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Cerebrovascular Complications of Cardiac Surgery
Background
Cardiac surgery has undergone a rapid and extraordinary development since mid-1940s. Many operations that were once considered experimental are now commonplace, with thousands of open heart procedures performed annually in the United States. At present, an estimated 1 million patients undergo cardiac surgery throughout the world every year. Neurological impairment is a well-known complication of cardiac surgery, resulting in longer hospitalizations, increased costs, and an escalation in morbidity and mortality. The types of neurological complications vary and can include peripheral neuropathy, encephalopathy, cognitive impairment, and stroke. Overall, in prospective studies, transient neurological complications have been noted in 61% of cardiac surgery patients . Although refinements in surgical and anesthesia techniques have improved neurological outcomes, the number of elderly patients undergoing cardiac surgery has also increased, and thus cerebrovascular complications in particular continue to occur.
One prospective study of 16,184 consecutive patients indicates that the specific stroke risk depends on the type of cardiac surgical procedure performed . While the overall incidence of stroke in cardiac surgery is generally estimated to be 4.6%, the risk of ischemic stroke varies depending on the actual surgical procedure undertaken: coronary artery bypass grafting (CABG), 3.8%; beating-heart CABG, 1.9%; aortic valve surgery, 4.8%; mitral valve surgery, 8.8%; double or triple valve surgery, 9.7%; and CABG and valve surgery, 7.4% . Regarding combined CABG and a left-sided cardiac procedure (such as aortic or mitral valve replacement, AVR or MVR, respectively), it has been estimated that 15.8% of patients have neurological complications: 8.5% with stroke or transient ischemic attack (TIA) and 7.3% with new intellectual deterioration . Thus, a combined procedure appears to carry a higher cerebrovascular risk than CABG performed in isolation.
Cardiac Surgical Procedures
Coronary Artery Bypass Graft Surgery
CABG is the most common major cardiovascular operation performed. Preoperative factors that elevate perioperative CABG stroke risk include the diagnoses of diabetes, prior stroke, older age, female gender, smoking, hypertension, left main coronary disease, mild renal impairment, and elevated high-sensitivity preoperative C-reactive protein. Additionally, both preoperative stroke and TIA are also risk factors for in-hospital mortality .
Early studies suggested a decrease in postoperative stroke rates in patients undergoing off-pump CABG compared to patients undergoing the traditional on-pump operation. This was thought to be due to less aortic manipulation during off-pump surgery, but conflicts in the literature exist . A single-center study of 2516 consecutive patients noted that off-pump CABG reduced the incidence of early postoperative stroke (symptoms noted just after emergence of anesthesia). However, the risk of delayed stroke (normal neurologically emerging from anesthesia, but symptoms presenting within 30 days after surgery) was no different between the on- and off-pump CABG patients . Similarly, in 2013, the CORONARY (CABG Off or On Pump Revascularization Study) trial enrolled 4752 patients, randomly assigning them to on-pump versus off-pump CABG. Stroke rates, as well as quality of life and cognitive function did not differ significantly between the two groups at 30 days and 1 year . The potential mechanisms of cerebral infarction in the cardiac surgery population is explored in a later section.
Valve Surgery: Aortic Valve Replacement and Mitral Valve Replacement
Aortic Valve Replacement
Patients aged 50–69 years who received mechanical valves had better long-term survival after AVR than those with bioprosthetic valves. The risk of stroke was similar; however, patients with bioprostheses had a higher risk of aortic valve reoperation and a lower risk of major bleeding. The specific risk of ischemic stroke during AVR is estimated to be 2.3–4.8% .
Mitral Valve Replacement
A systematic review and meta-analysis of data on octogenarians who underwent MVR or mitral valve repair (MVRpr) yielded 16 retrospective studies. The pooled proportion of postoperative stroke were 4% for patients undergoing MVR (6 studies, 2945 patients, 95% CI: 3–7%) and 3% in those undergoing MVRpr (3 studies, 348 patients, 95% CI: 1–8%) .
Minimally Invasive Cardiac Surgical Procedures
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