Dario Costanza 1, Adelaide Greco 1, Diego Piantedosi 2, Erica Castiello 1, Pierpaolo Coluccia 1, Camilla Sangiuliano 1, Luigi Navas 2, Leonardo Meomartino 1
Background
While echocardiography is the gold standard for diagnosing cardiac disease, thoracic radiography remains crucial due to its accessibility and ability to assess concurrent thoracic conditions. Accurate radiographic assessment of cardiac silhouette size is essential, but existing methods like the Vertebral Heart Size (VHS) are limited by vertebral abnormalities. The Heart-to-Single Vertebra Ratio (HSVR), initially validated in dogs, was proposed as a simpler and potentially more reliable alternative. This study aimed to evaluate the HSVR's reliability and agreement with VHS in cats.
Methods
This retrospective, single-center study evaluated right-lateral thoracic radiographs from 101 cats obtained between 2019 and 2023. Exclusion criteria eliminated radiographs with thoracic spinal abnormalities, excessive lordosis, poor cardiac silhouette visualization, technical errors, and skeletal immaturity. HSVRs were calculated by dividing the sum of cardiac long and short axes by the length of each vertebra from T4 to T8. Three observers with varying experience levels performed measurements, including repeated sessions for intraobserver reliability. Agreement with VHS was analyzed using Lin’s concordance correlation coefficient (CCC), Bland–Altman plots, mean absolute error (MAE), and intraclass correlation coefficients (ICC).
Results
HSVRT6 demonstrated the highest agreement with VHS (CCC = 0.95; MAE = 0.14), with low bias and narrow limits of agreement. Other HSVRs (T4-T5, T7-T8) also showed moderate to substantial agreement. HSVRs displayed excellent interobserver (ICC ≥ 0.95) and good to excellent intraobserver agreement (ICC range 0.75–0.94), with higher interobserver reliability than VHS. The simplified calculation method of HSVR reduced measurement variability.
Limitations
The study was limited by the observers' high level of experience and frequent collaboration, potentially inflating agreement metrics. The sample predominantly comprised domestic short-hair cats, limiting breed diversity. The study also excluded cats under 12 months and those with thoracic or sternal abnormalities.
Conclusions
The HSVR is a reliable, rapid, and user-friendly method for assessing cardiac silhouette size in cats, with HSVRT6 offering the best concordance with VHS. HSVR’s simplicity and robustness against spinal anomalies suggest it as a suitable alternative to VHS, particularly in patients where traditional methods are compromised.
Representative right-lateral thoracic radiographic image (73 kVp; 3.2 mAs) of a domestic short-hair cat depicting the measurements ofthe length of every single vertebral body between T4 and T8, including the corresponding caudal intervertebral disc spaces (white and grey doubled-headed dotted arrows, respectively, labeled T4–T8). The cardiac long axis (LA; doubled-headed grey arrow) and short axis (SA; doubled-headed whitearrow) were measured as described by Litster and Buchanan [12]. In this method, the LA was traced from the ventral border of the carina to the cardiacapex, and the SA was traced perpendicular to LA at the point of the maximum width of the cardiac silhouette and then transposed ventrally to thecolumn starting from the cranial endplate of T4
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