Phenotypes of cardiogenic shock after out-of-hospital cardiac arrest: the SCAI-V classification.
Roy R, Abd Razak M, et al. • EuroIntervention : journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology • 2026
The SCAI-V classification, grouping patients by SCAI shock grade and lactate level into four phenotypes, enhances phenotypic profiling of cardiogenic shock after resuscitated out-of-hospital cardiac arrest and displayed superior model fit, discrimination, and calibration compared to existing SCAI classifications.
Key Findings
Results
The majority of OHCA patients with cardiogenic shock had discordant haemodynamic parameters and lactate levels when the 2022 SCAI classification was applied.
In the derivation cohort, 60% of patients had discordant haemodynamic parameters and lactate levels under SCAI-2022.
This discordance highlights a fundamental challenge in applying non-arrested CS classifications to post-OHCA patients.
The derivation cohort included 627 patients from London, UK and Gdańsk, Poland.
Median age was 63 years (IQR 53-74) and 76% were male.
Methods
The SCAI-V classification stratifies post-OHCA patients into four phenotypes based on SCAI shock grade and lactate level.
The four phenotypes are: non-shock, systemic ischaemia, haemodynamic shock, and haemometabolic shock.
Classification uses a 2x2 factorial framework combining SCAI grade (shock absent or present) and lactate level (< 5 mmol/L or ≥ 5 mmol/L).
The framework was designed to capture the distinct pathophysiology of end-organ hypoperfusion in post-arrest cardiogenic shock.
External validation was performed in the TTM-2 trial cohort (n=1,781).
Results
The SCAI-V classification was significantly associated with both all-cause and non-neurological mortality.
Association with all-cause and non-neurological mortality was statistically significant (p<0.001) in both cohorts.
The primary outcome was mortality; the secondary outcome was non-neurological mortality at hospital discharge (derivation cohort) or at 180 days (TTM-2 cohort).
The classification performed consistently across both the derivation and external validation cohorts.
Results
Survival rates differed substantially across the four SCAI-V phenotypes in both the derivation and validation cohorts.
Survival was highest in the non-shock group: 78% in the derivation cohort and 68% in the TTM-2 validation cohort.
Haemodynamic shock group survival: 60% (derivation) and 51% (validation).
Systemic ischaemia group survival: 50% (derivation) and 42% (validation).
Survival was lowest in the haemometabolic shock group: 20% (derivation) and 27% (validation).
The ordering of survival across phenotypes was consistent between derivation and validation cohorts.
Results
The SCAI-V classification demonstrated superior model fit, discrimination, and calibration compared to both the 2019 and 2022 SCAI classifications in the derivation cohort.
SCAI-V outperformed SCAI-2019 and SCAI-2022 on model fit, discrimination, and calibration metrics in the derivation cohort.
In the TTM-2 external validation cohort, SCAI-V showed consistent model fit advantages and discrimination comparable to SCAI-2022.
These comparisons were made for both all-cause and non-neurological mortality outcomes.
Results
The systemic ischaemia phenotype — characterized by elevated lactate without overt haemodynamic shock — had worse survival than haemodynamic shock alone.
Systemic ischaemia survival was 50% (derivation) and 42% (validation), both lower than haemodynamic shock (60% and 51%).
This phenotype represents patients with shock absent by SCAI grade but lactate ≥ 5 mmol/L.
This finding underscores that lactate elevation independent of haemodynamic criteria carries significant prognostic weight in post-OHCA patients.
What This Means
When someone survives an out-of-hospital cardiac arrest, they often develop a serious condition called cardiogenic shock, where the heart cannot pump enough blood to meet the body's needs. Classifying how severe this shock is has been difficult because standard tools — developed for patients who did not have a cardiac arrest — often give conflicting results in this population. This study found that 60% of post-arrest patients had mismatched readings between blood pressure-related markers and lactate (a marker of insufficient oxygen delivery to tissues), making standard classifications unreliable.
Researchers developed a new system called SCAI-V, which groups post-arrest patients into four categories based on two factors: whether standard shock criteria are met and whether lactate levels are high (≥5 mmol/L). The four groups — non-shock, systemic ischaemia, haemodynamic shock, and haemometabolic shock — had clearly different survival rates. Patients with both shock and high lactate (haemometabolic) had the worst outcomes (around 20-27% survival), while those with neither had the best (68-78% survival). Importantly, patients with high lactate but no apparent haemodynamic shock (systemic ischaemia) had worse survival than those with haemodynamic shock but normal lactate, suggesting lactate is a critical and independent warning sign.
This research suggests that combining shock status with lactate levels gives doctors a more accurate picture of how critically ill a post-arrest patient is than existing tools. This improved classification could help guide decisions about which patients might benefit from aggressive, early treatments such as mechanical circulatory support or urgent heart procedures. The findings were confirmed in a large external dataset of nearly 1,800 patients, supporting the broader applicability of the SCAI-V framework.
Roy R, Abd Razak M, Mohanan S, Simpson R, Parczewska A, McGarvey M, et al.. (2026). Phenotypes of cardiogenic shock after out-of-hospital cardiac arrest: the SCAI-V classification.. EuroIntervention : journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology. https://doi.org/10.4244/EIJ-D-26-00092