Cardiogenic shock: From ECMO to Impella and beyond

Prognostic factors in cardiogenic shock

Several tools help predict outcome in a severely ill patient. End-organ function, indicated by blood lactate levels and estimated glomerular filtration rate, is perhaps the most informative and should be monitored serially.

CardShock³ is a simple scoring system based on age, mental status at presentation, laboratory values, and medical history. Patients receive 1 point for each of the following factors:

• Age > 75
• Confusion at presentation
• Previous myocardial infarction or coronary artery bypass grafting
• Acute coronary syndrome etiology
• Left ventricular ejection fraction < 40%
• Blood lactate level between 2 and 4 mmol/L, inclusively (2 points for lactate levels > 4 mmol/L)
• Estimated glomerular filtration rate between 30 and 60 mL/min/1.73 m², inclusively (2 points if < 30 mL/min/1.73 m²). 

Thus, scores range from 0 (best) to 9 (worst). A score of 0 to 3 points was associated with a 9% risk of death in the hospital, a score of 4 or 5 with a risk of 36%, and a score of 6 through 9 with a risk of 77%.³

The Survival After Veno-arterial ECMO (SAVE) score (www.save-score.com) is a prediction tool derived from a large international ECMO registry.⁴ It is based on patient age, diagnosis, and indicators of end-organ dysfunction. Scores range from –35 (worst) to +7 (best).

The mortality rate associated with postcardiotomy cardiogenic shock increases with the amount of inotropic support provided. In a 1996–1999 case series of patients who underwent open-heart surgery,⁵ the hospital mortality rate was 40% in those who received 2 inotropes in high doses and 80% in those who received 3. A strategy of early implementation of mechanical support is critical.

Selection criteria for destination therapy

Deciding whether a patient should receive a long-term device is frequently a challenge. The decision often must be based on limited information about not only the medical indications but also psychosocial factors that influence long-term success.

The Centers for Medicare and Medicaid Services have established criteria for candidates for left ventricular assist devices (LVADs) as destination therapy.⁶ Contraindications established for heart transplant should also be considered (Table 1).

CASE REVISITED

Several factors argued against LVAD placement in our patient. He had no health insurance and had been off medications. He smoked and said he consumed 3 hard liquor drinks per week. His Stanford Integrated Psychosocial Assessment for Transplantation score was 30 (minimally acceptable). He had hypoxia with subsegmental pulmonary edema, a strong contraindication to immediate transplant.

On the other hand, he had only mild right ventricular dysfunction. His CardShock score was 4 (intermediate risk, based on lactate 1.5 mmol/L and estimated glomerular filtration rate 52 mL/min/1.73 m²). His SAVE score was –9 (class IV), which overall is associated with a 30% risk of death (low enough to consider treatment).

During the patient’s time on temporary support, the team had the opportunity to better understand him and assess his family support and his ability to handle a permanent device. His surviving the acute course bolstered the team’s confidence that he could enjoy long-term survival with destination therapy.

CATHETERIZATION LABORATORY DEVICE CAPABILITIES

Although most implantation procedures are done in the operating room, they are often done in the catheterization laboratory because patients undergoing catheterization may not be stable enough for transfer, or an emergency intervention may be required during the night. Catheterization interventionists are also an important part of the team to help determine the best approach for long-term therapy.

The catheterization laboratory has multiple acute intervention options. Usually, decisions must be made quickly. In general, patients needing mechanical support are managed as follows:

• Those who need circulation support and oxygenation receive ECMO
• Those who need circulation support alone because of mechanical issues (eg, myocardial infarction) are considered for an intra-aortic balloon pump, Impella, or TandemHeart pump (Cardiac Assist, Pittsburgh, PA).

Factors that guide the selection of a temporary pump include:

• Left ventricular function
• Right ventricular function
• Aortic valve stenosis (some devices cannot be inserted through critical aortic stenosis)
• Aortic regurgitation (can affect some devices)
• Peripheral artery disease (some devices are large and must be placed percutaneously).

CHOOSING AMONG PERCUTANEOUS DEVICES

Circulatory support in cardiogenic shock improves outcomes, and devices play an important role in supporting high-risk procedures. The goal is not necessarily to use the device throughout the hospital stay. Acute stabilization is most important initially; a more considered decision about long-term therapy can be made when more is known about the patient.

Patient selection is the most important component of success. However, randomized data to support outcomes with the various devices are sparse and complicated by the critically ill state of the patient population.

SHORT-TERM CIRCULATORY SUPPORT: ECMO, IMPELLA, TANDEMHEART

A menu of options is available for temporary mechanical support. Options differ by their degree of circulatory support and ease of insertion (Table 2).

ECMO: A fast option with many advantages

ECMO has evolved and now can be placed quickly. A remote diagnostic platform such as CardioHub permits management at the bedside, in the medical unit, or in the cardiac intensive care unit.⁷

ECMO has several advantages. It can be used during cardiopulmonary bypass, it provides oxygenation, it is the only option in the setting of lung injury, it can be placed peripherally (without thoracotomy), and it is the only percutaneous option for biventricular support.

ECMO also has significant disadvantages

ECMO is a good device for acute resuscitation of a patient in shock, as it offers quick placement and resuscitation. But it is falling out of favor because of significant disadvantages.

Its major drawback is that it provides no left ventricular unloading. Although in a very unstable patient ECMO can stabilize end organs and restore their function, the lack of left ventricular unloading and reduced ventricular work threaten the myocardium. It creates extremely high afterload; therefore, in a left ventricle with poor function, wall tension and myocardial oxygen demand increase. Multiple studies have shown that coronary perfusion worsens, especially if the patient is cannulated peripherally. Because relative cerebral hypoxia occurs in many situations, it is imperative to check blood saturations at multiple sites to determine if perfusion is adequate everywhere.    

Ineffective left ventricular unloading with venoarterial ECMO is managed in several ways. Sometimes left ventricular distention is slight and the effects are subtle. Left ventricular distention causing pulmonary edema can be addressed with:

• Inotropes (in moderate doses)
• Anticoagulation to prevent left ventricular thrombus formation
• An intra-aortic balloon pump. Most patients on ECMO already have an intra-aortic balloon pump in place, and it should be left in to provide additional support. For those who do not have one, it should be placed via the contralateral femoral artery.

If problems persist despite these measures, apical cannulation or left ventricular septostomy can be performed.

Outcomes with ECMO have been disappointing. Studies show that whether ECMO was indicated for cardiac failure or for respiratory failure, survival is only about 25% at 5 years. Analyzing data only for arteriovenous ECMO, survival was 48% in bridged patients and 41% in patients who were weaned.

The Extracorporeal Life Support Organization Registry, in their international summary from 2010, found that 34% of cardiac patients on ECMO survived to discharge or transfer. Most of these patients had cardiogenic shock from acute myocardial infarction. Outcomes are so poor because of complications endemic to ECMO, eg, dialysis-dependent renal failure (about 40%) and neurologic complications (about 30%), often involving ischemic or hemorrhagic stroke.

Limb and pump complications were also significant in the past. These have been reduced with the new reperfusion cannula and the Quadrox oxygenator.  

Complications unique to ECMO should be understood and anticipated so that they can be avoided. Better tools are available, ie, Impella and TandemHeart.