Cardiogenic shock surgery

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2] Syed Musadiq Ali M.B.B.S.[3]

Overview

Cardiogenic shock is considered an emergency and irrespectively to the therapeutic approach, the target goal of any therapy is prompt revascularization of ischemic myocardium. This should be achieved in the shortest timespan possible. There are two major categories of treatment for cardiogenic shock, the medical/conservative approach and the interventional approach. The ideal treatment combines both mechanisms, in which medical therapy, after restored filling pressures, allows hemodynamical stabilization of the patient, until interventional methods, that contribute to the reversal of the process leading to the shock state, may performed. The interventional approach may include PCI or coronary artery bypass graft surgery (CABG) and in both techniques the goal is not only reperfusion of the occluded coronary artery, but also prevention of vessel reoclusion. If there is no access to a cardiac catheterization facility, nor the possibility of transferring the patient to one within 90 minutes, then immediately thrombolytic therapy should be considered. Other important factors to increase the chances of a better outcome are: mechanical ventilation, in order to improve tissue oxygenation, and close monitoring of the therapeutic dosages, particularly of vasoactive drugs, since these have been associated with excess mortality due to toxicity effects. Also, it is recommended invasive hemodynamic monitoring, in order to monitor and guide the effects of the therapy as well as the overall status of the patient. The success of reperfusion is usually suggested by the relief of symptoms, restoration of hemodynamic parameters and electrical stability, as well as the reduction of at least 50% in the ST-segment on the EKG, in the case of a STEMI.

Surgery

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, are 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.

Invasive Hemodynamic Monitoring

Considering the importance of proper blood pressure assessment in patients in shock, along with the fact that peripheral vasoconstriction may jeopardize blood pressure assessment through common manual sphygmomanometry, all patients should have an indwelling arterial pressure catheter placed in order to gather more accurate measurements. This method not only supplies continuous hemodynamic data, therefore allowing a beat-to-beat analysis, useful in evaluating the response to therapy, unlike other manual methods, but also allows for the collection of arterial blood gas samples. The most commonly used catheter is the flow-directed balloon-tipped pulmonary artery catheter, which not only allows for cardiac output determination, as it is a good method for hemodynamic assessment of these patients, as well as continuous monitoring of pulmonary artery and central venous pressure and waveforms. With this device it is also possible to collect blood from the pulmonary artery, therefore enabling determination of MVO₂, in order to evaluate oxygen delivery to peripheral tissues and at the same time also helping in the diagnosis of left-to-right shunts, usually associated with anatomic abnormalities. All these features make the flow-directed balloon-tipped pulmonary artery catheter a good tool for diagnosis, management and monitoring of therapy of cardiogenic shock patients.

Other monitoring techniques include:

• Oxymetry - although a useful tool in theory, since oxygen delivery will be directly affected by arterial oxygen saturation, it has some limitations, such as affected results from ambient lights, hypothermia and dyshemoglobinemias. Also, motion artifacts, vasoconstriction and hypoperfusion in the shock state will jeopardize the readings.

• Near Infrared Spectroscopy (NIRS) - an innovative technique that allows for monitoring of tissue oxygenation by measuring regional tissue blood flow, oxygen delivery and utilization. The near-infrared light passes through biological tissues, such as muscle and skin, and is absorbed by chromophores that is has passed through. The chromophores known to absorb the near-infrared light wavelength are cytochrome aa3, hemoglobin and myoglobin, depending on the level of oxygenation. Since peripheral tissue hypoperfusion is a good marker of cardiovascular stress, NIRS presents itself as a good method to assess, in real-time, tissue perfusion throughout the evaluation and treatment periods, as well as during resuscitation.
• Advanced echocardiography in the ICU - particularly with the development of more advanced echocardiographic techniques, such as TEE and contrast echocardiography, the inclusion of this noninvasive method in ICU has allowed for the decreased of more invasive techniques, such as pulmonary artery catheterization. This replacement has been seen due to the vast amount of important data that this method provides, such as assessment of of hemodynamic stability, cardiac output, stroke volume, preload, detection of anatomic abnormalities, intravascular volume status, pulmonary artery pressures, diagnosis of hemodynamically significant pulmonary embolism, among others.

ACC/AHA Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction (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)"

References

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