Characterization of sinoatrial node in four conduction system marker mice

The specialized cardiac conduction system (CCS) consists of the sinoatrial node (SAN) and the atrioventricular (AV) conduction system (AVCS), which includes proximal (AV node, bundle of His and bundle branches) and distal (Purkinje fibers) components. In four CCS marker mice [two transgenic (cGATA6|lacZ, CCS|lacZ) and two targeted gene knock-in (minK|lacZ, Hop|lacZ)] the expression of the lacZ gene (beta-gal) has been reported to mark portions of the proximal and distal AVCS; the expression of this marker in the adult SAN is unknown. The primary objective of this study was to analyze the utility of these marker mice in the identification of the SAN. Intercaval and interventricular septal regions, containing all the components of the CCS, were freshly dissected from adult mice based on the anatomical landmarks and sectioned. Immunohistochemical characterization was performed with SAN markers (Cx45, HCN4), compared to the reporter expression (beta-gal) and markers of the working myocardium (Cx40 and Cx43). In all four of the CCS marker mice, we found that beta-gal expression is consistently observed in the proximal and distal AVCS. However, the presence of lacZ gene expression in the working myocardium outside the CCS and/or the absence of this reporter expression in the SAN prevent the effective use of these mice to identify the SAN, leading us to conclude that none of the four CCS marker mice we studied specifically mark the SAN.

Detailed four-way comparative mapping and gene order analysis of the canine ctvm locus reveals evolutionary chromosome rearrangements

Canine tricuspid valve malformation (CTVM) maps to canine chromosome 9 (CFA9), in a region syntenic with gene-dense human chromosome 17q. To define synteny blocks, we analyzed 148 markers on CFA9 using radiation hybrid mapping and established a four-way comparative map for human, mouse, rat, and dog. We identified a large number of rearrangements, allowing us to reconstruct the evolutionary history of individual synteny blocks and large chromosomal segments. A most parsimonious rearrangement scenario for all four species reveals that human chromosome 17q differs from CFA9 and the syntenic rodent chromosomes through two macroreversals of 9.2 and 23 Mb. Compared to a recovered ancestral gene order, CFA9 has undergone 11 reversals of <3 Mb and 2 reversals of >3 Mb. Interspecies reuse of breakpoints for micro- and macrorearrangements was observed. Gene order and content of the ctvm interval are best extrapolated from murine data, showing that multispecies genome rearrangement scenarios contribute to identifying gene content in canine mapping studies.

Canine tricuspid valve malformation, a model of human Ebstein anomaly, maps to dog chromosome 9

BACKGROUND

Ebstein anomaly of the tricuspid valve is a congenital cardiac malformation characterised by downward displacement of the attachment of the septal and posterior leaflets of the tricuspid valve. Canine tricuspid valve malformation (CTVM) is morphologically similar to Ebstein anomaly; familial occurrence of CTVM has been described. Several observations suggest a genetic cause but most cases appear to be sporadic.

METHODS

Three purebred Labrador Retriever kindreds enriched for CTVM underwent clinical examination and echocardiography. DNA was extracted from whole blood. Genotyping was carried out using polymorphic repeat markers with an average spacing of 15 cM and polymorphic information content of 0.74.

RESULTS

Pedigree analysis identified CTVM segregating as an autosomal dominant trait with reduced penetrance. Genome wide linkage analysis in one kindred identified a CTVM susceptibility locus on dog chromosome 9 (CFA9) with a maximum multipoint lod score of 3.33. The two additional kindreds showed a conserved disease haplotype.

CONCLUSIONS

This study identifies a CTVM susceptibility locus on CFA9 and a founder effect in apparently unrelated Labrador Retriever kindreds. These results provide the basis for a positional candidate cloning effort to identify the CTVM disease gene. Identification of the CTVM gene will permit mutation screening of patients with Ebstein anomaly, which should provide additional insights into the genetic programmes of valve development.

NKX2.5 mutations in patients with tetralogy of fallot

BACKGROUND

Recent reports have implicated mutations in the transcription factor NKX2.5 as a cause of tetralogy of Fallot (TOF). To estimate the frequency of NKX2.5 mutations in TOF patients and to further investigate the genotype-phenotype correlation of NKX2.5 mutations, we genotyped 114 TOF patients.

METHODS AND RESULTS

Patients were recruited prospectively (November 1992 through June 1999) and tested for a 22q11 deletion; those with 22q11 deletion or recognized chromosomal alteration were excluded from the present study. Patients were screened for NKX2.5 alterations by conformation-sensitive gel electrophoresis and sequencing of fragments with aberrant mobility. Four heterozygous mutations were identified in 6 unrelated patients with cases of TOF, including 3 with pulmonary atresia and 5 with right aortic arch; none had ECG evidence of PR interval prolongation. Three of 4 mutations (Glu21Gln, Arg216Cys, and Ala219Val) altered highly conserved amino acids, of which 2 mapped in the conserved NK2 domain. The fourth mutation (Arg25Cys) was identified in 3 unrelated probands in the present study and has been previously reported. No homeodomain mutations were identified.

CONCLUSIONS

NKX2.5 mutations are the first gene defects identified in nonsyndromic TOF patients. NKX2.5 mutation is present in >/=4% of TOF patients. Mutations identified in the present study mapped outside of the homeodomain, were not associated with atrioventricular conduction disturbances, and were not fully penetrant, in contrast to mutations previously reported that impair homeodomain function.

Transmission of full-length echocardiographic images over ISDN for diagnosing congenital heart disease

OBJECTIVES

To study the feasibility of transmitting full-length diagnostic-quality echocardiograms with video conferencing systems linked by ISDN.

METHODS

Forty-three previously video-recorded full-length echocardiograms (22 complete two-dimensional Doppler studies, 21 separate M-mode studies) were transmitted from a site 30 miles distant using desktop video conferencing systems linked with one ISDN line (128 kbps). Blinded interpretations of the original recorded and transmitted studies were made by two pediatric cardiologists (two-dimensional Doppler) and a pediatric sonographer (M-mode).

RESULTS

Diagnoses of normal (N = 12) and abnormal (N = 10) conditions were made from the original tapes; the same interpretations were made from the transmitted studies. Twenty-one specific abnormalities in the 10 abnormal studies were seen on both original and transmitted videotapes. These abnormalities ranged from simple congenital heart defects, including ventricular septal defect, atrial septal defect, and patent ductus arteriosus, to complex ones, such as coronary artery fistula, double-outlet right ventricle, and complete atrioventricular canal. Qualitatively, there was mild degradation in gray scale, brightness, and contrast of the images. Six M-mode variables from the transmitted images had excellent concordance with the original tracings (P = 0.506 to 0.838; r = 0.86 to 0.97).

CONCLUSIONS

Although our sample size was small, this preliminary experience indicates that video conferencing equipment utilizing ISDN technology is a reliable method for transmitting full-length diagnostic-quality echocardiographic studies from remote sites. This technology may have a significant impact on the management of pediatric patients with suspected heart disease. Further evaluation is warranted.

Heart block in children. Evaluation of subsidiary ventricular pacemaker recovery times and ECG tape recordings

To evaluate subsidiary ventricular pacemaker function in 20 children with congenital or surgically induced complete heart block, we measured recovery times following overdrive ventricular pacing. Long-term ECG tape recordings were performed in eight of these children. Ages ranged from 1 month to 17 years. The resting R-R intervals ranged from 595 to 1,740 msec. The ventricles were paced at various cycle lengths of 400 to 1,000 msec with either transvenous electrode catheters or surgically implanted epicardial electrodes. His bundle recordings showed that the site of block did not allow separation of patients with symptoms from those without symptoms. Prolonged recovery times were present in patients with block above the His bundle recording site who had symptoms of syncope or dizziness, as well as in patients who had a wide QRS. However, some asymptomatic patient with heart block above the His bundle recording site also had long recovery times. None of the asymptomatic patients who had ECG tape recordings had paroxysmal tachycardia in more than 300 hours of recordings. However, one symptomatic patient with congenital heart block and a prolonged recovery time had brief episodes of paroxysmal ventricular tachycardia that produced no symptoms at the time of recording. The results suggest that the coexistence of prolonged recovery times and paroxysmal tachycardia may be predisposing factors to the development of symptoms in patients with complete heart block. We believe that further electrophysiologic investigation of this possibility is warranted in patients with heart block.

Evidence for autosomal recessive inheritance of infantile dilated cardiomyopathy: studies from the Eastern Province of Saudi Arabia

Familial dilated cardiomyopathy is being increasingly recognized, but affected individuals <10 y are rarely identified. We describe the natural history of dilated cardiomyopathy and evaluate the mode of inheritance among infants of Arab descent from the Eastern Province of Saudi Arabia. We evaluated 55 consecutive cases of dilated cardiomyopathy in patients <10 y of age seen during a 5-y interval. Echocardiography was the primary diagnostic modality. The 55 cases represented 20% of the offspring of 41 families of Arab descent. In 19 families (46%), parents were first cousins; there was no obvious consanguinity in 22 families (54%). Age at presentation was <30 mo (95%) (range, 1 to 100 mo); males (38%) and females (62%) were affected. Patients died (25 patients, 46%), improved (15 patients, 27%), or recovered (15 patients, 27%). The left ventricular shortening fraction at diagnosis ranged from 5 to 28% and did not differ in those who died, improved, or recovered. Complex segregation analysis of the family data using the mixed model of inheritance showed that a model of recessive inheritance best fits the data. Recessively inherited dilated cardiomyopathy has been infrequently reported, perhaps because it may be difficult to recognize in other patient groups in which consanguineous marriage is uncommon and the number of children per family is small. In the setting of consanguineous marriage, homozygosity mapping should lead to identification of the gene(s) causing dilated cardiomyopathy in the families we studied.

Advances in cardiovascular genetics and embryology: role of transcription factors in congenital heart disease

In spite of tremendous advances in diagnosis and treatment of cardiovascular disease in the young, our understanding of its cause is still incomplete. Recent studies have reported pleiotropic cardiac malformations resulting from mutations in transcription factors, a family of proteins known to play important roles in many aspects of development. Further evaluation of these important causes of cardiovascular disease in the young promises new insight into embryology of cardiac development and improved understanding of the pathophysiologic basis of cardiovascular disease in the young.

Loss of function and inhibitory effects of human CSX/NKX2.5 homeoprotein mutations associated with congenital heart disease

CSX/NKX2.5 is an evolutionarily conserved homeodomain-containing (HD-containing) transcription factor that is essential for early cardiac development. Recently, ten different heterozygous CSX/NKX2.5 mutations were found in patients with congenital heart defects that are transmitted in an autosomal dominant fashion. To determine the consequence of these mutations, we analyzed nuclear localization, DNA binding, transcriptional activation, and dimerization of mutant CSX/NKX2.5 proteins. All mutant proteins were translated and located to the nucleus, except one splice-donor site mutant whose protein did not accumulate in the cell. All mutants that had truncation or missense mutations in the HD had severely reduced DNA binding activity and little or no transcriptional activation function. In contrast, mutants with intact HDs exhibit normal DNA binding to the monomeric binding site but had three- to ninefold reduction in DNA binding to the dimeric binding sites. HD missense mutations that preserved homodimerization ability inhibited the activation of atrial natriuretic factor by wild-type CSX/NKX2.5. Although our studies do not characterize the genotype-phenotype relationship of the ten human mutations, they identify specific abnormalities of CSX/NKX2.5 function essential for transactivation of target genes.

Mutations in the cardiac transcription factor NKX2.5 affect diverse cardiac developmental pathways

Heterozygous mutations in NKX2.5, a homeobox transcription factor, were reported to cause secundum atrial septal defects and result in atrioventricular (AV) conduction block during postnatal life. To further characterize the role of NKX2.5 in cardiac morphogenesis, we sought additional mutations in groups of probands with cardiac anomalies and first-degree AV block, idiopathic AV block, or tetralogy of Fallot. We identified 7 novel mutations by sequence analysis of the NKX2.5-coding region in 26 individuals. Associated phenotypes included AV block, which was the primary manifestation of cardiac disease in nearly a quarter of affected individuals, as well as atrial septal defect and ventricular septal defect. Ventricular septal defect was associated with tetralogy of Fallot or double-outlet right ventricle in 3 individuals. Ebstein's anomaly and other tricuspid valve abnormalities were also present. Mutations in human NKX2.5 cause a variety of cardiac anomalies and may account for a clinically significant portion of tetralogy of Fallot and idiopathic AV block. The coinheritance of NKX2.5 mutations with various congenital heart defects suggests that this transcription factor contributes to diverse cardiac developmental pathways.

Electrophysiologic characteristics of accessory atrioventricular connections in an inherited form of Wolff-Parkinson-White syndrome

INTRODUCTION

A familial form of Wolff-Parkinson-White syndrome (WPW) occurs in association with hypertrophic cardiomyopathy and intraventricular conduction abnormalities. This syndrome, demonstrating autosomal dominant inheritance and segregating with a high degree of penetrance but variable expressivity, has been genetically linked to chromosome 7q3. The purpose of this study is to detail the electrophysiologic characteristics of accessory atrioventricular connections (AC) in four members of a kindred with this syndrome.

METHODS AND RESULTS

We clinically evaluated 32 members of a single kindred and identified 20 individuals with ventricular preexcitation, abnormal intraventricular conduction including complete AV block and/or ventricular hypertrophy. Genetic linkage analysis mapped the disease gene in this kindred to the chromosome 7q3 locus (maximum logarithm of the odds score = 6.88, theta = 0); recombination events in affected individuals reduced the genetic interval from 7 centimorgans (cM) to 5 cM. Electrophysiologic study of four individuals with preexcitation, identified seven AC (1 right sided, 3 septal, and 3 left sided). All four individuals had inducible orthodromic tachycardia; while three had multiple AC. Bidirectional conduction was demonstrated in 6 of 7 AC. Successful ablation was accomplished in 5 of 7 AC.

CONCLUSION

The electrophysiologic characteristics and location of AC in family members having this complex cardiac phenotype are similar to those seen in individuals with isolated WPW. Identification of WPW in more than one family member should prompt clinical evaluation of relatives for additional findings of ventricular hypertrophy or conduction abnormalities.

Familial dilated cardiomyopathy locus maps to chromosome 2q31

BACKGROUND

Inherited gene defects are an important cause of dilated cardiomyopathy. Although the chromosome locations of some defects and 1 disease gene (actin) have been identified, the genetic etiologies of most cases of familial dilated cardiomyopathy remain unknown.

METHODS AND RESULTS

We clinically evaluated 3 generations of a kindred with autosomal dominant transmission of dilated cardiomyopathy. Nine surviving and affected individuals had early-onset disease (ventricular chamber dilation during the teenage years and congestive heart failure during the third decade of life). The disease was nonpenetrant in 2 obligate carriers. To identify the causal gene defect, linkage studies were performed. A new dilated cardiomyopathy locus was identified on chromosome 2 between loci GCG and D2S72 (maximum logarithm of odds [LOD] score=4.86 at theta=0). Because the massive gene encoding titin, a cytoskeletal muscle protein, resides in this disease interval, sequences encoding 900 amino acid residues of the cardiac-specific (N2-B) domain were analyzed. Five sequence variants were identified, but none segregated with disease in this family.

CONCLUSIONS

A dilated cardiomyopathy locus (designated CMD1G) is located on chromosome 2q31 and causes early-onset congestive heart failure. Although titin remains an intriguing candidate gene for this disorder, a disease-causing mutation is not present in its cardiac-specific N2-B domain.

Congenital heart disease caused by mutations in the transcription factor NKX2-5

Mutations in the gene encoding the homeobox transcription factor NKX2-5 were found to cause nonsyndromic, human congenital heart disease. A dominant disease locus associated with cardiac malformations and atrioventricular conduction abnormalities was mapped to chromosome 5q35, where NKX2-5, a Drosophila tinman homolog, is located. Three different NKX2-5 mutations were identified. Two are predicted to impair binding of NKX2-5 to target DNA, resulting in haploinsufficiency, and a third potentially augments target-DNA binding. These data indicate that NKX2-5 is important for regulation of septation during cardiac morphogenesis and for maturation and maintenance of atrioventricular node function throughout life.

Reduced penetrance, variable expressivity, and genetic heterogeneity of familial atrial septal defects

BACKGROUND

Secundum atrial septal defect (ASD) is a common congenital heart malformation that occurs as an isolated anomaly in 10% of individuals with congenital heart disease. Although some embryological pathways have been elucidated, the molecular etiologies of ASD are not fully understood. Most cases of ASD are isolated, but some individuals with ASD have a family history of this defect or other congenital heart malformations.

METHODS AND RESULTS

Clinical evaluation of three families identified individuals with ASD in multiple generations. ASD was transmitted as an autosomal dominant trait in each family. ASD was the most common anomaly, but other heart defects occurred alone or in association with ASD in individuals from each kindred. Genome-wide linkage studies in one kindred localized a familial ASD disease gene to chromosome 5p (multipoint LOD score=3.6, theta=0.0). Assessment of 20 family members with the disease haplotype revealed that 9 had ASD, 8 were clinically unaffected, and 3 had other cardiac defects (aortic stenosis, atrial septal aneurysm, and persistent left superior vena cava). Familial ASD did not map to chromosome 5p in two other families.

CONCLUSIONS

Familial ASD is a genetically heterogeneous disorder; one disease gene maps to chromosome 5p. Recognition of the heritable basis of familial ASD is complicated by low disease penetrance and variable expressivity. Identification of ASD or other congenital heart defects in more than one family member should prompt clinical evaluation of all relatives.

The medical therapy of cardioinhibitory syncope in pediatric patients

A small percentage of pediatric patients with neurally mediated syncope will have an asystolic response during upright tilt table testing. The purpose of this study is to evaluate the incidence of asystole during tilt table testing, and to assess the outcome of medical management of such patients. Of 398 patients undergoing evaluation for recurrent syncope between January 1989 and 1994, 18 (4.5%) experienced asystole lasting > or = 5 seconds during baseline tilt test. Patients had experienced a mean of four episodes of syncope, with a mean age at the time of tilt test of 11.1 +/- 4.0 years. The median duration of asystole was 10 seconds (range 5-40 s). Treatment was individualized to increased fluids and salt intake (3 patients), metoprolol (8 patients), pseudoephedrine (4 patients), disopyramide (1 patient), or combination therapy with fludrohydrocortisone (2 patients). During a median duration of follow-up of 31 months, no additional syncope was experienced by 78% of patients. Recurrent syncope in 4 patients was associated with either noncompliance or discontinuation of therapy in 3 patients; in 1 patient, increasing the dose of metoprolol was effective in preventing recurrences. We conclude that young patients with recurrent syncope and asystole during tilt test may be safely and effectively managed with pharmacological therapy, without resorting to pacemaker implantation.

Echocardiographic prediction of neonatal ECMO outcome

Cardiopulmonary physiology was assessed by Doppler echocardiography in neonates undergoing pre-ECMO evaluation for meconium aspiration syndrome, congenital diaphragmatic hernia, persistent fetal circulation, and sepsis, from March 1987 through July 1992 (n = 136). Percent survival by diagnosis was: meconium aspiration syndrome, 86%; persistent fetal circulation, 68%; congenital diaphragmatic hernia, 63%; sepsis, 33%. Survival odds by diagnosis predicted a better outcome for meconium aspiration syndrome than for congenital diaphragmatic hernia and sepsis, and a better outcome for persistent fetal circulation than for sepsis. Percent survival for right-to-left patent ductus arteriosus flow (PDA) was 56%; other patent ductus arteriosus flow was 84%. In multivariate analysis, percent survival in congenital diaphragmatic hernia and persistent fetal circulation patients with right-to-left PDA flow suggested a worse outcome (% survival right-to-left vs other: congenital diaphragmatic hernia, 13% vs 70%; persistent fetal circulation, 25% vs 85%), whereas percent survival did not appear to suggest the same in meconium aspiration syndrome or sepsis patients. Similar analysis in non-ECMO patients suggested a worse outcome with right-to-left PDA flow in patients with meconium aspiration syndrome and congenital diaphragmatic hernia. Right-to-left PDA flow, sepsis, and congenital diaphragmatic hernia were associated with a poorer ECMO outcome. Initial assessment of PDA flow helps predict ECMO outcome.

New understandings in the genetics of congenital heart disease

In spite of the amazing success during the past half century in diagnosis and treatment of congenital heart disease, very little is known of its cause. However, a genetic cause has been clearly established for many forms of cardiovascular disease, and new understandings in the molecular genetics of congenital heart disease provide further insight. Progress has been quite impressive for some cardiovascular abnormalities, whereas in other areas the findings are more preliminary. For example, the molecular genetic cause of supravalvular aortic stenosis and the heart disease associated with Marfan syndrome has been clearly established. Impressive progress has been made in conotruncal defects, Holt-Oram syndrome, Alagille syndrome, and total anomalous pulmonary venous connection. In other areas, such as patent ductus arteriosus and atrioventricular septal defect, the findings are more preliminary. Taken as a whole, the prospect of understanding the genetic basis of congenital heart disease has never been better. Understanding the cause of congenital heart disease will provide new insights into both normal cardiac development and the pathophysiologic basis of congenital heart defects.

Fetal tachycardia: mechanisms and predictors of hydrops fetalis

OBJECTIVES

This study had three objectives: 1) to determine the electrophysiologic mechanisms of fetal supraventricular tachycardia at presentation and postnatally; 2) to identify the clinical and electrophysiologic predictors of hydrops fetalis; and 3) to describe the medium-term follow-up (1 to 7 years) of patients with fetal supraventricular tachycardia.

BACKGROUND

Fetal supraventricular tachycardia causes significant fetal and neonatal morbidity and mortality. Prenatal analysis and postnatal confirmation of fetal supraventricular tachycardia mechanisms have been limited.

METHODS

Supraventricular tachycardia mechanisms were evaluated by prenatal Doppler/M-mode echocardiography, immediate neonatal surface electrocardiography and postnatal transesophageal electrophysiologic procedures in 30 consecutive patients presenting with fetal supraventricular tachycardia (17 managed prenatally, 13 first managed postnatally).

RESULTS

The fetal supraventricular tachycardia mechanism was 1:1 atrioventricular conduction in 22 patients and supraventricular tachycardia with atrioventricular block (atrial flutter) in 8. At the postnatal transesophageal electrophysiologic procedure, tachycardia was induced in 27 of 30 patients; atrioventricular reentrant tachycardia in 25 (93%) of 27 and intraatrial reentrant tachycardia in only 2 (7%) of 27. Hydrops was present in 12 of 30 fetuses. Sustained supraventricular tachycardia (> 12 h) and lower gestation at presentation correlated with hydrops (p < 0.02, p < 0.05), but mechanism of tachycardia and heart rate did not. Gestational age at delivery was significantly greater in those who received intrauterine management (39 +/- 1.3 vs. 37 +/- 2.9 weeks, p = 0.04) despite earlier presentation (32.6 vs. 37.1 weeks). Cesarean section deliveries were reduced in the same group (3 of 17 vs. 11 of 13, p = 0.0006).

CONCLUSIONS

Atrioventricular reentrant tachycardia was the predominant mechanism of supraventricular tachycardia in the fetus. There was a high association of supraventricular tachycardia with atrioventricular block in utero and accessory atrioventricular connections. Outcome at 1 to 7 years was excellent regardless of severity of illness at clinical presentation.

Missense mutation in the pore region of HERG causes familial long QT syndrome

BACKGROUND

Long QT syndrome (LQT) is an inherited cardiac disorder that results in syncope, seizures, and sudden death. In a family with LQT, we identified a novel mutation in human ether-a-go-go-related gene (HERG), a voltage-gated potassium channel.

METHODS AND RESULTS

We used DNA sequence analysis, restriction enzyme digestion analysis, and allele-specific oligonucleotide hybridization to identify the HERG mutation. A single nucleotide substitution of thymidine to guanine (T1961G) changed the coding sense of HERG from isoleucine to arginine (Ile593Arg) in the channel pore region. The mutation was present in all affected family members; the mutation was not present in unaffected family members or in 100 normal, unrelated individuals.

CONCLUSIONS

We conclude that the Ile593Arg missense mutation in HERG is the cause of LQT in this family because it segregates with disease, its presence was confirmed in three ways, and it is not found in normal individuals. The Ile593Arg mutation may result in a change in potassium selectivity and permeability leading to a loss of HERG function, thereby resulting in LQT.

Ventricular relaxation in the stage 24 chick embryo following changes in volume and blockade of Na+ and Ca2+ channels

OBJECTIVE

Early in cardiac development, regulation of cytosolic Ca2+ has been thought to depend primarily on sarcolemmal Ca2+ transport. We hypothesized that perturbation of cytosolic Ca2+ in the embryonic ventricle would result in a change in ventricular relaxation which could be quantified by a monoexponential model. We reasoned that since it has been difficult to selectively block the Na(+)-Ca2+ exchanger in vivo, that blockade of Na+ (lidocaine) or Ca2+ (verapamil) channels in the embryonic heart may perturb cytosolic Ca2+ and thereby alter ventricular relaxation.

METHODS

All studies were performed in ovo in Hamilton-Hamburger stage 24 chick embryos. Isovolumic relaxation time (mean +/- standard deviation, 58 +/- 19 ms) was derived from dorsal aortic flow and atrioventricular inflow during 61 cardiac cycles in 4 embryos. Ventricular pressure was digitally recorded from 13 embryos during 188 cycles following intravenous injection of chick Ringer's solution (5 embryos), verapamil (4 embryos) or lidocaine (4 embryos). Ventricular relaxation was characterized by a monoexponential model: P(t) = P infinity + Poe-1/tau where P(t) = pressure at time (t), P infinity = pressure asymptote, Po = pressure at the onset of relaxation and tau = the isovolumic relaxation constant. Non-linear least-squares regression was used to estimate tau and P infinity during isovolumic relaxation at baseline and at 30 s and 60 s post-injection.

RESULTS

Ventricular end-diastolic pressure was increased by all three interventions. Both lidocaine and verapamil prolonged cycle length. Lidocaine prolonged tau while chick Ringer's solution and verapamil did not. No significant change in P chi was observed.

CONCLUSIONS

This study demonstrates that blockade of Na+ channels with lidocaine slows ventricular relaxation presumably by perturbing cytosolic Ca2+ via the Na(+)-Ca2+ exchange system. Changes following Ca2+ channel blockade with verapamil are less evident in the stage 24 chick embryo. Evaluation of ventricular relaxation may provide a useful way to study developmental aspects of Ca2+ transport.

Comparison of transesophageal and intracardiac electrophysiologic studies in characterization of supraventricular tachycardia in pediatric patients

OBJECTIVES

This study sought to determine the accuracy of transesophageal electrophysiologic studies in diagnosing and characterizing various mechanisms of supraventricular tachycardia in pediatric patients.

BACKGROUND

Transesophageal electrophysiologic studies are a relatively noninvasive means of characterizing supraventricular tachycardia. Although widely used, to our knowledge no data exist that directly compare information obtained from transesophageal electrophysiologic studies with that from intracardiac electrophysiologic studies.

METHODS

We reviewed the records of 57 pediatric patients undergoing both transesophageal and intracardiac electrophysiologic studies at our institution. The results of these studies were compared with respect to mechanism of tachycardia, localization of accessory atrioventricular (AV) connections (if present) and characterization of anterograde accessory connection conduction properties.

RESULTS

Tachycardia mechanisms were concordant in 56 of 57 patients: orthodromic reciprocating tachycardia in 43, antidromic reciprocating tachycardia in 1, both orthodromic and antidromic tachycardia in 2, AV node reentrant tachycardia in 5, atrial reentrant tachycardia in 4 and ectopic atrial tachycardia in 2. Of 29 patients with orthodromic reciprocating tachycardia using a concealed accessory connection, transesophageal study predicted the accessory connection site through changes induced by transient bundle branch block in 12. By the Bland-Altman method in 14 patients with pre-excitation, the anterograde accessory connection effective refractory period determined by transesophageal study compared favorably with that determined by intracardiac study (mean difference 5.0 ms, limits of agreement -55 and 65 ms).

CONCLUSIONS

Transesophageal electrophysiologic studies are a highly accurate means of diagnosing and characterizing various mechanisms of supraventricular tachycardia in pediatric patients.

Heart rate-dependent characteristics of diastolic ventricular filling in the developing chick embryo

The contributions of the early (passive) and late (active) components of ventricular filling have been reported to decrease and increase, respectively, during chick embryo cardiac development. We hypothesized that the observed changes in ventricular filling during early cardiac development results from a decrease in cycle length. We studied the effect of development and cycle length on atrioventricular inflow in 28 chick embryos, Hamilton-Hamburger stages 17, 24, and 26. Cycle length was perturbed (range 240-1040 ms) in ovo by transiently heating or cooling the sinus venosus. Atrioventricular inflow and dorsal aortic velocities were obtained by 20-MHz pulsed Doppler flow-meter and digitally recorded at 500 samples per second. Stroke volume was calculated from dorsal aortic velocity and cross-sectional area. The atrioventricular inflow wave form was integrated and partitioned by area and percentage of total into early (passive) and late (active) components using three methods. Regardless of method, the proportion of filling volume due to the early and late components was cycle length and stage dependent (p < 0.05). The early and late filling volumes were large in the older embryos, and during cycle length decrease (heart rate increase) the early filling volume decrease was greater than the late filling volume decrease. When compared with the percentage of intrinsic heart rate, the percentage of stroke volume due to early filling decreased as heart rate increased and was greater in younger embryos at all heart rates. That due to late filling increased as the percentage of intrinsic heart rate increased. Ventricular filling characteristics are both developmentally determined and cycle length dependent.

Reversible cardiomyopathy due to carnitine deficiency from renal tubular wasting

The clinical course of a 4-month-old male infant with a dilated cardiomyopathy secondary to renal tubular losses of carnitine is outlined. He was admitted to the hospital with severe congestive heart failure. An echocardiogram demonstrated normal anatomy. The left ventricular shortening fraction measured 10%. A comprehensive cardiomyopathy evaluation was initiated. The total plasma carnitine level was only 25 mumol/ml, but the urine carnitine measured 434 nm/mg of creatinine. He was begun on oral L-carnitine and weaned from mechanical ventilation and inotropic support 10 days later. Two years later he remains asymptomatic with normal left ventricular function.

Normal left ventricular muscle mass and mass/volume ratio after pediatric cardiac transplantation

BACKGROUND

The adaptive growth of the transplanted heart within the growing child may contribute to long-term cardiac performance. The ability to achieve increased ventricular volume and appropriate muscle mass in the face of immunosuppression and cardiac denervation has not been studied. We previously reported normal left ventricular (LV) volume growth over a 3-year period after cardiac transplantation. This study was designed to assess changes in LV mass and mass/volume ratio and their relation to LV end-diastolic pressure (LVEDP) 1 to 4 years after cardiac transplantation.

METHODS AND RESULTS

Cardiac transplantation was performed in 18 patients, age 7 days to 18 years (median, 3.7 years). The indications for cardiac transplantation were cardiomyopathy (8 patients), hypoplastic left heart syndrome (7 patients), and postoperative structural congenital heart disease with ventricular failure (3 patients). The mean follow-up was 48 months, with a range from 29 to 70 months. Serial annual catheterizations were performed after 1 year (16 patients), 2 years (18 patients), 3 years (15 patients), and 4 years (8 patients). Cardiac index (Fick), LVEDP (baseline and after 10-mL/kg saline infusion delivered over 5 minutes), and systemic vascular resistance (SVR) were measured. LV diastolic volume index (LVDVI), LV mass index, and mass/volume ratio were determined angiographically according to the method of Lange and Rackley. The data were analyzed by repeated-measures ANOVA. Least-squares means and group SEM were calculated. No change in cardiac index, SVR, or baseline LVEDP was noted. The LVEDP doubled after fluid challenge, suggesting a restrictive process. The LVDVI remained near 60 mL/m2. The LV mass/volume ratio remained one.

CONCLUSIONS

Appropriate increases in muscle mass occurred after cardiac transplantation, preserving normal mass/volume ratios despite somatic growth deficits associated with immunosuppressive therapy and denervation of the donor heart.

Pharmacodynamics and pharmacokinetics of esmolol, a short-acting beta-blocking agent, in children

Esmolol, a short-acting intravenous cardioselective beta-blocking agent, was evaluated for age-dependent pharmacodynamic and pharmacokinetic features in 17 young patients (6 months to 14 years). A loading dose (500 micrograms/kg/min) alternating with a maintenance dose (25-200 micrograms/kg/min, titrating by 25 micrograms/kg/min every 4 min) was infused until the heart rate or mean arterial pressure decreased 10%. Cardiac index, left ventricular shortening fraction, and systemic vascular resistance were measured at baseline, peak esmolol effect, and recovery. Serum esmolol concentrations were obtained to determine the half-life and the elimination rate constant. Esmolol reduced the heart rate, blood pressure, shortening fraction, and cardiac index in all patients, but it did not change systemic vascular resistance. Maintenance esmolol dose was 118 +/- 49 micrograms/kg/min, and the half-life was 2.88 +/- 2.67 min. Blood pressure and heart rate returned to normal within 2-16 min, but cardiac index and shortening fraction took longer to recover. There were no statistically significant age-dependent pharmacodynamic effects, but blood pressure decreased prior to heart rate and cardiac index took longer to recovery in patients who weighed < or = 15 kg. The pharmacokinetic profile in young patients was similar to that of older patients, but the half-life was shorter. The only side effect was transient nausea and vomiting in one patient. Esmolol is a safe and efficacious beta-blocking agent in young patients.

Assessment of ventricular relaxation in the developing chick embryo using a monoexponential model

In this study, the ventricular pressure decline during isovolumic relaxation in early diastole was modeled by regressing pressure and pressure change vs. time to a monoexponential formula: P(t) = P infinity+P0e-t/tau, where P(t) is ventricular pressure at time t, P infinity is the pressure in the fully relaxed ventricle, P0 is the pressure at the end of ventricular ejection, and tau is the ventricular relaxation rate constant. Analysis was performed on 330 ventricular pressure waveforms from 22 chick embryos, stages 17, 23, and 26, during baseline and following cardiac cycle length perturbation. Three computational models were evaluated. Based on analysis of the confidence intervals of estimates of P infinity and analysis of residuals, a least-squares nonlinear regression of pressure vs. time, which allowed estimates of tau and P infinity, best approximated the pressure decline. Isovolumic pressure decline in the embryonic heart is well approximated by a monoexponential model if both P infinity and tau are estimated. Negative values of P infinity during early stages of cardiac morphogenesis support the idea that diastolic suction plays a role in ventricular filling in the developing heart.

Role of endomyocardial biopsy in rejection surveillance after heart transplantation in neonates and children

OBJECTIVES

The aim of this study was to retrospectively evaluate the sensitivity of noninvasive surveillance (physical examination, echocardiography) of rejection in accurately predicting histologically documented rejection episodes. Additionally, the usefulness of routine scheduled biopsy and its safety in pediatric patients was explored.

BACKGROUND

Endomyocardial biopsy has been utilized as the standard for rejection surveillance after heart transplantation in adults, but its role in documenting clinically suspected rejection and in routine surveillance of pediatric patients has not been agreed upon.

METHODS

Heart transplantation was performed in 14 neonates and 21 children. The immunosuppressive regimen consisted of cyclosporine, azathioprine and prednisone. All patients underwent routine noninvasive rejection surveillance that included clinical examination and echocardiography. In the neonates, biopsy was performed quarterly beginning 6 months after transplantation, after cessation of prednisone therapy. In the children, biopsy was performed 15 times in the 1st year. A minimum of five biopsy samples were interpreted using the Working Formulation for Heart Transplant Rejection.

RESULTS

In the neonates, 37 biopsies were performed. Evidence of rejection was present in only three biopsy samples obtained during eight episodes (38%) of clinically suspected rejection. In 29 biopsies performed when rejection was not clinically suspected, each biopsy was free of cellular infiltrate. In the children, 291 biopsies were performed. Evidence of rejection was present in only seven biopsies (41%) from 17 episodes of clinically suspected rejection. Cellular rejection was discovered during routine rejection surveillance biopsies in asymptomatic patients in 23 (8.4%) of 274 biopsies.

CONCLUSIONS

In neonates with clinically suspected rejection, endomyocardial biopsy identified which patients did not require rejection therapy. Endomyocardial biopsy surveillance did not detect any unsuspected cases of rejection. In children, noninvasive rejection surveillance was less reliable even in asymptomatic patients, suggesting that periodic endomyocardial biopsy should be utilized.

Restrictive ventricular septal defect: how small is too small to close?

Historically, indications for ventricular septal defect closure have included congestive heart failure, pulmonary hypertension, aortic insufficiency with or without aortic valve prolapse, and prior bacterial endocarditis. However, controversy exists as to how the lifetime risk of an isolated, nonoperated restrictive ventricular septal defect compares with the risk of surgical closure in an asymptomatic child. Between 1980 and 1991, cardiac catheterization and elective ventricular septal defect closure (age > 1 year, pulmonary to systemic flow ratio < 2.0) were performed in 141 patients aged 1 to 23 years (mean age, 6.1 +/- 4.7 years). Mean systolic pulmonary artery pressure was 26.9 +/- 13.0 mm Hg, and mean pulmonary to systemic flow ratio was 1.6 +/- 0.3. Aortic valve prolapse was present in 63 patients (45%), aortic insufficiency was present in 25 (18%), and 5 (3.5%) had prior bacterial endocarditis. There were no early or late deaths or major morbidity. No patient required a ventriculotomy to accomplish ventricular septal defect closure. Mean postoperative intensive care unit stay was 1.3 +/- 0.9 days, and mean hospital stay was 5.5 +/- 1.9 days. There were no instances of permanent complete atrioventricular dissociation, reoperations for bleeding, postoperative wound infections, or reoperations for residual or recurrent ventricular septal defect. These improved results justify a reevaluation of historic indications for ventricular septal defect closure.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic reduction of pretransplantation pulmonary vascular resistance predicts outcome after pediatric heart transplantation

Pulmonary hypertension leading to donor right ventricular dysfunction remains a major risk factor associated with poor outcome after heart transplantation. This study evaluated a pretransplantation protocol to assess pulmonary vascular resistance index and its response to pharmacologic modulation. Cardiac catheterization was performed in 25 patients (mean age, 8.6 years [range, 1 to 17 years]; mean weight, 27.3 kg [range, 8.1 to 54 kg]) with end-stage heart failure. Mean pulmonary artery and capillary wedge pressures and cardiac index were measured in the baseline state and during administration of 100% oxygen, dobutamine at 10 micrograms/kg/min, and nitroprusside at 1 to 4 micrograms/kg/min. Transpulmonary pressure gradient and pulmonary vascular resistance index were calculated. In 22 survivors, hemodynamics were reassessed 1 and 4 weeks after transplantation. The mean cardiac index significantly increased (2.2 to 3.2 L/min/m2); transpulmonary pressure gradient (12.7 to 9.6 mm Hg) and pulmonary vascular resistance index (6.2 to 3.0 units/m2) decreased during the drug study. In 12 patients with a baseline pulmonary vascular resistance index of more than 6 units/m2, 10 survived heart transplantation. This study shows that pharmacologic reduction of the pulmonary vascular resistance index in the pretransplantation protocol predicts reduced pulmonary vascular resistance index and a favorable outcome after heart transplantation.

Effectiveness of radiofrequency catheter ablation for treatment of atrial tachycardia

Catheter ablation has been used to treat atrioventricular node reentrant and atrioventricular reentrant tachycardias with extremely high success rates. The suitability of catheter ablation for treatment of atrial tachycardia, a much less common type of supraventricular tachycardia, has not been well addressed. Fifteen patients (8 females) ranging from 10 to 83 years (mean 38 +/- 22) were referred for catheter ablation of supraventricular tachycardia. The diagnosis of atrial tachycardia was established by standard electrophysiologic techniques. A combination of activation and pace mapping was used to identify a suitable site for radiofrequency current catheter ablation. Medical therapy was unsuccessful in all but 1 patient. Two patients had surgically corrected congenital heart disease, 2 had coronary artery disease and 1 had dilated cardiomyopathy. Seven patients had depressed left ventricular function. Six patients had incessant tachycardias. Presumed tachycardia mechanism was automatic in 11 patients and reentrant in 4. Mean tachycardia cycle length was 372 +/- 74 ms. Catheter ablation was acutely successful in 12 patients (80%) with application of 11.1 +/- 6.6 lesions at a mean voltage of 60 +/- 9 V. In the other 3 patients, 16 to 38 lesions were applied. At a mean follow-up of 18.5 +/- 6.5 months, 2 patients have had recurrences with different P-wave morphologies and underwent a second successful catheter ablation procedure. An additional 2 patients had recurrences with the same P-wave morphology and 1 underwent a second successful catheter ablation procedure. Thus, radiofrequency ablation can be used in a diverse population of patients with atrial tachycardia with an acute success rate of 80% and a long-term success rate of 73%.

Spectrum of humoral rejection after pediatric heart transplantation

The deposition of immunoglobulin and complement 3 in the coronary microvasculature (humoral rejection) has been associated with poor outcome after heart transplantation. The purpose of this study is to relate the incidence of immunoglobulin and complement 3 myocardial deposition to the clinical course of pediatric heart transplant patients. One hundred thirty-one biopsy specimens from 30 patients, whose mean age at transplantation was 4.9 years (range, 2 days to 17 years), were processed for light microscopy and immunofluorescence. The mean follow-up was 25 months (range, 6 to 63 months). All patients underwent annual selective coronary artery angiography. No cellular or humoral rejection was seen in 97 biopsy specimens. Humoral rejection without cellular infiltrate was found in eight biopsy specimens from four patients (13%). Of 19 grade 1A, B (mild) biopsy specimens, 17 showed only cellular rejection, and two showed a mixed pattern of cellular and humoral rejection. Of six grade 2,3 (moderate) biopsy specimens, four showed only cellular rejection, and two showed a mixed pattern. The only grade 4 (severe) biopsy specimen revealed a mixed pattern. Three patients have had persistent immunoglobulin M and complement 3 deposits. One of these had angiographic evidence of accelerated graft coronary artery disease 2 years after transplantation, which was later confirmed at autopsy. Coronary artery disease has not been detected by serial angiography at 1 year (28 patients), 2 years (18 patients), 3 years (15 patients), 4 years (five patients), and 5 years (one patient). Humorally mediated rejection occurs with and without cellular rejection after pediatric heart transplantation. Humoral rejection may persist after treatment and resolution of severe cellular rejection episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of metoprolol for unexplained syncope and positive response to tilt testing in young persons

The efficacy of intravenous metoprolol in preventing symptoms during a repeat tilt test was compared with the outcome of chronic oral treatment in 21 patients (14 female, 7 male), age 8 to 20 years (mean 13 +/- 3) with unexplained syncope (> or = 1 episode) and a positive response to tilt testing. A positive response was defined as the development of either syncope or presyncope. During the initial tilt test, a positive response occurred during baseline (14 patients) or isoproterenol (0.03 to 0.1 microgram/kg/min) infusion (7 patients) with a cardioinhibitory (1 patient), vasodepressor (5 patients) or mixed (15 patients) pattern. Metoprolol (0.1 to 0.2 mg/kg) was administered intravenously. During the repeat tilt test, response was negative in 18 patients, including 11 of 14 patients with a positive response in the baseline and 7 of 7 patients with a positive response during isoproterenol infusion. Metoprolol (0.8 to 2.8 mg/kg/day) was administered orally to 15 patients for an average of 10 months. Symptoms were absent (7 patients) or improved (2 patients); metoprolol was discontinued because of adverse effects (3 patients) or recurrence of symptoms (3 patients). In 7 of 12 patients with a negative response and 2 of 3 patients with a positive response after intravenous metoprolol, oral administration of metoprolol prevented or improved symptoms without adverse effects. Many young patients (60%) with recurrent syncope obtained symptomatic improvement from chronic oral metoprolol treatment without adverse effects; repeat tilt testing after intravenous metoprolol did not appear to offer any additional information than would have been obtained from a trial of chronic oral treatment.

Heart rate perturbation in the stage 17-27 chick embryo: effect on stroke volume and aortic flow

Heart rate (HR), stroke volume (SV), and aortic flow increase linearly between developmental stages 17 and 27, as the embryonic chick heart progresses from a bent tube to a rudimentary four-chambered structure and cardiac mass increases fourfold. We hypothesized that HR perturbation, expressed as percent of intrinsic HR (%HR), would have a developmentally dependent effect on flow and SV. HR was transiently perturbed to 40-250% of intrinsic rate with a 1-mm cooled or heated steel probe applied to the sinus venosus of 81 embryos. Aortic blood velocity, cross-sectional area, and HR were used to calculate flow and SV. At each stage, flow was maximal at intrinsic HR. The %HR vs. SV relationship was linear, inverse, and developmentally dependent. In spite of a tremendous change in ventricular shape, mass, and volume, HR control during development of the preinnervated heart maximizes blood flow to the developing embryo.

Successful radiofrequency energy ablation of automatic junctional tachycardia preserving normal atrioventricular nodal conduction

Automatic junctional tachycardia is frequently refractory to medical management and difficult to treat with nonpharmacological methods. A 12-year-old female with symptomatic, refractory automatic junctional tachycardia is reported. Earliest atrial activation during supraventricular tachycardia was in the posterior portion of the intraatrial septum. The patient underwent electrophysiological study and successful radiofrequency current ablation of the ectopic automatic focus within the atrioventricular junction. Normal atrioventricular junctional conduction was maintained, and at 7-month follow-up the patient has been free of tachycardia.

Ventricular volume growth after cardiac transplantation in infants and children

BACKGROUND

Intermediate-term survival after pediatric cardiac transplantation continues to improve. However, little is known about cardiac function and especially ventricular growth in young patients after cardiac transplantation. The purpose of this study was to evaluate serially the hemodynamics, left ventricular (LV) volume, and ventricular function after cardiac transplantation in infants and children.

METHODS AND RESULTS

Indications for cardiac transplantation were dilated cardiomyopathy (eight patients), hypoplastic left heart syndrome (six patients), and postoperative structural congenital heart disease (three patients). The age at time of transplant ranged from 7 days to 15 years (median, 3.5 years). The mean follow-up was 30.3 months (range, 13-46 months). Serial annual cardiac catheterizations were performed 1 year (17), 2 years (15), and 3 years (seven) after transplant. Measurements included right and left heart pressures, cardiac index, and LV volume and ejection fraction (Lange). Cumulative results (expressed as mean +/- SD) were pulmonary artery pressure, 14.9 +/- 3.2 mm Hg; LV end-diastolic pressure, 7.7 +/- 2.6 mm Hg; cardiac index, 3.5 +/- 0.52 l/min.m-2; and pulmonary vascular resistance, 2.02 +/- 0.76 units/m2. LV end-diastolic volume increased as patients grew, so that left ventricular end-diastolic volume remained 90 +/- 14% of that predicted for body surface area. The ejection fraction was 99 +/- 6% of that predicted. There was no evidence of chronic rejection by endomyocardial biopsy. No accelerated coronary artery atherosclerosis was identified.

CONCLUSIONS

Serial studies in these young patients demonstrate normal hemodynamics and LV function after cardiac transplantation. Cardiac transplantation is associated with normal LV volume growth despite immunosuppression and denervation.

Reproducibility of a symptomatic response to upright tilt in young patients with unexplained syncope

Serial upright tilt testing has been advocated as a possible therapeutic end point in treating patients with recurrent syncope, but the reproducibility of such testing has not been well-established in the absence of therapy. In 21 patients with recurrent syncope and a symptomatic response to upright tilt testing, tilt was repeated following a 25- to 30-minute recovery. Syncope or presyncope was reproduced in 14 of 21 patients on repeat tilt; 4 of 21 patients experienced milder symptoms, and 3 of 21 patients remained entirely asymptomatic on repeat tilt. The pattern of physiologic response was different during initial and repeat tilt in 7 of the 21 patients. Blood pressure and heart rate (before and during symptoms) were similar for the group on initial and repeat tilt. The abnormal physiologic response and associated symptoms elicited during upright tilt testing for unexplained syncope can be reproduced on immediate repeat tilt testing in most patients. However, the frequently attenuated response during repeat testing may limit its use as a therapeutic end point in individual patients.

Pediatric cardiology research in 1990: a review of abstracts submitted to the Society for Pediatric Research, American Academy of Pediatrics, and American Heart Association Scientific Sessions

We assessed pediatric cardiology research by reviewing pediatric cardiology abstracts submitted in 1990 to the Society of Pediatric Research, American Academy of Pediatrics, and American Heart Association national meetings. Included were accepted and rejected studies. Abstracts were reviewed for disease being studied, methodology used to answer the research question, study design, and acceptance/rejection. Abstracts were analyzed from 123 institutions, 81 American and 42 foreign. Out of 423 abstracts, 307 (72.6%) were clinical and the remainder were basic science investigations. Slightly more than half of the clinical submissions were related to congenital heart disease. Coronary artery disease and inflammatory diseases accounted for 12% of clinical submissions. Echocardiography, clinical outcome measures, and electrophysiology were the most common research methodologies. Almost 80% of basic science research was performed in normal tissues; animal physiology, fetal physiology, and cellular/biochemical studies were the most common methodologies. With regard to study design, half of the clinical studies were retrospective and only 6% were either prospective epidemiologic or prospective controlled intervention trials. For basic sciences, 38% of abstracts were descriptions of phenomena and 62% were hypothesis testing, with developmental hypotheses being most common. Acceptance rates favored higher quality study design. However, areas of greatest interest to cardiologists, congenital heart disease, cardiomyopathy, and electrophysiology, had poorer quality study design than did other areas. We have shown broad interest in pediatric cardiology research. However, clinical studies frequently were retrospective or had uncontrolled study designs. Basic science research was performed at a small number of institutions and emphasized either description of phenomena or developmental biology of normal tissues.

Relationship between cardiac cycle length and ventricular relaxation rate in the chick embryo

We hypothesized that during chick embryo cardiac development, cycle length decrease (heart rate increase) may be associated with developmental changes in the ventricular relaxation rate constant, tau, which can be estimated from ventricular pressure decrease by the function P(t) = P0e-t/tau, where P0 = pressure at the time of minimum time derivative of ventricular pressure and t = time. Natural logarithm conversion results in a linear relation between In P(t) and t with slope of -1/tau. We determined tau in Hamburger-Hamilton stage 17-27 (d 3-5) embryos (n = 35) at intrinsic cycle length and in stage 24 embryos (n = 5) during cardiac cycle length perturbations with the hot-cold probe technique. Regression analysis of In P(t) from the minimum dP/dt until t = 30 ms was used to estimate tau. Intrinsic cycle length decreased during development from stage 17 to 27 and tau decreased linearly as cycle length decreased (r = 0.39, p less than 0.005). Thus, during early development, both tau and cycle length decrease (relaxation rate and heart rate increase). In stage 24 embryos, cycle length perturbation yielded a nonlinear cycle length-dependent relation with tau, with a plateau at cycle lengths less than intrinsic, i.e. tau decreased with cycle length decrease to intrinsic cycle length, then tau plateaued with further cycle length decrease. These findings demonstrate that ventricular relaxation rate is both maturation and cycle length dependent. The plateau effect of the tau-cycle length relationship may be due to developmental limitations of the calcium transport system.

Supraventricular tachycardia mechanisms and their age distribution in pediatric patients

To better define the natural history of supraventricular tachycardia (SVT) in young patients, age distribution of SVT mechanisms was examined in 137 infants, children and adolescents. Patients with a history of cardiac surgery or neuromuscular diseases were excluded. An electrophysiologic study was performed in each patient: transesophageal (110 patients) or transvenous (14 patients) or both (13 patients). Mechanisms were classified as SVT using accessory atrioventricular (AV) connection (SVT using accessory connection, including orthodromic and antidromic reciprocating tachycardia), primary atrial tachycardia (including chaotic, automatic and reentrant atrial tachycardia), and tachycardia due to reentry within the AV node. SVT using accessory connection occurred in 100 of 137 patients (73%) and was the most prevalent mechanism. Primary atrial tachycardia and reentry within the AV node were present in 19 of 137 (14%) and 18 of 137 (13%) patients, respectively. Using a multinomial logit model, relative probabilities for tachycardia mechanisms for 5 age groups--prenatal, less than 1, 1 to 5, 6 to 10 and greater than 10 years--were determined. Primary atrial tachycardia (11 to 16%) and SVT using accessory connection (58 to 84%) appeared throughout infancy, childhood and adolescence. On the other hand, tachycardia due to reentry within the AV node (0 to 31%) rarely appeared before age 2 years. Mechanisms of SVT appear to have age-dependent distributions. SVT using accessory connection is the most common mechanism in young patients. We speculate that the propensity to tachycardia due to reentry within the AV node occurs during postnatal development.

Heart transplantation in neonates and in children

Between May 1988 and July 1991, 28 neonates and children underwent orthotopic heart transplantation at Children's Memorial Hospital in Chicago. Indications for heart transplantation were hypoplastic left heart syndrome (10), dilated cardiomyopathy (13), aortic stenosis with endocardial fibroelastosis (1), complex D-transposition of the great arteries after Senning repair (1), L-transposition of the great arteries with single ventricle after shunt (1), cor biloculare, pulmonary atresia, and situs inversus after Fontan (1), and chronic rejection after heart transplantation for hypoplastic left heart syndrome (1). The age at time of transplantation ranged from 2 days to 17 years (mean, 5.3 +/- 6.1 years). Early deaths were from intraoperative donor right ventricular failure (2) and acute rejection after a second transplant procedure at 21 days (1), for an in-hospital mortality rate of 10.7%. Immunosuppression was with cyclosporine, azathioprine, and prednisone, with an attempt to discontinue the prednisone in neonates at age 6 months as guided by endomyocardial biopsy. Rejection episodes were treated with methylprednisolone pulse (34) or with OKT3 (4). Endomyocardial biopsy (in patients older than 6 months) was used extensively, and acute rejection was diagnosed in 29 of 301 biopsies. Three late deaths occurred (mean follow-up, 16.3 +/- 11.8 months): one of acute rejection at 13 months, one of viral pneumonia at 7 months, and one of intraabdominal sepsis as a complication of peritoneal dialysis at 5 months. Actuarial survival at 2 years is 77% +/- 9% (standard error of the estimate). Heart transplantation for neonates and for children can be performed with acceptable operative mortality. Intermediate results with triple therapy immunosuppression and an intensive rejection surveillance regimen relying on endomyocardial biopsy are encouraging.

Echocardiographic evaluation of the aortic root and mitral valve in children and adolescents with isolated pectus excavatum: comparison with Marfan patients

Pectus excavatum, mitral valve prolapse (MVP), and dilated aortic root occur frequently in patients with Marfan's syndrome (MS). Patients with isolated pectus excavatum (IPE) have a high prevalence of MVP, but it is not known whether aortic root dilatation is a risk in those patients. To test the hypothesis that IPE and MS represent a spectrum of connective tissue dystrophy with MV and aortic root involvement, two-dimensional (2D) echocardiography was used to measure the aortic root diameter and assess for MVP in IPE (n = 31), MS (n = 14), and normal (n = 16) gender- and age-matched patients. Aortic root was measured in parasternal long- and short-axis views, just above the aortic sinuses, at end systole, in six cardiac cycles, and averaged. Parasternal long-axis view was used to assess for MVP. Aortic root diameter in IPE patients was not different from that in normal subjects, 24 +/- 4 mm vs 22 +/- 4 mm (p = NS), respectively, both were significantly smaller than that in MS patients (30 +/- 5 mm; p less than 0.05). MVP was present in 17 of 31 (55%) IPE patients vs 12 of 14 (86%) MS patients (p = NS) and in only 1 of 16 (6%) normal subjects (p less than 0.05) vs both IPE and MS. We conclude that young patients with IPE represent an isolated form of connective tissue abnormality because of the presence of pectus excavatum and MVP, but this is different from the systemic involvement of MS because of the lack of other systemic findings, including aortic root dilatation and changes in body habitus.