Cardiogenic Shock
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Direct answer
Cardiogenic shock is inadequate tissue perfusion caused by primary cardiac pump failure, defined by systolic pressure below 90 mmHg or vasopressor need together with a cardiac index below 2.2 litres per minute per square metre and raised filling pressures. Acute myocardial infarction is the commonest cause, and survival depends on rapid revascularisation, perfusion-guided vasopressor and inotrope support, and an early decision about mechanical circulatory support.
What you must remember
- Haemodynamics: low cardiac output with high systemic vascular resistance and raised pulmonary capillary wedge pressure, the cold and wet profile of shock.
- SCAI staging: stage A is at risk; stage B is beginning, with hypotension but no hypoperfusion; stage C is classic shock requiring intervention beyond fluids; stage D is deteriorating despite initial therapy; stage E is extremis with arrest.
- First-line vasopressor: norepinephrine to maintain mean arterial pressure around 65 mmHg; vasopressin is added for refractory hypotension, and dopamine is an alternative.
- Inotropes: dobutamine suits low output with adequate pressure; adrenaline is used when shock is refractory; milrinone adds vasodilation and hypotension risk.
- Avoid: vasodilators in hypotension, and fluid boluses in pulmonary oedema, with right ventricular infarction as the principal exception because that ventricle is preload-dependent.
- Mechanical support: intra-aortic balloon pump, microaxial flow pumps such as Impella, and veno-arterial ECMO for refractory shock; the IABP-SHOCK II trial showed no survival benefit from routine balloon counterpulsation.
- Revascularisation: emergency PCI for the infarct-related artery; the SHOCK trial showed early revascularisation improved survival, and CULPRIT-SHOCK found culprit-only PCI superior to immediate multivessel PCI.
A large anterior infarct with shock
A 59-year-old diabetic man presents four hours after an anterior STEMI with blood pressure 78 over 50 mmHg, cold clammy skin, urine output of 15 mL/h and lactate of 5 mmol/L, with pulmonary oedema on examination. This is cardiogenic shock with hypoperfusion, SCAI stage C at least.
- Measure output: An arterial line and echocardiography come first, to measure output and exclude mechanical complications such as ventricular septal rupture or papillary muscle rupture, which would change the surgical plan.
- Restore pressure: Norepinephrine is started to restore pressure, and dobutamine is added if cardiac output remains low despite adequate filling.
- Give fluid with care: Fluids are given cautiously, since the lungs are already congested, and vasodilators are withheld.
- Reperfuse the culprit: Emergency angiography follows, and the culprit lesion is treated first, with staged revascularisation of the other vessels deferred in a patient this unstable.
- Escalate for stage D: If the patient deteriorates into stage D, with worsening lactate and rising vasopressor needs, a percutaneous microaxial pump or venoarterial ECMO is considered at a centre able to offer it.
- Keep the principle: Restoring flow to the infarct-related artery is the only definitive treatment, and everything else buys time.
Where the exam tries to catch you
Examiners set the same fluid, vasopressor and balloon-pump traps in every shock vignette.
- Trap: giving a fluid bolus to a patient with pulmonary oedema Correct: this is harmful, whereas in right ventricular infarction the same bolus is correct, because the right ventricle fails from lack of preload.
- Trap: reaching for dopamine by habit Correct: norepinephrine is the first-line agent in cardiogenic shock, with less arrhythmic risk.
- Trap: using the intra-aortic balloon pump as routine therapy Correct: the IABP-SHOCK II trial showed no mortality benefit, so it is no longer recommended as routine treatment.
- Trap: waiting for mechanical support before reperfusion in a centre where it is scarce Correct: in Indian centres the priority is the same as anywhere, to reperfuse the culprit artery quickly and transfer early rather than wait for further deterioration.
Frequently asked questions
What is the most common cause of cardiogenic shock?
Acute myocardial infarction is the most common cause of cardiogenic shock, usually from left ventricular pump failure after a large infarct. Mechanical complications of infarction and advanced heart failure are other important causes.
Which vasopressor is first-line in cardiogenic shock?
Norepinephrine is the first-line vasopressor in cardiogenic shock, titrated to maintain mean arterial pressure around 65 mmHg. Vasopressin is added for refractory hypotension, and dopamine is an alternative where norepinephrine is unavailable.
What does SCAI stage C signify in cardiogenic shock?
SCAI stage C denotes classic cardiogenic shock, with hypoperfusion that requires intervention beyond fluids, such as a vasopressor or inotrope. It is the clinical point at which the patient needs a critical-care pathway and an urgent decision about reperfusion.
Why is the intra-aortic balloon pump no longer used routinely in cardiogenic shock?
The IABP-SHOCK II trial showed no survival benefit from routine intra-aortic balloon counterpulsation in cardiogenic shock complicating myocardial infarction. It is therefore reserved for selected patients rather than used as a standard part of treatment.