A stroke occurring during or immediately following heart surgery is termed a perioperative stroke, representing a serious complication of cardiac procedures. This event involves an interruption of blood flow to the brain, leading to cell death and neurological impairment. While significant advancements in surgical techniques have been made, the risk remains a concern for patients and medical teams. The incidence of perioperative stroke ranges from 0.8% to 5.2% of all cardiac surgeries, but this rate can be significantly higher for complex procedures like combined valve and coronary artery bypass operations. Experiencing a stroke in the perioperative period increases the risk of mortality and can result in major long-term disability for survivors.
Mechanisms of Stroke During Cardiac Procedures
The majority of perioperative strokes are ischemic, caused by a blockage rather than bleeding. The single most common cause is cerebral embolization, where particulate matter or air travels from the surgical field to the brain’s blood vessels. This embolic material can consist of fragments of atherosclerotic plaque, calcium deposits, or clotted blood dislodged during the manipulation of the aorta.
Aortic manipulation, such as the application and removal of the cross-clamp or the insertion of cannulas, is a frequent trigger for releasing these emboli from the aortic wall. The use of the cardiopulmonary bypass (CPB) machine, which temporarily takes over heart and lung function, also contributes to the embolic load.
The CPB circuit can generate microemboli, including microscopic air bubbles or debris, which are pumped into the systemic circulation. Beyond embolization, a second major mechanism involves cerebral hypoperfusion, a reduction in blood flow to the brain. This often occurs when blood pressure drops significantly during the CPB run, leading to inadequate oxygen supply. Hypoperfusion can cause “watershed” strokes, occurring at the border zones between major cerebral vascular territories. Maintaining the Mean Arterial Pressure (MAP) below 64 mmHg for sustained periods during CPB is strongly associated with an increased risk of this ischemic injury.
Key Patient Risk Factors
Advanced age is consistently identified as the most significant risk factor, with the incidence of stroke rising sharply in patients over 75 years old. These older patients often have pre-existing, silent cerebrovascular disease that makes their brains more vulnerable to the stressors of surgery.
A prior history of stroke or a transient ischemic attack (TIA) acts as a strong independent predictor for a recurrent event. The presence of severe atherosclerosis in the ascending aorta greatly increases risk due to the high likelihood of plaque dislodgement during manipulation.
Chronic conditions like uncontrolled diabetes and kidney disease also contribute to a heightened risk profile. Postoperative atrial fibrillation (POAF), an irregular heart rhythm, is a major trigger for clot formation and subsequent stroke. The risk associated with POAF is compounded when it is accompanied by low cardiac output, which can lead to blood pooling and clot formation within the heart chambers. Patients undergoing emergency surgery or complex procedures combining multiple interventions also face a higher intrinsic risk due to prolonged surgical time and increased physiological stress.
Strategies for Prevention
Before surgery, pre-screening protocols often include epiaortic ultrasound to visualize the ascending aorta for hidden atherosclerotic plaque. Identifying significant plaque burden allows the surgical team to adjust their technique to avoid manipulating heavily diseased segments of the artery.
Intraoperatively, surgeons employ “no-touch” aortic techniques, which minimize or eliminate the need for an aortic cross-clamp, significantly reducing the chance of dislodging plaque. When a heart-lung machine is used, a single cross-clamp strategy is preferred over multiple clamps to limit manipulation. For high-risk patients who have recently suffered a stroke, elective cardiac surgery is often delayed for six to nine months to allow for neurological recovery.
To reduce embolic risk, techniques like insufflating the surgical field with carbon dioxide can help displace and absorb microscopic air bubbles before they travel to the brain. During the CPB run, perfusionists actively monitor and manage blood pressure, aiming to keep the Mean Arterial Pressure above a target of 70 mmHg, especially in patients with pre-existing vascular disease, to ensure adequate cerebral blood flow.
Post-operatively, management shifts to strict hemodynamic and metabolic control. Aggressive management of blood pressure and blood glucose levels is paramount. The management of Postoperative Atrial Fibrillation presents a challenge, requiring a careful balance between the need for anticoagulation to prevent stroke and the risk of major bleeding at the surgical site.
Immediate Treatment and Prognosis
Rapid diagnosis is crucial, but challenging since patients are often sedated or recovering from anesthesia. A complete neurological examination is performed immediately, followed by computed tomography (CT) or magnetic resonance imaging (MRI) to confirm the diagnosis and determine if the stroke is ischemic or hemorrhagic.
Acute treatment for ischemic stroke involving tissue plasminogen activator (tPA) is often restricted in this population. Major surgery within the preceding two weeks is considered a strong contraindication for tPA due to the risk of catastrophic bleeding. This limitation forces medical teams to rely on alternative treatments or supportive care.
In cases where a large vessel in the brain is blocked, endovascular thrombectomy, a procedure to mechanically remove the clot, may be considered. Acute management focuses on neuroprotective supportive care, including maintaining oxygenation, controlling fever, and managing blood glucose.
The prognosis for patients who suffer a perioperative stroke is worse than for those who experience a stroke outside of the surgical setting. The in-hospital mortality rate for cardiac surgery patients who have a stroke can be as high as 30%. For survivors, long-term disability is common, with moderate to severe disability affecting over two-thirds of these patients.