VLAS provides an objective measurement of left atrial size on thoracic radiographs and is a reliable predictor of left atrial enlargement in dogs with MMVD.4,9 Although echocardiography remains the gold standard for diagnosing cardiac chamber enlargement, it may not be an option due to pet owner financial limitations, lack of patient cooperation, and/or clinician inexperience performing and interpreting echocardiography. In contrast, thoracic radiography is less expensive, more readily available, and more easily interpreted by clinicians.
Due to individual variability among dogs and lack of breed-specific reference ranges, VLAS should be used with clinical examination findings (eg, presence of murmur, typical signalment [ie, small breed, middle aged or senior]), other radiographic diagnostic findings (eg, chamber enlargement patterns), or additional imaging modalities (eg, thoracic-focused point-of-care ultrasonography, echocardiography) to diagnose MMVD.
Studies including healthy dogs and dogs with stage B1 to D MMVD found positive correlation among VLAS and LVIDDN, VHS, and LA:Ao ratio, suggesting VLAS is an indicator of cardiac remodeling and left atrial enlargement.4,5,8,10 In one study of dogs with suspected or diagnosed cardiovascular disease, VLAS was a more specific indicator of left atrial enlargement than increased VHS.3 Another study, however, found VLAS did not significantly improve detection of left atrial enlargement compared with VHS, and there was a low correlation between VLAS and echocardiographic LA:Ao ratio.11 This discrepancy may be due to differences in patient populations—only dogs with preclinical MMVD (stage B1 and B2) were investigated in the latter study.
VLAS increases based on severity of MMVD and decreases after treatment (alongside a decrease in VHS, LA:Ao ratio, and LVIDDN).10 VLAS ≥2.8 is highly specific for dogs with LA:Ao ratio ≥1.6 and therefore can help differentiate stage B1 MMVD from stage B2; VLAS 2.5 to 2.8 can help identify dogs that may benefit from echocardiography to determine whether they have reached stage B2.5,11