SCAI Classification of Heart Failure
The SCAI (Society for Cardiovascular Angiography and Interventions) classification is NOT used for general heart failure—it is specifically designed for cardiogenic shock severity staging, not routine heart failure classification. 1
Standard Heart Failure Classification Systems
Heart failure is classified using two complementary systems that serve different purposes:
ACC/AHA Staging System (Disease Progression)
This staging system reflects the progressive, largely irreversible nature of heart failure and determines treatment strategies 2, 3:
Stage A (At Risk for HF): Patients with risk factors (hypertension, diabetes, coronary disease, obesity, cardiotoxic exposure, genetic variants) but no structural heart disease, symptoms, or elevated biomarkers 2, 3
Stage B (Pre-HF): Structural heart disease present (reduced EF, ventricular hypertrophy, chamber enlargement, wall motion abnormalities, valvular disease, elevated filling pressures) but no current or previous symptoms; also includes patients with elevated BNP/NT-proBNP or persistently elevated troponin without competing diagnoses 2, 3
Stage C (Symptomatic HF): Current or previous heart failure symptoms with underlying structural heart disease; patients remain Stage C even if symptoms resolve with treatment 2, 4
Stage D (Advanced HF): Marked symptoms interfering with daily life and recurrent hospitalizations despite optimal guideline-directed medical therapy; requires consideration for mechanical circulatory support, continuous inotropes, transplantation, or palliative care 2, 3
Critical point: Patients advance through stages but cannot regress—a Stage C patient who becomes asymptomatic remains Stage C and requires continued Stage C therapies 4, 5
NYHA Functional Classification (Symptom Severity)
This subjective assessment by clinicians measures current functional capacity and changes frequently with treatment 2, 4:
- Class I: No limitation; ordinary activity does not cause symptoms 3, 4
- Class II: Slight limitation; comfortable at rest but ordinary activity causes symptoms 3, 4
- Class III: Marked limitation; less than ordinary activity causes symptoms 3, 4
- Class IV: Symptoms at rest; unable to perform any physical activity without symptoms 3, 4
Important caveat: NYHA classification has significant limitations—it shows substantial overlap in objective measures (NT-proBNP, 6-minute walk distance, ejection fraction) between classes, with poor discrimination between Class I and II patients 6, 7. Patient-rated and physician-rated NYHA classes differ in 50% of cases, and physician ratings correlate better with mortality 8.
Classification by Left Ventricular Ejection Fraction
LVEF classification is critical because it determines treatment eligibility 2, 4:
- HFrEF (Reduced EF): LVEF ≤40% 2, 4
- HFmrEF (Mildly Reduced EF): LVEF 41-49% 4
- HFpEF (Preserved EF): LVEF ≥50% 4
When SCAI Classification IS Used
The SCAI staging system applies specifically to cardiogenic shock (including heart failure-related cardiogenic shock), not routine heart failure 1:
- SCAI Stage C: Beginning cardiogenic shock
- SCAI Stage D: Deteriorating shock
- SCAI Stage E: Extremis
In heart failure-related cardiogenic shock, patients with de novo presentation escalate more rapidly to maximum SCAI stage severity and have higher in-hospital mortality (63% with cardiac arrest vs 21% without) compared to acute-on-chronic presentations 1.
Practical Application Algorithm
For routine heart failure classification:
- Determine ACC/AHA stage based on risk factors, structural disease, and symptom history 2, 3
- Measure LVEF to classify as HFrEF, HFmrEF, or HFpEF 2, 4
- Assess current NYHA class for symptomatic patients (Stage C or D) 2, 4
- Use ACC/AHA stage to guide treatment strategy; use NYHA class to determine device/intervention eligibility 4
Reserve SCAI classification exclusively for cardiogenic shock scenarios 1