What is the likely cause of a seizure in a patient with a history of vascular disease who has undergone Coronary Artery Bypass Grafting (CABG) and carotid endarterectomy?

Seizure Post-CABG and Carotid Endarterectomy

The most likely cause of seizure in this patient is cerebral hyperperfusion syndrome, occurring in approximately 1% of cases following carotid endarterectomy, particularly in patients with severe bilateral carotid disease and compromised cerebral circulation. 1

Primary Mechanism: Cerebral Hyperperfusion Syndrome

Hypoperfusion-related seizures are the predominant mechanism following carotid revascularization procedures, occurring when chronically ischemic brain tissue is suddenly exposed to normal or elevated perfusion pressures after removal of a high-grade stenosis. 1

Key Pathophysiological Features:

• Impaired cerebrovascular autoregulation in chronically hypoperfused brain regions leads to inability to regulate blood flow when perfusion pressure suddenly increases after endarterectomy 2, 3, 4

• Severe bilateral carotid disease (present in patients requiring both CABG and carotid endarterectomy) significantly increases seizure risk, as these patients have the most compromised collateral circulation 2, 4

• Timing is characteristic: seizures typically occur 3-8 days postoperatively (range 5-13 days), though some occur within 36 hours 2, 3, 4

• Hypertension is universally present at seizure onset, with all patients in reported series having significantly elevated blood pressure when seizures develop 2, 3, 4

Clinical Presentation Pattern

Seizure Characteristics:

• Focal motor seizures contralateral to the side of endarterectomy are the typical initial presentation 3

• Progression to generalized tonic-clonic seizures occurs in approximately 75% of cases 3

• Associated symptoms include severe headache, confusion, and focal neurological deficits 5, 2, 3

High-Risk Patient Profile:

• Severe bilateral carotid stenosis (>70% stenosis causing >25% reduction in cerebral perfusion pressure) 4

• Labile hypertensives with poor preoperative blood pressure control 2

• Concurrent vertebral or subclavian stenoses further compromising collateral circulation 2

• >50% drop in middle cerebral artery blood flow velocity during carotid clamping 2

Differential Considerations

Embolic Stroke:

• Embolization of atherothrombotic debris from the ascending aorta during CABG is the most common cause of perioperative stroke, but typically presents immediately postoperatively, not days later 1

• Microembolism during carotid stenting procedures causes subclinical ischemic injury but rarely presents as isolated seizures 1

Intracranial Hemorrhage:

• Hemorrhagic transformation occurs in <1% of cases and is associated with severe hypertension and anticoagulation 1

• CT scanning in seizure patients shows normal scans (37.5%), white matter edema (37.5%), or hemorrhage (25%) 2

Diagnostic Approach

Immediate Evaluation:

• Emergency CT scan to exclude intracranial hemorrhage and identify white matter edema characteristic of hyperperfusion syndrome 5, 2

• CT perfusion imaging reveals reduced time-to-peak, reduced mean-transit-time, increased cerebral blood volume, and increased cerebral blood flow in the affected hemisphere 5

• Transcranial Doppler demonstrates elevated middle cerebral artery velocities if performed acutely 2

• Blood pressure measurement will invariably show significant hypertension at seizure onset 2, 3, 4

Imaging Findings:

• White matter edema on CT is the most common finding in hyperperfusion syndrome 5, 2

• Normal CT scan does not exclude the diagnosis, occurring in approximately one-third of cases 2

• MRI with diffusion-weighted imaging can identify concurrent ischemic injury if embolic stroke is suspected 6

Management Algorithm

Acute Seizure Control:

• Lorazepam for immediate seizure termination 3

• Phenytoin sodium for ongoing seizure prophylaxis 3

Blood Pressure Management:

Aggressive antihypertensive therapy is critical, as hypertension is both a precipitant and perpetuating factor in hyperperfusion syndrome. 1, 2

• Target blood pressure reduction to prevent ongoing hyperperfusion injury while avoiding hypotension 2

• Continuous monitoring in intensive care setting is required 5, 2

Critical Pitfall:

Clinicians in acute medical units are frequently unaware of post-carotid endarterectomy hyperperfusion syndrome and may fail to treat hypertension aggressively enough, leading to worse outcomes. 2 The combination of severe hypertension and elevated cerebral blood flow velocities requires immediate recognition and treatment.

Prognosis and Outcomes

• Post-ictal neurological deficits develop in approximately 87.5% of patients (stroke in 62.5%, TIA in 25%) 2

• Complete recovery occurs in approximately 62.5% of patients without evidence of stroke on CT scan 3

• Chronic seizure disorder develops in approximately 12.5% of cases 3

• Death or disabling stroke occurs in approximately 25% of patients who develop post-endarterectomy seizures 2

Preventive Strategies:

• Meticulous postoperative blood pressure control is essential, particularly in patients with severe bilateral disease 1, 2, 4

• Identification of high-risk patients (severe bilateral stenosis, labile hypertension, poor collateral circulation) allows for enhanced monitoring 2, 4

• Dual antiplatelet therapy (aspirin 81-325 mg plus clopidogrel 75 mg daily) for minimum 30 days after carotid procedures 1