FREQUENCY AND PREDICTORS OF COGNITIVE DECLINE IN PATIENTS UNDERGOING CORONARY ARTERY BYPASS GRAFT SURGERY IN MIXED PAKISTANI POPULATION

ABSTRACT 

Background: Significant neuro-cognitive decline have been documented from developed countries in patients who have undergone coronary artery bypass grafting (CABG) surgery. Cognitive aspects are important in terms of quality of life and outcome. 

Aims:  To document the frequency of cognitive impairment in patients who underwent first time CABG at National Institute of Cardiovascular Diseases, Karachi and see the predictors of cognitive decline. 

Setting and duration of study: This was a prospective, observational/descriptive study where non-probability convenient sampling was done. Study period was one year from 15 DEC.2008-15 Dec.2009. 

Patients and methods: Patients over the age of 18 year were consecutively listed from the list of those undergoing first-time elective CABG surgeries. Those who were operated in emergency, additional cardiac procedures, and myocardial infarction(MI) within one month, with symptomatic CVA, psychiatric illness, renal and liver disease, history of alcohol or drug abuse, and lack of understanding of local national language for cognitive testing, were excluded from the study. Two full-time research assistants (one psychologist and other a medical doctor) carried out assessments under supervision. Each patient was assessed for socio-demographic profile, medical characteristics/risk factors, intra-operative, anesthetic and surgical techniques, post-operative complications/therapy in ICU, and cognitive evaluation before surgery at discharge, 6 weeks, and 6 months post surgery. A validated scale of Mcnnair’s and Kahn Auto-evaluation, Mini Mental State Examination (MMSE) was applied for neuro-cognitive assessment. Decline in post-operative cognitive function was defined as a drop of 1SD or more in the score on these tests. Hamilton Depression Rating Scale (HDRS) was added to see if it is a confounding factor for cognitive impairment.  

Results: A total of 138 patients were enrolled who underwent pump CABG. Mean age was 54.22 ± 9.67. Majority (82.6%) were males. Thirteen patients died, thus leaving 134 patients that were followed up till discharge, 73 were followed up at 6-week and 74 at 6-months. Diabetes Mellitus was seen in 31.9%, Hypertension in 42%, previous history of MI was seen in 55%, CVA in 9.4% Canadian cardiovascular society -IV angina in 44% American society of anesthesiology risk IV 37%, and pre-operative atrial fibrillation in10% cases. Duration of CABG and cross-clamping was 98.56±30.9 and 46.56±18.44 minutes respectively.  Prevalence of combined cognitive decline with both McNair and MMSE scale was 22.7%, 32.7%, 23.6%, and 24.5% preoperatively, at discharge,6-week and 6 month, respectively. Mean Mcnair score was 50.48±4.3, 52.39.8±10.8, 30.38±10.0, 50.20±4.6 from baseline to 6-months respectively, while mean MMSE was 23.95±3.1, 23.20±3.5, 24.64±2.7, and 22.8±3.9 from baseline to 6-months. Depression was seen maximally before operation where it was seen in 96% cases and then it declined to 80% at discharge after surgery, it further dropped at 6weeks to 60.3%, and further dropped to 27% at 6-months.Age, female gender, preoperative ejection fraction% duration of cardiopulmonary bypass, education, duration of cross clamping, ventilator support and obesity were important predictors for cognitive decline. 

Conclusions: A high prevalence and persistence of cognitive decline was seen after pump CABG surgery. There was a high prevalence of depression before surgery (a confounding factor for neuro-cognitive impairment) which showed significant reduction over time. Active measures need to be taken to address depression and other prevalent predictors for cognitive decline in these cases.