AHA Statement for managing acute MI complicated by cardiogenic shock

Cardiogenic shock (CS) remains the most common cause of mortality in patients with acute myocardial infarction. After an initial improvement in mortality related to revascularization, mortality rates have plateaued and no contemporary trial has validated a comprehensive algorithm for acute care delivery. In particular, important uncertainties remain in the appropriate use, selection, and management of MCS devices in patients with acute MI associated with cardiogenic shock (AMICS). The latest statement by American Heart Association published in March 2021 outlines the best practices for the contemporary interventional management of AMICS, including coronary revascularization, the use of MCS, and special considerations such as the treatment of patients with AMICS with cardiac arrest.

Mortality associated with AMICS remains high, with 30-day mortality approximating 40% to 45% in contemporary randomized trials. After the SHOCK trial which demonstrated survival benefit with early revascularization in AMICS and with growth in availability of primary percutaneous coronary intervention (PCI), AMICS-associated mortality declined. Data from AMICS registry suggests that in-hospital mortality of all patients with AMICS decreased from 62.2% in 1997 to 36.3% in 2017.

Defining cardiogenic shock and Redefining its management: the current statement advocates the recently proposed SCAI algorithm for CS classification (Figure 1.) An important aspect of the SCAI classification is a cardiac arrest modifier. At every stage of SCAI shock, the presence of cardiac arrest significantly increases mortality. Hence, this classification appears useful to risk stratify hospitalized patients.

Stable patients with risk factors for shock (stage A) or early shock (stage B) can generally proceed directly to coronary angiography and culprit lesion. Revascularization with continuous reassessment for signs and symptoms of progression of shock. Patients presenting in shock (stages C–E) may first require acute stabilization with attention to blood pressure, endorgan perfusion status, oxygenation, and acid-base status (Figure 1)

Initial stabilisation:

1. The minimum necessary dose of vasopressor should be used to maintain mean arterial blood pressure >65 mmHg, favoring norepinephrine as first-line therapy. Alternative agents may be preferred in addition to or instead of norepinephrine in specific circumstances such as unstable bradycardia- increased chronotropic effect of dopamine or epinephrine may be desired; dynamic left ventricular (LV) outflow tract obstruction- pure vasopressor such as phenylephrine or vasopressin may be preferred; or refractory hypoxemia or acidosis- efficacy of catecholamine vasopressors may be attenuated, favoring the use of vasopressin.

2. Strong consideration should be given to early endotracheal intubation and mechanical ventilation. Caution is advised in patients with AMICS and predominant right ventricular failure, including patients with right ventricular myocardial infarction, noting that initiation of positive pressure ventilation can abruptly lower systemic arterial pressure. Early intubation and ventilatory support may facilitate revascularization because of improved oxygenation, greater sedation, and enhanced metabolic profile.

3. Besides an initial physical examination and 2DEcho, left heart catherization for documenting LV end-diastolic pressure (LVEDP) should be considered when Echo is not available. Selective coronary (or bypass graft) angiography should identify the culprit lesion and define the complete extent of disease.

4. Right-sided heart catheterization provides access to quantitative data to sharpen characterization of individual patient hemodynamics over time. Key parameters to assess and monitor include central venous pressure, pulmonary capillary wedge pressure, cardiac output, cardiac power output, pulmonary artery pulsatility index, and mixed venous oxygen saturation.

5. Cardiac power output (Watts) is calculated as follows: cardiac output×mean arterial pressure÷451.

6. Pulmonary artery pulsatility index is calculated with the following equation: (pulmonary artery systolic pressure−pulmonary artery diastolic pressure)/right atrial pressure.

7. Invasive measures, including central venous pressure >10 mmHg, central venous pressure/pulmonary capillary wedge pressure >0.63 mmHg, pulmonary artery pulsatility index <2 may help identify concomitant RV dysfunction (usually seen in more then one-third patients of AMICS.

8. Of note, right-sided heart catheterization is not required to diagnose shock. In cases of AMICS in which performance of right-sided heart catheterization would cause an undue delay in timely reperfusion therapy, consideration should be given to deferring its performance until completion of PCI.

Mode of revascularisation: PCI of the infarct-related artery is the recommended method of reperfusion for patients with AMICS regardless of time delay. To save 1 life, only 8 patients need to be treated according to SHOCK trial. In the vast majority of patients with AMICS, PCI should be limited to the culprit lesion with possible staged revascularization of other lesions based on the results from CULPRIT -SHOCK trial. However, the role of multivessel PCI in AMICS remains under active investigation.

Role of MCS : The rationale for initiation of MCS early in AMICS is to reduce ventricular workload (unloading), increase systemic perfusion, enhance myocardial perfusion, and provide hemodynamic support during PCI.

Persistent clinical hypoperfusion, hypotension, vasopressor requirement, or cardiac power output <0.6 W despite adequate filling pressures may indicate a role for MCS as an adjunct to stabilization before coronary revascularization. For patients with predominant LV failure, MCS options include intra-aortic balloon counterpulsation (IABP), a transvalvular axial flow pump (Impella LP/CP/5.0/5.5), and the TandemHeart percutaneous LV assist device. Venoarterial (VA) extracorporeal membrane oxygenation (ECMO) may be considered to provide systemic circulatory support, but close monitoring for LV distension and worsening pulmonary edema is required.

For patients with predominant right ventricular failure, MCS options include the transvalvular axial flow Impella RP pump and TandemHeart Protek- Duo percutaneous right ventricular assist device. Patients with biventricular failure may be supported with bilateral Impella pumps or VA-ECMO with a concomitant LV venting mechanism. Patients with concurrent refractory respiratory failure should be considered for VA-ECMO. Guide to type of MCS selection is highlighted in figure 2.

Timing of MCS: Observational studies examining outcomes with MCS devices used for AMICS have reported variable results. The Detroit Cardiogenic Shock Initiative encouraged an aggressive protocol of early MCS in the management of patients with AMICS.

Putative benefits of early MCS include support of systemic perfusion, reduced cardiac workload, enhanced coronary perfusion and decongestion, and, through these mechanisms, arrest of the progression of shock to endorgan injury and death. Offsetting these benefits are variable, device-dependent risks of bleeding, hemolysis, vascular complications, and limb ischemia, as well as the additive complexity of postimplantation management.

In the context of STEMI, there is a theoretical concern that benefits of MCS may be further offset by increased delay to reperfusion therapy. The Door to Unload-STEMI pilot study, which did not include patients with CS, did not identify harm with a strategy of first unloading the LV for up to 30 minutes before reperfusion but also did not show benefit.

AHA statement concludes that early MCS placement before PCI may be considered for patients with AMICS who exhibit refractory hemodynamic instability despite aggressive medical therapy. (Figure 3).

Special consideration to cardiac arrest: Patients successfully resuscitated from cardiac arrest with return of spontaneous circulation and neurological function (Glasgow Coma Scale score ≥8) and a diagnosis of AMICS should be triaged to the cardiac catheterization laboratory as soon as possible for complete assessment.

Patients with AMICS and resuscitated cardiac arrest who remain comatose (Glasgow Coma Scale score <8) or unable to follow simple commands should be treated with targeted temperature management as soon as possible.

The statement thus outlines the best practices for the contemporary interventional management of AMICS, including coronary revascularization, the use of MCS, and special considerations such as the treatment of patients with AMICS with cardiac arrest.

Source: Circulation. 2021;143:00–00. DOI: 10.1161/CIR.0000000000000959