue
• Visual disturbances
• Halos around lights
• Alteration of color perception
• Hallucinations
• Disorientation

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Therapeutic Uses of Digitalis

• Congestive Heart Failure
• Indicated in patients with severe LV dysfunction
• Primarily used after diuretics and vasodilators
• Not useful in diastolic dysfunction or
  right-sided heart failure
• Most efficacious when S3 noted on examination
• Atrial arrhythmias
• Indicated in atrial fibrillation and atrial
  flutter
• Used to slow ventricular response
• Therapeutic serum levels
• Digoxin 0.5-2.2 ng/ml
• Digitoxin 9-25 ng/ml

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Digoxin Pharmacokinetics

• Variable oral absorption
• Liquid more complete and less variable than
  tablets
• VD 6-7 L/kg
• Binds strongly to proteins in extravascular space
• Renal excretion
• Clearance slowed in renal dysfunction
• 37 excreted per day
• Minimal hepatic metabolism (lt20)
• Half-life 1.6 days (30-40 hours)
• 5xhalf-life to attain plateau (7 days)
• Digitalization
• Oral and IV administration

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Digitoxin Pharmacokinetics

• Absorption almost complete (gt90)
• Less polar and more lipid soluble than Digoxin
• Cholestyramine can alter enterohepatic cycling
• Elimination primarily via hepatic metabolism
  (gt80)
• Large capacity of the liver to metabolize
• Inducible
• gt95 bound to albumin
• VD 0.6 L/kg
• Half-life 7 days
• 4 weeks to reach plateau
• Oral administration
• Of Historical Interest No longer available

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Bipyridines

• Inamrinone, formerly amrinone
• Milrinone (Primacor)
• More potent, higher selectivity for PDE
• Phosphodiesterase III inhibitors
• Results in increase in cAMP
• Increases Ca during action potential
• Similar effects to b-receptor stimulation
• Vasodilator effects occur
• Decreases preload and afterload
• Partially responsible for improved C.O.
• Little change in BP
• Used via IV route by continuous infusion

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Bipyridines Inamrinone and Milrinone

• Indicated for short-term management of severe CHF
  not responding to digitalis, diuretics,
  vasodilators
• Inamrinone has not been shown to prolong survival
  or reduce incidence of sudden death
• Milrinone has been shown to increase mortality
  without definite benefit

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Bipyridines

• Inamrinone metabolized by conjugative pathways
• t1/2 2-3 hours (Milrinone 30-60 minutes)
• Excreted in urine as inamrinone and metabolites
• Potentiate arrhythmias in high-risk patients
  treated
• Adverse effects
• Thrombocytopenia (3 with inamrinone)
• Hepatic toxicity

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Vasodilators in CHF

• Useful in reducing preload and/or afterload
• Arterial dilators primarily reduce afterload
• Decrease SVR
• Decrease impedance
• Venous dilators primarily reduce preload
• Cause increase in venous capacitance
• Pooling of blood in veins
• Decrease in venous return
• Relief of congestion

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Vasodilators in CHF

• Organic nitrates
• Direct vasodilators
• Angiotensin-converting enzyme inhibitors
• Beneficial effects in the treatment and
  prevention of heart failure
• Decrease morbidity and mortality

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Assessment of LV Function (Echocardiogram,
Radionuclide Ventriculogram)
EF lt 40
Assessment of Volume Status
Signs and Symptoms of Fluid Retention
No Signs and Symptoms of Fluid Retention
ACE Inhibitor
Diuretic (Titrate to Euvolemic State)
Digoxin
B-Blocker
Recommended Approach to the Patient with Heart
Failure
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New Vasodilators

• Neseritide (Natrecor)
• Natriuretic peptide
• Bosentan (Tracleer)
• Endothelin receptor antagonist
• Epoprostenol (Flolan)
• Prostacyclin (PGI2)

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Nesiritide (Natrecor)

• Human B-type natriuretic peptide (hBNP)
• Endogenous 32-amino acid peptide hormone
• Structurally similar to atrial natriuretic
  peptide (ANP)
• Manufactured from E. coli using recombinant DNA
  technology
• Binds to particulate guanylate cyclase receptor
• Vascular smooth muscle
• Endothelial cells
• Increases intracellular cGMP smooth muscle
  relaxation
• Relaxes arterial and venous tissue pre-contracted
  with endothelin-1 or phenylephrine

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Nesiritide (Natrecor)

• Pharmacological Actions
• Hemodynamics
• Venodilatation
• Arterial Dilatation
• Coronary Artery Dilatation
• Neurohumoral
• ? aldosterone
• ? norepinephrine
• Renal
• Diuresis
• Natriuresis

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Nesiritide (Natrecor)

• Pharmacological Actions
• Produces dose dependent reductions in PCWP and
  systemic arterial pressure in patients with heart
  failure
• Improves dyspnea
• No effect on cardiac contractility
• No effect of conduction or refractory times
• Indicated in acutely decompensated CHF

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Nesiritide (Natrecor)

• Pharmacokinetics
• IV Bolus and Infusion
• Biphasic disposition from plasma
• Mean terminal elimination half-life 18 min.
• Mean initial elimination half-life 2 min.
• Cleared from circulation via 3 independent
  mechanisms
• Binding to cell surface clearance receptors with
  cellular internalization and lysosomal
  proteolysis
• Proteolytic cleavage of peptide by endopeptidase
• Renal filtration

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Bosentan

• Indicated for pulmonary hypertension
• Approved Nov. 20, 2001
• Endothelin-1 receptor antagonist
• Binds to ETA and ETB receptors
• Specific and competitive antagonist
• Located in endothelium and vascular smooth muscle
• ET-1 levels increased in PAH suggesting
  pathogenic role for ET-1

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Bosentan

• Pharmacokinetics
• Oral administration
• 50 bioavailable
• Unaffected by food
• Highly protein bound (albumin)
• 3 metabolites, 1 active contributing to 10-20 of
  effect
• Inducer of CYP2C9 and CYP3A4
• Eliminated by biliary excretion and hepatic
  metabolism

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Bosentan

• Pregnancy category X
• Teratogenic in rats
• Pregnancy should be excluded before start of
  treatment
• May impair fertility
• Hepatotoxic
• Carcinogenic in mice