Radiographic quantification of left atrial size in dogs with myxomatous mitral valve disease

Abstract

Background: In the absence of echocardiography, identification of cardiomegaly via thoracic radiography is a necessary criterion for classification of disease severity in dogs with myxomatous mitral valve disease (MMVD).

Objective: Modified-vertebral left atrial size (M-VLAS) facilitates objective radiographic assessment of the left atrium (LA) in 2 dimensions and identifies LA enlargement more accurately than existing methods.

Animals: Sixty-four dogs with various stages of MMVD and 6 control healthy dogs.

Methods: Retrospective case-control study. Medical records were searched for dogs with varying severity of MMVD. Modified-vertebral left atrial size, vertebral left atrial size (VLAS), vertebral heart size (VHS), and radiographic left atrial dimension (RLAD) were measured from thoracic radiographs and compared with echocardiographically derived measurements.

Results: Positive correlation to LA/Ao was identified for M-VLAS (r = 0.77, P < .001), VLAS (r = 0.76, P < .001), RLAD (r = 0.75, P < .001), and VHS (r = 0.67, P < .001). Receiver operating characteristic analyzes provided an area under the curve of 0.97 (95% CI, 0.94-1.00) for M-VLAS, which was superior to VHS (0.90, 95% CI, 0.94-1.00, P = .03) in identifying dogs with LA/Ao ≥1.6. A cut-off value of ≥3.4 vertebrae using M-VLAS provided 92.7% sensitivity and 93.1% specificity in predicting LA enlargement.

Conclusions and clinical importance: M-VLAS, which is superior to VHS, offers an accurate and repeatable way to radiographically identify LA enlargement in dogs with MMVD.

Keywords: left atrial enlargement; modified-vertebral left atrial size; pimobendan; radiographic left atrial dimension; vertebral heart size; vertebral left atrial size.

FIGURE 1

Measurements of M‐VLAS, VLAS, VHS, and RLAD demonstrated on the same right lateral inspiratory radiograph of a dog with stage B2 MMVD. All methods take their respective measurements from the cranial edge of the T4 vertebral body extending caudally, parallel to the vertebral column, rounded to the nearest 0.1 vertebrae. A. MVLAS—an initial line (yellow)—is drawn from the centre of the most ventral aspect of the carina to the intersection between the most caudal aspect of the left atrium and the dorsal border of the caudal vena cava. A second additional line (red) is then drawn from the most distal border of the left atrium towards the first line, intersecting it perpendicularly. Two separate straight lines corresponding to the lengths of the first 2 lines (yellow + red) were then drawn from the cranial edge of the T4 vertebral body extending in a caudal direction, ventral and parallel to the vertebral canal. The M‐VLAS for this dog is 2.2 + 1.4 = 3.6 vertebrae (v). (Note: the first value being the VLAS.) B. Vertebral left atrial size (VLAS = 2.2v)—yellow line C. Vertebral heart score (VHS = 5.7 + 4.6 = 10.3v), vertical axis—thick white line; horizontal axis—thin white line. D. Radiographic left atrial dimension (RLAD = 2.0v)—dashed white lines represent the VHS vertical and horizontal axes, constituting the foundation for the RLAD measurement (green line), which bisects the VHS intersection. Note the horizontal axis is always set at the level extending between the cranial cardiac silhouette and the dorsal border of the caudal vena cava for the RLAD measurement, whereas the original VHS method ¹⁵ places the horizontal axis at the widest cardiac width in the central third of the cardiac silhouette regardless of where the caudal vena cava inserts

FIGURE 2

Receiver operating characteristic (ROC) curves of M‐VLAS, VLAS, VHS, and RLAD measured in 29 dogs with LA/Ao < 1.6, and 41 dogs with LA/Ao ≥1.6. Significant difference in AUC was observed between M‐VLAS (AUC 0.97, 95% CI 0.90‐1.00) and VHS (AUC 0.90, 95% CI 0.80‐0.96) (P = .03). Blue solid—M‐VLAS, green dashed—VLAS, orange dotted—VHS, and black dot‐dashed—RLAD