Cardiogenic shock (CS) is being recognized more often in critically ill patients. This increased prevalence is likely due to a better understanding of CS and the benefit of improving cardiac output (CO) to ensure adequate oxygen delivery (DO2).
CS is often, but not always, caused by a cardiac dysfunction. The heart is not able to provide adequate DO2 to the tissues. Hypoperfusion ensues. The body attempts to compensate for the poor perfusion by increasing heart rate, vasoconstriction, and shunting blood flow to vital organs. These compensatory mechanisms worsen perfusion by increasing myocardial ischemia which further worsens cardiac dysfunction. This is known as the downward spiral of CS (Ann Intern Med. 1999 Jul 6;131[1]).
Dr. John P. Gaillard
There is a number of different etiologies for CS. Historically, acute myocardial infarctions (AMI) was the most common cause. In the last 20 years, AMI-induced CS has become less prevalent due to more aggressive reperfusion strategies. CS due to etiologies such as cardiomyopathy, myocarditis, right ventricle failure, and valvular pathologies have become more common. While the overarching goal is to restore DO2 to the tissue, the optimal treatment may differ based on the etiology of the CS. The Society for Cardiovascular Angiography and Intervention (SCAI) published CS classification stages in 2019 and then updated the stages 2022 (J Am Coll Cardiol. 2022 Mar 8;79[9]:933-46). In addition to the stages, there is now a three-axis model to address risk stratification. These classifications are a practically means of identifying and treating patients presenting with or concern for acute CS.
Stage A (At Risk) patients are not experiencing CS, but they are the at risk population. The patient’s hemodynamics, physical exam, and markers of hypoperfusion are normal. Stage A includes patients who have had a recent AMI or have heart failure.
Stage B (Beginning) patients have evidence of hemodynamic instability but are able to maintain tissue perfusion. These patients will have true or relative hypotension or tachycardia (in an attempt to maintain CO). Distal perfusion is adequate, but signs of ensuing decompensation (eg, elevated jugular venous pressure [JVP]) are present. Lactate is <2.0 mmol/L. Clinicians must be vigilant and treat these patients aggressively, so they do not decompensate further. It can be difficult to identify these patients because their blood pressure may be “normal,” but upon investigation, the blood pressure is actually a drop from the patient’s baseline.
Chronic heart failure patients with a history of depressed cardiac function will often have periods of cardiac decompensation between stages A and B. These patients are able to maintain perfusion for longer periods of time before further decompensation with hypoperfusion. If and when they do decompensate, they will often have a steep downward trajectory, so it is advantageous to the patient to be aggressive early.
Stage C (Classic) patients have evidence of tissue hypoperfusion. While these patients will often have true or relative hypotension, it is not a definition of stage C. These patients have evidence of volume overload with elevated JVP and rales throughout their lung fields. They will have poor distal perfusion and cool extremities that may become mottled. Lactate is ≥ 2 mmol/L. B-type natriuretic peptide (BNP) and liver function test (LFTs) results are elevated, and urine output is diminished. If a pulmonary arterial catheter is placed (highly recommended), the cardiac index (CI) is < 2.2 L/min/m2 and the pulmonary capillary wedge pressure (PCWP) is > 15 mm Hg. These patients look like what many clinicians think of when they think of CS.
These patients need better tissue perfusion. Inotropic support is needed to augment CO and DO2. Pharmacologic support is often the initial step. These patients also benefit from volume removal. This is usually accomplished with aggressive diuresis with a loop diuretic.
Stage D (Deteriorating) patients have failed initial treatment with single inotropic support. Hypoperfusion is not getting better and is often worsening. Lactate is staying > 2 mmol/L or rising. BNP and LFTs are also rising. These patients require additional inotropes and usually need vasopressors. Mechanical cardiac support (MCS) is often needed in addition to pharmacologic inotropic support.
Stage E (Extremis) patients have actual or impending circulatory collapse. These patients are peri-arrest with profound hypotension, lactic acidosis (often > 8 mmol/L), and unconsciousness. These patients are worsening despite multiple strategies to augment CO and DO2. These patients will likely die without emergent veno-arterial (VA) extracorporeal membrane oxygenation (ECMO). The goal of treatment is to stabilize the patient as quickly as possible to prevent cardiac arrest.
In addition to the stage of CS, SCAI developed the three-axis model of risk stratification as a conceptual model to be used for evaluation and prognostication. Etiology and phenotype, shock severity, and risk modifiers are factors related to patient outcomes from CS. This model is a way to individualize treatment to a specific patient.
Shock severity: What is the patient’s shock stage? What are the hemodynamics and metabolic abnormalities? What are the doses of the inotropes or vasopressors? Risk goes up with higher shock stages and vasoactive agent doses and worsening metabolic disturbances or hemodynamics.
Phenotype and etiology: what is the clinical etiology of the patient’s CS? Is this acute or acute on chronic? Which ventricle is involved? Is this cardiac driven or are other organs the driving factor? Single ventricle involvement is better than bi-ventricular failure. Cardiogenic collapse due to an overdose may have a better outcome than a massive AMI.
Risk modifiers: how old is the patient? What are the comorbidities? Did the patient have a cardiac arrest? What is the patient’s mental status? Some factors are modifiable, but others are not. The concept of chronologic vs. physiologic age may come into play. A frail 40 year old with stage 4 cancer and end stage renal failure may be assessed differently than a 70 year old with mild hypertension and an AMI.
The SCAI stages of CS are a pragmatic way to assess patients with an acute presentation of CS. These stages have defined criteria and treatment recommendations for all patients. The three-axis model allows the clinician to individualize patient care based on shock severity, etiology/phenotype, and risk modification. The goal of these stages is to identify and aggressively treat patients with CS, as well as identify when treatment is failing and additional therapies may be needed.
Dr. Gaillard is Associate Professor in the Departments of Anesthesiology, Section on Critical Care; Internal Medicine, Section on Pulmonology, Critical Care, Allergy, and Immunologic Diseases; and Emergency Medicine; Wake Forest School of Medicine, Winston-Salem, N.C.