Paul R. Wotton, BVSc, PhD, DVC, MRCVS
There is some controversy about, and little 'evidence-based medicine' to support, many of the therapeutic approaches currently employed in treating heart disease and heart failure in cats. Case studies will be used to illustrate the following therapeutic principles.
Key considerations in planning a therapeutic regime are the major presenting clinical signs/ problems and prognostic factors such as:
The pathophysiological form of cardiac disease, as identified by echocardiography
Any underlying cause if identified
Treatment of a primary or predisposing disease where present improves the prognosis, and it is possible that cardiac function may return to normal. The functional state of the ventricles determines whether inotropic support is indicated.
The treatment of cardiac failure can be considered under the following headings:
Management of underlying disease, e.g., hypertension, hyperthyroidism, taurine deficiency. (Other potential causes of myocardial dysfunction in cats include acromegaly, infiltrative diseases (e.g., lymphoma), myocarditis (viral?), ischaemia (e.g., embolic disease--may occur secondary to other forms of cardiomyopathy).)
Management of volume overload, oedema and effusions, e.g., diuresis, oxygen, angiotensin converting enzyme (ACE) inhibitors, nitrates, spironolactone, thoracocentesis.
Vasodilation and reduction of cardiac workload, e.g., ACE inhibitors, pimobendan, hydralazine/amlodipine, nitrates.
'Cardio-protection', e.g., ACE inhibitors, aldosterone antagonists, beta-blockers.
Improving diastolic function--this is indicated in situations such as hypertrophic cardiomyopathy (HCM), so this is of particular relevance in cats; e.g., beta blockade, diltiazem, ACE inhibitors.
Improving systolic function, e.g., pimobendan, digoxin, dobutamine.
Management of dysrhythmias, e.g., beta blockers, digoxin.
Management and/or prevention of thromboembolism, e.g., aspirin, clopidogrel, low molecular weight heparin (e.g., Fragmin), cyproheptadine, pimobendan.
Cardiovascular drugs are listed in Figure 1.
Previous thoughts on the treatment of myocardial disease in cats have been thrown somewhat into disarray by a large multicentre study of the treatment of feline heart failure associated with myocardial disease with predominantly diastolic dysfunction (published so far only in abstract form) headed by Phil Fox. A total of 118 cats with congestive heart failure were enrolled and randomised to receive one of the following:
Furosemide with placebo
Furosemide with atenolol
Furosemide with enalapril
Furosemide with diltiazem (slow-release preparation)
Interim results indicated that cats with atenolol had an increased risk of an adverse outcome (i.e., worsening heart failure) than cats receiving placebo, and cats with ACE inhibitor therapy had a slightly reduced risk of an adverse outcome. Diltiazem appeared to make little difference to placebo. These data indicate that we should be very cautious prescribing beta-blockers to cats until no longer in congestive heart failure and that the use of ACE inhibitors is preferable, even in the presence of dynamic left ventricular outflow tract obstruction. Many cardiologists, however, still use beta-blockers (usually atenolol), particularly for the obstructive form of hypertrophic cardiomyopathy (HCM), HOCM (i.e., HCM with dynamic outflow tract obstruction due to 'systolic anterior motion' (SAM) of the mitral valve) in cats that are not yet in, or that have been effectively treated for, congestive heart failure (CHF).
Figure 1. Selected cardiovascular drugs, formulations and doses.
ACE, angiotensin converting enzyme; cut., cutaneously; CRI, constant rate infusion; dil., dilute; SR, sustained-release preparation
|
Drug |
UK trade name1 |
Form |
Dose2 (mg/kg) |
|
Diuretics: |
|
Furosemide |
Frusedale; Frusecare; Dimazon (was Lasix) |
10, 40 mg 50 mg/ml |
Acute: 2-8 q2-6h orally, i.v.; Maint: 1-2 q8-12-24h |
|
Spironolactone |
Prilactone d |
|
1-2 q24-12h 3 |
|
Ace inhibitors: |
|
Benazepril |
Fortekor rc |
2.5, 5 mg |
0.25-0.5 q24h |
|
Other vasodilators: |
|
Glyceryl trinitrate |
Percutol h |
2% oint. |
1/8-1/4 inch cut. q6-8h c |
|
Pimobendan |
Vetmedin d |
1.25, 2.5, 5 mg |
0.1-0.3 q12h 4 |
|
Positive inotropes: |
|
Digoxin |
Lanoxin h |
62.5, 125, 250 mg |
1/2 x 62.5 mg/cat q24-48h c |
|
Dobutamine |
Dobutrex h |
12.5 mg/ml dil. to 25 mg/ml |
2-10 mg/kg/min i.v. CRI c |
|
Pimobendan |
See above |
|
|
|
Beta blockers 5: |
|
Atenolol |
Generic h; Tenormin h |
25, 50, 100 mg |
6.25-12.5 mg/cat q24h c |
|
Sotalol |
Beta-Cardone h |
40 mg |
0.5-2 q12h |
|
Calcium channel blockers: |
|
Amlodipine |
Istin h |
5 mg |
0.625-1.25 mg/cat q24h |
|
Diltiazem |
Hypercard c |
10 mg |
1.5-2.5 q8h |
|
Other antiarrhythmics: |
|
Atropine |
Atrocare |
0.6 mg/ml |
0.01-0.04 i.v., i.m., s.c. |
|
Digoxin |
See under positive inotropes |
|
|
|
Lignocaine/lidocaine
(without adrenaline) |
Generic h |
10, 20 mg/ml |
0.25-1 slow i.v. c then 10-40 mg/kg/min i.v. CRI c |
|
Bronchodilators: |
|
Terbutaline |
Bricanyl h |
1.5 mg/ml syrup |
0.3-1.25 mg/cat q12h |
|
Theophylline (SR) |
Corvental-D |
100, 200 mg |
10 c q12-24h |
|
Others: |
|
Aspirin |
Generic |
75, 300 mg |
5-25 q72h c |
|
Butorphanol |
Torbutrol |
1, 5, 10 mg 0.5, 10 mg/ml |
0.5-1 q6-12h 0.05-0.1 q6-12h s.c. |
|
Clopidogrel 6 |
Plavix |
75 mg |
(1/8-)1/4 x 75 mg/cat q24h |
|
Dalteparin |
Fragmin h |
100,000 IU/4 ml |
100 IU/kg q8-24h? s.c. |
|
Heparin |
Generic h |
1000-25,000 units/ml |
100-200 IU/kg i.v. then 100-300 IU/kg q8h s.c. 7 |
|
Methimazole |
Felimazole c |
5 mg |
5 mg/cat q12h |
|
Potassium gluconate |
Tumil K |
720 mg (3.1 mmol)/g |
2-6 mmol/cat/day c
0.2-0.5 mmol/kg q8h d |
|
Streptokinase |
Kabikinase, Streptase |
250,000, 750,000 and 1,500,000 IU/vial |
90000 IU/cat IV over 1h then 45000 IU/h IV CRI for 6-8h |
|
Taurine |
Pro-Taur; generic |
250, 500 mg |
250 mg/cat q12h |
|
Tissue plasminogen
activator (t-PA) |
Activase h |
1 mg/ml, 50, 100 mg vials |
0.25-1mg/kg/h, to a max. dose 1-10 mg/kg |
|
Warfarin |
Generic |
1, 3, 5 mg |
0.1-0.2 q24h 7 |
This table was first prepared for a specialist session at BSAVA Congress 2006 on treating heart failure in dogs and cats.
Products specific to dogs have been removed.1 The unmarked products are licensed for use in dogs and cats in the UK; however, many of these products are licensed for humansh only; clicensed for cats only; dlicensed for dogs only; rclicensed for renal disease in cats. 2 Doses are for dogs and cats unless otherwise stated: cusual cat dose; dusual dog dose. All doses are for oral administration and are mg/kg unless otherwise stated.3 Usually used as adjunct to other diuretics not as monotherapy; monitor renal function and electrolytes, especially potassium if used with ACE inhibitors. Administer with food.4 Should be given 30-60 minutes before a meal.5 Beta blocker doses should be titrated and should not be stopped abruptly.6 Used in combination with aspirin in cats at high risk of thromboembolism; the combination may increase risk of bleeding.7 Coagulation parameters should be monitored.
Please note: This table is for guidance only. Doses and evidence of efficacy may be based on anecdotal reports rather than peer-reviewed publications and adverse effects are possible. It is the responsibility of each individual veterinary surgeon to ensure that the drug/dose used is suitable for individual patients under their care, to obtain informed, written consent when using non-authorised products and to work within the prescribing cascade.
References
1. Fox PR. Evidence based approach to feline diastolic heart failure. Proceedings of the 21st ACVIM Forum, Charlotte, North Carolina, USA 2003; 74-76.
2. Fox PR. Prospective, double-blinded, Multicenter Evaluation of chronic therapies for feline diastolic heart failure: Interim analysis. Proceedings of the 21st ACVIM Forum, Charlotte, North Carolina, USA 2003; Abstract 78: 952.