When to include loop diuretics in treatment of veterinary cardiac patients?

Current guidelines suggest that diuretic treatment is indicated only in patients that are in congestive heart failure. Giving loop diuretics before that time carries the risk of dehydration, electrolyte imbalance, and undesirable RAAS activation, promoting sodium and water retention, as well as sympathetic stimulation, which can cause more rapid progression of heart disease.

Reliably diagnosing congestive heart failure can be challenging, and many primary care clinicians consider cough to be a sign of congestive heart failure. However, this is a very inconsistent and unreliable symptom when it comes to diagnosing left-sided congestive heart failure. Dogs can cough for many other reasons, while cats almost never cough due to cardiogenic pulmonary oedema.

Bronchomalacia and tracheal collapse, which predispose dogs to chronic cough, are common comorbidities in small dogs with myxomatous mitral valve disease. Cardiac enlargement is also likely to trigger cough in susceptible patients due to mechanical compression of the bronchial tree, activating cough receptors in the mainstem bronchi. However, many dogs with cardiogenic pulmonary oedema do not cough simply because there are no cough receptors in the lower respiratory airways, where fluid accumulation primarily occurs.

During clinical examination, clinicians should pay attention to the patient's breathing pattern and effort, as well as lung sounds, and utilise thoracic imaging whenever possible to diagnose left-sided congestive heart failure.

Sleeping respiratory rate is a very good way of monitoring cardiac patients and correlates well with pulmonary congestion. Sleeping respiratory rate should consistently be below 30 breaths per minute, but clinicians should keep in mind individual variations. For example, a sleeping respiratory rate of 25 breaths per minute may not be completely normal for very fit individuals that normally have a sleeping respiratory rate below 15 breaths per minute.

Sometimes it is difficult to draw a line, and things are often not black and white. Occasionally, patients that appear asymptomatic may have echocardiographic findings that are suggestive of early left-sided congestive heart failure. For patients who seem in imminent danger of developing left-sided congestive heart failure in the near future, it may be prudent to dispense a low dose of a loop diuretic for the owner to start when needed. Alternatively, one may consider starting such a patient on a low dose of a loop diuretic with close monitoring (e.g. furosemide 1 mg/kg twice daily). This may be a useful strategy for avoiding an emergency visit to an out of hours service provider in the middle of the night with a dyspnoeic animal.

When it comes to loop diuretics, it is important to remember that furosemide, the most commonly used first -line loop diuretic in veterinary patients, is a short acting drug and is therefore inappropriate for once daily dosing. Torasemide, a second generation loop diuretic, has different pharmacodynamic properties and a much longer duration of action, which is allowing once daily administration. Torasemide is approximately 20 times more potent than furosemide, has better bioavailability, and has been shown to have some beneficial antifibrotic effects.

In conclusion, it seems best to tailor treatment to each patient individually, taking all clinical findings into consideration while following current guidelines to ensure the best possible clinical outcomes.