Impact of Door-to-Balloon Time in Patients With ST-Elevation Myocardial Infarction Who Arrived by Self-Transport　― Acute Myocardial Infarction-Kyoto Multi-Center Risk Study Group ―

Abstract

Background: Patients with ST-elevation myocardial infarction (STEMI) who arrive at a hospital via self-transport reportedly have a delayed door-to-balloon time (DBT). However, the clinical impacts of delayed DBT on in-hospital mortality among such patients are not well known.

Methods and Results: In total, 1,172 STEMI patients who underwent primary percutaneous coronary intervention between January 2009 and December 2013 from the Acute Myocardial Infarction (AMI) Kyoto Registry were analyzed. Compared with the emergency medical service (EMS) group (n=804), the self-transport group (n=368) was younger and had a significantly longer DBT (115 min vs. 90 min, P<0.01), with fewer patients having a Killip classification of 2 or higher. The in-hospital mortality rate was lower in the self-transport group than in the EMS group (3.3% vs. 7.1%, P<0.01). A DBT >90 min was an independent predictor of in-hospital mortality in EMS patients (odds ratio (OR)=2.43, P=0.01) but not in self-transport patients (OR=0.89, P=0.87).

Conclusions: The present study demonstrated that there was no relationship between in-hospital prognosis and DBT ≤90 min in STEMI patients using self-transport. The prognosis of these patients cannot be improved by focusing only on DBT. Treatment strategies based on means of transport should also be considered.

ST-elevation myocardial infarction (STEMI) is an emergency, and prompt reperfusion therapy focusing on percutaneous coronary intervention (PCI) is important. Many studies have revealed the association between early reperfusion using primary PCI and decreased mortality and morbidity for STEMI.^1–3 Current guidelines recommend that the time from hospital arrival to reperfusion (door-to-balloon time: DBT) should be within 90 min,^4,5 and various facilities have been striving to achieve this standard, which is also used for the evaluation of treatment results.^6–8

However, patients with myocardial infarction often arrive at the hospital using their own means of transport, “self-transport,” instead of using an emergency medical service (EMS).⁹ Compared with EMS patients, patients using self-transport may face a possible time delay in the initiation of treatment.^10–12 Mathews et al reported that the DBT and time from arrival to thrombolytic therapy were significantly longer in the self-transport group compared with the EMS group.¹² In addition, So et al reported that while DBT in the self-transport group was significantly longer than that in the EMS group, the in-hospital mortality rate was lower in the self-transport group.¹³ However, the impact of delay in DBT on in-hospital mortality in self-transport patients is not completely understood. Thus, in the present study, we investigated the impact of DBT on the in-hospital mortality rate of STEMI patients using self-transport in the era of primary PCI.

Methods

Study Population

From January 2009 to December 2013, 2,494 consecutive patients with a diagnosis of acute myocardial infarction (AMI) admitted to AMI-Kyoto Multi-Center Risk Study Group Hospitals were enrolled in the present study. The AMI-Kyoto Multi-Center Risk Study, a large multi-center observational study, in which collaborating hospitals in Kyoto City and its surrounding areas collected demographic, procedural and outcome data on AMI patients, was established across 20 primary PCI-capable hospitals in the year 2000. The diagnosis of AMI required the presence of at least 2 of the following 3 criteria: (1) characteristic clinical history of ischemic-type chest pain lasting more than 20 min; (2) serial changes on 12-lead electrocardiogram (ECG) suggesting infarction (Q-waves) or injury/ischemia (ST-segment elevation); and (3) a transient increase in the creatine phosphokinase (CK) level to more than twice the normal laboratory value.¹⁴ All in-hospital data were transmitted to the Department of Cardiovascular Medicine in Kyoto Prefectural University School of Medicine for analysis. Because this study was an observational study using existing data from medical records, we took verbal informed consent, without the written concent. We described the records of informed concent in the medical record. After each institute confirmed its participation in this study, the study was approved by the ethics committee of Kyoto Prefectural University of Medicine, as a general organization. In addition, this study was approved by each participating institution’s ethics committee.

Among the 2,494 enrolled patients, those admitted over 24 h after the onset of symptoms (n=261), those with unknown onset time (n=123), and those with in-hospital onset of symptoms (n=77) were excluded. Also excluded were those patients transferred from another institution (n=385), those for whom information about transport means was not available (n=37), those with non-ST elevation myocardial infarction (n=314), those with uncertain ST segment deviation (n=20), those who suffered cardiopulmonary arrest on hospital arrival (CPAOA) (n=50), and those with no primary PCI (n=55). The final population for this study consisted of 1,172 patients with STEMI who underwent primary PCI within 24 h of onset. We divided the 1,172 patients into 2 groups: patients directly transferred to the hospital by the public ambulance system were placed in the EMS group and those who arrived at hospitals using self-transport (such as a taxi, public transport, a private car or by walking) were placed in the “self-transport” group (Figure 1).

Figure 1.

Study protocol and flow chart. AMI, acute myocardial infarction; NSTEMI, non-ST-elevation myocardial infarction; CPAOA, cardiopulmonary arrest on arrival; PCI, percutaneous coronary intervention; EMS, emergency medical services.

Data Collection and Definitions

We retrospectively analyzed the clinical background, angiographic characteristics, and in-hospital mortality rate between the EMS group and self-transport group. Emergency coronary angiography (CAG) was performed by using a standard technique. Coronary flow was evaluated using the Thrombolysis in Myocardial Infarction (TIMI) classification.¹⁵ Coronary stenosis was evaluated based on the American Heart Association (AHA) classification, and significant coronary artery stenosis was defined as a reduction of at least 75% of the internal diameter in the right coronary artery, left anterior descending artery, left circumflex artery and their major branches: or a reduction of at least 50% of the internal diameter in the left main trunk. Multi-vessels involvement was defined as simultaneous thrombosis of multiple coronary arteries or an undetermined culprit artery in the presence of multiple stenotic vessels as seen on the initial CAG. Primary PCI and other treatment strategies were left to the discretion of the attending cardiologist.

We set the cut-off point of 90 min for DBT based on the recommendation in the American College of Cardiology (ACC)/AHA guideline for STEMI.⁴ Onset time was defined as the time at which initial myocardial ischemia-related symptoms were felt by the patient. Door time was the time at which the patient’s arrival was recorded at the primary PCI-capable hospital. ECG time was the time at which the first ECG was recorded. Balloon time was the time at which a revascularization device, including a thrombus aspiration catheter or a coronary balloon, reached the causative lesion for the first time. No 12-lead ECG was taken during pre-hospital care in the study. We investigated the independent predictors for in-hospital prognosis, including a DBT of ≤90 min in each of the EMS patients and self-transport patients. In-hospital mortality was defined as all-cause death during hospitalization.

Statistical Analysis

Continuous variables were presented as mean and standard deviation or median and interquartile range, and categorical variables were presented as numbers and percentages. A Chi-squared test was used when appropriate; and Fisher’s exact test was used to compare categorical variables. Based on the distribution, the Student’s t-test or the Mann-Whitney U-test was used to compare continuous variables. Non-adjusted odds ratios of in-hospital mortality were revealed using univariate analysis. In this study, variables were decided based on the TIMI risk score.¹⁶ Among these variables, the variables with high odds ratios were analyzed using multivariate logistic regression analysis to explore the independent prognostic factor in each patient group. P<0.05 was considered statistically significant. All statistical analyses were performed with SPSS statistics version 23 (SPSS Institute Inc., Chicago, IL, USA).

Results

Baseline and Lesion Characteristics in the EMS and Self-Transport Groups

Among 1,172 patients, 804 patients (69%) were classified into the EMS group and 368 patients (31%) were classified into the self-transport group (Figure 1). The self-transport group was younger than the EMS group (67.4±12.2 vs. 68.9±12.1 years, P=0.03). Gender distribution was comparable in both groups. Traditional major risk factors (hypertension, hyperlipidemia, diabetes mellitus, and smoking) were equally distributed in both groups. The Killip class was significantly higher in the EMS group than the self-transport group (P<0.01). Systolic blood pressure and heart rates at the time of arrival to the hospital were significantly higher in the self-transport group than in the EMS group (137±31 vs. 130±33 mmHg, P<0.01; 75.4±19.4 vs. 72.7±22.4 beats/min, P=0.01, respectively). The culprit vessel was similar in the self-transport group and EMS group. The proportion of TIMI III coronary flow before primary PCI and attained TIMI III flow after primary PCI were not significantly different in the self-transport group and EMS group (11.2 vs. 12.1%, P=0.70; 93.8 vs. 93.8%, P=1.00, respectively). The EMS group was treated using the trans-femoral approach and with assist devices more frequently than the self-transport group. The serum creatinine level was comparable in both groups (Table 1).

Table 1. Baseline Characteristics and Angiography Findings of Patients

	Self-transport (n=368)	EMS (n=804)	P value
Age*, years	67.4±12.2	68.9±12.1	0.03
≥65, n (%)	218 (60.6)	487 (63.7)	0.32
Female, n (%)	78 (21.4)	202 (25.3)	0.16
Weight <67 kg, n (%)	225 (62.5)	532 (69.6)	0.02
Hypertension, n (%)	218 (59.4)	454 (58.5)	0.80
Hyperlipidemia, n (%)	160 (43.6)	329 (42.3)	0.70
Diabetes mellitus, n (%)	110 (30.0)	214 (27.6)	0.40
Smoking, n (%)	152 (41.4)	340 (43.8)	0.48
Killip classification I/II/III/IV, n	304/34/16/16	545/123/54/82	<0.01
SBP*, mmHg	137±31	130±33	<0.01
HR*, beats/min	75.4±19.4	72.7±22.4	0.01
Serum creatinine*, mg/dL	0.81±0.65	0.97±0.28	0.69
Infarcted artery
LAD, n (%)	186 (52.2)	375 (47.8)	0.18
LCx, n (%)	41 (11.1)	65 (8.1)	0.17
RCA, n (%)	127 (35.0)	327 (40.7)	0.12
LMT, n (%)	3 (0.8)	18 (2.3)	0.10
Multi-vessel disease, n (%)	141 (39.0)	297 (38.1)	0.80
Pre TIMI 3, n (%)	41 (11.2)	97 (12.1)	0.70
Post TIMI 3, n (%)	345 (93.8)	751 (93.8)	1.00
Approach site			0.01
TRI, n (%)	132 (37)	210 (27.9)
TFI, n (%)	222 (62.2)	537 (71.3)
TBI, n (%)	3 (0.8)	6 (0.8)
Prior MI, n (%)	31 (8.7)	69 (9.1)	0.83
Prior CABG, n (%)	2 (0.6)	9 (1.2)	0.32
Support device
IABP, n (%)	32 (8.9)	112 (14.7)	<0.01
Respirator, n (%)	12 (3.3)	54 (7.1)	0.01
PCPS, n (%)	3 (0.8)	13 (1.7)	0.25
CHDF, n (%)	4 (1.1)	16 (2.1)	0.25

*Data are presented as mean±SD or percentage of patients (indicated in brackets). CABG, coronary artery bypass graft; CHDF, continuous hemodiafiltration; EMS, emergency medical service; HR, heart rate; IABP, intra-aortic balloon pump; LAD, left ventricular descending coronary artery; LCx, left circumflex coronary artery; LMT, left main trunk; MI, myocardial infarction; PCPS, percutaneous cardiopulmonary support; RCA, right coronary artery; SBP, systolic blood pressure; Smoking, past or current smoker; TBI, trans-brachial intervention; TFI, trans-femoral intervention; TIMI, Thrombolysis in Myocardial Infarction flow grade; TRI, trans-radial intervention.

Timeframe From Onset of Symptoms to Primary PCI in the EMS and Self-Transport Groups

Table 2 shows the time interval from the onset of symptoms in the 2 groups. Similar to previously published reports, the DBT was significantly longer in the self-transport group as compared with the EMS group (115 (Inter quatile range: IQR 85–158) vs. 90 (IQR 70–119) min, P<0.01), and the proportion of DBT ≤90 min achieved was significantly lower in the self-transport group compared to the EMS group. In the self-transport group, a significantly lower number of cases had a time from arrival to initial ECG ≤10 min compared to the EMS group (60.8 vs. 79.3%, P<0.01). Onset to door time (ODT) was almost doubled in the self-transport group compared to the EMS group (150 (IQR 61–350) vs. 70 (IQR 43–136) min, P<0.01). Consequently, the onset to balloon time (OBT) (i.e., the total ischemic time) was markedly longer in the self-transport group than in the EMS group (271 (IQR 176–508) vs. 175 (IQR 135–265) min, P<0.01).

Table 2. Time Intervals

	Self-transport (n=368)	EMS (n=804)	P value
Onset-to-door time, min	150 (61–350)	70 (43–136)	<0.01
Door-to-balloon time, min	115 (85–158)	90 (70–119)	<0.01
Onset-to-balloon time, min	271 (176–508)	175 (135–265)	<0.01
Door-to-ECG time ≤10 min, n (%)	224 (60.8)	638 (79.3)	<0.01
Door-to-balloon time ≤90 min, n (%)	108 (30.0)	394 (50.3)	<0.01

Data are presented as median (IQR) or percentage of patients. ECG, electrocardiogram. Other abbreviations as in Table 1.

Clinical Outcomes

Even with delayed DBT, the in-hospital mortality rate was significantly lower in the self-transport group than in the EMS group (3.3% (n=12) vs. 7.1% (n=67), P=0.01) (Figure 2). Accordingly, we compared the in-hospital mortality rate between the patients with a DBT of ≤90 min and the patients with a DBT of >90 min in each group (Figure 3). Among EMS patients, the in-hospital mortality rate of the patients with a DBT of ≤90 min was significantly lower than that of patients with a DBT of >90 min (3.6 vs. 11.1%, P<0.01). In contrast, among the self-transport patients, as compared with a DBT of >90 min, a DBT of ≤90 min had no significant effect on mortality (2.8 vs. 3.2%, P=0.84).

Figure 2.

In-hospital mortality rates in patients transported using self-transport and EMS. Abbreviations as in Figure 1.

Figure 3.

In-hospital mortality rates in patients with a DBT ≤90 min and >90 min. DBT, door-to-balloon time. Other abbreviations as in Figure 1.

Predictors of In-Hospital Mortality

In the univariate analysis, age ≥65 years, female sex, systolic blood pressure <100 mmHg, heart rate >100 beats/min, weight <67 kg, Killip class >1, DBT of >90 min, and self-transport were associated with in-hospital mortality (Table 3). To identify independent prognostic factors, multivariate analysis was performed with variables with a high odds ratio according to univariate analysis. In the entire cohort, age ≥65 years, Killip class >1, and DBT >90 min were independently associated with a poor in-hospital mortality rate. We confirmed that self-transport was not an independent predictor of in-hospital prognosis in all cases (Table 4). We therefore analyzed the independent predictor in each group separately. A DBT >90 min did not have a significant effect on in-hospital mortality in patients using self-transport (odds ratio (OR)=0.89 (95% confidence interval (CI): 0.21–3.68), P=0.87); however, it remained an independent predictor of in-hospital mortality in the patients using EMS (OR=2.43 (CI: 1.20–4.92), P=0.01) (Table 5).

Table 3. Univariate Risk of In-Hospital Mortality in All Cases

	OR	95% CI	P value
Age ≥65 years	5.48	2.33–12.9	<0.01
Female	2.95	1.73–5.04	<0.01
SBP <100 mmHg	1.50	1.25–1.81	<0.01
HR >100 beats/min	1.96	1.44–2.67	<0.01
Weight <67 kg	2.42	1.21–4.83	0.01
Anterior or LBBB	1.53	0.89–2.63	0.12
HT or DM	1.83	0.94–3.45	0.08
Killip >1	3.15	2.31–4.29	<0.01
OTD >240 min	1.53	0.83–2.81	0.17
DBT >90 min	2.33	1.27–4.22	0.01
Self-transport	0.43	0.21–0.85	0.02

CI, confidence interval; DM, diabetes mellitus; HR, heart rate; HT, hypertension; LBBB, left bundle branch block; OR, odds ratio; OTD, onset-to-balloon time. Other abbreviations as in Table 1.

Table 4. Multivariate Risk of In-Hospital Mortality in All Cases

	OR	95% CI	P value
Age ≥65 years	3.26	1.34–7.95	<0.01
Female	2.18	1.22–3.90	<0.01
Killip >1	6.40	3.31–12.4	<0.01
DBT >90 min	2.14	1.14–4.04	0.02
Self-transport	0.55	0.26–1.14	0.11

Abbreviations as in Tables 1,3.

Table 5. Multivariate Risk of In-Hospital Mortality in the Self-Transport and EMS Groups

	Self-transport (n=368)			EMS (n=804)
	OR	95% CI	P value	OR	95% CI	P value
Age ≥65 years	3.53	0.41–30.3	0.25	3.10	1.16–8.32	0.02
Female	4.27	1.11–16.5	0.04	1.91	0.99–3.68	0.06
Killip >1	2.70	0.71–10.3	0.15	11.1	5.02–24.4	<0.01
DBT >90 min	0.89	0.21–3.68	0.87	2.43	1.20–4.92	0.01

Abbreviations as in Tables 1,3.

Discussion

In this study, we found that a DBT ≤90 min had no significant influence on the in-hospital mortality rate in patients using self-transport; however, it was a significant independent predictor in patients in the EMS group.

There have been several observational studies showing a strong association between a shorter DBT and improved mortality rates.^3,17 Thus, current guidelines recommend achieving a DBT of ≤90 min as the clinical goal for patients with STEMI being treated with primary PCI.^4,5 However, in recent years, there have been an increasing number of reports stating that the in-hospital mortality rate has not reduced despite the improvement in DBT.^7,8,18,19 The prognosis in patients with low risk and patients presenting late after the onset of symptoms has not shown any improvement by achieving a DBT of 90 min or less.^20–22

Some reports have focused on the difference in the type of transport among STEMI patients. So et al revealed that patients with STEMI transported by EMS had higher in-hospital mortality rates despite shorter door-to-needle time and DBT than patients using self-transport.¹³ However, in his study, there were fewer patients treated using primary PCI. From the reports of a large observational study in the United States, patients who arrived at hospitals using self-transport were on average younger, males, with a relatively lower risk, or hemodynamically stable on presentation.^10,12 In our study, 31% patients were in the self-transport group, and 69% were in the EMS group. The finding that there was a larger number of older patients in the EMS group with a higher Killip classification is consistent with past reports. Moreover, similar to past reports, time intervals of ODT, DBT, and OBT were longer in the self-transport group. However, there are few reports that examined, in detail, the influences of difference of transportation and delayed DBT on prognosis. Therefore, we investigated the effect of DBT on the in-hospital mortality rate in the STEMI patients using self-transport in the era of primary PCI.

There seem to be some reasons for initial treatment delay in the self-transport group. The ACC/AHA guidelines recommend that an ECG should be performed within 10 min or less in a patient with symptoms indicating a possible acute coronary syndrome (ACS).⁴ In the present study, while 79.8% patients in the EMS group underwent an ECG within 10 min, a smaller proportion of patients in the self-transport group achieved this criterion (60.8%, P<0.001). This result suggests that a longer time to diagnosis was one of the factors for the longer DBT in the self-transport group. Another factor leading to shorter DBT in the EMS group seemed to be the information sent by the ambulance team to the medical facility before the patient’s arrival at the hospital.²³ Bradley et al reported that the hospital’s coordination with EMS was strongly associated with the DBT.²⁴ The information leads to facilitation of emergency PCI protocols, including early preparation for a catheterization laboratory and activating a catheterization team, and may contribute to shortening the treatment time in the EMS group.^25–27

Self-transport patients had better in-hospital prognosis in spite of the strikingly longer DBT. One of the reasons could be the difference in severity of disease. In the multivariate analysis of both patient groups, we found that a DBT of >90 min was not an independent prognostic predictor in the self-transport group; however, a DBT >90 min was an independent predictor in the EMS group. The lower severity of disease in the self-transport group might have reduced the effect of DBT on in-hospital mortality. In addition, we considered that the effect of DBT on in-hospital mortality was attenuated by the time delay of ODT. The proportion of DBT in the total ischemic time was smaller in the self-transport group. These findings demonstrate the difference in the importance of DBT on the in-hospital mortality in the STEMI patients transported by EMS and self-transport.

From the present study findings, early reperfusion therapy within 90 min is preferable for the patients with STEMI using EMS. However, it had no impact on the in-hospital mortality in the STEMI patients using self-transport. Therefore, to improve the outcome of the STEMI patients using self-transport, it is important not only to shorten the DBT, but also to consider other clinical factors depending on patient’s characteristics.

Study Limitations

The present study has several limitations. First, this is a retrospective observational study; therefore, the impact of confounding factors that we did not analyze should be taken into account. Second, we did not have detailed data regarding left ventricular function and in-hospital medical treatment, which might be predictors for in-hospital mortality of the STEMI patients. Third, the average DBT in this study is longer than in other reports. This difference might affect the influence of DBT on in-hospital mortality. It is also not clear whether delayed DBT can affect the long-term prognosis in patients using self-transport. Primary PCI was performed in all cases, and more than 90% were able to obtain TIMI III grade coronary flow after primary PCI, which is similar to actual clinical conditions. No patient received transvenous fibrinolytic therapy.

Conclusions

The present study demonstrated that there was no relationship between in-hospital prognosis and a DBT ≤90 min in patients with STEMI using self-transport. The prognosis of STEMI patients using self-transport may not be improved by focusing on DBT alone, and treatment strategies based on the means of transportation should be considered.

Acknowledgments

The authors appreciate the help of all members from the committee for this project, and members of the institutes that participated in the AMI-Kyoto Multi-Center Risk Study. We would like to thank Editage (www.editage.jp) for English language editing.

Disclosures

The authors declare no competing financial interests.

Names of Grants

None.

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