Group B

Blood Supply–Demand Mismatch (Type 2 MI)

A heart injury happens when the heart muscle needs more oxygen than it receives — not because an artery is blocked, but because something else has tilted the balance (for example severe anaemia, very fast heart rhythm, low blood pressure or infection).

1) What does “supply–demand mismatch” mean?

Think of the heart like an engine that needs fuel (oxygen). In Group B MINOCA, oxygen supply is too low, the heart’s demand is too high, or both — leading to muscle injury. The arteries can still be non-obstructed (less than 50% narrowed on an angiogram, the x-ray dye test of the heart arteries). Typical triggers include:

  • Severe anaemia (low haemoglobin) — less oxygen carried in the blood.
  • Tachyarrhythmia (very fast heartbeat, e.g., atrial fibrillation) — the heart uses more oxygen and fills less efficiently.
  • Low blood pressure or shock (bleeding, dehydration, sepsis) — reduced flow to the heart.
  • Very high blood pressure — the heart works harder than usual.
  • Low oxygen states (lung disease, sleep apnoea, severe infection).
Deep-dive

Coronary Microvascular Dysfunction & Spasm

Sometimes the problem is in the small heart vessels that can’t be seen on a standard angiogram. These tiny vessels can behave abnormally — either too narrow at rest, too slow to widen when you need more blood, or prone to spasm (sudden tightening). This can cause chest pain and the same blood test changes seen in a heart attack, even when the main arteries look clear.

How is it diagnosed?

Coronary function testing (invasive)

  • Vasoreactivity testing with acetylcholine (ACh): looks for epicardial (big-artery) or microvascular spasm. A positive test reproduces symptoms/ECG changes with visible artery narrowing or microvascular signs.
  • Flow measures such as CFR (coronary flow reserve) and IMR (index of microvascular resistance): tell us if the small vessels are not delivering enough flow.

These tests are done in expert centres during/after an angiogram and help tailor treatment.

Non-invasive options

  • Stress perfusion CMR (cardiac MRI) or PET: shows areas getting less blood during stress despite open large arteries.
  • Stress echo or CT-based methods: used in some centres to look for microvascular problems.

Your team chooses the least invasive test that answers the key question.

Treatment options (plain-English)

If spasm is the problem

  • Calcium-channel blockers (e.g., diltiazem, amlodipine) relax the arteries.
  • Nitrates (tablets or sprays) relax arteries and relieve pain.
  • Avoid triggers: cold exposure, tobacco, caffeine/amphetamines; review medicines that may worsen spasm.
  • Stress, sleep and anxiety support can reduce flares.

If flow is limited in small vessels

  • Beta-blockers (if no spasm concern) lower demand and steady the rate.
  • ACE inhibitor/ARB and statin support vessel health.
  • Ranolazine can reduce chest pain from microvascular angina.
  • Cardiac rehabilitation and paced return to exercise improve day-to-day flow and confidence.

Plans are personalised — many people need a combination, reviewed over time.

2) Tests you might have (beyond the small vessels)

Blood tests

  • Haemoglobin for anaemia; kidney and thyroid function; infection markers.
  • Troponin — a heart-injury signal (rise & fall pattern helps confirm an acute event).

ECG & rhythm monitoring

  • 12-lead ECG to look for fast/irregular rhythm or strain.
  • Holter/patch monitoring if palpitations or spells are suspected.

Heart scans

  • Echocardiogram (ultrasound) — checks pump function and any wall-motion changes.
  • Cardiac MRI (CMR) — confirms the pattern of injury and helps rule out inflammation (myocarditis) or Takotsubo.

When artery tests are needed

If hidden artery disease is possible, your team may use an angiogram or a CT coronary angiogram (CTCA). Some centres assess small-vessel function (CFR/IMR — measures of how well the small vessels deliver blood), especially if symptoms persist.

Not everyone needs every test — your team will tailor this to your situation.

3) Treatment — fixing the balance

Treat the trigger

  • Anaemia — find the cause (e.g., bleeding or iron deficiency) and correct it (iron; transfusion if appropriate).
  • Fast rhythm — slow/reset the rhythm (medicines, cardioversion) and prevent recurrence.
  • Low blood pressure/shock — fluids, medicines, and treat the underlying cause (e.g., antibiotics for sepsis).
  • Very high blood pressure — careful blood-pressure control to reduce the heart’s workload.
  • Low oxygen — treat lung problems; assess for sleep apnoea; optimise inhalers or CPAP where relevant.

Medicines after the event

  • Secondary prevention is personalised. Your team may use:
    • Statin (cholesterol-lowering) for artery health and risk reduction.
    • ACE inhibitor/ARB to support heart function and blood pressure.
    • Beta-blocker if helpful for rate control, BP or after significant injury.
    • Antiplatelet/anticoagulant only with a clear reason (e.g., atrial fibrillation, suspected plaque, or a heart-chamber clot).

Rehabilitation & lifestyle

  • Cardiac rehabilitation: safe exercise plan, education, and confidence building.
  • Stop smoking; optimise blood pressure, glucose and cholesterol.
  • Sleep, stress and mental-health support — all reduce future risk.

4) What’s the outlook?

Many people do well once the trigger is treated and the oxygen balance is restored. If small-vessel problems (microvascular dysfunction or spasm) coexist, symptoms can persist — but these often improve with targeted medicines, rehabilitation and follow-up.

5) Quick FAQs

  • Is this a “proper” heart attack? It’s a real heart injury, but the cause is an oxygen imbalance rather than a blocked artery. It still deserves careful care and follow-up.
  • Will I need a stent? Usually not, unless tests show a culprit narrowing that truly needs one.
  • Can it happen again? It can if the trigger returns (e.g., anaemia or fast rhythm). Treating the cause and regular checks reduce the risk.

6) What we still don’t know (research)

  • Who benefits most from which medicines when arteries aren’t blocked.
  • Best ways to test and treat small-vessel dysfunction alongside supply–demand problems.
  • Clearer, standardised pathways for follow-up and rehab across different triggers.

Research & support

Explore studies and patient networks via our research hub, and connect with others in our community forum.