Excerpt from Shock, Cardiogenic

Synonyms, Key Words, and Related Terms: cardiogenic shock, cardiac shock, shock, global hypoperfuse, acute myocardial infarction, AMI, decreased pumping of the heart, decreased urine output, altered mentation, hypotension, jugular venous distension, cardiac gallop, pulmonary edema, acute cardiac ischemia

Please click here to view the full topic text: Shock, Cardiogenic

Background: Cardiogenic shock is characterized by a decreased pumping ability of the heart that causes a shocklike state (ie, global hypoperfusion). It most commonly occurs in association with, and as a direct result of, acute myocardial infarction (AMI).

Similar to other shock states, cardiogenic shock is considered to be a clinical diagnosis characterized by decreased urine output, altered mentation, and hypotension. Other clinical characteristics include jugular venous distension, cardiac gallop, and pulmonary edema. The most recent prospective study of cardiogenic shock defines cardiogenic shock as sustained hypotension (systolic blood pressure [BP] less than 90 mm Hg lasting more than 30 min) with evidence of tissue hypoperfusion with adequate left ventricular (LV) filling pressure (Hochman, 1999). Tissue hypoperfusion was defined as cold peripheries (extremities colder than core), oliguria (<30 mL/h), or both.

Pathophysiology: The most common initiating event in cardiogenic shock is AMI. Dead myocardium does not contract, and classical teaching has been that when more than 40% of the myocardium is irreversibly damaged (particularly, the anterior cardiac wall), cardiogenic shock may result. On a mechanical level, a marked decrease in contractility reduces the ejection fraction and cardiac output. These lead to increased ventricular filling pressures, cardiac chamber dilatation, and ultimately univentricular or biventricular failure that result in systemic hypotension and/or pulmonary edema. The SHOCK trial, however, demonstrated that left ventricular ejection fraction is not always depressed in the setting of cardiogenic shock. Additional surprising findings included nonelevated systemic vascular resistance on vasopressors and that most survivors have only New York Heart Association (NYHA) class I congestive heart failure.

A systemic inflammatory response syndrome–type mechanism has been implicated in the pathophysiology of cardiogenic shock. Elevated levels of white blood cells, body temperature, complement, interleukins, and C-reactive protein are often seen in large myocardial infarctions. Similarly, inflammatory nitric oxide synthetase (iNOS) is also released in high levels during myocardial stress. iNOS induces nitric oxide production, which may uncouple calcium metabolism in the myocardium resulting in a stunned myocardium. Additionally, iNOS leads to the expression of interleukins, which may themselves cause hypotension.

Myocardial ischemia causes a decrease in contractile function, which leads to left ventricular dysfunction and decreased arterial pressure; these, in turn, exacerbate the myocardial ischemia. The end result is a vicious cycle that leads to severe cardiovascular decompensation. Other pathophysiological mechanisms responsible for cardiogenic shock include papillary muscle rupture leading to acute mitral regurgitation (4.4%); decreased forward flow, ejection fraction, and ventricular septal defect (1.5%); and free wall rupture (4.1%) as a consequence of AMI.

Right ventricular (RV) infarct, by itself, may lead to hypotension and shock because of reduced preload to the left ventricle. The management of RV infarcts is discussed elsewhere but should be considered in the setting of inferior wall MI.

Cardiac tamponade may result as a consequence of pericarditis, uremic pericardial effusion, or in rare cases systemic lupus erythematosus.

Whenever patients who present in shock have been exposed to medications that may cause hypotension, these drugs should be considered as possible culprits in the disease. Calcium channel blockers may cause profound hypotension with a normal or elevated heart rate. Beta-blocking agents may also cause hypotension. Hypotension can be seen with or without bradycardia, or AV node block can be seen with either of these types of medications. If these medications are the culprits, therapy dire .....