Treatment delays in ST elevation myocardial infarctionBMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39475.482419.80 (Published 21 February 2008) Cite this as: BMJ 2008;336:401
- Christian Juhl Terkelsen, senior registrar,
- Jens Flensted Lassen, consultant cardiologist
Quickly re-establishing coronary blood flow is vital in patients with ST elevation myocardial infarction. Two recently published systematic reviews summarise the evidence on this form of treatment.1 2 The first review concluded that primary percutaneous coronary intervention (PCI) is the best reperfusion strategy if performed quickly, and it identified “door to balloon time” (the time from arrival at hospital to balloon inflation) as a key predictor of outcome in people given this treatment.1 The second review stated that “inevitable transport delays commonly limit the benefit of PCI.”2 The reviews reflect an ongoing controversy in cardiology—when is PCI the best reperfusion strategy, and when should fibrinolysis be considered as an alternative?
What is an acceptable time window in which to deliver PCI? The review by Boden and colleagues and current guidelines recommend using fibrinolysis if the extra time needed to perform percutaneous coronary intervention (the PCI related delay) is more than 60 minutes, or if the time from the onset of symptoms to presentation is less than three hours.2 3 4 However, one of the recent systematic reviews found no clear definition of an acceptable PCI related delay.1 The idea of a 60 minute maximal PCI related delay was derived from an earlier meta-analysis by the same author that included 23 randomised trials comparing fibrinolysis with PCI.5 For each trial, the benefit to mortality achieved when performing PCI instead of administering fibrinolysis was plotted against the PCI related delay seen at trial level. The 60 minute standard was derived from this regression analysis and introduced into subsequent guidelines.3 4
Unfortunately, the values used in this analysis to denote delay were underestimates. Also, in one trial, instead of separating data from patients who were transferred to an interventional hospital versus those directly admitted to an interventional hospital, a single value of 55 minutes was used for the PCI related delay. When the regression analysis is recalculated using the originally tabulated data the acceptable PCI related delay is 119 minutes, and if the data on transferred versus non-transferred patients are split the acceptable PCI related delay becomes 171 minutes. The idea of a 60 minute maximal PCI related delay has also been questioned in another meta-analysis.6 It found a benefit of PCI over on-site fibrinolysis even when PCI was performed after 80-120 minutes.6 Assuming that a PCI related delay of 120 minutes is acceptable, the maximal transport times to intervention centres may vary from 35 to 140 minutes depending on optional reperfusion strategies and the in-hospital delays in the particular region (figure⇓).
Is door to balloon time an accurate predictor of outcomes, as a recent systematic review suggests?1 It is logical that reducing any of the components of treatment delay (patient delay, emergency medical system delay, delay at local hospital, transfer delay, door to balloon delay at the invasive hospital) will reduce mortality. If patients are admitted to a local hospital and then transferred to another hospital for invasive treatment, door to balloon time comprises only a small component of the total system delay (figure). Accordingly, system delay (time from patient alerting the health system to balloon inflation) would seem a better indicator of outcome than door to balloon time. Out of hospital strategies such as prehospital diagnosis combined with bypassing local hospitals and re-routing patients directly to catheterisation laboratories would eliminate many components of system delay (figure).7
What strategies could increase the number of patients with ST elevation myocardial infarction who are eligible for PCI? Low volume intervention centres were set up in local areas on the basis of the assumption that they would provide easier access to a catheterisation laboratory. However, these centres cannot quickly activate catheterisation laboratories on a 24 hour basis. This may explain why the door to balloon time is consistently around 100 minutes in the United States, where two thirds of centres perform fewer than 40 percutaneous coronary interventions each year.8 On average, patients wait 10 minutes for an electrocardiogram; 60 minutes in the emergency room, coronary care unit, or intensive care unit; and 30 minutes in the catheterisation laboratory (figure).8
Setting up large volume centres in more remote locations might be the best option because treatment at such centres is associated with better outcomes, and door to balloon times of 30 minutes can be achieved. If door to balloon times were shorter, catchment areas could be bigger because longer transport times would be acceptable (figure). Prehospital diagnosis and rerouting directly to the catheterisation laboratory would be essential to achieve the optimum door to balloon time at high volume centres. This would bypass the local hospital, as well as the emergency room, coronary care unit, or intensive care unit at the interventional hospital (figure).7 9
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.