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.
In order to understand what pulmonic stenosis is, it is necessary to understand some normal heart anatomy. The heart sits more or less centrally in the chest and is divided into a left side, which receives oxygen-rich blood from the lung and pumps it to the rest of the body, and a right side, which receives “used” blood from the body and pumps it to the lung to pick up fresh oxygen. Because the left side of the heart must supply blood to the whole body, its muscle is especially thick and strong while the right side, which only pumps to one nearby area tends to be thinner. When the ventricles pump, the blood from the left shoots through a valve called the “aortic valve” and the blood from the right side shoots through the “pulmonic valve” (also called the “pulmonary valve.)” These valves snap sharply closed after the pumping is done. The area where the blood exits the right ventricle is called the “right ventricular outflow tract” and consists of the exit area of the ventricle, the pulmonic valve, and the main pulmonary artery.
See it in animation
Still confused or need a better visual? The following short video demonstrates the normal human heart and its valves but the principles hold true for the canine heart as well.
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 becomes thick from all this extra work but in doing so its normal electrical conduction may not be normal . The rhythm of the heart’s filling and pumping cycle can be disturbed as the muscle becomes abnormal.
The heart on the left is normal showing its pulmonic valve wide open accepting blood. The heart on the right has pulmonic stenosis. Note how little blood flow can get through its pulmonic valve
The Boxer and Bulldog tend to show a special form of pulmonic stenosis. Coronary arteries feed the heart itself, bringing oxygen-rich blood while the coronary veins carry away used oxygen-poor blood. The Boxer and Bulldog have a special type of pulmonic stenosis where a coronary artery actually wraps around the pulmonary artery exiting the heart constricting it.
An especially harmful form of pulmonic stenosis is accompanied by what is called “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.
Another congenital problem that can complicate pulmonic stenosis is called a “patent foramen ovale.” The foramen ovale is basically a hole in the septum that divides the heart into right and left sides. This is a normal structure in the unborn embryo and normally closes after birth separating the right atrium from the left atrium. 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 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:
Fainting spells (from the abnormal electrical heart rhythm)
Fluid accumulation in the belly
Blue-tinge to the gums especially with exertion
In one study 30% of dogs with severe disease experienced sudden death.
HOW IS DIAGNOSIS MADE?
The turbulent blood flow resulting from the heart attempting to pump blood through the narrow pulmonic valve generates a sound called a “murmur.” (A murmur is not specific for pulmonic stenosis; anytime there is turbulent blood flow, it may be audible as a murmur.) If the electrical conduction of the heart is affected, the rhythm will sound irregular as well.
Often a murmur or an abnormal rhythm is detected when the dog is still a puppy and is receiving one of his or her initial examinations. Possibly, disease might not be detected until there are more obvious signs of heart failure present, such as fluid in the belly.
Once physical findings suggest heart disease, radiographs and ideally an echocardiogram follow.
Normal canine chest radiograph
This dog has pulmonic stenosis. The heart looks somewhat pregnant in the front as this is where the right ventricle is enlarged.
Two sample radiographs are shown above but it is easy to see that changes could be subtle. 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 they type of pulmonic stenosis that have a coronary artery wrapped around the pulmonary artery 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.