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22-11-2011 | Article

Ultrasound valuable for diagnosing feline heart disease


Free abstract

MedWire News: Arrhythmia and gallop sounds are the reliable clinical signs for diagnosing heart disease in cats, UK researchers say.

Heart rate, by contrast, is unreliable for diagnosing heart disease whereas ultrasound measures can help distinguish between cardiac and respiratory etiologies, the team writes in the Journal of Small Animal Practice.

Jo Dukes-McEwan and Sarah Smith, specialists in veterinary cardiology at the University of Liverpool Small Animal Teaching Hospital, sought to describe the clinical and echocardiographic characteristics of feline heart disease in general practice.

They prospectively recruited 151 consecutive cats seen at a small-animal hospital over an 18-month period for investigation of cardiac or respiratory disease. The cats represented 13 breeds (predominantly domestic short- or long-hair) and the average age was 9 years.

The final diagnosis was heart disease in 103 cats. This included 77 with primary acquired disease (mainly hypertrophic cardiomyopathy), 16 with heart disease secondary to other causes, and 10 cases with congenital disease.

The remaining diagnoses included respiratory disease in 19 cats and no abnormalities in 29 cats.

The researchers then classified the animals into three groups: group 1 (no heart disease); group 2 (heart disease with no clinical signs); and group 3 (symptomatic heart disease).

A comparison of the groups found that cats in group 3 tended to be significantly older than cats in groups 1 and 2 (14.0 vs 9.0 and 8.5 years, respectively), whereas there were no differences in terms of gender.

Median heart rate was signficantly lower in groups 1 and 3 than in group 2 (180 and 185 vs 200 bpm) but the researchers say this difference may have been confounded by "outliers."

On auscultation, heart murmurs were significantly more prevalent in group 2 cats than in groups 1 or 3 (86 vs 42 and 48%) while gallop sounds were more common in group 3 than in groups 2 or 1 (48 vs 10 and 0%). Arrhythmia was most common in group 3, intermediate in group 2, and least common in group 1 (48.0, 24.0, and 6.3%).

Finally, cats in group 1 had the highest frequent of cough, followed by group 2 and group 3 cats (27, 12, and 5%).

Ultrasound also revealed some differences between the groups, most notably in left atrial diameter, which was greatest in group 3, intermediate in group 2, and lowest in group 1 (18.5, 15.5, and 12.0 mm).

Finally, Dukes-McEwan and Smith used receiver-operating characteristic curves to test the value of echocardiographic parameters for discriminating between cardiac and respiratory disease.

They found that a left atrial diameter cutoff of 16.5 mm had a sensitivity and specificity of 87% for diagnosing heart failure in cats with dyspnea. Similarly, a left atrial:aortic ratio cutoff of 1.5 had a sensitivity of 81% and specificity of 79% for the same endpoint.

The researchers conclude: "Cats with dyspnoea due to heart failure are unlikely to cough, may not have a murmur and in some cases may have a depressed heart rate. Arrythmia is a significant sign of heart disease, as are diastolic gallops.

"A brief ultrasound examination, minimally stressful for the cat, may provide highly sensitive and specific information to identify heart failure."

By Joanna Lyford