A heart attack is one of the most protocol-driven emergencies in medicine, and every step in the protocol has a time attached: ten minutes, one hour, two hours, seventy-two hours. This chapter sets out what should happen in a UK hospital, by NICE recommendation, with the numbers behind each step, and where the 2025 American guideline goes further. It is written so that a patient or a relative can tell whether it happened, and so that a clinician can use it as the one-page version.
1. The first ten minutes: the ECG decides the road
A 12-lead ECG within ten minutes of arrival (or of the ambulance crew's arrival at the patient) sorts chest pain into two roads. ST elevation in a pattern matching an artery, or a new left bundle branch block with the right story, is a STEMI, and the rest of section 2 applies at once. Anything else — ST depression, T-wave changes, or a normal trace — goes down the troponin road in section 3. A single normal ECG does not exclude a heart attack; it is repeated if pain recurs and at intervals, and the posterior and right-sided leads are added when the story is strong and the standard leads are unconvincing.
2. STEMI: the 120-minute rule
Primary PCI — a catheter from the wrist to the blocked artery, a wire through the clot, a balloon and a stent — is the treatment, and NICE's rule (NG185) is that it should be delivered within 120 minutes of the time a clot-busting drug could have been given, for anyone presenting within 12 hours of onset. In practice the ambulance ECG starts the clock, the crew pre-alert the heart attack centre, and the patient goes straight to the catheter laboratory. The UK's audit (MINAP) reports call-to-balloon times, and most centres achieve under 150 minutes for most patients; the best achieve under 90.
If PCI cannot be delivered in 120 minutes — a rural presentation, a transfer that will take too long — the alternative is fibrinolysis, a clot-busting drug into a vein (tenecteplase, as a single bolus), given within 30 minutes of the ECG, followed by transfer for an angiogram within 24 hours whether or not it appears to have worked. Fibrinolysis opens the artery in about two-thirds of cases and carries a roughly 1% risk of a brain bleed, so PCI is preferred wherever it can be reached in time.
Beyond 12 hours, PCI is still done if there is ongoing pain, instability or a dangerous rhythm; a stable patient who arrives late is assessed for whether the muscle is still salvageable.
Why the number is 120 and not "as soon as possible". The benefit of opening the artery falls with every half-hour; the mortality advantage of PCI over fibrinolysis disappears when the PCI-related delay exceeds about two hours, which is where the rule comes from. Within that, faster is better: door-to-balloon under 90 minutes is the standard the American guideline names, and the difference between 60 and 120 minutes is measurable in muscle saved and lives.
3. Everyone else: the troponin pathway
Troponin leaks from injured heart muscle within hours, and modern high-sensitivity assays detect it early. NICE's diagnostic guidance (DG40) supports early rule-out pathways: a troponin on arrival and a second one at one to three hours, with assay-specific thresholds, which together rule a heart attack out in most people within a few hours and rule it in when the level is high or rising. The European 0/1-hour algorithm, used in many UK departments, gives an answer in an hour for the majority. Points that matter:
- A single normal troponin on arrival is not the end of it unless the pain started more than a few hours earlier and the assay's rule-out threshold is met; a second sample is the rule.
- A raised troponin is not the same as a heart attack. It rises in kidney failure, sepsis, a pulmonary embolism, a fast rhythm, heart failure and myocarditis. What makes it an infarction is a rise and fall with a clinical picture (the Universal Definition). The spectrum chapter is the map.
- A patient with ongoing pain, an unstable rhythm, a falling blood pressure or heart failure does not wait for the pathway: they go to the catheter laboratory now.
4. NSTEMI and unstable angina: the 72-hour rule
Once the troponin pathway has diagnosed a heart attack without ST elevation, the artery is not completely blocked and the timescale is days rather than minutes, but it is still a timescale. NICE uses the GRACE score (age, heart rate, blood pressure, kidney function, troponin, ECG changes, and whether the heart is failing) to estimate six-month mortality:
- Intermediate or higher risk (GRACE-predicted six-month mortality over 3%): coronary angiography within 72 hours of admission, with a stent or, for complex disease, bypass surgery. The 2025 American guideline says the same: an invasive approach during the admission for intermediate- and high-risk patients.
- Very high risk — ongoing pain, instability, heart failure, a dangerous rhythm — angiography immediately, within two hours.
- Low risk: a stress test or a CT coronary angiogram, and an angiogram if either shows a problem.
Angiography is via the wrist (radial artery) rather than the groin in both countries' guidance: it bleeds less and kills fewer people. Multivessel disease found at a STEMI angiogram is treated completely during the admission (NG185 and the American guideline agree), except in cardiogenic shock, where only the culprit artery is opened.
5. Every drug, with its reason
| Drug | Why | UK (NG185) | US (2025) |
|---|---|---|---|
| Aspirin 300 mg, then 75 mg daily | Halves the chance of the clot in the artery growing; reduces death by about a fifth | Immediately, chewed, for everyone unless truly allergic; lifelong | Same (162–325 mg loading) |
| A second antiplatelet: ticagrelor or prasugrel, or clopidogrel | Adds to aspirin; protects the stent | Ticagrelor with aspirin for most; prasugrel if going for PCI; clopidogrel if bleeding risk is high or an anticoagulant is needed. Continue 12 months | Loaded on arrival; prasugrel or ticagrelor preferred over clopidogrel with PCI; 12 months, shortened to 1–3 months on one agent where bleeding risk is high, and in that case aspirin is the one dropped |
| An anticoagulant: fondaparinux, or heparin | Stops the clot extending while the angiogram is arranged | Fondaparinux for NSTEMI unless the angiogram is within 24 hours or bleeding risk is high; heparin in the catheter laboratory | Heparin or bivalirudin; continued until revascularisation |
| Oxygen | Only if saturations are low | Only if below 94% (or 88–92% in COPD) | Not routinely above 90%: no benefit, possible harm |
| Pain relief: GTN, and morphine if needed | Comfort and lower cardiac work | GTN unless blood pressure is low; morphine for persisting pain | Same; morphine used sparingly because it delays antiplatelet absorption |
| High-intensity statin: atorvastatin 80 mg | Stabilises plaque; reduces recurrence | Started in hospital, lifelong; LDL rechecked at 2–3 months against the NG238 target | Started immediately, with the option of ezetimibe from the start; a non-statin added if LDL stays at or above 1.8 mmol/L (70 mg/dL), and reasonable at 1.4–1.8 |
| ACE inhibitor (or ARB) | Protects the heart from remodelling; reduces death, most in those with a weakened pump, diabetes or high blood pressure | Started once stable, continued indefinitely, dose titrated | Same, with the strongest recommendation for reduced ejection fraction |
| Beta-blocker | Reduces rhythm deaths and re-infarction after a large heart attack; less certain after a small one | For 12 months if the pump is normal; indefinitely if it is weakened | Started within 24 hours if stable; continued long term with reduced ejection fraction; see the note below |
| SGLT2 inhibitor, mineralocorticoid antagonist | For a weakened pump or heart failure | Per the heart failure guidance | Same |
| GTN spray to take home | Symptom relief; the two-dose rule | Everyone | Everyone |
Beta-blockers: where the evidence moved in 2025 and the UK guideline has not. The case for a routine beta-blocker after every heart attack came from trials done before stents and statins. Four modern trials tested it in people whose heart pump was not weakened, and an analysis of all 17,801 patients published in November 2025 found no benefit when the ejection fraction was 50% or more, and a benefit when it was mildly reduced (40–49%). NICE's 2020 guideline still says twelve months for everyone; the European and American guidelines have moved to "may be considered" for a preserved pump. If your echocardiogram showed a normal pump and you are on a beta-blocker with side effects — fatigue, cold hands, low mood, erectile problems — that is a conversation worth having at the review, not a reason to stop it yourself.
6. What else is done in the first days
- An echocardiogram before discharge: how much of the pump was lost (the ejection fraction), which decides the beta-blocker, the ACE inhibitor, the heart failure drugs and, later, whether a defibrillator is needed.
- Continuous rhythm monitoring for at least the first 24–48 hours: the days when ventricular fibrillation and heart block happen.
- Bloods: full blood count, kidney function, glucose and HbA1c, a lipid profile within 24 hours (after that the illness lowers it), liver function, and a repeat troponin to see the peak. The full list is in the every-test chapter.
- Blood pressure and glucose controlled; hyperglycaemia treated but not to tight targets.
- Mobilisation within a day; a cardiac rehabilitation referral before discharge, with the first contact within days, not weeks.
- A named diagnosis on the discharge letter: STEMI, NSTEMI, type 2, MINOCA, SCAD or takotsubo, because the follow-up for each differs.
7. Cardiogenic shock
Around one heart attack in fifteen is complicated by the pump failing to hold the blood pressure, and it is the commonest cause of death in hospital after a heart attack. The treatment is to open the culprit artery at once, support the circulation with drugs, and in selected patients place a microaxial flow pump (a miniature pump threaded into the left ventricle through a leg artery). In the DanGer Shock trial of 2024 that device reduced death at six months from around 58% to around 46%, the first mechanical support to do so, at the cost of more bleeding, limb problems and kidney injury. The 2025 American guideline calls it "reasonable" in selected patients with careful attention to the complications; the intra-aortic balloon pump, used for decades, is not recommended routinely because it did not save lives. UK availability is patchy and centre-dependent, and the decision is made by the shock team at the receiving centre.
8. Where UK and US guidance differ
- Timing: both use 120 minutes for PCI over fibrinolysis; the US names door-to-balloon under 90 as the target; both say angiography within the admission for NSTEMI and NICE gives the 72-hour number.
- Antiplatelets: both load early and prefer the potent agents with PCI; the US guideline is more specific about shortening to 1–3 months with high bleeding risk and dropping aspirin rather than the second drug.
- Lipids: the US starts ezetimibe alongside the statin from day one as an option and sets 1.8 (and reasonably 1.4) as the trigger for adding; NICE's target is LDL 2.0 or less, non-HDL 2.6 or less, with ezetimibe added at the first review if not met.
- Beta-blockers: NICE 12 months for all; the US and Europe now weaker for a preserved pump, and the 2025 meta-analysis supports them.
- Shock: the US endorses the microaxial pump in selected patients; UK access is by centre.
- Intracoronary imaging to guide stenting of complex lesions is a US recommendation; UK practice uses it selectively.
- Everything else — radial access, complete revascularisation, culprit-only in shock, no routine oxygen, the echo, cardiac rehab — is shared.