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Biomedical subjects

I M Rebeyka

Publications and source records attributed to I M Rebeyka.

At least 37 records · Page 2Linked to original sources
PubMed1995

Reoperation for recurrent aortic coarctation.

BACKGROUND: Recurrence of stenosis is a complication of coarctation repair associated with major long-term morbidity. Persistent or exercise-provoked hypertension may indicate recurrent coarctation. Patients failing or not amenable to balloon dilation should be managed surgically. METHODS: A retrospective chart review was performed. RESULTS: Forty-three patients were identified as having undergone repeat surgical intervention for recurrent aortic coarctation between the years 1976 and 1993 at The Hospital for Sick Children in Toronto. Seventy percent of the children had other congenital cardiac anomalies. Eighty-six percent of patients initially treated by subclavian flap aortoplasty or end-to-end anastomosis were managed at reoperation by patch aortoplasty, and 26% of patients also required augmentation of the transverse arch (under hypothermic circulatory arrest) for accompanying hypoplasia. Three patients underwent a second reoperation; all were treated at this reoperation with tube graft interposition. CONCLUSIONS: No ischemic spinal injury occurred in patients managed with either simple proximal aortic cross-clamping or cardiopulmonary bypass. No patient treated with transverse arch augmentation required further surgical intervention. Mortality at reoperation was 7% (3 patients), similar to that of first-time coarctation repair. At follow-up (mean duration, 4.5 years), 57% of patients are normotensive, with no measurable arm-leg gradient.

Adolescent↗
PubMed1995

Experience with repair of congenital heart defects using adjunctive endovascular devices.

The use of endovascular devices as an adjunct to repair of congenital heart anomalies represents a novel but unproven therapeutic approach. Intraoperative implantation of pulmonary arterial stents (5 to 15 mm diameter) was done in 11 patients with pulmonary atresia with ventricular septal defect (n = 4), classic tetralogy of Fallot (n = 2), truncus arteriosus (n = 1), hypoplastic left heart syndrome (stage II [n = 1] and stage III [n = 1] Norwood procedure), and miscellaneous pulmonary arterial stenoses (n = 3), as well as in patients with congenital (n = 1) and postoperative (n = 3) pulmonary venous obstruction and in 1 patient with combined pulmonary arterial and venous obstruction. The stents were effective at achieving immediate patency in all patients. There were two early deaths, one related to acute thrombosis of a small-diameter left pulmonary artery stent. Reintervention because of stent-related pulmonary arterial stenosis was frequently necessary. In five of seven patients who survived more than 1 month after implantation of stent size 8 mm or smaller severe stent-related pulmonary arterial obstruction developed. In four of the five patients with pulmonary vein stent implantation intractable obstruction developed, resulting in death in all three patients who had bilateral pulmonary vein stent implantation. Intraoperative occlusion of apical muscular ventricular septal defect with use of a clamshell device inserted from the right atrial approach was accomplished in four patients. One patient who underwent associated aortic arch reconstruction died as a result of left ventricular hypoplasia. The results in the remaining three patients were favorable on the basis of absence of significant late residual intraventricular shunting, left ventricular dysfunction, or arrhythmia. We conclude that recurrent intraluminal obstruction as a result of neointimal hyperplasia appears to be an eventual certainty in currently designed small-diameter endovascular stents. For this reason, we would recommend standard surgical techniques for repair of obstructive lesions of the pulmonary arterial confluence to maximize growth potential. Device occlusion of muscular ventricular septal defects is feasible but probably only indicated for complex cases of ventricular septal deficiency that otherwise necessitate a left ventriculotomy.

Adolescent↗
PubMed1995

Subaortic stenosis in the spectrum of atrioventricular septal defects. Solutions may be complex and palliative.

UNLABELLED: From July 1982 through September 1994, 19 children had operative treatment of subaortic stenosis associated with an atrioventricular septal defect. Specific diagnosis were septum primum defects in 7, Rastelli type A defects in 6, transitional defects in 4, inlet ventricular septal defect with malattached chordae in 1, and tetralogy of Fallot with Rastelli type C defect in 1. Twenty-seven operations for subaortic stenosis were performed. Surgical treatment of the outlet lesion was performed at initial atrioventricular septal defect repair in 3 children and in the remaining 16 from 1.2 to 13.1 years (mean 4.9 years, median 3.9 years) after repair. Eighteen of the 19 children had fibrous resection and myectomy for relief of obstruction. Seven children had an associated left atrioventricular valve procedure. One child received an apicoaortic conduit. Seven children (36.8%) required 8 reoperations for previously treated subaortic stenosis. Time to the second procedure was 2.8 to 7.4 years (mean 4.9 years). Follow-up is 0.4 to 14.0 years (median 5.6 years). Six-year actuarial freedom from reoperation is 66% +/- 15%. The angle between the plane of the outlet septum and the plane of the septal crest was measured in 10 normal hearts (86.4 +/- 13.7) and 10 hearts with atrioventricular septal defects (22.2 +/- 26.0; p < 0.01). The outflow tract can be effectively shortened, widened, and the angle increased toward normal by augmenting the left side of the superior bridging leaflet and performing a fibromyectomy. CONCLUSION: Standard fibromyectomy for subaortic stenosis in children with atrioventricular septal defects leads to a high rate of reoperation. Leaflet augmentation and fibromyectomy may decrease the likelihood of reoperation.

Adolescent↗
PubMed1995

Determinants of success in pediatric cardiac patients undergoing extracorporeal membrane oxygenation.

BACKGROUND: The purpose of this retrospective study is to determine the possible predictors of successful cardiac recovery using extracorporeal membrane oxygenation (ECMO) and the practical limits of ECMO support. METHODS: Information was gathered on 31 consecutive children with myocardial failure who could not be resuscitated with other means and underwent ECMO at the Hospital for Sick Children before January 1994. RESULTS: Of the children who underwent ECMO as a means of cardiac rescue, 14/31 (45%) were weaned successfully. Two distinct groups of children were evident based on their initial indications for ECMO: those who had postcardiotomy myocardial dysfunction (n = 25) and those with cardiomyopathy or myocarditis (n = 6). Children with residual defects after cardiotomy (n = 10) did not survive ECMO. Four of the 6 children with cardiomyopathy or myocarditis were weaned successfully. In either group of patients ECMO support beyond 6 days failed to resuscitate the myocardium; all attempts to violate this "time barrier" in our study inevitably failed. CONCLUSIONS: Postcardiotomy residual defects are a contraindication to ECMO. If children with residual defects are excluded, successful weaning from ECMO can be achieved in almost 70%, with almost all recovery occurring with the first 6 days of ECMO.

Cardiac Catheterization↗
PubMed1994

Tolerance of epicardial coronary endothelium and smooth muscle to hyperkalemia.

Results of previous studies have suggested that high K+ concentrations in cardioplegic solutions may be detrimental to coronary endothelium in perfused hearts, as determined from changes in the coronary flow rate, but the direct functional changes in endothelium secondary to hyperkalemia have not been fully studied. To determine the effect of the K+ concentration in a physiologic solution (Krebs') and in St. Thomas' cardioplegic solution, and the effect of exposure time on endothelium and smooth muscle, porcine coronary artery rings were set up in organ baths under a physiologic pressure. The effect of exposure to Krebs' solution containing 5.9 or 50 mmol/L K+ or to St. Thomas' solution containing 16 or 50 mmol/L K+, for either 2 hours (group I) or 4 hours (group II), was examined. The solutions were continuously aerated with 95% oxygen and 5% carbon dioxide to exclude the effects of ischemia and hypoxia. The rings were then washed and contracted with K+ (25 mmol/L). The ability to release endothelium-derived relaxing factor (EDRF) in response to an EDRF stimulus (substance P) was used as an index of endothelial function. Smooth muscle function was evaluated in terms of the K(+)-induced contraction force and the relaxation induced with glyceryl trinitrate, in addition to the maximal substance P-induced relaxation. The maximal relaxation induced by substance P did not decrease by incubation with 50 mmol/L K+ in any group (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Small aortic root in childhood: surgical options.

Aortic valve replacement in the pediatric population is complicated by the often complex nature of the left ventricular outflow tract obstruction. Techniques to enlarge the annulus frequently are necessary. From 1977 to 1991, 32 children underwent an annular enlargement procedure at The Hospital for Sick Children, Toronto. During this same era, 110 children underwent a total of 138 aortic valve replacements. Eleven had the annulus enlarged with a posterior patch technique and implantation of a valve (mechanical 8, porcine heterograft 2, homograft 1) ranging from 20 to 25 mm in diameter. Twenty-two children had an anterior annular enlargement (aortoventriculoplasty) and aortic valve replacement with a valve (mechanical 8, porcine 2, homograft 12) 12 to 27 mm in diameter. One child had a posterior patch enlargement performed, followed by a second operation involving anterior annular enlargement. There was one early death in the posterior annuloplasty group and one late death due to failure of a bioprosthetic valve. There were five hospital deaths in the anterior annuloplasty group (22%; 70% confidence interval [CI], 14% to 32%) and two late deaths. Actuarial survival for the 32 children was 78% (70% CI, 70% to 86%) at 5 years and 65% (70% CI, 48% to 82%) at 10 years after repair. Younger children (age less than 1 year) had a significantly worse survival at 5 years (33%; 70% CI, 14% to 52%) than older children (88%; 70% CI, 82% to 95%). The survivors are well, and no reoperations have been necessary because of the children's outgrowing their valve.

Adolescent↗
PubMed1994

Orotic acid improves left ventricular recovery four days after heterotopic transplantation.

Orotic acid accelerates compensatory myocardial hypertrophy after regional ischemia and improves left ventricular function acutely after global ischemia. In this study, the effect of orotic acid on left ventricular function was investigated 4 days after global ischemia (75 minutes, 21 degrees C) using heterotopically transplanted rabbit hearts (n = 18). Experimental animals received daily 100-mg/kg doses of intraperitoneally administered orotic acid, starting 1 day before transplantation, and showed a threefold increase in the serum level of orotic acid by 4 days. After 1 hour of reperfusion, the developed pressure was equally depressed in both the control and experimental groups; however, 4 days later, the developed pressure in control animals was decreased by 3 +/- 3 mm Hg (versus the developed pressure measured at 1 hour) while the developed pressure in experimental animals was significantly increased by 25 +/- 8 mm Hg. Heterotopically transplanted hearts manifested diminished systolic function (stemming from ischemia and unloading) as well as decreased expression of adult myosin. Because orotic acid has been observed to produce an increase in protein synthesis in other models, we investigated whether this improvement in systolic function resulted from an orotic acid-mediated augmentation (or preservation) or normal adult myosin expression. Both orotic acid-treated and untreated hearts manifested decreased expression of the beta-myosin heavy chain protein and steady-state messenger RNA levels. Because function improved with decreased beta-myosin heavy chain expression, an alternate mechanism underlying orotic acid-mediated improvement in function is implicated. Nevertheless, orotic acid may be a therapeutic agent facilitating long-term recovery from global ischemia.

Animals↗
PubMed1994

Cooling and pH jump-induced calcium release from isolated cardiac sarcoplasmic reticulum.

Rapid-cooling contracture in cardiac muscle preparations is thought to be caused by the release of Ca2+ from the sarcoplasmic reticulum (SR), but the mechanism of this release is unknown. Cooling of isolated canine cardiac SR from 37 to 4 degrees C resulted in the net release of enough Ca2+ to account for rapid-cooling contracture. The release of Ca2+ on cooling appeared to be a relaxation between different steady-state levels of Ca2+ uptake. Cooling release of Ca2+ was also observed in the presence of ryanodine or ruthenium red to block the ryanodine-sensitive Ca2+ efflux pathway. In the presence of ryanodine, the extent and initial rate of rapid-cooling release were increased due to increased steady-state uptake of Ca2+ by the SR. The first-order rate constant of rapid-cooling Ca2+ release was unchanged by ryanodine or ruthenium red, suggesting that the rapid-cooling release does not occur through the ryanodine-sensitive pathway. The alkalinization on cooling was not the major cause of the Ca2+ release, as comparable Ca2+ release was observed with cooling and no alkalinization. However, alkalinization without cooling produced a rapid net Ca2+ release, which was also observed in the presence of ryanodine.

Animals↗
PubMed1993

Survival analysis of infants under age 18 months presenting with tetralogy of Fallot.

The trend to perform early primary repair of tetralogy of Fallot prompted us to review our experience in the current era with the traditional protocol consisting of palliation during infancy, if required, and repair after infancy. During a 10-year period, 270 infants with tetralogy of Fallot presented aged less than 18 months. Thirteen infants (4.8%) had major noncardiac lesions that precluded definitive care for their congenital heart disease. Twenty infants (7.4%) had major associated cardiac lesions (atrioventricular septal defect or absent pulmonary valve syndrome, or both). Survival in this group was poor, with only 58% +/- 12% reaching the age of 10 years. Four of the seven deaths occurred before intracardiac repair was performed. The remaining 237 infants presented with isolated tetralogy of Fallot. Eight-nine percent +/- 2.3% survived to age 10 years. Sixty percent of these infants required palliation, and survival in these infants did not differ from that in those who never required palliation. However, 19 infants (8%) required palliation in the first month of life. In these children, survival to age 10 years was significantly lower (77%), secondary palliation was frequently required (n = 11), and a transannular patch or conduit at the time of repair (10 of 14 patients) was more likely needed than it was in children who had not undergone a palliative procedure during the neonatal period. The survival in infants with tetralogy of Fallot is unlikely to be different, regardless of whether primary repair or a staged repair is carried out. The quality of survival, including the exercise capability and absence of arrhythmias, must be assessed to determine which protocol is superior.

Abnormalities, Multiple↗
PubMed1993

Experience with the Damus-Kaye-Stansel procedure for children with Taussig-Bing hearts or univentricular hearts with subaortic stenosis.

Anastomosis of the pulmonary artery to the ascending aorta is the essence of a technique for repair of complete transposition proposed by Damus, Kaye, and Stansel. Our Institutional experience with the Damus-Kaye-Stansel procedure (DKS) is limited to 9 children with double-outlet right ventricle and 38 with univentricular heart plus subaortic stenosis. Thirty-eight children (81%) survived the DKS procedure, and there were three late deaths during the mean follow-up of 3.1 years. Five-year survival is 72% (+/- 8%). All six children surviving a DKS and biventricular repair of double-outlet right ventricle have required conduit replacement at a mean interval of 46 months. In the children with univentricular heart, relief of subaortic stenosis with the DKS was successful in all except two. The late function of the semilunar valves is of concern, as 36% of the aortic and 52% of the pulmonary valves have some degree of incompetence.

Aorta↗
PubMed1992

Limiting edema in neonatal cardiopulmonary bypass with narrow-range molecular weight hydroxyethyl starch.

The marked edema observed in neonatal cardiopulmonary bypass is thought to result from pathologic increases in capillary permeability. Pentafraction is a subfraction of hydroxyethyl starch that is thought to be of appropriate size and shape to be retained by leaking capillaries and seal endothelial gaps in capillary basement membranes. To test the hypothesis that pentafraction would reduce edema in neonatal cardiopulmonary bypass, we established a model of edema formation in neonatal bypass in which neonatal piglets underwent 2 hours of normothermic cardiopulmonary bypass with crystalloid prime and no myocardial ischemia. Before initiation of bypass, experimental animals (n = 11) received intravenous pentafraction, 3 gm/kg. Control animals (n = 10) received an equivalent volume of saline. Hemodynamic parameters, animal weight, fluid redistribution, and percent tissue water of individual organs were assessed during and after bypass. Pentafraction treatment resulted in significant differences in (1) lowered percent body weight gain from baseline (11% versus 48%), (2) lowered volume requirement to maintain venous reservoir during cardiopulmonary bypass (148 ml/kg versus 581 ml/kg), (3) less fluid loss from the peritoneum (11 ml/kg versus 115 ml/kg), and (4) lowered percent tissue water of kidney, pancreas, stomach, jejunum, colon, and skeletal muscle (p less than 0.05 by unpaired t test). Pentafraction had no effect on hemodynamic parameters during bypass nor in percent tissue water of heart, lung, liver, spleen, skin, or brain. In summary, pentafraction lessened weight gain and fluid requirements during cardiopulmonary bypass, favorably influencing the percent tissue water of certain organs. If pentafraction functions as proposed, it may have wide applicability not only in cardiopulmonary bypass (or extracorporeal membrane oxygenation) but also in other clinical scenarios with altered capillary permeability.

Animals↗
PubMed1992

The recognition, identification of morphologic substrate, and treatment of subaortic stenosis after a Fontan operation. An analysis of twelve patients.

Twelve children were identified with subaortic stenosis after Fontan's operation. All had absent resting and isoproterenol-provoked pressure gradient before the Fontan procedure. Six had a univentricular heart of left ventricular morphology, three had a single ventricle of right ventricular morphology, one had tricuspid atresia with transposition of the great arteries, one had pulmonary atresia, intact ventricular septum, and hypoplastic right ventricle, and one had corrected transposition with hypoplastic systemic ventricle. The median interval between the Fontan operation and the recognition of subaortic stenosis was 2.5 years. Ten patients underwent surgical treatment after a prior Fontan operation: Five had myectomy and enlargement of ventricular septal defect with two operative deaths; two had placement of a valved conduit from the ventricular apex to the descending aorta, and both died postoperatively; two with single ventricle had subaortic myectomy, and one had enlargement of ventricular septal defect and pulmonary aortic connection. Complete heart block developed in only one patient. Postoperative testing with Doppler echocardiography with color flow imaging demonstrated good relief of subaortic stenosis. All six children who survived the operation are well 4 months to 4 years later. Subaortic stenosis is a progressive lesion that may develop after a Fontan operation. Its surgical treatment continues to carry a significant mortality. Myectomy and enlargement of ventricular septal defect achieve direct relief of the obstruction with minimal risk of heart block.

Adolescent↗
PubMed1992

Failure of cryopreserved homograft valved conduits in the pulmonary circulation.

BACKGROUND: This study evaluates our experience with the cryopreserved homograft valved conduit used for reconstruction of the pulmonary circulation in patients with congenital heart disease. METHODS AND RESULTS: Between July 1, 1985, and December 31, 1990, 219 patients had cryopreserved homograft extracardiac valved conduits placed in the pulmonary circuit. Average age at operation was 7.2 years. Of these, 132 patients had a pulmonary homograft, and 87 had an aortic homograft. Twenty-four patients (11%) died in hospital. Hospital survivors (n = 195) have been followed an average of 29.8 months (SD, +/- 18.4 months). Fourteen patients died during follow-up, almost all related to the complexity of their original cardiac malformation. Thirty-two patients (15%) have required reoperation for conduit-related problems. Actuarial freedom from conduit reoperation is 55 +/- 12% at 5 years. The most common indication for reoperation was calcific stenosis (n = 27). Other indications for reoperation were pseudoaneurysm (n = 2), conduit infection (n = 2), and pulmonary insufficiency (n = 1). Reoperation rate for patients with aortic homografts (16 of 87) compared with that for pulmonary homografts (16 of 132) was not significantly different by the actuarial method. CONCLUSIONS: Long-term function of cryopreserved homograft valved conduits in the pulmonary circulation is disappointing.

Actuarial Analysis↗
PubMed1992

Surgical connections from ventricle to pulmonary artery. Comparison of four types of valved implants.

BACKGROUND: Four types of valved conduits used to correct venous ventricle to pulmonary artery (V-PA) discontinuity were compared. METHODS AND RESULTS: Four hundred fifty-seven patients with congenital heart defects requiring a V-PA connection during the past 25 years were reviewed. Age at implant varied from 1 day to 64 years (mean, 9.1 years). Four types of valved prostheses were used: 1) homograft conduit (HC, n = 178), 2) valved Dacron conduit (VDC, n = 126), 3) polystan conduit (PC, n = 47), and 4) orthotopic pulmonary valve implant (PVI, n = 106). There were 83 early deaths (18.2%) and 34 late deaths (8.5%). Follow-up ranged from 1 month to 22 years (mean, 3.5 years). One hundred eight conduit replacements were performed in 93 patients (21%). The overall patient survival was 73 +/- 2.3%, 67 +/- 3.2%, and 56 +/- 6.8% at 5, 10, and 15 years, respectively. Factors predictive of patient survival were diagnosis (p < 0.001) and valve size (p < 0.001). Age at operation (p < 0.001) and type of valve (p < 0.001) were the only risk factors for valve survival. At 5 years, survival of PVI (89 +/- 5%) and VDC (89 +/- 4%) was significantly better than survival of HC (46 +/- 13%) or PC (57 +/- 9%). CONCLUSIONS: Patients who survived the initial construction of a V-PA conduit had a reasonable long-term survival. A PVI was the most durable prosthesis. A Dacron porcine-valved conduit had significantly better durability than either a cryopreserved homograft or a PC.

Actuarial Analysis↗
PubMed1991

Results of the Fontan procedure for patients with univentricular heart.

One hundred twenty-four consecutive patients with univentricular heart undergoing the Fontan operation were reviewed. Patients with tricuspid atresia or biventricular heart with hypoplasia of one ventricle were excluded. Eighty-four patients had left ventricular morphology. Atrioventricular connection was double-inlet (n = 76), common (n = 29), absent left atrioventricular connection (n = 14), and absent right atrioventricular connection (n = 5). Actuarial survival was 77% (70% confidence limits, 73% to 81%) at 1 year, 66% (70% confidence limits, 60% to 72%) at 5 years, and 49% (70% confidence limits, 36% to 61%) at 10 years, indicating a continuing risk for premature death. Multivariate analysis identified preoperative ventricular function and hypertrophy as risk factors for survival. High postrepair right atrial pressure (greater than 15 mm Hg) emerged as a strong intraoperative predictor of survival. Logistic regression analysis of these factors predicts high probability of death for certain subgroups of patients after the Fontan operation. Forty-four percent (n = 53) of these original 124 patients are alive and in New York Heart Association class I at follow-up. Thirty-eight percent (n = 33) of survivors have worse ventricular function than preoperative. Long-term survival is disappointing. Certain identifiable subgroups of patients with univentricular heart have unacceptable risks for the Fontan operation and should have alternate management. High postrepair right atrial pressure is an ominous sign, and if it persists the Fontan should be fenestrated or taken down.

Adolescent↗
PubMed1991

Effect of rapid cooling contracture on ischemic tolerance in immature myocardium.

Hypothermic perfusion before cardioplegic ischemic arrest is commonly used in neonatal cardiac surgery. However, perfusion cooling of the heart in the nonarrested state results in an inotropic response and may induce myocardial contracture secondary to a sustained elevation of intracellular calcium levels. The effect of prearrest cardiac cooling was examined in two groups of isolated parabiotic, blood-perfused neonatal rabbit hearts. Group C (cooling group, n = 12) was exposed to 15 minutes of cold perfusion to 12 degrees C before 1 hour of cardioplegic arrest. Group N (normothermia group, n = 11) underwent identical arrest conditions but without prearrest cold perfusion. Developed pressure at constant volume in group C fell from 109 +/- 8.7 mm Hg at baseline to 55.2 +/- 5.5 mm Hg after 30 minutes of reperfusion versus no significant change in group N. Diastolic compliance showed significant deterioration in group C, with marked elevation of diastolic pressure from 9.8 +/- 0.4 mm Hg at baseline to 22.0 +/- 4.4 mm Hg after ischemia and reperfusion. This experimental data demonstrates that profound hypothermic perfusion of the myocardium in the nonarrested state may induce a rise in resting myocardial tension and that cardioplegic ischemic arrest in the presence of cooling contracture may result in important myocardial injury.

Animals↗