The Killip classification is a system used in individuals with an acute myocardial infarction (heart attack), in order to risk stratify them. Individuals with a low Killip class are less likely to die within the first 30 days after their myocardial infarction than individuals with a high Killip class.^[1]

The study was a case series with unblinded, unobjective outcomes, not adjusted for confounding factors, nor validated in an independent set of patients. The setting was the coronary care unit of a university hospital in the USA.

250 patients were included in the study (aged 28 to 94; mean 64, 72% male) with a myocardial infarction. Patients with a cardiac arrest prior to admission were excluded.

Patients were ranked by Killip class in the following way:

• Killip class I includes individuals with no clinical signs of heart failure.
• Killip class II includes individuals with rales or crackles in the lungs, an S₃ gallop, and elevated jugular venous pressure.
• Killip class III describes individuals with frank acute pulmonary edema.
• Killip class IV describes individuals in cardiogenic shock or hypotension (measured as systolic blood pressure lower than 90 mmHg), and evidence of peripheral vasoconstriction (oliguria, cyanosis or sweating).

Within a 95% confidence interval the patient outcome was as follows:

• Killip class I: 81/250 patients; 32% (27 to 38%). Mortality rate was found to be at 6%.
• Killip class II: 96/250 patients; 38% (32 to 44%). Mortality rate was found to be at 17%.
• Killip class III: 26/250 patients; 10% (6.6 to 14%). Mortality rate was found to be at 38%.
• Killip class IV: 47/250 patients; 19% (14 to 24%). Mortality rate was found to be at 81%.

The Killip-Kimball classification has played a fundamental role in classic cardiology, having been used as a stratifying criteria for many other studies. Worsening Killip class has been found to be independently associated with increasing mortality in several studies.

Killip class 1 and no evidence of hypotension or bradycardia, in patients presenting with acute coronary syndrome, should be considered for immediate IV beta blocker therapy.

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