Simulation of the Strain Amplification in Sulci Due to Blunt Impact to the Head

Traumatic brain injury (TBI) has become a concern in sports, automobile accidents and combat operations. A better understanding of the mechanics leading to a TBI is required to cope with both the short-term life-threatening effects and long-term effects of TBIs, such as the development chronic traumatic encephalopathy (CTE). Kornguth et al. (1) proposed that an inflammatory and autoimmune process initiated by a water hammer effect at the bases of the sulci of the brain is a mechanism of TBI leading to CTE. A major objective of this study is to investigate whether the water hammer effect is present due to blunt impacts through the use of computational models. Frontal blunt impacts were simulated with 2D finite element models developed to capture the biofidelic geometry of a human head. The models utilized the Arbitrary Lagrangian Eulerian (ALE) method to model a layer of cerebrospinal fluid (CSF) as a deforming fluid allowing for CSF to move in and out of sulci. During the simulated impacts, CSF was not observed to be driven into the sulci during the transient response. However, elevated shear strain levels near the base of the sulci were exhibited. Further, increased shear strain was present when differentiation between white and gray matter was taken into account. Both of the results support clinical observations of (1).

Fate of the right ventricle after fenestrated right ventricular exclusion for severe neonatal Ebstein anomaly

OBJECTIVES

Neonates with Ebstein anomaly can have severe left ventricular dysfunction caused by right ventricular enlargement and ventricular septal displacement. Fenestrated right ventricular exclusion and Blalock-Taussig shunt (Starnes procedure) have been performed to mitigate this problem; however, the fate of the excluded ventricle and its effect on the systemic ventricle have yet to be documented.

METHODS

Intermediate-term data have been retrospectively collected on the 12 survivors of neonatal right ventricular exclusion. Echocardiographic examinations were compared from the time of the original right ventricular exclusion and before second-stage Glenn palliation. Measurement of the Great Ormond Street ratio (area of right atrium plus atrialized right ventricle divided by area of trabeculated right ventricle plus left atrium and left ventricle), ratio of right ventricular to left ventricular area, degree of ventricular septal impingement into the left ventricle, and left ventricular shortening fraction have been documented.

RESULTS

In the 12 survivors of right ventricular exclusion, a decrease in the mean Great Ormond Street ratio was observed (before fenestrated right ventricular exclusion: 1.04 +/- 0.49 vs before Glenn palliation: 0.31 +/- 0.10, P = .01). The average pre-Glenn right ventricular/left ventricular ratio was substantially less than 1.0 (mean, 0.63 +/- 0.27), demonstrating right ventricular regression. The degree of left ventricular septal impingement decreased by an average of 38% (P = .008), normalizing left ventricular morphology. At the time of Glenn palliation, the left ventricular shortening fraction was normal in all patients (mean, 42% +/- 7%).

CONCLUSIONS

After neonatal right ventricular exclusion (Starnes procedure) for severe Ebstein anomaly, there is a reduction in right ventricular size, as demonstrated by echocardiographic evidence of a significant decrease in Great Ormond Street ratios. This regression correlates with ventricular septal realignment and normalization of left ventricular function.

Current surgical therapy for Ebstein anomaly in neonates

OBJECTIVE

Neonates with profound heart failure resulting from Ebstein anomaly have historically had poor outcomes. We report our institutional experience with the surgical management of Ebstein anomaly in severely symptomatic neonates.

METHODS

A retrospective review of all patients (n = 16) undergoing neonatal intervention for Ebstein anomaly between 1992 and 2005 has been carried out. The indications for operation were overt heart failure, cyanosis, and acidosis associated with tricuspid regurgitation, depressed right ventricular function, and severe cardiomegaly. The magnitude of cardiac enlargement was assessed by cardiothoracic ratio and Great Ormond Street ratio (area of right atrium + atrialized right ventricle/area of functional left atrium + left ventricle). The operative strategy was first to assess for the possibility of tricuspid valve repair with or without right ventricular outflow tract reconstruction. If this was not feasible, then right ventricular exclusion was performed by oversewing the tricuspid valve with a pericardial patch. A reduction atrioplasty was done and, depending on the extent of the atrialized portion of the right ventricle, plication was performed. A modified Blalock-Taussig shunt provided pulmonary blood flow. This univentricular approach (Starnes procedure) evolved to include a fenestration in the tricuspid valve patch to allow for right ventricular decompression. Analysis included overall and group-specific survival as well as the testing of perioperative clinical, morphologic, and surgical variables for correlation with mortality and morbidity.

RESULTS

Mean age and weight at operation were 8 +/-10 days and 3.1 +/- 0.4 kg. Tricuspid valve repair was undertaken in 3 patients with 1 requiring conversion to right ventricular exclusion 3 months after the initial operation. In those with right ventricular exclusion, the tricuspid valve patch was fenestrated in 10 and nonfenestrated in 3. One patient had heart transplant as the initial procedure. There were 5 hospital deaths (31%) and no late deaths among the survivors. Survival in the cohort with a fenestrated tricuspid valve patch was 80% (8/10) versus 33% (1/3) for the nonfenestrated group. This difference did not reach statistical significance, although the trend seems clinically important. There was no difference in the cardiothoracic ratio (0.82 fenestrated vs 0.84 nonfenestrated: P = .802) or the Great Ormond Street ratio (1.2 fenestrated vs 1.02 nonfenestrated: P = .477) between the two groups. Among the 9 survivors of right ventricular exclusion, 3 have had completion of their Fontan, and all 9 have undergone a bidirectional Glenn procedure. All operations including homograft placement in the right ventricular outflow tract, whether during repair or during right ventricular exclusion, ended in death.

CONCLUSION

Right ventricular exclusion with a fenestrated tricuspid valve patch combined with right atrioplasty and right ventriculoplasty and a Blalock-Taussig shunt (Starnes procedure) has provided effective palliation for neonates presenting with critical Ebstein anomaly and a tricuspid valve that cannot be repaired.