Results
Between January 1, 2002 and December 31, 2011, an estimated total of 422,371 patients underwent shoulder arthroplasty (59.3% TSA, 40.7% HSA). Of these patients, 1174 (0.28%) had a perioperative MI, and 421,197 (99.72%) did not (Table 1). Patients with a primary diagnosis of proximal humerus fracture (33.8% vs 16.6%; P < .001) or rotator cuff arthropathy (10.1% vs 9.9%; P < .001) were more likely than patients with other diagnoses to have an in-hospital MI.
Our review of the demographics found that patients who underwent shoulder arthroplasty and had a perioperative MI were likely older (75±8.9 years vs 69±11 years; P < .001), Caucasian (94.2% vs 91.9%; P = .002), male (43.2% vs 39.7%; P = .013), in the highest median household income bracket of $63,000 or more (30.8% vs 25.6%; P < .001), and using Medicare (80.9% vs 66.3%; P < .001). They were more likely to be treated in a medical center of medium size (25.6% vs 23.7%; P = .042) or larger (61.8% vs 61.2%; P = .042). MIs occurred more often in urban environments (91.4% vs 88.5%; P = .002) and in HSA patients (55% vs 40.6%; P < .001), resulting in longer hospital stays (9.4±7.9 days vs 2.7±2.5 days; P < .001) and higher probability of death (6.5% vs 0.1%; P < .001).
We then analyzed the 2 cohorts for medical comorbidities (Table 2). Patients in the MI cohort presented with a significantly higher incidence of congestive heart failure, previous MI, angina pectoris, chronic lung disease, hypertension, diabetes, renal failure, fluid and electrolyte disorders, pulmonary circulatory disease, coagulopathy, and deficiency anemia (P < .001) but not liver disease and obesity. Bivariate analysis of perioperative outcomes (Table 3) indicated that these patients also had a statistically higher rate of numerous other complications: pulmonary embolism (4.9% vs 0.2%; P < .001), pneumonia (15.1% vs 1.2%; P < .001), deep venous thrombosis (2.6% vs 0.2%; P < .001), cerebrovascular event (1.6% vs 0.1%; P < .001), acute renal failure (15.1% vs 1.2%; P < .001), gastrointestinal complication (1.2% vs 0.3%; P < .001), mechanical ventilation (1.2% vs 0.3%; P < .001), transfusion (33.4% vs 8.8%; P < .001), and nonroutine discharge (73.3% vs 36.0%; P < .001).
Multivariable logistic regression analysis was performed to determine independent predictors of perioperative MI after shoulder arthroplasty (Table 4). Patients with a primary diagnosis of proximal humerus fracture (odds ratio [OR], 1.38; 95% confidence interval [CI], 1.15-1.65; P < .001) were more likely than patients with a primary diagnosis of osteoarthritis to have an MI. The odds of postoperative MI increased with age (OR, 1.04 per year; 95% CI, 1.03-1.05; P < .001) and were higher in males (OR, 1.72; 95% CI, 1.52-1.96; P < .001). Compared with Caucasians, African Americans (OR, 0.19; 95% CI, 0.09-0.40; P < .001) were less likely to have an in-hospital MI after shoulder arthroplasty. After shoulder arthroplasty, the odds of MI in the perioperative period increased with each subsequent day of care (OR, 1.10; 95% CI, 1.10-1.11; P < .001).
Regarding independent comorbidities, multivariable logistic regression analysis also determined that history of congestive heart failure (OR, 4.86; 95% CI, 4.20-5.61; P < .001), angina pectoris (OR, 2.90; 95% CI, 2.02-4.17; P < .001), complicated diabetes (OR, 1.96; 95% CI, 1.49-2.57; P < .001), renal failure (OR, 1.42; 95% CI, 1.17-1.72; P < .001), fluid and electrolyte disorders (OR, 1.42; 95% CI, 1.21-1.67; P < .001), and deficiency anemia (OR, 1.62; 95% CI, 1.40-1.88; P < .001) were significant predictors of perioperative MI after shoulder arthroplasty.
Discussion
Results of other studies have elucidated 30- and 90-day mortality rates and postoperative complications after shoulder arthroplasty, but, relative to hip and knee arthroplasty,17-19 little has been done to determine predictors of perioperative MI in a large sample of shoulder arthroplasty patients. Given the increasing rates of shoulder arthroplasty1-3 and the demographics of this population,4-6 it is likely that postoperative cardiovascular events will increase in frequency. We found that, in order of decreasing significance, the top 4 risk predictors for acute MI after shoulder arthroplasty were congestive heart failure, angina pectoralis, complicated diabetes mellitus, and male sex. Other pertinent risk factors included older age, Caucasian ethnicity, and a primary diagnosis of proximal humerus fracture. The rate of acute MI in patients who were older than 75 years when they underwent HSA for proximal humerus fracture was 0.80%.
Demographics
We found that patients who had an acute MI after shoulder arthroplasty were likely older, male, and Caucasian. Age and male sex are well-established risk factors for increased cardiac complications after arthroplasty.27-29 Previous studies have indicated that the rate of cardiac events increases in arthroplasty patients older than 65 years.19,28,29 In our study, more than 50% of the patients who had an acute perioperative MI were older than 85 years. Less explainable is the increased occurrence of acute MI in Caucasian patients and wealthy patients, given that minorities in the United States have higher rates of cardiovascular disease.30 Shoulder arthroplasty is an elective procedure, more likely to be undertaken by Caucasians. Therefore, at-risk minority groups and financially challenged groups may be less likely to have this procedure.