Ischemic Optic Neuropathy in Cardiac Surgery: Incidence and Risk Factors in the United States from the National Inpatient Sample 1998 to 2013

Abstract

Background: Ischemic optic neuropathy is the most common form of perioperative visual loss, with highest incidence in cardiac and spinal fusion surgery. To date, potential risk factors have been identified in cardiac surgery by only small, single-institution studies. To determine the preoperative risk factors for ischemic optic neuropathy, the authors used the National Inpatient Sample, a database of inpatient discharges for nonfederal hospitals in the United States.

Methods: Adults aged 18 yr or older admitted for coronary artery bypass grafting, heart valve repair or replacement surgery, or left ventricular assist device insertion in National Inpatient Sample from 1998 to 2013 were included. Risk of ischemic optic neuropathy was evaluated by multivariable logistic regression.

Results: A total of 5,559,395 discharges met inclusion criteria with 794 (0.014%) cases of ischemic optic neuropathy. The average yearly incidence was 1.43 of 10,000 cardiac procedures, with no change during the study period (P = 0.57). Conditions increasing risk were carotid artery stenosis (odds ratio, 2.70), stroke (odds ratio, 3.43), diabetic retinopathy (odds ratio, 3.83), hypertensive retinopathy (odds ratio, 30.09), macular degeneration (odds ratio, 4.50), glaucoma (odds ratio, 2.68), and cataract (odds ratio, 5.62). Female sex (odds ratio, 0.59) and uncomplicated diabetes mellitus type 2 (odds ratio, 0.51) decreased risk.

Conclusions: The incidence of ischemic optic neuropathy in cardiac surgery did not change during the study period. Development of ischemic optic neuropathy after cardiac surgery is associated with carotid artery stenosis, stroke, and degenerative eye conditions.

Figure 1. CONSORT diagram of ION in cardiac surgery

Data collection was through patient discharges recorded in the NIS from 1998 to 2013. Only patients ≥18 years old who underwent a specified cardiac procedure (CABG-only, valve repair or replacement-only, CABG-valve repair or replacement as a combined procedure, or left ventricular assist device) were included in the analysis, and all other patients were excluded. The primary outcome, ION, was reported as volume (n) and incidence per 10,000 [95% confidence interval]. Results are nationwide estimates using NIS weighting and STATA survey function. Abbreviations: CABG-only = only received coronary artery bypass graft; CABG-Valve = received both coronary artery bypass graft and cardiac valve repair or replacement; ION = ischemic optic neuropathy; LVAD = received left ventricular assist device; NIS = National Inpatient Sample; Valve-only = only received cardiac valve repair or replacement.

Figure 2. ION Incidence in Cardiac Surgery Cases in the NIS, 1998–2013

Results are nationwide estimates using NIS weighting and STATA survey function. After adjusting for changes in procedural volume in the multivariable analysis, there was no significant change in yearly incidence of ION (OR: 1.01, P = 0.574). Cardiac surgery cases include: coronary artery bypass grafts only, coronary artery bypass graft with valve repair or replacement, valve repair or replacement only, and left ventricular assist device insertion. To calculate incidence of ION per 10,000, yearly estimates of ION were divided by yearly estimates of cardiac surgical procedures. Errors bars are 95% confidence intervals. Abbreviations: ION = ischemic optic neuropathy; NIS = National Inpatient Sample.

Figure 3

To calculate incidence of cardiac procedures per 1 million, yearly estimates of each procedure type were divided by the yearly US population estimate based on US Census Bureau data (http://www.census.gov/popest/data/historical/index.html). Results are nationwide estimates using NIS weighting and STATA survey function. There was a 60% decrease in CABG as the sole procedure from 1998 to 2013 [1,725 to 686 per million adults], 1,092% increase in LVAD (1.3 to 14.2 per million), 53% increase in valve replacement alone (206 to 315 per million) and a 22% decrease in combined CABG-Valve (176 to 137 per million) [p=0.0001]. Cardiac procedure types include: (A) CABG only, (B) Valve repair or replacement only, (C) CABG-Valve repair or replacement, and (D) LVAD. Errors bars are 95% confidence intervals. Abbreviations: CABG = coronary artery bypass graft; CABG-Valve = coronary artery bypass graft and cardiac valve repair or replacement; LVAD = ventricular assist device insertion; NIS = National Inpatient Sample; Valve = cardiac valve repair or replacement.

Figure 4. Odds ratios for conditions that increase and decrease odds of ION in Cardiac Surgery

Odds ratios from the multivariable analysis for patient conditions that increase and decrease odds of developing perioperative ischemic optic neuropathy after cardiac surgery. (A): Conditions and procedures that increase odds of developing ION (odds ratio and 95% CI’s). Of note, hypertensive retinopathy and left ventricular assist device procedure were left off of the graph secondary to large confidence intervals. (B): Conditions that decrease odds of developing ischemic optic neuropathy after cardiac surgery (odds ratios and 95% CI’s). Abbreviations: CABG = coronary artery bypass graft; CI = confidence interval; ION = ischemic optic neuropathy.