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Signalment, presentation, history and clinical examination
A nine-month-old female neutered Miniature Schnauzer was referred for the investigation of intermittent collapse episodes of two months' duration. The episodes occurred on excitement and exertion and lasted only seconds, with a rapid and complete recovery.
On presentation, the dog was bright, alert and responsive. Its bodyweight was 8·4 kg and the body condition score was 4/9. Pulses were synchronous and normokinetic. Its heart rate was 120 beats per minute (bpm) and the rhythm was regular. A grade V/VI ejection quality murmur was audible with a point of maximum intensity over the left heart base (at the third to fourth intercostal space), which also radiated to the right heart base. Thoracic auscultation was otherwise unremarkable, with a normal respiratory rate and effort. Abdominal palpation was unremarkable. Neurological examination was within normal limits.
Problems to consider
▪ Collapse episodes on excitement/exertion
▪ Grade V/VI left basilar systolic murmur
Reasons for collapse
Episodes of collapse (loss of postural tone) were considered most likely to be consistent with a syncopal event, given their transient nature, association with periods of high sympathetic drive or exertion and the absence of seizure-like activity (eg, mouth-champing or tonic–clonic activity). Given the clinical finding of a grade V/VI left basilar systolic murmur, the most likely differential diagnosis for syncope was considered to be an outflow tract obstruction (ie, an aortic or pulmonic stenosis). Alternative causes for syncope or neurological causes for collapse could not be completely excluded.
Echocardiography, performed with the dog conscious, revealed subjective concentric right ventricular hypertrophy (RVH) and flattening of the interventricular septum, suggestive of elevated right ventricle (RV) filling pressures. Tricuspid valve morphology appeared normal, with mild tricuspid regurgitation. The pulmonic valve (PV) leaflets appeared thickened and fused, with doming of the leaflets during systole. An estimation of the pulmonic stenosis pressure gradient (PG) was achieved via Doppler-derived measurement of the …
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