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Ann Thorac Surg 2001;72:182-186
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Atrioventricular valve replacement in patients with a single ventricle

Accepted for publication March 29, 2001.

Address reprint requests to Dr Mahle, The Children’s Hospital of Philadelphia, 34th & Civic Center Blvd, Philadelphia, PA 19104
e-mail: mahle{at}email.chop.edu

	Abstract

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Background. Significant atrioventricular valve (AVV) insufficiency has been associated with increased mortality and morbidity in patients with single ventricle. Although many patients can be managed with valvuloplasty alone, some patients require AVV replacement. The optimal timing, outcome, and risk factors for AVV replacement in this population have not been described.

Methods. We retrospectively reviewed our experience with AVV replacement in patients with single ventricle from January 1984 to August 2000. Outcome variables included mortality and valve-related complications.

Results. Seventeen patients required AVV replacement. Prosthetic valve types included: St. Jude’s valve in 14, Bjork-Shiley in 1, Hall-Kaster in 1, and Carpentier-Edwards in 1. Valve size ranged from 17 to 33 mm. Median age at valve replacement was 3.0 years (range 7 days to 17.3 years). Of the 16 subjects with normal atrioventricular conduction preoperatively, 7 (44%) developed postoperative complete heart block. Hospital mortality was 29%. Hospital mortality decreased significantly from 56% in 1984 to 1993 to no deaths from 1994 to 2000 (p = 0.03). Younger age (less than 2 years) at operation was also a risk factor for hospital mortality (p = 0.03). There were four late deaths in this series and 1 patient underwent heart transplantation. Of the surviving patients, none has required replacement of the prosthetic valve. No patients have had cerebrovascular accident subsequent to AVV replacement. Functional status is New York Heart Association functional class I in 5, class II in 1, and Class III in 1.

Conclusions. Atrioventricular valve replacement can be performed in patients with single ventricle with acceptable morbidity and mortality. The development of postoperative complete heart block is common. Survival after AVV replacement has improved in recent years, and intervention before patients develop ventricular dysfunction and atrial arrhythmias may further improve outcome.

	Introduction

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Significant atrioventricular valve (AVV) insufficiency has been reported in up to 37% of patients with single ventricle who undergo surgical palliation [1–3]. Several studies have found that AVV insufficiency is associated with an increased risk of mortality at the time of the cavopulmonary operation and may be a risk factor for late death in these patients [1, 3]. Atrioventricular valve insufficiency has also been linked to the development of atrial arrhythmias, presumably based on atrial dilation, and progressive ventricular dysfunction [4]. As such, there has been considerable interest in improving AV function in the single ventricle population.

Several investigators have reported excellent early results of AV valvuloplasty before or at the time of cavopulmonary operation [1, 2]. Although techniques such as annuloplasty, chordal elongation, and the use of pericardial patches can improve AVV function in many patients, a number of patients continue to have significant AVV insufficiency and may require AVV replacement [5]. Recent series have reported the use of a prosthetic valve in the mitral position for pediatric patients with two-ventricle circulation [6–9]. However, data regarding AVV replacement in patients with single ventricle are lacking. This population may be at particular risk because of the heterogeneous nature of the AVV apparatus, the course of the AV conduction pathway, and the inherent limitations of single ventricle reserve. We reviewed our surgical experience in patients with a single ventricle heart who underwent AVV replacement.

	Material and methods

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Patient population
We retrospectively reviewed the surgical database at our institution to identify all patients with single ventricle lesions who underwent AVV replacement between January 1, 1984, and August 1, 2000. Data from operative notes, cardiac catheterization, and echocardiography were reviewed to identify the mechanism of AVV insufficiency and whether previous valvuloplasty had been performed. The primary outcome variable was hospital mortality. Additional outcome measures included late death, arrhythmia, heart block, reoperation, and cerebrovascular accidents (CVA). Preoperative and postoperative two-dimensional echocardiograms were also reviewed to assess ventricular shortening in a semiquantitative fashion (normal, mildly depressed, markedly depressed). Potential risk factors for hospital mortality and postoperative complications were identified from the medical records and are shown in Table 1. Follow-up status was determined by direct patient contact. Recent clinical data including echocardiographic reports were also examined.

Statistical analysis
Data are expressed as mean ± standard deviation or median and range, where appropriate. Survival was estimated by the Kaplan-Meier method, defined as the elapsed time from the date of valve replacement to the date of death or last known follow-up. Analysis was performed with Fisher’s exact test for categorical variables. Cox proportional hazard was used to compare survival. Analysis was performed with Stata 6.0 (Stata Corporation, College Station, TX). Significance was determined at p value of less than 0.05. All p values are two-sided and confidence intervals are 95%.

	Results

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Patient data
Preoperative characteristics
Between January 1, 1984, and August 1, 2000, more than 1,700 patients with single ventricle underwent operations at our institution. AVV replacement was undertaken in 17 of these patients. The median age at operation was 3.0 years (range 7 days to 17.3 years). The median weight at operation was 22.7 kg (range 2.6 to 50.6 kg). The incompetent AVV was of tricuspid morphology in 7 (41%), mitral in 2 (12%), common AV canal in 6 (35%), double-inlet left ventricle in 1 (6%), and straddling tricuspid valve in 1 subject (1%). Heterotaxy was present in 4 patients (12%), and atrioventricular discordance—L-looping of the ventricles—was present in 4 patients (12%). Seven subjects (41%) were receiving pharmacotherapy for atrial arrhythmia before valve replacement.

Most patients (15 of 17) had undergone previous palliative procedures (Table 2). Prior valvuloplasty had been attempted in 10 patients. Reparative techniques included annuloplasty, suture closure of cleft, and leaflet resection. Descriptions of the AVV morphology and the apparent mechanisms of insufficiency were available for 14 patients. Abnormalities included dysplastic or myxomatous valve tissue in 9, severe prolapse in 6, tethering of the septal leaflet in 1, and a double orifice valve in 1. The insufficiency—as determined by color Doppler echocardiography or angiography—was graded as moderate in 2 (12%) and severe in 15 patients (88%). Ventricular systolic performance was "normal" in 3 (18%), "mildly depressed" in 8 (47%), and "markedly depressed" in 6 (35%). Ventricular systolic dysfunction appeared to be a complication of AV valve regurgitation for most patients. Of the 6 subjects with markedly diminished ventricular function at the time of valve replacement, 5 had normal or only mildly diminished ventricular shortening when significant valve regurgitation was first detected. Preoperative cardiac catheterization was performed in 16 patients. The median end-diastolic pressure was 15.5 mm Hg (range 7 to 20 mm Hg). For the 12 patients who had undergone prior cavopulmonary operation, the median pulmonary artery pressure was 21.5 mm Hg (range 14 to 25 mm Hg).

Late mortality and morbidity
There were four deaths after hospital discharge in these series. Two deaths that occurred within 6 months of valve replacement were attributed to progressive ventricular dysfunction and pneumonia. Two deaths occurred more than 1 year after the operation. One patient died at the time of subsequent revision of the Fontan baffle. One patient had sudden death thought to be secondary to atrial arrhythmia. One additional subject underwent orthotopic heart transplantation 10 months after valve replacement because of progressive ventricular dysfunction.

Follow-up was obtained for the remaining 7 patients at a median of 1.8 years after valve replacement (range 4 months to 10.3 years). There were no reports of valve thrombosis, late CVA, bleeding complications, or endocarditis. Four subjects continue to receive antiarrhythmic medications for atrial arrhythmias; however, no patients have been diagnosed with new atrial arrhythmias after hospital discharge. Of the 7 survivors, 5 were in New York Heart Association (NYHA) functional class I, 1 was in NYHA class II, and 1 was in NYHA class III. No patients have required replacement of the prosthetic valve. All survivors were taking a daily oral anticoagulant agent and an angiotensin-converting enzyme inhibitor at follow-up. Review of subsequent echocardiography suggested improvement in qualitative ventricular systolic function in 4 of the 7 patients. The remaining 3 subjects had no change in ventricular shortening.

Risk factors for mortality and morbidity
Over the 17-year study, there was a significant decrease in mortality associated with AVV replacement. Hospital mortality decreased from 56% in the early part of these series (1984 to 1993) to no deaths among the 8 patients who underwent AVV replacement from 1994 to 2000, p = 0.03. Hospital mortality was also significantly higher for patients less than 2 years of age (66%) compared with those older than 2 years (8%), p = 0.03. In this series, no patient who underwent valve replacement before 2 years of age survived more than 6 months after the operation. The only factor significantly associated with improved overall survival was valve replacement in the more recent era (Fig 1). None of the patient- or procedure-related variables such as valve morphology, age at operation, sex, or prosthetic valve size were significantly associated with the development of postoperative CHB.

View larger version (8K): [in this window] [in a new window]   Fig 1. Kaplan-Meier survival plot stratified by era of operation. time 0 = time of valve replacement.

	Comment

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Recent reports have demonstrated excellent early and intermediate-term results for mitral valve replacement in pediatric patients with two-ventricle circulation [6–9]. Cabalka and associates [7] reported a relatively low early mortality of 12% for mitral valve replacement. The freedom from valve-related events was 77% at 10 years. Even in the subset of patients less than 6 years of age, hospital mortality was less than 20% and survival had improved significantly in the more recent surgical era. Data regarding systemic AVV replacement in patients with single ventricle, however, are lacking. In a single institution series of 500 patients, Gentles and colleagues [10] reported that systemic AVV replacement had been undertaken in 3 of 363 long-term survivors of the Fontan operation. Another large single institution series reported that AVV replacement had been performed in 12 of 499 (2.4%) of patients who had undergone a modified Fontan procedure [4]. The outcome for this subset of patients, however, was not detailed. Several factors may make valve replacement particularly complicated in the single ventricle population. The AVV morphometry can vary considerably among the various forms of single ventricle and can make sizing the prosthesis difficult. The single ventricle may not tolerate the acute changes in afterload and ventricular volume that may occur with valve replacement.

Data from our center would support the notion that the single ventricle population is at increased risk for mortality after AVV replacement when compared with other pediatric populations. The hospital mortality for valve replacement was 29%, and there was a significant risk for late death or transplantation. Factors that may have contributed to the higher mortality include atrial arrhythmias, which were present in 41% of patients. Durongpisitkul and colleagues [4] have also reported an increased incidence of atrial arrhythmias in patients requiring AVV replacement. It is possible that interventions such as a modified Maze procedure, which was used in some patients in the latter part of this series, may improve the outcome for these patients. Many patients in this series also had relatively poor preoperative hemodynamic measurements—the median preoperative end-diastolic pressure was 15.5 mm Hg and the median pulmonary artery pressure for those patients who had previously undergone the cavopulmonary procedure exceeded 20 mm Hg. Although echocardiography suggested that ventricular function improved in some patients after AVV replacement, a number of patients continued to demonstrate deterioration in ventricular contractility. This same phenomenon has been described in patients with congenitally corrected transposition of the great arteries (CCTGA) who develop systemic right ventricular dysfunction [11]. Lundstrom and colleagues [11] suggested that patients with CCTGA should have tricuspid valve replacement before significant right ventricular dilation. In the present study we were unable to demonstrate that qualitative ventricular contractility as assessed by echocardiography or ventricular end-diastolic pressure were risk factors for mortality after AVV replacement. Whether intervening earlier in patients with single ventricle and significant AVV insufficiency will preserve ventricular function remains a matter of speculation. Further studies will be needed to define the appropriate time to undertake valve replacement in the single ventricle population.

An additional risk factor for mortality appears to be younger age at valve replacement. Of the 6 patients who underwent valve replacement before 2 years of age none survived more than 6 months after operation. In most of these younger patients pulmonary blood flow was supplied by arterial-pulmonary shunt. It is possible that the acute changes in afterload that occur with AVV replacement may be poorly tolerated in patients with single ventricle and shunt-dependent pulmonary blood flow. In addition, the small size of the prosthesis may be a factor contributing to increased mortality in younger subjects. The poor outcome for young patients in these series raises questions about the appropriate management of this complex group. It is possible that heart transplantation may represent the best opportunity for long-term survival.

This series did demonstrate an improvement in survival for patients undergoing AVV replacement in the more recent surgical era. This finding parallels a trend toward improved overall survival for patients with single ventricle reported from many centers, including our own [10, 12, 13]. The improved survival has been attributed to a variety of factors including advances in surgical and perfusion techniques and postoperative management. In addition, in recent years we have attempted to optimize preoperative hemodynamics in some patients with an elective course of intravenous inotropic medications such as phosphodiesterase inhibitors. Lastly, the surgical technique of AVV replacement may have some impact on postoperative ventricular function. In the latter part of this series, an attempt was made to preserve chordal attachments of the papillary muscle to the native AVV. This method may contribute favorably to single-ventricle hemodynamics as previous investigators have shown the downward movement of the AVV annulus during ventricular systole accounts for much of the forward flow in the systemic venous pathway [14].

The major morbidity after AVV replacement was the development of CHB, which occurred in more than 40% of patients. The reported incidence of CHB after mitral valve replacement in patients with two-ventricle circulation has varied considerably. There were no reported cases of postoperative complete heart block in 34 cases reported by Cabalka and coworkers [7] or 35 cases reported by Gunther and colleagues [6]. However, other series have reported postoperative CHB in as many as 37.5% of patients with endocardial cushion defects who required valve replacement [9, 15]. There are several reasons why patients with single ventricle may be at particular risk with AVV replacement. Both heterotaxy and atrioventricular discordance, which were present in several patients in the present series, are known to be predisposing factors for CHB. In addition, because the prosthetic valve is secured with circumferential sutures, it is difficult to avoid placing sutures near the AV conduction pathway, which usually passes posteriorly in patients with single ventricle [16]. Because of the increased risk of postoperative CHB, there may be a role for elective placement of permanent pacing wires at the time of AVV replacement. The risk of CVA is also of considerable importance after AVV replacement and may be even higher after the Fontan procedure, which is known to produce a prothrombotic state. In the present series, 1 patient had a CVA, which was thought to be secondary to an intraoperative embolus. There were no patients who suffered a postoperative CVA.

The major limitation to the current study is the small number of patients, which limits risk factor analysis. In addition, the complex geometry of many single ventricle lesions limited quantitative assessment of ventricular function by standard two-dimensional echocardiography.

In conclusion, AVV replacement can be performed in patients who have single ventricle with acceptable mortality, although survival is lower than that reported for patients with two-ventricle circulation. There is a significant risk for postoperative CHB. Younger age is associated with greater mortality after AVV replacement. Survival has improved in recent years, and earlier intervention—before the development of significant ventricular dysfunction or atrial arrhythmias—may further improve outcome in the future.

	References

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