Cerebral microhemorrhages in children with congenital heart disease: Prevalence, risk factors, and impact on neurodevelopmental outcomes

Background

Infants with complex congenital heart disease (CHD) require life-saving corrective/palliative heart surgery in the first weeks of life. These infants are at risk for brain injury and poor neurodevelopmental outcomes. Cerebral microhemorrhages (CMH) are frequently seen after neonatal bypass heart surgery, but it remains unknown if CMH are a benign finding or constitute injury. Herein, we investigate the risk factors for developing CMH and their clinical significance.

Methods

192 infants with CHD undergoing corrective cardiac surgery with cardiopulmonary bypass (CPB) at a single institution were prospectively evaluated with pre-(n = 183) and/or postoperative (n = 162) brain magnetic resonance imaging (MRI). CMH severity was scored based on total number of microhemorrhages. Antenatal, perioperative, and postoperative candidate risk factors for CMH and neurodevelopmental (ND) outcomes were analyzed. Eighteen-month neurodevelopmental outcomes were assessed using the Bayley-III Scales of Infants and Toddler Development in a subset of patients (n = 82). Linear regression was used to analyze associations between risk factors or ND outcomes and presence/number of CMH.

Results

The most common CHD subtypes were hypoplastic left heart syndrome (HLHS) (37%) and transposition of the great arteries (TGA) (33%). Forty-two infants (23%) had CMH present on MRI before surgery and 137 infants (85%) post-surgery. No parameters evaluated were significant risk factors for preoperative CMH. In multivariate analysis, cardiopulmonary bypass (CPB) duration (p < 0.0001), use of extracorporeal membrane oxygenation (ECMO) support (p < 0.0005), postoperative seizure(s) (p < 0.03), and lower birth weight (p < 0.03) were associated with new or worsened CMH postoperatively. Higher CMH number was associated with lower scores on motor (p < 0.03) testing at 18 months.

Conclusion

CMH is a common imaging finding in infants with CHD with increased prevalence and severity after CPB and adverse impact on neurodevelopmental outcomes starting at a young age. Longer duration of CPB and need for postoperative ECMO were the most significant risk factors for developing CMH. However, presence of CMH on preoperative scans indicates non-surgical risk factors that are yet to be identified. Neuroprotective strategies to mitigate risk factors for CMH may improve neurodevelopmental outcomes in this vulnerable population.

Prevalence of Patent Foramen Ovale in a Cohort of Children With Cryptogenic Ischemic Stroke

BACKGROUND AND OBJECTIVES

To determine the significance of patent foramen ovale (PFO) in childhood stroke, we compared PFO prevalence, PFO features, and stroke recurrence risk in 25 children with cryptogenic arterial ischemic stroke (AIS), 54 children with AIS from a known etiology, and 209 healthy controls.

METHODS

We performed a case-control analysis of a 14-year prospectively enrolled single-center cohort of children with AIS who underwent transthoracic echocardiogram (TTE) and compared them to TTEs of otherwise healthy children evaluated for benign cardiac concerns. Stroke patients 29 days to 18 years of age at stroke ictus with confirmed acute AIS on imaging, availability of complete diagnostic studies of stroke risk factors, including TTE images available for central review, and at least 1 follow-up evaluation after index stroke were included. Presence of PFO and high-risk PFO features were assessed by 2 independent, blinded reviewers and compared between groups with the Fisher exact test. Stroke/TIA recurrence risk was determined from Cox proportional hazards models.

RESULTS

Of 154 children with first-ever AIS, 79 were eligible; 25 had cryptogenic AIS, and 54 had a known cause. PFO prevalence was higher in the cryptogenic group (7, 28%) compared to both the known stroke etiology group (3, 5.6%, p = 0.009) and controls without stroke (24, 11.5%, p = 0.03). There were no significant differences in presence of right-to-left shunt and atrial septal aneurysm. Median follow-up time for entire stroke cohort was 20.9 months. Stroke-free recurrence at 2-years did not differ between children with and without PFO (HR 2.0, 95% CI 0.4-9.3, p = 0.39).

DISCUSSION

PFO prevalence was higher in children with cryptogenic stroke compared to patients with AIS with known etiology and healthy controls. PFO was not associated with increased recurrence risk. Optimal secondary preventive treatment in children with cryptogenic stroke and PFO remains uncertain and requires further study.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that children with cryptogenic ischemic stroke have an increased frequency of PFO compared to children with ischemic stroke of known etiology and healthy controls.

Abstract TP282: Increased Resiliency of Astrocytic Mitochondria After Focal Ischemic Stroke in Juvenile Mice

Introduction: Astrocytes provide bioenergetic support to neurons, mediate neurovascular coupling, buffer extracellular ions, and limit excitotoxicity. They undergo many rapid changes following ischemic brain injury, which may shape the extent of damage. The role of astrocytic mitochondria in astroglial functioning and response to brain injury remain underexplored. We investigated age dependent changes to astrocytic mitochondria following focal ischemic stroke in vivo using a clot-based mouse model of middle cerebral artery (MCA) occlusion.

Methods: Male and female wildtype C57BL/6N neonatal mice underwent retro-orbital injections of AAV2/5 viral vectors containing mitochondrial targeted enhanced green fluorescent protein under the control of the astrocyte-specific glial fibrillary acidic protein promoter. Mice were allowed to age to 21-35 days (juvenile group) or 10-20 weeks (adult group). Proximal right MCA occlusion was provoked via photothrombosis using Rose Bengal dye and a targeted 532 nm laser beam. Control mice underwent sham procedures. Mice were perfused at 1, 3 or 24 hours post-stroke onset. Brains were processed and sectioned for mitochondrial analysis ( n = 3 animals/30 cells per time point per age group). Quantitative analyses were performed using a novel mitochondrial morphology scoring system.

Results: Penumbral astrocytic mitochondria are markedly reduced in density, demonstrate decreased network complexity and adopt punctate spherical morphology compared to contralateral non-stroke hemisphere and sham animals. These changes are present within 1 hour of stroke onset. Preliminary data indicate at least 50% change in adult mice. These changes are attenuated in juvenile mice, with increased recovery seen at 24 hours post-stroke ictus.

Conclusions: Astrocytic mitochondria within the penumbra undergo rapid loss and morphologic changes suggestive of dysfunction following proximal MCA occlusion. These changes are less severe in young mice indicating age-dependent resiliency of astrocytic mitochondria to ischemic injury. Further investigation into the mechanisms underlying astrocytic mitochondrial resiliency in the developing brain may reveal new strategies to limit stroke injury and improve outcomes.

Role of Astrocytic Mitochondria in Limiting Ischemic Brain Injury?

Until recently, astrocyte processes were thought to be too small to contain mitochondria. However, it is now clear that mitochondria are found throughout fine astrocyte processes and are mobile with neuronal activity resulting in positioning near synapses. In this review, we discuss evidence that astrocytic mitochondria confer selective resiliency to astrocytes during ischemic insults and the functional significance of these mitochondria for normal brain function.

The Spontaneous Ataxic Mouse Mutant Tippy is Characterized by a Novel Purkinje Cell Morphogenesis and Degeneration Phenotype

This study represents the first detailed analysis of the spontaneous neurological mouse mutant, tippy, uncovering its unique cerebellar phenotype. Homozygous tippy mutant mice are small, ataxic, and die around weaning. Although the cerebellum shows grossly normal foliation, tippy mutants display a complex cerebellar Purkinje cell phenotype consisting of abnormal dendritic branching with immature spine features and patchy, non-apoptotic cell death that is associated with widespread dystrophy and degeneration of the Purkinje cell axons throughout the white matter, the cerebellar nuclei, and the vestibular nuclei. Moderate anatomical abnormalities of climbing fiber innervation of tippy mutant Purkinje cells were not associated with changes in climbing fiber-EPSC amplitudes. However, decreased ESPC amplitudes were observed in response to parallel fiber stimulation and correlated well with anatomical evidence for patchy dark cell degeneration of Purkinje cell dendrites in the molecular layer. The data suggest that the Purkinje neurons are a primary target of the tippy mutation. Furthermore, we hypothesize that the Purkinje cell axonal pathology together with disruptions in the balance of climbing fiber and parallel fiber-Purkinje cell input in the cerebellar cortex underlie the ataxic phenotype in these mice. The constellation of Purkinje cell dendritic malformation and degeneration phenotypes in tippy mutants is unique and has not been reported in any other neurologic mutant. Fine mapping of the tippy mutation to a 2.1 MB region of distal chromosome 9, which does not encompass any gene previously implicated in cerebellar development or neuronal degeneration, confirms that the tippy mutation identifies novel biology and gene function.