Cerebral embolization during transcatheter aortic valve implantation

Role of Transcranial Doppler in Cardiac Surgery Patients

Abstract

Purpose of Review

This review discusses applications of transcranial Doppler (TCD) in cardiac surgery, its efficacy in preventing adverse events such as postoperative cognitive decline and stroke, and its impact on clinical outcomes in these patients.

Recent Findings

TCD alone and in combination with other neuromonitoring modalities has attracted attention as a potential monitoring tool in cardiac surgery patients. TCD allows not only the detection of microemboli and measurement of cerebral blood flow velocity in cerebral arteries but also the assessment of cerebral autoregulation.

Summary

Neuromonitoring is critically important in cardiac surgery as surgical and anesthetic interventions as well as several other factors may increase the risk of cerebral embolization (gaseous and particulate) and cerebral perfusion anomalies, which may lead to adverse neurological events. As an experimental tool, TCD has revealed a possible association of poor neurological outcome with intraoperative cerebral emboli and impaired cerebral perfusion. However, to date, there is no evidence that routine use of transcranial Doppler can improve neurological outcome after cardiac surgery.

Transcranial doppler and near infrared spectroscopy in the perioperative period

PURPOSE OF REVIEW

Maintenance of adequate blood flow and oxygen to the brain is one of the principal endpoints of all surgery and anesthesia. During operations in general anesthesia, however, the brain is at particular risk for silent ischemia. Despite this risk, the brain still remains one of the last monitored organs in clincial anesthesiology.

RECENT FINDINGS

Transcranial Doppler (TCD) sonography and near-infrared spectroscopy (NIRS) experience a revival as these noninvasive technologies help to detect silent cerebral ischemia. TCD allows for quantification of blood flow velocities in basal intracranial arteries. TCD-derived variables such as the pulsatility index might hint toward diminished cognitive reserve or raised intracranial pressure. NIRS allows for assessment of regional cerebral oxygenation. Monitoring should be performed during high-risk surgery for silent cerebral ischemia and special circumstances during critical care medicine. Both techniques allow for the assessment of cerebrovascular autoregulation and individualized management of cerebral hemodynamics.

SUMMARY

TCD and NIRS are noninvasive monitors that anesthesiologists apply to tailor cerebral oxygen delivery, aiming to safeguard brain function in the perioperative period.

Embolic Protection Devices in Transcatheter Aortic Valve Replacement

The initially reported periprocedural neurological events rates associated with transcatheter aortic valve replacement raised concerns that ultimately led to the development and to the clinical research of novel embolic protection devices. Although the reduction of clinical stroke is a desired goal, the current research design of embolic protection devices focuses on surrogate markers of the clinical disease, primarily on silent central nervous system lesions observed in postprocedural diffuse-weighted magnetic resonance imaging and cognitive function testing. As the mere presence of particulate debris in brain matter may not correlate with the extent of brain injury, cognitive function, or quality of life, the clinical significance of embolic protection devices has yet to be determined, and interpretation of study results with regard to real-life clinical use should be viewed accordingly. The purpose of this article is to provide an overview of the updated ongoing clinical research on embolic protection devices and present its major caveats.

Neurological complications of cardiac surgery

As increasing numbers of elderly people undergo cardiac surgery, neurologists are frequently called upon to assess patients with neurological complications from the procedure. Some complications mandate acute intervention, whereas others need longer term observation and management. A large amount of published literature exists about these complications and guidance on best practice is constantly changing. Similarly, despite technological advances in surgical intervention and modifications in surgical technique to make cardiac procedures safer, these advances often create new avenues for neurological injury. Accordingly, rapid and precise neurological assessment and therapeutic intervention rests on a solid understanding of the evidence base and procedural variables.

Mechanisms and management of TAVR-related complications

Patients with severe aortic stenosis who are at high surgical risk or not considered to be suitable candidates for surgical aortic valve replacement are increasingly being treated with transcatheter aortic valve replacement (TAVR). Although this novel treatment modality has been proven to be effective in this patient population, serious complications occur in approximately one-third of patients during the month after the procedure. Such events include myocardial infarction, cerebrovascular events, vascular complications, bleeding, acute kidney injury, valve regurgitation, valve malpositioning, coronary obstruction, and conduction disturbances and arrhythmias, which can all lead to death. Prevention of these complications should be based on patient screening and selection by a dedicated 'heart team' and the use of multimodality imaging. Anticipation and early recognition of these complications, followed by prompt management using a wide range of percutaneous or surgical rescue interventions, is vital to patient outcome. Continuous patient assessment and reporting of complications according to standardized definitions, in addition to growing operator experience and upcoming technological refinements, will hopefully reduce the future rate of complications related to this procedure.