Congenital ventricular outflow tract obstructions in Boxer dogs: Results of a 17-year cardiovascular breed screening program in France (3126 dogs)

Abstract

Introduction: Ventricular outflow tract obstructions including aortic (AS) and pulmonic stenosis (PS) are the most common canine congenital heart diseases, with Boxer dogs being predominantly affected. This has led to the French Boxer club adopting a mandatory national control program against AS and PS. The objective of this retrospective study was to analyze the results of 17 years of this cardiovascular breed screening program (2005-2021).

Materials and methods: The records of untreated and non-anesthetized adult Boxer dogs screened between 2005 and 2021 were retrospectively reviewed. All dogs underwent physical examination and standard transthoracic echocardiography with concomitant ECG tracing. All examinations were reviewed by one single board-certified specialist in cardiology.

Results: Out of the 3126 dogs screened during the study period, 3001 dogs (female:male sex ratio = 2.2, median age [IQR] = 1.6 years [1.2-2.1]) were recruited for data analysis. A total of 218 operators were involved in the screening program. For most Boxer dogs (i.e., 93.8% for AS and 94.5% for PS), a single examination was required to obtain a definitive cardiac status, although most operators were non-specialist general practitioners. A left basilar systolic heart murmur was detected in all dogs with AS and PS, but also in 7.4% dogs free of heart diseases. A significantly higher proportion of the latter was detected when operators were board-certified specialists (P<0.001). Lastly, when comparing the start and the end of the breeding program, among dogs diagnosed with AS and PS (n = 364) in a French referral cardiology center, Boxer went from the 1st affected breed by AS to the 3rd, and from the 3rd affected breed by PS to the 6th.

Conclusion: This 17-year screening program has experienced a strong involvement of veterinarians, breeders, and owners throughout France. This may have contributed to reduce AS and PS prevalence in Boxer dogs at the studied referral cardiology center.

Fig 1. Representative continuous-wave Doppler echocardiographic view of a Boxer dog with severe congenital aortic stenosis showing an increased peak systolic aortic flow velocity recorded from the left apical 5-chamber view (peak systolic trans-stenotic pressure gradient (ΔP) = 82 mmHg).

Fig 2. Geographical distribution of echocardiographic examinations (n = 3260) performed in 218 screening veterinary centres on 2995 Boxer dogs for which information was available (i.e., a total of 3269 echocardiographic examinations were performed on 3001 Boxer dogs, and for 9 of which information regarding the veterinary centre location was lacking).

Map of France from the Institut National de l’Information Géographique et Forestière, France (https://ign.fr/institut/ressources-pedagogiques).