Pulmonary Valve Stenosis

Pathophysiology

Pulmonary valve stenosis results from fusion of the valve cusps during mid- to late fetal development. The most common form of isolated right ventricular (RV) obstruction, pulmonary valvular stenosis, occurs in approximately 7% of individuals with congenital heart disease (see also Chapters 50 and 52). Pulmonary valve stenosis may be associated with significant RV hypertrophy and infundibular narrowing. The fusion of the valvular cusps produces a classic systolic “doming” appearance angiographically (Fig. 40-1). Tissue pads within the valve sinuses may exist and result in a thickened, rigid valve that is considered dysplastic (a common finding in Noonan’s syndrome). Excessive thickening in dysplastic valves renders the valve unsuitable for percutaneous valvuloplasty, although attempts have occasionally been successful. Similarly, narrowing of the RV outflow tract limits the efficacy of percutaneous balloon techniques. Acquired forms of stenosis are rare (i.e., carcinoid).

Figure 40-1 Pulmonary stenosis.

Percutaneous Balloon Pulmonary Valvuloplasty

Figure 40-2 demonstrates the gradient between the right ventricle and the pulmonary artery (PA) before and after successful percutaneous balloon valvuloplasty. The RV outflow tract may have considerable muscular subpulmonic stenosis, which may be masked when valvular obstruction is present. The sudden removal of the valvular stenosis after the procedure may result in acute decompensation from marked RV infundibular obstruction, sometimes called the “suicide RV.” Fluid loading, calcium channel blockers, and β-blockers can be used for emergent treatment. After pulmonary valvuloplasty, the subpulmonic hypertrophy may regress considerably over the next several months.

Figure 40-2 Pulmonary balloon valvuloplasty.

PA, pulmonary artery; RV, right ventricular.

Indications

Valvular regurgitation is generally graded from 1+ (mild) to 4+ (severe). In patients with less than 2+ pulmonic regurgitation and a doming pulmonic valve, American College of Cardiology/American Heart Association (ACC/AHA) guidelines suggest that a peak pulmonary valve gradient of greater than 60 mm Hg or a mean gradient of greater than 40 mm Hg by echo-Doppler warrants balloon valvuloplasty, even without symptoms. Any evidence of RV dysfunction or associated RV failure and tricuspid regurgitation should also prompt intervention if the mean gradient is greater than 30 mm Hg. Procedural success is much lower in patients with pulmonary valve dysplasia and may have only limited value when there is carcinoid plaque involvement of the pulmonic valve. The procedure is effective in reducing the RV outflow tract gradient in the presence of RV conduit obstruction from prosthetic valve dysfunction, although the patient generally experiences an increase in pulmonic regurgitation in these situations.

Technique

Before the procedure, RV angiography in the cranial right anterior oblique and straight lateral views is performed. Pulmonary angiography assesses preprocedural pulmonic regurgitation. Severe pulmonic regurgitation (3+ or more) is a contraindication to valvuloplasty; severe regurgitation as a result of the procedure represents an adverse outcome. Baseline annular size is determined by echocardiography, MRI, or contrast angiography. In the cardiac catheterization laboratory, a catheter (with radiopaque markers a known distance apart) may be used for angiography at the valve level to determine appropriate balloon size. Quantitative angiographic methods may be similarly applied.

The dilating balloon or balloons are percutaneously inserted into the femoral vein without a sheath. The maximum inflation of the balloon(s) should be equal to 1.2 to 1.4 times the estimated annular size (see Fig. 40-2). In contrast to the aortic valve (see “Aortic Valve Stenosis”), the pulmonic valve is elastic and often requires oversizing for adequate results. The goal of the procedure is a final peak-to-peak valvular gradient less than 30 mm Hg by cardiac catheterization. Recurrence rates are much lower if that threshold is reached. A single balloon, often 23 mm in diameter in adults, may be used, although two balloons side by side may be necessary in patients with a large annulus. In some laboratories, trefoil or bifoil balloon catheters are available and preferred. The Inoue mitral valvuloplasty balloon (Toray Industries, Inc., Tokyo, Japan) has increasingly been used for pulmonary valvuloplasty because of its stability during inflation.

Careful measurement of postprocedural gradients allows differentiation of infundibular stenosis from residual valvular stenosis. Postprocedural PA angiography evaluates the severity of pulmonic regurgitation as a result of the procedure, while postprocedural RV angiography addresses the presence and significance of infundibular stenosis.

Short-Term Results and Complications

Numerous groups have reported excellent short-term results in children and adults, as exemplified by a report of 66 infants and children in whom the peak gradient across the pulmonic valve fell from 92 ± 43 mm Hg to 29 ± 20 mm Hg with no change in cardiac output. The NHLBI Adult Registry included 37 adult patients with successful completion of the procedure in 97%, and a reduction in the average peak gradient from 46 to 18 mm Hg. Larger balloon sizes, up to 30% to 50% larger than the annulus, resulted in greater reductions in the valvular gradient without increasing complications.

Minimal complications in the acute setting include vagal symptoms and ventricular ectopy from catheters in the right ventricle. Pulmonary edema, presumably from increasing pulmonary flow to formerly underperfused lungs, perforation of a cardiac chamber, high-grade atrioventricular nodal block, and transient RV outflow obstruction (as noted earlier) have also been reported. Pulmonary valve regurgitation occurs in approximately two thirds of the patients after the procedure, but it is rarely clinically significant.

Long-Term Results

Long-term data are available for over 10 years after percutaneous balloon valvuloplasty of the pulmonary valve. In one representative study, 62 children undergoing this procedure, with an average balloon-to-pulmonary annulus ratio of 1.4, were followed for a mean of 6.4 ± 3.4 years. Persistent pulmonary valve regurgitation was found in 39% of the patients, there was evidence of a progressive resolution of infundibular hypertrophy, and the restenosis (>35 mm Hg gradient) rate was only 4.8%. Restenosis was more common in patients with dysplastic valves. If restenosis occurred, repeat valvuloplasty seemed to be effective in patients without dysplastic pulmonary valves.

These data compare favorably with the outcomes of surgical valvotomy. One large study of surgical valvotomy in children reported a surgical mortality rate of 3%, with poor surgical results (residual gradient >50 mm Hg) in 4%. Restenosis rates after surgery were 14% to 33% at up to 34 months of follow-up. Thus, percutaneous balloon valvuloplasty for valvular, nondysplastic, pulmonic stenosis is the treatment of choice and provides excellent short- and long-term relief from pulmonary valvular obstruction.

Percutaneous Pulmonary Valve Replacement

In 1992, the first percutaneous catheter-mounted pulmonary heart valve procedure using a stented porcine bioprosthetic valve was implanted in an animal model. In 2000, Bonhoeffer and colleagues were the first to treat a human with a percutaneous pulmonary valve implanting of a stent-mounted bovine jugular vein valve in an RV-to-PA conduit of a 12-year-old. The remarkable success of the index case led quickly to its application in eight additional cases, with major hemodynamic improvement in both stenosis and regurgitation seen in five of the eight. The procedure has now been applied to a wider group of patients with available follow-up at a median of 3 years. The overall results remain encouraging.

Aortic Valve Stenosis

Pathophysiology

The normal aortic valve has thin, flexible cusps composed of three tissue layers sandwiched between layers of endothelium on both sides of the valve. The layers include a fibrosa with collagen fibers oriented parallel to the leaflet that support the major leaflet, a ventricularis layer composed of elastic fibers oriented perpendicularly to the leaflet edge that provide flexibility, and a spongiosa layer of loose connective tissue in the basal third of each leaflet.

Congenitally deformed aortic valves have fused commissures and can generally be described as either unicuspid or bicuspid. Unicuspid valves are inherently stenotic at birth and cause symptoms early in life. Unicuspid aortic valves account for approximately 10% of all cases of isolated aortic valve stenosis in adulthood, whereas bicuspid aortic valves account for approximately 60% of isolated aortic valve stenosis in patients aged 15 to 65 years of age. Bicuspid aortic valves generally have two cusps of nearly equal size with a false commissure (raphe). Over time, progressive valvular fibrosis and calcium deposition occur, worsening the functional stenosis. Some commissural fusion between the functioning leaflets may occur, but the major limitation is often valvular rigidity from calcium buildup and scarring. High serum lipids may contribute to the degeneration of these valves similarly to those patients with calcific aortic stenosis.

Aortic valve stenosis in elderly persons generally involves a trileaflet valve and probably represents a continuum, from benign aortic valvular sclerosis to severe aortic valvular stenosis. The prevalence of aortic valve sclerosis has been reported to be 25% in individuals older than 65 years of age, with severe aortic valve stenosis evident in 1% to 2% of the population. There is growing evidence that the mechanism of calcific aortic valve stenosis in the elderly is related to atherosclerosis and not to what has commonly been referred to as a “degenerative” process. Little commissural fusion exists; large accretions of calcium can be present in the sinuses of Valsalva. The leaflets gradually lose their flexibility as a result of these calcium deposits. In calcific aortic valve stenosis, the minimal reduction in the gradient that can be obtained by balloon procedures has generally been attributed to cracks in the calcific nodules, cuspal tears, and aortic wall expansion (Fig. 40-3).

Figure 40-3 Effect of valvuloplasty on aortic valve area (AVA).

The position and size of the aortic valvuloplasty balloon is shown (B). EF, ejection fraction; LVEF, left ventricular ejection fraction.

When left ventricular (LV) outflow is obstructed at the valvular level, a gradient develops between the left ventricle and the aorta (see Fig. 40-3). The relationship between the gradient and the aortic valve area (AVA) is complex, however, and depends on the severity of the lesion as measured by the AVA and on the cardiac output or the aortic flow. After aortic valvuloplasty, aortic flow may increase because of an improvement in the cardiac output or the development of aortic regurgitation. Either result could increase the gradient, even if the actual AVA also increases. Alternatively, the cardiac output may fall, and the gradient may appear lower even if the AVA has increased. Thus, the short-term postprocedural valvular gradient change may not always reflect the actual change in the AVA.

Using just the change in the AVA can also be problematic for other reasons. For instance, if the baseline AVA is severe, an improvement in the AVA of 0.3 cm² from baseline has a dramatic effect on the peak LV systolic pressure (e.g., when the AVA increases from 0.5 to 0.8 cm²), but if the baseline AVA is less severe, the same incremental change may have much less consequence (e.g., when the AVA increases from 0.8 to 1.1 cm²). Hence, either an improvement in the gradient or an improvement in both the gradient and the final valve area can be used to define a successful result (i.e., a final valve gradient of <50 mm Hg, a 50% improvement in the AVA, or both).