Cardiogenic shock is defined as a primary cardiac disorder that results in both clinical and biochemical evidence of tissue hypoperfusion. Clinical criteria include a systolic blood pressure of less than or equal to 90 mm Hg for greater than or equal to 30 minutes or support to maintain systolic blood pressure less than or equal to 90 mm Hg and urine output less than or equal to  30 mL/hr or cool extremities. Hemodynamic criteria include a depressed cardiac index (less than or equal to 2.2 liters per minute per square meter of body surface area) and an elevated pulmonary-capillary wedge pressure greater than 15 mm Hg.

Cardiogenic shock is a clinical entity characterized by a low cardiac output state of circulatory failure that results in end-organ hypoperfusion and tissue hypoxia. The most common cause of cardiogenic shock is acute myocardial infarction, though other disorders leading to impairment of the myocardium, valves, conduction system, or pericardium also can result in cardiogenic shock. Despite advances in reperfusion therapy and mechanical circulatory support treatments, morbidity, and mortality among patients with cardiogenic shock remain high.

Etiology

Various forms of cardiac dysfunction can cause cardiogenic shock. 

The most common causes of cardiogenic shock include:

• Acute myocardial ischemia 
• Mechanical defect: acute mitral regurgitation (papillary muscle rupture), ventricular wall rupture (septal or free wall), cardiac tamponade, left ventricular outflow obstruction (hypertrophic obstructive cardiomyopathy [HOCM], aortic stenosis [AS]), Left ventricular inflow obstruction (MS, atrial myxoma)
• Contractility defect: ischemic and non-ischemic cardiomyopathy, arrhythmias, septic shock with myocardial depression, myocarditis
• Pulmonary embolus (right ventricular with or without left ventricular failure)
• Right ventricular failure
• Aortic dissection
• Other causes include cardiotoxic drugs (doxorubicin), medication overdose (beta/calcium channel blockers), metabolic derangements (acidosis), electrolyte abnormalities (calcium or phosphate)

Risk of Cardiogenic shock after ST-elevation myocardial infarction (STEMI):

• Age more than 70 years
• Systolic blood pressure less than 120 mmHg
• Sinus tachycardia or bradycardia
• A long duration of symptoms before treatment

Epidemiology

The incidence of cardiogenic shock is in decline, which can be attributed to increased rates of use of primary percutaneous coronary intervention (PCI) for acute MI. However, approximately 5% to 8% of STEMI and 2% to 3% of NON-STEMI cases can result in cardiogenic shock. This can translate to 40,000 to 50,000 cases per year in the United States.

Cardiogenic shock has a higher incidence in the following classes of patients:

• Elderly population
• Patient population with diabetes
• Prior history of left ventricular injury
• Female gender

Pathophysiology

The pathophysiology of cardiogenic shock is complex and not fully understood. Ischemia to the myocardium causes derangement to both systolic and diastolic left ventricular function, resulting in a profound depression of myocardial contractility. This, in turn, leads to a potentially catastrophic and vicious spiral of reduced cardiac output and low blood pressure, perpetuating further coronary ischemia and impairment of contractility. Several physiologic compensatory processes ensue. These include:

• The activation of the sympathetic system leading to peripheral vasoconstriction may improve coronary perfusion at the cost of increased afterload, and
• Tachycardia increases myocardial oxygen demand and subsequently worsens myocardial ischemia.

These compensatory mechanisms are subsequently counteracted by pathologic vasodilation that occurs from the release of potent systemic inflammatory markers such as interleukin-1, tumor necrosis factor-a, and interleukin-6. Additionally, higher levels of nitric oxide and peroxynitrite are released, which also contribute to pathologic vasodilation and are known to be cardiotoxic. Unless interrupted by adequate treatment measures, this self-perpetuating cycle leads to global hypoperfusion and the inability to effectively meet the metabolic demands of the tissues, progressing to multiorgan failure and eventually death.

History and Physical

The presenting symptoms of cardiogenic shock are variable. The most common clinical manifestations of shock, such as hypotension, altered mental status, oliguria, and cold, clammy skin, can be seen in patients with cardiogenic shock.

History plays a very important role in understanding the etiology of the shock and thus helps in the management of cardiogenic shock.

The patient should also be assessed for cardiac risk factors:

• Diabetes mellitus
• Tobacco smoking
• Hypertension
• Hyperlipidemia
• A family history of premature coronary artery disease
• Age older than 45 in men and older than 55 in women
• Physical inactivity

Physical examination findings in patients with cardiogenic shock include the following:

• Altered mental status, cyanosis, cold and clammy skin, mottled extremities
• Peripheral pulses are faint, rapid, and sometimes irregular if there is an underlying arrhythmia.
• Jugular venous distension
• Diminished heart sounds, S3 or S4, may be present, murmurs in the presence of valvular disorders such as mitral regurgitation or aortic stenosis.
• Pulmonary vascular congestion may be associated with rales. 
• Peripheral edema may be present in the setting of fluid overload

Evaluation

Rapid diagnosis with prompt supportive therapy and coronary artery revascularization plays a vital role in achieving good outcomes in patients with cardiogenic shock.

Diagnostic evaluation of cardiogenic shock includes the following:

• Complete blood picture, comprehensive metabolic panel, magnesium, phosphorous, coagulation profile, thyroid-stimulating hormone
• Arterial blood gas
• Lactate
• Brain natriuretic peptide
• Cardiac enzyme test
• Chest x-ray
• Electrocardiogram
• Two-dimensional echocardiography
• Ultrasonography to guide fluid management
• Coronary angiography

Treatment / Management

Cardiogenic shock is an emergency requiring immediate resuscitative therapy before the irreversible damage of vital organs. Rapid diagnosis with prompt initiation of pharmacological therapy to maintain blood pressure and to maintain respiratory support along with a reversal of underlying cause plays a vital role in the prognosis of patients with cardiogenic shock.

Early restoration of coronary blood is the most important intervention and is the standard therapy for patients with cardiogenic shock due to myocardial infarction.