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Evaluation of supply-side initiatives to improve access to coronary bypass surgery Sobolev, Boris G; Fradet, Guy; Kuramoto, Lisa; Sobolyeva, Rita; Rogula, Basia; Levy, Adrian R Sep 11, 2012

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Sobolev et al. BMC Health Services Research 2012, 12:311http://www.biomedcentral.com/1472-6963/12/311RESEARCH ARTICLE Open AccessEvaluation of supply-side initiatives to improveaccess to coronary bypass surgeryBoris G Sobolev1,3*, Guy Fradet2, Lisa Kuramoto3, Rita Sobolyeva4, Basia Rogula3 and Adrian R Levy5AbstractBackground: Guided by the evidence that delaying coronary revascularization may lead to symptom worsening andpoorer clinical outcomes, expansion in cardiac surgery capacity has been recommended in Canada. Provincialgovernments started providing one-time and recurring increases in budgets for additional open heart surgeries toreduce waiting times. We sought to determine whether the year of decision to proceed with non-emergencycoronary bypass surgery had an effect on time to surgery.Methods: Using records from a population-based registry, we studied times between decision to operate and theprocedure itself. We estimated changes in the length of time that patients had to wait for non-emergency operationover 14 calendar periods that included several years when supplementary funding was available. We studied waitingtimes separately for patients who access surgery through a wait list and through direct admission.Results: During two periods when supplementary funding was available, 1998–1999 and 2004–2005, the weekly rateof undergoing surgery from a wait list was, respectively, 50% and 90% higher than in 1996–1997, the period with thelongest waiting times. We also observed a reduction in the difference between 90th and 50th percentiles of thewaiting-time distributions. Forty percent of patients in the 1998, 1999, 2004 and 2005 cohorts (years whensupplementary funding was provided) underwent surgery within 16 to 20 weeks following the median waiting time,while it took between 27 and 37 weeks for the cohorts registered in the years when supplementary funding was notavailable. Times between decision and surgery were shorter for direct admissions than for wait-listed patients. Amongpatients who were directly admitted to hospital, time between decision and surgery was longest in 1992–1993 andthen has been steadily decreasing through the late nineties. The rate of surgery among these patients was the highestin 1998–1999, and has not changed afterwards, even for years when supplementary funding was provided.Conclusions: Waiting times for non-emergency coronary bypass surgery shortened after supplementary fundingwas granted to increase volume of cardiac surgical care in a health system with publicly-funded universal coverage forthe procedure. The effect of the supplementary funding was not uniform for patients that access the services throughwait lists and through direct admission.Keywords: Access to care, CABG, Surgical wait lists, Provincial registry, Health policyBackgroundIn Canada, provincial health insurance plans provide uni-versal, single-payer coverage for surgical coronary revas-cularization, a procedure indicated for the treatment ofcoronary artery disease [1]. Responsible for the delivery of*Correspondence: boris.sobolev@ubc.ca1School of Population and Public Health, The University of British Columbia,Vancouver, BC, Canada3Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal HealthResearch Institute, Vancouver, BC, CanadaFull list of author information is available at the end of the articlecare, regional Health Authorities budget a fixed number ofopen heart surgeries on an annual basis using population-based rates of the disease [2]. As argued elsewhere, thosewhomake allocation decisions have no tools to predict thevolume of demand at each hospital and at each point dur-ing the calendar period [3].When demand exceeds fundedcapacity, cardiac centers across Canada use wait lists tomanage access to the procedure. As a result, operations forpatients with less severe coronary artery disease may bedelayed when a surgical service experiences an extendeddemand for more urgent procedures [4-10]. Guided by the© 2012 Sobolev et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.Sobolev et al. BMC Health Services Research 2012, 12:311 Page 2 of 15http://www.biomedcentral.com/1472-6963/12/311evidence that delaying the operation may lead to symp-tom worsening and poorer clinical outcomes, expansionin cardiac surgery capacity has been recommended inCanada. Federal and provincial governments started pro-viding one-time and recurring increases in budgets foradditional open heart surgeries to reduce the numberof patients waiting for coronary artery bypass grafting(CABG) and their waiting times.In a previous study of access to non-emergency CABGin British Columbia, Canada, between 1991 and 2000, wefound that waiting times for the procedure shortened after1998 when annual supplementary funding was granted totertiary care hospitals that had been providing cardiac sur-gical care to adult residents of the province [8]. Between1995–1996 and 1999–2000, there was a 12% increasein the total number of CABG operations and a declinein median waiting time from 15 to 10 weeks, althoughthe change in waiting times was different across urgencygroups. In addition, between 1995–1996 and 1999–2000there was a decrease from 54% to 41% in the proportionof patients undergoing the procedure through wait lists.Considering that cardiac surgeons in British Columbiahave discretion for direct admission of their patients onthe basis of the estimated urgency of treatment, place ofresidence and other factors, this might indicate that sup-plementary funding had been used to provide more treat-ments without delay. One plausible explanation for theseresults was that the hospitals had capacity to increase thenumber of operations and thereby reduce wait times [10].However, a limitation of the previous study was the shortperiod for analysis of the effects of supplementary fund-ing (two years). In addition, data were not available forthe total amount of time between cardiac catheterizationand surgical revascularization. As such, in the previousstudy we did not estimate the effect of the supplementaryfunding on waiting times in full.Since our previous analysis, another $2 million of addi-tional funding from the provincial Ministry of Health wasdirected in each of 2003 and 2004 toward open heartsurgery to increase the volume. However, the effect of thisincrease in funding on wait-list sizes and waiting timesfor CABG remains unknown. The longer time frame afterthe original increase in annual budgets for CABG since1998 and the additional funding in 2003 and 2004 makesit feasible to generate more precise assessment of thissupply-side initiative to improve access to care. The effectof the additional funding has not been contrasted for twodifferent pathways of accessing surgical coronary revascu-larization for non-emergency patients as well. Access tonon-emergency CABG could be provided either througha wait list or through direct admission to hospital, and itremains unclear whether the effect of the supplementaryfunding was uniform for the wait-listed and directly-admitted patients. However this information is importantfor deciding on policy to reduce wait lists by adding extrafunding.To evaluate the effect of providing the additional fund-ing to tertiary care hospitals on access to non-emergencysurgical revascularization within a single publicly fundedhealth system, we estimated temporal changes in thelength of time between decision to proceed with surgeryand performed CABG. We used all relevant records fromthe provincial population-based registry of patients withangiographically-proven coronary artery disease iden-tified as needing bypass surgery on a non-emergencybasis. To adjust for changes in time between cardiaccatheterization and decision to operate, we used themost recent catheterization date from hospital dischargereports assuming that the results of this procedure (coro-nary angiography or intervention) were most likely linkedto the decision to operate. Primary comparisons havebeen done across synthetic cohorts of patients definedby the calendar period of the decision to proceed withsurgery. The temporal changes in treatment delays havebeen estimated separately for patients who access surgeryby registration on a wait list and among patients whoaccess surgery by direct admission.MethodsData sourcesData were obtained from the British Columbia CardiacRegistries (BCCR) to identify the study participants andtheir characteristics. This population-based patient reg-istry contains demographic, clinical and treatment data,along with the dates of booking request for operatingroom time and procedures for all adult patients under-going CABG in any of the four cardiac centers in theprovince [8]. To identify cardiac catheterization dates,hospital admission and discharge dates, and coexistingmedical conditions, we used each patient’s provincialhealth number to deterministically link BCCR recordsto the Canadian Institute for Health Information (CIHI)Discharge Abstract Database (DAD) [11].PatientsUsing records from the registry, we studied two groupsof patients: (1) those who were registered on a wait listfor first-time isolated CABG surgery; and (2) those whounderwent the procedure by direct admission to hospitalon a non-emergency basis. Patients who accessed surgerythrough a wait list were registered by the surgeon’s officeon the wait list after an outpatient consultation with a car-diac surgeon. In contrast, patients who accessed surgerythrough direct admission were admitted to a hospital’scardiac ward directly from the catheterization labora-tory or after an outpatient consultation with a cardiacsurgeon if the patient had disabling symptoms or high-risk anatomy of the coronary lesion(s). Patients in bothSobolev et al. BMC Health Services Research 2012, 12:311 Page 3 of 15http://www.biomedcentral.com/1472-6963/12/311groups were classified as urgent, semiurgent, or nonurgentbased on the patient’s need for treatment, as definedelsewhere [8].The inception cohort of wait-listed patients had atotal of 14,049 records of registration for CABG fromJanuary 1, 1991 through December 31, 2005. We excluded567 records of patients for various reasons: procedure atregistration was not isolated CABG (312), procedure atregistration or at surgery was not first-time CABG (62),emergency cases at the time of registration (34), missingoperating room reports (4), removed on the registrationdate (101), registration was on a weekend and admissionwas the day after (14), or the patient hadmultiple episodes(40). We also excluded 1,452 records of patients who wereregistered in 1991 (797) or did not have a catheterizationdate (655).The inception cohort of direct admissions had a totalof 16,014 records of CABG surgery from January 1, 1991throughDecember 31, 2005.We excluded 1,282 records ofpatients for various reasons: procedure at surgery was notisolated CABG (211), procedure at surgery was not first-time CABG (54), emergency case at the time of surgery(861), or the patient had multiple episodes (156). We alsoexcluded 1,914 records of patients who had surgery in1991 (1,031), did not have a catheterization date (838),did not have an admission date (38), or had a decision tooperate in 1991 (7).The final study cohort had a total of 12,030 wait-listedpatients who had a decision to undergo first-time isolatedCABG surgery and 12,818 direct admissions who under-went first-time isolated CABG surgery from January 1,1992 through December 31, 2005. Among the wait-listedpatients 10,339 (85.9%) underwent surgery within 1 yearof registration and the remaining were removed from thelist without surgery: 104 (0.9%) died, 257 (2.1%) continuedto receive medical treatment, 231 (1.9%) declined surgery,86 (0.7%) were transferred to another surgeon or hospi-tal, 321 (2.7%) were removed for other reasons, and 692(5.8%) remained on the list after 52 weeks or at the end ofthe study period.Primary study variableThe primary study variable was calendar period ofdecision to operate classified into 7 two-year periods:1992–93, 1994–95, 1996–97, 1998–99, 2000–01, 2002–03, 2004–05. Calendar periods are often used as a proxyfor changes in the availability of hospital resources, suchas, surgical staffing, operating room time, special equip-ment, and beds, in studies that attempted to explain vari-ations in the patient’s waiting time for surgery [12,13].Because the budget for open heart surgeries is deter-mined annually, calendar period provides an appropriateindicator for changes in the funded procedures.OutcomeThe outcome was time between decision to operate andsurgical revascularization. This time was measured in cal-endar weeks for wait-listed patients and in days for directadmissions. We used the date of the registration on await list as a proxy for the decision to operate for wait-listed patients and the date of catheterization or the dateof admission to hospital, whichever was most recent, asa proxy for the date of decision to operate for directly-admitted patients. This latter rule reflects variation in carepaths of the patients: following angiography the patientmay be admitted for in-hospital consultation with a car-diac surgeon, or patients who live far away are admittedfor angiography, stay in hospital to undergo tests, andare booked for surgery or discharged with planned re-admission.Potential confoundersThe existing literature suggests that elderly patients aremore likely to undergo revascularization as an urgent pro-cedure [14], that smaller diameter of the coronary vesselsmay account for the higher risk of adverse cardiovascu-lar events among women [15], that co-existing conditionsmay delay open heart surgery [16], that post-operativesurvival depends on institutional constraints and indi-vidual care providers [17], and that changes in practicemay reduce the waiting time until surgery [8]. To iden-tify comorbidities at the time of decision to operate, weused diagnoses reported in the DADwithin one year priorto decision. The reference category was defined as nocoexisting conditions. The first comparison category wasdefined as patients with any of the following conditionsat presentation: congestive heart failure, diabetes mel-litus, chronic obstructive pulmonary disease, cancer, orrheumatoid arthritis [4]. The second comparison categorywas defined as patients presenting with other coexistingchronic conditions, as defined elsewhere [18].In addition, we used time between cardiac catheteri-zation and decision to operate as a covariate that mightreflect changes in practice over time. The time betweencatheterization and decision measured in calendar weeks.The catheterization dates were obtained from the DADand defined as the most recent diagnostic (Canadian Clas-sification of Procedure (CCP) codes 4892–4898, 4996,4997) or therapeutic (CCP codes 4802, 4803, 4809)catheterization performed within one year preceding andincluding the date of booking for wait-listed patientsor within one year preceding and including the date ofsurgery for direct admissions. We used the date of mostrecent catheterization procedures (diagnostic or thera-peutic) because the results of this procedure are mostlikely linked to decision to operate [19]. We used calendarweeks as the unit of time because scheduling of surgicalprocedures is done on a weekly basis [13].Sobolev et al. BMC Health Services Research 2012, 12:311 Page 4 of 15http://www.biomedcentral.com/1472-6963/12/311Statistical analysisWe used chi-square testing to compare the distributionsof patient characteristics across calendar period of deci-sion for wait-listed patients and direct admissions. Weestimated percentiles and conditional median times tosurgery to characterize the variation in times to surgi-cal revascularization, by calendar period for each type ofaccess. Percentiles of time to surgery were estimated usingthe product-limit method [13,20]. The conditional medianwaiting time at a given moment after decision is definedas the period during which one half of the patients whowait for surgery are expected to have it [13]. For wait-listedpatients, average weekly surgery rates were calculated asthe number of procedures divided by the sum of observedtimes from decision to surgery or removal from the waitlist. For direct admissions, the average daily surgery rateswere calculated as the number of procedures divided bythe sum of observed times from decision to surgery.Discrete-time survival regression methods were used tomodel the relation between the time to surgical revascu-larization and calendar period of decision for each type ofaccess [13,21]. We restricted the regression analysis to thefirst 52 weeks after decision for wait-listed patients and tothe first 7 days after decision for direct admissions. Thecalendar period was entered into the regression model asa set of 6 binary indicators. The 1996–1997 group (i.e., thereference group) took a value of 0 for all indicator vari-ables. The exponential of the regression coefficient for anindicator variable for a period gave the odds of surgery inthat period relative to the odds of surgery in 1996–1997. Ina multivariable model, we adjusted for sex, age at decision,urgency at decision, institution at decision, comorbidi-ties at decision, coronary anatomy at decision, and timebetween catheterization and decision.To explore the effect of the supplementary funding ondirect admissions and wait-listed patients, we classifiedall patients using the algorithm developed by NorthernNew England Cardiovascular Disease Study Group [22].For each patient, we calculated the prognostic risk ofin-hospital death that summarized the effect of clinicaland patient characteristics. We then compared the dis-tribution of these risks between direct admissions andwait-listed patients for each calendar period of surgeryusing chi-square testing.The Behavioural Research Ethics Board of the Univer-sity of British Columbia approved the study protocol,Certificate of Approval H06-80651.ResultsPatients characteristicsOverall 24,848 patients had a decision for first-time, iso-lated CABG between 1992 and 2005: 12,030 (48%) wereregistered on a wait list and 12,818 (52%) were directlyadmitted to hospital.For wait-listed patients, the distribution of patient char-acteristics varied across periods (Table 1). The majority ofthe wait-listed patients who had a decision for CABGweremen (83%). Later periods tended to have older patients(p < 0.001), fewer urgent cases at decision (p < 0.001),more patients with major comorbidities at the time ofdecision (p < 0.001), and more limited coronary anatomyaffected (p < 0.001). The distribution of cases by insti-tution at decision seemed to increase over periods forhospital 1, but decreased for hospital 2 (p < 0.001). Themajority of wait-listed patients had a decision to oper-ate within a week of catheterization. This majority rangedfrom about 42% in 1992–1993 and increased to 65% in2002–2003 (p < 0.001).For direct admissions, the trends in changes in thedistributions of patient characteristics over periods weresimilar to wait-listed patients (Table 2). Later periodstended to have older patients (p < 0.001), fewer urgentcases at decision (p < 0.001), and more patients withmajor comorbidities at the time of decision (p < 0.001).In contrast to wait-listed patients, later periods tended tohave more direct admissions who had less limited coro-nary anatomy affected (p < 0.001) and more decisionsto operate within a week of catheterization (p < 0.001).About two-thirds of direct admissions had a decision tooperate within a week of catheterization across all calen-dar periods.When compared over calendar periods, wait-listedpatients were more prevalent in the low risk groupand directly-admitted patients were more prevalent inhigh risk group (see Table 3). The percentage of lowrisk patients accessing surgery through direct admis-sion declined considerably in years when supplementaryfunding was provided.Access to surgery through wait-list registrationFigure 1 shows the cumulative distribution functions ofwaiting time for each calendar period, which could beused to derive the number of weeks required for a spec-ified proportion of patients to undergo the operation.The differences in the proportion of patients undergo-ing CABG within a certain time of decision were sig-nificant across periods (Log-rank statistic = 545.6, df=6,p < 0.001), with longer waiting times when the deci-sion was made in 1996–1997 and 2002–2003. The waitingtimes for these years were such that half of the wait-listedpatients underwent surgery within 16 to 17 weeks, and90% underwent surgery within 46 to 51 weeks. In contrast,during the other years about half of patients underwentsurgery within 8 to 14 weeks of decision. Comparing the1998, 1999, 2004 and 2005 cohorts (the periods when sup-plement funding was provided) with the rest, we observeda compression in access to surgery, i.e., reduction in theSobolevetal.BMCHealthServicesResearch2012,12:311Page5of15http://www.biomedcentral.com/1472-6963/12/311Table 1 Characteristics of 12,030 wait-list registered patients, who had decision for coronary artery bypass grafting in British Columbia 1992–2005, by calendarperiod of decisionAll periods 1992–1993 1994–1995 1996–1997 1998–1999 2000–2001 2002–2003 2004–2005Characteristic (n = 12030) (n = 1726) (n = 1793) (n = 1862) (n = 1610) (n = 1791) (n = 1889) (n = 1359)Age group at decision (years)<50 761 (6.3) 140 (8.1) 147 (8.2) 118 (6.3) 99 (6.1) 113 (6.3) 85 (4.5) 59 (4.3)50–59 2559 (21.3) 362 (21.0) 390 (21.8) 367 (19.7) 337 (20.9) 419 (23.4) 426 (22.6) 258 (19.0)60–69 4468 (37.1) 703 (40.7) 655 (36.5) 717 (38.5) 551 (34.2) 619 (34.6) 717 (38.0) 506 (37.2)70–79 3786 (31.5) 500 (29.0) 542 (30.2) 602 (32.3) 567 (35.2) 573 (32.0) 551 (29.2) 451 (33.2)≥80 456 (3.8) 21 (1.2) 59 (3.3) 58 (3.1) 56 (3.5) 67 (3.7) 110 (5.8) 85 (6.3)SexMen 9981 (83.0) 1425 (82.6) 1487 (82.9) 1500 (80.6) 1334 (82.9) 1502 (83.9) 1595 (84.4) 1138 (83.7)Women 2049 (17.0) 301 (17.4) 306 (17.1) 362 (19.4) 276 (17.1) 289 (16.1) 294 (15.6) 221 (16.3)Urgency at decision∗Urgent 739 (6.1) 113 (6.5) 162 (9.0) 177 (9.5) 66 (4.1) 72 (4.0) 87 (4.6) 62 (4.6)Semiurgent 8769 (72.9) 1331 (77.1) 1240 (69.2) 1295 (69.5) 1107 (68.8) 1315 (73.4) 1401 (74.2) 1080 (79.5)Nonurgent 2304 (19.2) 269 (15.6) 375 (20.9) 369 (19.8) 432 (26.8) 390 (21.8) 354 (18.7) 115 (8.5)Institution at decision1 2668 (22.2) 328 (19.0) 356 (19.9) 378 (20.3) 361 (22.4) 449 (25.1) 533 (28.2) 263 (19.4)2 3575 (29.7) 724 (41.9) 589 (32.8) 467 (25.1) 555 (34.5) 475 (26.5) 409 (21.7) 356 (26.2)3 2914 (24.2) 438 (25.4) 429 (23.9) 492 (26.4) 265 (16.5) 401 (22.4) 472 (25.0) 417 (30.7)4 2873 (23.9) 236 (13.7) 419 (23.4) 525 (28.2) 429 (26.6) 466 (26.0) 475 (25.1) 323 (23.8)Comorbidities at decisionMajor conditions† 2901 (24.1) 373 (21.6) 386 (21.5) 418 (22.4) 368 (22.9) 452 (25.2) 518 (27.4) 386 (28.4)Other conditions‡ 2856 (23.7) 520 (30.1) 496 (27.7) 526 (28.2) 384 (23.9) 379 (21.2) 354 (18.7) 197 (14.5)None 6273 (52.1) 833 (48.3) 911 (50.8) 918 (49.3) 858 (53.3) 960 (53.6) 1017 (53.8) 776 (57.1)Coronary anatomy affected at decisionLeft main 1780 (14.8) 251 (14.5) 287 (16.0) 299 (16.1) 256 (15.9) 265 (14.8) 284 (15.0) 138 (10.2)Multivessel§ 8715 (72.4) 1361 (78.9) 1407 (78.5) 1418 (76.2) 1202 (74.7) 1320 (73.7) 1274 (67.4) 733 (53.9)Limited‖ 1535 (12.8) 114 (6.6) 99 (5.5) 145 (7.8) 152 (9.4) 206 (11.5) 331 (17.5) 488 (35.9)Sobolevetal.BMCHealthServicesResearch2012,12:311Page6of15http://www.biomedcentral.com/1472-6963/12/311Table 1 Characteristics of 12,030 wait-list registered patients, who had decision for coronary artery bypass grafting in British Columbia 1992–2005, by calendarperiod of decision (Continued)Time between catheterization and decision for surgical revascularization (weeks)0–1 6651 (55.3) 726 (42.1) 932 (52.0) 1005 (54.0) 912 (56.6) 1093 (61.0) 1236 (65.4) 747 (55.0)2–3 2066 (17.2) 422 (24.4) 377 (21.0) 350 (18.8) 269 (16.7) 245 (13.7) 215 (11.4) 188 (13.8)4–5 1041 (8.7) 209 (12.1) 174 (9.7) 157 (8.4) 150 (9.3) 139 (7.8) 102 (5.4) 110 (8.1)6–7 642 (5.3) 122 (7.1) 92 (5.1) 123 (6.6) 74 (4.6) 84 (4.7) 66 (3.5) 81 (6.0)≥8 1630 (13.5) 247 (14.3) 218 (12.2) 227 (12.2) 205 (12.7) 230 (12.8) 270 (14.3) 233 (17.1)*218 patients had unknown values for urgency at decision.†Congestive heart failure, diabetes mellitus, chronic obstructive pulmonary disease, rheumatoid arthritis, or cancer.‡Peripheral vascular disease, cerebrovascular disease, dementia, peptic ulcer disease, hemiplegia, renal disease, or liver disease.§Two or three-vessel disease with stenosis of the proximal left anterior descending (PLAD) artery.‖Two-vessel disease with no stenosis of the PLAD artery or one-vessel disease with stenosis of the PLAD artery.Sobolevetal.BMCHealthServicesResearch2012,12:311Page7of15http://www.biomedcentral.com/1472-6963/12/311Table 2 Characteristics of 12,818 direct admissions, who had decision for coronary artery bypass grafting in British Columbia 1992–2005, by calendar period ofdecisionAll periods 1992–1993 1994–1995 1996–1997 1998–1999 2000–2001 2002–2003 2004–2005Characteristic (n = 12818) (n = 1204) (n = 1474) (n = 1621) (n = 2089) (n = 2121) (n = 1940) (n = 2369)Age group at decision (years)<50 920 (7.2) 111 (9.2) 97 (6.6) 129 (8.0) 142 (6.8) 157 (7.4) 139 (7.2) 145 (6.1)50–59 2604 (20.3) 228 (18.9) 275 (18.7) 313 (19.3) 435 (20.8) 432 (20.4) 414 (21.3) 507 (21.4)60–69 4354 (34.0) 442 (36.7) 569 (38.6) 571 (35.2) 715 (34.2) 676 (31.9) 615 (31.7) 766 (32.3)70–79 4341 (33.9) 389 (32.3) 481 (32.6) 550 (33.9) 726 (34.8) 747 (35.2) 663 (34.2) 785 (33.1)≥80 599 (4.7) 34 (2.8) 52 (3.5) 58 (3.6) 71 (3.4) 109 (5.1) 109 (5.6) 166 (7.0)Sex*Men 10067 (78.5) 914 (75.9) 1104 (74.9) 1247 (76.9) 1659 (79.4) 1687 (79.5) 1525 (78.6) 1931 (81.5)Women 2750 (21.5) 290 (24.1) 370 (25.1) 374 (23.1) 430 (20.6) 434 (20.5) 415 (21.4) 437 (18.4)Urgency at decisionUrgent 5944 (46.4) 727 (60.4) 944 (64.0) 900 (55.5) 1046 (50.1) 887 (41.8) 698 (36.0) 742 (31.3)Semiurgent 6445 (50.3) 453 (37.6) 485 (32.9) 654 (40.3) 906 (43.4) 1148 (54.1) 1211 (62.4) 1588 (67.0)Nonurgent 429 (3.3) 24 (2.0) 45 (3.1) 67 (4.1) 137 (6.6) 86 (4.1) 31 (1.6) 39 (1.6)Institution at decision1 2437 (19.0) 89 (7.4) 206 (14.0) 295 (18.2) 381 (18.2) 473 (22.3) 427 (22.0) 566 (23.9)2 2962 (23.1) 342 (28.4) 369 (25.0) 333 (20.5) 466 (22.3) 426 (20.1) 457 (23.6) 569 (24.0)3 4964 (38.7) 417 (34.6) 623 (42.3) 838 (51.7) 870 (41.6) 799 (37.7) 683 (35.2) 734 (31.0)4 2455 (19.2) 356 (29.6) 276 (18.7) 155 (9.6) 372 (17.8) 423 (19.9) 373 (19.2) 500 (21.1)Comorbidities at decisionMajor conditions† 5458 (42.6) 413 (34.3) 552 (37.4) 626 (38.6) 885 (42.4) 949 (44.7) 914 (47.1) 1119 (47.2)Other conditions‡ 6248 (48.7) 708 (58.8) 809 (54.9) 885 (54.6) 1033 (49.4) 1027 (48.4) 857 (44.2) 929 (39.2)None 1112 (8.7) 83 (6.9) 113 (7.7) 110 (6.8) 171 (8.2) 145 (6.8) 169 (8.7) 321 (13.6)Coronary anatomy affected at decisionLeft main 3184 (24.8) 282 (23.4) 358 (24.3) 377 (23.3) 466 (22.3) 539 (25.4) 534 (27.5) 628 (26.5)Multivessel§ 8855 (69.1) 814 (67.6) 1019 (69.1) 1136 (70.1) 1501 (71.9) 1470 (69.3) 1307 (67.4) 1608 (67.9)Limited‖ 779 (6.1) 108 (9.0) 97 (6.6) 108 (6.7) 122 (5.8) 112 (5.3) 99 (5.1) 133 (5.6)Sobolevetal.BMCHealthServicesResearch2012,12:311Page8of15http://www.biomedcentral.com/1472-6963/12/311Table 2 Characteristics of 12,818 direct admissions, who had decision for coronary artery bypass grafting in British Columbia 1992–2005, by calendar period ofdecision (Continued)Time between catheterization and decision for surgical revascularization (weeks)0–1 8576 (66.9) 885 (73.5) 1021 (69.3) 991 (61.1) 1381 (66.1) 1465 (69.1) 1246 (64.2) 1587 (67.0)2–3 2232 (17.4) 164 (13.6) 215 (14.6) 326 (20.1) 334 (16.0) 372 (17.5) 406 (20.9) 415 (17.5)4–5 592 (4.6) 46 (3.8) 54 (3.7) 81 (5.0) 87 (4.2) 85 (4.0) 113 (5.8) 126 (5.3)6–7 364 (2.8) 25 (2.1) 38 (2.6) 45 (2.8) 76 (3.6) 46 (2.2) 58 (3.0) 76 (3.2)≥8 1054 (8.2) 84 (7.0) 146 (9.9) 178 (11.0) 211 (10.1) 153 (7.2) 117 (6.0) 165 (7.0)*1 direct admission with decision date in 2004–2005 had unknown sex.†Congestive heart failure, diabetes mellitus, chronic obstructive pulmonary disease, rheumatoid arthritis, or cancer.‡Peripheral vascular disease, cerebrovascular disease, dementia, peptic ulcer disease, hemiplegia, renal disease, or liver disease.§Two or three-vessel disease with stenosis of the proximal left anterior descending (PLAD) artery.‖Two-vessel disease with no stenosis of the PLAD artery or one-vessel disease with stenosis of the PLAD artery.Sobolev et al. BMC Health Services Research 2012, 12:311 Page 9 of 15http://www.biomedcentral.com/1472-6963/12/311Table 3 Prognostic risk of in-hospital death, by calendar period of surgery and type of accessCalendar period of surgery Risk∗, %Access type <1.0 1.0–3.0 >3.0 p value†1992–1993 <0.001Wait-listed 808 (58.4) 555 (40.1) 20 (1.4)Direct admission 559 (46.2) 581 (48.0) 70 (5.8)1994–1995 <0.001Wait-listed 920 (61.3) 549 (36.6) 32 (2.1)Direct admission 694 (46.9) 673 (45.5) 112 (7.6)1996–1997 <0.001Wait-listed 929 (58.2) 625 (39.2) 41 (2.6)Direct admission 761 (46.9) 776 (47.9) 84 (5.2)1998–1999 <0.001Wait-listed 829 (52.9) 675 (43.1) 62 (4.0)Direct admission 867 (41.2) 984 (46.8) 251 (11.9)2000–2001 <0.001Wait-listed 525 (37.6) 724 (51.8) 148 (10.6)Direct admission 413 (19.4) 1119 (52.6) 594 (27.9)2002–2003 <0.001Wait-listed 691 (40.6) 876 (51.4) 136 (8.0)Direct admission 458 (23.6) 1037 (53.5) 444 (22.9)2004–2005 <0.001Wait-listed 489 (37.6) 692 (53.2) 119 (9.2)Direct admission 461 (19.3) 1242 (52.1) 683 (28.6).*Based on Northern New England Cardiovascular Disease Study Group [22].†Compares the distribution of risk between wait-listed patients and direct admissions for each period.length of the waiting-time interval required for a speci-fied proportion to undergo the operation. As measured bythe difference between 90th and 50th percentiles of thewait time distributions, 40% of the 1998, 1999, 2004 and2005 cohorts underwent surgery within 16 to 20 weeksfollowing the median waiting time (50th percentile), whileit took between 27 and 37 weeks for the cohorts in yearswhen supplementary funding was not available (Figure 2).Periods 1992–1993 and 2004–2005 showed the short-est waiting time and showed a notable difference inchanges of conditional remaining times between the peri-ods (Figure 3). For each period, the remaining time duringwhich half of the patients were expected to access surgerydid not change for about the first 10 weeks since decision.After the first 10 weeks, the conditional median timesfor surgery remained relatively constant for period 2004–2005, but these times increased with longer waits forperiod 1992–1993. In contrast, in the two periods showingthe longest waiting times, namely 1996–1997 and 2002–2003, the conditional median time decreased with thelonger waits, indicating perhaps an active wait-list man-agement in years when the supplementary funding wasnot provided.Once wait-listed patients had a decision to operate, theaverage weekly number of operations was lowest in 1996–1997, 2000–2001, and 2002–2003 (Table 4). The averagerate of undergoing surgery from a wait list was about 5procedures per 100 patient-weeks in these periods withthe lowest rates. After adjustment for patient-related fac-tors, compared to the surgery rate in 1996–1997, theweekly odds that a patient would undergo operation werehighest in 1992–1993, decreased to a low in 1996–1997,rose in 1998–1999, decreased to another low in 2000–2001 and 2002–2003, and then rose again in 2004–2005(Table 4).Access to surgery through direct admissionAmong patients who had a decision to operate for CABGand were directly admitted to hospital, times betweendecision to operate and surgical revascularization werelongest in the periods 1992–1994, but were much shorterthan the times for wait-listed patients (Figure 4). Duringthese periods 80% of patients underwent surgery within 7days. Half of patients underwent surgery within 1 day ofdecision to operate and 80% within 5 days during periods1995 and later.Sobolev et al. BMC Health Services Research 2012, 12:311 Page 10 of 15http://www.biomedcentral.com/1472-6963/12/3110 4 8 12 16 20 24 28 32 36 40 44 48 5200.10.20.30.40.50.60.70.80.911992−19931994−19951996−19971998−19992000−20012002−20032004−2005Time  since  decision  (weeks)Probability  of  surgical  revascularizationFigure 1 Estimated probability of surgical revascularization within a certain time of decision for surgical revascularization, by calendarperiod of decision, among patients who accessed surgery through registration on a wait list.92 93 94 95 96 97 98 99 00 01 02 03 04 050481216202428323640444852Calendar  period  of  decisionTime  between  decision  and  surgery  (weeks)Figure 2 Time between decision to operate and surgical revascularization among patients who accessed surgery through registration ona wait list, by calendar period of decision. Bottom of bar = 50th percentile, top of bar = 90th percentile.Sobolev et al. BMC Health Services Research 2012, 12:311 Page 11 of 15http://www.biomedcentral.com/1472-6963/12/3110 4 8 12 16 20510152025301992−19931994−19951996−19971998−19992000−20012002−20032004−2005Time  since  decision  (weeks)Conditional  median  time  for  surgical  revascularization  (weeks)Figure 3 Conditional median time of surgical revascularization at a certain time since decision for surgical revascularization, by calendarperiod of decision, among patients who accessed surgery through registration on a wait list.Once direct admissions had a decision to operate, theaverage daily number of operations was lowest in 1992–1993 at about 23 procedures per 100 patient-days, roseto about 36 procedures per 100 patient-days in 1998–1999, after which the rate remained stable (Table 5). Afteradjustment for patient-related factors, compared to theTable 4 Average weekly rate of coronary artery bypass procedure in relation to calendar period of decision to proceedwith surgery, for patients registered on a wait listType of access by No. of No. of Total Crude rate† Crude OR‡ Adjusted OR ‡§‖calendar period of decision patients procedures waiting time∗ (95% CI) (95% CI) (95% CI)1992–1993 1726 1519 20462 7.4 (7.1–7.8) 1.7 (1.6–1.9) 2.0 (1.9–2.2)1994–1995 1793 1545 26452 5.8 (5.5–6.1) 1.3 (1.2–1.4) 1.4 (1.3–1.5)1996–1997 1862 1555 35054 4.4 (4.2–4.7) 1.0 1.01998–1999 1610 1426 21266 6.7 (6.4–7.1) 1.5 (1.4–1.6) 1.5 (1.4–1.7)2000–2001 1791 1509 31887 4.7 (4.5–5.0) 1.1 (1.0–1.2) 1.1 (1.0–1.2)2002–2003 1889 1613 35447 4.6 (4.3–4.8) 1.0 (0.9–1.1) 1.0 (0.9–1.1)2004–2005 1359 1172 14252 8.2 (7.8–8.7) 1.9 (1.7–2.0) 1.9 (1.8–2.1)All periods 12030 10339 184820 5.6 (5.5–5.7) – –Abbreviations: OR = odds ratio; CI = confidence interval.*To measure waiting times, patients were followed for a maximum of 52 weeks.†Per 100 patient weeks calculated as the number of procedures performed divided by the sum of waiting times.‡As measured by odds ratios derived from discrete-time survival models, adjusting for consecutive weeks of waiting (0.5–52 weeks).§Adjusted for sex, age at decision, urgency at decision, institution at decision, comorbidities at decision, coronary anatomy at decision, and time betweencatheterization and decision.‖218 patients with unknown values for urgency at decision were excluded.Sobolev et al. BMC Health Services Research 2012, 12:311 Page 12 of 15http://www.biomedcentral.com/1472-6963/12/31192 93 94 95 96 97 98 99 00 01 02 03 04 05012345678Calendar  period  of  decisionTime  between  decision  and  surgery  (days)Figure 4 Time between decision to operate and surgical revascularization among patients who accessed surgery through directadmission, by calendar period of decision. Bottom of bar = 50th percentile, top of bar = 80th percentile.surgery rate in 1996–1997, the daily odds of surgery werelower prior to 1996–1997, but higher after this period(Table 5).Time between catheterization and surgeryWe found that for those who underwent CABG, timesbetween catheterization and surgical revascularizationwere shorter among patients who accessed surgerythrough direct admission compared to access throughwait-list registration. In the urgent group, half of directadmissions underwent surgery within 1 week, whereashalf of wait-listed patients underwent surgery within 7weeks. In addition, half of direct admissions and halfof wait-listed patients underwent surgery within 1 and13 weeks respectively, in the semiurgent group. In thenonurgent group these timeframes were 8 and 23 weeks,respectively. The weekly odds of surgery after catheteriza-tion were 4, 5, and 3 times higher among direct admissionscompared to wait-listed patients in the urgent, semiur-gent, and nonurgent groups, respectively, after adjustmentfor age, sex, hospital at catheterization, mode of admis-sion at catheterization, comorbidity at surgery, hospital atsurgery, and coronary anatomy at surgery. We also foundthat time between catheterization and decision to operatebecame shorter in the 2000s compared to the 1990s for thesemiurgent group; the weekly rate of registration was 16%and 25% higher in 2000–2001 and 2002–2003 comparedto 1996–1997. In the urgent group, these rates were 2.5and 1.6 times higher in 2002–2003 and 2004–2005 com-pared to 1996–1997. The weekly rates of decision were notdifferent across calendar periods in the nonurgent group,after adjustment.DiscussionCoronary revascularization is indicated to alleviate chestpain and to reduce the risk of death among patients whohave limiting angina that persists despite optimal medicaltreatment and who have coronary anatomy that is suitablefor the procedure. However, in healthcare systems thatuse wait lists to manage access to care, patients requir-ing non-emergency surgical revascularization may haveto wait after the decision to operate. In this paper, wesought to determine whether the year of decision to pro-ceed with non-emergency CABG had an effect on timeto surgery in a health system with publicly-funded uni-versal coverage for the procedure. We estimated temporalchanges in the length of time that patients had to waitbetween decision to operate and the procedure itself over14 years that included several years with increases in fund-ing.We focused on isolated CABG surgery because accessSobolev et al. BMC Health Services Research 2012, 12:311 Page 13 of 15http://www.biomedcentral.com/1472-6963/12/311Table 5 Average daily rate of coronary artery bypass procedure in relation to calendar period of decision to proceed withsurgery, for direct admissionsType of access by No. of No. of Total Crude rate† Crude OR‡ Adjusted OR‡§‖calendar period of decision patients procedures waiting time∗ (95% CI) (95% CI) (95% CI)1992–1993 1204 1003 4228 23.7 (22.3–25.2) 0.7 (0.6–0.7) 0.7 (0.6–0.8)1994–1995 1474 1270 4489 28.3 (26.7–29.8) 0.8 (0.7–0.9) 0.9 (0.8–0.9)1996–1997 1621 1442 4173 34.6 (32.8–36.3) 1.0 1.01998–1999 2089 1920 5301 36.2 (34.6–37.8) 1.1 (1.0–1.2) 1.2 (1.1–1.3)2000–2001 2121 1895 5579 34.0 (32.4–35.5) 1.0 (0.9–1.1) 1.2 (1.1–1.3)2002–2003 1940 1740 5145 33.8 (32.2–35.4) 1.0 (0.9–1.1) 1.1 (1.0–1.2)2004–2005 2369 2140 6206 34.5 (33.0–35.9) 1.0 (1.0–1.1) 1.2 (1.1–1.3)All periods 12818 11410 35121 32.5 (31.9–33.1) – –Abbreviations: OR = odds ratio; CI = confidence interval.*To measure waiting times, patients were followed for a maximum of 7 days.†Per 100 patient days calculated as the number of procedures performed divided by the sum of waiting times.‡As measured by odds ratios derived from discrete-time survival models, adjusting for consecutive days of waiting (0–7 days).§Adjusted for sex, age at decision, urgency at decision, institution at decision, comorbidities at decision, coronary anatomy at decision, and time betweencatheterization and decision.‖1 patient with unknown value for sex was excluded.to surgery could have been managed differently for com-bined procedures than for isolated CABG. As a result, wedid not consider data from 312 (2%) wait-listed patientsand 211 (1%) directly-admitted patients whose procedurewas not isolated CABG.We found that during two periods when supplemen-tary funding was available, 1998–1999 and 2004–2005, theweekly rate of undergoing surgery from a wait list was,respectively, 50% and 90% higher than in 1996–1997, theperiod with the longest waiting times. We also observeda reduction in the difference in 90th and 50th percentilesof the waiting-time distributions. Forty percent of patientsin the 1998, 1999, 2004 and 2005 cohorts (years whensupplementary funding was provided) underwent surgerywithin 16 to 20 weeks following the median waiting time,while it took between 27 and 37 weeks for the cohorts reg-istered in the years when supplementary funding was notavailable. Among patients who were directly admitted tohospital, time between decision and surgery was longestin 1992–1993 and then steadily decreased through thelate nineties. The rate of surgery among patients directlyadmitted to hospital was the highest in 1998–1999, andhas not changed afterwards, even in years when supple-mentary funding was provided.The most important contribution of this analysis isproviding a more complete picture of access times forthe patient population requiring surgical revasculariza-tion on a non-emergency basis in a health care system thatbudgets the number of CABG procedures and uses sup-plementary funding to reduce the number patients whohave to wait for the procedure and their waiting times. Wecontrasted two pathways for accessing CABG. If angio-plasty is not indicated when the cardiologist evaluates thearterial lesions on the coronary angiogram, then a car-diac surgeon is consulted to assess the patients’ suitabilityfor CABG. Patients are transferred to an in-patient warddirectly from the catheterization laboratory if expeditedassessment is necessary and, if deemed suitable, thesepatients wait for the operation in hospital without regis-tration on a wait list. Alternatively, a consultation with thesurgeon is scheduled at a later date. Surgeons register ontheir wait lists patients who need CABG and for whom theoperation can be safely delayed. To address this issue, westudied access to surgical coronary revascularization fornon-emergency patients through direct admission to hos-pital at the surgeon’s discretion, and contrasted the totalamount of time between cardiac catheterization and sur-gical revascularization for the two pathways: through await list and through direct admission.In this analysis, a potential concern is the misclassi-fication of the recorded urgency for treatment, becausesurgeons may manage access to surgery on the basis ofvarious considerations, such as the best use of operatingtime or the availability of hospital resources. Therefore,the outcome might have been influenced by the individualsurgeon’s threshold for accepting a patient for nonurgenttreatment. It is plausible that the time to surgery maydiffer between patients treated by surgeons with a highvolume of CABG procedures and surgeons who performa diverse range of cardiac procedures.We did not have access to detailed information aboutphysicians’ decision-making on access to the procedure.To explore further the effect of the supplementary fund-ing, we classified all patients using the algorithm devel-oped by Northern New England Cardiovascular DiseaseStudy Group [22]. The percentage of low risk patientsSobolev et al. BMC Health Services Research 2012, 12:311 Page 14 of 15http://www.biomedcentral.com/1472-6963/12/311accessing surgery through direct admission declined con-siderably in years when supplementary funding was pro-vided.More research is needed to evaluate whether waitingtimes for non-emergency surgery vary because of chancealone after adjustment for clinical factors and variation insupply. For example, it remains unclear whether directlyadmitting patients of low risk is done to circumvent longwait lists, or to substitute for cancellations on the operat-ing room schedule.Since 2002, percutaneous coronary intervention hasbecome an increasingly common method of coronaryrevascularization, leading to a considerable change in thecomposition of patient population for both catheter-basedand surgical procedures. We only had data for the periodbefore 2005, and therefore our analysis could not adjustfor changes in the proportional use of surgical revascular-ization over the past decade.ConclusionsOur study provides evidence that waiting times for non-emergency coronary bypass surgery shortened after sup-plementary funding was granted to increase volume ofcardiac surgical care in a health system with publicly-funded universal coverage for the procedure. The effect ofthe supplementary funding was not uniform for patientsthat access the services through wait lists and throughdirect admissions. This might indicate that surgical ser-vices have used supplementary funding and direct admis-sions as two independent mechanisms to provide moretreatments without delay. Considering that the hospitalshad capacity to increase the number of operations, thesupply-side initiatives indeed were effective in reducingwaiting times. Perhaps it was an empirical way to findthe level to budget the number of surgeries in the welldefined population. In our view, some further options forimproving access to cardiac care should include policiesfor effective management of patient flow.Competing interestsThe authors declare that they have no competing interests.Author’s contributionsBS conceived the study concept and design, participated in analysis andinterpretation, and drafted the manuscript. GF participated in data acquisitionand critically revised the manuscript. LK participated in analysis andinterpretation, and drafted the manuscript. AL participated in data acquisition.RS performed database analysis and has been involved in drafting themanuscript. BR performed statistical analysis and drafted the manuscript. Allauthors read and approved the final manuscript.AcknowledgementsThis study received financial support from the Canada Research ChairsProgram (BS), the Canada Foundation for Innovation (BS, AL), the MichaelSmith Foundation for Health Research (AL), the Vancouver Coastal HealthResearch Institute (BS, LK), and the St. Paul’s Hospital Foundation (AL, RS).None of the sponsors had a role in the study design; in the collection, analysis,and interpretation of data; in the writing of the report; or in the decision tosubmit the paper for publication. We are indebted to nurses, cardiac surgeonsand cardiologists in the participating hospitals for their efforts to ensure thecompleteness and accuracy of the registry data.Author details1School of Population and Public Health, The University of British Columbia,Vancouver, BC, Canada. 2Department of Surgery, The University of BritishColumbia, Vancouver, BC, Canada. 3Centre for Clinical Epidemiology andEvaluation, Vancouver Coastal Health Research Institute, Vancouver, BC,Canada. 4Utilitas Consulting, Vancouver, BC, Canada. 5Community Health &Epidemiology, Dalhousie University, Halifax, NS, Canada.Received: 14 December 2011 Accepted: 30 August 2012Published: 11 September 2012References1. Rihal CS, Raco DL, Gersh BJ, Yusuf S: Indications for coronary arterybypass surgery and percutaneous coronary intervention in chronicstable angina: review of the evidence andmethodologicalconsiderations. Circulation 2003, 108(20):2439–2445.2. Naylor CD: A different view of queues in Ontario. Health Affairs 1991,10(3):110–128.3. Fierlbeck K: Health Care in Canada: A Citizen’s Guide to Policy and Politics.Toronto: University of Toronto Press; chap. Funding Health Care; 2011:3–43.4. Naylor CD, Levinton CM, Baigrie RS: Adapting to waiting lists forcoronary revascularization. Do Canadian specialists agree on whichpatients come first? Chest 1992, 101(3):715–722.5. Morgan CD, Sykora K, Naylor CD: Analysis of deaths while waiting forcardiac surgery among 29,293 consecutive patients in Ontario,Canada. Heart 1998, 79(4):345–349.6. Ray AA, Buth KJ, Sullivan JA, Johnstone DE, Hirsch GM:Waiting forcardiac surgery: results of a risk-stratified queuing process.Circulation 2001, 104(12 Suppl 1):I92–I98.7. Sampalis J, Boukas S, Liberman M, Reid T, Dupuis G: Impact of waitingtime on the quality of life of patients awaiting coronary arterybypass grafting. CMAJ 2001, 165(4):429–433.8. Levy A, Sobolev B, Hayden R, Kiely M, FitzGerald M, Schechter M: Time onwait lists for coronary bypass surgery in British Columbia, Canada,1991 - 2000. BMC Health Services Res 2005, 5:22.9. Sobolev BG, Levy AR, Kuramoto L, Hayden R: Chances of late surgery inrelation to length of wait lists. BMC Health Services Res 2005, 5:63.10. Sobolev B, Levy A, Hayden R, Kuramoto L: Does wait-list size atregistration influence time to surgery? analysis of apopulation-based cardiac surgery registry. Health Services Res 2006,41:23–49.11. Chamberlayne R, Green B, Barer ML, Hertzman C, Lawrence WJ, Sheps SB:Creating a population-based linked health database: a new resourcefor health services research. Can J Public Health 1998, 89(4):270–273.12. Blake JT, Carter MW: Surgical process scheduling: a structured review.J Soc Health Syst 1997, 5(3):17–30.13. Sobolev B, Kuramoto L: Analysis of Waiting-Time Data in Health ServicesResearch. New York, NY: Springer; 2008.14. Christenson JT, Simonet F, Schmuziger M: The influence of age on theoutcome of primary coronary artery bypass grafting. J CardiovascSurg (Torino) 1999, 40(3):333–338.15. O’Connor NJ, Morton JR, Birkmeyer JD, Olmstead EM, O’Connor GT: Effectof coronary artery diameter in patients undergoing coronarybypass surgery. Northern New England Cardiovascular DiseaseStudy Group. Circulation 1996, 93(4):652–655.16. Naylor CD, Baigrie RS, Goldman BS, Basinski A: Assessment of priorityfor coronary revascularisation procedures. Lancet 1990,335(8697):1070–1073.17. DeLong ER, Nelson CL, Wong JB, Pryor DB, Peterson ED, Lee KL, Mark DB,Califf RM, Pauker SG: Using observational data to estimate prognosis:an example using a coronary artery disease registry. Stat Med 2001,20(16):2505–2532.18. Romano PS, Roos LL, Jollis JG: Adapting a clinical comorbidity indexfor use with ICD-9-CM administrative data: differing perspectives. JClin Epidemiol 1993, 46(10):1075–1079.19. King KM, Ghali WA, Faris PD, Curtis MJ, Galbraith PD, Graham MM,Knudtson ML: Sex differences in outcomes after cardiacSobolev et al. BMC Health Services Research 2012, 12:311 Page 15 of 15http://www.biomedcentral.com/1472-6963/12/311catheterization - Effect modification by treatment strategy andtime. Jama-J AmMed Assoc 2004, 291(10):1220–1225.20. Bland JM, Altman DG: Survival probabilities (the Kaplan-Meiermethod). BMJ: Br Med J 1998, 317(7172):1572.21. Allison PD: Discrete-timemethods for the analysis of event histories.Sociological Methodology 1982, 13:61–98.22. O’Connor GT, Plume SK, Olmstead EM, Coffin LH, Morton JR, Maloney CT,Nowicki ER, Levy DG, Tryzelaar JF, Hernandez F:Multivariate predictionof in-hospital mortality associated with coronary artery bypass graftsurgery. Northern New England Cardiovascular Disease StudyGroup. Circulation 1992, 85:2110–2118.doi:10.1186/1472-6963-12-311Cite this article as: Sobolev et al.: Evaluation of supply-side initiatives toimprove access to coronary bypass surgery. BMC Health Services Research2012 12:311.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submit

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