Heart Failure, Treatment
Goals of Treatment
The goals of treatment of heart failure are to either cure it, or to slow it down or prevent the progression of the disease. If no 'treatment' can be given then drugs can be used to provide symptomatic relief. Treatments vary from surgical correction of underlying conditions, such as correction of a PDA, to management changes and pharmacological treatments.
Management Changes
Certain things owners need to be made aware of in order to prevent exacerbation of the disease include avoiding strenuous exercise and feeding reduced salt diets as this reduces preload. They may also wish to give potassium supplements or in cats with dilated cardiomyopathy, taurine supplements. L-carnitine supplements can be given to dogs with dilated cardiomyopathy. Nutraceuticals (e.g. Omega-3 fatty acids, Anti-oxidants, Co-enzyme Q10) can also be given.
Heart failure patients can suffer from cardiac cachexia due to the high metabolic demands of this condition. Make sure the patient is eating enough calories per day to maintain their body weight.
Pharmacological Intervention
The following terms are useful when describing the effects of various pharmacological agents. These are 'Preload'. This is the amount of maximal myocardial stretch (during diastole). 'Afterload' is the amount of maximal myocardial tension (during systole).
Drug treatments can be used to:
Decrease Preload
This decreases venous tone and fluid volume which can help to relieve congestion & oedema. Drugs in this class include:
Diuretics: These decrease blood volume by increasing sodium loss from the kidneys. They include loop diuretics, that act on the renal loop of Henle such as Frusemide, and thiazide diuretics that act on the renal distal convoluted tubule, such as Chlorothiazide or Hydrochlorothiazide. Potassium sparing diuretics act on the renal collecting duct and include Spironolactone and Amiloride.
Venodilators , as their name suggests, dilate veins causing decreased venous pressures, blood redistribution, and increased capacitance. Venodilators include Glyceryl trinitrate and a group of drugs classified as balanced vasodilators, which includes ACE inhibitors (Enalapril (dogs & cats), Benazepril (cats), alpha-antagonists and Nitroprusside.
The side effects of preload reduction include: hypovolemia, dehydration, hypokalemia, hyponatremia.
Decrease Afterload
Decreasing afterload increases flow by decreasing arterial tone. This reduces resistance to outflow which reduces the cardiac workload by decreasing systolic myocardial tension and increasing systemic blood flow. Arterial vasodilators include Hydralazine or any member of the balanced vasodilators mentioned above. ACE inhibitors such as Enalapril and Benazepril are commonly used - side effects include vomiting, anorexia, diarrhea, hypotension, and azotaemia.
Increase Myocardial Systolic Function
This helps with dilated cardiomyopathy and mitral valve disease (dog & cat) but is contraindicated in animals with hypertrophic cardiomyopathy (dog & cat). Positive Inotropes can be used to stimulates myocardial contractility to improve cardiac output regardless of preload. This class of drug includes digitalis compounds (e.g. Digoxin, Digitoxin), calcium sensitisers/ phosphodiesterase III. inhibitor (e.g. Pimobendan), pure phosphodiesterase inhibitors (e.g. Milrinone, Amrinone) and catecholamines (e.g. Dobutamine, Dopamine).
The disadvantage of positive inotropes is that increased myocardial work causes increased myocardial oxygen demand.
Increase Myocardial Diastolic Function
This helps with hypertrophic cardiomyopathy and myocardial fibrosis where ventricular filling is compromised. Drugs include the beta blockers (e.g. Atenolol, Propranolol) and calcium channel blockers (e.g. Diltiazem).
References
Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company
Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) W.B. Saunders Company
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier
Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier
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