The occurrence of paradoxical embolus is always a consideration in pregnancy because of a tendency to form clots in the pelvic and leg veins, coupled with increased right heart pressures. Amniotic fluid embolus may rarely cause stroke in this manner and should be suspected in multiparous women who have had uterine tears; there are almost invariably signs of acute pulmonary disease from simultaneous occlusion of lung vessels. A rare peripartum cardiomyopathy is yet another source of embolic stroke.
Incident to cardiac arrest and bypass surgery, there is risk of both generalized and focal ischemia of the brain. Improved operative techniques have lessened the frequency of these complications but they are still distressingly frequent. Fortunately, most are transient. Atherosclerotic plaques may be dislodged during cross-clamping of the proximal aorta and are an important source of cerebral emboli. In the last decade, the incidence of stroke related to cardiac surgery has dropped to between 2 and 3 percent in large series numbering thousands of patients (Libman et al; Ahlgren and Arén). Advanced age, congestive heart failure, and more complex surgeries have been listed as risk factors for stroke from various reports.
Representative is a retrospective study by Dashe and colleagues, in which 2 percent had strokes; most minor, but the risk was greatly increased on the side of a carotid stenosis. Curiously, almost one-fifth of postoperative strokes in some series have been of lacunar type. In one prospective study of 2,108 patients who underwent coronary operations in several institutions, 3 percent had strokes or TIAs; the adverse effects mostly occurred in older patients and were transient (Roach et al). Mohr and coworkers (1978) examined 100 consecutive cases preand postoperatively and observed two types of stroke-like complications—one occurring immediately after the operation and the other after an interval of days or weeks. The immediate neurologic disorder consisted of a delay in awakening from the anesthesia; subsequently there was slowness in thinking, disorientation, agitation, combativeness, visual hallucinations, and poor registration and recall of what was happening. These symptoms, in the form of a confusional state sometimes verging on delirium or acute psychosis, usually cleared within 5 to 7 days, although some patients were not entirely normal mentally weeks later. As the confusion cleared, about half of the patients were found to have small visual field defects, dyscalculia, Balint syndrome (see Chap. 21), alexia, or defects of perception suggestive of lesions in the parietooccipital regions. The immediate effects were attributed to hypotension and various types of embolisms (atherosclerotic, air, silicon, fat, platelets). The delayed effects were more clearly embolic and were especially frequent in patients having prosthetic valve replacements or other valve repairs.
In addition to overt and covert strokes detected only by imaging, a degree of cognitive decline and depression is to be expected in a proportion of patients undergoing coronary artery bypass grafting. The frequency of these changes is reported to be between 40 and 70 percent. It is our impression that many of these neurologic complications, both small strokes and cognitive abnormalities, pass unnoticed in many cardiac surgical units. This was emphasized in the study by McKhann and colleagues, who tested several neuropsychologic functions and found that only 12 percent of patients escaped some type of early cognitive problem. However, his group and others, for example, Mülges and colleagues, have shown that only a small proportion (13 percent in the latter series) retained permanent effects 5 years after operation. Others have reported higher rates, but it is clear that the cognitive problems improve over time in the majority of patients.