Predictors of early- and late-onset supraventricular tachyarrhythmias after Fontan operation

BACKGROUND

The objectives of our study were to determine the frequency of supraventricular tachyarrhythmias (SVTAs) among modifications of the Fontan operation and identify risk factors for developing SVTA.

METHODS AND RESULTS

The population consisted of all patients who had any modification of the Fontan operation at the Mayo Clinic between 1985 and 1993. Clinically significant SVTAs were those requiring initiation or change of antiarrhythmic treatment, and they were divided into early SVTAs (<30 days after the operation) and late SVTAs (>/=30 days after the operation). Clinical histories were reviewed, and health status questionnaires were sent. Four hundred ninety-nine patients had various modifications of the Fontan operation. Frequency of early SVTA was 15%. Risk factors identified by multivariate analysis for early SVTA were AV valve regurgitation, abnormal AV valve, and preoperative SVTA. Frequency of late SVTA was 6% by 1 year, 12% by 3 years, and 17% by 5 years. Risk factors for late SVTA were age at operation (<3 or >/=10 years) and systemic AV valve replacement. By univariate and multivariate analysis, the type of Fontan operation was not a significant risk factor for late SVTA when all 6 modifications were considered. However, when we analyzed the frequency of late SVTA for the 2 recently used modifications, we found a lower frequency of late SVTA in patients with atriopulmonary connection with lateral tunnel compared with those with total cavopulmonary connection.

CONCLUSIONS

Postoperative SVTA continues to be a significant problem. Risk factors for SVTA are AV valve regurgitation, abnormal AV valve, preoperative SVTA, and age at operation. Frequency of SVTA does not appear to be related to type of Fontan procedure except for slightly lower frequency in patients with atriopulmonary connection with lateral tunnel compared with those with total cavopulmonary connection.

Use of heparin in the treatment of protein-losing enteropathy after fontan operation for complex congenital heart disease

Protein-losing enteropathy (PLE) is a serious complication of the Fontan operation and is associated with pronounced mortality. Medical management of PLE has been only partially successful. A recent report noted dramatic improvement in patients with PLE within 3 weeks of subcutaneous administration of heparin. We report a case of reversal of PLE with resolution of clinical symptoms and normalization of serum albumin, total protein, and fecal alpha1-antitrypsin values after several months of heparin treatment. Our findings substantiate those recently reported but suggest that reversal of PLE may necessitate more than a few weeks of heparin therapy.

Methylenetetrahydrofolate reductase deficiency in a patient with phenotypic findings of Angelman syndrome

Deficiency of methylenetetrahydrofolate reductase (MTHFR) is associated with a variable phenotype that includes mental retardation, gait abnormalities, and seizures. Many of the same clinical findings are also seen in patients with Angelman syndrome. We report on a patient with MTHFR deficiency who was initially diagnosed as having Angelman syndrome. This case illustrates that MTHFR deficiency can mimic the phenotype of Angelman syndrome and that MTHFR deficiency should be excluded in patients with manifestations of Angelman syndrome whose molecular studies of chromosome 15 are normal.

Prevalence of 22q11 region deletions in patients with velopharyngeal insufficiency

Velo-cardio-facial syndrome, DiGeorge syndrome, conotruncal anomaly face syndrome, tetralogy of Fallot, and pulmonary atresia with ventricular septal defect are all associated with hemizygosity of 22q11. While the prevalence of the deletions in these phenotypes has been studied, the frequency of deletions in patients presenting with velopharyngeal insufficiency (VPI) is unknown. We performed fluorescence in situ hybridization for locus D22S75 within the 22q11 region on 23 patients with VPI (age range 5-42 years) followed in the Craniofacial Clinic at the University of Florida. The VPI occurred either as a condition of unknown cause (n=16) or as a condition remaining following primary cleft palate surgery (n=7). Six of sixteen patients with VPI of unknown cause and one of seven with VPI following surgery had a deletion in the region. This study documents a high frequency of 22q11 deletions in those presenting with VPI unrelated to overt cleft palate surgery and suggests that deletion testing should be considered in patients with VPI.

Klippel-Trénaunay syndrome: spectrum and management

OBJECTIVE

To describe a series of 252 patients with Klippel-Trénaunay syndrome (KTS), a rare congenital malformation characterized by the triad of capillary malformations, atypical varicosities or venous malformations, and bony or soft tissue hypertrophy usually affecting one extremity.

MATERIAL AND METHODS

We reviewed the clinical characteristics and findings in 136 female and 116 male patients with KTS who underwent assessment at Mayo Clinic Rochester between January 1956 and January 1995. In addition, management options are discussed.

RESULTS

Capillary malformations (port-wine stains) were found in 246 patients (98%), varicosities or venous malformations in 182 (72%), and limb hypertrophy in 170 (67%). All three features of KTS were present in 159 patients (63%), and 93 (37%) had two of the three features. Atypical veins, including lateral veins and persistent sciatic vein, occurred in 182 patients (72%). Operations performed in 145 patients with KTS included epiphysiodesis, stripping of varicose veins or venous malformations, excision of vascular malformations, amputations, and debulking procedures.

CONCLUSION

Most patients with KTS should be managed conservatively. The clearest indication for operation is a leg length discrepancy projected to exceed 2.0 cm at skeletal maturity, which can be treated with epiphysiodesis in the growing child. If a functioning deep vein system is present, removal of symptomatic varicosities or localized superficial venous malformations in selected patients can yield good results.

Unexpected familial recurrence in Angelman syndrome

We report on two instances of familial recurrence of Angelman syndrome which, from pedigree analysis, appear incompatible with currently known mechanisms of inheritance of this disorder. In these two families, deletion-positive Angelman syndrome has recurred in cousins. Several established mechanisms for deletion-positive familial recurrence have been ruled out. In each family, molecular cytogenetic studies show typical chromosome 15 deletions, and DNA methylation analysis verifies the maternal origin of the deleted chromosomes in all four individuals. Since the mothers of the affected individuals in each family are not known to be related, these recurrences appear to be secondary to coincidental, de novo events. This conclusion is consistent with direct and indirect estimates of the population frequency of Angelman syndrome.

Exercise tolerance in patients with Ebstein's anomaly

OBJECTIVES

The purpose of this study was to identify the determinants of exercise tolerance in patients with Ebstein's anomaly.

BACKGROUND

Patients with Ebstein's anomaly of the tricuspid valve may have exercise limitation that improves after surgical repair.

METHODS

One hundred seventeen patients performed cycle ergometry for a total of 124 tests (preoperative test in 76 patients, postoperative test in 23, test but no operation in 18, preoperative and postoperative test in 7). Multiple linear regression analysis was used to identify predictors of maximal oxygen uptake, oxygen saturation and heart rate at peak exercise.

RESULTS

Age at the time of exercise ranged from 6 to 60 years (median 15). An atrial septal defect was present in 67 patients (88%) preoperatively. Compared with the preoperative group, the postoperative group had significantly higher maximal oxygen uptake (mean [+/- SD] 20.5 +/- 7.4 vs. 25.3 +/- 7.0 ml/kg body weight per min, p = 0.006). Postoperative rest and exercise blood oxygen saturation was higher than that measured preoperatively (p = 0.0001). Six of seven patients tested before and after the operation showed improved exercise tolerance. Preoperatively, major predictors of maximal oxygen uptake were oxygen saturation at rest (p = 0.01) and age (p = 0.0001). Preoperatively, the major predictor of oxygen saturation at peak exercise was rest oxygen saturation (p = 0.0001), and major predictors of peak exercise heart rate were rest heart rate (p = 0.01) and rest oxygen saturation (p = 0.01). In the postoperative group, predictors of maximal oxygen uptake included age at exercise testing, male gender and heart size.

CONCLUSIONS

Definitive operation for Ebstein's anomaly results in improved exercise tolerance. Before the operation, rest oxygen saturation is the major predictor of exercise tolerance, oxygen saturation at peak exercise and peak heart rate. Postoperatively, age, gender and heart size influenced maximal oxygen uptake.

Syncope in children and adolescents

OBJECTIVES

The objectives of this study were to 1) define the incidence of syncope coming to medical attention among children and adolescents, 2) determine the outcome of syncope in these patients, and 3) determine changes over time in the evaluation and charges for evaluating this problem.

BACKGROUND

Syncope occurs commonly in children and adolescents. However, the mid- and long-term outcome of children and adolescents who experience syncope is unknown.

METHODS

Utilizing the Rochester Epidemiology Project, we determined the incidence, outcome and charges for medical evaluation for patients seeking medical attention for syncope during an early 5-year period (1950 to 1954) and a more recent 5-year period (1987 to 1991).

RESULTS

The incidence of syncope coming to medical attention was 71.9 and 125.8/100,000 population for the early and more recent cohort, respectively. The incidence was higher for female than for male patients. The incidence peaked in 15- to 19-year old patients. Acute illness and noxious stimuli were associated with 24% and 23% of the episodes, respectively. Although long-term survival was not different from that of the general population, one child died suddenly, and another had hereditary prolonged QT interval syndrome. These were two of only six patients who had exertional syncope. Total charges for evaluation of syncope were similar in the two time periods. However, charges for testing procedures were greater for the more recent cohort.

CONCLUSIONS

In general, syncope in children and adolescents is a benign event. Syncope occurring during exercise may identify patients with a potentially fatal condition. Detailed evaluation should be considered for patients who have syncope during exercise or who have a family history of syncope, sudden death, myocardial disease or arrhythmias. It may be prudent to obtain an electrocardiogram for all patients who seek medical attention for syncope.

Genomic imprinting: potential function and mechanisms revealed by the Prader-Willi and Angelman syndromes

The Prader-Willi (PWS) and Angelman (AS) syndromes are two clinically distinct syndromes which result from lack of expression of imprinted genes within chromosome 15q11-q13. These two syndromes result from 15q11-q13 deletions, chromosome 15 uniparental disomy (UPD), imprinting centre mutations and, for AS, probable mutations in a single gene. The differential phenotype results from a paternal genetic deficiency in PWS patients and a maternal genetic deficiency in AS patients. Within 15q11-q13, four genes (SNRPN, IPW, ZNF127, FNZ127) and two expressed sequence tags (PAR1 and PAR5) have been found to be expressed only from the paternally inherited chromosome, and therefore all must be considered candidate genes involved in the pathogenesis of PWS. A candidate AS gene (UBE3A) has very recently been identified. The mechanisms of imprinted gene expression are not yet understood, but it is clear that DNA methylation is involved in both somatic cell expression and inheritance of the imprint. The presence of DNA methylation imprints that distinguish the paternally and maternally inherited alleles is a common characteristic of all known imprinted genes which have been studied extensively, including SNRPN and ZNF127. Recently, several PWS and AS patients have been found that have microdeletions in a region upstream of the SNRPN gene referred to as the imprinting centre, or IC. Paternal IC deletions in PWS patients and maternal IC deletions in AS patients result in uniparental DNA methylation and uniparental gene expression at biparentally inherited loci. The IC is a novel genetic element which controls initial resetting of the parental imprint in the germline for all imprinted gene expression over a 1.5-2.5 Mb region within chromosome 15q11-q13.

Cardiorespiratory response to exercise after modified Fontan operation: determinants of performance

OBJECTIVES

This study sought to measure the cardiorespiratory responses to exercise and to identify the perioperative determinants of exercise performance in children, adolescents and young adults who underwent the modified Fontan operation.

BACKGROUND

Several studies of the cardiorespiratory responses to exercise after the Fontan operation have demonstrated subnormal maximal oxygen uptake and exercise heart rate, but the perioperative variables that ultimately affect exercise responses have not been assessed systematically.

METHODS

The study included 59 of the 548 patients who underwent a modified Fontan operation between January 1, 1984 and December 31, 1993 at the Mayo Clinic. Spirometry was performed at rest in all patients before exercise testing. The patients then exercised using a previously calibrated cycle ergometer and a 3-min incremental cycle exercise protocol. Multiple linear regression analysis was used to determine a subset of variables associated with oxygen uptake at peak exercise (VO2max), blood oxygen saturation (O2sat) and heart rate at peak exercise (HRmax).

RESULTS

VO2max ranged from 29% to 95% of normal value; O2sat at peak exercise ranged from 77% to 96%; and HRmax ranged from 39.7% to 97.4% of normal value. Multivariate analysis showed that log VO2max/kg2/3 was associated with age at exercise, male gender, body surface area, preoperative confluent pulmonary arteries and rest VO2max/kg2/3. Preoperative left pulmonary artery stenosis, the presence of a classic Glenn anastomosis at exercise and rest O2sat were associated with O2sat at peak exercise. Age, body surface area at exercise, heart rate at rest and diastolic blood pressure were associated with HRmax at exercise.

CONCLUSIONS

Subnormal VO2max and HRmax values were demonstrated at peak exercise. Several perioperative variables were associated with VO2max and O2sat at peak exercise. The presence of a classic Glenn anastomosis was associated with decreased O2sat at peak exercise, suggesting intrapulmonary shunting with the classic Glenn anastomosis.

Clinical spectrum and molecular diagnosis of Angelman and Prader-Willi syndrome patients with an imprinting mutation

Recent studies have identified a new class of Prader-Willi syndrome (PWS) and Angelman syndrome (AS) patients who have biparental inheritance, but neither the typical deletion nor uniparental disomy (UPD) or translocation. However, these patients have uniparental DNA methylation throughout 15q11-q13, and thus appear to have a mutation in the imprinting process for this region. Here we describe detailed clinical findings of five AS imprinting mutation patients (three families) and two PWS imprinting mutation patients (one new family). All these patients have essentially the classical clinical phenotype for the respective syndrome, except that the incidence of microcephaly is lower in imprinting mutation AS patients than in deletion AS patients. Furthermore, imprinting mutation AS and PWS patients do not typically have hypopigmentation, which is commonly found in patients with the usual large deletion. Molecular diagnosis of these cases is initially achieved by DNA methylation analyses of the DN34/ZNF127, PW71 (D15S63), and SNRPN loci. The latter two probes have clear advantages in the simple molecular diagnostic analysis of PWS and AS patients with an imprinting mutation, as has been found for typical deletion or UPD PWS and AS cases. With the recent finding of inherited microdeletions in PWS and AS imprinting mutation families, our studies define a new class of these two syndromes. The clinical and molecular identification of these PWS and AS patients has important genetic counseling consequences.

Protein-losing enteropathy after the Fontan operation

Patients were observed after the Fontan operation to determine the frequency and severity of protein-losing enteropathy. A total of 427 patients who survived for 30 days after the Fontan operation, performed between 1973 and January 1987, were analyzed and, thus far, protein-losing enteropathy has developed in 47 of 427. The cumulative risk for the development of protein-losing enteropathy by 10 years was 13.4% among 30-day survivors, and 5-year survival after the diagnosis was 46%. Hemodynamic studies done coincident with the diagnosis of protein-losing enteropathy have shown increased systemic venous pressure, decreased cardiac index, increased pulmonary vascular resistance, and increased ventricular end-diastolic pressure. Medical management of protein-losing enteropathy was only partially successful. Statistical analysis has shown that factors related to protein-losing enteropathy were ventricular anatomy, increased preoperative ventricular end-diastolic pressure, longer operative bypass time, increased length of hospital stay, and postoperative renal failure. This study suggests that scrupulous selection of cases for the Fontan operation is mandatory and that certain perioperative factors may predispose to this serious complication of the Fontan procedure.

Improved early morbidity and mortality after Fontan operation: the Mayo Clinic experience, 1987 to 1992

OBJECTIVES

This study sought to evaluate changes in early morbidity and mortality as well as predictors of outcome in our most recent 339 patients undergoing modified Fontan operations.

BACKGROUND

The Fontan operation is the preferred definitive palliation for patients with functional single ventricles. Previously reported early mortality rates after Fontan operation have been substantial.

METHODS

Records of 339 consecutive patients who had a Fontan operation at the Mayo Clinic between 1987 and 1992 (recent cohort) were reviewed. This cohort was compared with the previous 500 patients who had Fontan operations performed between 1973 and 1986 (early cohort).

RESULTS

Recently, overall early mortality after Fontan has decreased significantly compared with that for the early cohort (from 16% to 9%, p = 0.002). This decline occurred despite increased anatomic complexity of patients. Short-term posthospital survival has also improved significantly in recent patients. One-year survival improved to 88% from 79%, and 5-year survival to 81% from 73% (p = 0.006). Patients with common atrioventricular valves and those who took daily preoperative diuretic medication or had either postoperative renal failure or elevated postbypass right atrial pressure were at increased risk for early mortality. Young age was not found to be a risk factor for early mortality. Early mortality for patients with heterotaxia decreased dramatically: recent 30-day mortality was 15% compared with 41% in the early heterotaxy cohort.

CONCLUSIONS

Many factors may have contributed to decreased early mortality after Fontan. Improved patient selection, younger age at time of operation, refinements in surgical techniques and postoperative management may all have had important roles. Proposed technical modifications of the Fontan operation must be evaluated in light of these improved results.

Minimal definition of the imprinting center and fixation of chromosome 15q11-q13 epigenotype by imprinting mutations

Patients with disorders involving imprinted genes such as Angelman syndrome (AS) and Prader-Willi syndrome (PWS) can have a mutation in the imprinting mechanism. Previously, we identified an imprinting center (IC) within chromosome 15q11-ql3 and proposed that IC mutations block resetting of the imprint, fixing on that chromosome the parental imprint (epigenotype) on which the mutation arose. We now describe four new microdeletions of the IC, the smallest (6 kb) of which currently defines the minimal region sufficient to confer an AS imprinting mutation. The AS deletions all overlap this minimal region, centromeric to the PWS microdeletions, which include the first exon of the SNRPN gene. None of five genes or transcripts in the 1.0 Mb vicinity of the IC (ZNF127, SNRPN, PAR-5, IPW, and PAR-1), each normally expressed only from the paternal allele, was expressed in cells from PWS imprinting mutation patients. In contrast, AS imprinting mutation patients show biparental expression of SNRPN and IPW but must lack expression of the putative AS gene 250-1000 kb distal of the IC. These data strongly support a model in which the paternal chromosome of these PWS patients carries an ancestral maternal epigenotype, and the maternal chromosome of these AS patients carries an ancestral paternal epigenotype. The IC therefore functions to reset the maternal and paternal imprints throughout a 2-Mb imprinted domain within human chromosome 15q11-q13 during gametogenesis.

Multiple imprinted genes associated with Prader-Willi syndrome and location of an imprinting control element

Our studies aim to identify the mechanisms and genes involved in genomic imprinting in mammalian development and human disease. Imprinting refers to an epigenetic modification of DNA that results in parent-of-origin specific expression during embryogenesis and in the adult. This imprint is reset at each generation, depending on the sex of the parental gametogenesis. Prader-Willi (PWS) and Angelman (AS) syndromes are excellent models for the study of genomic imprinting in humans, since these distinct neurobehavioural disorders are both associated with genetic abnormalities (large deletions, uniparental disomy, and imprinting mutations) of inheritance in chromosome 15q11-q13, dependent on the parental origin (reviewed in ref. 1). Some AS patients have biparental inheritance, consistent with a single imprinted gene (active on the maternal chromosome), whereas similar PWS patients are not found suggesting that at least two imprinted genes (active on the paternal allele) may be necessary for classical PWS. We have previously shown that the small ribonucleoprotein associated protein SmN gene (SNRPN), located in the PWS critical region [2], is only expressed from the paternal allele and is differentially methylated on parental alleles [3]. Therefore, SNRPN may have a role in PWS. Methylation imprints have also been found at two other loci in 15q11-q13, PW71 [4] and D15S9 [5], which map 120 kb and 1.5 Mb proximal to SNRPN, respectively. We have now characterized in detail the gene structure and expression from two imprinted loci within 15q11-q13, SNRPN and D15S9, which suggests that both loci are surprisingly complex, with important implications for the pathogenesis of PWS.

Familial cryptic translocation resulting in Angelman syndrome:implications for imprinting or location of the Angelman gene?

Angelman syndrome (AS) is associated with a loss of maternal genetic information, which typically occurs as a result of a deletion at 15q11-q13 or paternal uniparental disomy of chromosome 15. We report a patient with AS as a result of an unbalanced cryptic translocation whose breakpoint, at 15q11.2, falls within this region. The proband was diagnosed clinically as having Angelman syndrome, but without a detectable cytogenetic deletion, by using high-resolution G-banding. FISH detected a deletion of D15S11 (IR4-3R), with an intact GABRB3 locus. Subsequent studies of the proband's mother and sister detected a cryptic reciprocal translocation between chromosomes 14 and 15 with the breakpoint being between SNRPN and D15S10 (3- 21). The proband was found to have inherited an unbalanced form, being monosomic from 15pter through SNRPN and trisomic for 14pter to 14q11.2. DNA methylation studies showed that the proband had a paternal-only DNA methylation pattern at SNRPN, D15S63 (PW71), and ZNF127. The mother and unaffected sister, both having the balanced translocation, demonstrated normal DNA methylation patterns at all three loci. These data suggest that the gene for AS most likely lies proximal to D15S10, in contrast to the previously published position, although a less likely possibility is that the maternally inherited imprinting center acts in trans in the unaffected balanced translocation carrier sister.

Distinct 15q genotypes in Russell-Silver and ring 15 syndromes

Individuals with a ring 15 chromosome [r(15)] and those with Russell-Silver syndrome have short stature, developmental delay, triangular face, and clinodactyly. To assess whether the apparent phenotypic overlap of these conditions reflects a common genetic cause, the extent of deletions in chromosome 15q was determined in 5 patients with r(15), 1 patient with del 15q26.1-qter, and 5 patients with Russell-Silver syndrome. All patients with Russell-Silver syndrome were diploid for genetic markers in distal 15q, indicating that Russell-Silver syndrome in these individuals was unlikely to be related to the expression of single alleles at these or linked genetic loci. At least 3 distinct sites of chromosome breakage close to the telomere were found in the r(15) and del 15q25.1-qter patients, with 1 r(15) patient having both a terminal and an interstitial deletion. Although the patient with del 15q25.1-qter exhibited the largest deletion and the most profound growth retardation, the degree of growth impairment among the r(15) patients was not correlated with the size of the deleted interval. Rather, the parental origin of the ring chromosome in several patients was associated with phenotypes that are also seen in patients with either Prader-Willi (PWS) or Angelman (AS) syndromes, conditions that result from uniparental expression of genes on chromosome 15. In fact, unequal representation of chromosome 15 alleles in 1 patient with r(15) suggests the possibility that a mosaic karyotype composed of the constitutional cell line and cell line(s) possibly deficient in the ring chromosome might be present. The PWS-like or AS-like phenotypes could be explained by postzygotic loss of the ring chromosome, leading to uniparental inheritance of the intact chromosome in some tissues of r(15) patients.