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Original Articles: Pediatric Cardiac

Assessment of the Relationship Between Contegra Conduit Size and Early Valvar Insufficiency

^a Department of Pediatrics, The Heart Institute, Children's Hospital Colorado, University of Colorado, Aurora, Colorado
^b Department of Surgery, Pediatric Cardiac Surgery, Children's Hospital Colorado, University of Colorado, Aurora, Colorado
^c Department of Surgery, University of Colorado School of Medicine, Aurora, Colorado

Accepted for publication October 14, 2011.

^_* Address correspondence to Dr Gist, Department of Pediatrics, Children's Hospital Colorado Heart Institute, 13123 E 16th Ave, B100, Aurora, CO 80045 (Email: katja.gist{at}childrenscolorado.org).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Background: Contegra bovine jugular vein (BJV) conduit results vary widely, and little attention has been directed at assessment of early conduit insufficiency. Conduit insufficiency is graded subjectively, and criteria vary. Several studies have used branch pulmonary artery flow reversal (BPAFR) to define severe conduit insufficiency. BJV valves are larger than human pulmonary valves of similar diameter. We hypothesize that anatomic differences between BJV and human pulmonary valves limit the use of BPAFR in the evaluation of BJV competence. Our purposes were to (1) assess the prevalence of early and 6-month BJV conduit insufficiency in our patients, (2) determine if conduit size affects BJV competence, and (3) determine if BPAFR is a specific discriminator of severe conduit insufficiency.

Methods: We reviewed 135 BJV conduits. One cardiologist blinded to original reports reviewed postoperative and 6-month echocardiograms. Conduits were grouped by size: group 1, 12 to 14 mm (n = 51), and group 2, 16 to 22 mm (n = 84). Moderate or greater insufficiency was considered clinically significant.

Results: Early conduit insufficiency was common in group 1 (37%) and rare in group 2 (5%, p < 0 .0001). After excluding conduits with significant insufficiency, BPAFR occurred in 18% (group 1, 27%; group 2, 13%; p = 0.02). At follow-up, insufficiency worsened in group 1 but was stable in group 2.

Conclusions: Early conduit insufficiency is common and worsens with follow-up in small BJVs. Conduit insufficiency is limited in larger sizes and remains stable. BJV exhibits BPAFR commonly in the absence of significant conduit insufficiency. BPAFR should not be used as a primary criterion for grading insufficiency in BJV conduits.

	Introduction

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The Contegra (Medtronic, Minneapolis, MN) bovine jugular vein (BJV) conduit is a right ventricle (RV)-to-pulmonary artery (PA) conduit used for RV outflow tract reconstruction in children. Clinical reports on performance vary. Some describe excellent midterm competence with minimal gradients [1–3], whereas others report concerning issues with early stenosis [4, 5] or conduit insufficiency (CI), or both [6–10]. These discrepancies are likely due to heterogeneous patient populations and variations in technique [6]. The evaluation of conduit performance is primarily based on echocardiogram. Techniques to estimate gradients are relatively standardized. In contrast, the assessment of CI is more subjective. Grading scales and criteria used to report CI vary considerably. Many reports on BJV conduits do not detail the criteria used to grade CI. Others base CI assessment only on clinical reports performed by multiple cardiologists.

Directional blood flow can be determined using pulse-wave Doppler. Diastolic flow reversal at the pulmonary valve indicates incompetence. Flow reversal in the branch PAs is an accepted marker of severe native pulmonary valve insufficiency. Many BJV series have used branch PA flow reversal (BPAFR) to define severe CI [1, 2, 5, 6]. When we began using the BJV conduit, we observed patients in whom early BPAFR was present but other measures of CI were absent. Two factors may explain this finding. First, numerous authors note that BJV valves have a longer profile than human pulmonary valves of equal diameter [4, 9, 11, 12]; therefore, the volume required to initiate leaflet coaptation is greater than that of a human pulmonary valve of the same diameter. Second, the wall of the BJV conduit is pliable [5, 9], and increased compliance could contribute to a larger diastolic closing volume.

We hypothesize that the fraction of RV stroke volume (RVSV) required to achieve BJV valve closure may be enough to cause BPAFR in the absence of significant CI and that BPAFR should not be used to discriminate severe CI for the BJV. The purposes of this study were to (1) assess the prevalence of early clinically important CI after BJV conduit placement, (2) determine if BJV conduit size and position influence early CI, and (3) determine if BPAFR is specifically predictive of severe BJV CI.

	Patients and Methods

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Demographics
Institutional Review Board approval was obtained, and all BJV conduits implanted at our site from March 2004 to August 2010 were identified. Nonsurvivors and patients for whom baseline postoperative echocardiograms were not available were excluded. Each conduit was considered independently. We assessed 135 conduits in 126 patients. Prior studies report performance differences by patient age at implant and BJV size [6, 13]. Conduits were grouped by size: group 1, 12 to 14 mm (n = 51) and group 2, 16 to 22 mm (n = 84). Data collected were diagnosis, age, and weight at implant, BJV size and position (orthotopic or heterotopic), and prior conduit. Diagnoses were grouped according to Table 1.

Morphometric Comparisons
Valve closing volume and cusp heights of the BJV and pulmonary allograft (each 12 mm) were determined. Internal diameter was verified with a Hegar dilator. Conduits were transected 1-mm distal to the commissural posts, and a 0.4-mm patch (Atrium Medical Corp, Hudson, NH) was sutured to the outflow end and sealed. Dry weight was measured. Water was injected in the inflow end, air was evacuated, and valves were filled to achieve leaflet coaptation. Wet weight was measured. Valve closing volume was the difference between wet and dry weights. Conduits were opened longitudinally, and cusp heights were measured from nadir to the level of the commissures. The valve length/diameter ratio was calculated using mean cusp height. Leaflet heights for 18- and 22-mm BJV (1 each) were measured similarly.

Statistical Analysis
Data were collected using Research Electronic Data Capture (REDCap) [15]. Continuous data are presented as mean ± standard deviation. Data were compared with student t tests or ² tests, as appropriate. CI was considered as a binary outcome: less than moderate regurgitation (grade 0 to 3) vs moderate or greater regurgitation (grade 4 to 6). Data were analyzed using SAS 9.2 software (SAS Institute, Cary, NC). A value of p 0.05 was considered significant.

	Results

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Demographics and conduit position are presented in Table 2. Heterotopic position was more prevalent in group 1, but this difference only trended toward significance (49% vs 33%, p = 0.10). Fewer group 1 conduits were placed after prior RV-PA conduit than in group 2 (4% vs 38%, p < 0 .0001).

View larger version (9K): [in this window] [in a new window]   Fig 1. Conduit insufficiency by grade (Grd) and group. *Grd 4-6 were considered clinically significant conduit insufficiency. Statistical significance in conduit insufficiency between group 1 and 2 was present for group 0, 1, 4-6 (p < 0.05).

Branch PA Flow Reversal
BPAFR was present in 30% of conduits at early assessment. BPAFR was present in the 10 conduits with severe CI, 1 of 2 with moderately severe CI, and 5 of 11 with moderate CI. Importantly, 61% of the conduits with early BPAFR had less than moderate insufficiency (trace, 3 of 30; mild, 18 of 55; mild-moderate, 4 of 14). BPAFR was more common in 12- to 14-mm conduits (57% in group 1 vs 14% in group 2; p < 0 .0001). Because the degree and incidence of significant CI was greater in group 1, BPAFR among groups was compared after excluding conduits with significant CI. BPAFR was still more common in smaller conduits (27% in group 1 vs 13% group 2; p = 0.02).

BPAFR at early and follow-up studies were compared. In group 1, 25 conduits had early and follow-up studies. Of the 17 without significant CI at early evaluation, 9 had early BPAFR. Of these 9 conduits, significant CI developed in 6 at follow-up (3 moderate, 3 severe), and all 6 had BPAFR at follow-up. Of the remaining 3 conduits, follow-up studies demonstrated no change in insufficiency grade or BPAFR in 2, and 1 had a decrease in CI grade (mild to trace) with resolution of BPAFR. In group 2, 55 conduits had early and 6-month evaluations. Nine had early BPAFR (all without significant early CI). At follow-up, BPAFR was not present in any group 2 conduit, and none had significant CI; thus, larger conduits remained competent and BPAFR resolved in those with early BPAFR.

Morphometric Comparisons
The closing volume of the 12-mm BJV was 1.6 mL vs 0.7 mL for the 12-mm pulmonary allograft. Mean cusp height of the 12-mm BJV was 14 mm vs 6 mm in the pulmonary allograft (Fig 2 A). The valve length/diameter ratio for the 12-mm BJV was 1.2 vs 0.5 for the 12-mm pulmonary allograft. Consequently, volume and morphometric comparisons between the BJV and pulmonary valve correlated well. Allografts in larger sizes were not available. Mean cusp height for the 18-mm BJV was 14 mm (valve length/diameter ratio = 0.8). Mean cusp height for the 22-mm BJV was 13 mm (valve length/diameter ratio = 0.6).

View larger version (74K): [in this window] [in a new window]   Fig 2. Cusp heights in bovine jugular vein (BJV) conduits and pulmonary allografts. (A) 12-mm BJV (left), 12-mm pulmonary allograft (right). (B) 18-mm BJV (lower), 22-mm BJV (upper).

	Comment

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

Our series is one of the largest single-center reports on the BJV conduit, but mean follow-up is short (2.9 ± 1.7 years). Although most published concerns related to BJV performance report conduit stenosis, we had the impression of a significant prevalence of early CI in patients with small conduits. Thus, we focused our report on the early evaluation of CI. We have, however, had only a few conduit replacements. To date, 10 BJV (7 group 1, 3 group 2) have been replaced (9 repeat BJV, 1 allograft). Five were replaced at operations indicated for causes unrelated to the conduits. Indications for the five failures were one for severe stenosis/insufficiency (12 mm at 44 months), three for severe insufficiency (all 12 mm; range, 4 to 44 months), and one for endocarditis (18 mm at 23 months).

Several prior 1-center or 2-center–based studies with a lower relative prevalence of very young patients reported encouraging assessments of BJV competence in all sizes [1–3, 9]. In these reports echocardiographic data were extracted from clinical reports rather than from a complete review by a single observer. Other studies have reported a significant incidence of CI, primarily in smaller conduits, as observed in our series [6–8, 10, 13, 16].

Factors associated with CI include small size, young age at operation, truncus arteriosus, branch PA obstruction, and elevated pulmonary vascular resistance [6–8, 10, 13, 16]. Reports containing higher percentages of neonates and infants are less promising. In a series of 64 conduits in which most were 12 to 14 mm (nearly one-third had pulmonary atresia/ventricular septal defect/major aortopulmonary collateral arteries), significant dilation with severe CI related to distal obstruction developed in 27%. The time to development of CI and the competence of remaining conduits were not reported [7]. Rastan and colleagues [6] reported similar findings, with moderate or greater CI present at hospital discharge in 44% of infants. Both series associated elevated RV pressure (right-to-left ventricle ratio > 0.6) with CI [6]. In the Congenital Heart Surgeon's Society comparison of allograft vs BJV for truncus arteriosus, most BJV had at least moderate CI within the first year [10]. The European Contegra Multicenter Study, the largest multicenter series, reported a 30% incidence of moderate or greater CI in 12- to 14-mm conduits at 1 year [13]. In our report, 38% of conduits were sizes 12 to 14 mm. Given that significant CI occurred almost entirely in this group, the incidence of CI we observed in the first year is comparable to other reports that had a similar percentage of small conduits.

In our experience CI is more common with heterotopic position. Several reports indicate that allograft RV-PA conduit performance is superior for orthotopic vs heterotopic position [18]. A reported advantage of the BJV is that heterotopic placement with minimal distortion is readily accomplished because the valved portion can be placed distally away from the sternum [1–3]. Our study adds to the data available on BJV performance relative to conduit position by presenting compared conduit position and function.

Even in the evaluation of native pulmonary valve function, the assessment of pulmonary insufficiency is subjective. This factor is of significant importance in the evaluation of RV-PA conduit, and comparison of CI among published reports is therefore problematic. Most cardiologists consider BPAFR to be a reliable sign of severe native pulmonary valve insufficiency, and several BJV studies have defined severe CI using BPAFR. However, the American Society of Echocardiography guidelines do not consider this variable in grading pulmonary insufficiency [14]. After our initial experience with the BJV, we observed patients who had BPAFR in the absence of other echocardiographic evidence of significant CI. In fact, the current study was in part motivated by controversy among our group about the clinical relevance of BPAFR in grading BJV CI. BPAFR occurs consistently with severe CI. However, our data demonstrate that BPAFR cannot be used to distinguish severe CI because 61% of the conduits with early BPAFR did not have significant CI.

Significant anatomic differences between BJV and the human pulmonary valve may explain our findings. Other authors have reported that BJV leaflet heights are substantially longer than those in human pulmonary valves of the same diameter [3, 9, 11, 12]. In a recent study, Boethig and colleagues [12] stated that BJV cusp height approximated conduit diameter and that leaflet height for the human pulmonary valve was approximately 50% of the diameter. Whether these differences are consistent across the clinical size spectrum has not been previously been assessed. Assuming Boethig and colleagues are correct, the diastolic closing volume of BJV should be double the volume of a human valve of the same diameter.

The highly compliant wall of the BJV may also contribute to a larger relative closing volume. We have postulated that the larger fraction of RVSV required to close a BJV could cause detectable BPAFR in the absence of significant CI. Our comparison of the 12-mm BJV with allograft valves supports this hypothesis, with closing volumes of 1.6 and 0.7 mL, respectively. There are no data for the normal RVSV in a small baby. Assuming that RVSV and left ventricular SV are equal, a cardiac index of 2.5 L/min, body surface area of 0.2 m², and a heart rate of 150 beats/min, extrapolation yields an approximate RVSV for a 3.0-kg baby of 3.3 mL. A perfectly competent 12-mm BJV with a closing volume of 1.2 mL would equate to a regurgitant fraction of 36% compared with only 20% for a 12-mm human pulmonary valve. In this size range, mild CI is typical; thus, the combined closing volume and actual regurgitant fraction of BJV in a small infant are sufficient to result in BPAFR in the absence of significant CI.

BPAFR in clinically competent valves was less common (14%) in larger conduits. Two factors may explain this difference. First, our study of BJV anatomy suggests that minimal disparity in closing volume between BJVs and human pulmonary valves. There are no published data to indicate if pulmonary valve height/diameter ratio is consistent across the human size spectrum. However, unpublished data indicate that the mean valve height/diameter ratio for the human pulmonary valve is 0.6 ± 0.1, and that this ratio is consistent across the human size range (personal communication from CryoLife Inc, Kennesaw, GA). Second, BPAFR observed at early assessment in larger conduits was absent at the 6-month follow-up examination. We speculate that early BPAFR in larger conduits may be due to the high compliance of some conduits and that scarring probably reduces conduit compliance, thereby eliminating BPAFR over time.

Clinical reports indicate that over-sizing RV-PA conduits increases freedom from reoperation [19]. However, this practice warrants caution when a BJV is intended for a small baby because of the large difference in valve closing volumes between BJV and allografts at sizes typically used for these patients. There are numerous reports of early BJV thrombosis, likely resulting from stasis within the valve cusps [7, 9, 20]. This complication is more likely when valve capacity represents a significant proportion of RVSV, and we agree with recommendations to administer aspirin after BJV implantation.

This study has several limitations beyond the retrospective design. Firstly, echocardiographic assessment of CI is inherently subjective. We sought to minimize this limitation by using a single cardiologist blinded to the original clinical reports. Secondly, follow-up in this study was relatively short. Lastly, conclusions related to the anatomic differences between BJV and human pulmonary valve were based on measurements from a limited number of conduits.

In summary, there remains no ideal conduit for RV outflow tract reconstruction. BJV offers important advantages, particularly in conduit sizes appropriate for children above the infant age range. However, our experience suggests that significant early CI occurs with high prevalence in 12- to 14-mm conduits. The clinical ramifications of this finding remain to be determined due to limited follow-up time. In contrast, larger conduits had excellent performance at current follow-up. BPAFR occurs commonly in the absence of clinically important CI, and BPAFR should not be used to distinguish severe conduit insufficiency. Finally, there are significant anatomic differences between BJVs and allograft human valves that warrant consideration during conduit selection, particularly in small infants.

	Appendix

 

Classification of Insufficiency ^a

Grade Category Echocardiographic Description 0 None No color Doppler jet 1 Trivial Barely noticeable color Doppler jet 2 Mild Thin color Doppler jet; soft-density spectral Doppler jet with slow deceleration 3 Mild-moderate Between mild and moderate 4 Moderate Intermediate color Doppler jet; dense spectral Doppler jet with variable deceleration 5 Moderate-severe Between moderate and severe 6 Severe Large color Doppler jet; dense spectral Doppler jet with steep deceleration; early termination of diastolic flow a Data from reference 14.

	Acknowledgments

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
We thank CryoLife Inc, for providing sample allograft, Medtronic Inc, for providing sample Contegra conduits for this study, and Sheri Crumback, for assistance with data collection.

	References

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Max B. Mitchell James Jaggers Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gist, K. M. Articles by Landeck, B. F. Search for Related Content PubMed PubMed Citation Articles by Gist, K. M. Articles by Landeck, B. F., II Related Collections Congenital - cyanotic