Cardiogenic shock

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Diagnosis

History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | Chest X Ray | CT | MRI | Echocardiography or Ultrasound | Other Imaging Findings | Other Diagnostic Studies

Electrocardiogram

An electrocardiogram may be useful in distinguishing cardiogenic shock from septic shock or neurogenic shock. A diagnosis of cardiogenic shock is suggested by the presence of ST segment changes, new left bundle branch block or signs of a cardiomyopathy. Cardiac arrhythmias may also be present.

Radiology

The chest x ray will show pulmonary edema, pulmonary vascular redistribution, enlarged hila, Kerley's B lines, and bilateral pleural effusions in patients with left ventricular failure. In contrast, a pneumonia may be present in the patient with septic shock.

The heart may be enlarged (cardiomegaly) in the patient with tamponade. A widened mediastinum may be present in the patient with aortic dissection.

The chest x ray may also be useful in excluding a tension pneumothorax that may be associated with hypotension

Echocardiography

Echocardiography is important imaging modality in the evaluation of the patient with cardiogenic shock. It allows the clinician to distinguish cardiogenic shock from septic shock and neurogenic shock. In cardiogenic shock due to acute MI, poor wall motion will be present. In septic shock, a hypercontractile ventricle may be present. Mechanical complications such as papillary muscle rupture, pseudoaneurysm, and a ventricular septal defect may also be visualized. Valvular heart disease such as aortic stenosis, aortic insufficiency and mitral stenosis can also be assessed. Dynamic outflow obstruction such as HOCM can also be indentified and quantified. The magnitude of left ventricular dysfunction in patients with cardiomyopathy can be evaluated.

Swan-ganz catheter

The Swan-ganz catheter or pulmonary artery catheter may be helpful in distinguishing cardiogenic shock from septic shock and in optimizing the patient's left ventricular filling pressures (see section on Treatment below). The presence of significant V waves (greatly exceeding the pulmonary capillary wedge pressure) on the pulmonary artery tracing suggests either acute mitral regurgitation or a ventricular septal defect.

Biopsy

In case of suspected cardiomyopathy a biopsy of heart muscle may be of benefit in establishing a definitive diagnosis.

Treatment

Urgent revascularizaiton

If the patient has an ST elevation myocardial infarction, then primary angioplasty should be considered to restore flow to the culprit artery. Consideration should also be given to restoration of flow in the non-culprit territories in the setting of cardiogenic shock.

Administration of streptokinase therapy to patients with cardiogenic shock has not been associated with an improvement in survival. These studies, however, oare older and are limited by the infrequent use of adjunctive PCI. If a patient is not deemed a candidate for primary angioplasty, then consideration should be given to fibrinolyitc administration.

Volume management

The goal of managing the patient with cardiogenic shock is to optimize the filling of the left ventricle so that the Starling relationship and mechanical performance and contractility of the heart is optimized. In the setting of acute MI, a pulmonary capillary wedge pressure of 18 to 20 mm Hg may optimize left ventricular filling. Filling pressures higher than this may lead to LV dilation, and poorer left ventricular function.

Pharmacologic hemodynamic support

If hypotension persists despite adequate left ventricular filling pressures, then the addition of vasconstrictors and/or inotropes is suggested. Hemodynamic monitoring is essential to assure that a target mean arterial pressure (MAP) of 60 to 65 mmHg is acheived to maintain perfusion to vital organs (brain, kidney, heart).

Selection of a vasopressor or an inotrope

Systolic blood pressure (SBP) > 80 mm Hg

Dobutamine may be preferable over dopamine at this blood pressure. Dopamine increase contractility and heart rate and thereby increases myocardial oxygen demand. Dobutamine reduces the systemic vascular resistance and may not increase oxygen demands as much as dopamine, and is preferable at this systolic blood pressure. Phosphodiesterase inhibitors (PDIs) such as milrinone and inamrinone (formerly known as amrinone) are not dependent upon the adrenoreceptor activity and patients may not develop tolerance, and they may be less likely to increase myocardial oxygen demands. However, the addition of a vasopressor is often required as these agents reduce preload and afterload. PDIs are more likely to be associated with tachyarrhythmias than dobutamine.

Systolic blood pressure (SBP) < 80 mm Hg

At systolic blood pressures < 80 mm Hg dopamine should be initiated first. The patient may not tolerate the vasodilating effects of dobutamine at this blood pressure. The initial dose of dopamine is 5 to 10 mcg/kg/min.

If the dopamine at doses of 20 mcg/kg/min does not achieve a MAP of 60-65 mm Hg, then norepinephrine can be added at an initial dose of 0.5 mcg/kg/min which can then be titrated up to 3.3 mcg/kg/min. Norepinephrine is avoided as a first line agent because of its adverse impact upon renal perfusion.

If norepinephrine does not generate a MAP of 60 mm Hg, then epinephrine can be added. Epinephrine increases both the stroke volume and heart rate, but is associated with lactic acidosis

Mechanical support

Intra-aortic balloon placement

In the setting of acute MI, the placement of an intra-aortic balloon pump (which reduces workload for the heart, and improves perfusion of the coronary arteries) should be considered.

A recent meta-analysis of randomized trial data, however, challenges this common practice and class 1B recommendation. In a meta-analysis of seven randomized trials enrolling 1009 patient, IABP placement in STEMI was not associated with an improvement in mortality or in left ventricular function but was associated with a higher rate of stroke and bleeding. When data from non-randomized cohort studies were evaluated in a meta-analysis (n=10,529 STEMI patients with cardiogenic shock), IABP placement was associated with an 18% relative risk reduction in 30 day mortality among patients treated with a fibrinolytic agent. This particular analysis is confounded by the fact that those patients in whom an IABP was placed underwent adjunctive percutaneous intervention (PCI) more frequently. In this non-randomized cohort analysis, IABP placement in patients undergoing primary angioplasty was associated with a 6% relative increase in mortality (p<0.0008). Thus, neither randomized nor observational data support IABP placement in the setting of primary PCI for cardiogenic shock, and careful consideration should be given to the risk of stroke and bleeding prior to IABP placement in this population.

Left ventricular assist device placement

In the setting of pronounced hypotension despite medical therapy and IABP placement, placement of a left ventricular assist device (which augments the pump-function of the heart) should be considered. A ventricular assist device should only be placed in those patients in whom the cardiogenic shock is deemed to be reversible or if it is being used as a bridge option.

Coronary artery bypass graft (CABG) placement

CABG in this setting is associated with high rates of mortality and morbidity and is generally not performed if primary angioplasty can be performed.

Mechanical ventilation

Mechanical ventilation is often required in patients with cardiogenic shock to assure adequate oxygenation.

ACC/AHA Guidelines (DO NOT EDIT)

“

Class I 1. Intra-aortic balloon counterpulsation is recommended for STEMI patients when cardiogenic shock is not quickly reversed with pharmacological therapy. The IABP is a stabilizing measure for angiography and prompt revascularization. (Level of Evidence: B) 2. Intra-arterial monitoring is recommended for the management of STEMI patients with cardiogenic shock. (Level of Evidence: C) 3. Early revascularization, either PCI or CABG, is recommended for patients less than 75 years old with ST elevation or LBBB who develop shock within 36 hours of MI and who are suitable for revascularization that can be performed within 18 hours of shock unless further support is futile because of the patient’s wishes or contraindications/unsuitability for further invasive care. (Level of Evidence: A) 4. Fibrinolytic therapy should be administered to STEMI patients with cardiogenic shock who are unsuitable for further invasive care and do not have contraindications to fibrinolysis. (Level of Evidence: B) 5. Echocardiography should be used to evaluate mechanical complications unless these are assessed by invasive measures. (Level of Evidence: C) Class IIa 1. Pulmonary artery catheter monitoring can be useful for the management of STEMI patients with cardiogenic shock. (Level of Evidence: C) 2. Early revascularization, either PCI or CABG, is reasonable for selected patients 75 years or older with ST elevation or LBBB who develop shock within 36 hours of MI and who are suitable for revascularization that can be performed within 18 hours of shock. Patients with good prior functional status who agree to invasive care may be selected for such an invasive strategy. (Level of Evidence: B)

”

See also

• Intra-aortic balloon pump
• Ventricular assist device

Sources

• Irwin, R.S., Rippe, J.M., Curley, F.J., Heard, S.O. (1997) Procedures and Techniques in Intensive Care Medicine (3rd edition). Boston: Lippincott, Williams and Wilkins.
• Marino, P. (1997) The ICU Book. (2nd edition). Philadelphia: Lippincott, Williams and Wilkins.

References

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