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Mortality outcome of out-of-hours primary percutaneous coronary intervention in the current era

Awsan Noman , Javed M. Ahmed , Ioakim Spyridopoulos , Alan Bagnall , Mohaned Egred
DOI: http://dx.doi.org/10.1093/eurheartj/ehs261 3046-3053 First published online: 4 September 2012

Abstract

Aims To assess the impact of the time of primary percutaneous coronary intervention (PPCI) on in-hospital and long-term all-cause mortality in ST-segment elevation myocardial infarction (STEMI).

Methods and results The study retrospectively analyses the prospectively collected data on 2571 consecutive PPCI-treated STEMI patients between March 2008 and June 2011. Of these, 1036 patients (40.3%) underwent PPCI during a weekday between 08:00 and 18:00 (routine-hours group) and 1535 patients (59.7%) underwent PPCI on a weekday between 18:00 and 08:00 or a weekend (out-of-hours group). Compared with the routine-hours group, the out-of-hours group had a lower mean age, fewer patients with previous angina, longer call-to-hospital time, and fewer multivessel PCI. The overall in-hospital mortality rate was 4.5% with no significant difference [0.2%, 95% confidence interval (CI): −1.4 to 1.9%] between the routine-hours group (4.3%) and the out-of-hours group (4.6%) (adjusted odds ratio: 1.33, 95% CI: 0.73–2.40, P = 0.35). During a mean follow-up period of 560 days, 295 patients (11.5%) died, 12.2% in the routine-hours group and 11.0% in the out-of-hours group (difference of −0.1%, 95% CI: −0.4 to 0.2%). In the multiple Cox proportional hazards model, there was no difference in mortality between the two groups (adjusted hazard ratio: 1.09, 95% CI: 0.82–1.46, P = 0.57). Similarly, no increase in mortality was seen in patients who underwent PPCI later at night (22:00–06:00).

Conclusion This study of real-world, unselected STEMI patients demonstrates that in a large, well-staffed centre, PPCI outside routine-working hours is safe with no difference in outcome of in-hospital and long-term mortality compared with PPCI during routine-working hours.

  • PPCI
  • STEMI
  • Out of hours
  • Mortality

Introduction

Primary percutaneous coronary intervention (PPCI) has been shown to improve the short- and long-term outcomes in ST-segment elevation myocardial infarction (STEMI) patients.1 It is now recognized as the preferred treatment for these patients in all recent guidelines.2,3

Currently, it remains unclear whether the outcomes of STEMI patients treated with PPCI outside routine-working hours are as favourable as those treated during routine-working hours. Studies assessing the impact of the time of PPCI on outcome are limited and have reported conflicting results.410 Furthermore, these studies have included a mixture of STEMI and non-STEMI (NSTEMI)6,10 as well as PPCI and thrombolysis-treated patients.6,7,10 Studies analysing the outcomes of only PPCI-treated STEMI patients are scarce, particularly in the modern era of PPCI.

The aim of this study was to compare the in-hospital and long-term all-cause mortality of out-of-hours PPCI with routine-hours PPCI.

Methods

Study population

This consisted of all STEMI patients undergoing PPCI between March 2008 and June 2011 at Freeman Hospital, Newcastle-upon-Tyne, UK. This is a large tertiary centre performing ∼3000 PCI a year, of which over 800 are PPCI cases, delivered by 10 interventional cardiologists.

The diagnosis of STEMI was based on the presence of chest pain suggestive of myocardial ischaemia >30 min, time of onset of symptoms within 12 h and new ST-segment elevation or left bundle branch block on the electrocardiogram (ECG).

Study design

The study retrospectively analyses the prospectively collected data on all PPCI patients. The primary source of data was our local coronary artery disease (CAD) database (Dentrite). This database holds information on every PCI procedure performed at our hospital, including baseline demographics, clinical presentation, procedure details, timings, and complications. This information is prospectively entered at the end of each PCI procedure. Clinical data and medications are updated on discharge.

Service arrangement

Our centre is staffed with seven full-time and three part-time interventional cardiologists. The centre covers a population of 2.3 million and seven satellite hospitals. The on-call team is composed of an interventional cardiologist, a senior cardiology trainee, two cardiac catheterisation laboratory nurses, a cardiac physiologist, and a radiographer. All the on-call team members are non-resident and live within 3–10 mile radius from the hospital. The exception is the senior cardiology trainee who is resident in hospital during out of hours. Patients accepted for PPCI are admitted to the catheterisation laboratory. They pass through coronary care unit (CCU) on their way to the catheterization laboratory, as the PPCI arrival gate opens directly into our CCU, which is adjacent to the catheterization laboratory. To minimize unnecessary delays,11 patients do not stop in CCU for assessment unless further evaluation is required, e.g. in those where the ECG changes are equivocal.

Referral pattern

There are two sources of referral for PPCI. The first is a direct referral to our centre by the ambulance paramedics from the community. The second is inter-hospital transfer where the patient has presented to an emergency department of a satellite hospital and was identified as having STEMI and then referred to our centre. The latter pattern of referral takes longer time due to the logistics of requesting an ambulance for a patient in the emergency room.

Any patient with chest pain who contacts the emergency service will be attended to by the ambulance paramedics, who are trained in the interpretation of ECGs. An ECG is obtained and then telemetered to our CCU, where an experienced senior cardiac nurse will review the ECG and if the criteria for STEMI are met, then the patient is accepted for PPCI with all relevant clinical information. In the case of uncertainty about the ECG, the on-call senior cardiology trainee is asked to review the ECG and make the decision with consultation with the on-call interventional cardiologist.

During out of hours and immediately upon acceptance of a patient for PPCI, the on-call team members are contacted and one of the CCU nurses will open the catheterization laboratory. The majority of the on-call team members will be in the hospital within 10–15 min of the original call and the catheterization laboratory will be ready to take the patient as soon as they arrive to CCU. In the majority of cases, the on-call team will be in the hospital before the arrival of the patient. Patients are given aspirin by the paramedics and on arrival to the hospital are given clopidogrel or prasugrel by the CCU staff. Explanation and verbal consent for PPCI are provided as patients being transferred to the catheterization laboratory. These are the arrangements outside routine-working hours.

During routine-working hours, the on-call team is in the hospital and the catheterization laboratories are fully functioning. Upon accepting a patient, the CCU coordinator informs the catheterization laboratory coordinators who in turn inform the on-call interventional cardiologist and the next available free catheterization laboratory is identified. The patient is taken to the catheterization laboratory and PPCI is performed by the interventional cardiologist who is working in that laboratory.

Outcome measures

The main outcome measures were in-hospital and long-term all-cause mortality. Mortality data were provided by the Office of National Statistics, which records all mortality in the UK. This information was linked to our database using National Health Service (NHS) patient-unique identification numbers (NHS numbers). Patients' identities were further confirmed by birth date and home address. Mortality was assessed up to the 31 July 2011, and patient follow-up was censored when they died.

Data on procedure-related complications were obtained from our CAD database.

Procedure timing

Patients were classified into two groups: routine-hours group where PPCI was performed between 08:00 and 18:00 during weekdays (Monday to Friday) and out-of-hours group where PPCI was performed during weekdays between 18:00 and 08:00 and at weekends (anytime on Saturday or Sunday).

Further analysis to compare those who underwent PPCI during late-night time (22:00–06:00) and those who underwent PPCI outside these late-night hours was also performed.

Statistics

Data are presented as percentages for categorical variables and as means ± standard deviations (SD) or medians and inter-quartile ranges (25–75th) for continuous variables. Comparisons between groups were made using χ2 test for categorical variables and independent t-test or the Mann–Whitney U-test for continuous variables, as appropriate. Multiple logistic regression analysis was used to test for the impact of out-of-hours PPCI on in-hospital mortality and correct for known confounders (age, gender, admission systolic blood pressure (SBP), admission heart rate (HR), total ischaemic time, admission creatinine and haemoglobin, previous CABG, anterior MI, multivessel disease, and diabetes).12,13 For the longitudinal analysis, the Kaplan–Meier survival curves were generated and the log-rank test was used to assess differences in survival. The effects of known prognostic variables on the mortality of STEMI patients were examined using the Cox proportional hazards regression analysis. The following covariates were included in this analysis: age, sex, previous MI, diabetes mellitus, anterior MI site, baseline haemoglobin and creatinine, admission HR and SBP, cardiogenic shock, onset of symptoms to balloon (total ischaemic time), the presence of multivessel disease, and Thrombolysis in Myocardial Infarction (TIMI) Flow 3 post-PPCI.12,13 The Cox proportional hazards analysis was repeated in the subgroup of patients in whom left ventricular systolic function (LVSF) data were available. A P-value of <0.05 (two-sided) was considered statistically significant. All analysis was performed using SPSS (SPSS version 16, SPSS, Inc., Chicago, IL, USA).

Results

Patient and procedural characteristics

Two thousand five hundred seventy one patients underwent PPCI for STEMI during the study period (mean age 63.2 ± 13.4 years, 70.4% male). One thousand and thirty-six patients were treated during routine hours (40.3%) and 1535 patients out of hours (59.7%).

Table 1 shows the baseline demographics and procedure characteristics of the two groups. The out-of-hours group was younger (mean age 62.5 vs. 64.1 years, P = 0.001) and had a smaller proportion of patients with a history of angina (20 vs. 23.4%, P = 0.037) compared with the routine-hours group. The two groups were otherwise similar in all other baseline demographics, past medical history, and clinical presentation. Differences in procedure characteristics included a lower proportion of patients undergoing multivessel PCI during the index procedure and a lower rate of radial access in the out-of-hours group compared with routine-hours group, although the later did not reach statistical significance (Table 1).

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Table 1

Demographics, clinical, and procedural characteristics of the routine-hours and out-of-hours groups

Routine hours (n = 1036)Out of hours (n = 1535)P-value
Age (years)64.1 ± 13.762.5 ± 13.10.001
Male (%)69.371.10.36
Bloods
 Haemoglobin (g/dL)13.7 ± 1.813.8 ± 1.80.16
 Creatinine (µmol/L)100.5 ± 54.197.9 ± 43.40.17
 Glucose (mmol/L)8.6 ± 3.48.6 ± 3.50.87
 Cholesterol (mmol/L)5.0 ± 1.34.9 ± 1.40.71
 Body mass index (kg/m2)27.3 ± 5.027.6 ± 5.10.25
Risk factors
 Hypertension (%)41.140.90.46
 Hypercholestrolaemia (%)34.032.20.35
 Family history (%)43.747.00.12
 Diabetes mellitus (%)11.211.40.90
 Current smoking (%)43.446.30.16
Previous history
 Prior angina (%)23.420.00.037
 MI (%)15.914.70.46
 CABG (%)1.82.60.23
 PCI (%)8.27.20.36
 CVA/TIA (%)6.85.30.12
 PVD (%)4.33.60.26
 Heart failure (%)1.20.90.55
 Airways disease (%)13.712.00.24
Clinical
 Heart rate (b.p.m.) 76 ± 20 76 ± 200.77
 Systolic BP (mmHg)131 ± 30129 ± 290.24
 Cardiogenic shock (%)5.24.20.21
 Ventilated (%)2.31.50.16
 Procedure for IST (%)3.43.30.99
 Anterior MI (%)37.539.20.13
Procedure
 Radial access (%)70.366.80.057
 TIMI 3 or 2 pre-PCI (%)25.822.80.09
 TIMI 3 post-PCI (%)91.891.00.51
 GP IIb/IIIa (%)79.582.10.11
 Atherothrombectomy (%)41.643.40.39
 Drug-eluting stent (%)56.158.20.29
 Multivessel PCI (%)13.99.20.002
 Total contrast (mL)142 ± 64147 ± 650.08
 Culprit vessel diameter (mm)3.5 (3.0–3.75)3.5 (3.0–3.75)0.39
 Culprit lesion length (mm)23 (17–30)23 (18–30)0.64
  • Data are presented as mean ± SD unless indicated otherwise. MI, myocardial infarction; CABG, coronary artery bypass graft; PCI, percutaneous coronary intervention; CVA/TIA, cerebrovascular accident/transient ischaemic attack; PVD, peripheral vascular disease; BP, blood pressure; IST, instent thrombosis; TIMI, Thrombolysis in Myocardial Infarction; CAD, coronary artery disease; GP IIb/IIIa, glycoprotein IIb/IIIa inhibitor; IQR, inter-quartile range; LVSF, left ventricular systolic function.

Comparisons between the two groups in procedural timings are shown in Table 2. The door-to-balloon time did not differ between the two groups. The medians for call-to-hospital and subsequently call-to-balloon times were longer in the out-of-hours group compared with the routine-hours group.

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Table 2

Procedure timings in patients undergoing primary percutaneous coronary intervention during routine vs. out of hours

Routine hoursOut of hoursP-value
Onset to call (min)60 (25–151)60 (27–147)0.14
Call to hospital (min)57 (46–74)58 (46–81)0.017
Door to balloon (min)24 (18–34)25 (19–35)0.12
Call to balloon (min)85 (70–109)87 (72–115)0.002
Onset to hospital (min)130 (86–228)135 (90–223)0.41
Onset to balloona (min)160 (114–256)165 (118–252)0.38
  • Results are presented as median (inter-quartile range).

  • aTotal ischaemic time.

The breakdown of the source of referral and the different time parameters are shown in Table 3. There was a higher percentage of inter-hospital transfer in the out-of-hours group compared with the routine-hours group (33.7 vs. 28.1%, P = 0.03).

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Table 3

Procedure timings (minutes) in patients undergoing primary percutaneous coronary intervention according to the admission route

 Direct admissionP-valueInter-hospital transferP-value
AllAll
Routine hoursOut of hoursRoutine hoursOut of hours
Call to hospital55 (45–66)93 (54–139)<0.0001
55 (45–67)55 (45–66)0.5985 (51–138)95 (56–139)0.26
Door to balloon25 (19–35)24 (18–34)0.69
24 (18–33)26 (19–36)0.00325 (19–36)23 (18–32)0.14
Call to balloon82 (70–98)121 (82–168)<0.0001
82 (69–97)82 (71–99)0.004122 (80–169)120 (83–165)0.44
Onset to hospital113 (81–191)194 (135–301)<0.0001
112 (82–190)115 (81–191)0.94196 (135–329)193 (135–294)0.61
Onset to balloon144 (109–226)220 (163–322)<0.0001
141 (107–226)146 (109–229)0.85222 (164–356)219 (162–317)0.80
Onset to call56 (25–133)79 (30–204)<0.0001
56 (23–134)54 (26–133)0.1790 (30–210)72 (30–199)0.40

Complications

The rates of different in-hospital complications (excluding in-hospital death) were similar in both groups. The figures for the routine-hours and out-of-hours groups, respectively, were as follow: 3.6 vs. 3.7% (P = 0.91) for procedure-related cardiac complications (dissection, no reflow, side branch occlusion, perforation, and tamponade), 1.5 vs. 1.1% (P = 0.37) for arterial access complications (significant local and retroperitoneal bleeding, false aneurysm, dissection) and 7.2 vs. 6.3% (P = 0.51) for all other complications (cerebrovascular accident, in-hospital re-intervention, non-access site bleeding).

Mortality outcomes

A total of 115 patients (4.5%) died during the index hospital stay, 45 patients [4.3%, 95% confidence interval (CI): 3.2–5.8%] in the routine-hours group and 70 patients (4.6%, 95% CI: 3.6–5.7%) in the out-of-hours group. There was no significant difference in in-hospital mortality between groups (0.2%, 95% CI: −1.4 to 1.9%). The unadjusted OR for out-of-hours PPCI was 1.05 (95% CI: 0.72–1.54, P = 0.79). In a logistic regression model adjusted for several known confounders, there was no difference in the in-hospital all-cause mortality between the routine-hours and out-of-hours groups (adjusted OR: 1.33, 95% CI: 0.73–2.40, P = 0.35). Predictors of in-hospital all-cause mortality are shown in Table 4.

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Table 4

Multiple logistic regression for predictors of in-hospital mortality following primary percutaneous coronary intervention

OR (95% CI)P-value
Age (per 10-year increase)1.75 (1.33–2.29)<0.0001
Creatinine (per 10 µmol/L increase)1.04 (1.01–1.07)0.004
Systolic BP (per 10 mmHg increase)0.87 (0.78–0.97)0.018
Heart rate (per 10 b.p.m. increase)1.20 (1.06–1.34)0.003
Total ischaemic time (per 10 min increase)1.003 (1.002–1.004)0.046
Female gender1.41 (0.74–2.66)0.29
Diabetes0.62 (0.25–1.54)0.31
Haemoglobin (per 1 g/dL increase)0.80 (0.68–0.94)0.010
Previous MI0.85 (0.38–1.88)0.69
Cardiogenic shock4.25 (1.71–10.51)0.002
Previous CABG5.09 (1.42–18.2)0.012
Anterior MI1.17 (0.63–2.17)0.61
TIMI 3 post-PCI0.22 (0.11–0.43)<0.0001
Multivessel CAD2.96 (1.59–5.48)0.001
Out-of-hours PPCI1.33 (0.73–2.40)0.35
  • See Table 1 for abbreviations. OR, odds ratio.

During a mean follow-up period of 560 days (567 days in the routine-hours group and 556 days in the out-of-hours group), there were 295 deaths (11.5%), of which 126 (12.2%, 95% CI: 10.2–14.4%) were in the routine-hours group and 169 (11.0%, 95% CI: 9.4–12.8%) in the out-of-hours group. There was no significant difference in long-term mortality between groups (−0.1%, 95% CI: −0.4 to 0.2%). The unadjusted HR for out-of-hours PPCI was 0.92 (95% CI: 0.73–1.15, P = 0.45). Figure 1 illustrates the total number of patients undergoing PPCI at different hours of the day and on different days of the week with their corresponding total deaths at long-term follow-up. Figure 2 compares the cumulative survival of the routine-hours and out-of-hours groups using the Kaplan–Meier analysis and log-rank test. In the multiple Cox proportional hazards model, the timing of the procedure had no effect on all-cause mortality (adjusted hazard ratio: 1.09, 95% CI: 0.82–1.46, P = 0.57). Predictors of long-term all-cause mortality are shown in Table 5.

View this table:
Table 5

Predictors of long-term mortality following primary percutaneous coronary intervention in the Cox proportional hazard model

HR (95% CI)P-value
Age (per 10-year increase)1.74 (1.20–2.52)<0.0001
Creatinine (per 10 µmol/L increase)1.03 (1.02–1.04)<0.0001
Systolic BP (per 10 mmHg increase)0.94 (0.89–0.99)0.030
Heart rate (per 10 b.p.m increase)1.11 (1.04–1.17)<0.0001
Total ischaemic time (per 10 min increase)1.002 (1.001–1.003)<0.0001
Female gender0.86 (0.62–1.19)0.35
Diabetes0.98 (0.64–1.51)0.94
Haemoglobin (per 1 g/dL increase)0.82 (0.75–0.89)<0.0001
Serum glucose (per 1 mmol/L increase)1.05 (1.02–1.09)0.002
Previous MI1.44 (1.02–2.05)0.040
Cardiogenic shock2.032 (1.23–3.36)0.006
Anterior MI1.36 (1.01–1.83)0.041
Previous CABG2.64 (1.35–5.19)0.005
TIMI 3 post-PCI0.47 (0.32–0.68)<0.0001
Multivessel CAD1.74 (1.20–2.52)0.003
Out of hours PPCI1.09 (0.82–1.46)0.57
  • See Table 1 for abbreviations. HR, hazard ratio.

Figure 1

Total number of patients undergoing PPCI at (A) different hours of the day and (B) different days of the week with the corresponding total deaths at long-term follow-up.

Figure 2

The Kaplan–Meier survival curves for adjusted cumulative survival in the routine-hours and out-of-hours groups.

The analysis was repeated in the subgroup of patients (n = 1044, 41.9%) in whom LVSF data were available and LVSF was entered as a confounder in the Cox model. There was still no difference in the long-term all-cause mortality between the routine-hours and out-of-hours groups (adjusted HR: 1.04, 95% CI: 0.73–1.49, P = 0.81).

Similarly, no difference in all-cause mortality (0.8%, 95% CI: −0.3 to 0.4%) was found between those who underwent PPCI at late-night time (n = 577, 11.8% of whom died) and non-late-night time (n = 1994, 11.4% of whom died) (adjusted HR: 1.04, 95% CI: 0.79–1.36, P = 0.80).

Discussion

This study of real-world, unselected STEMI patients demonstrates that there are no differences in outcome of in-hospital and long-term mortality following PPCI whether it is performed during or outside routine-working hours. The study also shows that the majority of STEMI patients present and undergo PPCI outside routine-working hours. In a well-staffed, high-volume centre, the timing of PPCI has no impact on either short- or long-term mortality.

There are several reasons why the outcomes of PPCI may differ in patients presenting outside compared with during routine-working hours. These include possible differences in patients' baseline characteristics, diurnal variation in the pathophysiological responses to myocardial ischaemia,1416 and procedure-related differences (such as procedure delays, complication rates, and use of adjunct therapies).7 More importantly, the out-of-hours logistical and staffing level may also have a major impact if they differ from normal working hours.

In our cohort, the overall in-hospital and long-term mortality rates were consistent with recently reported studies.17 However, while some previous studies have reported longer door-to-balloon time in patients treated out of routine-working hours,8,10 the door-to-balloon and total ischaemic times were similar in both groups in our study. Eliminating such differences is an important indicator and in fact may be used as a measure of the quality and effectiveness of the organization of the out-of-hours PPCI service, given the importance of door-to-balloon time on outcomes following PPCI.18 The use of adjunct therapies, such as thrombectomy and glycoprotein IIb/IIIa inhibitors, and drug-eluting stents did not differ between groups in our cohort. Although, the groups were similar in most baseline and other procedure characteristics, our study highlights some differences. Older patients and those with prior angina were less likely to present outside routine-working hours. Similar observation for older patients was noted in other studies.7,10 Patients with previous history of angina have more knowledge and access to immediate treatment, such as sublingual nitrates. This, in combination with the potential effect of ischaemic preconditioning, may have led to the observed difference in our cohort. In addition, we found a more frequent use of the radial approach during routine-working hours. This was likely to be due to the fact that 3 of the 10 operators in our unit were mainly femoral operators at the start of this study. They subsequently converted to the radial approach during the course of this study but may have been less likely to use it outside routine-working hours during the learning period. Another difference was the higher proportion of multivessel PCI during the index procedure in the routine-hours compared with out-of-hours groups, despite no apparent difference in the rate of documented cardiogenic shock, which is the usual indication for multivessel PCI in this setting. This could be explained at least in part by the participation of our centre in the Preventive Angioplasty in Myocardial Infarction (PRAMI) trial, which is comparing culprit only with full revascularization during PPCI, and the fact that the recruitment for this trial was limited to routine-working hours.19

In our study, the overall increase in the call-to-hospital and subsequently call-to-balloon time in the out-of-hours group may be explained by the higher percentage of inter-hospital transfers in the out-of-hours group compared with routine-hours group as it usually takes longer to arrange for an ambulance transfer. This in turn allows a longer time for the out-of-hours on-call team to be ready as evident in the numerically shorter, albeit not statistically significant, door-to-balloon time in the inter-hospital transfer patients in comparison to the direct admission group (23 vs. 26 min). Furthermore, although it is assumed that the pre-hospital period may be shortened because of less intensive traffic during off-business hours, following discussion with the ambulance control in our region, this may be negated by the fact that the ambulance crew tend to drive slower during night time, which may have added to the difference in some timing parameters.

The debate on the effect of hospital admission time on patients' mortality is not limited to myocardial infarction. In one large study, reduced level of hospital staffing was proposed as a possible reason for the increased mortality in patients presenting outside routine-working hours with serious medical conditions.20 Similarly, higher mortality and poor outcomes were reported in several studies of MI patients when presenting outside routine-working hours.69 These studies noted longer door-to-balloon times and lower revascularization rates in out-of-hours patients. On the other hand, other studies have reported no significant impact for hospital admission or procedure times on the mortality of MI patients. 4,5,10 It should be noted that the majority of these studies included a mixture of STEMI and NSTEMI, as well as PPCI and thrombolysis-treated patients.

The findings of our study further confirm that PPCI outside routine-working hours is safe with similar in-hospital and long-term mortality as during routine-working hours. These findings should be viewed in the setting of a high-volume, well-staffed tertiary centre, offering PPCI 24 h 7 days a week, with short and similar door-to-balloon time in those presenting during as well as out of routine-working hours. Further work should be done to assess whether smaller and low-volume centres, especially those with longer door-to-balloon time, have similar outcomes.

Study limitations

This is a retrospective, single-centre observational study with all inherent limitations including the inability to account for all confounders. For example, we did not have information on Killip class and LVSF data were documented in only 42% of the patients at discharge. However, observational cohort design is the only method to address the question of this study as randomization is not feasible in this setting. Furthermore, our study reflects contemporary PPCI practice and is a study of real-world, consecutive patients with the hard endpoint of mortality. Finally, given the in-hospital mortality rate, it remains possible that our study was not sufficiently powered to detect small differences between groups.

Conclusion

This large observational study demonstrates that there are no differences in mortality following PPCI whether it is performed during or outside routine-working hours. The study provides reassurance on the safety of out-of-hours PPCI in the setting of a high-volume, well-staffed tertiary centre. Such reassurance is essential, particularly given the fact that providing out-of-hours PPCI service is costly and demands significant resources. These findings need to be assessed and replicated in smaller centres with fewer operators and more frequent on-call commitment.

Acknowledgements

We are grateful to Sheila Jamieson for her assistance with the CAD database and to our colleagues at Freeman Hospital, Drs R. Edwards, A. Zaman, I. Purcell, R. Das, and V. Kunadian, and Professor B. Keavney for their help in collecting data. A.N. had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Conflict of interest: none declared.

References

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