Feasibility and findings of different radiographic methods in diagnosing canine heartworm disease

Heartworm disease (HWD) represents the pathological consequences of heartworm (HW) (Dirofilaria immitis) infection on different organs and organ systems, primarily the lungs and heart. Radiography can objectively assess the severity of cardiopulmonary disease secondary to HW infection. However, interpreting dogs' radiographs can be quite challenging with respect to choosing an appropriate radiographic method.

The aim of this article is to review the published literature on radiographic methods, both subjective and objective, emphasizing their advantages and disadvantages. In order to define the feasibility and findings of the used radiographic methods, radiographs (laterolateral-LL and dorsoventral-DV) of dogs (N = 40) naturally infected with HWD were retrospectively analysed.

Subjective radiographic assessment included all parameters of abnormal lung patterns and right-sided cardiomegaly in HWD. Objective methods used for the assessment of cardiac size and shape were: modified vertebral heart size (modified VHS), manubrium heart score, sternebral heart size (SHS), thoracic inlet heart size, and cardiac sphericity index (CSI). Blood vessels were measured and expressed in relation to different skeletal structures or the aorta, depending on the blood vessels.

While the increased sternal contact, reversed D heart shape, and loss of pulmonary vessel margination were the most feasible subjective parameters, the modified VHS, SHS, and CSI (VHS-LL = 10.52 ± 0.97, VHS-DV = 10.79 ± 1.12; SHS-LL = 9.22 ± 1.04; SHS-DV = 9.49 ± 0.96; CSI-LL = 0.86 ± 0.08, CSI-DV = 0.75 ± 0.07) were the most feasible objective methods. The ratios of the right cranial lobar artery (RCrLA) to the fourth thoracic vertebra (T4) and the fourth rib (4.r) were the most feasible blood vessel measurements (RCrLA/T4 = 0.27 ± 0.08, RCrLA/4.r = 0.89 ± 0.25). In 5% of the dogs, radiographs could only be assessed subjectively. The most prevalent subjective parameters were increased sternal cardiac contact (91.89%), reversed D heart shape (89.65%), RCaLA enlargement (86.67%), and loss of pulmonary vessel margination (84.21%). The main pulmonary artery enlargement in LL, and the areas of increased opacity that tend to coalesce, significantly changed after successful HWD therapy.

The most feasible and prevalent subjective parameters were the increased sternal contact, reversed D heart shape, and loss of pulmonary vessel margination. The most feasible objective methods were the modified VHS, SHS, and CSI.