What are the diagnostic criteria and treatment options for refractory cardiogenic shock?

Determining Refractory Cardiogenic Shock

Refractory cardiogenic shock is defined by persistent tissue hypoperfusion despite adequate doses of two vasoactive medications and treatment of the underlying etiology, with specific hemodynamic criteria including cardiac power output <0.6 W, cardiac index <2.2 L/min/m², and elevated lactate despite maximal medical therapy. 1, 2

Hemodynamic Criteria for Refractory Shock

The diagnosis requires invasive hemodynamic monitoring demonstrating:

• Cardiac Power Output (CPO) <0.6 W - This is the most critical threshold for identifying refractory shock 1
• Cardiac Index (CI) <2.2 L/min/m² despite vasopressor and inotropic support 1, 3
• **Systolic Blood Pressure <80 mmHg** despite maximal treatment or requiring high-dose vasopressors to maintain SBP >90 mmHg 1
• Elevated filling pressures: Pulmonary Capillary Wedge Pressure (PCWP) >15 mmHg in LV-dominant shock 1, 3
• Right Atrial (RA) pressure patterns help differentiate phenotypes: RA >15 mmHg suggests RV involvement, while RA <15 mmHg suggests LV-dominant shock 1

Clinical Markers of Persistent Hypoperfusion

Beyond hemodynamics, refractory shock demonstrates ongoing end-organ dysfunction:

• Elevated lactate levels (>2 mmol/L) that persist or worsen despite therapy 3, 4
• Decreased urine output (<0.5 mL/kg/h) indicating renal hypoperfusion 3
• Altered mental status from cerebral hypoperfusion 3
• Cool extremities with livedo reticularis from peripheral vasoconstriction 5
• Progressive multiorgan failure including hepatic dysfunction (bilirubin ≥1.3 mg/dL) 3

Phenotype-Specific Criteria

The determination of refractory shock must account for the specific ventricular failure pattern 1:

LV-Dominant Refractory Shock

• CPO <0.6 W with PCWP >15 mmHg and RA <15 mmHg 1
• Pulmonary Arterial Pulsatility Index (PAPi) >1.0 1

RV-Dominant Refractory Shock

• CPO <0.6 W with RA >15 mmHg and PCWP <15 mmHg 1
• PAPi <1.0 indicating RV failure 1

Biventricular Refractory Shock

• CPO <0.6 W with both RA >15 mmHg and PCWP >15 mmHg 1
• PAPi >1.0 but with elevated bilateral filling pressures 1

Temporal Criteria

The timing element is critical for defining refractory status:

• Precardiotomy setting: Progressive deterioration requiring increasing doses of intravenous inotropes and/or IABP to maintain hemodynamic targets, with failure to wean from inotropes 1
• Failure to wean from cardiopulmonary bypass: Prolonged weaning time >1 hour with deteriorating hemodynamics or cardiac arrest 1
• Postcardiotomy setting: Persistent shock despite maximal medical therapy including inotropes and IABP 1

Contraindications to Escalation

Before labeling shock as truly refractory, exclude absolute contraindications to mechanical circulatory support 1:

• Anoxic brain injury 1
• Irreversible end-organ failure 1
• Prohibitive vascular access 1
• Do Not Resuscitate (DNR) status 1

SCAI Staging Context

Refractory shock typically corresponds to SCAI Stage D (deteriorating/doom) or Stage E (extremis) 3, 5:

• Stage D: Worsening despite initial interventions, requiring multiple/high-dose pressors/inotropes, or mechanical support 3
• Stage E: Cardiac arrest requiring ongoing CPR and/or ECMO 3

Practical Algorithm for Determination

1. Confirm adequate treatment of underlying cause (e.g., revascularization for AMI) 2
2. Document failure of two vasoactive medications at adequate doses 2
3. Obtain invasive hemodynamics via pulmonary artery catheter showing CPO <0.6 W and CI <2.2 L/min/m² 1, 4
4. Verify persistent hypoperfusion markers (lactate, urine output, mental status) 3, 4
5. Identify shock phenotype (LV, RV, or biventricular) using RA pressure, PCWP, and PAPi 1
6. Assess for contraindications to mechanical circulatory support 1
7. Escalate to MCS consideration if no contraindications exist 1, 6

Common Pitfalls

• Delaying invasive monitoring: Early pulmonary artery catheter placement is essential for accurate phenotyping and should not be delayed 4, 5
• Inadequate treatment of underlying cause: Shock may appear refractory when the primary lesion (e.g., ongoing ischemia, mechanical complication) remains untreated 2
• Confusing late septic shock with cardiogenic shock: Septic shock can develop myocardial depression but maintains decreased SVR as the primary pattern 3
• Prolonged attempts at medical optimization: Application of IABP within 30 minutes and MCS within 1 hour from first weaning attempts is suggested to prevent complications 1