Treatment

Treatment of heart disease

• Treatment aims
• Medical therapy
• American College Veterinary Internal Medicine (ACVIM) treatment guidelines

Treatment aims

The aims of treating heart disease are to improve the dog’s quality of life and to increase life expectancy. This is achieved by improving cardiac function and slowing disease progression by reducing cardiac workload, reducing volume overload and improving myocardial efficiency.

Non-medical interventions include adjusting the animal’s lifestyle, for example, controlled exercise, optimising bodyweight and avoiding salty food.

Medical treatment needs and aims will vary between acute and chronic stages.

Acute patients

Some patients present with sudden onset severe signs, for example, due to the rupture of chordae tendinae. In these patients, the priority is oxygen supplementation and to reduce pulmonary oedema, which may be life threatening at this stage. These patients require hospitalisation and aggressive therapy to remove the oedema fluid and to support the patient’s haemodynamic function. Treatment is focused on therapies that have rapid short-term benefits (such as diuretics and oxygen supplementation). The long-term effects (beneficial or harmful) of treatments are relatively unimportant. Within a few days, at most the patient should be through their acute crisis and is then treated as a chronic patient.

1. Angiotensin-converting enzyme inhibitors (ACE inhibitors): block the adverse effects of the renin-angiotensin-aldosterone system (RAAS) and reduce the workload on the heart

2. Diuretics: remove fluid build-up

3. Inotropes/inodilators: increase contractility of the heart

4. Anti-arrhythmics: a wide variety of human drugs are used to treat specific rhythm disturbances

A combination of therapies is almost always used, as no one drug has all the effects needed. In addition, heart failure is a progressive disease and therefore needs progressive treatments.

ACE inhibitors 

“All dogs with heart failure due to valvular endocardiosis or dilated cardiomyopathy should receive treatment with an ACE inhibitor.”

Mike Martin, DVC, MRCVS

ACE inhibitors act on the RAAS by blocking the production of angiotensin II. ACE inhibitors therefore have the following benefits: vasodilation, less retention of sodium and water, normalises the sympathetic nervous system, slows cardiac remodelling, and prevents degenerative renal changes.

The overall effect is to reduce the workload on the heart and to make it more efficient. ACE inhibitors have been shown to improve quality of life and life expectancy, and are the gold standard treatment in human and canine heart disease.

ACE inhibitors currently licensed for veterinary use include:

• Fortekor® (benazepril)
• Enalapril (Enacard®, various generics such as prilenal)
• Ramipril (Vasotop®)
• Imidapril (Prilium®)

ACE inhibitors are one of the most investigated classes of therapy in veterinary medicine and there is strong (Class A) evidence of their benefit in terms of quality of life and survival.

Diuretics

Fluid build-up in the lungs (oedema) and other parts of the body is a major problem in congestive heart failure, and can be life threatening. Diuretics remove excessive fluid build-up by causing loss of water and sodium via the kidneys. Diuretics can be lifesaving if the dog has severe pulmonary oedema, but they activate the RAAS, therefore the dose is often adjusted to the lowest effective dose.

The side effects of diuretics include dehydration, lethargy and reduced appetite (due to low blood pressure), excessive thirst (polydipsia) and urination (polyuria) and loss of electrolytes (for example, potassium). It is therefore important to monitor electrolytes and kidney function during treatment and to use the lowest effective dose. The most commonly used diuretic is frusemide. This can be administered orally or by injection, and is given 1-3 times daily.

Other diuretics can be used in combination with frusemide, for example, spironolactone and hydrochlorothiazide. Spironolactone is an aldosterone antagonist and has additional benefits (such as reduced cardiac remodelling) over and above its diuretic effects. ACE inhibitors and diuretics are essential therapy for congestive heart failure.

It is important to note that any dog receiving a diuretic should always be on an ACE inhibitor at the same time, in order to block the diuretic-induced activation of the RAAS.

Positive inotropes/inodilators

Positive inotropes increase the contractility of the heart, i.e. they make it beat more powerfully. They are used where there is intrinsic heart muscle weakness, such as in dilated cardiomyopathy.

In dogs with normal heart muscle function, like in the earlier stages of degenerative mitral valve disease, they may make regurgitation into the left atrium worse. The most commonly used positive inotropes are pimobendan (an inodilator) and digoxin (mostly used to slow the heart rate – it is not a good inotrope). Pimobendan works by increasing the heart’s sensitivity to calcium. This results in an increase in myocardial contractility without increasing energy requirements. It also has some vasodilating effect. It does not block the RAAS.

ACVIM treatment guidelines

The American College of Veterinary Internal Medicine (ACVIM) has provided the following guidelines for treatment of heart disease patients:

Chronic patients

The majority of patients first present with mild to moderate clinical signs and can be managed with oral medication and on an outpatient/home care basis. The treatment objectives for a chronic patient are focused on causing haemodynamic improvements (i.e. reducing the workload on the heart), slowing disease progression, prolonging survival and improving quality of life/reducing clinical signs. In these patients, the speed of action of therapies is rarely relevant. Treatments such as angiotensin-converting enzyme (ACE) inhibitors form the foundation of chronic therapy.

Most cardiac patients will fall into the ACVIM category ‘Stage C chronic’.

Medical therapy

The main classes of medical therapy are:

1. ACE inhibitors: block the adverse effects of the renin-angiotensin-aldosterone system (RAAS), particularly the harmful effects of angiotensin II, and reduce the workload on the heart

2. Diuretics: remove fluid build-up

3. Inotropes/inodilators: increase contractility of the heart +/- causing vasodilation

4. Anti-arrhythmics: a wide variety of human drugs are used to treat specific rhythm disturbances

5. Aldosterone antagonists: block the harmful effects of aldosterone

A combination of therapies is used, as no one drug has all the effects needed. In addition, heart failure is a progressive disease and therefore needs a progressive approach to treatment, with therapy being adjusted according to clinical needs.

ACE inhibitors  

“All dogs with heart failure due to valvular endocardiosis or dilated cardiomyopathy should receive treatment with an ACE inhibitor.”

Mike Martin, DVC, MRCVS

ACE inhibitors act on the RAAS by blocking the production of angiotensin II. Benefits of ACE inhibitors include: vasodilation, less retention of sodium and water (by blocking aldosterone), slowing cardiac remodelling and hypertrophy, prevention of degenerative renal changes.

The overall effect is to reduce the workload on the heart and to make it more efficient. ACE inhibitors have been shown to improve quality of life and life expectancy and are considered the gold standard treatment in human and canine heart disease.

ACE inhibitors currently licensed for veterinary use include:

• Fortekor® (benazepril hydrochloride)
• Enalapril maleate
• Ramipril
• Imidapril hydrochloride

ACE inhibitors are one of the most investigated classes of therapy in veterinary medicine and there is strong (Class A) evidence of their benefit in terms of quality of life and survival.

Diuretics

Fluid build-up in the lungs (oedema) and other parts of the body is a major problem in congestive heart failure, and can be life threatening. Diuretics remove excessive fluid build-up by causing loss of water and sodium via the kidneys. Diuretics can be lifesaving if the dog has severe pulmonary oedema, but they activate the RAAS, therefore the dose is often adjusted to the lowest effective dose.

The side effects of diuretics include dehydration, lethargy and reduced appetite (due to low blood pressure), excessive thirst (polydipsia) and urination (polyuria) and loss of electrolytes (for example, potassium). It is therefore important to monitor electrolytes and kidney function during treatment and to use the lowest effective dose. The most commonly used diuretic is frusemide. This can be administered orally or by injection, and is given 1-3 times daily.

Other diuretics can be used in combination with frusemide, for example, spironolactone and hydrochlorothiazide. Spironolactone is an aldosterone antagonist and has additional benefits (such as reduced cardiac remodelling) over and above its diuretic effects. ACE inhibitors and diuretics are essential therapy for congestive heart failure.

It is important to note that any dog receiving a diuretic should always be on an ACE inhibitor at the same time, in order to block the diuretic-induced activation of the RAAS.

Positive inotropes/inodilators

Positive inotropes increase the contractility of the heart, i.e. they make it beat more powerfully. They are used where there is intrinsic heart muscle weakness, such as in dilated cardiomyopathy.

In dogs with normal heart muscle function, like in the earlier stages of degenerative mitral valve disease, they may make regurgitation into the left atrium worse. The most commonly used positive inotropes are pimobendan (an inodilator) and digoxin (mostly used to slow the heart rate – it is not a good inotrope). Pimobendan works by increasing the heart’s sensitivity to calcium. This results in an increase in myocardial contractility without increasing energy requirements. It also has some vasodilating effect. It does not block the RAAS.

ACVIM treatment guidelines

The American College of Veterinary Internal Medicine (ACVIM) has provided the following guidelines for treatment of heart disease patients:

Diuretics

Fluid build-up (oedema) in the lungs and other parts of the body is a major problem in congestive heart failure, and can be life threatening. Diuretics remove oedema by causing loss of water and sodium via the kidneys, and are therefore essential therapy for CHF. Diuretics can be lifesaving if the dog has severe pulmonary oedema, but as they reduce blood volume and thus blood pressure, they activate the RAAS. The side effects of diuretics include dehydration, lethargy and reduced appetite (due to low blood pressure), excessive thirst (polydipsia) and urination (polyuria) and loss of electrolytes (for example, potassium). It is therefore important to monitor electrolytes and kidney function during treatment and to use the lowest effective dose. The most commonly used diuretic is furosemide. This can be administered orally or by injection, and is usually given 2-3 times daily.

Other diuretics such as hydrochlorothiazide can be used in combination with furosemide, in refractory cases.

It is important to note that any dog receiving a diuretic should be on an ACE inhibitor at the same time, in order to block the diuretic-induced activation of the RAAS.

Positive inotropes/inodilators

Positive inotropes increase the contractility of the heart, i.e. they make it beat more powerfully. They are beneficial where there is systolic dysfunction.

The most commonly used positive inotropes are pimobendan (an inodilator) and digoxin (mostly used to slow the heart rate – it is not a strong inotrope). Pimobendan works by increasing the heart’s sensitivity to calcium. This results in an increase in myocardial contractility without increasing energy requirements. It also has vasodilating effects, but it does not block the RAAS.

Aldosterone antagonists

Spironolactone is an aldosterone antagonist and has beneficial effects on cardiac remodelling/fibrosis as well as its potassium-sparing diuretic effects.

ACVIM treatment guidelines

The American College of Veterinary Internal Medicine (ACVIM) Consensus Panel has provided the following guidelines for treatment of heart disease patients: