A 72-year-old gentleman with past medical history significant for hypertension, hyperlipidemia, type 2 diabetes, and tobacco use is brought to the ED with chief complaint of chest tightness. He is found to have ST elevations in leads V1 to V4 and is taken for emergency coronary angiography, which demonstrates 99% proximal LAD occlusion. During the procedure, he becomes hypotensive (BP 74/55 mm Hg) and tachycardic (HR 122 bpm). Norepinephrine is initiated. Right heart catheterization demonstrates elevated left and right-sided filling pressures with low cardiac index. Besides immediate revascularization, which of the following would be the best next step? 

A

Cannulate for VA-ECMO

B

Placement of microaxial intravascular flow pump

C

Administration of intravenous fluid

D

Placement of an intraaortic balloon pump

Explanation 

The correct answer is B – Placement of microaxial intravascular flow pump.

Cardiogenic shock is estimated to occur in approximately 10% of patients with STEMI and is associated with an early mortality rate of 40% to 50%. Several types of devices for temporary mechanical circulatory support (MCS) are available and have been studied in patients with cardiogenic shock, with variable efficacy and increased risk of vascular complications. IABP counterpulsation improves coronary perfusion and reduces cardiac afterload. It is relatively easy to use and has a smaller insertion profile (8 French), which is associated with lower rates of vascular access site complications when compared with other MCS devices. Left ventricular percutaneous microaxial flow pumps unload the LV by draining blood from the LV and pumping it to the ascending aorta. They are dependent on adequate right ventricular function to fill the LV and require adequate oxygenation of blood. VA-ECMO provides both blood flow and gas exchange, providing full cardiopulmonary bypass, but increases afterload. 

Randomized trials of MCS devices remain challenging to conduct due to relative lack of equipoise on the part of treating physicians, leading to selective patient enrollment and limiting the generalizability of study results. The DanGer-Shock randomized 360 patients presenting with STEMI and cardiogenic shock of <24 hours duration to either microaxial flow pump or standard of care. The trial demonstrated a 26% reduction of all-cause mortality at 180 days (HR, 0.74 [95% CI, 0.55-0.99]; P = 0.04; absolute risk reduction, 12.7%; number needed to treat = 8) compared with standard of care. However, this came at the cost of increased risk of complications like bleeding, limb ischemia and renal replacement therapy in the microaxial flow pump group.

In light of this and other trial data, the guidelines give a Class 2a, LOE B recommendation for the use of a microaxial intravascular flow pump in patients with STEMI complicated by severe or refractory cardiogenic shock to reduce mortality. These patients should be noncomatose and have adequate peripheral vasculature to accommodate large-bore access.

Answer choice A is not correct as the use of VA-ECMO cannulation in this setting has been given a class 3 recommendation for lack of benefit. VA-ECMO has not been shown to reduce death compared with medical therapy alone in patients with cardiogenic shock in the setting of MI but increases major bleeding and vascular complications. In the absence of severe concomitant respiratory failure requiring oxygenation support, this strategy is not indicated in the patient described here. Further fluid resuscitation (answer choice C) is not likely to be helpful as right heart catheterization demonstrated elevated filling pressures. Placement of an intraaortic balloon pump (IABP) is not the next best step.  The IABP-SHOCK II trial, which randomized patients with acute MI and severe cardiogenic shock to IABP or medical therapy showed no differences at 30 days or at long-term follow-up in the primary outcome of all-cause death. The use of IABP has a class 3 recommendation for lack of benefit in patients with cardiogenic shock secondary to acute myocardial infarction.

Main Takeaway

In selected patients with STEMI and severe or refractory cardiogenic shock, insertion of microaxial intravascular flow pump is reasonable to reduce death in a noncomatose patient with adequate vascular access. 

Guideline Loc.

Section 8.2