Pulmonary Atresia with Intact Ventricular Septum (PA-IVS): A Physiologic and Surgical Overview

Pulmonary atresia with intact ventricular septum (PA-IVS) is a morphologically heterogeneous congenital heart lesion defined by complete obstruction of the right ventricular outflow tract in the absence of a ventricular septal defect. Its clinical behavior is determined not only by the atretic pulmonary valve, but also by the degree of tricuspid valve hypoplasia, the size and morphology of the right ventricle, and the presence or absence of coronary abnormalities. As a result, PA-IVS should not be viewed as a single lesion with a uniform treatment pathway. Rather, it represents a spectrum in which the central management question is whether the patient can safely undergo right ventricular decompression and progress toward a biventricular circulation, or whether single-ventricle palliation is the more appropriate strategy [1-3]. (PubMed)

1. Fundamental anatomic and physiologic framework

In the neonatal period, pulmonary blood flow in PA-IVS is usually ductal-dependent because there is no native antegrade egress from the right ventricle to the pulmonary artery. At the same time, the right ventricle is frequently hypertensive and variably hypoplastic. This hypertensive right ventricle may range from a relatively well-formed tripartite chamber to a severely underdeveloped unipartite ventricle. The tricuspid valve generally parallels right ventricular development, and together these two structures form the principal anatomic basis for pathway selection [1-3]. (PubMed)

From a practical surgical standpoint, four factors should be assessed at the outset:

Tricuspid valve size
Right ventricular size
Right ventricular morphology (tripartite, bipartite, or unipartite)
Coronary circulation, especially the presence of right ventricle-dependent coronary circulation (RVDCC) [1-4]. (PubMed)

2. Pulmonary blood flow patterns in PA-IVS

A. Ductal-dependent pulmonary blood flow

In the classic presentation, pulmonary perfusion depends on patency of the ductus arteriosus. For this reason, prostaglandin infusion is essential in the early neonatal period, and in selected patients ductal stenting may be used to stabilize pulmonary blood flow. This is the baseline physiology from which further pathway decisions are made.

B. Antegrade RV-PA flow after decompression

If pulmonary valvotomy, perforation, or surgical decompression establishes antegrade right ventricular outflow, pulmonary blood flow becomes increasingly dependent on right ventricular pressure generation and functional capacity. This is the physiologic basis of RV rehabilitation. Decompression, however, is not merely a technical step to improve oxygen saturation; it is a strategic intervention intended to test and promote right ventricular recruitment toward a more complete circulation [1,3].

C. Dual pulmonary blood supply

Some patients enter a transitional state in which pulmonary blood flow is provided by both the ductus and antegrade RV-PA flow. In this setting, regulation of pulmonary blood flow becomes more complex because oxygen saturation, RV performance, ductal contribution, and branch pulmonary artery flow all interact. This mixed physiology often requires particularly careful interpretation in the early post-intervention period.

3. Tricuspid valve size and right ventricular morphology as determinants of circulation

Among the structural variables in PA-IVS, tricuspid valve size and RV morphology are the principal determinants of suitability for biventricular versus single-ventricle repair. In the contemporary cohort reported by Sukhavasi and colleagues, patients directed toward a biventricular pathway had a substantially larger tricuspid valve than those managed along a single-ventricle pathway, with a median tricuspid valve Z-score of -1.59 versus -5.12, respectively [1]. Earlier series similarly showed that successful biventricular repair is associated with a larger tricuspid valve and a more adequately formed right ventricle [2,5]. (PubMed)

Right ventricular morphology provides an additional layer of stratification. A tripartite RV, with preserved inlet, trabecular, and outlet portions, is the most favorable substrate for biventricular recruitment. In contrast, bipartite or unipartite morphology suggests more profound hypoplasia and reduced potential for full right-sided recruitment. In the UK and Ireland population-based study, unipartite RV morphology was an independent risk factor for death, underscoring that RV morphology is not only descriptive anatomy but also a clinically meaningful prognostic marker [3]. (PubMed)

Accordingly, the determinants of final circulation can be conceptualized as follows:

More favorable for BiV repair

Larger tricuspid valve
RV size closer to normal
Tripartite RV morphology
Absence of RVDCC

More favorable for SV palliation

Severe tricuspid hypoplasia
Markedly hypoplastic RV
Bipartite or unipartite RV morphology
Presence of RVDCC or major coronary obstruction [1-3,5]. (PubMed)

4. Coronary abnormalities and the significance of RVDCC

The most important modifier of treatment strategy in PA-IVS is the coronary circulation. Elevated right ventricular pressure may produce ventriculocoronary connections and coronary sinusoids. In some patients, especially when there is proximal coronary stenosis, interruption, or ostial atresia, myocardial perfusion becomes dependent on the hypertensive RV cavity. This is right ventricle-dependent coronary circulation (RVDCC). In such cases, the RV is not simply abnormal; it is functionally supporting coronary perfusion [4,6]. (PubMed)

This distinction is crucial because RVDCC is the strongest adverse prognostic factor in many modern PA-IVS series and may override the anatomic appeal of RV decompression. In the 119-patient study by Sukhavasi et al., RVDCC was present in 26% of patients and was associated with markedly worse mortality: 41.9% in patients with RVDCC versus 7.3% in those without RVDCC [1]. In a dedicated single-ventricle cohort reported by Cheung et al., survival was 100% in non-RVDCC patients but only 40% in those with RVDCC; mortality was especially severe in the subgroup with coronary ostial atresia [4]. Similarly, Guleserian et al. showed that among patients with PA-IVS and RVDCC managed toward Fontan-type palliation, aortocoronary atresia carried 100% mortality in their series [6]. (PubMed)

These data explain why coronary anatomy must be defined before RV decompression is pursued. In simple coronary artery fistulae, runoff and coronary steal may occur, but the coronary circulation is not necessarily pressure-dependent on the RV. In contrast, in true RVDCC, decompression of the RV may abruptly reduce coronary perfusion pressure and provoke myocardial ischemia, ventricular dysfunction, or death [4,6]. (PubMed)

5. Imaging assessment and prediction of coronary risk

Echocardiography is central to early triage because it allows rapid assessment of tricuspid valve size, RV morphology, RV cavity dimensions, tricuspid regurgitation, and the possible presence of coronary sinusoids. Among echocardiographic variables, the tricuspid valve Z-score is particularly useful. Satou et al. demonstrated that a tricuspid valve Z-score of -2.5 or less predicted RV-dependent coronary arteries with 100% sensitivity, 83% specificity, 80% positive predictive value, and 100% negative predictive value [2]. This finding remains highly relevant because it provides a simple imaging threshold that helps identify neonates in whom detailed coronary evaluation is especially important. (PubMed)

Nevertheless, echocardiography alone is not always sufficient. If coronary dependency is suspected, angiographic definition remains critical because the safety of RV decompression depends on the pattern and extent of coronary obstruction. The key practical question is not merely whether ventriculocoronary connections exist, but whether a substantial portion of myocardial perfusion depends on sustained RV systolic pressure [2,4,6]. (PubMed)

6. RV decompression: opportunity and hazard

In anatomically favorable patients without coronary dependency, RV decompression can establish antegrade pulmonary blood flow, reduce ductal dependence, and initiate a process of RV recruitment. This may ultimately support a biventricular or one-and-a-half ventricular circulation. However, decompression should not be understood as universally beneficial. Its value depends entirely on the coronary substrate and the underlying recruitability of the RV [1,5]. (PubMed)

By contrast, in patients with significant coronary obstruction or true RVDCC, RV decompression may be dangerous. Gentles et al. showed that myocardial ischemia after right ventricular decompression is a real risk in PA-IVS with coronary abnormalities, particularly when coronary obstruction is more extensive [7]. Contemporary interpretation of this principle is straightforward: extensive multivessel coronary obstruction, coronary ostial atresia, or clear RV-dependent coronary perfusion strongly argues against routine RV decompression and favors single-ventricle palliation or, in selected cases, transplantation-oriented planning [4,6,7]. (PubMed)

7. Contemporary pathway selection

The final circulation in PA-IVS is best viewed as a spectrum rather than a binary endpoint. Potential end states include:

Biventricular repair
One-and-a-half ventricular repair
Single-ventricle palliation
Cardiac transplantation

In broad terms, a larger tricuspid valve, better RV morphology, and absence of RVDCC favor progression toward a biventricular circulation. Severe right-heart hypoplasia and coronary dependency favor the single-ventricle pathway. Borderline patients may evolve toward an intermediate one-and-a-half ventricular circulation depending on growth and functional response after initial intervention [1,3,5]. (PubMed)

8. Summary

PA-IVS is fundamentally a disease of anatomic triage and physiologic pathway selection. The initial physiology is defined by ductal-dependent pulmonary blood flow, but the long-term strategy is determined by the interaction among tricuspid valve size, RV size, RV morphology, and coronary anatomy. Of these, tricuspid valve size and RV morphology are the major structural determinants of whether a biventricular circulation is feasible, whereas RVDCC is the most important adverse coronary feature and one of the strongest predictors of mortality regardless of pathway [1,4,6]. Safe management therefore depends on recognizing not only whether the RV can be opened, but whether it should be opened. In favorable anatomy, decompression may support RV rehabilitation and eventual BiV or 1.5V repair. In unfavorable coronary anatomy, especially with RVDCC or coronary atresia, decompression may be harmful, and single-ventricle palliation or transplantation should be considered early [1,4,6,7]. (PubMed)

References

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[2] Satou GM, Perry SB, Gauvreau K, Geva T. Echocardiographic predictors of coronary artery pathology in pulmonary atresia with intact ventricular septum. Am J Cardiol. 2000;85(11):1319-1324.

[3] Daubeney PEF, Wang D, Delany DJ, Keeton BR, Anderson RH, Slavik Z, Flather M, Webber SA; UK and Ireland Collaborative Study of Pulmonary Atresia with Intact Ventricular Septum. Pulmonary atresia with intact ventricular septum: predictors of early and medium-term outcome in a population-based study. J Thorac Cardiovasc Surg. 2005;130(4):1071.

[4] Cheung EW, Richmond ME, Turner ME, Bacha EA, Torres AJ. Pulmonary atresia/intact ventricular septum: influence of coronary anatomy on single-ventricle outcome. Ann Thorac Surg. 2014;98(4):1371-1377.

[5] Rychik J, Levy H, Gaynor JW, DeCampli WM, Spray TL. Outcome after operations for pulmonary atresia with intact ventricular septum. J Thorac Cardiovasc Surg. 1998;116(6):924-931.

[6] Guleserian KJ, Armsby LB, Thiagarajan RR, del Nido PJ, Mayer JE Jr. Natural history of pulmonary atresia with intact ventricular septum and right-ventricle-dependent coronary circulation managed by the single-ventricle approach. Ann Thorac Surg. 2006;81(6):2250-2257.

[7] Gentles TL, Colan SD, Giglia TM, Mandell VS, Mayer JE Jr, Sanders SP. Right ventricular decompression and left ventricular function in pulmonary atresia with intact ventricular septum. The influence of less extensive coronary anomalies. Circulation. 1993;88(5 Pt 2):II183-II188.