Killip class
The Killip class is a bedside clinical classification system developed in 1967 by cardiologists Thomas Killip III and John T. Kimball to assess the severity of heart failure in patients hospitalized with acute myocardial infarction (AMI), stratifying them into four categories based on physical examination findings of pulmonary congestion, cardiogenic shock, or both, with the goal of predicting short-term mortality and guiding management in coronary care units.[1]Classification Criteria
The system relies on simple, non-invasive clinical signs observed upon admission, without requiring laboratory tests or imaging, making it particularly valuable in resource-limited settings.[2]Prognostic Significance
Originally derived from a cohort of 250 AMI patients treated in a university hospital coronary care unit, the Killip class demonstrated a strong correlation with in-hospital mortality, ranging from approximately 6% in Class I to over 80% in Class IV, underscoring the progression from uncomplicated infarction to life-threatening complications.[1] Despite advances in reperfusion therapy and pharmacotherapy, the classification remains a robust, independent predictor of adverse outcomes, including 30-day and long-term mortality, in contemporary populations with ST-segment elevation myocardial infarction (STEMI).[2] For instance, in a 2020 institutional study of 485 STEMI patients, in-hospital mortality escalated dramatically from 9.9% in Class I to 100% in Class IV, validating its utility for early risk stratification even in low-resource environments.[2] Higher classes are associated with older age, greater comorbidity burden (such as diabetes or prior infarction), and larger infarct sizes, further emphasizing the system's role in identifying high-risk subgroups for intensified monitoring and intervention.[3]Background and Development
Historical Context
In the mid-20th century, acute myocardial infarction (AMI) emerged as a leading cause of death in developed countries, particularly in the United States, where coronary heart disease surpassed other conditions to become the primary killer by the 1950s, peaking in incidence and mortality around the mid-1960s.[4] This epidemic was driven by factors such as increasing industrialization, smoking prevalence, and dietary changes, resulting in high in-hospital and pre-hospital fatality rates, often exceeding 30% for AMI cases.[5] At the time, diagnostic capabilities were severely limited, relying heavily on patient history, electrocardiography (introduced in the early 20th century but not universally available until later), and basic chest X-rays, with no routine use of echocardiography (which emerged in the 1970s) or cardiac biomarkers like troponins (developed in the 1980s).[6] Assessment of heart failure complicating AMI prior to 1967 depended almost entirely on bedside physical examination, as advanced imaging and laboratory tests were unavailable or impractical in acute settings. Clinicians evaluated signs such as rales (crackles in the lungs indicating pulmonary congestion), hypotension (low blood pressure signaling cardiogenic shock), elevated jugular venous pressure, and peripheral edema to gauge the severity of left ventricular dysfunction and overall prognosis.[7] These rudimentary methods, while accessible, were subjective and lacked standardization, often leading to delayed recognition of high-risk patients and contributing to poor outcomes in an era when AMI management was primarily supportive, involving bed rest, oxygen, and analgesics.[8] The establishment of coronary care units (CCUs) in the early 1960s marked a pivotal shift in AMI care, with the first units opening in the United States around 1962 to provide continuous monitoring for arrhythmias and other complications that caused sudden deaths outside hospital settings.[9] These specialized wards, pioneered by cardiologists like Desmond Julian and Lawrence E. Meltzer, reduced mortality by enabling rapid interventions such as defibrillation, but they also underscored the need for simple, bedside tools to stratify patient risk based on heart failure status amid limited resources.[10] This evolving landscape of intensive monitoring and recognition of heart failure's role in AMI fatalities directly prompted the development of structured classification systems.Original Study
The Killip classification originated from a seminal 1967 study conducted by Thomas Killip III and John T. Kimball, published in the American Journal of Cardiology under the title "Treatment of Myocardial Infarction in a Coronary Care Unit: A Two-Year Experience with 250 Patients."[11] This work detailed the experiences in one of the early coronary care units (CCUs) established in the mid-1960s, amid evolving management strategies for acute myocardial infarction (AMI) that emphasized continuous monitoring to address arrhythmias and complications.[11] The study employed a prospective observational design, tracking 250 patients admitted to the CCU at New York Hospital-Cornell Medical Center over a two-year period from 1965 to 1967.[11] AMI was confirmed in these patients using electrocardiographic (ECG) changes and serum enzyme elevations, standard diagnostic tools of the era.[11] The cohort primarily consisted of middle-aged males, reflecting the typical demographic profile of AMI cases at the time, with a focus on bedside physical examinations to assess signs of heart failure rather than relying solely on invasive or radiographic methods.[11] Central to the study were initial observations linking clinical manifestations of left ventricular failure—such as pulmonary congestion, cardiogenic shock, and third heart sound—to elevated in-hospital mortality rates among AMI patients.[11] Killip and Kimball noted that mortality varied significantly with the severity of these physical signs, prompting the development of a simple four-class system to stratify patients based on the presence and extent of heart failure or shock upon admission.[11] This classification emerged as a practical tool for prognostic assessment within the CCU setting, highlighting how aggressive monitoring and intervention could mitigate risks in lower-severity cases.[11]Classification System
Overview and Purpose
The Killip class is a four-tier clinical classification system used to evaluate the severity of acute heart failure in patients with acute myocardial infarction (AMI), based exclusively on physical examination findings.[12] Introduced in a seminal 1967 study by Killip and Kimball, it provides a straightforward method for initial assessment without relying on laboratory tests or imaging.[11] The primary purpose of the Killip class is to facilitate rapid risk stratification upon patient presentation, enabling clinicians to estimate short-term mortality risk, such as 30-day outcomes, in a timely manner.[2] This approach supports immediate decision-making in acute care settings by categorizing heart failure severity through readily observable signs, including rales, gallop rhythms, pulmonary edema, and shock, without the need for any equipment.[13] Its design emphasizes accessibility, making it particularly valuable in resource-limited environments where advanced diagnostics may not be immediately available.[14] Originally developed for AMI, the Killip class has since been applied more broadly to both ST-elevation myocardial infarction (STEMI) and non-ST-elevation myocardial infarction (NSTEMI) scenarios, maintaining its utility across these subtypes of acute coronary syndromes.[13]Detailed Criteria
The Killip classification system delineates four classes of heart failure severity in patients with acute myocardial infarction based on physical examination findings observed at the bedside. These classes reflect escalating degrees of left ventricular dysfunction and pulmonary congestion, assessed through auscultation, inspection, and vital signs evaluation. The criteria emphasize observable signs such as lung sounds, cardiac rhythms, venous pressure, and perfusion status, allowing for rapid stratification without advanced imaging or laboratory tests.[1] Class I represents the absence of clinical heart failure, characterized by no rales on lung auscultation, absence of an S3 gallop, no jugular venous distension, and normal vital signs including stable blood pressure and heart rate. Patients in this class exhibit no signs of pulmonary congestion or systemic hypoperfusion.[1] Class II indicates mild to moderate heart failure, with physical findings such as rales or crackles involving ≤50% of the lung fields, presence of an S3 gallop, elevated jugular venous pressure, or mild dyspnea, but without acute respiratory distress or hemodynamic instability. These signs suggest early left ventricular impairment without widespread edema.[1][15] Class III denotes severe heart failure accompanied by acute pulmonary edema, marked by rales in >50% of the lung fields, marked dyspnea at rest, and often pink frothy sputum, indicating significant alveolar flooding and respiratory compromise.[1][15] Class IV signifies cardiogenic shock superimposed on pulmonary congestion, defined by systolic blood pressure <90 mmHg, along with signs of inadequate tissue perfusion such as oliguria, altered mental status, cold extremities, and cyanosis, in the context of heart failure signs from higher classes. This class reflects profound circulatory failure.[1] The following table summarizes the Killip classes, key physical signs, and associated severity:| Class | Key Physical Findings | Severity Level |
|---|---|---|
| I | No rales, no S3 gallop, no jugular venous distension, normal vital signs | No heart failure |
| II | Rales/crackles in ≤50% of lung fields, S3 gallop, elevated jugular venous pressure, mild dyspnea | Mild to moderate heart failure |
| III | Rales in >50% of lung fields, marked dyspnea, pink frothy sputum | Severe heart failure with pulmonary edema |
| IV | Systolic BP <90 mmHg, oliguria, altered mentation, cold extremities, plus pulmonary congestion | Cardiogenic shock |