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Original article
Case fatality rates for South Asian and Caucasian patients show no difference 2.5 years after percutaneous coronary intervention
  1. D A Jones1,2,3,
  2. K S Rathod1,
  3. N Sekhri1,
  4. C Junghans1,
  5. S Gallagher1,
  6. M T Rothman1,
  7. S Mohiddin1,2,3,
  8. A Kapur1,3,
  9. C Knight1,3,
  10. A Archbold1,3,
  11. A K Jain1,3,
  12. P G Mills1,3,
  13. R Uppal1,2,3,
  14. A Mathur1,2,3,
  15. A D Timmis1,2,3,
  16. A Wragg1,2,3
  1. 1Department of Cardiology, Barts and the London NHS Trust, London, UK
  2. 2Department of Clinical Pharmacology, William Harvey Research Institute, Queen Mary and Westfield University, London, UK
  3. 3NIHR Cardiovascular Biomedical Research Unit, London Chest Hospital, London, UK
  1. Correspondence to Dr A Wragg, Department of Cardiology, London Chest Hospital, Bethnal Green, E2 9JX London, UK; Andrew.wragg{at}bartsandthelondon.nhs.uk

Abstract

Objective To compare short and medium-term prognosis in South Asian and Caucasian patients undergoing percutaneous coronary intervention (PCI) to determine if there are ethnic differences in case death rates.

Design Retrospective cohort study.

Setting A cardiology referral centre in east London.

Patients 9771 patients who underwent PCI from October 2003 to December 2007 of whom 7966 (81.5%) were Caucasian and 1805 (18.5%) were South Asian.

Main outcome measures In-hospital major adverse cardiac events (MACE; death, myocardial infarction, stroke and target vessel revascularisation), subsequent revascularisation rates (PCI and coronary artery bypass grafting; CABG) and all-cause mortality during a median follow-up of 2.5 years (range 1.5–3.6 years).

Results South Asian patients were younger than Caucasian patients (59.69±0.27 vs 64.69±0.13 years, p<0.0001), and more burdened by cardiovascular risk factors, particularly type II diabetes mellitus (45.9%±1.2% vs 15.7%±0.4%, p<0.0001). The in-hospital rates of MACE were similar for South Asians and Caucasians (3.5% vs 2.8%, p=0.40). South Asians had higher rates of clinically driven PCI for restenosis and subsequent CABG, although Kaplan–Meier estimates of all-cause mortality showed no significant differences; this was regardless of whether PCI was performed post-acute coronary syndrome or as an elective procedure. The adjusted hazard of death for South Asians compared with Caucasians was 1.00 (95% CI 0.81 to 1.23).

Conclusion In this large PCI cohort, the in-hospital and longer-term mortality of South Asians appeared no worse than that of Caucasians. South Asians had higher rates of restenosis and CABG during follow-up. Data suggest that the excess coronary mortality for South Asians compared with Caucasians is not explained by differences in case-fatality rates.

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South Asians have a higher prevalence of coronary artery disease (CAD) than Caucasians.1 CAD also presents earlier in South Asians2 and is more diffuse and extensive.3 4 These differences in disease prevalence and severity have been attributed to a higher incidence of conventional risk factors, such as diabetes mellitus, hypertension, smoking and hyperlipidaemia5 as well as differences in other potential risk factors such as lipoprotein a3, adipokines and haemostatic factors.6

The high prevalence of CAD in South Asians is associated with an increased coronary mortality but whether case death rates in patients with established CAD are higher compared with Caucasians remains unclear. The question is important to both clinicians and policy makers because of its implications for targeting preventive treatment to populations at greatest risk. Previous studies have often been small, yielding conflicting results. Some studies have reported increased case death rates for South Asians, related either to diabetes or undertreatment, others have reported case death rates that are comparable to Caucasians.7–14 More recent data from Canada suggest that the long-term survival after acute myocardial infarction (MI) may be better in South Asian than Caucasian patients.15

In the present study we report outcomes for a large cohort of consecutive patients undergoing percutaneous coronary intervention (PCI). The study was based in east London where South Asians comprise 21.1% of the local population.16 The main aim of the study was to compare the characteristics and outcomes of South Asian and Caucasian patients undergoing PCI for stable angina and acute coronary syndromes (ACS).

Methods

We undertook a retrospective observational cohort study to investigate the relation between South Asian ethnicity and outcome after PCI at a single high volume cardiac centre in east London. The study period was from January 2003 to September 2008. Indications for PCI included stable angina and ACS (ST segment elevation MI, non-ST segment elevation MI and unstable angina). Data were prospectively entered into a clinical PCI database at the time of the procedure. Data collected included patient characteristics (age, previous MI/PCI/coronary artery bypass grafting (CABG), hypertension, diabetes mellitus, hypercholesterolaemia, peripheral vascular disease, New York Heart Association class, smoking status, chronic renal impairment (creatinine >200 μMol/l or on renal replacement therapy), left ventricular function and cardiogenic shock) and procedure-related data (indications for PCI, target vessel, number of diseased vessels, use of intravascular ultrasound/pressure wire, use of drug-eluting stent (DES) and glycoprotein IIb/IIIa inhibitor). The ethnicity recorded was that declared by the patient. South Asian describes patients of Pakistani, Indian, Bangladeshi or Sri Lankan origin. Patients who subsequently went on to have CABG were identified from a similarly generated surgical database.

During the study period 13 447 patients underwent PCI. Of these, 10 457 (78%) had complete datasets and NHS numbers and were included in the analysis. The study comprised 9771 patients of either Caucasian or South Asian origin who underwent PCI between October 2003 and December 2007. There were 1805 South Asian patients (18%) and 7966 (81%) Caucasian patients (figure 1). Patients of other ethnic origins (240 African (2%), 67 Oriental (0.6%), 379 not-specified (3.6%)) were not included. The group of patients excluded from the study due to incomplete data entry or absent NHS number contained similar proportions of each ethnic group as the study population (19% South Asian, 78% Caucasian and 3% other).

Figure 1

Flow diagram of patients treated by percutaneous coronary intervention between October 2003 and December 2007 describing patient exclusions and ethnic make up of study population.

Procedural complications and major adverse cardiac events (MACE) were recorded prospectively. In hospital MACE were defined as death, MI (new pathological Q waves in the distribution of the treated coronary artery with an increase of creatine kinase (myocardial type) to two or more times the reference value or significant rise in troponin T values), stroke and target vessel revascularisation. Procedural complications recorded included MI, emergency CABG, arterial complications, aortic/coronary dissection, side branch occlusion and arrhythmia. Procedural complications were recorded at the time of the procedure and in-hospital complications were entered into the database at the time of discharge. Repeat PCI rates due to target vessel revascularisation were identified from the PCI database, and subsequent surgical revascularisation rates were calculated from analysis of the surgical database. All-cause mortality data were recorded as of 1 September 2008 and obtained via the British Cardiovascular Intervention Society UK Central Cardiac Audit Database. This national database is periodically linked to the UK Office of National Statistics and provides life/death status of treated patients. Only patients who had complete database records and NHS unique numbers (allowing life/death status to be assessed) were included in the analysis. A retrospective data quality audit of 100 randomly selected medical records established that 94.8% of data fields, including complications, were entered correctly into the database.

The data were collected as part of a national cardiac audit and all patient-identifiable fields were removed before analysis. The local ethics committee advised us that formal ethical approval was not required.

Statistical analysis

Clinical characteristics of South Asian and Caucasian patients were compared using the Pearson χ2test for categorical variables and Student's t test for continuous variables. We calculated Kaplan–Meier product limits for the cumulative probability of reaching an endpoint and used the log rank test for evidence of a statistically significant difference between the groups. Time was measured from the first admission for a procedure to outcome (all-cause mortality). Cox regression analysis was used to estimate HR for the effect of ethnicity in age-adjusted and fully adjusted models, based on covariates (p<0.05) associated with the outcome. A propensity score analysis was carried out using a non-parsimonious logistic regression model comparing Caucasian and South Asian patients. Multiple variables were included in the model, including all variables with significant interactions. We then undertook a regression adjustment incorporating the propensity score into a proportional hazard model as a covariate. We used SPSS for Mac version 18.0 for all analyses.

Results

Patients

South Asian patients undergoing PCI were younger than Caucasian patients. South Asian patients had more conventional CAD risk factors (diabetes, hypercholesterolaemia, hypertension and more smokers) than Caucasian patients. South Asian patients were more likely to have had previous coronary revascularisation procedures (both PCI and CABG). Overall, similar proportions of South Asians and Caucasians presented with ACS, although South Asians were more likely to present with ST-elevation MI than Caucasians (table 1).

Table 1

Baseline characteristics according to ethnic group

Procedural characteristics

There was a higher incidence of multivessel disease in the South Asian cohort compared with the Caucasian group, with a higher mean number of diseased vessels. Procedural details were similar for South Asians and Caucasians with no difference in the mean number of stents deployed (DES and bare metal stents). However, South Asians were more likely to receive a DES, and when inserted, a greater number of DES per lesion compared with Caucasians. South Asians were more likely than Caucasians to receive glycoprotein IIb/IIIa inhibitors and to have a pressure wire assessment, but there was no difference in the utilisation of intravascular ultrasound (table 2).

Table 2

Procedural characteristics according to ethnic group

PCI outcome

Procedural outcome

Procedural success was similar for South Asians and Caucasians, with no significant difference between the groups for in-hospital MACE or any of its components (stroke/MI/ emergency bypass surgery/death) (table 3).

Table 3

In-hospital outcomes, complications and long-term cumulative events post-PCI according to ethnic group

All-cause mortality

Patient follow-up was for a median of 2.5 years (range 1.5–3.6 years; figure 2). Kaplan–Meier estimates of all-cause mortality showed no significant differences for South Asians and Caucasians, regardless of whether PCI was performed post-ACS or as an elective procedure (figure 3). Although estimated mortality rates were higher for women than for men, there were no differences by South Asian and Caucasian ethnicity either for women (8.8%, 95% CI 5.9 to 11.6 vs 7.8%, 95% CI 6.7 to 8.9) or for men (5.8%, 95% CI 4.5 to 7.0 vs 7.0%, 95% CI 6.4 to 7.8).

Figure 2

Kaplan–Meier curves showing cumulative probability of all-cause mortality after percutaneous coronary intervention according to ethnic group.

Figure 3

Kaplan–Meier curves showing the cumulative incidence of subsequent revascularisation after percutaneous coronary intervention (PCI) of Caucasian and Asian patients. (A) coronary artery bypass grafting (CABG) rates; (B) PCI target lesion revascularisation rates.

The age-adjusted Cox analysis (table 4) showed a small increase in the hazard of death for South Asians compared with Caucasians (HR 1.23, 95% CI 1.01 to 1.51) but the difference was lost with multiple adjustment (HR 0.96, 95% CI 0.75 to 1.23; figure 4). In addition, after regression adjustment incorporating the propensity score into a proportional hazard model as a covariate (calculated from age, ACS presentation, gender, diabetes, hypertension, hypercholesterolaemia, previous CABG, previous PCI, previous MI, multivessel disease, chronic renal impairment, ejection fraction and glycoprotein IIb/IIIA use) there was no observed difference in long-term mortality between the South Asian and Caucasian groups (HR 1.04, 95% CI 0.8 to 1.3).

Table 4

Cox proportional model of univariate and multivariate analysis of mortality in South Asians versus Caucasians after PCI

Figure 4

Adjusted HR of the Cox analysis for all-cause mortality after percutaneous coronary intervention with 95% CI. ACS, acute coronary syndrome; CABG, coronary artery bypass grafting; CRF, chronic renal impairment; EF, ejection fraction; MI, myocardial infarction.

Need for repeat revascularisation

Kaplan–Meier estimates of repeat revascularisation showed significant differences between South Asians and Caucasians during the first 5 years. There were higher rates of CABG in the South Asian group (4.7%, 95% CI 3.9 to 9.3) versus the Caucasian group (2.9%, 95% CI 1.8 to 4.1; p=0.004; figure 3A) and also higher rates of percutaneous target vessel revascularisation for restenosis (9.5%, 95% CI 6.1 to 9.9 vs 8.3%, 95% CI 3.4 to 9.1; p=0.01; figure 3B).

Discussion

This is the largest observational study yet reported comparing outcomes for South Asian and Caucasian patients after PCI. South Asians presented at a younger age, had more conventional CAD risk factors and more extensive angiographic disease than Caucasians. However, contrary to many earlier reports of adverse outcomes for South Asian patients with CAD,7–10 we found no difference in either the short or medium-term mortality of South Asians compared with Caucasians undergoing PCI, irrespective of whether procedures were performed electively or for ACS and despite an increased requirement for repeat revascularisation in South Asian patients.

Our understanding of the effect of South Asian ethnicity on the prognosis of CAD and related clinical outcomes is still evolving, particularly with the dynamic population changes due to immigration.7 It is clear that South Asian ethnicity is associated with an increased prevalence of CAD and increased cardiovascular mortality.8 13 17 18 Our finding of a higher prevalence of CAD risk factors in South Asians, particularly diabetes and hypertension, has been widely reported.2 5 15 19 There is less consistency in the reported case death rates in South Asians compared with Caucasians, some investigators reporting similar rates for South Asians and Caucasians20 others higher rates for South Asians.21–23 Recent data report similar survival rates after cardiac arrest for South Asians and Caucasians,24 and one study has reported lower mortality after MI for South Asians, a finding attributed to a higher rate of invasive procedures.15 Certainly, national registry data provide no evidence of undertreatment of South Asians with ACS,25 26 and our study confirms that with contemporary treatment equitably applied across ethnic groups, case death rates for patients with established CAD undergoing PCI are no higher for South Asians than for Caucasians.

If our finding of comparable outcomes for South Asian and Caucasian patients undergoing PCI in a contemporary setting can be extended to other coronary populations it sends an important message to policy makers. The WHO27 and other agencies have emphasised the importance of early identification and treatment of CAD in South Asians as a means of reducing the excess coronary mortality in this group. This is relevant, as we have found that South Asians present at a younger age, with more extensive coronary disease. As the mortality after treatment is comparable between South Asians and Caucasians it seems that further reductions in coronary mortality in South Asians would be best achieved through targeted disease prevention rather than modification of existing treatment strategies.

Strengths and limitations of this study

The rich ethnic demographic of east London provides a unique opportunity to investigate the role of ethnicity on survival after PCI. As all patients were treated at a single centre with standardised care protocols and pathways the effect of bias due to differing treatment strategies is limited. Our cohort was large and included a high proportion of South Asian patients. The long-term follow-up based on all-cause mortality and the investigation of both acute and elective cases adds to the study strengths. The univariate, multivariate and propensity analysis highlights the quality of the data with well-recognised predictors of mortality associated with adverse outcome in our dataset.

There are a number of important limitations common to observational studies of this type. We cannot account for the effects of residual confounding or of selection bias caused by the exclusion of 22% of patients with missing data. However, this is unlikely as the distribution of South Asian and Caucasian patients was the same in the excluded and analysed cohorts. Categorising patients as South Asian may obscure important outcome differences between the different constituent ethnic subgroups.28

Conclusions

In this contemporary cohort of patients undergoing PCI, adjusted case death rates after follow-up for up to 5 years were similar for South Asians and Caucasians. This was regardless of whether the procedure was elective or for the treatment of ACS. We did observe increased rates of clinically important restenosis and repeat revascularisation, including CABG, in South Asian patients, but this did not have a palpable effect on mortality. Our data add further weight to an emerging consensus that the excess coronary mortality for people of South Asian origin reflects only their propensity for developing premature CAD and is not related to differences in case death rates compared with Caucasian patients.

Acknowledgments

The authors would like to thank the following: interventional colleagues at the London Chest Heart Attack Centre: Andrew Deaner, Mark Westwood, Simon Kennon, Rajiv Amersey, David Wald, John Hogan, Rex Dawson, Duncan Dymond, Tat Koh and Elliot Smith. Senior nursing staff and specialist nurses: Eileen Ferguson and Samantha Cliffe. Nursing staff of CCU and Cardiac Step-down (Riviere) senior nursing sister Cardiac Catheterisation Lab: Noel Cleary.

References

Footnotes

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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