Radiographic Clues to Early Hypertension: What Vets Need to Know

VRU 2022

Merrilee Holland, Judith Hudson, Erik Hofmeister

Background
Systemic hypertension (SH) in dogs can cause target organ damage (TOD), including changes in the thoracic aorta. In humans, SH-associated aortic dilation precedes aneurysm formation and manifests radiographically. This study aimed to determine whether thoracic radiographs could detect aortic remodeling in dogs with SH and whether trained reviewers could reliably identify these changes.

Methods
A retrospective, cross-sectional study compared thoracic radiographs of 145 dogs with confirmed SH (systolic blood pressure >150 mmHg) and 21 normotensive controls. Three blinded reviewers, trained using a custom module, evaluated radiographic signs of aortic remodeling. Aortic shape and size were analyzed across orthogonal projections, and a ratio of thoracic cavity width to aortic-tracheal distance (TC/AT) was calculated to normalize for body size.

Results
Blinded reviewers achieved 74% agreement (Fleiss’ Kappa = 0.50), indicating moderate consistency. Aortic changes included enlargement of the ascending and proximal descending aorta and lateral bowing of the aortic arch (the "aortic knob"). The TC/AT ratio was significantly lower in SH dogs (median 3.4) versus controls (median 4.1). Even experienced reviewers misclassified some SH cases as normal. Only 52% of dogs with SH received treatment.

Limitations
Limitations included retrospective design, lack of histopathology, and inconsistent blood pressure data pre-treatment. Radiographic measurements were potentially affected by obliquity, and control numbers for TC/AT ratio analysis were low. Breed and conformational variations may also have introduced variability.

Conclusions
Radiographic identification of aortic remodeling, particularly the presence of an aortic knob and altered aortic proportions, can aid in early SH diagnosis in dogs. The authors propose recognizing these signs as TOD, encouraging earlier intervention and sustained treatment of SH to prevent cardiovascular complications.

Bulging and disparity in the size of the ascending aorta, aortic arch, and proximal descending thoracic aorta compared to the descending thoracic aorta (arrows) cranial to the diaphragm on left lateral radiographs were a sign of SH in some dogs. A, A Labrador retriever with diabetes and systolic blood pressure (SBP) of 243 mm Hg. B, A Lhasa apso with a history of chronic renal disease and SBP of 220 mm Hg. C, A Greyhound presenting with osteosarcoma and SBP of 178 mm Hg that was treated with palladia®. Additionally, the aorta (arrows) is undulating

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