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Evidence-based guidelines recommend that after a heart attack, the blocked coronary artery needs to be reopened quickly by either fibrinolysis (or “clot-busting” drugs) or primary percutaneous coronary intervention (primary PCI), which aims to open the artery using balloons and stents. However, there are several reasons for delay in these treatments.

Firstly, “patient delay” is the delay from the onset of chest pain or symptoms to when a call is made to emergency medical services, and can only really be reduced by better public education about heart attacks. Secondly, “system delay” is a combination of “transportation delay” (the time taken for the patient to get to the hospital) and “door-to-balloon delay” (the time taken for the patient to receive the artery-opening therapy once they are in the hospital). In terms of training of doctors and measurement of outcomes within hospitals and across health systems, there has been a huge focus on the “door-to-balloon” delay. However, to know the effect of delaying therapy on outcome, we need to look at “system delay”, which is what a Danish study does in this week’s JAMA.

Due to excellent public medical databases in Denmark, the authors were able to study over 6000 patients with the particular form of heart attack (“STEMI”) which is best treated by primary PCI, and obtain estimates for the various types of delay outlined above. The authors excluded patients with a treatment delay greater than 12 hours or a system delay greater than 6 hours.

Interestingly, treatment delay and patient delay were not associated with mortality, but the authors are quick to assert that “should not deter encouraging patients to seek medical help as soon as possible after the onset of symptoms”. On the other hand, system delay predicted mortality, with a hazard ratio of 1.10 per 1-hour delay. In other words, for every one hour of system delay, there is a 10% increase in mortality. When the authors analysed further, they found that a 1-hour transportation delay led to 10% increase in mortality, whereas a 1-hour door-to-balloon delay led to a 14% increase in mortality. In other words, time does really mean muscle (and life) when it comes to the heart.

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