Neuroprotection during cardiac surgery

Prevention of Oxidative Damage in Spinal Cord Ischemia Upon Aortic Surgery: First-In-Human Results of Shock Wave Therapy Prove Safety and Feasibility

Background Spinal cord ischemia (SCI) remains a devastating complication after aortic dissection or repair. A primary hypoxic damage is followed by a secondary damage resulting in further cellular loss via apoptosis. Affected patients have a poor prognosis and limited therapeutic options. Shock wave therapy (SWT) improves functional outcome, neuronal degeneration and survival in murine spinal cord injury. In this first-in-human study we treated 5 patients with spinal cord ischemia with SWT aiming to prove safety and feasibility. Methods and Results Human neurons were subjected to ischemic injury with subsequent SWT. Reactive oxygen species and cellular apoptosis were quantified using flow cytometry. Signaling of the antioxidative transcription factor NRF2 (nuclear factor erythroid 2-related factor 2) and immune receptor Toll-like receptor 3 (TLR3) were analyzed. To assess whether SWT act via a conserved mechanism, transgenic tlr3^-/- zebrafish created via CRISPR/Cas9 were subjected to spinal cord injury. To translate our findings into a clinical setting, 5 patients with SCI underwent SWT. Baseline analysis and follow-up (6 months) included assessment of American Spinal Cord Injury Association (ASIA) impairment scale, evaluation of Spinal Cord Independence Measure score and World Health Organization Quality of Life questionnaire. SWT reduced the number of reactive oxygen species positive cells and apoptosis upon ischemia via induction of the antioxidative factor nuclear factor erythroid 2-related factor 2. Inhibition or deletion of tlr3 impaired axonal growth after spinal cord lesion in zebrafish, whereas tlr3 stimulation enhanced spinal regeneration. In a first-in-human study, we treated 5 patients with SCI using SWT (mean age, 65.3 years). Four patients presented with acute aortic dissection (80%), 2 of them exhibited preoperative neurological symptoms (40%). Impairment was ASIA A in 1 patient (20%), ASIA B in 3 patients (60%), and ASIA D in 1 patient (20%) at baseline. At follow-up, 2 patients were graded as ASIA A (40%) and 3 patients as ASIA B (60%). Spinal cord independence measure score showed significant improvement. Examination of World Health Organization Quality of Life questionnaires revealed increased scores at follow-up. Conclusions SWT reduces oxidative damage upon SCI via immune receptor TLR3. The first-in-human application proved safety and feasibility in patients with SCI. SWT could therefore become a powerful regenerative treatment option for this devastating injury.

Selective Cerebrospinal Fluid Hypothermia: Bioengineering Development and In Vivo Study of an Intraventricular Cooling Device (V-COOL)

Hypothermia is a promising therapeutic strategy for severe vasospasm and other types of non-thrombotic cerebral ischemia, but its clinical application is limited by significant systemic side effects. We aimed to develop an intraventricular device for the controlled cooling of the cerebrospinal fluid, to produce a targeted hypothermia in the affected cerebral hemisphere with a minimal effect on systemic temperature. An intraventricular cooling device (acronym: V-COOL) was developed by in silico modelling, in vitro testing, and in vivo proof-of-concept application in healthy Wistar rats (n = 42). Cerebral cortical temperature, rectal temperature, and intracranial pressure were monitored at increasing flow rate (0.2 to 0.8 mL/min) and duration of application (10 to 60 min). Survival, neurological outcome, and MRI volumetric analysis of the ventricular system were assessed during the first 24 h. The V-COOL prototyping was designed to minimize extra-cranial heat transfer and intra-cranial pressure load. In vivo application of the V-COOL device produced a flow rate-dependent decrease in cerebral cortical temperature, without affecting systemic temperature. The target degree of cerebral cooling (- 3.0 °C) was obtained in 4.48 min at the flow rate of 0.4 mL/min, without significant changes in intracranial pressure. Survival and neurological outcome at 24 h showed no significant difference compared to sham-treated rats. MRI study showed a transient dilation of the ventricular system (+ 38%) in a subset of animals. The V-COOL technology provides an effective, rapid, selective, and safe cerebral cooling to a clinically relevant degree of - 3.0 °C.

Decreasing postoperative cognitive deficits after heart surgery: protocol for a randomized controlled trial on cognitive training

Background

The occurrence of postoperative cognitive deficits, especially after heart surgery, has been demonstrated in several studies. These deficits can clearly be noticed by the patients and by their close relatives in daily life. Furthermore, postoperative cognitive deficits can decrease quality of life in social functioning and earning capacity. The aim of this study is to investigate whether early postoperative cognitive training can reduce subjective and objective postoperative cognitive deficits.

Methods

The proposed study is a multicenter, two-arm, randomized controlled trial involving 144 elderly patients undergoing elective heart-valve surgery with extracorporeal circulation. Patients will be assigned to either a training group or a control group. The intervention involves paper-and-pencil-based cognitive training, which is conducted for 36 min over a period of 18 days. The training starts about 1 week after surgery and is carried out during the hospitalized rehabilitation phase. The control group will not receive cognitive training or a placebo intervention. A detailed assessment of psychological functions and health-related quality of life prior to surgery at discharge from rehabilitation and 3 and 12 months after discharge will be performed. The primary outcome of this trial is the training effect on objective cognitive functions at discharge from rehabilitation. Secondary outcomes are the training effect on objective and subjective cognitive functions (3 and 12 months after discharge), depression, health-related quality of life, and the impact of perioperative cerebral ischemia on the training effect. Perioperative cerebral ischemia will be measured with postoperative magnetic resonance imaging including diffusion-weighted sequences.

Discussion

Should it be shown that our cognitive training can improve postoperative cognitive deficits and quality of life, one possibility could be to integrate this intervention into early rehabilitation. Furthermore, we hope that the investigation of perioperative ischemia by diffusion-weighted magnetic resonance imaging will improve our understanding of neurobiological factors influencing the course of postoperative cognitive plasticity.

Trial registration

German Clinical Trials Register (DRKS), DRKS00015512. Retrospectively registered on 21 September 2018.

Upregulation of GLT-1 via PI3K/Akt Pathway Contributes to Neuroprotection Induced by Dexmedetomidine

Perioperative ischemic stroke usually leads to neurological dysfunction caused by neuron death. During the ischemic condition, excitotoxity due to extracellular glutamate accumulation is a main mechanism of neuron damage. The clearance of glutamate mainly depends on glutamate transporter-1 (GLT-1) which is expressed in astrocytes. Dexmedetomidine, an α2 adrenergic receptor agonist, is proved to induce neuroprotection. This study was set out to investigate the glutamate-related mechanism involved in the neuroprotective effect of dexmedetomidine. Middle cerebral artery occlusion (MCAO) was used as a model of ischemic stroke in our study. We determined Neurological deficit scores (NDS) and Magnetic resonance imaging (MRI) at three points (2, 6, and 24 h) after middle cerebral artery occlusion (MCAO) to evaluate the neuroprotective effect of dexmedetomidine. Besides, we performed western blot (6 and 24 h after MACO) and immunofluorescent staining (24 h after MCAO) to observe the expression of GLT-1. The effect and mechanism of dexmedetomidine on GLT-1 in primary cultured astrocytes were investigated using western blot and RT-PCR. Our results showed that pretreatment with dexmedetomidine improved NDS and reduced infarct volume as well as upregulating GLT-1 expression. Furthermore, using Atipamezole and LY294002, we found that dexmedetomidine significantly increased GLT-1 levels in astrocytes via activating α2 adrenergic receptor and PI3K/AKT pathway both in vitro and in vivo study. Overall, our present study indicated that dexmedetomidine had neuroprotective effects on ischemia stroke and upregulation of GLT-1 levels by PI3K/AKT dependent pathway might be the potential mechanism.

Effects of hypoxic preconditioning on memory evaluated using the T-maze behavior test

Perioperative brain ischemia and stroke are leading causes of morbidity and mortality. Brief hypoxic preconditioning is known to have protective effects against hypoxic-ischemic insult in the brain. Current studies on the neuroprotective effects of ischemic preconditioning are based on histologic findings and biomarker changes. However, studies regarding effects on memory are rare. To precondition zebrafish to hypoxia, they were exposed to a dissolved oxygen (DO) concentration of 1.0 ± 0.5 mg/L in water for 30 s. The hypoxic zebrafish were then exposed to 1.0 ± 0.5 mg/L DO until the third stage of hypoxia, for 10 min ± 30 s. Zebrafish were assessed for memory retention after the hypoxic event. Learning and memory were tested using the T-maze, which evaluates memory based on whether or not zebrafish moves to the correct target compartment. In the hypoxic preconditioning group, infarct size was reduced compared with the hypoxic-only treated zebrafish group; memory was maintained to a degree similar to that in the hypoxia-untreated group. The hypoxic-only group showed significant memory impairments. In this study, we used a hypoxic zebrafish model and assessed the effects of ischemic preconditioning not only on histological damages but also on brain function, especially memory. This study demonstrated that a brief hypoxic event has protective effects in hypoxic brain damage and helped maintain memory in zebrafish. In addition, our findings suggest that the zebrafish model is useful in rapidly assessing the effects of ischemic preconditioning on memory.

Combined carotid endarterectomy and transcatheter aortic valve replacement: Technique and outcomes

BACKGROUND

Stroke and transient ischemic attack after transcatheter aortic valve replacement results in significantly higher morbidity and mortality. Severe carotid artery disease may be a contributing factor to this increased risk. We report our technique and outcomes of combined carotid endarterectomy (CEA) with transcatheter aortic valve replacement (TAVR).

METHODS

From March 2013 to November 2017 a total of 753 TAVRs were performed at our institution for symptomatic severe aortic stenosis. Of this group, 16 patients underwent concomitant TAVR and CEA. A retrospective review was performed to assess risk, outcomes, and short-term survival.

RESULTS

Sixteen patients underwent concomitant CEA/TAVR procedures for severe carotid and severe aortic stenosis. The mean Society of Thoracic Surgeons (STS) Risk Score was 7.0 ± 4.7. All patients had severe carotid artery stenosis and aortic stenosis. Nine patients had a transfemoral TAVR approach and eight patients had a transapical TAVR approach. The mean length of stay was 6.4 ± 3.7 days. At 30 days there were no cerebrovascular events and no mortalities.

CONCLUSIONS

The use of concomitant CEA and TAVR in patients with severe aortic stenosis and severe carotid stenosis can be done safely without increased risk of complications. This approach may reduce the risk of stroke associated with TAVR in appropriately selected patients.

Incidence and causes of silent and symptomatic stroke following surgical and transcatheter aortic valve replacement: a comprehensive review

Stroke associated with aortic valve replacement in calcific aortic stenosis, either via transcatheter implantation (TAVR) or via surgical replacement (SAVR), is one of the most devastating complications. However, data concerning the clinical impact and incidence of clinical and silent stroke complicating SAVR and TAVR are varying. This comprehensive review of the literature explores the genuine incidence of neurological events after these procedures. Additionally, potential factors responsible for the discrepancies in stroke rates in the current literature are analysed and a lack of uniform neurological definitions and standardized neurological assessments revealed. Current stroke rates after TAVR show a decline from 7 to 1.7-4.8% in recent studies. Randomized studies comparing TAVR with SAVR yielded initially a significantly higher stroke rate after TAVR procedures as opposed to SAVR. Recently published data showed opposite results with strokes being higher following SAVR. Current data concerning stroke after surgical valve replacement report significantly higher rates of clinical strokes (17%) than previously mentioned in the literature (≤4.9%). Silent cerebral lesions were detected in 68-93% after TAVR and 38-54% after SAVR. A broader application of cerebral protection devices may help to reduce embolic cerebral events.

Cerebral ischemia during surgery: an overview

Cerebral ischemia is the pathophysiological condition in which the oxygenated cerebral blood flow is less than what is needed to meet cerebral metabolic demand. It is one of the most debilitating complications in the perioperative period and has serious clinical sequelae. The monitoring and prevention of intraoperative cerebral ischemia are crucial because an anesthetized patient in the operating room cannot be neurologically assessed. In this paper, we provide an overview of the definition, etiology, risk factors, and prevention of cerebral ischemia during surgery.

Shock Wave Treatment Protects From Neuronal Degeneration via a Toll-Like Receptor 3 Dependent Mechanism: Implications of a First-Ever Causal Treatment for Ischemic Spinal Cord Injury

Background

Paraplegia following spinal cord ischemia represents a devastating complication of both aortic surgery and endovascular aortic repair. Shock wave treatment was shown to induce angiogenesis and regeneration in ischemic tissue by modulation of early inflammatory response via Toll‐like receptor (TLR) 3 signaling. In preclinical and clinical studies, shock wave treatment had a favorable effect on ischemic myocardium. We hypothesized that shock wave treatment also may have a beneficial effect on spinal cord ischemia.

Methods and Results

A spinal cord ischemia model in mice and spinal slice cultures ex vivo were performed. Treatment groups received immediate shock wave therapy, which resulted in decreased neuronal degeneration and improved motor function. In spinal slice cultures, the activation of TLR3 could be observed. Shock wave effects were abolished in spinal slice cultures from TLR3^−/− mice, whereas the effect was still present in TLR4^−/− mice. TLR4 protein was found to be downregulated parallel to TLR3 signaling. Shock wave–treated animals showed significantly better functional outcome and survival. The protective effect on neurons could be reproduced in human spinal slices.

Conclusions

Shock wave treatment protects from neuronal degeneration via TLR3 signaling and subsequent TLR4 downregulation. Consequently, it represents a promising treatment option for the devastating complication of spinal cord ischemia after aortic repair.

Predictors of electrocerebral inactivity with deep hypothermia

OBJECTIVE

Cooling to electrocerebral inactivity (ECI) by electroencephalography (EEG) remains the gold standard to maximize cerebral and systemic organ protection during deep hypothermic circulatory arrest (DHCA). We sought to determine predictors of ECI to help guide cooling protocols when EEG monitoring is unavailable.

METHODS

Between July 2005 and July 2011, 396 patients underwent thoracic aortic operation with DHCA; EEG monitoring was used in 325 (82%) of these patients to guide the cooling strategy, and constituted the study cohort. Electroencephalographic monitoring was used for all elective cases and, when available, for nonelective cases. Multivariable linear regression was used to assess predictors of the nasopharyngeal temperature and cooling time required to achieve ECI.

RESULTS

Cooling to a nasopharyngeal temperature of 12.7°C or for a duration of 97 minutes was required to achieve ECI in >95% of patients. Only 7% and 11% of patients achieved ECI by 18°C or 50 minutes of cooling, respectively. No independent predictors of nasopharyngeal temperature at ECI were identified. Independent predictors of cooling time included body surface area (18 minutes/m(2)), white race (7 minutes), and starting nasopharyngeal temperature (3 minutes/°C). Low complication rates were observed (ischemic stroke, 1.5%; permanent paraparesis/paraplegia, 1.5%; new-onset dialysis, 2.2%; and 30-day/in-hospital mortality, 4.3%).

CONCLUSIONS

Cooling to a nasopharyngeal temperature of 12.7°C or for a duration of 97 minutes achieved ECI in >95% of patients in our study population. However, patient-specific factors were poorly predictive of the temperature or cooling time required to achieve ECI, necessitating EEG monitoring for precise ECI detection.

Avoiding stroke during cardiac surgery

The life saving benefits of cardiac surgery are frequently accompanied by negative side effects such as stroke, that occurs with an incidence of 2%-13% dependent to type of surgery. The etiology is most likely multifactorial with embolic events considered as main contributor. Although stroke presents a common complication, no guidelines for any routine use of pharmacological substances or non-pharmacological strategies exist to date. Non-pharmacological strategies include monitoring of brain oxygenation and perfusion with devices such as near infrared spectroscopy and Transcranial Doppler help. Epiaortic and transesophageal echocardiography visualize aorta pathology, enabling the surgeon to sidestep atheromatous segments. Additionally can the use of specially designed aortic cannulae and filters help to reduce embolization. Brain perfusion can be improved by using antero- or retrograde cerebral perfusion during deep hypothermic circulatory arrest, by tightly monitoring mean arterial blood pressure and hemodilution. Controlling perioperative temperature and glucose levels may additionally help to ameliorate secondary damage. Many pharmacological compounds have been shown to be neuroprotective in preclinical models, but clinical studies failed to confirm these results so far. Remacemide, an NMDA-receptor-antagonist showed a significant drug-based neuroprotection during cardiac surgery. Other substances currently assessed in clinical trials whose results are still pending are acadesine, an adenosine-regulating substance, the free radical scavenger edaravone and the local anesthetic lidocaine. Stroke remains as significant complication after cardiac surgery. Non-pharmacological strategies allow perioperative caregivers to detect injurious events and to ameliorate stroke and its sequelae. Considering the multi-factorial etiology though, stroke prevention will likely have to be addressed with an individualistic combination of different strategies and substances.