Reviewed and updated by Valerie Dziados, MSN, CRNP, ANP-BC, AGACNP-BC: February 5, 2024

The advances in the treatment of acute myocardial infarction (AMI) over the past five decades, including immediate percutaneous coronary intervention, have been proven to dramatically improve outcomes. Patients suffering from AMI may develop cardiogenic shock (CS) before or after coronary reperfusion. CS in association with AMI is associated with a 40-50% overall 30-day mortality rate that, despite advances, has not changed over the past 20 years. In May 2019, the Society for Cardiovascular Angiography and Interventions (SCAI) released a clinical expert consensus statement on the classification of cardiogenic shock.

CS is defined by the National Cardiovascular Data Registry as systolic blood pressure (SBP) ≤ 90 mm Hg and cardiac index < 2.2 L/min/m² and/or the requirement for parental inotropic or vasopressor agents to maintain systolic blood pressure and cardiac index above these levels due to failure of myocardial function (Baran et. al, 2019). In other words, CS is the reduction in systemic blood pressure with tissue hypoperfusion due to low cardiac output/index in the absence of hypovolemia. Hypoperfusion is evidenced by clinical signs such as cool, clammy extremities, poor urine output, and mental confusion.

The purpose of the classification schema is to assist in clear communication among clinicians and researchers regarding the patient’s current clinical status, recognizing that CS encompasses a spectrum, including those at high risk of developing shock from myocardial dysfunction to those who develop hemodynamic collapse and cardiac arrest. The writing committee focused on the following guiding principles when developing the classification system:

• Easily and rapidly applied at the bedside for initial assessment and reassessments
• Applicable to past and future research
• Usability across all clinical settings (i.e. emergency departments, intensive care units, catheterization laboratories)
• Actionable and would lead to behavior changes to improve outcomes
• Possess prognostic discriminatory potential to reflect differences of mortality and morbidity as determined by the specific type of shock

The CS classification schema includes five stages of shock labeled A through E. The authors categorized patients in three domains, including laboratory findings, physical exams findings, and hemodynamics.  When cardiac arrest has occurred the modifier (_A) is added to stage classification (i.e. stage C_A). Here is a brief description of each stage, including the domains of patient characteristics that you can expect to find within each stage.

Stage A or “At Risk”:

• Patient identified at risk of developing, but is not yet displaying signs or symptoms of CS
• Diagnoses such as non-ST elevated myocardial infarction, ST elevated myocardial infarction (especially in the anterior wall distribution or large infarcts), and decompensated heart failure (both systolic and diastolic)
• Physical exam, laboratory, and hemodynamics are within normal limits

Stage B or “Beginning CS”:

• Also referred to as pre-shock or compensated shock
• Patient with relative hypotension (SBP < 90 mm Hg or mean arterial pressure [MAP] < 60 mm Hg or drop in MAP of > 30 mm Hg from baseline) or tachycardia (pulse ≥ 100 bpm) without hypoperfusion
• Physical exam findings may include elevated jugular vein distension (JVP), rales in lung fields, warm skin with strong distal pulses, normal mentation
• Laboratory findings may include normal lactate, minimal renal function impairment, and elevated brain natriuretic peptide (BNP)
• Hemodynamic findings include relative hypotension, tachycardia, normal cardiac index (≥ 2.2 L/min/m²) and pulmonary arterial (PA) oxygen saturation ≥ 65%

Stage C or “Classic CS”:

• Patient with hypotension and signs of hypoperfusion that require various interventions beyone volume resuscitation to restore perfusion (i.e., inotropes, pressor, mechanical support, or extracorporeal membrane oxygenation [ECMO])
• Physical exam findings may include distressed/panicked appearance, ashen/mottled/ dusky skin color, extensive rales in lung fields, cold/clammy skin temperature, altered mentation, decreased urine output (< 30 mL/h)
• Laboratory findings may include lactate ≥ 2 mmol/L, decreased renal function (creatinine doubling or > 50% drop in glomerular filtration rate (GFR), increased liver function tests (LFTs), elevated BNP
• Hemodynamic findings may include SBP <90 mm Hg or MAP < 60 mm Hg or drop in MAP > 30 mm Hg from baseline and devices/medications utilized to maintain adequate SBP, cardiac index < 2.2 L/min/m², pulmonary artery capillary wedge pressure (PCWP) > 15 mm Hg, cardiac power output ≤ 0.6 W/m²

Stage D or “Deteriorating or Doom CS”:

• Patient who fails to stabilize after at least 30 minutes of initial treatment methods
• Treatment efforts are escalated, including the addition of multiple pressors; mechanical circulatory support may be initiated
• Physical exam, laboratory, and hemodynamic findings are similar to those found in stage C, but deteriorating

Stage E or “Extremis”:

• Patient with circulatory collapse, possibly with cardiac arrest with ongoing cardiopulmonary resuscitation (CPR) and/or ECMO
• Patient requires multiple interventions (mechanical ventilation, defibrillation) and assistance from multiple clinicians
• Physical exam findings may include near pulselessness, severe hypotension, lethal cardiac disturbances (pulseless electrical activity [PEA], ventricular tachycardia, ventricular fibrillation)
• Laboratory findings may include lactate ≥ 5 mmol/L and pH ≤ 7.2
• Hemodynamic findings include no SBP without resuscitation, PEA or ventricular arrythmias, hypotension despite maximum medical interventions

PA catheters play the important role of allowing clinicians the ability to obtain hemodynamic data to establish diagnosis, monitor response to therapy, and to help distinguish CS from other forms of shock.   While the classic “cold, wet” CS is associated with low CI, high systemic vascular resistance (SVR) and PCWP, there are four different hemodynamic presentations of CS. PA catheters allow for real-time hemodynamic indices that are imperative to caring for these critically ill patients. There is also the possibility of a patient presenting with or developing mixed shock as CS develops. Fever and leukocytosis may be present and represent systemic inflammation rather than absolute infection. Vasodilation (low SVR) that is seen with inflammation and/or infection can further impair coronary and systemic perfusion. Some data reports the use of PA catheters is associated with lower mortality in CS patients, but the widespread use of this invasive monitoring remains controversial.

The classification schema is simple and highly adaptable in clinical settings. It offers clinicians a common language when diagnosing and treating patients at risk for or those that have developed CS. As the patient's clinical condition evolves, the patient can fluidly move throughout the stages and allow for clear documentation of the patient’s status and will assist in data collection in research trials. This new and widely endorsed tool will hopefully improve outcomes, guide management, and lead future research.

References:
Baran, D.A., Grines, C.L, Bailey, S., Burkhoff, D., Hall, S., Henry, T., Hollenberg, S., Kapur, N., O’Neill, W., Oranto, J., Stelling, K., Thiele, H., van Diepen, S., Naidu, Srihari. (2019). SCAI clinical expert consensus statement on the classification of cardiogenic shock. Catheterization & Cardiovascular Interventions, 94(1), 29-37. https://doi.org/10.1002/ccd.28329

Naidu, S., Baran, D., Jentzer, J., Hollenberg, S., van Diepen, S., Basir, M., Grines, C., Diercks, D., Hall, S., Kapur, N., Kent, W., Rao, S., Samsky, M., Thiel, H., Truesdell, A., Henry, T. (2022). SCAI SHOCK Stage Classification Expert Consensus Update: A Review and Incorporation of Validation Studies: This statement was endorsed by the American College of Cardiology (ACC), American College of Emergency Physicians (ACEP), American Heart Association (AHA), European Society of Cardiology (ESC) Association for Acute Cardiovascular Care (ACVC), International Society for Heart and Lung Transplantation (ISHLT), Society of Critical Care Medicine (SCCM), and Society of Thoracic Surgeons (STS) in December 2021.. Journal of American College of Cardiology, 79 (9) 933–946. https://doi.org/10.1016/j.jacc.2022.01.018