Pulmonic stenosis is a birth defect consisting of a narrowing in a region of the heart, the pulmonic valve (or adjacent area). A narrowing of the pulmonic valve increases the level of strain and workload on the chamber of the heart feeding into it, the right ventricle. Since normal blood flow requires heart valves to open fully for proper circulation, incomplete opening of the pulmonic valve (the hallmark of pulmonic stenosis) creates a "logjam" effect that disturbs blood flow and in the worst cases, may create life-threatening symptoms.
In mild and moderate pulmonic stenosis, where there is a small or medium degree of narrowing, respectively, the outlook for an individual dog is usually good to excellent: few dogs experience problems due to their pulmonic stenosis if it is mild or moderate in degree. Dogs with severe pulmonic sytenosis, however, may develop symptoms that become life-threatening in the future.
Screening for pulmonic stenosis is done at an early age: 8 weeks onward. The degree of severity of pulmonic stenosis may worsen as a puppy reaches adulthood. Therefore, mild or moderate pulmonic stenosis in a puppy should be followed until the dog is 12 to 18 months of age in order to know the final degree of seriousness of the condition.
Pulmonic stenosis appears to be inherited as a polygenic threshold trait. This means that more than one genetic aberration contributes to pulmonic stenosis; a genetic test for identifying it does not exist at this time.
Pulmonic stenosis is usually suspected based on a veterinarian's detecting a heart murmur when listening to a dog's heart with a stethoscope. Murmurs may be caused by many, many disorders, including pulmonic stenosis, so it is important to know that just having a heart murmur (of any grade) is not definitive for pulmonic stenosis.
If a heart murmur is detected and the veterinarian feels it could be due to pulmonic stenosis, he/she will recommend tests to confirm pulmonic stenosis or eliminate it from consideration. These tests are noninvasive and very accurate (see below), and they mainly help to answer two questions: "Is it pulmonic stenosis?" and if it is, "Is it severe enough that something needs to be done?".
The first indication of pulmonic stenosis is generally a heart murmur detected in a young dog (typically during puppy vaccine visits between the ages of 2 and 4 months). Much less commonly, dogs with severe pulmonic stenosis may develop symptoms such as abdominal enlargement -a bloated appearance to the belly, caused by fluid retention- or laboured breathing or collapse/fainting. Either way, a veterinarian's suspicion of pulmonic stenosis justifies doing thoracic radiographs (chest X-rays) and an echocardiogram (also called cardiac ultrasound, or sonogram of the heart). These tests help to pinpoint whether pulmonic stenosis is present and if it is, whether it is mild, moderate, or severe. Specifically, the echocardiogram can detect whether secondary changes such as thickening of the right ventricle or other distortion of the heart's structure has occurred, and the degree of strain under which the heart is forced to operate. The extra workload that pulmonic stenosis imposes on the heart is identified through Doppler ultrasound calculation of a pressure gradient between the right ventricle and pulmonary arteries. Based on this ultrasound-derived calculation, the degree of pulmonic stenosis is determined, and in turn it is then possible to know whether treatment is essential, or not required at all.
Since pulmonic stenosis is a narrowing of a region in the heart, the degree of concern depends directly on the degree of narrowing. Mild or moderate stenosis generally does not require any intervention at all. In some cases, additional findings on X-rays or cardiac ultrasound may justify starting daily medication, but with mild or moderate pulmonic stenosis, this is uncommon.
With severe pulmonic stenosis, there is a strong likelihood of life-threatening problems at some point if treatment is not undertaken. Conversely, a good/normal quality of life and lifespan are expected with surgical treatment in the vast majority of cases. Surgery for pulmonic stenosis consists of enlarging the narrowed pulmonic valve so that circulation is improved and the strain on the heart is reduced. This is usually accomplished through minimally-invasive surgery: under general anesthesia, a catheter (long tube) is threaded through a blood vessel in the neck or groin and a balloon on it is inflated when it is positioned at the area of the pulmonic stenosis. The inflation of the balloon stretches the narrowed space in a way that tends to remain permanent, even after the balloon is deflated and the catheter removed. The long-term result is that the resistance to blood flow is lessened and the heart resumes a more normal degree of work.
Some dogs are not candidates for this type of surgery: severe pulmonic stenosis may sometimes be inoperable. In these cases, treatment with beta-blocking drugs, which protect the heart against the damaging effects of adrenaline rushes, may be advocated by the veterinarian as a preventive measure.
Dogs with mild pulmonic stenosis and most dogs with moderate pulmonic stenosis enjoy normal lives without treatment. Some dogs with moderate pulmonic stenosis and virtually all dogs with severe pulmonic stenosis have a shortened lifespan if it is left untreated. It is important to note that pulmonic stenosis does not cause pain, and it is not "wrong" or "unfair" to have a dog live with pulmonic stenosis of any degree of severity. The treatments described above are aimed at improving lifespan and quality of life in the future.
- MURMUR: systolic ejection murmur, loudest in pulmonic area near left cranial sternal border/left axilla, often radiating to the right cranial sternal border.
- ELECTROCARDIOGRAM: evidence of RV hypertrophy (right axis shift), right atrial enlargement (P pulmonale), and arrhythmia associated with hypertrophy are possible; however, these abnormalities occur sporadically and may not exist even in severely-affected dogs. Therefore, electrocardiography should not be considered a screening test for trying to rule in or rule out pulmonic stenosis with any degree of certainty.
- RADIOGRAPHS: evidence of right ventricular hypertrophy and poststenotic dilation of pulmonary artery are possible in cases of severe pulmonic stenosis. Many impostors (particularly related to positioning and chest conformation) mimic these findings, and radiographs should be used less as a screening test and more as an adjunct, particularly for identifying pleural effusion if right-sided congestive heart failure is suspected.
- ECHOCARDIOGRAPHY: diagnostic test of choice for pulmonic stenosis. Typical findings include concentric RV hypertrophy, deformity and narrowing in the pulmonic valve, and poststenotic dilation of the pulmonary artery; the Doppler-derived gradient across the stenotic valve identifies the severity of the lesion.
- OTHER: On physical exam, jugular pulses may be evident in severe cases (beware the impostor of carotid pulsations radiating through a normal jugular vein).
In English bulldogs and boxers, pulmonic stenosis is commonly caused by a left coronary artery anomaly which has important implications for surgical correction: these cases cannot be safely operated under normal circumstances, and referral to a cardiologist is recommended both for confirmation and to discuss treatment and outlook.
Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening. If any affected offspring are born, breeding of the parents should be discontinued.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.
Sisson DD. Pulmonic stenosis. In Cote E, ed. Clinical Veterinary Advisor, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 941-943.
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