Faculty Bibliography

OBJECTIVE:Junctional ectopic tachycardia complicates the postoperative recovery from open heart surgery in children. The reported risk factors include younger age, prolonged cardiopulmonary bypass times, and administration of inotropic agents. Junctional ectopic tachycardia occurs early after open heart surgery, in the setting of relative postoperative sinus node dysfunction, and exhibits QRS morphology consistent with an origin from the atrioventricular node or proximal conduction system. Our goal was to develop a reproducible animal model for postoperative junctional ectopic tachycardia. METHODS:Eleven pigs, aged 2 to 4 months, underwent open heart surgery after induction of general anesthesia. Electrodes were sewn to the left atrium and right ventricle. RESULTS:Sinus node dysfunction was created using clamp crushing without or with radiofrequency ablation (successful in 1 of 5 pigs) or sinus node removal (successful in 4 of 4). After prolonged cardiopulmonary bypass (>120 minutes) alone and with isoproterenol infusion, no spontaneous junctional ectopic tachycardia developed. Junctional ectopic tachycardia or fascicular tachycardia could be initiated after either slow atrioventricular nodal pathway ablation and/or digoxin administration. Junctional ectopic tachycardia occurred in 8 of 9 pigs (mean ventricular rate, 171 ± 32 bpm), and fascicular tachycardia occurred in 9 of 9 pigs (mean ventricular rate, 187 ± 39 bpm). His and right bundle recordings confirmed the conduction system origin. CONCLUSIONS:Experimental junctional ectopic tachycardia or fascicular tachycardia can occur in the intraoperative setting of sinus node dysfunction, prolonged cardiopulmonary bypass, and enhanced conduction system automaticity. Conduction system automaticity occurred after either physical injury (ablation or tricuspid valve stretch) or measures to augment the transient inward current of the conduction system (isoproterenol and digoxin). This animal model can serve as the basis to assess new treatments of postoperative junctional ectopic tachycardia.

OBJECTIVE:Our objective was to evaluate the effects of glutaraldehyde (GA) concentration, time of pretreatment, and type of tissue (porcine vs bovine) on quantitative and qualitative postimplant calcification of tissues. METHODS:Freshly obtained porcine and bovine pericardial tissues were each treated with increasing concentrations of GA (controls, 0.3125%, 0.625%, and 1.2%) for a fixed time (15 minutes) or increasing exposure times (5, 10, 20, and 30 minutes) at a fixed concentration of GA (0.625%). Pretreated tissues were subcutaneously implanted in 10-week-old Sprague-Dawley rats for 45 days before explantation. Quantitative calcium analysis was performed by flame atomic spectrophotometry. Histologic examination of tissue samples with hematoxylin and eosin and von Kossa staining was performed for cellular and inflammatory response, autolysis, and calcification. RESULTS:Two-way analysis of variance indicated significantly greater calcium levels at 1.2% compared with each lower concentration for both porcine and bovine samples (P < .01). Significantly lower calcium levels were detected with increased exposure time in porcine samples (F = 6.97; P < .001); however, no significant differences in calcium levels were observed between different exposure times for bovine samples (F = 1.46; P = .23). Histologic evidence of inflammatory response with infiltration with mononuclear cells, fibroblasts, and histiocytes was seen in all grafts; however, it varied from mild to severe without any pattern. There were no differences in degree or pattern of inflammatory response according to GA concentration or time of exposure. Estimation of amount of calcification by histologic examination correlated with the quantitative assay. CONCLUSIONS:Increasing GA concentration leads to greater calcification with a sharp rise in calcium levels above a concentration of 0.625%, in both bovine and porcine pericardial tissues. At a concentration of 0.625%, increasing pretreatment time is inversely related to tissue calcification for porcine pericardium but not for bovine pericardium. Differences in the tissue composition in terms of cellular content and composition of the extracellular matrix could account for the observed findings.

OBJECTIVE:Blood pressure gradients that are noted early after repair of coarctation in neonates and infants are often attributed to proximal arch hypoplasia. Rapid growth of the hypoplastic proximal arch is usually observed, although in some individuals an early gradient predicts the subsequent need for reintervention. To define the predictive reliability of blood pressure gradients between arms and legs and to identify predictors of arch growth, we undertook a retrospective study. METHODS:Between January 2000 and June 2008, 77 infants underwent surgical repair of coarctation. Data collected included preoperative dimensions of aortic segments. Blood pressure gradients between arms and legs determined by cuff were compared intraoperatively and postoperatively, as well as 2-dimensional echocardiographic dimensions of the aorta between those who did not require reintervention for recoarctation (group A) and those who did (group B). Receiver operating characteristic curve analysis was applied to evaluate discrimination of the systolic gradient in differentiating the 2 groups of patients. RESULTS:At surgery, patients' median age was 10 days and weight was 3.3 kg. There was 1 early death. Median follow-up was 40 months (interquartile range, 24-63 months). Recoarctation developed in 11 patients (14.3%), defined as a resting blood pressure gradient of greater than 20 mm Hg with a corresponding decrease in the diameter of the aorta by 50%. Freedom from recoarctation was 87% at 1 year and 85% at 5 years. Multivariable logistic regression analysis identified the size of the ascending aorta as a risk factor for recoarctation. Blood pressure gradient at the end of surgery was not predictive of recoarctation. The ascending aorta and transverse arch showed rapid growth in group A, and this was associated with a decrease in blood pressure gradient over time. In comparison, the growth of the ascending aorta and arch in group B was significantly less than in group A and associated with worsening of gradients. Receiver operating characteristic curve analysis revealed that gradients at the time of hospital discharge (>13 mm Hg) had excellent discriminative accuracy in identifying patients in whom subsequent recoarctation developed. CONCLUSIONS:Small size of the ascending aorta is a risk factor for recoarctation. Limb gradient in the operating room at completion of surgery is not a reliable tool to assess repair of coarctation, although the gradient at the time of hospital discharge can be used to accurately predict recoarctation. Rapid growth of both the ascending and the transverse aorta is frequently observed and associated with improvement in gradients over time.

Down syndrome is known to be an independent risk factor for mortality after surgical repair of congenital heart anomalies. It is also associated with neurodegenerative disease and accelerated aging. The mechanism of the latter features has been attributed to abnormal handling of oxygen-free radicals as well as mitochondrial dysfunction. These properties also place the child with Down syndrome at a risk of an exaggerated myocardial ischemia/reperfusion injury. A 6 month old child with Down syndrome is reported who suffered from obvious clinical ischemia/reperfusion injury following an uncomplicated repair of complete AV canal. Both intraoperative as well as postoperative echocardiography documented a satisfactory technical repair. After resting the heart on ECMO the child's myocardial function returned to normal. The mechanisms by which patients with Down syndrome are at risk of ischemia/reperfusion injury are reviewed. Future studies should focus on specific approaches for myocardial protection in the child with Down syndrome undergoing cardiac surgery.

Common atrioventricular canal (CAVC) is a common congenital heart lesion resulting from a defect in development of the endocardial cushions during early embryogenesis. Depending on the type of defect, CAVC can encompass a spectrum of lesions ranging from partial atrioventricular (AV) canal to complete AV canal. We describe a case of CAVC with unique anatomy in a 4-month-old male infant with Down syndrome.

Extracorporeal membrane oxygenation is widely used to support and rest the heart before or following repair of congenital cardiac lesions in children. The beneficial effects of extracorporeal membrane oxygenation for the failing myocardium are undisputed. It is often an automatic choice whenever the heart seems incapable of supporting the circulation. However, its use may prove detrimental in patients with coronary anomalies, as illustrated by the case reports presented here.