# Acute Effect of Furosemide on Left Atrium Size in Cats with Acute Left-Sided Congestive Heart Failure

## TL;DR

This study shows that furosemide, a diuretic, quickly reduces left atrium size and breathing rate in cats with heart failure, which could lead to misdiagnosis if not accounted for.

## Contribution

The study is the first to systematically investigate furosemide's acute effect on left atrium size in cats with heart failure.

## Key findings

- Furosemide significantly reduced left atrial size and respiratory rate within three hours in cats with heart failure.
- Normalization of left atrium size occurred in 32% of cats, and respiratory rate in 50%.
- Prior furosemide treatment may lead to underestimation or absence of echocardiographic signs of heart failure.

## Abstract

Cats with heart failure often struggle to breathe because fluid builds up in or around their lungs. Because breathing difficulties can arise from several conditions, it is essential to find out the underlying cause. For this, veterinarians often use ultrasound to measure the size of the left atrium, a chamber of the heart, to help diagnose heart failure and choose appropriate treatment. Furosemide, a commonly used diuretic medication, is given to remove excess fluid from the body and with that ease breathing, but its direct effect on heart size in cats has not been studied yet. Some dyspneic cats are referred after receiving high doses of furosemide by the referring veterinarian without prior left atrium size measurements. If furosemide significantly reduced left atrium size, it could possibly lead to misdiagnosis and wrong treatment. In this study, we examined 25 cats with sudden breathing difficulties caused by heart failure. We measured the size of the left atrium and the breathing rate before diuretic treatment, and repeated this three hours after furosemide administration. We found that furosemide quickly reduced both the breathing rate and left atrial size. This study shows that while furosemide provides rapid relief, echocardiographic evidence of heart failure may be absent or underestimated, if the cat had already received diuretics before referral. Our results highlight the importance of careful history taking, especially in cats that may already have been treated with diuretics before referral.

Left-sided congestive heart failure (CHF) is a common cause of acute respiratory distress in cats, and echocardiographic assessment of left atrial (LA) size is an important test to differentiate it from respiratory diseases that cause similar clinical signs. Furosemide, a potent loop diuretic, is the first-line therapy for cardiogenic pulmonary edema, but its effect on LA size has not been systematically investigated in cats. Some dyspneic cats are referred after having received high doses of furosemide by the referring veterinarian without prior point-of-care ultrasound (POCUS). This can make the diagnosis of CHF challenging. If furosemide significantly reduces left atrial size, it could potentially lead to misdiagnosis, by erroneously categorizing these cats as not having CHF. This prospective, observational multicenter study enrolled 25 cats with acute left-sided CHF. Point-of-care ultrasound was used to assess LA to aortic ratio (LA:Ao) and maximal LA diameter (LAD) at admission and three hours after furosemide administration. Significant reductions were observed in LA:Ao (2.48 ± 0.35 to 2.17 ± 0.40; p < 0.001), LAD (21.0 ± 2.8 mm to 18.4 ± 3.2 mm; p < 0.001), and respiratory rate (64 ± 30 to 40 ± 14 breaths/min; p < 0.001). Normalization of respiratory rate occurred in 50% of cats, while normalization of maximum LAD occurred in 32%. One cat achieved normalization of LA:Ao. We found that furosemide induced rapid reduction in LA size and respiratory rate in cats with left-sided CHF. Clinicians should be aware that severe LA dilation can be absent in referred dyspneic cats that had already received furosemide.