Pulmonic valvular stenosis, sometimes referred to simply as pulmonic stenosis, is a narrowing of the opening through the pulmonic valve, the group of three leaflets that separate the right ventricle from the pulmonary trunk, or within the general vicinity of this valve. The most commo n cause of this restricted opening is congenital malformation (born with the condition), either as an isolated finding or as part of a more complex congenital heart defect.1 An example of this latter group is its inclusion as one of the four components of Tetralogy of Fallot, the most common cyanotic (impaired circulation of oxygen that leads to decreased delivery of this vital gas to the organs, leading to a bluish tinge to the lips and skin, among other complications) cardiac condition. Two-thirds of patients with Noonan syndrome (an autosomal dominant condition characterized by a short stature, abnormal facial appearance, and chest deformities, along with congenital heart defects) will have pulmonic stenosis.2,3 The most common acquired condition resulting in this valvular condition occurs with carcinoid heart disease, in which white plaques stick to the thin leaflets, eventually restricting their movement and narrowing the effective opening to the pulmonary vasculature.1 Pulmonic stenosis accounts for
approximately 10 percent of cases of congenital heart disease; this number may
be skewed and underestimated owing to a large percentage of patients tending to
be asymptomatic until adulthood.2
This valvular pathology can be categorized by its location in relation
to where the valve is positioned.4
If the narrowing actually involves the valve itself, the defect is
termed valvular stenosis, with etiologies including the aforementioned
congenital defect as well as the systemic effects of cancers (carcinoid heart
syndrome) and damage to the leaflets due to bacterial endocarditis. More than 90% of cases of pulmonic stenosis
arise from the valvular level.3
Narrowing that is focused within the main pulmonary artery, just beyond
the valve, is termed supravalvular stenosis; causes of this form of the defect
include a continuum of anomalies ranging from discrete stenosis to widespread
underdevelopment of the pulmonary trunk to mechanical compression of the vessel
by a nearby tumor.4 The third
variation involves narrowing within the right ventricular outflow tract (also
known as the infundibulum); it is deemed subvalvular or infundibular, with
etiologies including Tetralogy of Fallow and tumor compression. A final, most severe, form of the disease
involves a complete absence of the pulmonic valve, termed pulmonic atresia; in
these patients, maintenance of the ductus arteriosus is paramount for blood
flow entering the pulmonary vasculature and ensuring some degree of
oxygenation. Most individuals who have
isolated pulmonic stenosis tend to be asymptomatic.1 When patients with this valvular anomaly do
develop clinical manifestations, it typically is a result of concomitant
pulmonic regurgitation (where the valve fails to close properly and allows
leaking of blood from the pulmonary arteries backward into the right ventricle
during diastole) or pulmonary hypertension (elevated pressures within the
pulmonary vasculature owing to a wide range of causes). Common symptoms expressed by patients include
gradually worsening exertional difficulty breathing, chest pain, and fatigue,
with the intensity of onset directly related to the increasing pressure
gradient across the diseased valve. Right
ventricular hypertrophy (thickening of the heart muscle) arises in an attempt
to generate greater contractile force to push blood through the narrowed
valvular opening. This compensatory
mechanism is only effective at overcoming the increased resistance to forward
propulsion of blood (termed “afterload”) to a certain point, with subsequent
diastolic (the phase of the cardiac cycle involved with ventricular filling and
relaxation) compliance being compromised.5 Ultimately, systolic contractions are
impaired and right heart failure ensues, manifested by venous congestion with
jugular venous distention (backfilling of blood into the neck veins), ascites
(fluid accumulation within the abdominal cavity), enlargement of the liver and
spleen, and peripheral edema. In the
setting of an intra-cardiac shunt (e.g., atrial septal defect, ventricular
septal defect), cases of significant restriction lead to decreased access to
the pulmonary vasculature and ventricular contraction will propel the blood
through the path of least resistance (through the shunt, with minimal blood
entering the pulmonary vasculature) and into the left side of the heart,
potentially leading to decreased blood oxygen levels (hypoxemia) and cyanosis.6 This can be further worsened by compression
of the coronary arteries during systolic contractions by the massive right
ventricular mass and the increased oxygen demands of the myocardium, resulting
in ischemia (condition in which the tissues fail to receive adequate oxygen).5 As is prudent with most
congenital heart anomalies, women who are of child-bearing age with pulmonic
stenosis should consider the risks associated with becoming pregnant. As an isolated abnormality, most women can
carry a child to term without compromise from the narrowed valve. In one study, 11 patients with various NYHA
functional classes were followed; all proceeded with their pregnancies without
complication, but two remained stable, with one digressing from functional
class I to class II and one going from class II to class III transiently.7 Also of note, there was no statistically
significant correlation between the neonatal outcomes and the degree of
valvular stenosis in the mother. This
study does not take into account, however, cases where pulmonic stenosis is a
part of a more complex congenital defect. Evaluation of the severity of pulmonic stenosis can be performed using a right heart catheter, such as a Swan-Ganz catheter. By measuring the gradient across the lesion, one can classify the degree of obstruction, assuming that forward cardiac output is preserved.3 If the peak systolic transvalvular pressure gradient is 50 mmHg or less, such a stenosis would be considered as mild. Gradients in the range of 50 to 80 mmHg typify moderate stenosis, while measurements in excess of 80 mmHg define severe cases. These measurements can by made either in the cardiac catheterization laboratory as part of a right heart catheterization study or at the bedside within the critical care unit. The central venous waveform, also evaluated via the above catheter, yields a prominent a wave with otherwise normal waveform characteristics.1 Physical examination of patients
with pulmonic stenosis tends to reveal evidence of right heart
enlargement. There is commonly a
prominent “a” wave noted during evaluation of the jugular venous patterns,
owing to forceful right atrial contraction against a stiffened, noncompliant
right ventricle.8 A
pronounced palpable impulse over the right side of the sternum correlates with
right ventricular hypertrophy. The
murmur of pulmonic stenosis occurs during systole, has a crescendo-decrescendo
characteristic (gets louder, then tapers off), and is best auscultated at the
left upper sternal border. The second
heart sound typically is split, with the degree of splitting proportional to
the degree of valvular narrowing.1
Further auscultation over the left upper sternal border may reveal an
ejection click resulting from abrupt leaflet opening or from dilation of the main
pulmonary artery.8 Echocardiography is a very useful
modality for imaging various aspects of pulmonic stenosis. This allows for evaluation of the lesion's
morphology and location, the pressure gradient across this region, and
computing the orifice area.9
One can also determine the compensatory effects of this condition on the
right side of the heart (such as right ventricular hypertrophy, right atrial
enlargement, and venous congestion). Aspects
of more complex congenital defects can be evaluated, such as the ventricular
septal defect and overriding aorta found in Tetralogy of Fallot. Cardiac catheterization, in the form of a
right heart study, can is recommended for adolescents and young adults with
echocardiographic evidence of significant pressure gradients (peak velocities
exceeding 3 meters per second), as well as in those who are deemed to be ideal
candidates for balloon valvuloplasty.1 Other means of evaluations reveal
nonspecific findings.
Electrocardiography can be used to demonstrate the right ventricular
strain due to compensatory hypertrophy (thickening of the heart muscle); other
findings include right bundle branch block, right axis deviation, and possibly
right atrial enlargement.1
Chest radiography may show nonspecific enlargement of the right
ventricle and pulmonary arteries (due to associated pulmonary
regurgitation). One of the best
indicators of pulmonic stenosis via chest radiography is dilation of the main
pulmonary artery (noted due to both valvular narrowing and pulmonary
hypertension). Management is dependent on the
severity of the stenosis and its location, as well as the presence of other
congenital malformations. Mild cases of
narrowing usually involve very slow progression of the disease and the
compensatory effects on the heart and therefore do not require treatment.3 The most common method of relieving moderate
to severe cases of stenosis is through the use of balloon valvuloplasty,
utilizing specialized catheters to position a noncompliant balloon across the
narrowing and then forcing the fused leaflets apart during inflation. This method of valvular repair has
consistently proven beneficial, with decreases in right ventricular systolic
pressure, pulmonary transvalvular and peak-to-peak systolic pressure (the
primary ones used to determine stenosis severity) noted in a majority of patients
undergoing this procedure.10
All of the patients in Boshra’s study had symptom improvement and there
was no significant morbidity or mortality noted. Surgical replacement of the
diseased valve is rarely necessary, occurring typically from severe
malformation of the valve’s leaflets or if there is already significant
valvular insufficiency (as balloon valvuloplasty almost invariably creates some
degree of such valve leakage).2
Although many patients who undergo valvuloplasty will have persistent
right-to-left shunting of blood and continued hypoxemia, over the course of 3
to 6 months, ventricular hypertrophy regression and shunting will typically
diminish to less clinically significant levels.11 Neonatal patients found to have severe pulmonic stenosis should receive a prostaglandin E1 infusion in order to keep the ductus arteriosus open (this conduit normally closes within approximately 7 days following birth) in order to reduce resistance and thus ensure blood flow into the pulmonary vasculature.6 Some patients with pulmonic valve issues may need lifelong endocarditis prophylaxis prior to dental or invasive procedures, regardless of if valvuloplasty is performed or not; however, the incidence of such valvular infection is low and prophylactic antibiotics is considered by some as controversial and unnecessary.8 Prognosis in patients with pulmonic stenosis is dependent on the severity of the condition and whether balloon valvuloplasty has been performed or not. In cases of mild disease, prognosis is considered excellent with greater than 90 percent living more than 20 years after diagnosis.2 By comparison, patients with severe disease have a mortality rate approaching 60 percent within 10 years if no intervention is performed. These patients have significant improvement in these statistics following valvuloplasty or valve replacement. References and Further
Reading: 1. Crawford, M.H. (2009). Current Cardiology Diagnosis & Treatment, 3rd ed. Lange Medical Books / McGraw-Hill, New York, et al. 2. Brickner, M.E. (2000). "Congenital Heart Disease in Adults (First of Two Parts)." New England Journal of Medicine, 342 (4), 256-263. 3. Lilly, L.S. (2007). Pathophysiology of Heart Disease: A Collaborative Project of Medical Students and Faculty, 4th ed. Lippincott, Williams, & Wilkins, Baltimore and Philadelphia. 4. Weissman, N.J. & Adelmann, G.A. (2004). Cardiac Imaging Secrets. Hanley & Belfus, Philadelphia. 5. Russell, I.A., Rouine-Rapp, K., Startmann, G., & Miller-Hance, W.C. (2006). “Congenital Heart Disease in the Adult: A Review with Internet-Accessible Transesophageal Echocardiographic Images.” Anesthesiology & Analgesia, Vol. 102, 694-723. 6. Peacock, W.F. & Tiffany, B.R. (2006). Cardiac Emergencies. McGraw-Hill, New York, et al. 7. Hameed, A.R. (2007). "Effect of Pulmonary Stenosis on Pregnancy Outcomes – A Case-Control Study." American Heart Journal, Vol. 154(5), 852-854. 8. Wu, J.C. & Child, J.S. (2004). "Common Congenital Heart Disorders in Adults." Current Problems in Cardiology 2004, 29, 641-700. 9. Otto, C. M. (2007). The Practice of Clinical Echocardiography, 3rd ed. Saunders / Elsevier, Philadelphia. 10. Boshra, H. (2011). "Balloon Pulmonary Valvuloplasty in Adults with Congenital Valvular Pulmonary Stenosis." Heart Mirror Journal from Affiliated Egyptian Universities and Cardiology Centers, Vol. 5(1), 288-292. 11. Taeusch, H.W., Ballard, R.A., & Gleason, C.A. (2005). Avery's Diseases of the Newborn, 8th ed. Elsevier, Philadelphia. Contributor: Sean M. Hancock, RDCS (AE), RCS, RCSA, RCIS, CCT Staff Echo Sonographer and Clinical Educator Cardiac Study Center, Puyallup, WA September 2012 |
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