From January 2000 to December 2009, 553 patients underwent isolated AVR at our institution and comprise the cohort for this analysis. The mean age was 67.0 ±14.1 years with 40% females(n=222). The race distribution of the cohort was: 81% Caucasian(n=447), 14% African American(n=76), and 0.5% Hispanic(n=2) and 4.5% other(n=26). Forty-three (8%) reported a history of smoking. Throughout the study period, the number of yearly adult isolated AVR procedures remained relatively constant, ranging from 42–86 procedures annually.
Mean STS risk score for the entire isolated AVR cohort was 2.95(±3.4). Isolated AVR patients were grouped into the following STS quartiles: Q1, 0.37–1.02, n=139; Q2, 1.03–1.90, n=138; Q3, 1.91–3.44, n=138; Q4, 3.49–30.29, n=138. Baseline demographic information was compared between patients in Q1–3 against patients in Q4. As expected, patients in Q4 were older with significantly greater cardiovascular co-morbidities. A history of smoking was more common in patients in Q1–3.
Outcomes and Mortality Rates
By quartile, operative mortality rates for isolated AVR were 1(0.72%) Q1; 0(0%) Q2; 2(1.5%) Q3; and 16(11.6%) Q4. Median hospital LOS was longer in Q4: 10 days (IQR:7–17) versus 7 days (IQR:5–9) for Q1–3. Median duration of mechanical ventilation was also greater in Q4: 17 hours (IQR:11–37) compared with 9 hours (IQR:5–13). Postoperative CVA, RRT, and pneumonia were also more common in Q4, though deep sternal infection rates were equivalent. Demographic information and postoperative complications for isolated AVR are shown in .
Baseline Demographics and Postoperative Complications
For isolated AVR, median index admission charges were higher in STS Q4 patients: $62,301 (IQR45,952–97,103) for Q4 compared with $39,949 (IQR32,708–51,323) for Q1–3, p<0.001. Median index admission charges for individual quartiles were: Q1, $33,820 (IQR:29,641–42,243); Q2, $39,534 (IQR: 33,156–45,929); Q3, $49,571 (IQR: 38,710–62,554); and Q4, $62,301 (IQR: 45,952–97,103). When examining each of the four STS quartiles by non-parametric ANOVA, there was an overall global difference in the group medians (P<0.001). Multiple pairwise comparisons with an adjusted significance level for the Bonferroni correction revealed that all of the quartiles were significantly different from each other for isolated AVR ().
Figure 2 Side-by-side pie charts showing breakdown of total hospital charges by individual category for isolated AVR patients only. Chart on left corresponds to STS risk score quartile 1–3 patients combined and chart on right depicts STS quartile 4 patients. (more ...)
For STS Q4 and Q1–3, the relative contributions of each charge category to total index hospitalization charges for isolated AVR patients are depicted in . Hospital charges according to category were compared between STS Q4 and Q1–3. When analyzing index admission charges, the following categories were higher for STS Q4: routine ward and ICU care, OR supplies charges, OR facilities charges, pharmacy charges, laboratory services, radiology, and physical therapy services.
Results of univariate linear regression analysis for isolated AVR with STS risk score as independent variable. Log charges used as dependent variable (outcome measure).
Isolated AVR patients who died prior to discharge had greater median charges than those who survived to discharge (survivors: $42,917 (IQR: 33,829–59,222) vs non-survivors: $136,769 (IQR:65,855–316,461, p<0.01). Additional sub-analysis was performed revealing isolated AVR patients with STS risk score >10% had significantly increased median hospital charges (<10%: $42,785 (IQR: 33,820–59,391) vs >10%: $88,241 (IQR: 58,518–129,693), p<0.01).
Area under the ROC curve was 0.72 (95% CI: 0.61–0.83). An STS risk score of 3.13% had the best discriminatory power for predicting the upper 5% of index admission charges, with sensitivity of 68% and specificity 73%.
Linear Regression Analysis
Linear regression of charges data after logarithmic transformation revealed a significant positive correlation between STS predicted risk score and index admission charges (correlation coefficient: 0.06, 95%CI 0.05–0.07, p<0.01), with a Spearman R-value of 0.51 (). Using the binary independent variable of STS risk score >10%, there was a positive correlation (coefficient: 0.64, 95% CI 0.39–0.89, p<0.01) with increased hospital charges.
Following adjustment with multivariable linear regression, STS predicted risk score (coefficient: 0.04, 95% CI 0.03–0.05, p<0.01), diabetes mellitus (coefficient: 0.07, 95% CI 0.01–0.14, p=0.04), a major post-operative complication (coefficient: 0.45, 95% CI 0.35–0.55, p<0.01), and in-hospital mortality (coefficient: 0.54, 0.40–0.69, p<0.01) were all independently associated with increased hospital charges. The remaining variables did not reach significant associations and are shown in .
Multivariable Regression Analysis