Congestive Heart Failure and Digitalis

1. Congestive Heart Failure and Digitalis October 11, 2007 Frank F. Vincenzi

2. New York Heart Association: Classifications of Heart Failure • Class I - no limitation of physical activity • Class II - slight limitation of activity • dyspnea with moderate physical activity • Class III - marked limitation of activity • dyspnea with minimal physical activity • Class IV - severe symptoms at rest

3. Cardiovascular responses to heart failure Inadequate cardiac output Adrenergicnervoussystem (norepinephrine) Reninangiotensinsystem(aldosterone) Tachycardia Systemic vasoconstriction

4. Infections Arrhythmias Myocardial infarction Pulmonary embolism Undue physical exertion Excessive Na intake Hemorrhage, anemia Pregnancy In- and trans-fusions Anesthesia/surgery High altitude Hypertension D/C digitalis Conditions that may precipitate CHF

5. Pharmacotherapeutic approaches in heart failure • Reduction of volume overload (reduce preload) • Diuretics (more about these later when we consider diuretics) • Ventricular unloading (reduce afterload) • Acute: nitroglycerin, sodium nitroprusside • Chronic: inhibit renin-angiotensin-aldosterone system, diuretics, ACE inhibitors, angiotensin antagonists(More about these later - when we consider hypertension) • Beta-blockers (also reduce sympathetic activation) • Inotropic interventions (improve Starling function) • Acute: dobutamine • Chronic: phosphodiesterase inhibitors, digitalis

6. Effects of ouabain on cardiac function in a patient with CHF

7. Effects of ouabain on the CV system of a patient in CHF

8. Effects of ouabain on the CV system of a normal human volunteer

9. Digitalization can increase myocardial efficiency in CHF

10. Digitalization can increase myocardial efficiency in CHF

11. Determinants of myocardial oxygen demand • Intramyocardial tension • blood pressure, ventricular volume • Myocardial contractility • Heart rate • Fiber shortening (Fenn effect) • Activation energy • Basal (resting) metabolism

12. Ventricular function (Starling) curves:normal, CHF and with digitalis Cardiac Output normal CHF + digitalis adequate CHF inadequate, fatigue congestive symptoms, edema, dyspne a ventricular end-diastolic volume

13. Mechanism of positive inotropic effect of digitalis ROC digitalis

14. Effect of ouabain on cardiac cellular functions

15. Digitalis: standard swindle of the positive inotropic mechanism • Inhibition of Na, K ATPase • Altered balance of Na/Ca exchange • Enhanced Ca storage/release • Increased binding of Ca to troponin • Increased actin/myosin ATPase • Increased contractility

16. Pharmacotherapeutic approaches in heart failure • Reduction of volume overload (reduce preload) • diuretics • Ventricular unloading (reduce afterload) • Acute: nitroglycerin, sodium nitroprusside • Chronic: inhibit renin-angiotensin-aldosterone system, diuretics, ACE inhibitors, angiotensin antagonists • Beta-blockers (also reduce sympathetic activation) • Inotropic interventions (improve Starling function) • Acute: dobutamine • Chronic: phosphodiesterase inhibitors, digitalis

17. dobutamine (Dobutrex®) • Positive inotropic effect via beta-1 receptors • Reduces afterload via beta-2 receptors • Minor activation of alpha-1 receptors • May promote sinus tachycardia, PVCs, angina, headache, hypertension • Half life about 2 minutes. IV infusion to titrate dobutamine effects.

18. milrinone (Primacor®) • Relatively selective inhibitor of type III cyclic nucleotide phosphodiesterase (cGMP inhibited cAMP hydrolysis) (exerts positive inotropic effect and vasodilation and bronchodilation). • Indicated for IV treatment of heart failure. Chronic oral dosage associated with increased mortality. Half life is about 2 hours. Excreted mainly in urine, adjust dosage in renal disease. • Adverse reactions included PVCs, SVT, VT and VF

19. Cardiovascular responses to heart failure Inadequate cardiac output Beta blockers Adrenergicnervoussystem (norepinephrine) Reninangiotensinsystem(aldosterone) Tachycardia Systemic vasoconstriction

20. Beta adrenergic blockers:decrease renin release and afterload (and decrease sympathetic activation of heart) • Propranolol (Inderal®) • Metoprolol (Lopressor®) • Carvedilol (Coreg®) • decreases afterload in part by alpha adrenoceptor antagonism Use of beta-blockers in carefully monitored patients CHF may be beneficial. Until recently, beta blockers were considered to be contraindicated in CHF.

21. Impact of atrial tachycardia on circulation

22. Effect of digitalis on a supra-ventricular tachycardia

23. Effects of lanatoside C on paroxysmal atrial flutter

24. Circus movement atrial flutter model: effect of digitalis

25. Vagal (ACh) actions on supraventricular parts of the heart • Decreases SA node automaticity (and slows heart rate) • Decreases duration of atrial muscle action potential (and decreases refractory period) • Slows AV nodal conduction velocity and increases AV nodal refractory period All of the above effects are caused by a single mechanism of action: increased potassium permeability

26. Effects of transient release of acetylcholine on atrial action potential and contractile force

27. Vagal (ACh) actions on supraventricular parts of the heart • Decreases SA node automaticity (and slows heart rate) • Decreases duration of atrial muscle action potential (and decreases refractory period) • Slows AV nodal conduction velocity and increases AV nodal refractory period

28. Effect of digoxin on AV nodal conduction in normally innervated human heart

29. Lack of effect of digoxin on AV nodal conduction in transplanted (denervated) human heart

30. Pharmacokinetics of digoxin • Well, but variously absorbed from GI tract, bioavailability = 70 ± 13% • Vd = (3.12 CLcr + 3.83) ± 30% and proportional to thyroid status • Most excreted in urine unchanged, elimination depends on kidney function • Half life = 39 ± 13 hours (1.6 days)

31. Accumulation of digoxin during chronic dosing

32. Pharmacokinetics of digitoxin • Well absorbed from GI tract, bioavailability > 90% • Vd = 0.54 ± 0.14 liters/kg • Non-polar compound, elimination depends on liver function • Half life = 6.7 ± 1.7 days

33. Non-uniform bioavailability of several generic and trade name digoxin preparations

34. Some adverse reactions to digitalis CNS headache, malaise, confusion, dizziness, changes in color vision GI anorexia, nausea, vomiting, diarrhea CV bradycardia, heart block (various degrees), arrhythmias, ventricular tachycardia, fibrillation, hyperkalemia

35. digoxin in hospitalized patients • 22.4% of patients (est. failure 8%) • CHF (78%), arrhythmias (21%), other (1%) • Route • PO (79%), IV (15%), IM (6%) • Adverse reactions • Arrhythmias 8.5% • GI disturbances 3.1% • CNS toxicity 0.1% • Gynecomastia 0.1%

36. Digitalis toxicity • In various studies • The minimal inotropic dose of = about 1/5 of the lethal dose • The minimal toxic dose = about 2/3 of the lethal dose • Thus, the therapeutic window is narrow

37. Diagnosis of digoxin toxicity • Are there predisposing factors? • large dose, decreased elimination • Are there extracardiac symptoms? • anorexia, nausea/vomiting, visual signs • Arrhythmias present? • Arrhythmias change when digoxin withheld? • What is serum digoxin concentration?

38. Serum digoxin levels in 179 patients Serum concentrations at which the probability of digoxin induced arrhythmias is 10% = 1.7, 50% = 2.5, 90% = 3.3

39. Treatment of acute digoxin intoxication by digoxin immune Fab (Digibind®)

40. Simplified diagram of apparent digitalis-induced changes in ANS activity VF - death VT sympathetic CNS output of autonomic tone PVCs partial AV block slowing parasympathetic Dose of digitalis

41. Digoxin overview • About 50% of patients with CHF have elevated endogenous ouabain (EO) • EO level is inversely correlated with the cardiac index. Digoxin reduces hospitalization for worsening heart failure • Digoxin increases the risk of death from any cause in women, but not in men. • Digoxin only benefits some patients - perhaps patients with low levels of EO (untested at this time) • Improves the quality but not the length of life