Toward optimal hemodynamics: computer modeling of the Fontan circuit.

The construction of efficient designs with minimal energy losses is especially important for cavopulmonary connections. The science of computational fluid dynamics has been increasingly used to study the hemodynamic performance of surgical operations. Three-dimensional computer models can be accurately constructed of typical cavopulmonary connections used in clinical practice based on anatomic data derived from magnetic resonance scans, angiocardiograms, and echocardiograms. Using these methods, the hydraulic performance of the hemi-Fontan, bidirectional Glenn, and a variety of types of completion Fontan operations can be evaluated and compared. This methodology has resulted in improved understanding and design of these surgical operations.

Dynamic modelling in a study of surgical error management.

We demonstrate the use of dynamic longitudinal models to investigate error management in cardiac surgery. Case study data were collected from a multicentre study of the neonatal arterial switch operation (ASO). Information on two types of negative events, or 'errors', observed during surgery, major and minor events, was extracted from case studies. Each event was judged to be recovered from (compensated) or not (uncompensated). The aim of the study was to model compensation given the occurrence of past events within a case. Two models were developed, one for the probability of compensating for a major event and a second model for the probability of compensating for a minor event. Analyses based on dynamic logistic regression models suggest that the total number of preceding minor events, irrespective of compensation status, is negatively related with the ability to compensate for major events. The alternative use of random effects models is investigated for comparison purposes.

MRI-based multiscale models for the hemodynamic and structural evaluation of surgically reconstructed aortic arches.

The surgical reconstruction of the aortic arch is necessary in pediatric patients suffering from different types of congenital heart malformations, in particular, coarctation of the aorta. Among the reconstruction techniques used in surgical practice end-to-end anastomosis (E/E), Gore-tex graft interposition (GGI) and Gore-tex patch graft aortoplasty (GPGA) are compared in this study with a control model, employing a computational fluid-structure-interaction scheme. This study analyzes the impact of introducing synthetic materials on aortic hemodynamics and wall mechanics. Three-dimensional (3D) geometries of a porcine aortic arch were derived from magnetic resonance imaging (MRI) images. Inlet conditions were derived from MRI velocimetry. A multiscale approach was used for the imposition of outlet conditions, wherein a lumped parameter net provided an active afterload. Evidence was found that ring-like repairs increased blood velocity, whereas GPGA limited it. Vortex presence was greater and longer lasting in GGI. The highest power losses corresponded to GPGA. GGI had an intermediate effect, while E/E dissipated only slightly more than the control case. Wall stresses peak in a longitudinal strip on the subject's left side of the vessel, particularly in the frontal area. There was a concentration of stress at the suture lines. All surgical techniques performed equally well in restoring physiological pressures.

Identification of systems failures in successful paediatric cardiac surgery.

Patient safety will benefit from an approach to human error that examines systemic causes, rather than blames individuals. This study describes a direct observation methodology, based on a threat and error model, prospectively to identify types and sources of systems failures in paediatric cardiac surgery. Of substantive interest were the range, frequency and types of failures that could be identified and whether minor failures could accumulate to form more serious events, as has been the case in other industries. Check lists, notes and video recordings were employed to observe 24 successful operations. A total of 366 failures were recorded. Coordination and communication problems, equipment problems, a relaxed safety culture, patient-related problems and perfusion-related problems were most frequent, with a smaller number of skill, knowledge and decision-making failures. Longer and more risky operations were likely to generate a greater number of minor failures than shorter and lower risk operations, and in seven higher-risk cases frequently occurring minor failures accumulated to threaten the safety of the patient. Non-technical errors were more prevalent than technical errors and task threats were the most prevalent systemic source of error. Adverse events in surgery are likely to be associated with a number of recurring and prospectively identifiable errors. These may be co-incident and cumulative human errors predisposed by threats embedded in the system, rather than due to individual incompetence or negligence. Prospectively identifying and reducing these recurrent failures would lead to improved surgical standards and enhanced patient safety.

Echocardiographic assessment of conjoined twins.

OBJECTIVE: To determine the accuracy of prenatal and postnatal echocardiography in delineating the degree of cardiac fusion, intracardiac anatomy (ICA), and ventricular function of 23 sets of conjoined twins with thoracic level fusion presenting to a single centre over a 20 year period. METHODS: 13 thoracopagus, 5 thoraco-omphalopagus, and 5 parapagus pairs presenting to the authors' institution between 1985 and 2004 inclusive were assessed. Echocardiographic data were analysed together with operative intervention and outcome. Twins were classified according to the degree of cardiac fusion: separate hearts and pericardium (group A, n = 5), separate hearts and common pericardium (group B, n = 7), fused atria and separate ventricles (group C, n = 2), and fused atria and ventricles (group D, n = 9). RESULTS: The degree of cardiac fusion was correctly diagnosed in all but one set. ICA was correctly diagnosed in all cases, although the antenatal diagnosis was revised postnatally in three cases. Abnormal ICA was found in one twin only in two group A pairs, one group B pair, and both group C pairs. All group D twins had abnormal anatomy. Ventricular function was good in all twins scanned prenatally, and postnatally function correlated well with clinical condition. Thirteen sets of twins in groups A-C were surgically separated; 16 of 26 survived. None from groups C or D survived. CONCLUSIONS: Prenatal and postnatal echocardiography accurately delineates cardiac fusion, ICA, and ventricular function in the majority of twins with thoracic level fusion. It is integral in assessing feasibility of separation. The outcome in twins with fused hearts remains dismal.

Aortic tissue properties in porcine models: A comparison of ex vivo mechanical test results after simulated aortic arch reconstructions.

Surgical interventions on the arterial wall can produce modifications to its tissue characteristics, and the addition of synthetic materials of different types can have implications on hemodynamics and blood vessel wall behavior. This work studies the midterm effects of end-to-end anastomosis (E/E), Gore-tex graft interposition (GGI) and Gore-tex patch graft aortoplasty (GPGA) in aortic arch reconstruction. The study comprised of two groups of healthy Danish sows. The sows in the first group (short term (ST)) weighed about 40 kg, underwent a surgical operation and were sacrificed on the same day. The sows in the second group (midterm (MT)) weighed 5-10 kg, underwent a surgical operation and were then allowed to grow to a weight of about 30-40 kg, before being sacrificed. One sow in each group was scheduled for E/E and one sow for GGI. One sow in ST and two sows in MT received GPGA. The overall average wall thickness was 1.93 mm. Relaxation constant values were significantly higher for ST (5.221 +/- 1.832 sec) than for MT (2.184 +/- 1.216 sec). GPGA showed a greater impact on relaxation than other procedures, enhancing the viscous character. The working-point Young's modulus (Epw ) was not significantly different in ST and MT. Circumferential samples had different Epw (0.419 +/- 0.77 MPa) from longitudinal samples (0.902 +/- 0.378 MPa). There also appeared to be a significant difference between samples cut longitudinally on the left and the right sides of the wall. The overall average Epw value was 0.6609 +/- 0.3641 MPa.

Pitfalls of adverse event reporting in paediatric cardiac intensive care.

AIMS: To evaluate the pitfalls of incident reporting in a complex medical environment. METHODS: Retrospective review of 211 incident reports in a paediatric cardiac intensive care unit (CICU). Two adverse event reporting databases were compared: database A (DA), the hospital's official reporting system, is non-anonymous and reports are predominantly made by nurses; database B (DB) is anonymous and reports are submitted by a CICU consultant who collects data from daily ward rounds. Both databases classify adverse events into incident type (drug errors, ventilation, cannulae/indwelling lines, chest drains, blood transfusion, equipment, operational) and severity (0 = no, 1 = minor, 2 = major, 3 = life threatening consequences). RESULTS: Between 1 April 1998 and 31 July 2001 there were 211 adverse events involving 178 patients (11.87%), among 1500 patients admitted to CICU. A total of 112 incidents were reported in DA, 143 in DB, and 44 in both. In isolation, both databases gave an unrepresentative picture of the true frequency and severity of adverse events. Under-reporting was especially notable for less severe events (grade 0, or near misses) CONCLUSION: Incident reporting in the medical field is highly variable, and is heavily influenced by profession of the reporters as well as anonymity. When adverse event reporting is based predominantly on the observations of a single professional group, the data are grossly inaccurate.

Management of pulmonary venous obstruction after correction of TAPVC: risk factors for adverse outcome.

OBJECTIVE: Recurrent pulmonary venous obstruction (PVO) occurs in 0-18% of infants undergoing correction of total anomalous pulmonary venous connection (TAPVC). Limited published data suggest that PVO usually develops within 6 months of primary repair, and that outcomes of reoperations are poor. This study aimed to review our experience of reoperations for PVO post-TAPVC repair and to identify risk factors for adverse outcome. METHODS: Twenty patients underwent reoperation for PVO between 1982 and 2002. Clinical data were reviewed. TAPVC was mostly infracardiac (11 patients). TAPVC was obstructed in nine patients. PVO developed early (<6 months) in seven patients, and late in 13 (>6 months). Time of presentation was unrelated to type of PVO (anastomotic vs. ostial). Repair was accomplished using various techniques (anastomotic enlargement with native atrial tissue, enlargement with pericardium, free or in situ, or other prosthetic material). Follow-up ranged from 1 month to 15 years (average 44 months). RESULTS: Thirteen patients received one reoperation, while seven had multiple reoperations. In 13 patients, PVO was defined as new onset (no obstruction post-TAPVC repair), and in seven patients as residual (minimal obstructive changes post-TAPVC repair that progressed to PVO). Ten patients presented with anastomotic PVO, six with anastomotic and ostial PVO (involving the PVs), three with ostial PVO, and one with coronary sinus-left atrial junction stenosis. Mortality was 25% (5/20). Six of the ten patients with anastomotic PVO underwent one reoperation (2/6 died); the other four developed ostial PVO after reoperation, requiring multiple procedures (2/4 died). Mode of presentation (new onset vs. residual), site of obstruction (anastomotic vs. ostial), preoperative RV pressure (<0.8 vs. >0.8 systemic), number of reoperations (single vs. multiple), residual obstruction (presence or absence), and operative approach (Gore-tex or not) did not seem to affect outcomes. Risk factors for death were early presentation (<6 months) and persistence of pulmonary hypertension after reoperation; early presentation was also a risk factor for multiple reoperations. CONCLUSIONS: Our findings support the conclusion that early presentation and postoperative pulmonary hypertension have the greatest adverse impact on outcome. Of these, failure to achieve a low-pressure pulmonary vascular system seems to be the variable that most strongly prevents survival. In our series, neither ostial PVO nor multiple re-interventions significantly increased surgical risk. The negative impact of postoperative residual obstruction on outcome was not striking. However, an aggressive surgical approach to this disease is still warranted. Although the role of each technique in obtaining long-lasting relief of PVO remains to be established, the use of artificial material seems unwise.

Basal pulmonary vascular resistance and nitric oxide responsiveness late after Fontan-type operation.

BACKGROUND: The pulsatile nature of pulmonary blood flow is important for shear stress-mediated release of endothelium-derived nitric oxide (NO) and lowering pulmonary vascular resistance (PVR) by passive recruitment of capillaries. Normal pulsatile flow is lost or markedly attenuated after Fontan-type operations, but to date, there are no data on basal pulmonary vascular resistance and its responsiveness to exogenous NO at late follow-up in these patients. METHODS AND RESULTS: We measured indexed PVR (PVRI) using Fick principle to calculate pulmonary blood flow, with respiratory mass spectrometry to measure oxygen consumption, in 15 patients (median age, 12 years; range, 7 to 17 years; 12 male, 3 female) at a median of 9 years after a Fontan-type operation (6 atriopulmonary connections, 7 lateral tunnels, 2 extracardiac conduits). The basal PVRI was 2.11+/-0.79 Wood unit (WU) times m2 (mean+/-SD) and showed a significant reduction to 1.61+/-0.48 (P=0.016) after 20 ppm of NO for 10 minutes. The patients with nonpulsatile group in the pulmonary circulation dropped the PVRI from 2.18+/-0.34 to 1.82+/-0.55 (P<0.05) after NO inhalation. CONCLUSIONS: PVR falls with exogenous NO late after Fontan-type operation. These data suggest pulmonary endothelial dysfunction, related in some part to lack of pulsatility in the pulmonary circulation because of altered flow characteristics. Therapeutic strategies to enhance pulmonary endothelial NO release may have a role in these patients.

Hybrid approaches to complex congenital cardiac surgery.

OBJECTIVES: A hybrid operation is a joint procedure involving the interventional cardiologist and the cardiac surgeon concomitantly to optimise surgical management. The aim of our study was to demonstrate the conceptual development and the feasibility of a hybrid approach to complex congenital cardiac surgery. METHODS: Descriptive study of two different indications for concomitant intervention by the cardiologist and the cardiac surgeon. Seven patients with complex congenital heart defects requiring high risk operative interventions were included in the study. The indications were: (1) intraoperative stenting of a pulmonary artery stenosis with concomitant additional surgical procedures (n=4). (2) Balloon occlusion of Blalock-Taussig shunts or major aorto-pulmonary collateral artery to control pulmonary blood flow during surgical repair (n=3). RESULTS: All patients had successful hybrid procedures. There were no important complications related to the temporal proximity of the interventional procedure and cardiac surgery, the latter being significantly facilitated by the former. CONCLUSIONS: Intraoperative stenting of pulmonary artery stenosis with additional surgical repair and balloon occlusion on cardiopulmonary bypass can be performed safely and may be complementary in patients with complex lesions by providing a better result in combination than either alone can offer.

Impact of junctional ectopic tachycardia on postoperative morbidity following repair of congenital heart defects.

OBJECTIVE: To determine the incidence of postoperative junctional ectopic tachycardia (JET), we reviewed 343 consecutive patients undergoing surgery between 1997 and 1999. The impact of this arrhythmia on in-hospital morbidity and our protocol for treatment were assessed. METHODS: We reviewed the postoperative course of patients undergoing surgery for ventricular septal defect (VSD; n=161), tetralogy of Fallot (TOF; n=114), atrioventricular septal defect (AVSD; n=58) and common arterial trunk (n=10). All patients with JET received treatment, in a stepwise manner, beginning with surface cooling, continuous intravenous amiodarone, and/or atrial pacing if the haemodynamics proved unstable. A linear regression model assessed the effect of these treatments upon hours of mechanical ventilation, and stay on the cardiac intensive care unit (CICU). RESULTS: Overall mortality was 2.9% (n=10), with three of these patients having JET and TOF. JET occurred in 37 patients (10.8%), most frequently after TOF repair (21.9%), followed by AVSD (10.3%), VSD (3.7%), and with no occurrence after repair of common arterial trunk. Mean ventilation time increased from 83 to 187 h amongst patients without and with JET patients (P<0.0001). Accordingly, CICU stay increased from 107 to 210 h when JET occurred (P<0.0001). Surface cooling was associated with a prolongation of ventilation and CICU stay, by 74 and 81 h, respectively (P<0.02; P<0.02). Amiodarone prolonged ventilation and CICU stay, respectively, by 274 and 275 h (P<0.05; P<0.06). CONCLUSIONS: Postoperative JET adds considerably to morbidity after congenital cardiac surgery, and is particularly frequent after TOF repair. Aggressive treatment with cooling and/or amiodarone is mandatory, but correlates with increased mechanical ventilation time and CICU stay. Better understanding of the mechanism underlying JET is required to achieve prevention, faster arrhythmic conversion, and reduction of associated in-hospital morbidity.

Diagnosing "vulnerable system syndrome": an essential prerequisite to effective risk management.

Investigations of accidents in a number of hazardous domains suggest that a cluster of organisational pathologies-the "vulnerable system syndrome" (VSS)-render some systems more liable to adverse events. This syndrome has three interacting and self-perpetuating elements: blaming front line individuals, denying the existence of systemic error provoking weaknesses, and the blinkered pursuit of productive and financial indicators. VSS is present to some degree in all organisations, and the ability to recognise its symptoms is an essential skill in the progress towards improved patient safety. Two kinds of organisational learning are discussed: "single loop" learning that fuels and sustains VSS and "double loop" learning that is necessary to start breaking free from it.

Atrioventricular septal defect with 'absent' pulmonary valve in the setting of Down's syndrome: a rare association.

We report a rare case of a 2-year-old boy with Down's syndrome, atrioventricular septal defect and so-called 'absent pulmonary valve syndrome'. Diagnostic imaging also revealed the presence of an anomalous high origin of the right coronary artery from the ascending aorta. Surgical repair was successful.

A new percutaneously adjustable, thoracoscopically implantable, pulmonary artery banding: an experimental study.

BACKGROUND: In patients who undergo left ventricular retraining, multiple reoperations are often necessary to adjust the pulmonary artery banding. The availability of a percutaneously adjustable band would be very useful. METHODS: Ten lambs (10 to 25 kg) underwent pulmonary artery banding using a new device, 7 by thoracotomy and 3 by thoracoscopy. The possibility of percutaneously adjusting the band was evaluated immediately after operation in 10 animals and at 3 months in 8 animals. RESULTS: One death occurred on the day of the procedure from displacement of the device and another death was from infection. Immediate hemodynamic studies proved the feasibility of increasing right ventricular afterload in a precise and reversible way. After 3 months the band could still be precisely loosened or tightened in all but 1 animal. Autopsy revealed that all the devices were in the correct position and no fibrosis or adhesions were present around the devices, and there was no residual stenosis noted on the pulmonary artery. CONCLUSIONS: This new device may be a valuable alternative to the repeated pulmonary artery banding needed for ventricular preparation.

Traumatic disruption of the ascending aorta in a child after heart transplant.

We report a traumatic disruption of the ascending aorta in an 8-year-old boy who had undergone orthotopic cardiac transplant at 6.5 years of age for congenital heart block and dilated cardiomyopathy. At presentation his aortic injury was not immediately recognized, but persistence in identifying and confirming a suspicious aortic rupture was lifesaving.

The human factor in cardiac surgery: errors and near misses in a high technology medical domain.

In this review, we discuss human factors research in cardiac surgery and other medical domains. We describe a systems approach to understanding human factors in cardiac surgery and summarize the lessons that have been learned about critical incident and near-miss reporting in other high technology industries that are pertinent to this field.

A case for anatomic correction in atrioventricular discordance? Effects of surgery on tricuspid valve function.

OBJECTIVE: To assess tricuspid valve function in atrioventricular discordance after palliative procedures (pulmonary artery banding and Blalock-Taussig shunt) and corrective procedures (anatomic and physiologic repair). METHODS: Tricuspid valve dysfunction was assessed by transthoracic echocardiography and graded as no regurgitation (0), mild (1), moderate (2), and severe (3) before and after palliative and corrective procedures performed in 97 patients with atrioventricular discordance between 1988 and 1999. Thirty-two percent had an isolated ventricular septal defect, 43% had a ventricular septal defect and pulmonary stenosis, and 16% had pulmonary stenosis. Twenty-six patients underwent pulmonary artery banding and 28 had a Blalock-Taussig shunt. Seventy patients underwent physiologic and 19 underwent anatomic repair. Six patients underwent one-ventricle repair. RESULTS: After pulmonary artery banding, the tricuspid regurgitation score decreased from 1.7 +/- 0.8 to 0.9 +/- 0.6 (P <.001). In patients who underwent a Blalock-Taussig shunt, the tricuspid regurgitation score increased from 0.7 +/- 0.5 preoperatively to 1.4 +/- 0.6 postoperatively (P <.001). After physiologic repair, there was no significant change in the tricuspid regurgitation score; however, 7 patients required additional repair or replacement. The regurgitation score was significantly reduced from 1.5 +/- 0.8 to 0.4 +/- 0.5 (P <.001) after anatomic repair. The operative mortality in patients who underwent physiologic repair was 7% as compared with 0% in the anatomic repair group (P =.59). The median follow-up was 3.2 years. CONCLUSIONS: Right ventricular volume loading (shunt) worsens tricuspid regurgitation, whereas volume reduction (banding) or left-to-right septal shift (anatomic repair) has beneficial effects. We have not observed a significant change in the tricuspid regurgitation score after physiologic repair. Anatomic repair can be performed in selected patients with atrioventricular discordance and provides superior functional results.

Effect of fenestration on the sub-diaphragmatic venous hemodynamics in the total-cavopulmonary connection.

OBJECTIVE: To understand differences in the sub-diaphragmatic venous physiology between patients with fenestrated and non-fenestrated total-cavopulmonary connections (TCPC). METHODS: We studied the effects of respiration, retrograde flow, and gravity on the sub-diaphragmatic venous flows in 20 normal healthy volunteers (control), 25 Fontan patients with non-fenestrated TCPC, and 21 with fenestrated TCPC. Subhepatic inferior vena cava (IVC), hepatic vein (HV), and portal vein (PV) flow rates were measured with Doppler ultrasonography during inspiration and expiration in both supine and upright positions. The supine inspiratory-to-expiratory flow rate ratio was calculated to reflect the effect of respiration, the supine-to-upright flow rate ratio was calculated to assess the effect of gravity, and the magnitude of retrograde flow was evaluated with respect to total antegrade flow. Mean IVC, HV, and wedged hepatic venous (WHV) pressures were measured during cardiac catheterization in four TCPC patients before and after fenestration closure. The transhepatic venous pressure gradient (TVPG) was calculated as the difference between the HV and WHV pressure. RESULTS: Compared with control, HV flow in TCPC was heavily dependent on respiration; this inspiratory capacity was greater in fenestrated than non-fenestrated subjects (inspiratory-to-expiratory flow ratio 1.7, 4.4, and 3.0, respectively P<0.001). Normal retrograde HV flow was diminished in TCPC patients, furthermore, fenestrated subjects had less flow reversal than non-fenestrated (retrograde as percent of antegrade flow 43, 19, and 30%, respectively P<0.001). Gravity decreased IVC and HV flows more in TCPC subjects than control, but this effect was not different between the two TCPC groups. Closure of the fenestration resulted in higher IVC and HV pressures (pre-closure versus post-closure pressures [mmHg]: 11.2 +/- 4.0 vs. 12.3 +/- 3.9, and 11.5 +/- 3.8 vs. 12.4 +/- 3.8, respectively P< or =0.001). The normal TVPG was reduced in fenestrated TCPC, and worsened after fenestration closure (0.9 +/- 0.3 and 0.7 +/- 0.4, respectively P < 0.04). CONCLUSIONS: Fenestration of the inferior venous connection has important influences on sub-diaphragmatic venous return in TCPC patients. Although fenestration lowers venous pressures and partially restores TVPG, its beneficial effects on flow in TCPC patients are mediated primarily by an increase in inspiration-derived forward HV flow and reduced flow reversal. These observations suggest fenestration results in a more efficient and less congested splanchnic circulation in TCPC patients, and may have important implications in the early and late management of Fontan patients.