Introduction

The Shih-Tzu is a brachycephalic breed that frequently suffers from respiratory distress. Chronic respiratory distress may cause elevated pulmonary arterial pressure. Pulmonary hypertension (PH) is known as a negative prognostic factor for degenerative mitral valvular disease (DMVD) in small breed dogs.

Objectives

The aim of this study was to compare the incidence and severity of PH among Shih-Tzus and other small breed dogs with DMVD.

Methods

Sixty-three client-owned small breed dogs (BW <10 Kg) affected with ACVIM stage B2 DMVD were included. A full physical examination, noninvasive blood pressure measurement, blood checkups, electrocardiographic and echocardiographic examination were carried out in all dogs. Echocardiographically, high tricuspid regurgitation (TR) velocity >2.5 m/s considered as PH. Dogs, except Shih-Tzus, with brachycephalic obstructive airway syndrome were excluded from this investigation. Dogs with right bundle branch block, tracheal collapse, and primary/secondary lung tumors, positive reaction for circulating antigens of Dirofilaria immitis, and pulmonary stenosis were also excluded from this investigation.

Results

The incidences of PH (TR >2.5 m/s) in Shih-Tzus, Maltese terriers, and other small breed dogs were 72% (13/18), 30% (6/20), and 28% (7/25), respectively (p=0.007). No significant differences in fractional shortening, LA/Ao (1.39±0.17, 1.45±0.16, 1.41±0.15) were found. However, TR peak velocity (2.73±0.98, 2.04±0.73, 2.23±0.87 m/s) was significantly higher in Shih-Tzus (p<0.04).

Conclusions

Higher incidence PH was found in Shih-Tzus, compared with other small breed dogs with Stage B2 DMVD. Further studies of skull pattern in long-term management of DMVD are warranted.