Page 175 - Small Animal Internal Medicine, 6th Edition

CHAPTER 7 Myocardial Diseases of the Dog 147

electrolyte and acid-base abnormalities are common should be carefully monitored in such animals. Any vaso-
sequelae. Hypokalemia is often treated with addition of the dilator must be used cautiously in dogs with a low cardiac
VetBooks.ir potassium-sparing diuretic spironolactone, although dietary reserve because of the increased potential for hypotension.
Hydralazine is more likely to precipitate hypotension and
potassium supplementation can also be considered if needed.
An ACEI should be used in the chronic treatment of
activation. Therapy is initiated at a low dose; if this is well
DCM and may attenuate progressive ventricular dilation and therefore reflex tachycardia and further neurohormonal
secondary mitral regurgitation. ACEIs have a positive effect tolerated (monitored with blood pressure measurement), the
on survival in patients with myocardial failure. These drugs next dose is increased to a low maintenance level. Signs
minimize clinical signs and increase exercise tolerance. Enal- of worsening tachycardia, weakened pulses, or lethargy can
april or benazepril are used most commonly, but other indicate the presence of hypotension.
ACEIs have similar effects. A number of other therapies might be useful in certain
Spironolactone is thought to be useful because of its dogs with DCM, although additional studies are necessary
aldosterone-antagonist properties as well as potential mild to define optimal recommendations. These include omega-3
diuretic effects. Aldosterone is known to promote cardiovas- fatty acids, L-carnitine (in dogs with low myocardial carni-
cular fibrosis and abnormal remodeling and, as such, con- tine concentrations), taurine (in dogs with low plasma con-
tributes to the progression of cardiac disease. Spironolactone centrations), long-term β-blocker therapy, or possibly others
is therefore advocated as adjunctive therapy in combination (see Chapter 3, p. 72). Advanced therapeutics, including
with an ACEI, furosemide, and pimobendan for chronic gene transfer and stem cell transplantation, are under experi-
DCM therapy. mental investigation but are not currently recommended in
For dogs with AF, a combination of oral diltiazem and clinical settings. Biventricular pacing to better synchronize
oral digoxin is advocated for long-term control of ventricular ventricular contraction has improved clinical status in people
response rate (see Table 4.2). Digoxin is a weak positive with myocardial dysfunction, but there is little clinical expe-
inotrope with neurohormonal modulating and antiarrhyth- rience with resynchronization therapy in dogs with DCM.
mic effects. Although pimobendan has largely replaced Monitoring
digoxin for oral inotropic support, digoxin still is indicated Owner education regarding the purpose, dosage, and
for heart rate control in AF and can be given in conjunction adverse effects of each drug used is important. Monitoring
with pimobendan. The recommended oral maintenance the dog’s resting respiratory (and heart) rate at home helps
dose of digoxin is 0.003 to 0.005 mg/kg PO q12h, or approxi- in assessing how well the CHF is controlled (see Chapter 3,
mately 0.125 mg total dose, PO, q12h for typical Dobermans p. 73). The time frame for reevaluation visits depends on the
(~40 kg). Toxicity is uncommon at these low doses, but patient’s status. Recheck visits once or twice a week may be
monitoring is still recommended due to the narrow thera- necessary initially. Dogs with stable heart failure can be
peutic index of this drug. Serum digoxin concentration rechecked every 2 or 3 months. Current medications, diet,
should be measured 7 to 10 days after digoxin therapy is and any owner concerns should be reviewed. Patient activity
initiated or the dose is changed; serum samples should be level, appetite, and attitude, along with renal values and elec-
drawn 6 to 8 hours after the last oral dose (see p. 70). Diltia- trolytes, heart rate and rhythm, thoracic imaging to assess
zem is a cardiac-specific calcium-channel blocker that is very pulmonary edema or pleural effusion, blood pressure, body
effective at slowing AV nodal conduction and thus decreas- weight, and other appropriate factors should be evaluated
ing heart rate in AF. Because of its negative inotropic effect, and therapy adjusted as needed.
a low initial dose and gradual dosage titration to effect or a
maximum recommended level is advised. Diltiazem is avail- Prognosis
able in several dose formulations; typically, an extended- The prognosis for dogs with DCM is generally guarded. In
release formulation allowing twice daily dosing (Dilitazem Doberman Pinschers, occult disease tends to develop at 3
ER/XR, Dilacor) is used for chronic administration. to 6 years of age, with ventricular arrhythmias preceding
Heart rate control in dogs with AF is important, but spe- echocardiographic changes. Onset of CHF generally occurs
cific goals for rate control have yet to be firmly established. within 2 to 3 years, although addition of pimobendan delays
A maximum ventricular rate of 140 beats/min in the hospital disease progression. Sudden death occurs in about 20% to
(i.e., stressful) setting is the recommended target; lower heart 40% of affected Doberman Pinschers and may occur in the
rates (e.g., ≈100 beats/min or less) are expected at home. occult stage before CHF is present. Doberman Pinschers
Because heart rate assessment by auscultation or chest palpa- and Great Danes appear to have a worse prognosis than
tion in dogs with AF often is highly inaccurate, an ECG other breeds, with younger age of onset and more rapid
recording is recommended. Femoral pulses should never be progression of disease. Certain breeds, including Irish Wolf-
used to assess heart rate in the presence of AF. At-home rate hounds and Cocker Spaniels, have more protracted preclini-
assessment with Holter monitors or smartphone-based ECG cal periods and may live for years with mild to moderate
applications may assist with dose adjustment. LV systolic dysfunction. Prognosis following an episode
Additional afterload reduction with amlodipine or hydral- of CHF is poor. Median survival time with treatment is
azine (see Table 3.3) could be useful as adjunct therapy for in the realm of 4 to 6 months. Negative prognostic indi-
dogs with refractory CHF, although arterial blood pressure cators include presence of pleural effusion, severity of LV