Transfer distance effect on reperfusion: timeline of ST-elevation patients transferred for primary percutaneous coronary intervention

Abstract

Objectives

This study aims to establish if transfer distance impacts the outcome of ST-elevation myocardial infarction (STEMI) patients transferred to a percutaneous coronary intervention (PCI).

Background

Regional emergency care systems were designed to decrease delays in reperfusion of patients but the effect of transfer distance on outcome is less established.

Methods

We compare the characteristics and outcomes of STEMI patients transferred from a distance > 25 miles (GT25) to those transferred from distances ≤ 25 miles (LT25) by utilizing data from a regional STEMI care network in the greater Washington DC area.

Results

Within the transferred patients (n = 1065), 609 patients (57%) were transferred from GT25 (median distance 36 miles), while 456 (43%) were transferred from LT25 (median distance 13 miles). Most of the baseline characteristics between the groups were similar. Door-to-balloon (DTB) was defined as the time elapsed from the presentation to the center without PCI capability to flow restoration in the culprit artery. No differences were noted in the median DTB (GT25: 158 min [122–213] vs. 149 [118–219]; p = 0.5) or in in-hospital mortality (8% vs. 7.2%; p = 0.617). By implementing the regional STEMI care network, a constant decrease in DTB was noted throughout its years of operation.

Conclusions

For STEMI patients presenting to a non-PCI capable center, a network care system for PCI mitigates the distance factor on DTB time. This is turn translates into comparable outcomes.

1 Introduction

Time is of the essence in myocardial salvage of patients with ST-elevation myocardial infarction (STEMI). Pivotal trials have established the clinical benefits of primary percutaneous coronary intervention (PCI) as the preferred reperfusion strategy in patients presenting with STEMI, including in cases that require transfer to a PCI-capable center . Prior studies have demonstrated that time delays to reperfusion correlated with poor outcome , while timely reperfusion, even at the cost of transferring patients to a PCI-capable center, correlated with decreased mortality rates . However, the optimal ‘sweet-spot’ in which a long transfer delay still results in a beneficial reperfusion is unknown. The aim of this study was to compare the timeline for reperfusion and the outcome of patients transferred to a PCI-capable center from intermediate distances (≤ 25 miles; LT25) to those transferred from long distance (> 25 miles; GT25) by utilizing a regional STEMI care system. We hypothesize that a longer transfer distance will increase the door-to-balloon (DTB) time and will have a negative impact on outcome. The secondary hypothesis is that implementation of regional CodeHeart STEMI care program will result in decreased DTB time irrespective of the transfer distance.

2 Materials and methods

Consecutive patients admitted to MedStar Washington Hospital Center after being referred and transferred from a different hospital for primary PCI were included in the present analysis. All patients were referred through the CodeHeart STEMI care system. CodeHeart is a regional program initiated in November 2006, designed to facilitate STEMI patients’ transport from a non-PCI-capable facility to MedStar Washington Hospital Center (a tertiary PCI-capable center in Washington, DC, USA). This regional program is unique in the sense that it includes both private and state emergency medical services, patient transfer crosses several state lines (DC, Maryland and Virginia), and because most of the hospitals are considered ‘out-of-network’. Thus, no structured data sharing is available for rapid decision making. At present, 15 hospitals refer patients to MedStar Washington Hospital Center through this system. Some regional networks that report their results have limited the participation to only hospitals that are able to achieve the 30–90 minute goal . Others use an algorithm to dictate administration of thrombolysis in patients transferred from long distances. To promote “real-life” referrals, this network does not limit hospital participation, nor does it use a specific algorithm for thrombolysis in patients transferred from long distances.

The CodeHeart triage pathway and the corresponding recorded timeframes are depicted in Fig. 1 . Patients who present to a participating non-PCI-capable center with chest pain undergo a clinical evaluation. If ST-elevation is demonstrated on electrocardiogram, the emergency department physician is directed to consult with the interventional cardiologist in the tertiary center (available 24 hours/day, 7 days/week). This consult is currently performed over a designated on-line video conference between the emergency department physician and the on-call interventional cardiologist. This conference call can be made via tablet and/or cellular telephone and includes a joint analysis of clinical symptoms and the electrocardiogram. In the case of STEMI, the interventional cardiologist coordinates the patient’s transfer and notifies the CodeHeart cath lab team in the tertiary hospital to prepare for patient arrival.

In the GT25 group, the default mode of transfer is by air unless weather or air traffic control issues prevent it. Upon arrival, the patient is transported directly to the cath lab for prompt revascularization. Prior to revascularization, patients are pre-loaded with aspirin 325 mg and either 300- or 600-mg clopidogrel and are recommended to continue aspirin indefinitely and to continue clopidogrel 75 mg for 12 months. During the procedure, patients are treated with bivalirudin (0.75 mg/kg bolus followed by a 1.75 mg kg ^{− 1}hour ^{− 1}infusion) or unfractionated heparin (40 U/kg bolus with an additional dose to achieve an active clotting time of 250–300 s). The use of IIb/IIIa antagonists is at the operator’s discretion.

Data were collected by utilizing the CodeHeart database and the institutional PCI databases. Only patients transferred from a referring hospital were included. Patients who presented to the hospital by emergency medical services and those who were considered self-referrals were excluded. Patient data, including timeline to arrival, demographics, medical history, interventional and outcome indices, were collected and a comparison was made between those patients transferred from distances ≤ 25 miles away and those transferred from > 25 miles away. The 25-mile cutoff was chosen as the radius for the Washington, DC, metropolitan area, indicating a long- versus intermediate transfer distance.

The primary end point of this study was in-hospital mortality. Other secondary end points were Q-wave myocardial infarction, coronary artery bypass grafting surgery, target lesion revascularization, cerebrovascular events, vascular complications, bleeding complications and door-to-balloon (DTB) time. DTB time was defined as the time elapsed from the patient’s arrival to the referring hospital to the time of introduction of first device that restores antegrade flow – balloon, stent or thrombectomy device.

STEMI was defined as the presence of chest discomfort or symptoms of myocardial ischemia, associated with new or presumed new electrocardiographic abnormalities in the ST-segment (elevation at the J point of at least 0.2 mV in leads V1, V2 and V3 and at least 0.1 mV in at least two contiguous leads), or new left bundle branch block. Q-wave myocardial infarction was defined as an increment of creatine kinase-MB 2 × the maximum normal values, associated with the development of a new Q wave deeper than 1 mm in > 2 contiguous leads); target lesion revascularization was considered as ischemia-driven percutaneous or surgical repeat intervention in the stent or within 5 mm proximal or distal to the stent. Angiographic lesion definitions were in accordance with the Coronary Artery Surgery Study definitions . Angiographic success was defined as final stenosis after the procedure ≤ 30% or Thrombolysis In Myocardial Infarction flow grade 3. Hypercholesterolemia was defined as fasting cholesterol > 250 mg/dl or the use of lipid-lowering therapy. Systemic hypertension was defined as blood pressure > 140/90 mm Hg or the use of antihypertensive therapy. Chronic renal insufficiency was defined as previously diagnosed or treated with medication, diet, or dialysis by a physician or if a baseline creatinine level > 2.0 mg/dl is found. Congestive heart failure was defined as evidence of fluid retention from cardiac causes before admission.

The analysis was conducted in accordance with the local institutional review board regulations. STEMI diagnosis, procedure data and time intervals were all adjudicated independently by physicians, such that the time intervals and procedural times are verified against source documentations/clinical charts. Furthermore, each STEMI has a qualifying electrocardiogram such that no ambiguous cases were included, which may have skewed the time intervals.

Statistical analysis was performed using SAS version 9.1 (SAS Institute, Cary, NC, USA). Continuous variables are expressed as mean ± SD or median (25th–75th interquartile range) as appropriate according to the variable distribution. Categorical variables are expressed as percentages. Student’s t test was used to compare continuous variables. The chi-square test or Fisher’s exact test was used to compare categorical variables with normal distribution while the Wilcoxon rank-sum test was used for non-normal distribution. Non parametric hypothesis test was performed using the Kruskal-Wallis test. A p value < 0.05 was considered as statistically significant.