While your veterinary cardiology courses have likely covered a wide variety of cardiac diseases, both common and uncommon, there is one presentation that you are almost guaranteed to see in your first year as a new grad: a dog in congestive heart failure (CHF).
If you are comfortable with this, you will be able to handle the overwhelming majority of what’s expected of a general practice vet!
While your treatment approach may vary a bit, depending on whether the dog is presenting in acute, severe distress or receiving maintenance therapy, there are three basic medications that are used in the treatment of canine CHF.
Furosemide, or Lasix®, is the most commonly-used diuretic in small animal patients with congestive heart failure (CHF). It is a potent diuretic, acting on the Loop of Henle to remove excess fluid from the body.
Furosemide can be administered orally or parenterally. It has a wide dosing range, and your starting dose will depend on your patient’s condition. If your patient presents in a crisis, initial doses of 2-4 mg/kg IV are commonly used (in conjunction with oxygen therapy). A response to furosemide should be seen within an hour; if the patient is still dyspneic, you may need to administer higher doses, or start a furosemide CRI. Once the acute crisis is managed, dogs are often discharged on a dose of 2 mg/kg q8-12hrs, then gradually decreased to a maintenance dose of 1 mg/kg q12hrs.
Side effects of furosemide include nausea, vomiting, and dehydration (with azotemia). Hypochloremia, hypokalemia, and hyperglycemia may also occur. Patients receiving furosemide require frequent blood work monitoring, because treatment often requires a bit of a balancing act between controlling CHF and minimizing azotemia.
Pimobendan, or Vetmedin®, is a positive inotrope and arteriodilator that is labeled for the treatment of CHF in dogs. It can also be used off-label in cats.
Pimobendan is administered by mouth twice daily, on an empty stomach. The labeled dose in dogs is 0.5 mg/kg/day, divided into two doses. This medication should be started as soon as possible after the diagnosis of CHF, and dogs remain on this medication long-term.
Side effects include inappetance, lethargy, and diarrhea. In the case of an accidental overdose, hypotension may also be observed.
Enalapril, or Enacard®, is an ACE inhibitor that is often used to manage CHF in dogs and cats. Benazepril is another commonly-used ACE inhibitor in the United States, which may be substituted for enalapril in some situations. ACE inhibitors reduce circulating levels of angiotensin II (a vasoconstrictor) and aldosterone (which promotes sodium retention).
Enalapril is an oral medication. It is typically started at a dose of 0.5 mg/kg once daily, but may be increased to twice daily if needed. In many cases, once daily dosing is sufficient early in the course of disease, but dosing is increased to twice daily as the patient’s CHF becomes more advanced.
Side effects of enalapril include inappetance, vomiting, and diarrhea. Enalapril can exacerbate pre-existing kidney disease and, rarely, the combination of enalapril and furosemide can result in acute renal failure. Patients receiving enalapril require regular blood work monitoring.
Consider avoiding enalapril in pets with pre-existing renal disease, and instead using benazepril. While enalapril is eliminated entirely by the kidneys, benazepril is cleared by both the liver and kidneys.
Monitoring CHF Patients
In most cases, you will schedule your patient’s first recheck for one week after beginning treatment (or one week after discharge, if the pet was hospitalized). At that first recheck, thoracic radiographs and blood work are recommended. Potassium supplementation may be needed, if the patient is hypokalemic.
If your patient is doing well at the one-week recheck, schedule a recheck in approximately one month. If the patient’s exam, radiograph, and lab tests still look good at the one-month recheck, you can decrease your rechecks to every three months (unless the pet develops problems and needs to be seen sooner).
While the number of cardiac medications available can seem overwhelming, focusing on the three medications commonly used to treat CHF will prepare you to address most cardiology patients that you will encounter in your first job as a general practice vet.