Categorization and repair of recurrent and acquired tracheoesophageal fistulae occurring after esophageal atresia repair

PURPOSE

Recurrent trachea-esophageal fistula (recTEF) is a frequent (5%-10%) complication of congenital TEF (conTEF) and esophageal atresia (EA) repair. In addition, postoperative acquired TEF (acqTEF) can occur in addition to or even in the absence of prior conTEF in the setting of esophageal anastomotic complications. Reliable repair often proves difficult by endoluminal or standard surgical techniques. We present the results of an approach that reliably identifies the TEF and facilitates airway closure as well as repair of associated tracheal and esophageal problems.

METHODS

Retrospective review of 66 consecutive patients 2009-2016 (55 referrals and 11 local) who underwent repair via reoperative thoracotomy or cervicotomy for recTEF and acqTEF (IRB P00004344). Our surgical approach used complete separation of the airway and esophagus, which reliably revealed the TEF (without need for cannulation) and freed the tissues for primary closure of the trachea and frequently resection of the tracheal diverticulum. For associated esophageal strictures, stricturoplasty or resection was performed. Separation of the suture lines by rotational pexy of the both esophagus and the trachea, and/or tissue interposition were used to further inhibit re-recurrence. For associated severe tracheomalacia, posterior tracheopexy to the anterior spinal ligament was utilized.

RESULTS

The TEFs were recurrent (77%), acquired from esophageal leaks (26%), in addition to persistent or missed H-type (6%). Seven patients in this series had multiple TEFs of more than one category. Of the acqTEF cases, 6 were esophagobronchial, 10 esophagopulmonic, 2 esophagotracheal (initial pure EA cases), and 2 from a gastric conduit to the trachea. Upon referral, 18 patients had failed endoluminal treatments; and open operations for recTEF had failed in 18 patients. Significant pulmonary symptoms were present in all. During repairs, 58% were found to have a large tracheal diverticulum, and 51% had posterior tracheopexy for significant tracheomalacia. For larger esophageal defects, 32% were treated by stricturoplasty and 37% by segmental resection. Rotational pexy of the trachea and/or esophagus was utilized in 62% of cases to achieve optimal suture line separation. Review with a mean follow-up of 35months identified no recurrences, and resolution of pulmonary symptoms in all. Stricture treatment required postoperative dilations in 30, and esophageal replacement in 6 for long strictures. There was one death.

CONCLUSION

This retrospective review of 66 patients with postoperative recurrent and acquired TEF following esophageal atresia repair is the largest such series to date and provides a new categorization for postoperative TEF that helps clarify the diagnostic and therapeutic challenges for management.

Direct tracheobronchopexy to correct airway collapse due to severe tracheobronchomalacia: Short-term outcomes in a series of 20 patients

PURPOSE

Tracheobronchomalacia (TBM) is associated with esophageal atresia, tracheoesophageal fistulas, and congenital heart disease. TBM results in chronic cough, poor mucous clearance, and recurrent pneumonias. Apparent life-threatening events or recurrent pneumonias may require surgery. TBM is commonly treated with an aortopexy, which indirectly elevates trachea's anterior wall. However, malformed tracheal cartilage and posterior tracheal membrane intrusion may limit its effectiveness. This study describes patient outcomes undergoing direct tracheobronchopexy for TBM.

METHODS

The records of patients that underwent direct tracheobronchopexy at our institution from January 2011 to April 2014 were retrospectively reviewed. Primary outcomes included TBM recurrence and resolution of the primary symptoms. Data were analyzed by McNemar's test for matched binary pairs and logistic regression modeling to account for the endoscopic presence of luminal narrowing over multiple time points per patient.

RESULTS

Twenty patients were identified. Preoperative evaluation guided the type of tracheobronchopexy. 30% had isolated anterior and 50% isolated posterior tracheobronchopexies, while 20% had both. Follow-up was 5 months (range, 0.5-38). No patients had postoperative ALTEs, and pneumonias were significantly decreased (p=0.0005). Fewer patients had tracheobronchial collapse at postoperative endoscopic exam in these anatomical regions: middle trachea (p=0.01), lower trachea (p<0.001), and right bronchus (p=0.04).

CONCLUSION

The use of direct tracheobronchopexy resulted in ALTE resolution and reduction of recurrent pneumonias in our patients. TBM was also reduced in the middle and lower trachea and right mainstem bronchus. Given the heterogeneity of our population, further studies are needed to ascertain longer-term outcomes and a grading scale for TBM severity.

Abstract 167: Growth Induction to Reverse Congenital Aortic Developmental Hypoplasia

Objectives: Congenital heart disease may include hypoplastic heart valves, ventricles or great arteries. Infants with coarctation of the aorta (CoA) often have a hypoplastic transverse aortic arch (TAA) which can greatly complicate surgical repairs. Although these defects are often considered to be genetic in origin, our hypothesis was that they are problems of development which are potentially reversible. We tested the corollary hypothesis that hypoplastic TAAs retain normal developmental potential and the increased aortic flow after CoA repair provides the biomechanical signal for catch-up growth.

Methods: Infants (N = 19) with TAA hypoplasia who underwent surgical CoA repair were studied for TAA growth by echocardiography done prior to and at intervals up to 13 years later. The TAA diameters were indexed using nomograms and calculated as standard deviations from expected size (SDE). Normal range is ± 2 SDE and < −2 indicates hypoplasia.

Results: 1) TAA growth was rapid and significant within 3 months. 2) The initial average TAA SDE = −3.7 (range: −7.6 to −2.1) (0/19 normal); 3 months = −1.5 (-4.1 to 0.9) (12/17); 1 year = −1.0 (-4.2 to 1.3) (15/19); 5 to 13 years = −0.6 (-2.1 to 0.9) (16/17 normal).

Conclusions: 1) Hypoplastic aortic arches grew rapidly to normal size with increased flow following CoA repair. 2) The results suggest the cause of hypoplasia was underdevelopment from low flow and, when increased, flow provided the biomechanical signal to induce catch up growth. 3) Infants were a relevant model for demonstrating the aortic growth signal. 4) Growth induction by increased blood flow could be used to reverse aortic underdevelopment in other selected patients.

Surgical approaches to aortopexy for severe tracheomalacia

PURPOSE

The purpose of this study was to determine the outcomes among three different surgical approaches for performing an aortopexy to treat severe tracheomalacia (STM).

METHODS

A retrospective review was performed for all patients who underwent an aortopexy by pediatric surgeons at a single institution during 1997-2012. Data collected included details of the operative approaches and clinical results. The data were analyzed using Chi-square and Fisher exact test.

RESULTS

Forty-one patients underwent an aortopexy. The operation was chosen by the surgeon and not randomized. Exposure was by partial sternotomy (PS) (20), open thoracotomy (12), or thoracoscopic approach (7). Only the PS approach was done by a single team. All groups showed improvement in work of breathing, prevention of severe respiratory distress, and acute life threatening events. These effects were more dramatic for the PS group, especially regarding oxygen and/or ventilator dependence and the ability to undergo tracheostomy decannulation. Among the sixteen patients with failure-to-thrive before successful aortopexy by any technique, ten demonstrated significant improvement in their growth (p=0.025). The recurrence rate for the thoracoscopic approach was 38%, and there were no recurrences in the partial sternotomy and the thoracotomy groups, 38% vs 0% vs 0%, p=0.005. Simultaneous bronchoscopy was utilized more commonly in the PS group compared to the thoracotomy and thoracoscopic group, 95% vs 62% vs 38%.

CONCLUSIONS

In this series, the partial sternotomy technique had the most reliable resolution of symptoms and no recurrence requiring reoperation. The PS approach to STM has the technical advantages of an improved exposure with equal access to the vessels over the right and left mainstem bronchi, as well as the trachea and a more specific elevation of the arteries, including suspension of the pulmonary arteries and trachea itself when desirable. Simultaneous bronchoscopy during aortopexy and an experienced team also likely contribute to improved outcomes. The variations in populations, follow-up, and use of continuous intraoperative bronchoscopy, however, make firm conclusions difficult.

Surgical advances in the fetus and neonate: esophageal atresia

This article focuses on selected topics in the diagnosis and management of patients with esophageal atresia (EA) with or without tracheoesophageal fistula. The current status of prenatal diagnosis and recent advances in surgical techniques, including thoracoscopic repair for short-gap EA and tension-induced esophageal growth for long-gap EA, are reviewed. Although no consensus exists among pediatric surgeons regarding the role of these procedures in the treatment of EA, one can reasonably expect that, as they evolve, their application will become more widespread in this challenging patient population.

Abstract P116: The Physiological Ventricular Growth Signal Can Be Determined Using Infants with Congenital Heart Disease as Models

Objectives The signal for ventricular growth has not been defined. This basic developmental question was studied using infants with congenital heart lesions as models. Our first hypothesis was that clinical ventricular hypoplasia is a developmental rather than a primarily genetic defect and, therefore, catch-up growth can be induced. Our clinical observations also led to the hypothesis that forward flow across the atrioventricular (AV) valve (mitral or tricuspid) is what generates the growth signal. To test these hypotheses we analyzed clinical data from infants with a variety of congenital defects including three groups of patients with a hypoplastic ventricle in whom a procedure was carried out to increase flow across the AV valve.

Methods Infants with one of several congenital heart problems had right and left ventricular volumes (RV, LV) assessed by biplane echo and indexed to body surface area (m 2 ). The degree of hypoplasia was calculated using nomograms to determine the number of standard errors of the mean (SEM) below the expected volume (Table 1). Hypoplasia was considered significant when the SEM < −2.0. The three groups were studied before and after (3–6 months) procedures which increased AV flow.

Results Other possible growth mechanisms were assessed. (1) High wall stress with systemic or supra-systemic pressures produced no net cavitary growth unless AV valve flow was increased. (2) Significant retrograde flow from semilunar valve regurgitation did not increase ventricular size until failure developed. Therefore, no evidence was found for other growth mechanisms.

Conclusions 1) Patients with congenital heart disease have a variety of defects, some of which can serve as models to answer basic developmental questions. 2) Increased AV valve flow provides the signal which induces ventricular growth. 3) Operations which increased AV valve flow induced catch-up growth of hypoplastic ventricles and allowed beneficial two-ventricle repairs in these patients.

Abstract P139: Heart Failure Is Initiated By and Progresses Because of Normal Responses of Energy Metabolism to Stress

Objectives The mechanism underlying heart failure (HF) after an index cardiac event is unknown but should have several characteristics. HF is a modern problem, so it will likely be a general response and be able to encompass the variety of initiating cardiac lesions as well as significant stress (e.g. exertion). The consequences should lead to the many alterations found in HF.

[ATP] falls when energy demand outstrips supply (e.g. ischemia) but do not recover promptly with reperfusion because AMP is quickly catabolized and unavailable for recharging. [ATP] recovery is slow and limited by the availability of ribose-5-P. Ribose is not used as fuel and is channeled into nucleotide (ATP) synthesis allowing the effects of [ATP] recovery on function to be studied. Our hypothesis was that HF results from these responses of energy metabolism to stress which lower [ATP[ and affect the numerous myocardial reactions whose activity depends on [ATP]. The ability of ribose to quickly increase [ATP] allows these effects to be studied.

Methods The effects of ribose infusion on two models of myocardial stress were studied. (1) An intact canine model of global ischemia which allowed serial myocardial biopsies and detailed function analysis. (2) A rat myocardial infarction model which allowed ECHO analysis of the remote myocardium.

Results Table 1. Global ischemia (20') [ATP] recovery control w/ ribose infusion 9.9 ± 1.4 days
 2.8 ± 0.6 days Diastolic compliance recovery control w/ ribose infusion 9.4 ± 1.1 days
 2.4 ± 0.9 days Myocardial infarction Pre MI 2 weeks post MI LV systolic diameter (cm) control w/ ribose infusion 0.40 ± 0.03
 0.39 ± 0.06 0.73 ± 0.10
 0.47 ± 0.22 Remote LV wall thickness (cm) control w/ ribose infusion 0.13 ± 0.03
 0.13 ± 0.02 0.10 ± 0.01
 0.18 ± 0.12 LV ejection fraction control w/ ribose infusion 74 ± 5.9%
 76 ± 2.3% 22 ± 6.3%
 52 ± 5.0%

Conclusions 1) When energy demand outstripped supply (either from ischemia or increased work) myocardial [ATP] falls and recovery was slow. 2) Ribose is the limiting precursor for [ATP] recovery and infusion allowed the relationship between [ATP] and function to be studied. 3) In both myocardial ischemia recovery and increased load (from MI) ribose enhanced [ATP] and improved function. 4) The response of myocardial energy metabolism response to stress results in lower [ATP] which will decrease the activity of many function related reactions. 5) HF could begin and progress from these reactions of energy metabolism to cardiac stress.

Mitral and tricuspid valve repair and growth in unbalanced atrial ventricular canal defects

OBJECTIVE

Congenital mitral and tricuspid valve abnormalities in unbalanced atrioventricular canal defects are complex. We designed procedures to both repair and induce growth of hypoplastic atrioventricular valves and ventricles to achieve 2-ventricle repairs. Midterm data were assessed for reliability of catch-up growth, resulting quality of atrioventricular valves, and adequacy of 2-ventricle repairs.

METHODS

The 24 consecutive infants (14 female and 10 male) with unbalanced atrioventricular canal defects had significant hypoplasia of 1 atrioventricular valve and/or ventricle (an echocardiography-derived z value of ≤-3.0 standard errors of the mean below expected). Operative approaches included the following: (1) Staged repair was performed, with complete valve repair, partial closure of the atrial septal, and ventricular septal defects, and (usually) pulmonary artery banding. After adequate growth, repair was completed. A vestigial mitral valve (4-7 mm) in 3 patients led to partitioning the large tricuspid valve, creating a second mitral valve. (2) Repair with a shift in atrioventricular valve partitioning was performed to increase hypoplastic atrioventricular valve size. (3) Repair with snared atrial septal defects and ventricular septal defect was performed to allow intracardiac shunting. The hypoplastic atrioventricular valves and hypoplastic ventricles were reassessed on local follow-up (5-15 years).

RESULTS

The initial z scores were -2.8 to -7.4 for hypoplastic atrioventricular valves and -1.0 to -7.5 for hypoplastic ventricles. Follow-up z scores were -0.6 to -2.7 for hypoplastic atrioventricular valves and -2.0 to +1.8 for hypoplastic ventricles. Another 11 patients were also judged to be within normal limits. Three reoperations were for mitral valve regurgitation, and 1 reoperation was for mitral valve replacement. One patient died of central nervous system bleed just before extracorporeal membrane oxygenation weaning, and 2 patients died of late potassium overdose, for an 88% survival. Survivors are well with 2-ventricle repairs, and 15 of 19 patients are not taking cardiac medications.

CONCLUSIONS

Increasing atrioventricular valve flow reliably induced growth. Valve repair and growth achieved a 2-ventricle repair in all patients.

Esophageal stenting in children: indications, application, effectiveness, and complications

BACKGROUND

Use of esophageal stents is uncommon in children, and there are few reports. We report the first experience in predominantly small children and infants with retrievable, flexible stents designed for tracheobronchial use.

OBJECTIVE

Evaluation of initial experience with placement of esophageal stents for benign esophageal disorders in children.

DESIGN

A retrospective study.

SETTING

A pediatric, academic, tertiary-referral center.

PATIENTS

This study involved 7 pediatric patients.

INTERVENTIONS

Covered tracheobronchial stents were endoscopically placed in pediatric patients with benign esophageal conditions. Removal involved using forceps to pull the purse-string suture into the endoscope channel and collapsing the top of the stent for easy removal.

MAIN OUTCOME MEASUREMENTS

To evaluate the safety and feasibility of performing endoscopic stent placement in children and to establish criteria for early stent removal.

RESULTS

Six of 7 patients benefitted from stenting. There were no complications of placement. Novel techniques were developed for difficult retrievals. One patient did not benefit from esophageal stent placement, because the stent migrated downward from the uppermost part of the esophagus. One patient had some gagging, which led to early removal of the stent. A stent was removed emergently in 1 patient for respiratory distress.

LIMITATION

Small number of patients.

CONCLUSIONS

Retrievable, covered stents are easily placed and removed from the esophagus in small children. They should be considered for severe unrelenting strictures, especially when associated with esophageal leaks. A need exists for development of esophageal stents designed for pediatric use.

Achievement of feeding milestones after primary repair of long-gap esophageal atresia

OBJECTIVES

To determine the pattern of feeding milestones following primary repair of long-gap esophageal atresia (EA).

METHOD

A questionnaire based upon well established feeding milestones was used. Children after long-gap EA repair, n=40, were compared from after primary repair to healthy children from birth, n=102.

RESULTS

The age when surveyed of the EA group and controls was different: 6.2+/-4.7 (mean+/-standard deviation) years, range 1.1-20.9, versus 2.5+/-2.4 years, range 0.0-12.1, p=0.00. The esophageal gap length in the EA group was 5.1+/-1.2 cm and age at repair was 5.5+/-5.0 months. There was no statistically significant difference between the atresia group and controls for feeding milestones; Self feeding finger foods approached significance. There was, however, greater variability in the timing of milestones in the atresia group compared to controls. Feeding milestones were negatively correlated with age at primary repair: drinking with a covered sippy cup, rho=-0.51, p=0.01 and self feeding finger foods, rho=-0.36, p=0.04 were statistically significant. Drinking from a cup correlated with gestational age, rho=0.38, p=0.04, and negatively correlated to esophageal gap length, rho=-0.45, p=0.01.

CONCLUSIONS

Despite delayed onset of feeding, major milestones after EA repair occurred in similar pattern to normal infants. An early referral for primary repair is beneficial for earlier acquisition of milestones for infants with long-gap EA.

Long-gap esophageal atresia treated by growth induction: the biological potential and early follow-up results

This study had two purposes. The first was to determine whether the growth procedure would allow true primary repairs of the most severe end of the esophageal atresia (EA) spectrum with the longest gaps (LG) and most rudimentary lower esophageal segments. The second goal was to provide the first short- to mid-term (3-12 years) follow-up data on the esophageal function and quality of life (QOL) data on the patients in this series. From our series of 60 LG-EA patients who underwent a growth procedure, 42 had the true primary esophageal repair completed 3 years ago. Among these, 18 had gaps over 6 cm, and for 6, only a rudimentary lower esophagus existed well below the diaphragm. No patient was turned down and all had primary repairs. These results suggest that even the most rudimentary segment has the potential to achieve normal size and that the full EA spectrum can have a primary repair. Our follow-up studies indicated that the esophageal function of these previously grown segments was very good. All contacted (40) were eating normally with only 3 receiving supplemental g-tube feeds because of other significant defects. We have actively treated significant reflux and 41/42 had fundoplication. By endoscopy (N = 15) no esophagitis was visible, but on biopsy, mild inflammation was found in 3. No conditions were found which would suggest that there would be a late deterioration or adverse consequences would arise. Based on these ongoing evaluations, the outlook seems very favorable for a good long-term QOL.

Postoperative coagulopathy in a pediatric patient after exposure to bovine topical thrombin

Severe postoperative coagulopathy developed in a child with congenital heart disease due to a factor V inhibitor from repetitive exposure to bovine topical thrombin. This case report alerts pediatric providers to consider these inhibitors when postoperative coagulopathy occurs. Potential treatment options are reviewed.

Use of high-resolution endoscopic ultrasonography to examine the effect of tension on the esophagus during primary repair of long-gap esophageal atresia

BACKGROUND

We have shown that tension applied to the esophageal pouches in long-gap esophageal atresia allows primary repair without necessity for intestinal or gastric transposition.

OBJECTIVE

To determine whether the mural structure of the upper esophageal pouch is altered by tension.

MATERIALS AND METHODS

We examined the esophagus with high-resolution endoscopic ultrasonography. The upper pouch was examined before traction and the upper and lower esophagus were examined after primary repair. Of 11 patients examined, 7 were male. At initial surgery the age, weight and length of the patients (mean +/- SD) were 118 +/- 88 days, 4.7 +/- 1.2 kg and 54 +/- 4 cm, respectively. The gap length was 4.7 +/- 1.1 cm.

RESULTS

The pretraction measurement of the muscularis propria of the upper pouch was similar to the postanastomotic measurement of the upper esophagus, and there was no statistically significant difference from the lower esophageal segments after anastomosis: 0.83 +/- 0.19, 0.80 +/- 0.15 and 0.81 +/- 0.22 mm, respectively (P = 0.90). The thickness of combined mucosa and submucosa was also very similar in all three measurements, respectively: 0.93 (0.21) mm vs. 1.06 (0.08) mm vs. 1.0 (0.11) mm (P = 0.14).

CONCLUSION

The layers of the upper esophageal pouch are preserved in infants with esophageal atresia in whom esophageal length is increased with tension.

The effect of traction on esophageal structure in children with long-gap esophageal atresia

We examined the esophageal structure in children who underwent traction to achieve primary repair of long-gap esophageal atresia. High-resolution ultrasound was used to compare thickness of the proximal and distal esophagus in children who had traction to achieve primary repair (n=15) to cases of esophageal atresia with shorter gaps that did not require traction (n=8). The muscularis propria of the upper esophagus was thicker in the traction compared to the non-traction group, though not statistically significant (respectively, 0.79 (0.18) mm vs. 0.71 (0.16) mm; p=0.29), measurements were similar for the lower esophagus (respectively, 0.79 (0.21) mm vs. 0.75 (0.13) mm; p=0.64). Combined mucosa and submucosa was very similar in both groups for the upper (respectively, 1.03 (0.15) mm vs. 1.04 (0.16) mm; p=0.95) and lower esophagus (respectively, 1.09 (0.23) mm vs. 1.01 (0.13) mm; p=0.37). The thickness of individual mural layers is maintained after increasing esophageal length with traction.

A flexible approach to achieve a true primary repair for all infants with esophageal atresia

Our purpose is to present our results using a flexible surgical approach to achieve a true primary repair for all infants with esophageal atresia (EA). The proposed methods are designed to reach this goal, even when most of the intrathoracic esophagus is missing. What has made this goal attainable is the ability to rapidly induce esophageal growth. We reviewed the results of 63 consecutive patients who presented between 1984 and 2004 with an esophageal gap of greater than 2.5 cm, a distance where increasingly difficult repairs begin. Gaps of 4 cm or longer (46), 6.0 cm or longer (14), and over 10 cm (3) were included. Repairs begun elsewhere (20) included 17 spit fistulas. We present 3 surgical stages, designed to overcome tension and, for longer gaps, induce esophageal growth. For 25 infants, traction in the operating room was sufficient to dissipate tension and allow a primary repair. For the longest gaps, successful esophageal growth was induced over days in 38 patients by internal (5), external (23), and mixed internal/external traction (10). Growth quickly produced adequate esophagus for a primary repair. We conclude that adequate esophageal growth can be induced within days, even early in infancy, and this flexible approach allows the entire EA spectrum to be repaired primarily.

Open-lung biopsy guides therapy in children

BACKGROUND

Open-lung biopsy is uncommon in children. Modern indications and outcomes are unknown.

METHODS

This is a retrospective review of 64 open-lung biopsies (58 patients) from 1976 to 1996. Open-lung biopsies were used to grade vasculopathy in 8 patients (12% of 64) with pulmonary hypertension and in 10 patients (16% of 64) with combined pulmonary hypertension and lung parenchymal disease. Forty-six biopsies (72%) were obtained to diagnose parenchymal disease. Comparisons were made between biopsies performed from 1976 to 1989 and from 1990 to 1996.

RESULTS

In the period 1990 to 1996, there were significantly more infants (p = 0.03), comorbid disease (p = 0.009), extracorporeal membrane oxygenation support (p < 10(-4)), and ventilator dependence (p = 0.05) and significantly less immunocompromise (p = 0.04). A definitive diagnosis was made in 43 of 64 cases (67%) and altered workup in 63 of 64 cases (98%). No correlation existed between Heath-Edwards grade of microangiopathy and catheterization data. Definitive diagnosis was most strongly associated with a nonimmunocompromised patient (p < 10(-4)). Although only one death (1.5%) was related to open-lung biopsy, the procedure was associated with a 30% inhospital mortality rate and an 11% morbidity rate. Of the 19 deaths, 1 patient died from the procedure, 13 died from their diseases, and 5 had support withdrawn. Death was associated with preoperative ventilator dependence (p < 10(-4)) and extracorporeal membrane oxygenation (p = 0.007).

CONCLUSIONS

Pediatric open-lung biopsy commonly alters the diagnostic workup (98%). It is recommended for children who have been supported for 2 weeks by extracorporeal membrane oxygenation and for those with combined pulmonary hypertension and parenchymal lung disease. It is less useful in immunocompromised children.

Ion-exchange column chromatographic method for assaying purine metabolic pathway enzymes

High energy phosphate levels fall rapidly during cardiac ischemia and recover slowly (more than one week) during reperfusion. The slow recovery of ATP may reflect a lack of purine metabolic precursors and/or increased activity of purine catabolic enzymes such as 5'-nucleotidase (5'-NT, EC 3.1.3.5) and adenosine deaminase (ADA, EC 3.5.4.4). The activity of enzymes involved in both the catabolism of ATP precursors (5-NT and ADA) and the restoration of ATP from slow synthetic pathways [adenosine kinase (AK, EC 2.7.1.20), adenine phosphoribosyl transferase (APRT, EC 2.4.2.7) and hypoxanthine phosphoribosyl transferase (HPRT, EC 2.4.2.8)] may directly affect the rate of ATP recovery. Strategies to enhance recovery will depend on the relative activity of these enzymes following ischemia. Their activity in different species and their response to ischemia are not well characterized. Hence, rapid assay methods for these enzymes would facilitate detailed time course studies of their activities in postischemic myocardium. We modified a single ion-exchange column chromatographic method using DEAE-Sephadex to determine the products of incubation of 5'-NT, AK, APRT and HPRT with their respective substrates. The uniformity of the final product measurement procedure for all assays permits the activities of the four enzymes to be rapidly determined in a single tissue sample and facilitates the study of a large number of samples. This technique should also be useful for enzymes of the pyrimidine metabolic pathway.

Aortic arch anomalies associated with long gap esophageal atresia and tracheoesophageal fistula

PURPOSE

The purpose of this study was to determine whether aortic arch anomalies are associated with long gap esophageal atresia and tracheoesophageal fistula (EA-TEF).

METHODS

The authors performed a retrospective review of all infants who had EA-TEF from 1980 to 1996 at two pediatric surgery centers. Two hundred three infants who had EA-TEF were identified.

RESULTS

Twelve infants were noted to have both long gap EA-TEF defined as a gap length greater than 3 cm and aortic arch anomalies. Of these 12, 7 had aberrant right subclavian arteries originating from the descending aorta. Four of the seven infants who had aberrant right subclavian artery (SCA) had gap lengths greater than 4 cm. All four had their fistulae divided initially through a right thoracotomy with primary repair performed at a later date. The remaining five infants who had long gap EA-TEF had right-sided aortic arch with aberrant left subclavian arteries. All five initially underwent exploration through the right chest. On discovery of the long gap EA and concurrent vascular anomaly, the thoracotomies were closed, and the infants underwent definitive repair of both their EA-TEF and their vascular anomaly through a left thoracotomy.

CONCLUSIONS

The authors find that aortic arch anomalies are associated with long gap EA-TEF. Patients who have these two anomalies tend to have a long gap. Preoperative diagnosis of these anomalies may alter the timing and technique of surgical intervention. The embryogenesis of these vascular lesions may account for this more severe form of esophageal atresia.

Development of a true primary repair for the full spectrum of esophageal atresia

OBJECTIVE

To determine whether or not a true primary repair, without myotomies and with the gastroesophageal junction below the diaphragm, can be accomplished across the esophageal atresia (EA) spectrum. Our hypothesis is that the esophageal anastomosis can withstand significant tension. The consequences, particularly for those patients with a very long gap atresia, were assessed.

SUMMARY OF BACKGROUND DATA

Difficulties arise roughly in proportion to the size of the gap between esophageal segments. Reported surgical complications remain frequent, and particularly at the far end of the EA spectrum, not all children are left with a satisfactorily functioning esophagus or esophageal substitute.

METHODS

The outcomes of all infants who had a true primary repair of EA from 1976-1997 were determined. Surgically, the methods used to achieve a reliable true primary repair were expanded to accomplish this, even for a very long gap EA.

RESULTS

From 1976-97, 70 infants with or without associated tracheoesophageal fistula (TEF) had primary repairs performed with no surgery-related deaths and 11% later deaths. No interpositions were performed since 1983. There were no discernible anastomotic leaks and one late recurrent TEF related to the early use of balloon dilation. Ten infants had gaps of 5.0-6.8 cm and, among these, four had gaps of 5.5-6.8 cm that could not be pulled together initially. Traction sutures in the esophageal ends, however, produced sufficient lengthening within 6-10 days for a true primary repair. Very long gap repairs produced more reflux (10 of 10 required a fundoplication versus 24 of 70 overall) and more dilations to relieve strictures. Two infants underwent stricture resection with no recurrence. On follow-up, all patients over 2 years of age were eating well or satisfactorily, and none had a gastrostomy tube.

CONCLUSIONS

(1) The esophageal anastomosis can withstand considerable tension and allows a reliable true primary repair for the full EA spectrum. (2) Growth is rapid and traction sutures will produce significant esophageal lengthening within days. (3) With increasing tension, gastroesophageal reflux (GER) and strictures are more common; however, both are treatable. Follow-up reveals the benefits of true primary repair over other solutions.

Primary repair of ultra-long-gap esophageal atresia: results without a lengthening procedure

Ultra-long-gap esophageal atresia, defined as a gap length of 3.5 cm or greater, has proved difficult to repair. When primary repair has been attempted, even with bougienage, circular myotomy, or intraabdominal esophageal mobilization to lessen anastomotic tension, leaks, anastomotic disruptions, and recurrent tracheoesophageal fistulas are frequent. Consequently, interposition grafts are commonly used. For long-term function the intact native esophagus should be preferable to an interposition graft or the consequences of circular myotomy. Therefore, even when an ultra-long gap is present, we have carried out a primary repair using our single-layer technique without myotomies. Since 1979, 8 of 58 infants (14%) with esophageal atresia had gaps ranging from 3.5 to 6 cm. All had a primary repair with follow-up from 1 to 11 years. Despite severe anastomotic tension in all cases, there were no anastomotic leaks, disruptions, recurrent tracheoesophageal fistulas, or deaths. The tension, however, may have led to major gastroesophageal reflux in 5 of 8 patients (62.5%), all treated by a Nissen fundoplication, and a stricture in 4 of 8 infants (50%). Three strictures responded to dilation and one was resected. Now, all children are eating a normal diet for age. In conclusion, this technique has allowed primary repair of ultra-long-gap esophageal atresia. Although the severe tension may contribute to strictures needing dilation and gastroesophageal reflux requiring fundoplication, primary repair resulted in a clinically functional native esophagus.

Glucagon effect on postischemic recovery of intestinal energy metabolism

Glucagon is a potent mesenteric vasodilator, inotrope, and stimulant of intestinal metabolism that enhances survival when given during reperfusion after intestinal ischemia. However, the mechanism of improved survival is unclear and may be due to systemic hemodynamic effects rather than intestinal metabolic changes. We examined the effects of glucagon on intestinal energy metabolism during reperfusion after intestinal ischemia. Sprague-Dawley rats were subjected to 50 min intestinal ischemia by clamping the superior mesenteric artery. All received 10 ml/kg.hr 5% glucose in normal saline for 3 hr. One group (n = 17) received 1.6 micrograms/kg.min glucagon for 2 hr beginning at reperfusion. Control rats (n = 10) received only vehicle. Jejunal biopsies preischemia, end ischemia, 10, 20, 45, 80 min, and 24 hr after reperfusion were analyzed for ATP, ADP, and AMP. ATP decreased more than 60% with ischemia and recovered substantially in all animals by 10 min postischemia. ATP recovered steadily in control rats and by 24 hr was not distinguishable from baseline. In contrast, in glucagon-treated rats, ATP decreased at 20 and 45 min during reperfusion, but recovered incompletely by 24 hr after ischemia. Energy charge (EC = ([ATP] + 1/2[ADP]) divided by ([ATP] + [ADP] + [AMP])) decreased during ischemia but recovered immediately after reperfusion in both groups, implying that energy was available, energy metabolic enzyme systems were at least partially intact, and immediate recovery was not limited by available substrate and blood flow. However, energy charge decreased slightly during glucagon infusion, suggesting increased utilization of energy or some derangement of energy metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair of multiple mycotic aortic aneurysms in a newborn

Thoracoabdominal aortic and common and internal iliac artery mycotic aneurysms resulted from an umbilical arterial catheter in a 3 1/2-week-old boy. He underwent staged repair including an 8-mm Gore-tax tube graft, primary repair of the common iliac artery aneurysm, and resection of the internal iliac aneurysm. His operative and postoperative course was uneventful. He was asymptomatic at 17 months' follow-up, with equal blood pressure in the upper and lower extremities. Magnetic resonance imaging showed no stenoses or recurrent aneurysms at the anastomotic sites of the Gore-tex tube graft. Blood supply to his left leg came from collaterals, principally a large crossing vessel from the right iliac artery. This case represents the first successful aortic replacement in a 5 week old with extensive involvement of the thoracoabdominal aorta and its branch vessels.

Internal mammary artery for arterial pressure monitoring after pediatric cardiac operations

Establishing and maintaining arterial access in pediatric cardiac operations is a frequent and sometimes frustrating problem. We have modified a procedure commonly used in our research laboratory for arterial pressure monitoring and applied it successfully to the pediatric cardiac surgical patient. The internal mammary artery can provide reliable arterial access in the postoperative period.

The ivory tower from outside and in: a survey of Minnesota surgeons

BACKGROUND

Increasing competition has eroded the patient base of many university hospitals and may jeopardize their teaching programs.

METHODS

We questioned all private surgeons (PS), university surgeons (US), and resident surgeons (RS) in our state. Chi-squared analysis was used.

RESULTS

Most PS, US, and RS, respectively, answered "yes" when asked to respond to the following items: whether teaching hospitals were the best way to educate new surgeons (77% versus 96% versus 87%), whether surgery residencies should be based at a university hospital (72% versus 96% versus 91%), and whether PS should refer complicated clinical cases for teaching purposes (75% versus 87% versus 68%). Differences appeared when the groups were asked whether the university should take the lead in guaranteeing the quality of surgical care in the state (67% versus 100% versus 77%, p = 0.002) and whether PS are better teachers of surgery than US (40% versus 4% versus 59%, p = 0.0001). An unexpected and disturbing trend was observed in RS when groups were asked whether practicing surgeons had any obligation to the state's university (57% versus 74% versus 22%, p = 0.0001) and whether surgeons had an obligation to repay society for their education (77% versus 83% versus 56%, p = 0.005).

CONCLUSIONS

Despite recent changes in medical economics, most PS still feel residency programs should be university based. A significantly smaller percentage of RS feel an obligation to their university and to society than do either PS or US.

Myocardial carnitine metabolism in congestive heart failure induced by incessant tachycardia

Persistent tachycardia induces congestive heart failure (CHF), but the mechanism(s) of progressive ventricular dysfunction is (are) unclear. This study was designed to define possible metabolic causes of myocardial dysfunction in rapid ventricular pacing induced CHF. Twelve adult mongrel dogs were paced to 250 beats/min for 19 days. Plasma carnitine, norepinephrine and renin were measured at 0, 1, 2, and 3 weeks. Myocardial high energy phosphates, carnitine, glycogen, glucose, non-collagenous protein and collagen were measured at 19 days. Cardiac output, arterial pressure and pulmonary wedge pressure, measured at baseline and with CHF, showed a decrease in cardiac output and increase in pulmonary wedge pressure. Neurohumoral activation was evident by progressively increasing plasma norepinephrine and renin activity and depletion of myocardial norepinephrine. Plasma free carnitine rose significantly from 12.6 +/- 2.0 control to 28.3 +/- 3.8 nmol/ml at 19 days (p < 0.001), whereas myocardial total carnitine was lower in paced than in control dogs (6.0 +/- 1.9 vs. 14.1 +/- 3.5 nmol/mg non-collagenous protein, p < 0.001). Myocardial ATP ATP and ADP were unchanged, while AMP decreased 22%, and creatine phosphate decreased 30% compared to control animals. Myocardial glucose was normal but glycogen was decreased 54% (p < 0.005). The low myocardial carnitine and elevated plasma carnitine in pacing induced CHF suggests altered carnitine transport or membrane integrity.

Use of a modified van der Pol's oscillator to construct ventricular pressure-volume relations

Ventricular pressure-volume (PV) loops provide information about ventricular function. Methodologic constraints have limited derivation of PV loops to the laboratory. The present study addresses derivation of PV loops from a direct left ventricular pressure measurement and left ventricular volume derived from continuous cardiac output. The measurements were performed in vivo in intact, innervated, normal canine hearts. Data from a total of 5 dogs and 13 different cardiac work states were analyzed. A nonlinear oscillator, a van der Pol's oscillator, described the PV relationships. Comparison of left ventricular stroke work derived from the van der Pol's oscillator model with that obtained from ultrasound transducers sutured directly to the myocardium demonstrated a linear correlation, close to the identity line, with R2 = 0.90. Modelling of LV PV loops by this technique was similar to loops derived by experimental measurements. This technique could lead to increased clinical uses for PV relationships.

Results of a right ventricular outflow patch for pulmonary atresia with intact ventricular septum

BACKGROUND

Although overall outcome has improved, pulmonary atresia with intact septum remains a difficult surgical and clinical problem. To determine whether an early right ventricular outflow patch will result in biventricular repair for this lesion, we reviewed the long-term follow-up (5.8 +/- 0.8 years) of 19 newborns who underwent repair between 1979 and 1990.

METHODS AND RESULTS

An early right ventricular outflow patch was placed in 15 of 19 newborns; in the remaining four, this was preceded by an aortopulmonary shunt. Prostaglandin E1 infusion postoperatively eliminated the need for shunt in 14 of 15. Coronary sinusoids were ligated in three newborns. Based on right ventricular morphology, the newborns were divided into two groups: group 1 (tripartite, n = 9) and group 2 (bipartite and monopartite, n = 10). Before surgery, group 1 had significantly larger right ventricular volumes (23.6 +/- 3.7 versus 5.2 +/- 1.1 ml/m2, p < 0.002). Five-year survival was 79% for the entire series. Four infants, all group 2, died within 12 months of their initial surgery. Fourteen of 15 survivors (nine group 1 and five group 2) currently are acyanotic and New York Heart Association functional class I. A biventricular repair was achieved in 12 of 15, and three other children are awaiting evaluation. All 15 survivors had significant right ventricular and tricuspid annulus growth.

CONCLUSIONS

Our data suggest that early placement of a right ventricular outflow patch in infants with pulmonary atresia and intact ventricular septum, regardless of right ventricular anatomy, results in an excellent chance for biventricular repair.

Staged repair of interrupted aortic arch and ventricular septal defect in infancy

Staged repair of interrupted aortic arch and ventricular septal defect was carried out in 20 infants from 1979 through 1990. Among the important associated cardiac defects were transposition of the great arteries, truncus arteriosus, and anomalous origin of the right pulmonary artery. The first stage, usually consisting of the placement of an 8- or 10-mm polytetrafluoroethylene graft, pulmonary artery banding, and ligation of the patent ductus arteriosus, resulted in 20 survivors (100%) There were two interim deaths (10%) before the second stage of ventricular septal defect closure and pulmonary artery band removal, which had 15 survivors (83%, 15/18). Because the major morbidity and mortality early in this experience could be traced to leaving the pulmonary artery band on too long, early removal (within 2 to 3 months) was begun. Since 1985, 8 (100%) of 8 infants have survived both stages and are now doing well. Because of the relatively large polytetrafluoroethylene graft, only 1 child (aged 9 years) has experienced substantial late aortic arch obstruction and undergone placement of an 18-mm Dacron graft without difficulty. Of interest is the finding that in only 1 (5%) of the 20 patients has major (greater than or equal to 40-mm Hg gradient) left ventricular outflow tract obstruction developed. In summary, the staged repair of interrupted aortic arch with ventricular septal defect has become very reliable despite the condition of the infant or major associated cardiac anomalies and can be recommended for infants at high risk for primary repair. More long-term information will be needed to determine which approach will be the best choice for the majority of infants.

Ischemic contracture begins when anaerobic glycolysis stops: a 31P-NMR study of isolated rat hearts

The relationships among myocardial ATP, intracellular pH, and ischemic contracture in Langendorff-perfused rat hearts were investigated by 31P nuclear magnetic resonance spectroscopy during total global normothermic ischemia while the left ventricular pressure was recorded continuously via an intraventricular balloon. Glucose-perfused hearts (n = 63) were divided into five groups based on the time of onset of contracture (TOC), and three other groups of hearts were treated to vary the ischemic glycogen availability. ATP levels, which showed no evidence of accelerated ATP depletion during contracture, were significant and variable at TOC. Intracellular pH initially declined and then leveled off at TOC, with lower final pH in hearts with later TOC. We conclude that contracture began when anaerobic glycolysis (and thus glycolytic ATP synthesis) stopped. These results, though consistent with the concept that ischemic contracture in normal hearts results from rigor bond formation due to low ATP levels at the myofibrils, suggest that TOC is more closely related to glycolytic ATP production than to total cellular ATP content, thus providing evidence of some degree of subcellular compartmentation or metabolite channeling. In glycolytically inhibited hearts, the quite early contracture may have a Ca2+ component.

31P NMR measurement of mitochondrial uncoupling in isolated rat hearts

Mitochondrial uncoupling is often invoked as a mechanism underlying cellular dysfunction; however, it has not been possible to study this phenomenon directly in intact cells and tissues. In this paper, we report direct evaluation of mitochondrial uncoupling in the intact myocardium using 31P NMR magnetization transfer techniques. Langendorff perfused rat hearts were exposed to either a known uncoupler, 2,4-dinitrophenol (DNP), or a potential uncoupler, octanoate. Both DNP and octanoate decreased mechanical function as measured by the rate pressure product and caused an increase in the oxygen consumption rate (MVO2); with DNP this increase in MVO2 was dose-dependent. The ATP synthesis rate measured by 31P NMR, however, was not elevated commensurately with MVO2; instead, the P/O ratio declined. In contrast, the linear relationship between the ATP synthesis rate and rate pressure product was not altered by the uncoupling agents. These data demonstrate that 1) 31P NMR magnetization transfer can be utilized to measure uncoupling of oxidative phosphorylation in intact organs, 2) octanoate does not induce excess ATP utilization in the intact heart, and 3) high levels of octanoate induce mitochondrial uncoupling in the intact myocardium; and this may, in part, be the cause of the toxic effects associated with fatty acid exposure.

A comparison of different carbohydrates as substrates for the isolated working heart

Ribose has been shown to greatly enhance ATP recovery in situations such as postischemia when total adenine nucleotides have been depleted by catabolism. In addition, metabolic studies have reported that both five carbon sugars and alcohols (ribose and xylitol) can support energy metabolism presumably after conversion to substrates for glycolysis. Because of the importance of these two aspects of energy metabolism to myocardial function, we compared the ability of ribose and xylitol with glucose and pyruvate as exclusive substrates for the isolated working rat heart. Our studies revealed, however, that the utilization of ribose or xylitol as substrates by the myocardium is not sufficiently rapid to rely on these as exclusive oxidizable substrates. In fact, ribose or xylitol are no more effective than substrate-free medium in this regard. Myocardial glycogen was depleted in these groups and after a lag period consumption of oxygen also decreased. In contrast to the postischemic situation the total adenine nucleotide levels were preserved during ribose, xylitol or substrate-free perfusion. Consequently, the energy charge in these hearts fell significantly. In hearts perfused with ribose, xylitol or no substrate, the rate pressure product and the stroke volume rapidly declined after an initial brief stable period corresponding to glycogen depletion. Glycogen levels were 6% of the average control value in ribose- and xylitol-perfused hearts and were undetectable in substrate-free perfused hearts. In contrast, either glucose or pyruvate supported steady levels of ATP and myocardial oxygen consumption; maintained the energy charge; and supported the stroke volume, rate pressure product, and cardiac work. In glucose-perfused hearts the glycogen was reduced to 21% of control values, while in pyruvate-perfused hearts the average glycogen levels were 76% of control. Thus, although the heart is able to metabolize ribose and xylitol through the hexose monophosphate pathway, the rate of utilization through glycolysis and presumably the TCA cycle is not sufficient for these compounds to serve as exclusive substrates for the isolated working heart.

Alterations in oxidative function and respiratory regulation in the post-ischemic myocardium

In the normal and post-ischemic, isovolumic Langendorff perfused rat hearts, 31P NMR spectra and mechanical performance were evaluated over a wide range of myocardial oxygen consumption rates (MVO2). Hearts were perfused with either glucose and insulin, palmitate and glucose, or pyruvate and glucose as exogenous carbon sources. After ischemia at 38 degrees C until the onset of ischemic contracture and subsequent reperfusion, the "free" ADP levels were significantly reduced as compared to controls. In the control palmitate + glucose and glucose + insulin groups, the ADP levels were virtually independent of approximately 2.5-fold variation in MVO2; in contrast, they changed 4-fold with a approximately 30% variation in MVO2 in the post-ischemic myocardium following ischemia to contracture. In the pyruvate + glucose group, ADP levels varied with MVO2 in controls and post-ischemia; however, MVO2-ADP relationship was significantly altered following ischemia. Analysis of these observations within the concept of kinetic regulation of oxidative phosphorylation yielded the following significant conclusions: 1) the mode of respiratory regulation changed from a non-ADP to an "ADP:Pi limited" domain with non-pyruvate carbon sources; 2) respiratory regulation was in the ADP:Pi limited domain before and after ischemia in the pyruvate + glucose group; however, the Km for the relationship between MVO2 and ADP was reduced following the ischemia/reperfusion insult; 3) the post-ischemic oxidative capacity (Vmax for MVO2) was significantly reduced in all groups and this reduction would limit maximal post-ischemic mechanical performance.

Treatment of pulmonary manifestations of gastroesophageal reflux in children two years of age or less

Apnea and worsening bronchopulmonary dysplasia as well as recurrent aspiration pneumonia have been found to be consequences of gastroesophageal reflux in infants and young children. Antireflux procedures are effective in preventing gastroesophageal reflux; however, the effect of this operation on the course of these respiratory problems in very young patients is not known. We reviewed the results in 51 patients 2 years of age or less who underwent an antireflux fundoplication for pulmonary problems attributable to severe gastroesophageal reflux unresponsive to medical treatment. Twenty-eight patients had recurrent episodes of aspiration pneumonia, 14 had nonimproving or worsening bronchopulmonary dysplasia, and 9 had unexplained apneic episodes. Seventy-three percent of these patients had coexisting congenital anomalies or acquired problems. No operative deaths and no major surgical complications occurred. There were eight late deaths occurring between 1 and 25 months postoperatively: three were due to associated congenital anomalies or acquired problems, three to sepsis, and two to sudden infant death syndrome. Of the 43 surviving children, 91 percent with preoperative recurrent aspiration pneumonia had no additional episodes after Nissen procedure. Eighty-eight percent of the infants with unexplained apneic episodes showed marked benefit and 83 percent of those with bronchopulmonary dysplasia had clinical improvement. There were no late problems attributed to the operation even when it was performed in preterm infants. Therefore, we recommend fundoplication for patients 2 years of age or less who have a persistent pulmonary problem attributed to gastroesophageal reflux that does not respond to medical therapy.

Enhanced high energy phosphate recovery with ribose infusion after global myocardial ischemia in a canine model

High energy phosphate levels are depressed following global ischemia and require several days to completely recover. Short-term methods to enhance ATP recovery have included infusion of ATP precursors, inhibition of enzymes that catabolize AMP, and membrane transport stabilization. Several precursors have been used to augment adenine nucleotide synthesis including adenosine, inosine, adenine, and ribose. Because of the short-term nature of previous experiments, recovery had been incomplete and the effects in the intact animal unknown. The purpose of this study was to determine the effects of ribose infusion in a long-term model of global ischemia and attempt to identify the precursor which limits myocardial ATP regeneration in the intact animal. Global myocardial ischemia (20 min, 37 degrees C) was produced in dogs on cardiopulmonary bypass. With reperfusion either ribose (80 mM) in normal saline or normal saline alone was infused at 1 ml/min into the right atrium and the animals were followed for 24 hr. Ventricular biopsies were obtained through an indwelling ventricular cannula prior to ischemia, at the end of ischemia, and 4 and 24 hr postischemia and analyzed for adenine nucleotides and creatine phosphate levels. Radiolabeled microspheres were used to measure myocardial and renal blood flows and no significant difference was found between ribose-treated control groups. In both groups, myocardial ATP levels fell by at least 50% at the end of ischemia. No significant ATP recovery occurred after 24 hr in the control dogs, but in the ribose-treated animals, ATP levels rebounded to 85% of control by 24 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP synthesis kinetics and mitochondrial function in the postischemic myocardium as studied by 31P NMR

The effects of ischemia on mitochondrial function and the unidirectional rate of ATP synthesis (Pi----ATP rate) were studied using a Langendorff-perfused heart preparation and 31P NMR spectroscopy. There was significant postischemic depression of mechanical function assessed as the heart rate pressure product, and the myocardial oxygen consumption rate at a given rate pressure product was elevated. Experiments performed on glucose- and pyruvate-perfused hearts demonstrated the presence of a large contribution to the unidirectional Pi----ATP rate catalyzed by glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase. This rate was much greater than the maximal glucose utilization rate in the myocardium, demonstrating that the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase reactions are near equilibrium both before and after ischemia. In the pyruvate-perfused postischemic hearts, the glycolytic contribution was eliminated and the net rate of ATP synthesis by oxidative phosphorylation was measurable. Despite the reduced mechanical function and increased myocardial oxygen consumption rate, the ratio of the net rate of ATP synthesis by oxidative phosphorylation to oxygen consumption rate (the P:O ratio) was not altered subsequent to ischemia (2.34 +/- 0.12 and 2.36 +/- 0.09 in normal and postischemic hearts, respectively). Therefore, mitochondrial uncoupling cannot be the cause of postischemic depression in mechanical function; instead, the data suggest the existence of ischemia-induced inefficiency in ATP utilization.

Substrate effects in the post-ischemic myocardium

A study was undertaken to examine the effects of glucose versus pyruvate as the sole substrate following severe myocardial ischemia. Glycolysis usually contributes only a small amount to total ATP production and may be rate limiting in providing tricarboxylic acid (TCA) cycle substrates. Consequently, pyruvate may be a more effective substrate by bypassing glycolysis to feed directly to the TCA cycle and oxidative phosphorylation. Isolated rat hearts were studied in a retrograde (Langendorff) perfusion apparatus while in an NMR spectrometer. Rate pressure product (RPP), myocardial oxygen consumption (MVO2), and the unidirectional Pi----ATP rate were measured in control and postischemic hearts with or without the inotrope dobutamine. The undirectional Pi----ATP rate was higher in the glucose than the pyruvate hearts and the difference increased further postischemia. This increase over that of the pyruvate hearts has been attributed to a glycolytic component of ATP metabolism. Oxygen consumption was higher in pyruvate hearts at equivalent levels of performance. It thus appears that the glycolysis rate is significant and may be elevated following severe myocardial ischemia. Perfusion with pyruvate requires increased rates of oxidative phosphorylation to make up for the loss of glycolytically produced ATP. Optimal postischemic substrate delivery may require several compounds, one of which should be glucose.

31P NMR studies of ATP synthesis and hydrolysis kinetics in the intact myocardium

The origin of the nuclear magnetic resonance (NMR)-measurable ATP in equilibrium Pi exchange and whether it can be used to determine net oxidative ATP synthesis rates in the intact myocardium were examined by detailed measurements of ATP in equilibrium Pi exchange rates in both directions as a function of the myocardial oxygen consumption rate (MVO2) in (1) glucose-perfused, isovolumic rat hearts with normal glycolytic activity and (2) pyruvate-perfused hearts where glycolytic activity was reduced or eliminated either by depletion of their endogenous glycogen or by use of the inhibitor iodoacetate. In glucose-perfused hearts, the Pi----ATP rate measured by the conventional two-site saturation transfer (CST) technique remained constant while MVO2 was increased approximately 2-fold. When the glycolytic activity was reduced, the Pi----ATP rate decreased significantly, demonstrating the existence of a significant glycolytic contribution. Upon elimination of the glycolytic component, the measured Pi----ATP rates displayed a linear dependence on MVO (micromoles of O consumption rate) with a slope of 2.36 +/- 0.15 (N = 8, standard error of the mean). This linear relationship is expected if the rate determined by CST is the net rate of ATP synthesis by the oxidative phosphorylation process, in which case the slope must equal the P:O ratio. The ATP----Pi rates and rate:MVO ratios measured by the multiple-site saturation transfer method at two MVO2 levels were equal to the corresponding Pi----ATP rates and rate:MVO ratios obtained in the absence of a glycolytic contribution. The following conclusions are drawn from these studies: (1) unless the glycolytic contribution to the ATP in equilibrium Pi exchange is inhibited or is specifically shown not to exist, the myocardial Pi in equilibrium ATP exchange due to oxidative phosphorylation cannot be studied by NMR; (2) at moderate MVO2 levels, the reaction catalyzed by the two glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase is near equilibrium; (3) the ATP synthesis by the mitochondrial H+-ATPase occurs unidirectionally (i.e., the reaction is far out of equilibrium); (4) the "operative" P:O ratio in the intact myocardium under our conditions is significantly less than the canonically accepted value of 3.