Imputation of class I and II HLA loci using high-density SNPs from ImmunoChip and their associations with Kawasaki disease in family-based study

Kawasaki disease (KD) is the leading cause of acquired heart disease in children in most developed countries including the United States. The etiology of KD is not known; however, epidemiological and immunological data suggest infectious or immune-related factors in the manifestation of the disease. Further, KD has several hereditary features that strongly suggest a genetic component to disease pathogenesis. Human leucocyte antigen (HLA) loci have also been reported to be associated with KD, but results have been inconsistent, in part, because of small study samples and varying linkage disequilibrium (LD) patterns observed across different ethnic groups. To maximize the informativeness of single nucleotide polymorphism (SNP) genotypes in the major histocompatibility (MHC) region, we imputed classical HLA I (A, B, C) and HLA II (DRB1, DQA1, DQB1) alleles using SNP2HLA method from genotypes of 6700 SNPs within the extended MHC region contained in the ImmunoChip among 112 White patients with KD and their biological parents from North America and tested their association with KD susceptibility using the transmission disequilibrium test. Mendelian consistency in the trios suggested high accuracy and reliability of the imputed alleles (class I = 97.5%, class II = 96.6%). While several SNPs in the MHC region were individually associated with KD susceptibility, we report over-transmission of HLA-C*15 (z = +2.19, P = 0.03) and under-transmission of HLA-B*44 (z = -2.49, P = 0.01) alleles from parents to patients with KD. HLA-B*44 has been associated with KD in other smaller studies, and both HLA-C*15 and HLA-B*44 have biological mechanisms that could potentially be involved in KD pathogenesis. Overall, inferring HLA loci within the same ethnic group, using family-based information is a powerful approach. However, studies with larger sample sizes are warranted to evaluate the correlations of the strength and directions between the SNPs in MHC region and the imputed HLA alleles with KD.

Triidothyronine and epinephrine rapidly modify myocardial substrate selection: a (13)C isotopomer analysis

Triiodothyronine (T(3)) exerts direct action on myocardial oxygen consumption (MVO(2)), although its immediate effects on substrate metabolism have not been elucidated. The hypothesis, that T(3) regulates substrate selection and flux, was tested in isovolumic rat hearts under four conditions: control, T(3) (10 nM), epinephrine (Epi), and T(3) and Epi (TE). Hearts were perfused with [1,3-(13)C]acetoacetic acid (AA, 0.17 mM), L-[3-(13)C]lactic acid (LAC, 1.2 mM), U-(13)C-labeled long-chain free fatty acids (FFA, 0.35 mM), and unlabeled D-glucose (5.5 mM) for 30 min. Fractional acetyl-CoA contribution to the tricarboxylic acid cycle (Fc) per substrate was determined using (13)C NMR and isotopomer analysis. Oxidative fluxes were calculated using Fc, the respiratory quotient, and MVO(2). T(3) increased (P < 0.05) Fc(FFA), decreased Fc(LAC), and increased absolute FFA oxidation from 0.58 +/- 0.03 to 0.68 +/- 0.03 micromol. min(-1). g dry wt(-1) (P < 0.05). Epi decreased Fc(FFA) and Fc(AA), although FFA flux increased from 0.58 +/- 0.03 to 0.75 +/- 0.09 micromol. min(-1). g dry wt(-1). T(3) moderated the change in Fc(FFA) induced by Epi. In summary, T(3) exerts direct action on substrate pathways and enhances FFA selection and oxidation, although the Epi effect dominates at a high work state.

Human cardiac myosin heavy chain isoforms in fetal and failing adult atria and ventricles

The goal of this study was to test the hypothesis that the relative amounts of the cardiac myosin heavy chain (MHC) isoforms MHC-alpha and MHC-beta change during development and transition to heart failure in the human myocardium. The relative amounts of MHC-alpha and MHC-beta in ventricular and atrial samples from fetal (gestational days 47--110) and nonfailing and failing adult hearts were determined. The majority of the fetal right and left ventricular samples contained small relative amounts of MHC-alpha (mean < 5% of total MHC). There was a small significant decrease in the level of MHC-alpha in the ventricles between 7 and 12 wk of gestation. Fetal atria expressed predominantly MHC-alpha (mean > 95%), with MHC-beta being detected in most samples. The majority of adult nonfailing right and left ventricular samples had detectable levels of MHC-alpha ranging from 1 to 10%. Failing right and left ventricles expressed a significantly lower level of MHC-alpha. MHC-alpha comprised approximately 90% of the total MHC in adult nonfailing left atria, whereas the relative amount of MHC-alpha in the left atria of individuals with dilated or ischemic cardiomyopathy was approximately 50%. The differences in MHC isoform composition between fetal and nonfailing adult atria and between fetal and nonfailing adult ventricles were not statistically significant. We concluded that the MHC isoform compositions of fetal human atria are the same as those of nonfailing adult atria and that the ventricular MHC isoform composition is different between adult nonfailing and failing hearts. Furthermore, the marked alteration in atrial MHC isoform composition, associated with cardiomyopathy, does not represent a regression to a pattern that is uniquely characteristic of the fetal stage.

Major coronary artery anomalies in a pediatric population: incidence and clinical importance

OBJECTIVES

We sought to prospectively determine the incidence and clinical significance of major coronary artery anomalies in asymptomatic children using transthoracic two-dimensional echocardiography.

BACKGROUND

Anomalous origins of the left main coronary artery (ALMCA) from the right sinus of Valsalva or anomalous origins the right coronary artery (ARCA) from the left sinus are rarely diagnosed in children and can cause sudden death, especially in young athletes. Because most patients are asymptomatic, the diagnosis is often made post mortem. No study to date has prospectively identified anomalous coronary arteries in asymptomatic children in the general population.

METHODS

After serendipitously identifying an index case with ALMCA, we examined proximal coronary artery anatomy in children with otherwise anatomically normal hearts who were referred for echocardiography. In those diagnosed with ALMCA or ARCA, we performed further tests.

RESULTS

Within a three-year period, echocardiograms were obtained in 2,388 children and adolescents. Four children (0.17%) were identified with anomalous origin of their coronary arteries, and angiograms, exercise perfusion studies and/or stress tests were then performed. One ARCA patient had decreased perfusion in the right coronary artery (RCA) perfusion area and showed ventricular ectopy on electrocardiogram (ECG) at rest that diminished but did not resolve with exercise. A second patient with ALMCA had atrial tachycardia immediately after exercise, with inferior and lateral ischemic changes on ECG and frequent junctional and/or ventricular premature complexes both at rest and recovery.

CONCLUSIONS

This study demonstrates that although anomalous origins of coronary arteries are rare in asymptomatic children, the prevalence is greater than that found in other prospective studies. Ischemia can occur with both ALMCA and ARCA even though patients remain asymptomatic. Because of the high risk of sudden cardiac death, aggressive surgical management and close follow-up are necessary.

HOE-642 (cariporide) alters pH(i) and diastolic function after ischemia during reperfusion in pig hearts in situ

The specific Na(+)/H(+) exchange inhibitor HOE-642 prevents ischemic and reperfusion injury in the myocardium. Although this inhibitor alters H(+) ion flux during reperfusion in vitro, this action has not been confirmed during complex conditions in situ. Myocardial intracellular pH (pH(i)) and high-energy phosphates were monitored using (31)P magnetic resonance spectroscopy in open-chest pigs supported by cardiopulmonary bypass during 10 min of ischemia and reperfusion. Intravenous HOE-642 (2 mg/kg; n = 8) administered before ischemia prevented the increases in diastolic stiffness noted in control pigs (n = 8), although it did not alter the postischemic peak-elastance or pressure-rate product measured using a distensible balloon within the left ventricle. HOE-642 induced no change in pH(i) during ischemia but caused significant delays in intracellular realkalinization during reperfusion. HOE-642 did not alter phosphocreatine depletion and repletion but did improve ATP preservation. Na(+)/H(+) exchange inhibition through HOE-642 delays intracellular alkalinization in the myocardium in situ during reperfusion in association with improved diastolic function and high-energy phosphate preservation.

Thyroid hormone coordinates respiratory control maturation and adenine nucleotide translocator expression in heart in vivo

BACKGROUND

The signal transduction mechanism linking mitochondrial ATP synthesis with cytosolic ATP utilization in heart changes during postnatal development in vivo. This maturational process occurs in parallel with accumulation of mitochondrial adenine nucleotide translocator (ANT), which provides a possible site for respiratory control. We postulated that thyroid hormone regulates these maturational processes.

METHODS AND RESULTS

We used (31)P MR spectroscopy to determine the relationship between myocardial high-energy phosphates, phosphocreatine, and ADP and oxygen consumption (MVO(2)) during epinephrine stimulation in 32- to 40-day-old lambs thyroidectomized after birth (THY) and age-matched controls. Steady-state protein and mRNA levels for ANT isoforms and beta-F(1)-ATPase were assessed from left ventricular tissues by Western and Northern blotting. With greater doses of epinephrine, THY attained lower peak MVO(2) than controls (P:<0.05). Controls maintained high-energy phosphate levels, unlike THY, which demonstrated significantly decreased phosphocreatine/ATP and increased cytosolic ADP despite lower peak MVO(2). No significant differences in beta-F(1)-ATPase protein or mRNA occurred between groups. However, ANT isoform mRNA levels were 2-fold greater and protein levels 4-fold greater in control hearts.

CONCLUSIONS

These data imply that the maturational shift away from ADP-mediated respiratory control is regulated by thyroid hormone in vivo. Specific thyroid-modulated increases in ANT mRNA and protein imply that this regulation occurs in part at a pretranslational level.

Triiodothyronine repletion in infants during cardiopulmonary bypass for congenital heart disease

OBJECTIVE

Cardiopulmonary bypass suppresses circulating thyroid hormone levels. Although acute triiodothyronine repletion has been evaluated in adult patients after cardiopulmonary bypass, triiodothyronine pharmacokinetics and effects have not previously been studied in infants undergoing operations for congenital heart disease. We hypothesized that triiodothyronine deficiency in the developing heart after bypass may adversely affect cardiac function reserve postoperatively.

METHODS

Infants less than 1 year old undergoing ventricular septal defect or tetralogy of Fallot repair were randomized into 2 groups. Group T (n = 7) received triiodothyronine (0.4 microg/kg) immediately before the start of cardiopulmonary bypass and again with myocardial reperfusion. Control (NT, n = 7) patients received saline solution placebo or no treatment.

RESULTS

These groups underwent similar ischemic and bypass times and received similar quantities of inotropic agents after the operation. The NT group demonstrated significant depression in circulating levels, compared with prebypass levels, for free triiodothyronine and total triiodothyronine at 1, 24, and 72 hours after bypass. Group T demonstrated similar low thyroxine values, but free and total triiodothyronine levels were maintained at prebypass levels for 24 hours and remained elevated over those of group NT (P <.05) at 72 hours. Heart rate was transiently elevated in group T compared with group NT (P <.05), and peak systolic pressure-rate product increased after 6 hours.

CONCLUSION

These data imply that (1) triiodothyronine in the prescribed dose prevents circulating triiodothyronine deficiencies and (2) triiodothyronine repletion promotes elevation in heart rate without concomitant decrease in systemic blood pressure. Elevation of peak systolic pressure-rate product implies that triiodothyronine repletion improves myocardial oxygen consumption and may enhance cardiac function reserve after cardiopulmonary bypass in infants.

Signaling and expression for mitochondrial membrane proteins during left ventricular remodeling and contractile failure after myocardial infarction

OBJECTIVES

This study was conducted to test hypotheses stating that: 1) altered signaling for mitochondrial membrane proteins occurs during postinfarction remodeling, and 2) successful myocardial adaptation relates to promotion of specific mitochondrial membrane components.

BACKGROUND

Abnormalities in high-energy phosphate content and limitations in adenosine 5'-triphosphate (ATP) synthesis rate occur during the transition to contractile failure from compensatory remodeling after left ventricular infarction. The adenine nucleotide translocator (ANT) and F1-ATPase respectively regulate mitochondrial adenosine 5'-diphosphate (ADP)/ATP exchange and ADP-phosphorylation, which are key components of high-energy phosphate metabolism.

METHODS

Steady-state mRNA and protein expression for ANT isoform1 and the beta subunit of the F1-ATPase (betaF1) were analyzed in myocardium remote from the infarction zone eight weeks after left circumflex coronary artery ligation in pigs, demonstrating either successful left ventricular remodeling (LVR, n = 8) or congestive heart failure (CHF, n = 4) as determined by clinical and contractile performance parameters.

RESULTS

Substantial reductions in steady-state mRNA expression for ANT1 and betaF1 relative to normal (n = 8) occur in CHF, p < 0.01, but not in LVR. Relative expression for both proteins coordinated with their respective steady-state mRNA levels; CHF at 40% normal, p < 0.05 for ANT and 70% normal for betaF1, p < 0.05.

CONCLUSIONS

Maintained signaling for major mitochondrial membrane proteins occurs in association with successful remodeling and adaptation after infarction. Reduced expression of these proteins relates to limited ATP synthesis capacity and high energy phosphate kinetic abnormalities previously demonstrated in CHF. These findings imply that mitochondrial processes participate in myocardial remodeling after infarction.

Corrected QT interval (QTc) prolongation and syncope associated with pseudohypoparathyroidism and hypocalcemia

An adolescent presented with exercise-associated syncope and electrocardiographic corrected QT interval (QTc) prolongation. Pseudohypoparathyroidism-induced hypocalcemia was diagnosed. The QTc (485 to 505 milliseconds) shortened during normalization of calcium levels, and syncope has not reoccurred.

Mitochondrial protein and HSP70 signaling after ischemia in hypothermic-adapted hearts augmented with glucose

Hypothermia improves resistance to subsequent ischemia in the cardioplegic-arrested heart (CAH). This adaptive process produces mRNA elevation for heat shock protein (HSP) 70-1 and mitochondrial proteins, adenine nucleotide translocator (ANT(1)), and beta-F(1)-ATPase. Glucose in cardioplegia also enhances myocardial protection. These processes might be linked to reduced ATP depletion. To assess for synergism between these protective processes, isolated rabbit hearts (n = 91) were perfused at 37 degrees C and exposed to ischemic cardioplegic arrest for 2 h. Hearts were in four groups: control (C), hypothermia adapted (H) perfused to 31 degrees C 20 min before ischemia, 22 mM glucose (G) in cardioplegia, and hypothermic adaptation and glucose (HG). Developed pressure (DP), dP/dt(max), and pressure-rate product (PRP) improved (P < 0.05) in G, H, and HG compared with C during reperfusion. DP and PRP were elevated in HG over H and G. ATP was higher in G, H, and HG, although no additional increase in HG over H was found. Lactate and CO(2) production were elevated in G only. The mRNA expression for HSP70-1, ANT(1), and beta-F(1)-ATPase was elevated severalfold in H and HG, but not G over C during reperfusion. In conclusion, glucose provides additional functional improvement in H. Additionally, neither ATP levels nor anaerobic metabolism are linked to mRNA expression for HSP70, ANT(1), or beta-F(1)-ATPase in CAH.

Maturational changes in gene expression for adenine nucleotide translocator isoforms and betaF1-ATPase in rabbit heart

Maturational changes in myocardial respiratory control have been related to postnatal accumulation of adenine nucleotide translocator (ANT) in the inner mitochondrial membrane. Alternatively alterations in relative isoform distribution for this nuclear-encoded gene during myocardial maturation might be responsible for changing the kinetics of respiratory control. Rabbit hearts were analyzed for adenine nucleotide translocator isoform (ANT1, ANT2, ANT3) gene expression and distribution at four ages (fetal, 29/31 days of gestation; 1 h postnatal; 9 days postnatal; and 3-4 months postnatal). Transcript levels for the coordinately expressed betaF1-ATPase were also examined in these hearts. These studies demonstrated that mRNA expression for ANT1 in coordination with betaF1-ATPase increased substantially after 9 days of age in rabbit hearts. Expression of the minor isoform ANT3 parallels ANT1, though no change in expression of the kidney-specific isoform ANT2 occurs in heart during this developmental period. Previous work has demonstrated that ANT protein accumulation is closely coordinated with mRNA expression for ANT1. These results support previous studies, which indicate that the operational mode of myocardial respiratory control depends on adenine nucleotide mRNA expression. Changes in relative adenine nucleotide translocator isoform distribution do occur during fetal to mature transition and may contribute to observed changes in the mode of respiratory control.

Temperature threshold and preservation of signaling for mitochondrial membrane proteins during ischemia in rabbit heart

Temperature modulates both myocardial energy requirements and production. We have previously demonstrated that myocardial protection induced by hypothermic adaptation preserves expression of genes regulating heat shock protein and the nuclear-encoded mitochondrial proteins, the adenine nucleotide translocator isoform 1 (ANT1), and the beta subunit of F1-ATPase (beta F1-ATPase). This preservation is associated with a reduction in ATP depletion similar to that noted in cardioplegic arrested hearts preserved at a critical temperature (30 degrees C) or below. We tested the hypothesis that expression of these genes may also be subject to this temperature threshold phenomenon. Isolated perfused rabbit hearts were subjected to ischemic cardioplegic arrest at 4, 30, or 34 degrees C for 120 min. Cardiac function indices and steady-state mRNA levels for ANT1, beta F1-ATPase, and HSP70-1 were measured prior to ischemia (B) and after 45 min of reperfusion. Cardiac function was significantly depressed in the 34 degrees C group. Ischemia at 34 degrees C reduced steady-state mRNA levels for ANT1 and beta F1-ATPase from B, but these levels were similarly preserved at 4 and 30 degrees C. HSP70-1 levels were mildly elevated (fourfold) above B to similar levels at all three temperatures. These results indicate that mRNA expression for ANT1 and beta F1-ATPase is specifically preserved in a pattern consistent with the temperature threshold phenomenon. HSP70-1 expression is not influenced by ischemic temperature. Preservation of gene expression for these mitochondrial proteins implies that signaling for mitochondrial biogenesis or resynthesis is maintained after ischemic insult.

Hypothermia preserves function and signaling for mitochondrial biogenesis during subsequent ischemia

Hypothermia is known to protect myocardium during ischemia, but its role in induction of a protective stress response before ischemia has not been evaluated. As cold incites stress responses in other tissues, including heat shock protein induction and signaling mitochondrial biogenesis, we postulated that hypothermia in perfused hearts would produce similar phenomena while reducing injury during subsequent ischemia. Studies were performed in isolated perfused rabbit hearts (n = 77): a control group (C) and a hypothermic group (H) subjected to decreasing infusate temperature from 37 to 31 degrees C over 20 min. Subsequent ischemia during cardioplegic arrest at 34 degrees C for 120 min was followed by reperfusion. At 15 min of reperfusion, recovery of left ventricular developed pressure (LVDP), maximum first derivative of left ventricular pressure (LV dP/dtmax), LV -dP/dtmax, and the product of heart rate and LVDP was significantly increased in H (P < 0.01) compared with C hearts. Ischemic contracture started later in H (97.5 +/- 3.6 min) than in C (67.3 +/- 3.3 min) hearts. Myocardial ATP preservation and repletion during ischemia and reperfusion were higher in H than in C hearts. mRNA levels of the nuclear-encoded mitochondrial proteins adenine nucleotide translocase isoform 1 (ANT1) and beta-F1-adenosine-triphosphatase (beta-F1-ATPase) normalized to 28S RNA decreased in C hearts but were preserved in H hearts after reperfusion. Inducible heat shock protein (HSP70-1) mRNA was elevated nearly 4-fold after ischemia in C hearts and 12-fold in H hearts. These data indicate that hypothermia preserves myocardial function and ATP stores during subsequent ischemia and reperfusion. Signaling for mitochondrial biogenesis indexed by ANT1 and beta-F1-ATPase mRNA levels is also preserved during a marked increase in HSP70-1 mRNA.

Temperature threshold and modulation of energy metabolism in the cardioplegic arrested rabbit heart

Hypothermia protects ischemic tissues by reducing ATP utilization and accumulation of harmful metabolites. However, it also reduces ATP production, which might cause deterioration in the energy supply/demand ratio. Modulation of energy supply/demand according to temperature has not been previously studied in detail. In this study, isolated, perfused rabbit hearts (n = 60) were used to determine the effects of various temperatures on myocardial energy metabolism and function during cardioplegic arrest. Ischemia was induced by crystalloid cardioplegic solution at 4, 18, 30, and 34 degrees C for 120 min, respectively. At each temperature, the hearts were divided into a glucose-treated group which contained 22 mM glucose in cardioplegic solution as the only substrate and a control group which contained 22 mM mannitol to keep same osmolarity. Following 15 min reperfusion, recovery of left ventricular developed pressure (DP), +/- dP/dtmax, and the product of heart rate and DP were significantly higher in 30, 18, and 4 degrees C groups than those in 34 degrees C control group. The functional recovery was also significantly higher in the 34 degrees C glucose-treated group than that in the 34 degrees C control group, but there was no difference between those groups at 30 degrees C and the temperature below 30 degrees C. Myocardial ATP concentration was significantly lower in 34 degrees C control group than those in other groups. There is a close relationship between myocardial ATP concentration and functional recovery (R2 = 0.90). The accumulations of lactate and CO2 were significantly higher at 34 degrees C in glucose-treated group than those in the control group. However, there was no significant difference between these two groups at 30 degrees C and the temperature below 30 degrees C. These results indicate that under these study conditions: (1) a marked decrease in energy supply/demand occurs above 30 degrees C, implying that a temperature threshold exists; and (2) this can be ameliorated by provision of glucose as substrate in cardioplegia solution.

Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo

Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MVO2) were induced by epinephrine infusion in newborn (0-32 h, n = 6) and mature sheep (30-32 days, n = 6), and high-energy phosphates were monitored with 31P nuclear magnetic resonance. Western blot analyses for the ANT1 and the beta-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional (n = 9 total per group) as well as in fetal hearts (130-132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the 31P spectra data revealed that the ADP-MVO2 relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in beta-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and beta-F1-ATPase increased approximately 2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.

Influence of the pH of cardioplegic solutions on cellular energy metabolism and hydrogen ion flux during neonatal hypothermic circulatory arrest and reperfusion: a dynamic 31P nuclear magnetic resonance study in a pig model

OBJECTIVES

The pH of cardioplegic solutions is postulated to affect myocardial protection during neonatal hypothermic circulatory arrest. Neither optimization of cardioplegic pH nor its influence on intracellular pH during hypothermic circulatory arrest has been previously studied in vivo. Thus we examined the effects of the pH of cardioplegic solutions on postischemic cardiac function in vivo, including two possible operative mechanisms: (1) reduction in adenosine triphosphate use and depletion of high-energy phosphate stores or (2) reduction of H+ flux during reperfusion, or both.

METHODS

Dynamic 31P spectroscopy was used to measure rates of adenosine triphosphate use, high-energy phosphate depletion, cytosolic acidification during hypothermic circulatory arrest, and phosphocreatine repletion and realkalinization during reperfusion. Neonatal pigs in three groups (n = 8 each)--group A, acidic cardioplegia (pH = 6.8); group B, basic cardioplegia (pH = 7.8); and group N, no cardioplegia--underwent hypothermia at 20 degrees C with 60 minutes of hypothermic cardioplegia followed by reperfusion.

RESULTS

Recoveries of peak elastance, stroke work, and diastolic stiffness were superior in group B. Indices of ischemic adenosine triphosphate use, initial phosphocreatine depletion rate, and tau, the exponential decay half-time, were not different among groups. Peak [H+] in group A (end-ischemia) was significantly elevated over that of group B. The realkalinization rate was reduced in group B compared with that in groups A (p = 0.015) and N (p = 0.035), with no difference between groups A and N (p = 0.3). Cytosolic realkalinization rate was markedly reduced and the half-time of [H+] decay was increased during reperfusion in group B.

CONCLUSIONS

Superior postischemic cardiac function in group B is not related to alterations in ischemic adenosine triphosphate use or high-energy store depletion, but may be due to slowing in H+ efflux during reperfusion, which should reduce Ca++ and Na+ influx.

Hypoxic pHi and function modulation by Na+/H+ exchange and alpha-adrenoreceptor inhibition in heart in vivo

Regulation of intracellular pH (pHi) may contribute to maintenance of cardiac contractile function during graded hypoxia in vivo. To test this hypothesis, we disturbed pHi regulation in vivo using two approaches: alpha-adrenoreceptor antagonism with phentolamine (1 mg/kg) (Phen; n = 9); and Na+/H+ exchange inhibition with HOE-642 (2 mg/kg; n = 6) before graded hypoxia in open-chest sheep. Hemodynamic parameters including left ventricular maximal pressure development (dP/dtmax) cardiac index (CI), and left ventricular power were monitored continuously and simultaneously with high-energy phosphate levels and pHi, measured with 31P nuclear magnetic resonance spectroscopy in Phen, HOE-642, and control (Con; n = 9). In subgroups (n = 6) in Con and Phen, coronary flow, myocardial oxygen consumption (MVO2), and lactate uptake were also measured. During hypoxia, the functional parameters left ventricular dP/dtmax, CI, and left ventricular power decreased significantly compared with baseline and Con values. These decreases were preceded by a significant drop (P < 0.05) in pHi from 7.10 +/- 0.04 to 6.69 +/- 0.05 in Phen and corresponded temporally to a pHi drop from 7.10 +/- 0.02 to 6.77 +/- 0.03 in HOE-642. Decreases in pHi in Phen were not preceded by decreases in cardiac function or MVO2. In contrast, cardiac function parameters increased significantly in Con, whereas no significant pHi decrease occurred (7.07 +/- 0.03 to 6.98 +/- 0.04). We conclude that these data indicate that pHi regulation can be disrupted through alpha-adrenergic antagonism or Na+/H(+)-exchange inhibition in vivo. These studies demonstrate that pHi regulation performs a role in the modulation of cardiac function during hypoxia in vivo.

Developmental changes in ATP utilization during graded hypoxia and reoxygenation in the heart in vivo

Myocardial ATP utilization and resynthesis during hypoxia and reoxygenation were studied in vivo as a function of maturation. Graded hypoxia was performed in newborn (NB; 4-10 days old, n = 6) and mature sheep (MAT; 30-60 days old, n = 6). Time-resolved 31P-nuclear magnetic resonance was used to monitor myocardial phosphates throughout hypoxia and to monitor reoxygenation concomitant with rate of myocardial O2 consumption (MVO2) measurement. Oxygen delivery and MVO2 were constant in both groups throughout hypoxia, with substantial and similar increases in both parameters during reoxygenation. Hypoxic myocardial lactate release was similar in NB and MAT. Phosphocreatine (PCr), but not ATP, decreased in NB only during milder hypoxia. Rapid PCr and slower ATP depletion occurred with severe hypoxia, consistent with ATP utilization/synthesis imbalance. Depletion rates were higher in MAT. Creatine rephosphorylation rates, measures of mitochondrial function reported as percentage of predicted values, were similar. 34 +/- 12 in NB and 26 +/- 9% in mature lambs. In conclusion, 1) phosphorylation potential decreases in NB but not MAT in response to a decreasing oxygen gradient; 2) ATP utilization during hypoxia increases more in mature lambs; 3) anaerobic ATP production is not greater in NB; and 4) despite the greater energy imbalance imposed on MAT during hypoxia, mitochondrial function is similar to NB during reoxygenation.

Relation of myocardial oxygen consumption and function to high energy phosphate utilization during graded hypoxia and reoxygenation in sheep in vivo

This study investigates the relation between myocardial oxygen consumption (MVO2), function, and high energy phosphates during severe hypoxia and reoxygenation in sheep in vivo. Graded hypoxia was performed in open-chested sheep to adjust PO2 to values where rapid depletion of energy stores occurred. Highly time-resolved 31P nuclear magnetic resonance spectroscopy enabled monitoring of myocardial phosphates throughout hypoxia and recovery with simultaneous MVO2 measurement. Sheep undergoing graded hypoxia (n = 5) with an arterial PO2 nadir of 13.4 +/- 0.5 mmHg, demonstrated maintained rates of oxygen consumption with large changes in coronary flow as phosphocreatine (PCr) decreased within 4 min to 40 +/- 7% of baseline. ATP utilization rate increased simultaneously 59 +/- 20%. Recovery was accompanied by marked increases in MVO2 from 2.0 +/- 0.5 to 7.2 +/- 1.9 mumol/g per min, while PCr recovery rate was 4.3 +/- 0.6 mumol/g per min. ATP decreased to 75 +/- 6% of baseline during severe hypoxia and did not recover. Sheep (n = 5) which underwent moderate hypoxia (PO2 maintained 25-35 mmHg for 10 min) did not demonstrate change in PCr or ATP. Functional and work assessment (n = 4) revealed that cardiac power increased during the graded hypoxia and was maintained through early reoxygenation. These studies show that (a) MVO2 does not decrease during oxygen deprivation in vivo despite marked and rapid decreases in high energy phosphates; (b) contractile function during hypoxia in vivo does not decrease during periods of PCr depletion and intracellular phosphate accumulation, and this may be related to marked increases in circulating catecholamines during global hypoxia. The measured creatine rephosphorylation rate is 34 +/- 11% of predicted (P < 0.01) calculated from reoxygenation parameters, which indicates that some mitochondrial respiratory uncoupling also occurs during the rephosphorylation period.

Myocardial energy metabolism in the newborn lamb in vivo during pacing-induced changes in oxygen consumption

Myocardial energy metabolism was studied in newborn sheep to determine whether the metabolic responses to pacing-induced increases in heart rate were similar to those previously found during catecholamine stimulation. Open-chest newborn sheep, 3 to 9 d old (n = 11), underwent atrial pacing at a respiratory rate harmonic just above the intrinsic heart rate. Pacing rate was increased by 30 beats/min every 5 min until conduction block or a drop in systemic arterial pressure occurred. Phosphorous metabolites were monitored simultaneously (n = 7) using a 31P magnetic resonance surface coil over the heart within a magnet operating at 4.7 tesla. Myocardial oxygen consumption was monitoring via an extracorporeal shunt from the coronary sinus. Rate pressure product increased with heart rate and was found to relate to myocardial oxygen consumption (r = 0.75), which increased maximally by 47 +/- 9% due to increases in coronary blood flow. Phosphocreatine/ATP ratio decreased significantly, and calculated ADP increased between baseline and peak performance but returned to near baseline levels during recovery at the initial pacing rate. These findings indicate that intracellular high-energy phosphate concentrations do change with alterations in myocardial oxygen consumption induced by cardiac pacing in the newborn. These changes are similar to those found during epinephrine infusion. Furthermore, the ATP hydrolysis products probably participate in myocardial respiratory regulation in the newborn in vivo.

Myocardial buffering capacity and high-energy phosphate utilization during hypothermic circulatory arrest and recovery in the newborn lamb in vivo

The purpose of this study was to measure myocardial buffering capacity and adenosine triphosphate utilization rates in the newborn animal in vivo during hypothermic circulatory arrest and recovery.

METHODS

These studies were performed with 31P magnetic resonance spectroscopic techniques, which supplied a 12- to 16-second time resolution, to monitor intracellular pH and phosphocreatine and adenosine triphosphate levels. All experiments were performed with a radiofrequency surface coil on the pericardium with the sheep centered inside a 4.7 T magnet. Newborn sheep (n = 5, aged 16 days +/- 2.4 standard error) were supported by cardiopulmonary bypass, cooled to 20 degrees C, and subjected to 20 minutes of circulatory arrest.

RESULTS

During early ischemia, phosphocreatine hydrolysis progressed at a linear rate, 1.2 +/- 0.05 mumol/gm per minute, and was accompanied by intracellular alkalinization. Myocardial buffering capacity calculated from delta pH/delta phosphocreatine equals 25 +/- 3 mueq gm-1 delta pH-1, a value similar to that obtained from perfused heart studies. After the initial 4 minutes in ischemia, the decrease in phosphocreatine hydrolysis was accompanied by intracellular acidification, which is likely due to late induction of anaerobic metabolism.

CONCLUSIONS

In these studies, early phosphocreatine hydrolysis rate is nearly equivalent to adenosine triphosphate utilization rate. During the early period of ischemia phosphocreatine hydrolysis serves a buffering function and is associated with intracellular alkalinization. These techniques and measurements can be used to compare effects of myocardial preservation techniques on intracellular pH and adenosine triphosphate kinetics.

Measurement of unidirectional P(i)-->ATP flux in lamb myocardium in vivo

Unidirectional myocardial ATP synthesis, P(i)-->ATP flux, was studied in vivo using 31P magnetization transfer techniques in intact sheep hearts (n = 5) which were functioning aerobically. Myocardial oxygen consumption (MVO) expressed as mu moles of oxygen atoms/gm/min was estimated using linear regression analysis of data derived from sheep (n = 23), which had undergone continuous MVO measurement during graded stepups in epinephrine induced work loads. During the saturation transfer experiment, epinephrine, beginning at 1 microgram/kg per min was infused to achieve a higher steady-state work load and level of MVO. The unidirectional P(i)-->ATP flux was found to increase significantly (P < 0.05) during increases in rate pressure product and MVO. These data show that the unidirectional P(i)-->ATP flux is at least 3-times higher than the peak ATP synthesis rate, achieved through oxidative phosphorylation in these experiments, and more than a magnitude higher than the peak ATP synthesis rate through glycolysis. Therefore, forward P(i)-->ATP flux through glycolysis is the major contributor to the measured P(i)-->ATP flux and these ATP producing bidirectional glycolytic reactions are in a near equilibrium state. Furthermore, delta P(i)-->ATP/delta MVO, 2.70 +/- 0.29 (S.E.) elicited during epinephrine infusion is similar to classically derived P:O values, indicating that most of the change in unidirectional flux is due to oxidative phosphorylation and that minimal disturbance in the glycolytic near equilibrium occurs under these conditions.

Maturational changes in respiratory control through creatine kinase in heart in vivo

The role of creatine kinase in regulation of myocardial respiration was studied in vivo as a function of maturation. Unidirectional creatine kinase flux (JCK), phosphocreatine to gamma-ATP, was measured in newborn lambs (age 3-9 days, n = 8) and mature sheep (age 30-60 days, n = 6) using 31P saturation transfer techniques, and total creatine kinase activity was measured using standard methods. Myocardial oxygen consumption (MVO2) was measured simultaneously via an extracorporeal shunt from the coronary sinus as cardiac work was increased via epinephrine (1-3 micrograms.kg-1.min-1). Findings were as follows: 1) baseline newborn JCK was markedly lower than in mature sheep despite higher levels of MVO2, and this could be related to a decrease in total creatine kinase activity; 2) JCK was substantially higher than the rate of ATP synthesis in both groups at baseline rates of oxygen consumption; and 3) JCK decreased significantly in newborns during increases in MVO2, whereas there was no change in flux rate in the mature sheep during even larger relative changes in work and oxygen consumption. These data imply that creatine kinase does not limit oxidative phosphorylation. However, this enzyme system probably maintains at least an indirect role in respiratory control that is a function of the myocardial developmental state.

Cardiothoracic magnetic resonance angiography

At the current state of the art, cardiothoracic MR angiography offers the clinician information that is supplemental to that provided by other noninvasive imaging techniques. Indeed, in some areas MR angiography will likely surpass currently used methods as the technique of choice. Specifically, measurement of cardiac output, pulmonary blood flow, and lung perfusion can be performed relatively accurately and simply during a brief MR examination. Both standard spin-echo and angiographic evaluation of the thoracic aorta provide qualitative images with superior resolution. Additionally, development of pulmonary artery angiography is progressing rapidly and may soon be clinically useful. Phase incoherence caused by complex flow and resulting in a signal void is useful for location and qualitative assessment of abnormal flow jets induced by stenoses. However, this phenomenon represents the major limitation to quantitative assessment of flow abnormalities. Methods to increase signal to noise and/or reduce phase incoherence must be developed before MR angiography can be used effectively to assess abnormal flow conditions.

Adenosine release and high energy phosphates in intact dog hearts during norepinephrine infusion

Cardiac adenosine release is thought to depend on the oxygen supply/demand ratio, and this effect may be mediated by changes in high energy phosphate concentrations. Previous studies supporting this hypothesis have been done primarily in isolated hearts. We tested this hypothesis in intact dog hearts. Anesthetized, open-chest dogs were placed in a 4.7-T magnet where 31P nuclear magnetic resonance spectra were acquired via a surface coil over the heart at 2-minute intervals (60 scans, 2-second interpulse delay). Coronary sinus flow was shunted through a flow probe and returned via a jugular vein. After a control period, intracoronary norepinephrine was infused (12 micrograms/min) for 16 minutes and plasma samples were taken every 5 minutes. The phosphocreatine/ATP peak area ratio was used as an index of high energy phosphate changes. During norepinephrine infusion, arterial pressure, heart rate, coronary sinus flow, oxygen consumption, and adenosine release all increased significantly. Adenosine release peaked at 5 minutes but remained elevated after 15 minutes. There was a transient fall in the phosphocreatine/ATP ratio (9.2 +/- 3.1%, p less than 0.05) during the first 7 minutes, but the ratio returned to control levels by 9 minutes. The oxygen supply/consumption ratio increased after 5 minutes of norepinephrine infusion and then returned to control levels. We conclude that during norepinephrine infusion in vivo, persistent adenosine release can occur with only small transient changes in high energy phosphate concentrations and with no decrease in the oxygen supply/demand ratio.

Physiologic alterations in cranial blood flow demonstrated by magnetic resonance angiography

Two-dimensional phase contrast magnetic resonance angiography (MRA) was used to image alterations in cranial blood flow induced by changes in arterial PCO2 in an animal model. MRA was performed on five sheep; 64 acquisitions were obtained in each of three flow encode directions using a 256 x 256 matrix. Sheep were intubated and ventilated with oxygen and 1.5% halothane to prevent any movement. Femoral arterial cannulation was performed to monitor arterial blood gases and pressure. The sheep was secured in a cradle with its head and neck in a 6-inch imaging coil within the 26-cm-clear bore. Images were obtained during separate physiologic states, which were induced by changes in ventilatory parameters. These were normocapnia (PCO2 35-45 mm Hg), hypercapnia (greater than 90-130 mm Hg), and hypercapnia with superimposed hypoxia. Comparisons of images were performed using both a video flashback mode and image subtraction. The authors noted that 1) both venous and arterial flow velocity qualitatively increased during hypercapnia; 2) in addition to change in the caliber of blood vessels, redistribution of blood flow within the cranium could be demonstrated during the PCO2 changes; and 3) blood was directed away from superficial structures and toward the brain during superimposed hypoxia. MRA, previously used to show steady-state cranial flow also can demonstrate flow responses to physiologic stimuli.

Intra- and extracellular pH of the brain in vivo studied by 31P-NMR during hyper- and hypocapnia

Studies were performed to determine the pH relationships among the extracellular, intracellular, and arterial blood compartments in the brain in vivo. Resolution of the extracellular monophosphate resonance peak from the intracellular peak in 31P nuclear magnetic resonance (NMR) spectra of sheep brain with the calvarium intact enabled pH measurement in these respective compartments. Sheep were then subjected to both hyper- and hypoventilation, which resulted in a wide range of arterial PCO2 and pH values. Linear regression analysis of pH in these compartments yielded slopes of 0.56 +/- 0.05 for extracellular pH (pHe) vs. arterial pH, 0.43 +/- 0.078 for intracellular pH (pHi) vs. pHe, and 0.23 +/- 0.056 for pHi vs. arterial pH. These data indicate that CO2 buffering capacity is different and decreases from the intracellular to extracellular to arterial blood compartments. Separation of the extracellular space from the vascular space may be a function of the blood-brain barrier, which contributes to the buffering capability of the extracellular compartment. A marked decrease in the pH gradient between the extracellular and intracellular space occurs during hypercarbia and may influence mechanisms of central respiratory control.

Developmental adaptations in cytosolic phosphate content and pH regulation in the sheep heart in vivo

This study examines adaptations in myocardial cytosolic phosphate content and buffering capacity that occur in vivo as a function of development. Phosphate metabolites were monitored in an open chest sheep preparation using a 31P magnetic resonance surface coil over the left ventricle. Newborn lambs (aged 4-9 d, n = 5) underwent exchange transfusion with adult blood to reduce blood-borne 2,3-diphosphoglycerate contamination of the heart monophosphate and phosphomonoester resonances, thus allowing determination of these phosphate concentrations. The blood-exchanged newborns and mature controls (aged 30-60 d, n = 5) were infused with 0.4 N hydrochloric acid to decrease pH from greater than 7.35 to less than 7.00. Simultaneously, intracellular and extracellular pH were determined from the chemical shifts of the respective phosphate peaks and compared to arterial blood pH. Findings were as follows: (a) diphosphoglycerate contribution to the cardiac spectrum was found to be negligible, (b) significant decreases in cytosolic phosphate (P less than 0.03) and phosphomonoester (P less than 0.01) content occurred with maturation, and (c) large decreases in extracellular pH (greater than 0.5 U) in both groups were similarly associated with only small changes in intracellular pH (less than 0.1 U). Change in cytosolic phosphate content implies that alterations occur in the phosphorylation potential with resulting effects on regulation of myocardial respiration, and cardiac energetics.

Developmental changes in the relation between phosphate metabolites and oxygen consumption in the sheep heart in vivo

This study examines the role of phosphate metabolites in the regulation of mitochondrial oxygen consumption of the heart in vivo as a function of development. We used an open chest lamb/sheep preparation in which myocardial oxygen consumption (MVO2) was monitored via an extracorporeal shunt from the coronary sinus. Phosphate metabolites were monitored simultaneously using 31P nuclear magnetic resonance with a surface coil overlying the left ventricle. Graded infusions of epinephrine were used to increase MVO2 in both neonatal lambs (age 5-12 d, n = 8), and mature sheep (26-86 d, n = 6). The maximal increase in MVO2 achieved was 220 +/- 38% in the newborns and 350 +/- 66% in the mature animals. Associated with these increases in MVO2 in the newborn lambs are significant (P less than 0.001) decreases in PCr/ATP, and increases in calculated ADP and intracellular Pi. This was in contrast to the mature sheep, in which there were no significant changes in PCr/ATP, ADP, or Pi. In conclusion, we find that (a) there are changes in PCr/ATP, Pi, and ADP in newborn animals with moderate increases in work that are not apparent in mature animals of the same species and (b) that these changes suggest that cytosolic ATP hydrolysis products may be more important in regulation of myocardial energy metabolism in the newborn than in the adult.

Relation between phosphate metabolites and oxygen consumption of heart in vivo

The relation between induced increases in cardiac work and phosphate metabolites was investigated in the canine heart in vivo to evaluate the role of ATP hydrolysis products, ADP and inorganic phosphate (Pi), in the control of myocardial oxygen consumption (MVO2). In these studies, myocardial blood flow and oxygen consumption were simultaneously measured with the 31P-nuclear magnetic resonance (NMR)-detected phosphate metabolites. Three protocols were used to increase myocardial work: pacing, epinephrine, and phenylephrine infusions. When these protocols were used, no or only slight changes in myocardial ATP, Pi, and creatine phosphate were observed with a greater than threefold increase in MVO2. The calculated intracellular free Mg concentration, ADP, and pH were also only slightly affected by these increases in work. These data indicate that a simple model involving the feedback of cytosolic ADP and Pi to the mitochondria regulating respiration is inadequate to explain respiratory control in vivo. These data suggest that some other parameters or cooperativity effects involving the phosphate metabolites must play a role in the feedback between respiration and work in the heart in vivo.

Intracellular pH and inorganic phosphate content of heart in vivo: a 31P-NMR study

Studies were performed to determine the contribution of red blood cells to the 31P-nuclear magnetic resonance (NMR) spectrum of the canine heart in vivo and the feasibility of measuring myocardial intracellular phosphate and pH. This was accomplished by replacing whole blood with a perfluorochemical perfusion emulsion blood substitute, Oxypherol, and noting the difference in the 31P-NMR spectrum of the heart. NMR data were collected with a NMR transmitter-receiver coil on the surface of the distal portion of the left ventricle. These studies demonstrated that a small (approximately 10%) contribution from 2,3-diphosphoglycerate (2,3-DPG) and phosphodiesters in the blood could be detected. The magnitude and shift of these blood-borne signals permitted the relative quantification of intracellular inorganic phosphate (Pi) content as well as intracellular pH. Under resting conditions, the intracellular ATP/Pi was 7.0 +/- 0.8 (n = 19). This corresponds to a free intracellular Pi content of approximately 0.8 mumol/g wet wt. The intracellular pH was 7.10 +/- 0.01 (n = 19). Acute respiratory alkalosis and acidosis, with the arterial pH ranging from approximately 7.0 to 7.7, resulted in only small changes in the intracellular pH (approximately 0.1 pH unit). These latter results demonstrate an effective myocardial intracellular proton-buffering mechanism in vivo.

Simultaneous monitoring of coronary blood flow and 31P NMR detected myocardial metabolites

We report a method of dynamically measuring coronary blood flow in lambs, while simultaneously monitoring cardiac phosphate metabolism with 31P NMR at 81 MHz. This method uses an ultrasonic transit time probe in conjunction with a 4.7-T CSI spectrometer with a 33-cm magnet bore.

Left ventricular systolic circular index: an echocardiographic measure of transseptal pressure ratio

An echocardiographic index of left ventricular (LV) short axis circularity can be defined by the equation: left ventricular systolic circularity index (LVSCI) = 4 pi(LV area) X 100/(LV perimeter). This index was measured from two-dimensional echocardiograms in 98 children (ages 1 day to 19 years) with congenital heart disease, and results were compared to right ventricular/left ventricular peak systolic pressure ratios (RVP/LVP) determined at cardiac catheterization. LVSCI was also computed in 50 children without cardiovascular or pulmonary disease to define the normal range. A short axis image of the left ventricle at the level of the papillary muscles was obtained from the left parasternal position. Area and perimeter were determined by computer planimetry of the LV endocardium at end systole. LVSCI was measured from three consecutive beats and averaged. In the normal group all values of LVSCI exceeded 93% (mean 96%). In the group with congenital heart disease RVP/LVP correlated exponentially with LVSCI: RVP/LVP = e2.6-0.04 LVSCI; with r = 0.88, SEE = 0.39, and p less than 0.001. If patients with suprasystemic right ventricular pressures (RVP/LVP greater than 1.2) are excluded, there is a linear correlation between RVP/LVP and LVSCI: RVP/LVP = 2.3-0.021 LVSCI; with r = 0.80, SEE = 0.14, and p less than 0.001. LVSCI could distinguish between patients with normal, mildly elevated, moderately elevated, and severely elevated RVP/LVP. We conclude that LVSCI is a readily determined parameter that is independent of age or body size and predicts RVP/LVP in children with congenital heart disease.

Conduction abnormalities detected by electrophysiologic testing following repair of ostium primum atrioventricular septal defect

Since 1983 we have performed electrophysiologic studies in 6 patients who had previously undergone repair of an ostium primum atrioventricular septal defect. Information obtained during electrophysiologic studies was crucial in guiding appropriate pacemaker therapy in these patients. As judged from the resting electrocardiogram, sinus or junctional bradycardia was present in 3/6, atrial flutter / fibrillation in 2/6, and paced rhythm in 2 patients who had had ventricular pacemakers implanted for complete atrioventricular block. During maximal exercise testing 4 patients had reduced heart rates; 2 had sudden drops in heart rate at 1 min postexercise; 1 patient had exercise induced ventricular bigeminy; and 1 patient with atrial flutter and 2: 1-4: 1 block at rest developed 1: 1 conduction during Stage II with an effective ventricular rate of 220/min. During electrophysiologic studies, the maximum corrected sinus node recovery time was abnormal in five of the six, ranging from 410 to 5630 msec. There was no spontaneous atrial rhythm in the other patient. Complete atrioventricular block was present in 2 patients while the atrioventricular Wenckebach phenomenon occurred abnormally at atrial pacing cycle lengths greater than 450 msec in 2 others. Supraventricular tachycardia or atrial flutter/fibrillation, was either spontaneous or induced in 2/6 patients, while ventricular tachycardia was induced in 1/3 patients who underwent programmed ventricular stimulation. Electrophysiologic studies were important in unmasking severe sinus node disease in 3 patients and atrioventricular node disease in 2. We therefore recommend that electrophysiologic studies be strongly considered as part of the evaluation of conduction abnormalities following repair of ostium primum atrioventricular septal defect.

A 20-year review of ostium primum defect repair in children

Between July, 1963, and July, 1983, a total of 69 patients (35 boys and 34 girls) underwent ostium primum defect repair. There were four perioperative deaths and four patients were subsequently lost to follow-up, leaving 61 children followed for 6 months to 20 years (mean 5 years). Results of surgery were assessed by cardiac catheterization in 17 of 61 patients, while the remaining patients were evaluated noninvasively. Postoperative mitral insufficiency was found to be absent in 19 patients, mild to trivial in 35, moderate in four, and severe in two. Four patients were found to have large residual atrial septal defects. Significant late postoperative arrhythmias were found in 14 of 61 patients. The types of arrhythmias included isolated complete atrioventricular block in 5 of 14, complete atrioventricular block with sinus node dysfunction in 2 of 14, and isolated sinus node dysfunction in 7 of 14. Pacemakers have been implanted in 8 of 14 of these patients. Based on this 20-year review of a large number of children: (1) ostium primum defect repair is associated with a low mortality rate, (2) residual mitral insufficiency although common is usually mild to trivial and nonprogressive, and (3) significant arrhythmias are a frequent complication and often require pacemaker implantation.

Development of infundibular obstruction after percutaneous pulmonary balloon valvuloplasty

A 14 month old boy with suprasystemic right ventricular pressure secondary to pulmonary valvular stenosis and anular size of 10 mm underwent percutaneous balloon valvuloplasty with a 12 mm balloon. Right ventricular pressure almost doubled after valvuloplasty and the electrocardiogram revealed development of severe right ventricular strain. Both findings persisted on the following day. A postvalvuloplasty right ventriculogram demonstrated a severe systolic infundibular obstruction not present before. The patient underwent surgical relief of infundibular obstruction; successful opening of the pulmonary valve by the balloon valvuloplasty was observed. It is concluded that a balloon size 20% larger than anular size can be safe in human subjects and that infundibular obstruction may appear or even worsen after balloon valvuloplasty. Such an obstruction may be related to the severity of pulmonary valvular obstruction and a hypercontractile infundibulum.

Effects of electronic fetal heart rate monitoring on perinatal outcome and obstetric practices

Perinatal outcome and obstetric practices during 1970 and 1977 were compared. None of the 6,740 fetuses delivered with birth weights of 1,000 gm or greater in 1970 had electronic fetal monitoring (EFM). In 1977, 5,987 of 8,174 fetuses delivered had EFM (72.7%). High-risk factors were significantly more frequent in the pregnant patient population in 1977. The incidence of intrapartum stillbirths and severe birth asphyxia was significantly lower in 1977. These reductions remained significant when corrected for changes in obstetric practices other than EFM as well as for changes in patient population. The neonatal death rate was not significantly changed. The primary cesarean section rate increased from 4.4% to 10.1%, mostly because of a greater number of cesarean sections done for failure to progress in labor and breech presentation. Only 15% of the overall increase in cesarean section rate was because of a greater frequency of the indication of fetal distress. The incidence of severe birth asphyxia was the same among the unmonitored patients in 1970 and 1977. In 1977, however, the monitored patients had a significantly lower incidence of severe birth asphyxia than the unmonitored patients.