Cardiogenic shock complicating acute myocardial infarction: challenges and opportunities

Cardiogenic shock (CS) remains the leading mechanism of death in acute myocardial infarction (AMI) patients. Approximately 30% of all CS patients have AMICS¹ and despite modest earlier improvements in outcomes, mortality remains high² with significant variations between hospitals,³ highlighting the need for standardizing and optimizing the care of these high-risk patients. Building on the 2017 American Heart Association statement on the “Contemporary management of cardiogenic shock”,⁴ Henry et al provide a state-of-the-art update on the invasive management of AMICS, summarizing recent developments in the field, as well as future challenges and opportunities.⁵

There are 5 key "ingredients" for the managements of AMICS [(a) early diagnosis and triage; (b) initial stabilization and diagnostic evaluation including hemodynamic assessment; (c) culprit-only coronary revascularization; (d) judicious use of mechanic circulatory support; (e) expert in-hospital treatment]^6,7 which are discussed in detail in the Henry et al document:

First, early diagnosis and treatment of AMICS is key for improving outcomes and disrupting the downward spiral of CS. Cardiogenic shock is characterized by inadequate end organ perfusion due to cardiac dysfunction. Although the operational definition of CS varies between studies and clinical settings, a Society for Cardiovascular Angiography and Intervention (SCAI) clinical expert consensus statement on the classification of CS recently proposed 5 stages based on clinical findings, biomarkers and hemodynamics: stage A is “at risk” for CS, stage B is “beginning” shock, stage C is “classic” CS, stage D is “deteriorating”, and E is “extremis”⁸. The difference between stages B and C is the presence of hypoperfusion which is present in stages C and higher. Initial retrospective validation studies have demonstrated good correlation of the SCAI shock stages with mortality,⁹ but additional prospective studies are needed. The SCAI shock stages can help determine further treatment; stages A and B proceed with coronary angiography and revascularization, whereas stages C, D, and E first require stabilization.

Second, initial stabilization involves vasopressors (norepinephrine is preferred) at the lowest possible doses to maintain mean arterial pressure >65 mmHg and often intubation and mechanical ventilation. Physical examination can help determine the presence and severity of shock. Emergency echocardiography can help clarify the cause of shock including the occurrence of mechanical AMI complications that in most cases require urgent surgery. Coronary angiography can help define the culprit lesion(s) and plan revascularization. Right heart catheterization can help determine the severity of left and right ventricular dysfunction and guide further treatment potentially improving outcomes,¹⁰ but may need to be delayed in AMICS until after coronary revascularization has been achieved.

Third, the role of mechanical circulatory support (MCS) remains controversial in AMICS patients, given lack of randomized-controlled trial data showing benefit. Henry et al provide a balanced discussion of the potential benefits of MCS (improve systemic and myocardial perfusion, reduce myocardial workload, and reduce the need for vasopressors) and associated risks (bleeding, vascular access complications, delayed coronary reperfusion, and hemolysis). While awaiting the results of multiple ongoing trials of MCS in AMICS (including 4 trials on veno-arterial extracorporeal membrane oxygenators [VA-ECMO]) Henry et al recommend that “early MCS placement prior to PCI may be considered for patients with AMICS who exhibit refractory hemodynamic instability despite aggressive medical therapy”.

Fourth, early revascularization of the infarct-related artery remains the only treatment modality proven in randomized-controlled trials to improve the outcomes of AMICS.¹¹ Given potential time delays and the patients’ often critical condition, percutaneous coronary intervention (PCI) is performed in most cases, with coronary artery bypass graft surgery usually reserved for patients with mechanical AMI complications or after failure of PCI. In AMICS patients with multivessel coronary artery disease, PCI should only be performed in the culprit lesion in the acute setting, given higher mortality observed in the multivessel PCI arm of Culprit Lesion Only PCI versus Multivessel PCI in Cardiogenic Shock (CULPRIT-SHOCK) trial.¹² Whether the benefits of more aggressive antiplatelet treatments (reduce stent thrombosis and other thromboembolic complications) exceed the associated risks (bleeding) remains controversial and requires individualized clinical decision making.

Fifth, expert in-hospital treatment is key for patient recovery, as the catheterization laboratory is only the beginning of the patients’ hospitalization. Meticulous transition of care to the intensive care unit using a checklist can minimize the risk of various components of care “being lost in translation”. Management of AMICS patients by a multidisciplinary team that uses protocols to optimize hemodynamics through thoughtful use of MCS/vasopressors and promptly detects and treats any complications that may arise can maximize the likelihood of recovery.^13-15

Management of AMICS patients who have had cardiac arrest is even more complicated given the potential for hypoxic-ischemic encephalopathy, requiring careful assessment of the potential for recovery before proceeding with cardiac catheterization, as well as prompt targeted temperature management.

How should clinicians and researchers use the current document? Figure 4 provides a concise and practical step-by-step treatment algorithm for AMICS patients. Following this algorithm can help prevent overlooking critical aspects of the care of AMICS patients while individualizing use of the various treatment modalities. Moreover, the section “Conclusions and future directions” provides an up-to-date summary of key areas where additional research is needed, covering the entire spectrum of AMICS management from diagnosis to initial and subsequent in-hospital treatment.

Currently treatment of AMICS is similar to where PCI of chronic total occlusions was 10 years ago,^16-17 with tremendous variability between various physicians and centers and confusion about which treatment strategy to use and when. Standardization and technical innovations have led to remarkable improvements in the outcomes of chronic total occlusion PCI.¹⁸ Similarly, the field of AMICS offers tremendous opportunities for both building state-of-the-art clinical practices and for helping advance the basic and clinical science behind those practices. Henry et al should be congratulated for paving the way to better AMICS treatments.