Force Tracking with Feed-Forward Motion Estimation for Beating Heart Surgery

The manipulation of fast moving, delicate tissues in beating heart procedures presents a considerable challenge to the surgeon. A robotic force tracking system can assist the surgeon by applying precise contact forces to the beating heart during surgical manipulation. Standard force control approaches cannot safely attain the required bandwidth for this application due to vibratory modes within the robot structure. These vibrations are a limitation even for single degree of freedom systems driving long surgical instruments. These bandwidth limitations can be overcome by incorporating feed-forward motion terms in the control law. For intracardiac procedures, the required motion estimates can be derived from 3D ultrasound imaging. Dynamic analysis shows that a force controller with feed-forward motion terms can provide safe and accurate force tracking for contact with structures within the beating heart. In vivo validation confirms that this approach confers a 50% reduction in force fluctuations when compared to a standard force controller and a 75% reduction in fluctuations when compared to manual attempts to maintain the same force.

Electron transport chain dysfunction in neonatal pressure-overload hypertrophy precedes cardiomyocyte apoptosis independent of oxidative stress

OBJECTIVES

We have previously shown in a model of pressure-overload hypertrophy that there is increased cardiomyocyte apoptosis during the transition from peak hypertrophy to ventricular decompensation. Electron transport chain dysfunction is believed to play a role in this process through the production of excessive reactive oxygen species. In this study we sought to determine electron transport chain function in pressure-overload hypertrophy and the role of oxidative stress in myocyte apoptosis.

METHODS AND RESULTS

Neonatal rabbits underwent thoracic aortic banding at 10 days of age. Compensated hypertrophy (4 weeks of age), decompensated hypertrophy (6 weeks of age), and age-matched controls (n = 4-8 per group) as identified by serial echocardiography were studied. Electron transport chain complex activities were determined by spectophotometry in isolated mitochondria. Complex I was significantly decreased (P = .005) at 4 weeks and further decreased at 6 weeks (P = .001). Complex II was significantly decreased at both time points (4 weeks, P = .003; 6 weeks, P = .009). However, hyddrogen peroxide production, measured in isolated mitochondria by fluorescence spectroscopy, was significantly decreased at 4 weeks of age in banded animals compared with controls (P = .038), and mitochondrial DNA oxidative damage (measurement of 8- hydroxydeoxyguanosine by enzyme-linked immunosorbent assay) was also significantly decreased at 4 weeks of age (P = .031). Mitochondrial activated apoptosis was determined by Bax/Bcl-2 ratios (immunoblotting). Bax/Bcl-2 levels were significantly increased in banded animals at 6 weeks.

CONCLUSIONS

In pressure-overload hypertrophy, the transition from compensated left ventricular hypertrophy to failure and cardiomyocyte apoptosis is preceded by mitochondrial complex I and II dysfunction followed by an increase in Bax/Bcl-2 ratios. The mechanism of apoptosis initiation is independent of increased oxidative stress.

Development of left ventricular diastolic dysfunction with preservation of ejection fraction during progression of infant right ventricular hypertrophy

BACKGROUND

Progressive left ventricular (LV) dysfunction can be a major late complication in patients with chronic right ventricular pressure overload (eg, tetralogy of Fallot). Therefore, we examined LV function (serial echocardiography and ex vivo Langendorff) and histology in a model of infant pressure-load right ventricular hypertrophy (RVH).

METHODS AND RESULTS

Ten-day-old rabbits (n=6 per time point, total n=48) that underwent pulmonary artery banding were euthanized at 2 to 8 weeks after pulmonary artery banding, and comparisons were made with age-matched sham controls. LV performance (myocardial performance index) decreased during the progression of RVH, although the LV ejection fraction was maintained. In addition, RVH caused significant septal displacement, reduced septal contractility, and decreased LV end-systolic and end-diastolic dimensions, resulting in LV diastolic dysfunction with the appearance of preserved ejection fraction. Significant septal and LV free-wall apoptosis (myocyte-specific TUNEL and activated caspase-3), fibrosis (Masson trichrome stain), and reduced capillary density (CD31 immunostaining) occurred in the pulmonary artery banding group after 6 to 8 weeks (all P<0.05).

CONCLUSIONS

This is the first study showing that pressure overload of the right ventricular resulting in RVH causes LV diastolic dysfunction while preserving ejection fraction through mechanical and molecular effects on the septum and LV myocardium. In particular, the development of RVH is associated with septal and LV apoptosis and reduced LV capillary density.

Calcium sensitisation impairs diastolic relaxation in post-ischaemic myocardium: implications for the use of Ca(2+) sensitising inotropes after cardiac surgery

BACKGROUND

Calcium sensitising inotropes are increasingly being used in cardiac surgical patients. Theoretically, increasing contractile protein sensitivity to Ca(2+) prevents the Ca(2+) elevation associated arrhythmogenicity and potentiates the inotropic effect of catecholamines. On the other hand, we hypothesised that Ca(2+) sensitisation exacerbates post-ischaemic myocardial stunning by impairing diastolic relaxation, which might have deleterious effects in postoperative cardiac surgical patients.

METHODS

In an isolated rabbit heart model, 45 min normothermic ischaemia with potassium-induced cardioplegic arrest was followed by 120 min reperfusion. Isovolumetric left ventricular (LV) function and myocardial oxygen consumption (MvO(2)) were measured, and cytosolic Ca(2+) was monitored by rhod-2 surface spectrofluorometry. During reperfusion, ORG 30029 (250 microM) and levosimendan (0.5 microM) were used as Ca(2+) sensitisers (ORG, n=6, Levo, n=6), Ca(2+) de-sensitisation was induced with butanedione-monoxime (5mM, BDM, n=6), and dopamine (20 nM) served as a representative catecholamine (n=6). To counteract the PDE III inhibiting properties of ORG and Levo, IGF-1 (0.1 microM) and parathyroid hormone (0.05 microM) were used.

RESULTS

As expected, ischaemia/reperfusion induced moderate cytosolic calcium overload. Dopamine increased LV contractility and MvO(2) by augmenting the amplitude of the Ca(2+) transient, but relaxation was unchanged due to faster diastolic Ca(2+) removal. Dopamine-induced Ca(2+) handling was unchanged after uncoupling the Mg-ATPase with BDM, and MvO2 decreased in proportion with the reduced LV mechanical work load. ORG improved contractility without apparent effects on Ca(2+) handling, and MvO(2) remained constant despite increased contractile work. Conversely, ORG induced a rightward shift of the diastolic pressure-volume relationship in post-ischaemic hearts (diastolic pressure at 0.8 ml balloon volume 14.3+/-5 mmHg, p=0.01 vs control), but not in non-ischaemic control hearts. With levosimendan, the Ca(2+) sensitising effects were less pronounced (7.6+/-3 mmHg, p=0.4 vs control). By counteracting the PDE inhibiting effects of ORG and Levo using parathyroid hormone and IGF-1, the negative lusotropic effects of Ca(2+) sensitisation were unmasked.

CONCLUSIONS

Calcium sensitisation improves systolic function and energetic efficiency. However, Ca(2+) sensitisers should be used with caution during post-ischaemic reperfusion, as they may exacerbate myocardial stunning and thus impair cardiac output.

Effectiveness of balloon valvuloplasty for palliation of mitral stenosis after repair of atrioventricular canal defects

Closure of a mitral valve (MV) cleft, small left-sided cardiac structures, and ventricular imbalance all may contribute to mitral stenosis (MS) after repair of atrioventricular canal (AVC) defects. MV replacement is the traditional therapy but carries high risk in young children. The utility of balloon mitral valvuloplasty (BMV) in postoperative MS is not established and may offer alternative therapy or palliation. Since 1996, 10 patients with repaired AVC defects have undergone BMV at a median age of 2.5 years (range 8 months to 14 years), a median of 2 years after AVC repair. At catheterization, the median value of mean MS gradients was 16 mm Hg (range 12 to 22) and was reduced by 34% after BMV. Before BMV, there was mild mitral regurgitation in 9 of 10 patients, which increased to severe in 1 patient. All patients were alive at follow-up (median 5.4 years). Repeat BMV was performed in 4 patients, 10 weeks to 18 months after initial BMV. One patient underwent surgical valvuloplasty; 3 underwent MV replacement 2, 3, and 28 months after BMV. In the 6 patients (60%) with a native MV at most recent follow-up (median 3.2 years), the mean Doppler MS gradient was 9 mm Hg, the median weight had doubled, and weight percentile had increased significantly. In conclusion, BMV provides relief of MS in most patients with repaired AVC defects; marked increases in mitral regurgitation are uncommon. Because BMV can incompletely relieve obstruction and increase mitral regurgitation, it will not be definitive in most patients but will usually delay MV replacement to accommodate a larger prosthesis.

Oral tolerization with cardiac myosin peptide (614-629) ameliorates experimental autoimmune myocarditis: role of STAT 6 genes in BALB/CJ mice

INTRODUCTION

Experimental autoimmune myocarditis (EAM) is mediated by myocardial infiltration by myosin-specific T cells secreting inflammatory cytokines.

MATERIALS AND METHODS

To clarify the role of cytokines in EAM, we compared STAT 6-deficient ((-/-)) with STAT 4(-/-) and wild-type (BALB/CJ) mice following immunization with cardiac myosin peptide (614-629).

RESULTS

Wild-type mice developed severe disease with a small increase in severity in STAT 6(-/-) mice, while STAT 4(-/-) mice were resistant to EAM. STAT 6(-/-) mice had increased splenocyte proliferation and INF-gamma production versus wild type, while STAT 4(-/-) mice had decreased proliferation and INF-gamma. Following oral administration of myosin (614-629), tolerization was induced in wild-type mice evidenced by amelioration of myocarditis and up-regulation of IL-4. Adoptive transfer of splenocytes from orally tolerized mice resulted in inhibition of disease in STAT 6(-/-) mice.

CONCLUSION

These results demonstrate that oral tolerization ameliorates EAM in BALB/CJ mice and indicate a down-regulatory role for STAT 6 genes.

Mitral Annulus Segmentation from Three-Dimensional Ultrasound

An accurate and reproducible segmentation of the mitral valve annulus from 3D ultrasound is useful to clinicians and researchers in applications such as pathology diagnosis and mitral valve modeling. Current segmentation methods, however, are based on 2D information, resulting in inaccuracies and a lack of spatial coherence. We present a segmentation algorithm which, given a single user-specified point near the center of the valve, uses max-flow and active contour methods to delineate the annulus geometry in 3D. Preliminary comparisons to manual segmentations and a sensitivity study show the algorithm is both accurate and robust.

Factors associated with prolonged recovery after the fontan operation

BACKGROUND

Mortality and major morbidity after the Fontan operation is low in the current era. However, factors contributing to prolonged postoperative recovery are not clearly understood.

METHODS AND RESULTS

Data on all patients admitted to the cardiac intensive care unit (CICU) after a Fontan operation between June 2001 and December 2005 were retrospectively analyzed. We excluded all patients who died, required Fontan takedown, or required ECMO. The study cohort was further divided into a prolonged recovery group that included patients with >75%ile for duration of mechanical ventilation or pleural drainage, and a standard recovery group which included all other patients. A multivariable logistic regression model was used to compare demographic, anatomic, and physiological variables between the prolonged and standard recovery groups. There were 226 Fontan operations performed. Of the study population (n=218), the median age was 2.61 years (1.0 to 31.9 years) and weight was 12.45 kg (8.4 to 77.5 kg). The most common diagnosis was hypoplastic left heart syndrome (n=80, 36.7%). A systemic right atrioventricular valve was present in 139 (63.7%). The lateral tunnel fenestrated Fontan was the most common surgery (n=195, 89.4%). Within the study population, 81 (38%) patients meet criteria for prolonged recovery. Univariate risk factors for prolonged recovery included higher preoperative PVR (P=0.033), longer bypass times (P=0.009), higher postbypass lactate level (P=0.017), higher postoperative central venous (P<0.001) common atrial pressure (P=0.042), inotropic score (P<0.001), and need for greater volume resuscitation during the 24 postoperative hours (>75% for the entire group; P<0.001). In a multivariable model, need for greater volume resuscitation (OR 2.81, 95% CI 1.30, 6.05) was the only independent risk factor for prolonged outcome after the Fontan operation.

CONCLUSIONS

High volume expansion in the early postoperative period is an independent risk factor for prolonged recovery. The need for high volume expansion may represent the compound effects of multiple risk factors including preoperative hemodynamics and a marked systemic inflammatory response to surgery and cardiopulmonary bypass, which in turn may mediate prolonged recovery.

Patient-specific MRI-based 3D FSI RV/LV/patch models for pulmonary valve replacement surgery and patch optimization

A patient-specific right/left ventricle and patch (RV/LV/patch) combination model with fluid-structure interactions (FSIs) was introduced to evaluate and optimize human pulmonary valve replacement/insertion (PVR) surgical procedure and patch design. Cardiac magnetic resonance (CMR) imaging studies were performed to acquire ventricle geometry, flow velocity, and flow rate for healthy volunteers and patients needing RV remodeling and PVR before and after scheduled surgeries. CMR-based RV/LV/patch FSI models were constructed to perform mechanical analysis and assess RV cardiac functions. Both pre- and postoperation CMR data were used to adjust and validate the model so that predicted RV volumes reached good agreement with CMR measurements (error <3%). Two RV/LV/patch models were made based on preoperation data to evaluate and compare two PVR surgical procedures: (i) conventional patch with little or no scar tissue trimming, and (ii) small patch with aggressive scar trimming and RV volume reduction. Our modeling results indicated that (a) patient-specific CMR-based computational modeling can provide accurate assessment of RV cardiac functions, and (b) PVR with a smaller patch and more aggressive scar removal led to reduced stress/strain conditions in the patch area and may lead to improved recovery of RV functions. More patient studies are needed to validate our findings.

Outcome of fetuses and infants with double inlet single left ventricle

Double-inlet left ventricle (DILV) includes a diverse range of anatomic variables that affect the surgical strategy. The aim of this study was to determine the impact of anatomic subtype, associated anomalies, and fetal diagnosis on the management and outcomes of fetuses and infants with DILV. The outcomes of fetuses and infants with DILV diagnosed from 1990 to 2004 at 3 major referral centers were reviewed. Sixty-five cases of DILV were detected prenatally. Twenty-one of these pregnancies were terminated, including 17 of 37 (46%) in which the diagnoses were made at < or =24 weeks of gestation. An additional 106 patients were diagnosed with DILV within the first 3 months of life. The percentage of patients diagnosed prenatally increased significantly over the study period. Transplantation-free survival was 88%, 82%, 79%, and 76% at 1 month, 1 year, 5 years, and 10 years, respectively. Factors associated with improved survival in univariate analysis included year of birth after 1994, no neonatal Norwood or Damus procedure, and no neonatal surgery at all. In multivariate analysis, any neonatal surgery was the only factor associated with worse survival. Associated anomalies and prenatal diagnosis were not associated with postnatal outcome. In conclusion, although the frequency of prenatal diagnosis of DILV has increased significantly over the past 15 years, prenatal diagnosis is not associated with better postnatal survival. During this same period, postnatal survival has improved substantially. Neonatal surgery of any type was the only independent risk factor for worse survival.

Determinants of right ventricular outflow tract conduit longevity: a multinational analysis

OBJECTIVE

The need for conduit replacement in the growing child remains a major problem after right ventricular outflow tract reconstruction. We compared two diverse surgical centers with considerable practice variation in Europe and the United States to identify modifiable risk factors that can increase conduit longevity.

DESIGN

Retrospective analysis of 194 patients (56 Europe, 138 United States) who underwent primary right ventricular to pulmonary artery conduit placement between January 1987 and March 2003.

PATIENTS

Diagnoses included tetralogy of Fallot with pulmonary atresia, truncus arteriosus, transposition of the great arteries with ventricular septal defect and pulmonary stenosis, and double-outlet right ventricle.

RESULTS

Median age was 7.3 months (range 2 days-29.9 years). Types of conduits included aortic homografts (n = 111), pulmonary homografts (n = 48), Contegra conduits (Medtronic, Inc, Minneapolis, MN) (n = 23), and synthetic conduits (n = 12). Freedom from conduit failure at 5 years was 50% (58% Europe, 48% United States, P = NS). On multivariate analysis, smaller conduit diameter (hazard ratio [HR] 1.15, P < .001) and conduits other than pulmonary homografts (synthetic conduits [HR 3.17, P = .01], Contegra conduits [HR 2.80, P = .02], aortic homografts [HR 1.56, P = .05]) predicted shorter time to conduit failure. In addition, time to failure was longer for patients undergoing transcatheter intervention. Different surgical techniques in conduit preparation and insertion did not influence conduit longevity.

CONCLUSIONS

Analysis of the two diverse surgical centers showed that to increase conduit longevity, one should choose the largest possible conduit, use a pulmonary homograft, and consider children whose conduits develop obstruction as candidates for transcatheter intervention.

Fast block flow tracking of atrial septal defects in 4D echocardiography

We are working to develop beating-heart atrial septal defect (ASD) closure techniques using real-time 3D ultrasound guidance. The major image processing challenges are the low-image quality and the processing of information at high-frame rate. This paper presents comparative results for ASD tracking in time sequences of 3D volumes of cardiac ultrasound. We introduce a block flow technique, which combines the velocity computation from optical flow for an entire block with template matching. Enforcing adapted similarity constraints to both the previous and first frames ensures optimal and unique solutions. We compare the performance of the proposed algorithm with that of block matching and region-based optical flow on eight in vivo 4D datasets acquired from porcine beating-heart procedures. Results show that our technique is more stable and has higher sensitivity than both optical flow and block matching in tracking ASDs. Computing velocity at the block level, our technique tracks ASD motion at 2 frames/s, much faster than optical flow and comparable in computation cost to block matching, and shows promise for real-time (30 frames/s). We report consistent results on clinical intra-operative images and retrieve the cardiac cycle (in ungated images) from error analysis. Quantitative results are evaluated on synthetic data with maximum tracking errors of 1 voxel.

3D ultrasound-guided motion compensation system for beating heart mitral valve repair

Beating heart intracardiac procedures promise significant benefits for patients, however, the fast motion of the heart poses serious challenges to surgeons. We present a new 3D ultrasound-guided motion (3DUS) compensation system that synchronizes instrument motion with the heart. The system utilizes the fact that the motion of some intracardiac structures, including the mitral valve annulus, is largely constrained to translation along one axis. This allows the development of a real-time 3DUS tissue tracker which we integrate with a 1 degree-of-freedom actuated surgical instrument, real-time 3DUS instrument tracker, and predictive filter to devise a system with synchronization accuracy of 1.8 mm RMSE. User studies involving the deployment of surgical anchors in a simulated mitral annuloplasty procedure demonstrate that the system increases success rates by over 100%. Furthermore, it enables more careful anchor deployment by reducing forces to the tissue by 50% while allowing instruments to remain in contact with the tissue for longer periods.

Statistical segmentation of surgical instruments in 3-D ultrasound images

The recent development of real-time 3-D ultrasound (US) enables intracardiac beating-heart procedures, but the distorted appearance of surgical instruments is a major challenge to surgeons. In addition, tissue and instruments have similar gray levels in US images and the interface between instruments and tissue is poorly defined. We present an algorithm that automatically estimates instrument location in intracardiac procedures. Expert-segmented images are used to initialize the statistical distributions of blood, tissue and instruments. Voxels are labeled through an iterative expectation-maximization algorithm using information from the neighboring voxels through a smoothing kernel. Once the three classes of voxels are separated, additional neighboring information is combined with the known shape characteristics of instruments to correct for misclassifications. We analyze the major axis of segmented data through their principal components and refine the results by a watershed transform, which corrects the results at the contact between instrument and tissue. We present results on 3-D in-vitro data from a tank trial and 3-D in-vivo data from cardiac interventions on porcine beating hearts, using instruments of four types of materials. The comparison of algorithm results to expert-annotated images shows the correct segmentation and position of the instrument shaft.

Cardiac magnetic resonance imaging evaluation of sinus venosus defects: comparison to surgical findings

Sinus venosus defect (SVD) is an uncommon type of interatrial communication in which cardiac magnetic resonance (CMR) is increasingly used as an alternative imaging modality. The goal of this study was to determine the accuracy of CMR in patients with SVD compared with surgical findings. The diagnostic studies and operative reports of all patients who had CMR followed by surgical repair of SVD (n = 16) from 1996 to 2005 were reviewed and discrepancies were recorded. CMR studies included assessment of anatomy (evaluated by a combination of gradient echo cine, spin echo, and gadolinium-enhanced three-dimensional magnetic resonance angiography), ventricular volumes and function, and flow measurements. The median age at CMR was 14 years (range, 0.4-42). Compared with operative findings, there were no major discrepancies with CMR. The SVD was clearly imaged in all patients and 36 anomalously draining pulmonary veins were identified. The median pulmonary-to-systemic flow ratio was 2.4 (range, l.3-4.6). Patients had an average of 1.7 previous diagnostic tests (range, 1-3; 19 transthoracic echo, 5 catheterizations, and 3 transesophageal echo). Before CMR, SVD was diagnosed in 1 patient, suspected in 7, and not suspected in 8. Additional unsuspected findings identified by CMR included malposition of septum primum (n = 2), left superior vena cava to coronary sinus (n = 2), and aortic arch anomalies (n = 2). CMR accurately depicts SVD anatomy and associated anomalous pulmonary venous drainage, provides quantitative information on the hemodynamic burden, and reveals additional cardiovascular abnormalities. This experience indicates that CMR provides the information necessary for surgical planning of SVD repair.

Early postoperative outcomes in a series of infants with hypoplastic left heart syndrome undergoing stage I palliation operation with either modified Blalock-Taussig shunt or right ventricle to pulmonary artery conduit

OBJECTIVE

Previous publications using nonconcurrent series of patients indicate improved survival for patients with hypoplastic left heart syndrome (HLHS) undergoing stage I palliation with a right ventricle to pulmonary artery conduit (NW-RVPA) vs. a modified Blalock-Taussig shunt (NW-BT). We compared postoperative outcomes in a concurrent series of patients with HLHS undergoing an NW-BT procedure vs. NW-RVPA procedure.

DESIGN

Perioperative data from 66 consecutive patients who underwent NW-BT (n = 37) or NW-RVPA (n = 29) procedures were retrospectively analyzed.

SETTING

Cardiac intensive care unit in a tertiary pediatric hospital.

PATIENTS

Charts were reviewed for all patients with the diagnosis of HLHS undergoing the NW-BT or NW-RVPA procedure between January 2002 and December 2003.

RESULTS

Cardiopulmonary bypass time was longer in the NW-BT group than in the NW-RVPA group (152.5 +/- 52.0 vs. 134.5 +/- 36.1 mins; p = .04). Postoperative diastolic pressures were higher and the Pao2 to Fio2 ratio profiles were lower for the NW-RVPA group over the first 72 hrs. Time to sternal closure (2 [1-6] vs. 4 [2-41] days; p = .01), duration of mechanical ventilation (113 [49-386] vs. 136 [84-764] hrs; p = .01), time to establish enteral feeds (4 [2-8] vs. 5 [3-22] days; p = .01), length of intensive care unit stay (11 [7-55] vs. 15 [8-90] days; p = .04), and length of hospital stay (16 [11-67] vs. 27 [12-126] days; p = .01) were shorter in the NW-RVPA group. Postoperative mortality was not significantly different between the NW-RVPA group (7%) and NW-BT group (11%).

CONCLUSION

At an experienced institution with low stage I palliation mortality for HLHS, there were no differences in early morbidity and mortality between the NW-RVPA and NW-BT procedures. The primary advantage of the NW-RVPA procedure may be faster recovery following surgery and earlier discharge from the hospital.

3D ultrasound in robotic surgery: performance evaluation with stereo displays

BACKGROUND

The recent advent of real-time 3D ultrasound (3DUS) imaging enables a variety of new surgical procedures. These procedures are hampered by the difficulty of manipulating tissue guided by the distorted, low-resolution 3DUS images. To lessen the effects of these limitations, we investigated stereo displays and surgical robots for 3DUS-guided procedures.

METHODS

By integrating real-time stereo rendering of 3DUS with the binocular display of a surgical robot, we compared stereo-displayed 3DUS with normally displayed 3DUS. To test the efficacy of stereo-displayed 3DUS, eight surgeons and eight non-surgeons performed in vitro tasks with the surgical robot.

RESULTS

Error rates dropped by 50% with a stereo display. In addition, subjects completed tasks faster with the stereo-displayed 3DUS as compared to normal-displayed 3DUS. A 28% decrease in task time was seen across all subjects.

CONCLUSIONS

The results highlight the importance of using a stereo display. By reducing errors and increasing speed, it is an important enhancement to 3DUS-guided robotics procedures.

Minimal-access surgery for congenital heart defects

Improved results with lower operative mortality and morbidity for corrective surgery for many congenital cardiac defects has stimulated a renewed interest in the use of surgical approaches other than a full midline sternotomy. In an effort to decrease pain and discomfort, shorten the recovery period, and improve the cosmetic result, several alternative approaches have been proposed and implemented, with varying results. Anterior thoracotomy in the inframammary area has been the most widely used incision and is most applicable to females patients past puberty, in whom the extent of breast tissue can be assessed more accurately. Complications with this approach including phrenic nerve injury and breast and chest wall deformities have been reported, although most reports describe satisfactory cosmetic results. We have used a midline approach limiting the incision over the xyphoid process either without a sternal incision (infants) or with division of the lower segment (patients younger than 3 to 4 years) with cephalad retraction to expose the heart and great vessels. From May 1996 to June 1997, 54 children had repair of a secundum-type atrial septal defect using a transxyphoid or ministernotomy approach. In 29, arterial cannulation was performed through the ascending aorta, and in 25 via the femoral artery. There were no instances in which conversion to full sternotomy was required, and complete repair with comparable ischemic and bypass time to full sternotomy was achieved in all patients. We have also used the same technique for repair of other congenital cardiac lesions, including ventricular septal defect and partial or complete atrioventricular canal defects, and in selected infants with tetralogy of Fallot. With this approach, cardioplegia for myocardial protection and left ventricular venting to prevent distention and to remove air from the heart can be used routinely. The adaptability of this technique to various cardiac defects and the ability to extend the incision if necessary make it an attractive alternative to other approaches for minimal-access cardiac surgery for congenital defects. Copyright 1998 by W.B. Saunders Company

Surgical management of double-outlet right ventricle with subaortic ventricular septal defect

Double-outlet right ventricle (DORV) and subaortic ventricular septal defect (VSD) is defined anatomically as a defect where the entire pulmonary trunk and at least half of the aorta arises from the right ventricle (RV) and the VSD is most closely aligned with the aorta. The surgical management of DORV and subaortic VSD usually results in a 2 ventricle repair where the left ventricular outflow is diverted via the VSD to the aorta. Pulmonary and/or subpulmonary obstruction is found in a large portion of these patients and requires relief at the time of repair. Resection of subpulmonary muscular obstruction with right ventricular outflow augmentation with a patch is required in most to eliminate the obstruction. Important anatomic features to consider in constructing the left ventricular outflow tunnel include the prominence of the conal septum, tricuspid valve attachments to conal septum, and the distance between the pulmonary and tricuspid valves. Operative mortality is low and long-term complications and need for reoperation is uncommon. This report describes the surgically relevant anatomic features and operative techniques. Copyright 2000 by W.B. Saunders Company