What is Killip classification?

Killip Classification: A Prognostic Tool for Acute Myocardial Infarction

The Killip classification is a clinical system that stratifies the severity of heart failure in patients with acute myocardial infarction, providing valuable prognostic information about mortality risk and guiding treatment decisions. 1

Definition and Classes

The Killip classification consists of four classes based on clinical signs of cardiac decompensation:

• Class I: No heart failure; no clinical signs of cardiac decompensation
• Class II: Heart failure with rales in lower half of lung fields, S3 gallop, and pulmonary venous hypertension
• Class III: Severe heart failure with frank pulmonary edema and rales throughout the lung fields
• Class IV: Cardiogenic shock with hypotension (SBP <90 mmHg) and evidence of peripheral vasoconstriction such as oliguria, cyanosis, and sweating 1

Clinical Significance and Mortality Risk

Killip classification strongly correlates with mortality outcomes:

• Class I: 2-8% in-hospital mortality
• Class II: 8-15% in-hospital mortality
• Class III: 30-40% in-hospital mortality
• Class IV: 60-80% in-hospital mortality 2, 3

Recent data shows improved survival in higher Killip classes with modern interventions, particularly primary angioplasty for Class IV patients, though mortality remains significantly elevated 4.

Applications in Clinical Practice

The Killip classification is valuable for:

1. Initial risk stratification at presentation for patients with acute myocardial infarction
2. Treatment decision-making - higher classes may warrant more aggressive interventions
3. Prognostic assessment for both short and long-term outcomes
4. Resource allocation in cardiac care units 1

Comparison with Other Classifications

While the Killip classification focuses on clinical signs, the Forrester classification incorporates hemodynamic parameters:

• Forrester uses cardiac index (CI) and pulmonary capillary wedge pressure (PCWP) measurements
• Forrester provides complementary information but requires invasive monitoring
• Both classifications were developed for acute MI but have different applications based on available resources 1

Prognostic Value Beyond ST-Elevation MI

The Killip classification maintains strong prognostic value in:

• Non-ST elevation myocardial infarction (NSTEMI) - remains a powerful independent predictor of mortality 3
• Myocardial infarction with non-obstructive coronary arteries (MINOCA) - associated with three-fold increased mortality and four-fold risk of heart failure hospitalization 5
• Long-term outcomes - maintains predictive value for mortality at 5-year follow-up 6

Key Considerations in Application

• The classification should be determined at initial presentation
• It provides immediate risk stratification without requiring laboratory tests
• Five factors (age, Killip class, heart rate, systolic blood pressure, and ST depression) provide >70% of prognostic information for mortality 3
• Higher Killip classes should prompt consideration of early revascularization strategies and more intensive monitoring 1

Common Pitfalls

• Misclassification due to non-cardiac causes of pulmonary findings (e.g., COPD, pneumonia)
• Delayed recognition of cardiogenic shock in patients with initially stable presentations
• Underutilization of medical therapy in higher Killip classes despite its importance alongside interventional approaches 4
• Failure to reassess Killip class during hospitalization, as changes may indicate clinical deterioration requiring prompt intervention

The Killip classification remains a simple yet powerful tool for risk stratification in acute myocardial infarction, with enduring relevance in the modern era of interventional cardiology.