Changes

== Introduction ==

== Introduction ==

This is cardiovascular disease that is common in dogs and rare in cats and large animals.  

Pulmonic stenosis (PS) is one of the three most common congenital cardiac defects in dogs. It is much less common in cats, and is usually recognised in association with other congenital cardiac defects in this species.

The three possible areas for pulmonic stenosis to occur are:

Pulmonic stenosis may be '''subvalvular/infundibular'''  (occurs below the valve), '''valvular''' (occurs at the valve) or'''Supravalvular''' (occurs above the valve).'''Most '''cases of PS in the dog are '''valvular''', whilst supravalvular PS is rare. 

1. '''Subvalvular''' or '''subpulmonic''' (occurs below the valve)

'''Subvalvular (infundibular)''' PS is defined as a fibrous or fibromuscular diaphragm below the pulmonic valve or at the os infundibulum, or a more diffuse and extensive area of fibromuscular hypertrophy creating more of a tunnel or hour-glass deformity of the infundibulum.

2. '''Valvular''' (occurs at the valve)

'''Valvular''' PS can be further classified into type A or type B, based on valvular morphology. '''Type A''' cases have a '''normal pulmonary annulus diameter''' and '''type B''' cases have a '''narrow pulmonary annulus diameter''', often accompanied by hypoplasia of the pulmonary trunk. Type A cases are more likely to show a post-stenotic dilatation.

Concentric hypertrophy of the right ventricle develops as a consequence of the chronic pressure overload resulting from obstruction to right ventricular outflow. Right ventricular hypertrophy may cause an infundibular narrowing of the right ventricular outflow tract (RVOT), exacerbating the stenosis and resulting in a dynamic component to the obstruction. A further consequence of right ventricular hypertrophy is reduced right ventricular diastolic filling and therefore elevated right atrial pressures with resultant right atrial dilation.

 

'''Most '''cases of pulmonic stenosis are '''valvular''', whilst supravalvular pulomic stenosis is rare. Stenosis of the pulmonary outflow tract is the result of dysplastic changes in the pulmonic valve. Concentric hypertrophy of the right ventricle forms as a direct result of the chronic pressure overload needed to surpass the increased resistance from the stenotic pulmonary outflow tract. This concentric hypertrophy causes decreased ventricular filling during diastole and elevated right atrial pressure from the blood are unable to fill the ventricle causes atrial dilation. Tricuspid valve regurgitation can also be present and adds to the atrial pressure.

==Signalment==

==Signalment==