Delays in Transfer For Primary PCI in STEMI
Abstract & Commentary
By Andrew J. Boyle, MBBS, PhD, Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco. Dr. Boyle reports no financial relationships relevant to this field of study.
Source: Miedema M, et al. Causes of delay and associated mortality in patients transferred with ST-segment-elevation myocardial infarction. Circulation 2011;124:1636-1644.
Most patients with ST-elevation myocardial infarction (STEMI) present to hospitals that are not capable of percutaneous coronary intervention (PCI). Rapid transfer to PCI-capable facilities for primary PCI may result in earlier reperfusion of the infarct artery and better clinical outcomes. However, delays in transfer may diminish the mortality benefit achieved with primary PCI in STEMI. The specific reasons for and the clinical impact of delays in transfer for primary PCI are unknown. Accordingly, Miedema and colleagues prospectively studied 2034 patients with STEMI transferred to their institution for primary PCI and determined the causes of delay in transfer, as well as the clinical outcomes associated with these delays.
Between 2003 and 2009, 2034 patients suffering STEMI were transferred with the intent of primary PCI. All patients with ST-elevation or new left bundle branch block and chest pain of < 24 hours duration were included. There were no exclusion criteria. The time from first hospital contact to reperfusion (overall door-to-balloon time) was recorded and was also divided into three segments: referring center door-in-to-door-out time, transport time, and PCI receiving center door-to-balloon time. The total door-to-balloon time goal was 120 minutes and the segment goals were 45, 45, and 30 minutes, respectively. Reasons for delay were prospectively collected.
Patients with delayed overall door-to-balloon times (from arriving at referring center to balloon inflation at PCI center > 120 minutes) were older (64 vs 61 years, P < 0.001), were more likely to be non-smokers (63% vs 58%, P = 0.02) and diabetics (18.4% vs 14.4%, P = 0.02), and were more likely to be in cardiogenic shock (12.9% vs 9.6%, P = 0.04) than those who had no delay. Patients with delay to PCI had higher in-hospital mortality than those with no delay (6.4% vs 4.1%, P = 0.02), but this difference was no longer statistically significant at 30 days. The authors then examined where the delay occurred and its effect on mortality.
Delay at the referral center (door-in-to-door-out time > 45 minutes) occurred in 64% of cases. The most common reason for delay was waiting for transportation. The longest delays were for diagnostic dilemma, followed by non-diagnostic electrocardiogram (ECG), then cardiac arrest/shock, emergency department delay, and other. In-hospital mortality associated with delays was highest for those with cardiogenic shock (31%) and lowest in those with non-diagnostic ECG (0%).
Delays in transport (> 45 minutes) were less common (13%). These were usually due to weather or distance (some referral hospitals were up to 210 miles away). There was no excess mortality attributable to transport delays.
Delays at the PCI center (door-to-balloon time > 30 minutes) occurred in 16%. The most common reasons for delay were catheterization lab team delay and complex procedure. The longest delays were due to diagnostic dilemma. The highest mortality was in those with cardiogenic shock/cardiac arrest (44%). The authors conclude that treatment delays occur even in efficient systems for STEMI care, and that the clinical impact of the delay varies according to the cause of the delay.
Current treatment guidelines emphasize the importance of rapid reperfusion in the treatment of patients with STEMI. While PCI is a more effective reperfusion strategy than fibrinolysis when both are offered with little delay in clinical trial settings, delays at any stage of the process can prolong the ischemic time, increase myocardial damage, and reduce the benefit of PCI. Developing systems of rapid patient transfer for primary PCI are challenging, but should be a priority under the latest guidelines. The higher mortality in those with overall door-to-balloon times > 120 minutes confirms the importance of rapid reperfusion. This study defines the reasons for delay within these authors' system, which is an experienced high-volume primary PCI transfer system. Delays were very frequent at the referring hospital (64% of cases), and infrequent at the PCI center (16%). These data may inform other STEMI transfer systems that are being developed. Importantly, the reason for the delay was more important than the delay itself. Delay for an initially non-diagnostic ECG, for example, was associated with very low in-hospital mortality and this may represent a lower-risk patient group.
This study is observational in nature, and therefore a direct cause and effect relationship between the reason for delay and mortality rate cannot be assumed. It is an association. Furthermore, we are not told of the pharmacological strategies employed in their patients (how many received thienopyridines, glycoprotein IIb/IIIa inhibitors?), the procedural details (culprit lesion location, stent type, use of intra-aortic balloon pumps), or the bleeding rates. All of these may contribute to the outcomes in these patients.
Despite these limitations, this study underscores the importance of rapid transfer protocols, highlights the frequency of delays despite a rapid transfer protocol, and suggests that the reason for the delay may be more important than the delay itself.