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

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; <i>p</i> < 0.001), LAD (21.0 ± 2.8 mm to 18.4 ± 3.2 mm; <i>p</i> < 0.001), and respiratory rate (64 ± 30 to 40 ± 14 breaths/min; <i>p</i> < 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.