Delirium after heart surgery triples the risk of adverse cardiac events

Patients experiencing postoperative delirium (POD) after elective heart surgery shouldered more than triple the risk of experiencing a major adverse cardiac event (MACE) such as stroke, heart attack or cardiovascular death within one year of discharge, researchers reported in PLOS One.

“Delirium is defined as a temporary state of mental confusion and fluctuating consciousness, and it occurs in as many as 30 to 50 percent of patients after cardiac surgery,” wrote lead author Masato Ogawa and colleagues. “It was previously believed that delirium was a reversible cognitive impairment; however, recently, long-term adverse effects due to delirium were revealed. … Nevertheless, little evidence is available on the relationship between POD, postoperative frailty, and cardiovascular events.”

The researchers studied 329 consecutive patients—mean age 68.6; 55.8 percent men—undergoing elective cardiac surgery at Kobe University Hospital in Japan. They enrolled patients who required coronary artery bypass graft (CABG) surgery, valve replacement or repair, or CABG with concomitant valve replacement or repair.

A screening checklist was used to assess postoperative delirium (POD) every eight hours from the first day after surgery until up to five days after surgery. In addition, frailty—defined as diminished handgrip strength or walking speed—was measured within one week before surgery and again just before hospital discharge.

A total of 13.2 percent of patients were found to have POD, while 27 percent had postoperative frailty. The delirious individuals were nearly three times more likely than other patients to have postoperative frailty and 3.36 times more likely to experience MACE during the median follow-up of 311 days. In comparison, postoperative frailty was independently associated with MACE with a hazard ratio of 2.21.

“Both postoperative frailty and POD were associated with the incidence of MACE, while POD was the stronger predictor of MACE,” Ogawa et al. wrote. “Thus, POD and frailty play critical roles in the risk stratification of patients undergoing cardiac surgery.”

The authors said their study had lower rates of POD than previously reported, likely because it evaluated only elective surgeries and the average age of patients was lower. Older patients and those requiring urgent or emergency operations could be at greater risk of developing POD.

Ogawa and colleagues also noted patients who developed POD in their study endured longer surgery times than other individuals.

“Prolonged duration of surgery led to longer cardiopulmonary bypass times and aortic cross-clamp time,” they wrote. “During cardiac surgery using cardiopulmonary bypass, neuroinflammatory damage of the brain may occur due to microembolism, reduced cerebral flow, and fluid shift. These neurotransmitters may be responsible for the occurrence of POD in our cohort.”

The link between POD and MACE, they added, is multifactorial. Decline of cognitive function can lead to poor medication adherence and a drop in social activity and physical functioning, all of which could increase the risk of cardiac events.