Use of cardiac procedures and outcomes in elderly patients with myocardial infarction in the United States and Canada

BACKGROUND

Acute myocardial infarction is a leading cause of morbidity and mortality in the United States and Canada. We performed a population-based study to compare the use of cardiac procedures and outcomes after acute myocardial infarction in elderly patients in the two countries.

METHODS

We compared the use of invasive cardiac procedures and the mortality rates among 224,258 elderly Medicare beneficiaries in the United States and 9444 elderly patients in Ontario, Canada, each of whom had a new acute myocardial infarction in 1991.

RESULTS

The U.S. patients were significantly more likely than the Canadian patients to undergo coronary angiography (34.9 percent vs. 6.7 percent, P< 0.001), percutaneous transluminal coronary angioplasty (11.7 percent vs. 1.5 percent, P<0.001), and coronary-artery bypass surgery (10.6 percent vs. 1.4 percent, P<0.001) during the first 30 days after the index infarction. These differences in the use of cardiac procedures narrowed but persisted through 180 days of follow-up. The 30-day mortality rates were slightly but significantly lower for the U.S. patients than for the Canadian patients (21.4 percent vs. 22.3 percent, P=0.03). However, the one-year mortality rates were virtually identical (34.3 percent in the United States vs. 34.4 percent in Ontario, P= 0.94).

CONCLUSIONS

Short-term mortality after an acute myocardial infarction was slightly lower in the United States than in Ontario, but these differences did not persist through one year of follow-up. The strikingly higher rates of use of cardiac procedures in the United States, as compared with Canada, do not appear to result in better long-term survival rates for elderly U.S. patients with acute myocardial infarction.

Towards improved coding of acute myocardial infarction in hospital discharge abstracts: a pilot project

OBJECTIVE

To pilot-test a simple checklist designed to improve coding of acute myocardial infarction (AMI) in hospital discharge abstracts.

BACKGROUND

Health records technologists review hospital charts to code discharge diagnoses according to the International Classification of Diseases, 9th revision (ICD-9). Many studies have suggested that there is a high false positive rate in coding AMI, ie, ICD-9 410, on hospital discharge abstracts.

PATIENTS AND METHODS

The checklist required either at least two of suggestive symptoms, diagnostic electrocardiographic changes, or diagnostic rise in serum cardiac enzymes; or confirmation by autopsy. First case of use was confirmed-typical time to complete the checklist was 3 to 4 mins. Then 16 Ontario community hospitals were recruited to apply the checklist on a blinded basis to 1000 randomly drawn in-patient records-10% were audited for another study to confirm AMI; and 90% were originally coded with 'most responsible diagnosis' (MRD) of AMI, other cardiovascular diagnoses and various noncardiac conditions. Percentage agreement (95% CI) between the checklist and the confirmed or coded diagnosis was analyzed; coding of AMI as a secondary diagnosis was examined in further analyses.

RESULTS

One hospital withdrew for logistical reasons; the final useable sample from 15 hospitals was 943 records. The checklist correctly identified 100% of AMIs independently confirmed for another study; usual coding identified 89.7% of cases (70 of 78; 95% CI 80.8 to 95.5). For cases not confirmed, but where the physician had nonetheless diagnosed AMI, six of 11 charts were miscoded as AMI in hospital records; none were miscoded by the checklist. For records with AMI as MRD, 11.6% (44 of 380; 95% CI 8.5 to 15.2) were classified as false positives by the checklist. Where an AMI was coded as a secondary diagnosis, 52.9% (36 of 68; 95% CI 40.5 to 65.2) met the checklist criteria for AMI. Finally, among records where the MRD was other than AMI, 6.8% (38 of 563; 95% CI 4.8 to 9.2) met checklist criteria for AMI during admission, but 94.7% had an ICD-9410 code as a secondary diagnosis.

CONCLUSION

A simple checklist can be very easily applied, has extremely high sensitivity for confirming the presence of AMI, and identifies a clinically significant proportion of charts with false positive codes for AMI. Conversely, these findings support the high sensitivity (low false negative rates) of conventional coding practices for AMI in Canadian hospital records, be it as a primary or secondary diagnosis (eg, 95% detection rate). Usual coding, combined with the checklist for tentative ICD-9 410 diagnoses, would improve the accuracy of Canadian hospital records.

The influence of risk on the results of warm heart surgery: a substudy of a randomized trial

OBJECTIVE

The Warm Heart Investigators Trial randomized isolated coronary bypass patients to cold or warm cardioplegia, and demonstrated that warm cardioplegia significantly reduced the prevalence of low output syndrome and myocardial infarction (as defined by CKMB enzyme release). This study was designed prospectively as a subanalysis of the original trial, to determine the effect of warm heart surgery on high risk patients, who were anticipated to derive the major benefit from warm cardioplegia.

METHODS

The prespecified endpoint for this study was a composite outcome of morbidity and mortality (death and/or low output syndrome and/or enzymatic myocardial infarction). Only patients with complete data for all outcomes were included, totalling 1374 patients (692 warm cardioplegia, 682 cold cardioplegia) who were randomized in the Warm Heart Investigators Trial. High medium and low risk patients were identified by a multivariate model of predicted risk for the study outcome.

RESULTS

Analysis of the independent and interactive influence of cardioplegia technique and predicted risk demonstrated that warm cardioplegia significantly reduced the overall prevalence of morbidity and mortality (warm: 15.9 versus cold: 25.2%, P < 0.01). However, no significant differences in warm-cold effects were detected among risk terciles. Cardioplegia technique had a similar differential influence on mortality and morbidity in low risk patients (warm: 7.3, cold: 17.4%) as it did in high risk patients (warm: 31.1, cold: 39.9%).

CONCLUSIONS

Although our analysis confirms the overall benefits of warm cardioplegia, our unanticipated finding in high risk subjects may be explained by the fact that morbidity and mortality in that patient subgroup is caused not only by poor myocardial protection, but by other clinical and technical factors. Further studies are necessary to identify those patients who might benefit most from improved myocardial protection techniques.

Case selection and appropriateness of coronary angiography and coronary artery bypass graft surgery in British Columbia and Ontario

OBJECTIVES

To compare the types of patients selected for coronary angiography (CA) and coronary artery bypass graft (CABG) surgery, and the appropriateness of the procedures performed on these patients in a random sample of cases in British Columbia and Ontario.

DESIGN

Retrospective randomized medical record review.

SETTING

All hospitals performing CA and/or CABG in British Columbia and Ontario in fiscal year 1989/90.

PATIENTS

For CA, 395 randomly selected patients in Ontario and 139 randomly selected patients in British Columbia; for CABG, 431 randomly selected patients in Ontario and 125 randomly selected patients in British Columbia.

MAIN OUTCOME MEASURES

Case selection was measured in terms of the demographic and clinical characteristics of patients undergoing the procedures. Appropriateness was measured by comparing the clinical characteristics of patients undergoing the procedures with explicit criteria established by a panel of Canadian physicians. The yield from CA was measured as the proportion of patients who were found to have insignificant anatomical disease.

RESULTS

Analysis of patients selected for CA showed that sample patients from Ontario were less likely than those from British Columbia to be female (25% versus 37%, respectively, P = 0.012) and less likely to have undergone a previous revascularization (12% versus 24%, respectively, P = 0.005). The distribution of main indications for CA differed between the two provinces (P = 0.002), with Ontario patients more likely to have chronic stable angina (45% versus 24%) and less likely to have unstable angina (16% versus 26%). For CABG, sample patients from Ontario were less likely to be 65 years of age or older (32% versus 45%, P = 0.016) and more likely to have an ejection fraction less than 35% (14% versus 5%, P = 0.006). The distribution of the main indications for CABG differed (P < 0.001), with Ontario patients more likely to have chronic stable angina (68% versus 38%) and less likely to have unstable angina (20% versus 43%). There was no statistically significant difference in CA cases rated as inappropriate (8.4% in Ontario versus 10.8% in British Columbia, P = 0.396) or CABG cases rated as inappropriate (3.9% in Ontario versus 2.4% in British Columbia, P = 0.393). There were no statistically significant differences in the proportion of CA that yielded insignificant anatomical disease (17.5% in Ontario versus 18.4% in British Columbia, P = 0.355).

CONCLUSIONS

There were differences between Ontario and British Columbia in the demographic and clinical characteristics of patients selected for CA and CABG. This may indicate differences in the referral process in the two provinces. Despite these differences the rates of inappropriate procedures and the yield from CA were similar.

Is colour flow imaging needed to exclude clinically significant valvular regurgitation in adult patients undergoing transthoracic echocardiography?

OBJECTIVE

To establish whether clinically significant aortic and mitral valvular regurgitation can be excluded in adult patients undergoing transthoracic echocardiography without using colour flow imaging.

SETTING

Sunnybrook Health Science Centre, a tertiary referral centre with full cardiovascular services affiliated with the University of Toronto, Toronto, Ontario.

DESIGN

Logistic regression models were developed from a retrospective review of 14,051 unselected consecutive echocardiograms from 1991 through 1994. The dependent variable was more than mild aortic or mitral valvular regurgitation. Independent variables included age, sex and various functional and structural measures obtained during routine two-dimensional echocardiography. The negative predictive values and sensitivity of the models were estimated.

INTERVENTION

The number of patients correctly classified by these models, as well as the proportion for whom the colour flow imaging did not add to the baseline echocardiogram, was determined. Nonparametric bootsrapping was used to obtain confidence intervals for these statistics.

MAIN RESULTS

Ten models were developed, with negative predictive values ranging from 96.2% to 100%. Incorporation of such decision aids into the software of echocardiographic machinery would help echocardiographers to rule out significant aortic or mitral regurgitant lesions. In practices where colour flow imaging is routinely employed, 40% fewer procedures could be performed.

CONCLUSIONS

Models based on simple demographic and two-dimensional echocardiographic variables can reliably exclude significant valvular regurgitation and could potentially reduce the volumes and costs of colour flow imaging. Given the widespread diffusion of colour Doppler imaging, the models may also be helpful to avoid misinterpretation of flow imaging results, by defining subgroups in whom the prior probability of significant aortic or mitral regurgitation is extremely low.

Time to treatment with thrombolytic therapy: determinants and effect on short-term nonfatal outcomes of acute myocardial infarction. Canadian GUSTO Investigators. Global Utilization of Streptokinase and + PA for Occluded Coronary Arteries

OBJECTIVES

To characterize the extent of delay in administration of thrombolytic therapy to patients with acute myocardial infarction (AMI) in Canada, to examine patient-specific predictors of such delay and to measure the effect of delay on short-term nonfatal cardiac outcomes.

DESIGN

Secondary cohort analysis of data from the first international Global Utilization of Streptokinase and tPA for Occluded Coronary Arteries (GUSTO-I) trial.

SETTING

Sixty-three acute care hospitals across Canada.

SUBJECTS

All 2898 Canadian patients with an AMI enrolled in GUSTO-I.

MAIN OUTCOMES

Time before arrival at a hospital ("symptom-to-door" time) and time from arrival to administration of therapy ("door-to-needle" time) for patients who had an AMI outside of a hospital, in clinically relevant categories; proportions of patients with nonfatal, serious cardiac events, including shock, sustained ventricular tachycardia, ventricular fibrillation and asystole.

RESULTS

Of the total number of patients enrolled, records were complete for 2708; 2542 of these patients (93.9%) had an AMI outside of a hospital. These 2542 patients presented a median 81 (interquartile range 50 to 130) minutes after the onset of symptoms, and the median time to treatment in hospital was 85 (interquartile range 61 to 115) minutes. Whereas a greater proportion of Canadian patients than of patients enrolled in GUSTO-I in other countries reached hospital within 2 hours of symptom onset (71.5% v. 61.2%, p < 0.001), a greater proportion of Canadian patients experienced in-hospital treatment delays of more than 1 hour (75.3% v. 57.1%, p < 0.001). In an analysis of all 2708 patients with complete records, both the unadjusted and adjusted odds of nonfatal cardiac events for those treated 4 to 6 hours after symptom onset were significantly higher than for those treated within 2 hours (odds ratio 1.60, 95% confidence interval 1.09 to 2.37).

CONCLUSION

After arrival at a hospital, Canadian patients enrolled in GUSTO-I received thrombolytic therapy more slowly than trial enrollees in other countries. Such delays are already known to decrease the rate of short-term survival after AMI. The findings further show that long time to treatment also increases the odds of nonfatal, serious cardiac events. Hospitals and physicians caring for patients with AMI should routinely assess whether and how they can improve door-to-needle times.

The burden of waiting for hip and knee replacements in Ontario. Ontario Hip and Knee Replacement Project Team

The objectives of this study were to assess the impact of major joint replacements in reducing pain and disability and to describe the burden of pain and disability that could be avoided by ordering the queues with respect to severity of disease. A secondary goal was to compare the uses of a general health status measure, the Short Form Health Survey (SF-36), and a disease-specific measure, the Western Ontario McMaster Osteoarthritis Index (WOMAC), for accomplishing the objectives. The results are based on interviews with 209 patients before and after they had surgery. Only 15.9% of the patients had surgery within 3 months' waiting time, 19.2% waited 4-6 months, 30.7% waited 7-9 months, and the remaining 34.1% waited a year or more. The waiting times were unrelated to the severity of pain or disability reported in the initial interview. Following surgery, there were large reductions in the WOMAC scores for pain, stiffness and difficulty in functioning. The SF-36 showed substantial improvements in relief from pain and in physical functioning, and reductions in role limitation due to physical problems, but not for scores related to mental health. The WOMAC scores were more responsive to the benefits of surgery than the SF-36 scores. Queuing systems keyed on burden of symptoms could reduce the burden of pain and disability suffered by patients awaiting surgery. The improvements from hip and knee replacements suggest that equitable access for these procedures should be a priority in Ontario.

Coronary artery bypass graft surgery in Ontario and New York State: which rate is right? Steering Committee of the Cardiac Care Network of Ontario

BACKGROUND

Previous studies have shown that the rate of coronary artery bypass graft (CABG) surgery is much higher in New York State than in Ontario.

OBJECTIVE

To compare the service context and clinical characteristics of patients having CABG surgery in New York and Ontario.

DESIGN

Retrospective analysis of data from cardiac surgery registries in New York and Ontario.

PATIENTS

All 16,690 patients in New York and 5517 patients in Ontario who had isolated CABG surgery in 1993.

MEASUREMENTS

Clinical characteristics of patients having CABG surgery and rates of CABG surgery by coronary anatomy.

RESULTS

The overall age-adjusted rate of isolated CABG surgery was 1.79 times (95% CI, 1.74 to 1.85) greater in New York than in Ontario. Patients who had CABG surgery in New York were more likely to be elderly and female and to have recently had myocardial infarction (P < 0.001), whereas patients who had CABG surgery in Ontario were more likely to have had left ventricular dysfunction and severe coronary artery disease (two-vessel disease with proximal left anterior descending disease, three-vessel disease, or left main disease) (P < 0.001). The relative rate of CABG surgery for left main disease was 2.53 times (CI, 2.35 to 2.73) greater in New York than in Ontario but was 8.97 times (CI, 8.01 to 10.06) greater for patients with limited coronary artery disease (one-vessel or two-vessel disease without proximal left anterior descending disease).

CONCLUSIONS

The higher rates of CABG surgery in New York are associated with higher rates of CABG surgery among the elderly, women, and patients who recently had myocardial infarction. Potential underservicing in Ontario is suggested by a lower rate of CABG surgery for left main disease; however, the higher rate of CABG surgery in New York is also associated with a strikingly higher rate of surgery in patients with limited coronary disease. Such trade-offs highlight the difficulty of defining an optimal rate of CABG surgery.

Coronary artery bypass mortality rates in Ontario. A Canadian approach to quality assurance in cardiac surgery. Steering Committee of the Provincial Adult Cardiac Care Network of Ontario

BACKGROUND

This study was conducted to assess the overall mortality rate and the amount of interhospital variation in risk-adjusted mortality rates after coronary artery bypass graft (CABG) surgery in Ontario, Canada. CABG outcomes data are not publicly disseminated in Ontario.

METHODS AND RESULTS

Clinical risk factors and surgical outcomes were collected on 15,608 patients undergoing isolated CABG surgery between April 1, 1991, and March 31, 1994, at the nine hospitals performing adult cardiac surgery in Ontario. The data were analyzed on the basis of a fiscal year. The overall mortality rate was 3.01%, and the risk-adjusted mortality rate declined from 3.17% in 1991 to 2.93% in 1993. In 1991, one of the nine hospitals had a risk-adjusted mortality rate significantly lower than the provincial average. Otherwise, the hospitals all had risk-adjusted mortality rates within the expected range during the time period of the study. All hospitals performed > 300 CABG procedures in 1992 and 1993, and only 2 of 42 cardiac surgeons performed < 50 CABG procedures in 1993.

CONCLUSIONS

The in-hospital mortality rate after CABG surgery in Ontario is low, and the amount of interhospital variation in risk-adjusted mortality rates is no greater than that expected by chance alone. These outcomes are probably attributable to regionalization of CABG surgery and a very low prevalence of low-volume cardiac surgeons in Ontario.

Are the marginal returns of coronary artery surgery smaller in high-rate areas? The Steering Committee of the Provincial Adult Cardiac Care Network of Ontario

BACKGROUND

Population-based rates of surgery vary within and between health-care systems, causing concern that case selection is less appropriate in high-rate areas. This inverse relationship has not been shown with appropriateness criteria generated by expert panels. We applied a trials-based measure of the potential survival benefit of coronary artery bypass graft surgery (CABG) to patients in a provincial registry, to determine the relationship between survival gains and rates of CABG.

METHODS

We did a population-based retrospective review of linked registry and administrative datasets. 5058 patients in the linked datasets underwent isolated CABG in Ontario between April 1, 1992, and March 31, 1993. Potential survival benefit of surgery was scored with an algorithm derived from a published overview of trials comparing CABG to medical treatment, analysed by county and by referral regions.

FINDINGS

Overall, case selection was appropriate whether assessed clinically (96.3% had either severe disease as judged on the coronary arteries affected or moderate to severe angina) or on the basis of survival benefit scores (94.0% predicted to obtain moderate or high benefit). There was significant variation in benefit scores across referral regions (p < 0.001). Benefit scores correlated inversely with county surgical rate (r = -0.49, p < 0.005) and the proportion of low-benefit cases increased with rates (r = 0.50, p < 0.005). Referral regions served by high-rate surgical centres had lower mean benefit scores.

INTERPRETATION

Most patients undergoing CABG in Ontario are in the high-survival benefit category. Surgery is defensible for patients with low survival benefit on the grounds of symptom relief, but the proportion of cases with low benefit rises with higher local rates of surgery. The inverse relationship between surgery rates and appropriateness of case selection may be better understood as diminishing marginal returns for specific outcomes with rising local use of procedures.

Appropriateness of primary total hip and knee replacements in regions of Ontario with high and low utilization rates

OBJECTIVE

To compare the appropriateness of case selection for primary hip and knee replacements between two regions in Ontario: one with a high population-based utilization rate and one with a low rate.

DESIGN

Random audit of medical records sampled from hospital discharge abstracts, with subsequent implicit and explicit criteria-based assessments of the appropriateness of surgery.

STUDY POPULATION

People aged 60 years or over who underwent elective, single-joint, non-fracture-related, primary hip or knee replacement between Apr. 1, 1992, and Mar. 31, 1993, at one of seven hospitals in a high-rate region (comprising Brant, Huron and Oxford countries) or one of eight hospitals in a low-rate region (comprising the cities of Scarborough and Toronto).

INTERVENTIONS

Structured review of hospital medical records, with additional review of information from surgeons and family physicians' office charts if necessary. Three physicians reviewed patient data and rated the preoperative pain level and functional status of patients, with agreement among at least two reviewers. The proportion of inappropriate cases was then assessed according to explicit criteria defined by a multidisciplinary panel using the delphi process. Profiles of each case were also subjected to independent implicit review by two rheumatologists and two orthopedic surgeons.

OUTCOME MEASURES

Proportion of joint replacements deemed inappropriate in the high- and low-rate regions according to either the explicit criteria or the implicit review, as well as preoperative pain levels and functional status of patients in the high- and low-rate regions.

RESULTS

Hip replacements were more common among patients sampled in the low-rate region than among those in the high-rate region (57.3% v. 39.3%; p < 0.002), although the patients' baseline characteristics, including severity of preoperative pain and dysfunction, were otherwise similar between the regions. Inappropriate surgery, determined by explicit criteria, was equally uncommon in the two regions (6.4% and 6.1%). On implicit review, the two rheumatologists rated fewer cases as appropriate than did the two orthopedic surgeons (63.0% v. 80.0%; p < 0.001); however, the proportion of cases rated as inappropriate by the subspecialists was similar in the high- and low-rate regions (11.4% and 11.0%, respectively, by the rheumatologists, and 6.3% and 10.4%, respectively, by the orthopedic surgeons).

CONCLUSIONS

Patients selected for primary hip or knee replacement are similar in the high- and low-rate regions of Ontario. Inappropriate use of this procedure does not account for the high rate of surgery in some areas. Further studies will be required to determine which other factors account for the regional variations in the utilization rates and whether there is underservicing in low-rate areas.

Triiodothyronine augmentation in the treatment of refractory depression. A meta-analysis

BACKGROUND

Several trials have addressed the efficacy of liothyronine sodium therapy in euthyroid, nonpsychotic depressed patients refractory to tricyclic antidepressant therapy. We undertook a meta-analysis of these trials.

METHODS

The MEDLINE database (1966 to May 1995) and published reference lists were examined for controlled clinical trials of triiodothyronine augmentation in euthyroid patients with refractory depression. Quality assessment and data abstraction were performed independently by two reviewers. Results were aggregated three ways: the relative response rate compared with controls, accepting each trial's definition of clinical response; absolute improvement in response rates; and improvements in depression scores, analyzed as continuous variables without a prespecified threshold for clinical response.

RESULTS

Aggregating eight studies with a total of 292 patients, patients treated with triiodothyronine augmentation were twice as likely to respond as controls (relative response, 2.09; 95% confidence interval [CI], 1.31 to 3.32; P = .002). This corresponded to a 23.2% absolute improvement in response rates (95% CI, 4.5% to 41.9%; P = .02). Improvements in depression scores were moderately large (standardized effect size, 0.62; P < .001). However, study quality was uneven, and results were statistically heterogeneous. Among the four randomized double-blind studies, pooled effects were not significant (relative response, 1.53; 95% CI, 0.70 to 3.35; P = .29), but one study with negative results accounted for most of the intertrial heterogeneity in results.

CONCLUSIONS

Triiodothyronine augmentation may be an effective empirical method of increasing response rates and decreasing depression severity scores in a subgroup of patients with depression refractory to tricyclic antidepressant therapy, but the total number of patients randomized was small, and additional placebo-controlled data are required for a definitive verdict. Since therapeutic trends now favor other drugs, future trials might usefully examine triiodothyronine augmentation with selective serotonin reuptake inhibitors or compare potentiation strategies, eg, lithium vs triiodothyronine, for managing refractory depression. Such trials would benefit from much larger sample sizes than those reviewed here.

Cholesterol policy and the primary prevention of coronary disease: reflections on clinical and population strategies

Despite billions of dollars spent on targeted and population-wide strategies aimed at reducing human consumption of saturated fat and cholesterol, aspects of the diet-heart connection remain a source of debate. At least part of the uncertainty arises from a growing appreciation that the relationship between dietary habits, serum lipids, and atherosclerosis is more complex than was previously thought. While we wait for answers from clinical and basic research, what is to be done? This review examines evidence about clinical policies and population strategies for the primary prevention of coronary disease, with specific reference to diet and dyslipidemias. It also summarizes some current policies and offers conclusions about broad directions for further policy development.

Using a trade-off technique to assess patients' treatment preferences for benign prostatic hyperplasia

The probability-tradeoff technique may be used to assess treatment preferences in dichotomous choices. In this feasibility study, it was used to elicit benign prostatic hyperplasia (BPH) patients' attitudes towards three different treatments. Eighty-seven male outpatients used rating scales and the standard gamble to indicate the extents to which they were free of BPH symptoms. Paired descriptions of "watchful waiting" (WW), treatment with an alpha blocker (AB), and transurethral resection of the prostate (TURP) were presented, and the probability-tradeoff technique was used to obtain treatment-preference scores. The tradeoff task identified six internally consistent preference-order subgroups. The majority (n = 55; 63.2%) were in the two subgroups in which TURP was the least-preferred treatment. Compared with the other respondents, the members of these two subgroups reported significantly higher utilities for their BPH symptom status (89 vs 79; t = 2.87; p < 0.0005). Within each subgroup, preference scores for the middle- and top-ranked treatments were computed relative to the bottom-ranked treatment; for both WW and AB, significant across-subgroup differences were observed. In this preliminary study the probability-tradeoff technique was feasible, able to identify unique preference-order subgroups, and able to generate apparently meaningful preference scores in a clinical situation involving three alternative treatments. Further development of tradeoff tasks as the value-clarification component of decision aids for individual patients seems warranted.

Cardiopulmonary bypass, rewarming, and central nervous system dysfunction

BACKGROUND

During cardiopulmonary bypass a nasopharyngeal temperature greater than 38 degrees C at the end of rewarming may indicate cerebral hyperthermia. This could exacerbate an ischemic brain injury incurred during cardiopulmonary bypass.

METHODS

In a cohort of 150 aortocoronary bypass patients neuropsychologic test scores of 66 patients whose rewarming temperature exceeded 38 degrees C were compared with those who did not. There were no differences between groups with respect to demographic and intraoperative variables.

RESULTS

A trend was seen for hyperthermic patients to do worse on all neuropsychologic tests in the early postoperative period but not at 3-month follow-up. By analysis of covariance hyperthermic patients did worse on the visual reproduction subtest of the Weschler memory scale at 3 months (p = 0.02), but this difference was not found by linear regression (p = 0.10).

CONCLUSIONS

We were unable to demonstrate any significant deterioration in patients rewarmed to greater than 38 degrees C in the early postoperative period. The poorer performance in the visual reproduction subtest of the Wechsler memory scale at 3 months in the group rewarmed to more than 38 degrees C is interesting but far from conclusive. Caution with rewarming is still advised pending more in-depth study of this issue.

Characteristics and mortality outcomes of thrombolysis trial participants and nonparticipants: a population-based comparison

OBJECTIVES

This study was done to compare characteristics and outcomes of patients with acute myocardial infarction participating in two thrombolysis trials with those of nontrial patients at study hospitals and external hospitals.

BACKGROUND

Preferential recruitment of lower risk patients into randomized trials of thrombolysis has been suggested by earlier studies. However, to date there has not been a definitive population-based comparison of characteristics and outcomes for thrombolysis trial participants and nonparticipants.

METHODS

Population-based data on hospital admissions and mortality from acute myocardial infarction for all hospitals in Ontario from 1989 to 1992 were linked to data on trial participants in two distinct thrombolysis studies (GUSTO I and LATE). Included were 1,304 patients entered into GUSTO, 12,657 nonparticipants at GUSTO hospitals, 249 patients entered into LATE, 5,997 nonparticipants at LATE hospitals and 12,299 patients at external hospitals. The main outcomes were differences in age, gender, comorbidity scores, coronary revascularization and survival to hospital discharge.

RESULTS

Patients in both GUSTO and LATE were significantly more likely to be <70 years old (odds ratio [OR] 2.8 and 3.2, respectively), to be male (OR 2.0 and 2.1, respectively), to have low comorbidity scores (OR 2.0 and 2.3, respectively) and, for GUSTO alone, to undergo coronary revascularization (OR 2.4). Nontrial patients were similar between trial hospitals and external hospitals. In-hospital mortality rates for GUSTO and LATE patients were lower (6.9% and 6.6%, respectively) than for nonparticipants at study hospitals (16.8% and 19.7%, respectively; p<0.001 for both comparisons). Survival to hospital discharge remained higher among GUSTO (OR 1.9) and LATE patients (OR 2.0) than nonparticipants at study hospitals even after adjustment for age, gender, revascularization and comorbidity scores.

CONCLUSIONS

Compared with nontrial patients, thrombolysis trial participants are younger, more often male, undergo more revascularization and have less comorbid disease. Even after adjustment for these factors, participants have a survival advantage over nonparticipants that is larger than expected from thrombolysis alone. These findings are not attributable to inferior care or skewed populations at hospitals that did not join these major trials. Further study of these selection biases may guide future trial design and deepen our understanding of why thrombolytics have been underused for high risk patients in routine practice.

Cesarean delivery in relation to birth weight and gestational glucose tolerance: pathophysiology or practice style? Toronto Trihospital Gestational Diabetes Investigators

OBJECTIVES

To examine the relationship between birth weight and mode of delivery among women with untreated borderline gestational diabetes mellitus (GDM), treated overt GDM, and normoglycemia.

DESIGN

Prospective cohort study.

SETTING

Three Toronto, Ontario teaching hospitals.

PATIENTS

A total of 3778 volunteers aged 24 years or older.

INTERVENTIONS

Subjects underwent a 3-hour long, 100-g oral glucose tolerance test at 28 weeks' gestation, regardless of screening test results. Usual care was provided to 143 women who met the National Diabetes Data Group criteria for GDM. Physicians were blinded to glucose tolerance test results for all others, including 115 untreated women with borderline GDM by the broader criteria of Carpenter and Coustan.

MAIN OUTCOME MEASURES

Crude and adjusted rates of cesarean delivery and neonatal macrosomia (birth weight >4000 g).

RESULTS

Compared with normoglycemic controls, the untreated borderline GDM group had increased rates of macrosomia (28.7% vs 13.7%, P<.001) and cesarean delivery (29.6% vs 20.2%, P=.02). Cesarean delivery in this subgroup was associated with macrosomia (45.5% vs 23.5%, P=.03). Usual care of known GDM normalized birth weights, but the cesarean delivery rate was about 33% whether macrosomia was present or absent. A clearly increased risk of cesarean delivery among treated patients compared with normoglycemic controls persisted after adjustment for multiple maternal risk factors (adjusted odds ratio, 2.1; 95% confidence interval, 1.3 to 3.6).

CONCLUSIONS

Infant macrosomia was a mediating factor in high cesarean delivery rates for women with untreated borderline GDM. While detection and treatment of GDM normalized birth weights, rates of cesarean delivery remained inexplicably high. Recognition of GDM may lead to a lower threshold for surgical delivery that mitigates the potential benefits of treatment.

Hospital volume, calendar age, and short term outcomes in patients undergoing repair of abdominal aortic aneurysms: the Ontario experience, 1988-92

OBJECTIVE

To determine, for abdominal aortic aneurysm surgery, whether a previously reported relationship between hospital case volume and mortality rate was observed in Ontario hospitals and to assess the potential impact of age on the mortality rate for elective surgery.

DESIGN

Population based observational study using administrative data.

SETTING

All Ontario hospitals where repair of abdominal aortic aneurysm as a primary procedure was performed during 1988-92.

PATIENTS

These comprised 5492 patients with unruptured abdominal aortic aneurysms and 1203 patients with ruptured abdominal aortic aneurysms admitted to hospital between 1988-92 for repair of abdominal aortic aneurysm as a primary procedure.

MAIN OUTCOMES

In-hospital death and length of in-hospital stay.

RESULTS

The case fatality rate was 3.8% for unruptured abdominal aortic aneurysms and 40.0% for ruptured abdominal aortic aneurysms. For unruptured cases, after adjustment for patient and hospital covariates, each 10 case per year increase in hospital volume was related to a 6% reduction in relative odds of death (odds ratio (OR) 0.94, 95% confidence intervals 0.88, 0.99) and 0.29 days reduction (95% CI -0.22, -0.35) in postoperative in-hospital stay. Female sex (OR 1.53, 95% CI 1.08, 2.18) and transfer from another acute care hospital (OR 4.37, 95% CI 2.62, 7.29) were associated with increased case fatality rates among patients in the unruptured category. For ruptured cases, neither the case fatality rate nor postoperative in-hospital stay were significantly related to hospital volume. The case fatality rates increased linearly and substantially with advancing age both for unruptured and ruptured aneurysms, and the excess risk of postoperative death in ruptured as compared to unruptured aneurysms was substantially higher in older patients.

CONCLUSION

The relationship between hospital volume and mortality or morbidity was very modest and observed only for elective surgery. Case fatality rates in patients with ruptured abdominal aortic aneurysms remained 10 times higher than for patients with unruptured abdominal aortic aneurysms, despite improvements in overall mortality in comparison to previously published data. More effective detection of aneurysms, including elective repair for those once considered "high risk" older patients, might further reduce the toll from ruptured aortic aneurysms.