January 1, 2017Open Access

Reference intervals and allometric scaling of two-dimensional echocardiographic measurements in 150 healthy cats

Q: What is the clinical evidence from this study?

Study design: Observational. Population: Healthy (n=150). Intervention: Allometric scaling vs. Conventional reference intervals. Primary outcome: Effect of body weight on 2D echocardiographic variables (p=<0.05).

Key Result

Body weight had a significant independent effect on two-dimensional echocardiographic variables in healthy cats, demonstrating that allometric scaling and body weight-based 95% prediction intervals should be preferred over conventional reference intervals.

Study Design

Type

Observational (n=150)

Multicenter

PICO

Population

Healthy (n=150)

Intervention / Comparator

Allometric scaling vs Conventional reference intervals

Primary Outcome

Effect of body weight on 2D echocardiographic variables, p=<0.05

Main Result

p-value: p=<0.05

Limitations

Relatively low number of cats, particularly when partitioning into body weight groups
No definitive test was applied to determine if cats were free of myocardial disease or had occult HCM
Limited age range covered
Potential selection bias due to retrospective design
Suboptimal image quality in some cats
Images acquired by different observers with varying experience levels
Body condition score and heart rate were not considered

Abstract

The objective of the study was to evaluate the effects of body weight (BW), breed, and sex on two-dimensional (2D) echocardiographic measures, reference ranges, and prediction intervals using allometrically-scaled data of left atrial (LA) and left ventricular (LV) size and LV wall thickness in healthy cats. Study type was retrospective, observational, and clinical cohort. 150 healthy cats were enrolled and 2D echocardiograms analyzed. LA diameter, LV wall thickness, and LV dimension were quantified using three different imaging views. The effect of BW, breed, sex, age, and interaction (BW*sex) on echocardiographic variables was assessed using univariate and multivariate regression and linear mixed model analysis. Standard (using raw data) and allometrically scaled (Y=a × Mb) reference intervals and prediction intervals were determined. BW had a significant (P6 kg) and smaller (<3 kg) cats. A clinically relevant difference between thickness of the interventricular septum (IVS) and dimension of the LV posterior wall (LVPW) was identified. In conclusion, allometric scaling and BW-based 95% prediction intervals should be preferred over conventional 2D echocardiographic reference intervals in cats, in particular in small and large cats. These results are particularly relevant to screening examinations for feline hypertrophic cardiomyopathy.

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