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.
The most common causes of cardiogenic shock include:
The incidence of cardiogenic shock is in decline which can be attributed to increased rates of use of primary 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:
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:
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 effectively meet the metabolic demands of the tissues, progressing to multiorgan failure and eventually death.
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 the cardiogenic shock.
The patient should also be assessed for cardiac risk factors:
Physical examination findings in patients with cardiogenic shock include the following:
Diagnostic evaluation of cardiogenic shock includes the following:
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 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.
The management of the cardiogenic shock involves the following:
The goal of medical management is to restore cardiac output and prevent irreversible end-organ damage rapidly.
Percutaneous Coronary Intervention and Coronary Artery Bypass
SHOCK (Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock) trial data confirmed an approach that combines early revascularization with medical management in patients with cardiogenic shock is optimal.
Mechanical Circulatory Support
Due to poor prognosis associated with cardiogenic shock, medical therapy is often inadequate and mechanical circulatory support (MCS) therapy to improve end-organ perfusion may be required. Evaluation for MCS should be performed by an experienced multidisciplinary team.
Palliative Care in Cardiogenic shock
Cardiogenic shock is a life-threatening disorder and is the main cause of death after an acute MI. Even in the best of hands and the latest treatment, the condition carries a mortality rate in excess of 30%. The key to survival is to have prompt resuscitation with coronary artery revascularization. Unfortunately, even with revascularization, multiorgan failure is common, and the long-term survival is not guaranteed. Because cardiogenic shock affects almost every other organ in the body, the condition is best managed by a multidisciplinary team that also includes ICU nurses. Even though cardiogenic shock cannot be entirely prevented, patients must be educated on reducing risk factors for heart disease. Patients should be urged not to smoke, lower the lipids and ensure better control of blood sugars. In addition, enrollment in an exercise program can help lower body weight and help achieve better control of the blood pressure. (Level V)