ISSN : 1301-5680
e-ISSN : 2149-8156
TURKISH JOURNAL OF
THORACIC AND
CARDIOVASCULAR SURGERY
Turkish Journal of Thoracic and Cardiovascular Surgery     
The relationship between aortic calcification on chest radiograph and neurocognitive impairment after coronary artery bypass grafting
Abdulkerim Özhan1, Murat Baştopcu2, Canan Karakaya1, Erhan Güler1, Sinan Şahin3, Mehmet Erdem Memetoğlu1, Bülend Ketenci1, Mahmut Murat Demirtaş1
1Department of Cardiovascular Surgery, Dr. Siyami Ersek Thoracic and Cardiovascular Surgery Training and Research Hospital, İstanbul, Turkey
2Department of Cardiovascular Surgery, Tatvan State Hospital, Bitlis, Turkey
3Department of Radiology, Dr. Siyami Ersek Thoracic and Cardiovascular Surgery Training and Research Hospital, İstanbul, Turkey
DOI : 10.5606/tgkdc.dergisi.2021.21285

Abstract

Background: In this study, we aimed to investigate the possible relationship between aortic calcification as detected by preoperative chest radiography and postoperative neurocognitive impairment in patients undergoing coronary artery bypass grafting.

Methods: A total of 124 patients (101 males, 23 females; mean age: 59.9±8.8 years; range, 34 to 84 years) who underwent coronary artery bypass grafting in our clinic between January 2019 and July 2019 were included. Of these patients, 35 whose preoperative chest radiography revealed aortic calcification in the aortic knuckle were included as the patient group. The control group consisted of 89 patients without aortic calcification. The patients with aortic calcification underwent additional imaging with thoracic computed tomography angiography and ascending aorta and aortic arch calcium scores were calculated. Neurocognitive dysfunction was assessed using the Standardized Mini-Mental State Examination. Postoperative delirium was evaluated by confusion assessment method in the intensive care unit. Both groups were compared for demographic, operative and postoperative data.

Results: Of all patients included in the study, the overall cerebrovascular event incidence was 3.2%. Although not statistically significant, the number of patients with neurocognitive decline was higher in the patient group than the control group (48.6% vs. 34.8%, respectively; p=0.157). Both Standardized Mini-Mental State Examination score decline and percentage decline were significantly higher in the patients with high aortic arch calcium scores (>2,250 AU). Carotid artery stenosis was 3.2 times higher in the patient group. In the patients with carotid artery stenosis, the aortic arch calcium scores were also higher (p=0.042).

Conclusion: Aortic calcification detectable on chest radiography with high calcium scores may be associated with neurocognitive impairment and carotid artery stenosis in patients undergoing coronary artery bypass grafting.

Coronary artery bypass grafting (CABG) can be performed with acceptable mortality and morbidity rates in the current era. Despite advances in preoperative imaging and increased surgical experience, the operative technique inherently brings along inevitable complications. Neurological and neurocognitive impairments are among the most serious of these complications.[1-3]

Postoperative neurocognitive dysfunction (POND), characterized by impaired attention, concentration, and memory with possible long-term effects, frequently occurs following CABG.[4] Three main mechanisms are held responsible for POND: microembolism, insufficient cerebral perfusion, and systemic inflammatory response.[3,5] The CABG patients are often accompanied by advanced age, carotid artery stenosis, and diabetes mellitus (DM), which may all increase the risk of POND. The incidence of POND in the early postoperative period after CABG varies between 20 and 50%.[4]

Aortic calcification (AC) is an advanced complication of atherosclerosis that stems from atheroma plaques. In patients with AC, aortic manipulation, aortic cross-clamping, and mobilization of atheromatous debris in the ascending aorta by jet flow at the beginning of cardiopulmonary bypass (CPB) cause microembolizations.[5] Severe AC can be seen in 2% of cardiac surgery patients and this rate can be as high as 30% with the increased age.[6]

Detection of AC is possible on posteroanterior chest radiography (CR), which is a routine preoperative study of CABG patients.[7] Computed tomography (CT) of patients with AC can reveal the localization, structure, and calcium density of AC and, thus, may help to predict the risk of POND and to reduce the risk by optimal surgical planning. In the present study, we aimed to investigate the association between AC detected on preoperative CR and POND in patients undergoing elective CABG.

Methods

This single-center, prospective, case-control study was conducted at Dr. Siyami Ersek Thoracic and Cardiovascular Surgery Training and Research Hospital, Department of Cardiovascular Surgery between January 2019 and July 2019. The patients over 18 years of age who underwent isolated on-pump CABG were included in the study. Of 750 patients who underwent open heart surgery throughout the study period, 124 (101 males, 23 females; mean age: 59.9±8.8 years; range, 34 to 84 years) who met the inclusion criteria were screened. Among 124 patients, 35 whose CR revealed AC in the aortic knuckle were included as the patient group. The control group consisted of 89 patients without AC. Patients who had neuropsychiatric diseases such as psychosis, dementia, and mental retardation that could affect psychometric analysis and neurocognitive functions, previous cerebrovascular accident (CVA), illiteracy, visual and hearing impairment, underwent emergent CABG, had moderate and severe valvular disease, intracardiac thrombus, preoperative atrial fibrillation (AF) and flutter, underwent off-pump CABG, and previous open heart surgery were excluded from the study. A written informed consent was obtained from each patient. The study protocol was approved by the Haydarpaşa Numune Training and Research Hospital Clinical Research Ethics Committee (HNEAK-KAEK-2018/9). The study was conducted in accordance with the principles of the Declaration of Helsinki.

Definitions
Hypertension was defined as a systolic or diastolic pressure of ?140 or ≥90 mmHg, respectively. Diabetes mellitus was defined as a fasting glucose level greater than 126 mg/dL or the use of insulin, antidiabetic agents. Hyperlipidemia was defined as a serum total cholesterol of ≥240 mg/dL, serum triglyceride of ≥200 mg/dL, or low-density lipoprotein cholesterol of ≥130 mg/dL.

Glomerular filtration rate (GFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Carotid artery stenosis and vertebrobasilar insufficiency were assessed with preoperative Duplex ultrasound. A significant carotid artery lesion was defined as ≥50% stenosis. Bilateral vertebral artery flow less than 200 mL/min was accepted as vertebrobasilar insufficiency. The most recent values before surgery were taken into account for laboratory values.

Assessment of AC
All CRs were evaluated by at least two specialists from the radiology and cardiovascular surgery departments. As defined by Hashimoto et al.,[7] patients with AC in the aortic knuckle seen on CR were included in the patient group and those without AC were included in the control group (Figure 1).

Figure 1: Appearance of aortic calcification at aortic knuckle on chest radiograph.

All patients in the patient group underwent non-contrast thoracic CT angiography (Toshiba, Aquillion 64 CT) with 3-mm slices. The calcific lesion was defined as an increase of ?130 Hounsfield units (HU) in three consecutive pixels. Aortic calcification on CT scan was defined as any calcific lesion in the ascending and/or aortic arch. Ascending aorta calcium score (CS) and aortic arch CS were calculated using the method described by Agatston et al.,[8] using semi-automatic Vitrea® 2.0 (Vital Images, Minnetonka, MN) imaging software. The total aortic CS was calculated as the sum of ascending aorta and aortic arch CSs. High ascending aorta and aortic arch CSs were defined as CS ≥2,250 Agatston units (AU).[9]

Surgical procedure
General anesthesia was induced with propofol, fentanyl, and rocuronium bromide. The CPB was achieved by cannulation of the ascending aorta and two-stage right atrial venous cannulation. Aortic cross-clamp was applied. Cardiac arrest was achieved by antegrade hypothermic blood cardioplegia and the patients were cooled down to a body core temperature of 32°C. After completion of distal anastomoses, the aortic clamp technique for proximal anastomoses (cross or lateral) was decided by the surgeon according to the extent of AC.

Assessment of neurological impairment
Neurological examination was done in the pre- and postoperative periods. Neurological deficits such as paresis, plegia, aphasia, epileptic attack, and transient ischemic attack were recorded, and ischemic areas were evaluated by cranial CT and/or magnetic resonance imaging (MRI).

Postoperative delirium was evaluated at 24 h using the Confusion Assessment Method in Intensive Care Unit (CAM-ICU) test and defined as early-stage delirium.[10,11] Delirium emerging with ≥ 24 h of ICU stay or recurrent ICU admission were evaluated daily by the CAM-ICU test and defined as late-stage delirium.

We used the Standardized Mini-Mental State Examination (SMMSE) to assess postoperative neurocognitive impairment. The primary endpoints of the study were the SMMSE score decline and percentage decline. Secondary endpoints were the presence of delirium, and major cerebrovascular events. The SMMSE consists of several sections that evaluate orientation, recording memory, attention and calculation, recall, and language skills. Patients answer questions scored between 0 and 30.[12,13]

The SMMSE was conducted on the day before surgery and on postoperative Days 5-7 under appropriate communication conditions. The preoperative test result was accepted as the baseline value of the patient. Both pre- and postoperative SMMSE scores were compared, and score decline and percentage decline at the SMMSE scores were calculated. It was assumed that the patients with an increase in the postoperative SMMSE scores compared to the preoperative scores were not affected by surgery in terms of neurocognition, and positive SMMSE score changes were defaulted to zero. Both groups were compared for changes in the SMMSE scores and other perioperative factors which affect neurocognitive function.

Statistical analysis
Statistical analysis was performed using the IBM SPSS version 22.0 software (IBM Corp., Armonk, NY, USA). To test for normality, the Shapiro-Wilks test was used. Nominal variables were expressed in number and percentage, while normally distributed continuous variables were expressed in mean ± standard deviation (SD) and non-normally distributed continuous variables in median (interquartile range [IQR]). The chi-square test was used for nominal values in comparison of the groups, the Fisher exact chi-square test in case of expected frequencies below 5, the independent samples t-test for comparison of parametric data, and the Mann-Whitney U test for comparison of non-parametric data. Multiple groups without normal distribution were compared using the Kruskal-Wallis test with Bonferroni correction. A p value of < 0.05 was considered statistically significant.

Results

Both groups were compared in terms of demographic and operative variables (Table 1). The patient group was significantly older (65.4±6.8 years vs. 5 7.5±8.5 years, respectively; p <0.001) and had a higher number of cases with carotid artery stenosis (25.7% vs. 7.9%, respectively; p=0.011). Postoperative 24-h and 120-h GFRs were lower in the patient group (p=0.010, p=0.002, respectively).

Table 1: Baseline characteristics of study population

Of all 124 patients, there were four (3.2%) ischemic events: one patient had an ischemic stroke and three patients had transient ischemic attacks. There was no significant difference between the groups in terms of major neurological complications.

Patients with and without carotid artery stenosis were compared for their ascending aorta, aortic arch, and total aortic CSs (Table 2). The aortic arch CS was higher in the patients with carotid artery stenosis (p=0.042), while the ascending aorta and total aortic CS were not significantly different