Pulmonic stenosis, affectionately known as “PS,” is the third most common congenital heart disease in the dog. It can be accompanied by additional heart defects to create a constellation of disaster or it can be mild enough to be no more than a surprising incidental finding. Occasionally cats are affected as well.
“Pulmonic stenosis” refers to a “stenosis” or constriction of the pulmonic heart valve through which blood must pass on its way from the heart to the lung. This web page attempts to present a review of this condition including its diagnosis and treatment.
PULMONIC STENOSIS AND ITS FORMS
In pulmonic stenosis, the right ventricular outflow tract is narrowed either at the actual valve, just before it, or just after it. The most common form of pulmonic stenosis involves a deformed pulmonary valve such that the valve leaflets are too thick, the opening is too narrow, or the valve cusps are fused. The heart must pump extra hard to get the blood through this unusually narrow, stiff little valve. The right side of the heart eventually becomes thick from all this extra work and a "post stenotic dilation" (a large bulging area on the far side of the narrowed valve) results from the high pressure squirt the heart must generate to get blood through the stenosis. As the heart muscle builds up to become strong enough to pump through the stenosis, electrical conduction through the changed muscle tissue may not be normal. The rhythm of the heart’s filling and pumping cycle can be disturbed as the muscle becomes abnormal. Predisposed breeds for this condition include: Labrador retrievers, terrier breeds, miniature schnauzers, Samoyeds, English bulldogs, boxers, chow chows, beagles, cocker spaniels, basset hounds, and mastiffs.
A normal heart is on the left. A heart with pulmonic stenosis is on the right. In this graphic, the yellow arrow is pointing to a
CONCURRENT TRICUSPID INSUFFICIENCY
Another form of pulmonic stenosis which is especially harmful involves an accompanying “Tricuspid Valve Dysplasia.” The tricuspid valve is the three-leafed valve that separates the right atrium (blood accepting chamber) from the right ventricle (the pumping chamber). Normally this valve is closed when the ventricle pumps ensuring that all its blood pumps forward. If this valve is leaky then some of the blood, perhaps even most of it, pumps backwards. If the pulmonic valve is extra tight (as in pulmonic stenosis) and the tricuspid valve is extra loose (as in tricuspid dysplasia), it is easy to see that the right ventricle must become extra strong (thick) to pump enough blood through the tight pulmonic valve, and extra large (wide) to accommodate enough blood to send an adequate amount forward considering that most will go backwards. Right heart failure is not far behind as the right side of the heart simply cannot keep up with such a double whammy of circumstance.
CONCURRENT PATENT FORAMEN OVALE
Another congenital problem that can complicate pulmonic stenosis is called a “patent foramen ovale.” Before birth, one's oxygen comes from mom's bloodstream (obviously, there is no breathing of air going on in the womb). The unborn heart is developing a right (pump to the lung to pick up oxygen) side and left (send the oxygen to the rest of the body) side but during the actual development, the right and left blood mix together as there is no need for separation.
The foramen ovale is a hole in the septum of the developing heart allowing for right and left blood to mix together. Shortly after birth, when the lungs formally come into play, the foramen ovale closes up and the right and left sides of the heart are completely separated. If the patient has pulmonic stenosis, the pressures in the right side of the heart are so high that blood is pushed from the right atrium into the left atrium with every beat of the heart, thus preventing closure of the foramen. This allows unoxygenated blood to mix into the circuit reserved for oxygenated blood. If enough oxygen-poor blood is allowed into this circuit, the patient’s tissues may not receive enough oxygen but generally this is merely a mild phenomenon noticed on the echocardiogram.
WHAT DOES ALL THIS THIS MEAN FOR THE PET?
A mild case is of little concern and usually does not affect life expectancy. Luckily, most cases are mild and do not require treatment; fairly severe disease is needed for clinical signs to be present.
Approximately 35% of dogs with severe pulmonic stenosis will show some or all of the following signs:
In one study 30% of dogs with severe disease experienced sudden death.
HOW IS DIAGNOSIS MADE?
The diagnosis is clinched with the echocardiogram, where ultrasound is used to measure the diameter and thickness of the heart’s chambers. It is then easy to see the thick right ventricle (and actually measure its thickness). If there is tricuspid valve disease and backward flow of blood this can also be seen in a real time image. A patent foramen ovale can also be seen.
After the diagnosis of pulmonic stenosis is made the next most important issue is to grade its severity. This is done with a special type of ultrasound called Continuous Wave Doppler Echocardiography. A pressure gradient across the pulmonic valve can actually be measured in units called millimeters of mercury (“mm of Hg.”) A pressure gradient of less than 40 mm of Hg generally require no treatment at all. A gradient greater than 80 mm of Hg have a significant risk of sudden death and therapy should be pursued (generally balloon valvulplasty). Dogs with gradients between 40 and 80 not as predictable regarding benefit of valvuloplasty.
TREATMENT: BALLOON VALVULOPLASTY
Clearly if the obstruction at the pulmonic valve could be relieved, much of the problem would be solved. Severe pulmonic stenosis cases can be treated by doing just that. A special balloon is inserted into the pulmonic valve where it is inflated, breaking down the obstruction. The size of the balloon catheter is determined by echocardiography as described above. Dogs that have pressure gradients of greater than 80 mm Hg across the pulmonic valve should have this procedure regardless of whether or not they are showing clinical signs. Some experts feel 60 mm Hg is a high enough gradient to warrant valvuloplasty. Dogs with concurrent tricuspid valve dysplasia benefit from this procedure regardless of their pressure gradient.
Performing this procedure reduces the risk of sudden death by 53% and improves quality of life as well. Certain types of valve deformity are not amenable to this treatment and dogs with the type of pulmonic stenosis that has a coronary artery wrapped around the pulmonary artery (the R2A anomaly) are similarly not amenable to this treatment. For these dogs there is unfortunately, no treatment that can be recommended. Balloon valvuloplasty will tear the abnormal coronary artery and alternative therapy has not been successfully developed. For these dogs, prognosis is better without attempted therapy.
WHAT IS "SUICIDE RIGHT VENTRICLE?"
If the right ventricle and its outflow tract become too thickened, a pressure gradient problem can persist after the actual stenosis is relieved by valvuloplasty. "Suicide right ventricle" is a phenomenon that occurs immediately after pressure is relieved by valvuloplasty in a severely stenosed valve. The heart muscle has grown so stiff after pumping against the stenosis valve that a new obstruction occurs. Medication and fluid therapy can help prevent this complication of valvuloplasty. Other complications of valvuloplasty include heart arrhythmias, rupture of the valve or even puncture of the heart itself. Valvuloplasty is an advanced procedure and must be respected as such. Fortunately, serious complications are rare but it is important to be informed of potential problems and most patients are released to go home the same day as their valvuloplasty procedure. Pressure gradients continue to drop for several months after the procedure and medication is generally needed throughout this time. It takes a good 3-6 months before the success of the valvuloplasty can be judged.
Dogs for whom the stenosis is just before the valve rather than at the valve itself may benefit from surgery. There are several techniques that can be used to widen the pulmonary valve or to by-pass it. These procedures require a very experienced surgeon and bear significant risk. The balloon valvuloplasty is the preferred treatment for cases where treatment is recommended and where balloon valvuloplasty is applicable.
Unfortunately, medication is not very helpful for pulmonic stenosis except to manage any right-sided heart failure. In some cases, medications called “beta blockers” can be used in an attempt to relax the muscles of the heart and dilate the stenosis. This will not relieve the constriction but could palliate it.
A consultation with a veterinary cardiologist will likely be needed to obtain the most complete recommendations for this conditions. Your veterinarian is in the best position to make a local referral.
Page posted: 1/24/2012