Primary PCI or thrombolysis: the 120-minute rule, and the clock people get wrong

NICE NG185 sets one clock for the reperfusion decision, and it is not first medical contact. Getting the denominator wrong changes the answer.

Updated 2026-08-25 · 4 min read

The reperfusion decision in ST-elevation myocardial infarction turns on a single threshold, and it is very commonly misquoted — including in revision material.

NICE NG185, recommendation 1.1.6. Offer coronary angiography with follow-on primary PCI as the preferred reperfusion strategy if presentation is within 12 hours of symptom onset and primary PCI can be delivered within 120 minutes of the time when fibrinolysis could have been given.

The denominator is the point

The clock does not start at first medical contact, at the door, or at diagnosis. It starts at the moment fibrinolysis could have been given — that is, the moment you had a patient in front of you whom you could have thrombolysed.

The question the guideline asks is therefore a comparison, not a stopwatch: how much later than thrombolysis would PCI be? If the answer is under two hours, transfer for PCI. If it is over, thrombolyse.

Recommendation 1.1.19 is the mirror image: offer fibrinolysis to people presenting within 12 hours of symptom onset if primary PCI cannot be delivered within 120 minutes of the time fibrinolysis could have been given.

Why the wrong clock changes the answer

Consider a patient who arrives at a non-PCI hospital. Thrombolysis is available immediately. The PCI centre is 45 minutes away and could achieve balloon inflation 100 minutes from now.

Clock used	Reading	Decision
From when fibrinolysis could have been given	100 minutes	Primary PCI — 20 minutes inside the threshold
From first medical contact, some minutes earlier	Appears longer	Might tip you to thrombolysis incorrectly

In a question, the giveaway is usually that you are told both when thrombolysis could be given and when the balloon could go up. If a stem gives you only "X minutes from first medical contact", the stem itself is ambiguous — the comparison NICE asks for cannot be made from that number alone.

Two related points worth holding

Cardiogenic shock (1.1.7): offer angiography with follow-on PCI to people with acute STEMI and cardiogenic shock presenting within 12 hours, without the 120-minute test.
Level of consciousness after arrest (1.1.2) must not be used to decide eligibility for angiography.

Sources

NICE NG185: Acute coronary syndromes — recommendations 1.1.6 and 1.1.19

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Written for doctors preparing for postgraduate examinations. It is a revision aid, not clinical advice, and guidance changes — always work from the current guideline and your local protocols. Resus Review is independent and is not affiliated with or endorsed by the Royal College of Emergency Medicine, NICE, or Resuscitation Council UK.