Journal of The Indian Academy of Echocardiography & Cardiovascular Imaging

FOCUS ISSUE - CONGENITAL HEART DISEASE
Year
: 2020  |  Volume : 4  |  Issue : 3  |  Page : 276--286

Echocardiography to Evaluate Pulmonary Stenosis


Smita Mishra1, Praneet Lele2,  
1 Department of Pediatric Cardiology, Manipal Hospital Dwarka, Delhi, India
2 Consultant Pediatric Cardiologist, Kingsway Hospital, Nagpur, Maharashtra, India

Correspondence Address:
Dr. Smita Mishra
190, First Floor, Sukhdev Vihar, New Delhi - 110 025
India

Abstract

Congenital pulmonary stenosis (PS) is a common term for lesions causing right ventricular outflow obstruction. It can be further classified as the valvar, supravalvar, and infundibular PS. The PS may often present with other congenital heart diseases. In this article, echo imaging of isolated PS has been discussed. It is imperative to know that the guideline for intervention in isolated PS is totally based on echocardiography. Echocardiographic guidance is required for the selection of procedure, hardwares, evaluation of the outcome of the procedure, and long-term prognosis.



How to cite this article:
Mishra S, Lele P. Echocardiography to Evaluate Pulmonary Stenosis.J Indian Acad Echocardiogr Cardiovasc Imaging 2020;4:276-286


How to cite this URL:
Mishra S, Lele P. Echocardiography to Evaluate Pulmonary Stenosis. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2020 [cited 2021 Mar 1 ];4:276-286
Available from: https://www.jiaecho.org/text.asp?2020/4/3/276/303940


Full Text

 Introduction



Congenital pulmonary stenosis (PS) refers to lesions accountable for congenital right ventricular outflow obstruction (RVOTO).[1],[2] Acquired PS is rare and often caused by compression by external or internal structures. RVOTO is classified as valvular PS (VPS), subvalvular (infundibular pulmonary stenosis [IPS]), supravalvular PS (SVPS), and peripheral PS (PPS), according to the location of the obstruction. In this article, we are going to discuss isolated PS, its anatomical considerations, applied echocardiography in decision-making in terms of intervention and follow-up.[1],[2],[3],[4] Almost all guidelines for the management of PS are based on echocardiography [Table 1]. The prenatal echocardiographic scoring system has been proposed to prognosticate the postnatal outcome of fetuses with critical PS with the intact ventricular septum (CrPS/IVS) [Table 2].[5]{Table 1}{Table 2}

Incidence

The incidence of PS has been reported as 0.6–0.8/1000 live births, 5.8% of all congenital heart defects (CHDs), and almost 50% of the patient population with CHDs may also have PS.[1],[2],[6],[7]

Congenital dysmorphic syndromes and pulmonary stenosis

[Table 3] is a brief summary of congenital dysmorphic syndromes associated with the PS. PS associated with congenital syndromes is usually complicated by the presence of the dysplastic pulmonary valve (PV), multiple sites of RVOTO (subvalvular membrane, SVPS, and PPS) and may not be amenable for balloon pulmonary valvotomy (BPV).[1],[5],[8] Noonan's Syndrome is an autosomal dominant genetic condition, known to associate with varying level of right ventricular outflow obstruction in about 50% of its patient population. Owing to the presence of hypoplastic pulmonary annulus and dysplastic PV cusps, they often respond poorly to cath interventions. PS may also be associated with atrial septal defect (10%), asymmetrical septal hypertrophy (10%), ventricular septal defect (VSD) (5%), persistent ductus arteriosus (3%), peripheral pulmonary stenosis and mitral valve prolapse.[4],[9]{Table 3}

Clinical diagnosis

Clinical features of PS are narrated in [Table 4].[1],[2],[5],[7]{Table 4}

 Adaptive Changes of Right Ventricle in Response to the Pulmonary Stenosis



In the natural history of unresolved moderate to severe PS, echocardiography provides us evidence of the interplay of several adaptive and maladaptive changes. The presence of concentric hypertrophy coupled with predominantly end-systolic and early-diastolic flattening of the IVS in M-Mode echocardiogram, suggest adaptive changes in response to longstanding right ventricular (RV) pressure overload.[10] The tricuspid valve (TV) inflow velocities may show a restrictive pattern, but systolic parameters remain in the normal range. After a threshold when contractility can no longer overcome heightened afterload, maladaptive remodeling (heteromeric adaptation) takes-over. The combined onset of eccentric hypertrophy, progressive RV dilatation, and desynchrony observed in echo-imaging reflect catastrophic RV functional deterioration, eventually culminating into clinical deterioration.[1],[2],[10],[11]

Ventricular interdependence and left ventricular (LV) response - Hypertensive RV leads to IVS shifting, altered LV geography, lower values for the cardiac index, indexed LV end-diastolic volume, ejection fraction (EF) etc., and LV hypertrophy.[1],[12]

 Valvular Pulmonary Stenosis



Morphological consideration and echocardiography

RV is a tripartite (inlet, cavity, outlet portion) anterior-most chamber of the heart. Between the cavity and PV, a muscular sleeve (conus or infundibulum) exists, instigating fibrous discontinuity between PV and TV [Figure 1]a,[Figure 1]b,[Figure 1]c.[1] The main pulmonary artery (MPA) connects the ventricle to branch pulmonary arteries (right and left branch PA) and has a bicornuate appearance due to distal bifurcation [Figure 1]c. Essentially, RV muscle mass (RV to LV free wall ratio − 1:3) and systolic pressure (1/4th–1/5th of LV systolic pressure) are considerably lower than LV. PA systolic pressure is almost equal (within 10 mmHg) to RV systolic pressure; diastolic pressure of PA is very low due to less muscularity and high elasticity of PV, and it falls further in the presence of pulmonary regurgitation (PR).[1],[13],[14],[15] In severe PS, RV responds with muscular hypertrophy, disproportionately rise in RV systolic pressure in comparison to PA creating a significant gradient. The severity of PS is decided by this gradient.{Figure 1}

The goals of echo-imaging and views required to evaluate PS are described in [Table 5] and [Table 6], respectively.{Table 5}{Table 6}

In most of the autopsy series of VPS, PV were reported to be trileaflet.[1],[13] However, Gikonyo et al. found unicommissural (16%), were bicuspid (10%), tricuspid (6%), valve with hypoplastic annulus (6%) and dysplastic cusps (19%) and in rest (42%) they could not define morphology.[14]

Pulmonary cusp: Isolated VPS usually presents with thickened and domed cusps due to the commissural fusion, tethering of PV at sinotubular junction [Figure 2]. Infrequently, the PV may have dysplastic cusp and annular hypoplasia or an obstructive membrane at the supra or subpulmonary area

In echo, it is difficult to observe the enface view of PV and the number of cusps or PV area.[1],[15] Post stenotic dilatation of MPA, a hallmark of valvar PS is seen irrespective of the severity of PS [Figure 3]a and [Figure 3]b.[16] Absence of it or mild narrowing of MPA instead, suggests the possibility of covert SVPS [Figure 3]c and [Figure 3]d. The measurement of PV annulus (inner wall to inner wall distance) must be taken at the hinge-point plane, and Z score must be obtained [Figure 1]a. Z scores for the cardiac dimensions are available online.

Z score of PV gives an idea about: (1) capacity of native PV to handle RV output; (2) it helps in the balloon sizing in preparation of BPV. PV annulus is mostly muscular and can be stretched up to 120%–140%. However, severe PR may cause RV dilatation and desynchrony in the long run. Therefore, it is better to avoid balloon-annulus ratio above 1.2:1. It may not achieve a better PV area and may worsen the PR.Z Score values of TV annulus (TVA):[4],[14],[15] RV cavity volume and EF are important determinants of outcome of the intervention, which cannot be measured by Simpson's method due to the triangular shape cavity of RV.[1] Literature suggests, TV Z score corresponds well with RV volume.[1],[17],[18],[19] The TVA is a dynamic structure and can be measured in diastole by demarcating hinge point to hinge point distance carefully, in a apical four chamber view [Figure 4]. In severe neonatal PS, RV can be musclebound tripartite or may lack cavity (bipartite). Early removal of RVOTO helps in reverting the unfavorable effects of pressure overload on RV [Figure 5]a and [Figure 5]b. A grossly dysplastic TV may have Ebstenoid or Ebstein's anomaly of TV leaflets as well as anomalous papillary muscles of TV.[1],[20] In our experience, CrPS with severely dysplastic TV may present with massive cardiomegaly in a cyanosed newborn, requiring urgent fixing of TV in addition to the pulmonary valvotomy

Poor transthoracic window in older patients leads to poor imaging, and trans-oesophageal echo can be used for better understanding [Figure 6]a,[Figure 6]b,[Figure 6]c.

Post procedurefunctional PS: Hypertrophied septal and parietal bands (infundibular PS-IPS), if not noticed pre-procedure, may cause suprasystemic RV pressure and low cardiac output (suicidal RV) after a BPV procedure.[21]Fetal presentation of severe PS (CrPS with the intact ventricular system - CrPS/IVS): Fetal critical PS/IVS or pulmonary atresia/IVS (PA/IVS), may cause a variable degree of hypoplasia of the TV, PV, and RV resulting into postnatal duct dependence [Figure 7]a,[Figure 7]b,[Figure 7]c,[Figure 7]d,[Figure 7]e. Early intervention in fetal or postnatal life, gives an impetus to borderline RV (TVA Z score <−2) to have better ejection volume and growth; eventually, few of these neonates may escape the univentricular palliation.[4],[5],[11],[19] Ballooning of PV may not always improve the systemic saturation, requiring continuous prostaglandin infusion or additional procedures like duct stenting or systemic to pulmonary shunt surgery. To some extent, suboptimal results can be predicted by Z score of TVA.[22] Echocardiographic criteria has been described to make prenatal prediction of the eventual outcome of Cr-PS/IVS or PA/IVS [Table 3].[4]Differential diagnosis of CrPS:

Membranous pulmonary atresia/IVS (no antegrade flow at PV)Ebstein's anomaly of TV with functional pulmonary atresia (Severe tricuspid regurgitation (TR) leads to non-opening of PV as RV fails to overcome neonatal pulmonary arterial hypertension [PAH]).VSD, PS where VSD is not seen due to dynamic closure of VSD by TV tissue [Figure 5]c.{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Figure 7}

Primary pulmonary hypertension also presents with systemic/supra systemic RV pressure with eccentric RVH. Clinically, there is no ejection murmur, but a high pitched early diastolic murmur of PR will be heard and usually no cyanosis.[23]

 Severity of Pulmonary Stenosis



It is defined based on the Doppler peak gradient as follows:[24],[25]

Severe PS - A gradient of 64 mmHg and above or if RV systolic pressure has been estimated as ≥2/3rd of systemic, systemic, or suprasystemicModerate PS: PS gradient >36–<64 mmHg is considered as moderateMild PS: PS is considered mild if the gradient is below 36 mmHg.

 Fallacies of Doppler Echo-imaging



Accurate recording and interpretation of Doppler gradient are essential in decision making. Following fallacies are often seen during the echo-evaluation:

Underestimation of the severity of PS:

Low gain-settingPoor alignment of spectral Doppler cursor (inappropriate Doppler angle) or poor echo windowMultiple level of stenosis; (TR jet gradient may correlate better)In PS/PAH physiology like the presence of a large shunt beyond the PV (aortopulmonary window or patent ductus arteriosus) or transient pulmonary hypertension of neonateRV dysfunction.

Overestimation of the severity of PS:

High gain setting of spectral Doppler or not choosing well-enveloped signals (ghosting artifact)Systolic high-velocity jet of restrictive doubly committed VSD getting mixed with PS gradientSystolic high-velocity jet of perimembranous VSD may cause overestimation of infundibular PS.

Therefore, it is important to have a good 2D and color Doppler echo-image before recording the gradient. The anatomical site and extent of obstruction on 2D as well as restriction of the turbulent jet (color Doppler) must be noticed. Spectral Doppler cursor must be aligned to the turbulent jet to minimize the Doppler angle [Table 6].

Evaluation of the systolic and diastolic function of the right ventricle in pulmonary stenosis

[Table 7] summarizes echocardiographic evaluation of RV function [Figure 8] and [Figure 9].[26],[27],[28],[29],[30],[31],[32]{Figure 8}{Figure 9}{Table 7}

 Medical Follow up and Outcome



Follow up echo-studies are done to see gradient, RV/LV dysfunction, development of the complications like TR, infective endocarditis, thrombosis, subaortic stenosis. etc.

Fetal PS: For mild PS (normal pulmonary and tricuspid annulus), no specific protocol needed; For moderate to severe PS (± hypoplasia of TV, PV, and RV) close observation is recommended to detect cardiac dysfunction and pericardial effusion [Table 3]Postnatal PS: Children with mild PS may need to follow-up every 1–2 years. While patients with moderate PS may need more frequent follow-up. Those with Severe PS must go for intervention. Lange et al. observed that more than 80% of patients did not need intervention if PS was mild (pulmonary gradient <25 mmHg [5% of cohort] <40 mmHg [20% of cohort]) to begin with.[29] If initial gradient was between 40 and 49 mmHg, average rise in gradient was up to 8.6 mmHg/year.[29] Lueker et al., reported a decrease in PS gradient in a cohort presented with mild PS[33]Postprocedure assessment:[1],[34],[35] RV systolic pressure usually goes significantly down after the BPV. A transient but severe rise of RV pressure is seen in the presence of infundibular muscular hypertrophy and can be treated medically. Surgical intervention rarely needed. Transient RV systolic dysfunction may also be seen particularly in the presence of severe PR or TR. RV diastolic dysfunction may persist transiently (children) or for an extended period in grownup patients. PR may be high, as discussed above and may not be tolerated [Figure 10]. The babies who had pre-procedure TV Z score <−2 or PV Z score <−4 may have suboptimal outcomes after BPV and must be evaluated further for the requirement of additional procedure.{Figure 10}

Echocardiographic criteria for severe pulmonary regurgitation

The width of the vena contracta is >50% of the width of the PV annulusDiastolic flow reversal in branch PAThe duration of PR exceeds 2/3rd of the duration of diastolePressure half time <100 ms.[36] We have seen one adult patient who presented with severe RV dysfunction and atrial fibrillation after 30 years of BPV [Figure 10]a and [Figure 10]b.

d. Patient with PS (pre- or postintervention) presenting with fever: A careful observation would be needed to rule out pericardial effusion and any vegetation in a sick symptomatic baby.

 Exercise Testing Coupled with Transthoracic Echo



Exercise testing coupled with transthoracic echo may help in decision making for intervention or for sports advice for the adolescent and adults who become symptomatic on exertion despite of moderate gradient at RVOT. The post-intervention capacity to exercise improves in children but not in adults.[37],[38]

 Infundibular Pulmonary Stenosis



(Also see [Table 1] for guidelines on timing and mode of intervention; and [Table 6] for echocardiographic views.).

IPS is often a form of progressive subvalvular obstruction of RVOT. It can be classified as high and low IPS. It is associated with perimembranous VSD in 80%–90% patients. Gasul's hypertrophy of outlet septum in the presence of large perimembranous VSD, converts a shunt physiology into the acquired tetralogy of Fallot.[39] Partial closure of VSD and progressive conal septum hypertrophy, presents as IPS in adulthood. Associated abnormalities like subaortic membrane may also be found or may develop later in the natural history. One of our patients was operated for IPS at the age of 2 years and presented with syncope and underlying severe subaortic stenosis at the age of 10 years.

Assessment of the severity of infundibular pulmonary stenosis

Like VPS, recording of velocity and gradient by spectral Doppler is pivotal. Fallacies discussed VPS, are applicable for IPS also. To minimise Doppler angle, selection of view is utmost important [Table 4]. Multiple views must be used to record the gradient.

 High Infundibular Pulmonary Stenosis



It is also known as “napkin-ring stenosis” or “high double chamber RV” and “stenosis of infundibular ostium” [Figure 11]a and [Figure 11]b.[40]{Figure 11}

High IPS is caused by hypertrophied septal and parietal bands at ventriculo-infundibular (conal) junctions. The muscular ridge formed by hypertrophied muscle bundles creates two chambers (upper low pressure and lower high-pressure chamber) within the confines of the right ventricle. The upper chamber has also been designated as “moghul” chamber. Anatomical evaluation of RV cavity, moderator band (MB), and infundibulum are essential.

 Double Chamber Right Ventricle (Low Infundibular Stenosis)



Double chamber right ventricle is also considered as the septation of RV [Figure 12]a,[Figure 12]b,[Figure 12]c,[Figure 12]d. The septation happens due to the presence of an anomalous muscular bundle, which starts from the apex of RV, parallel to IVS and gets attached to the free wall of RV. These bundles are distinct from the trabecula septo-marginalis (TSM) and the MB; they vary grossly in its location and morphology.[41],[42]{Figure 12}

 Supra Valvar Pulmonary Stenosis



Congenital SVPS is rarer than post-surgery SVPS. A meta- analysis of 34 articles, only 20 (6%) patients had congenital SVPS. About 3.6% of patients of this group were syndromic, while all other patients had acquired SVPS [Table 2].[43]

Guidelines for intervention: [Table 1] and echocardiographic views [Table 4] have been described earlier in the article.

Anatomical type of supravalvular pulmonary stenosis

Single stenosis of either of MPA, right pulmonary artery (RPA), left pulmonary artery (LPA) no other branch involvement [Figure 13]a,[Figure 13]b,[Figure 13]c and [Figure 14]a,[Figure 14]b,[Figure 14]cStenosis at confluence extending up to the origin of branch PA, rest of RPA/LPA remain normalMultiple stenosis of distal branches and no involvement of central PAA combination of central and peripheral involvement is seen.[43],[44]{Figure 13}{Figure 14}

 Peripheral Pulmonary Stenosis



Discrete stenosis of one of the branch PA may be isolated diseases and need to be evaluated for evidence of diversion of blood (dilatation of contralateral artery), pressure overloadand function of RV [Figure 15]a and [Figure 15]b isolated LPA stenosis may be caused by constriction of ductal tissue extended into LPA (post duct closure) or post -device or coil closure of duct (over-sized device or device/coil migration). Measurement of RV systolic pressure (TR jet velocity) is the best echo method to assess the severity of PPS when diffuse and distal narrowing is present.{Figure 15}

 Physiological Peripheral Pulmonary Stenosis of Neonate - Innocent Murmurs of Neonates



Chatelain et al. did echo-study in 31 neonates (21 with the murmur-case group and 10 without murmur-control group) to find out the determinants of transient murmur.[45] They found 90% of these babies have relatively smaller diameter of branch PA's and had relatively higher Doppler velocities.[45] In 3 months, the murmur either disappeared (14/21) or diminished (9/21). None of them advanced to PPS. In our own experience, the majority of neonates presenting with a systolic murmur and increased Doppler velocity in one or both branch PA, get rid of murmur in 3–6 months of period and show normal velocity on echo-evaluation.

 Acquired Pulmonary Stenosis



Acquired PS is a name given to conditions which lead to flow acceleration or definable gradient across the RVOT mostly caused by any type of external compression by pericardial bands, tumors, aneurysmal dilatation of adjacent structure etc.[36],[46] Similar kinds of flow acceleration can be seen with intracardiac tumors (rhabdomyoma or metastasis), intracardiac goiter, thrombus or big vegetations. The identification of etiology of RVOT gradient must be identified correctly and managed accordingly.

 Conclusion



Isolated PS is a CHD that can be managed with timely interventions with minimum mortality and morbidity. Echo-evaluation includes morphological echo-based detailing of lesion or lesions, evaluation of volume and function of the right ventricle, quantitative assessment of pulmonary and TR, functional assessment of left ventricle and discovering other associated cardiac abnormalities. However, a subset of PS may have associated RV hypoplasia and need to be identified as early as possible. Early recognition and timely fetal or postnatal intervention remain the key to the optimum result. Long-term monitoring is required to monitor function, PR, TR, recurrence of PS or development of other complications like subaortic stenosis. An adequate echo-evaluation is pivotal to the best outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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