Methods
Prehospital care
The primary objectives of prehospital care are early recognition and management of AMI-CS. All patients require intravenous access, high-flow oxygen administered by mask and cardiac monitoring. A 12-lead ECG is performed in the field to decrease door-to-PCI times and/or time to the administration of thrombolytics by early identification of STEMI. The EMS and emergency medical department staff were trained to use the SCAI staging classification for CS at first medical contact (FMC) (figure 1).7 The first responders were trained to identify shock in patients with cool, clammy, pale skin, confusion/anxiety, rapid shallow breathing, systolic blood pressure (SBP) <90 mm Hg, heart rate greater than 100 bpm or supplemental oxygen requirement >5 L/min via NC. The emergency medical department and EMS staff will activate STEMI shock alert for patients with stages C, D or E shock using existing telephone-text provider notification system. The prehospital patient care will otherwise follow prescribed guideline directed medical management for STEMI and ACLS resuscitation protocols.8 9 The emergency department (ED) staff will escalate the STEMI alert to STEMI shock alert for patients with stages C, D or E shock with or without cardiac arrest after initial assessment in the ED. The STEMI shock team is multidisciplinary group composed of the attending or on-call physician providers (ED attending physician, interventional cardiology, critical care, nephrology), ED charge nurse, lead nurse cardiac catheterisation laboratory, CV tech cardiac catheterisation laboratory (cardiovascular laboratory, CVL), facility nursing supervisor and aeromedical transport team. The STEMI shock team will complete ad hoc case review within 72 hours of case presentation and participate in institutional quality improvement meetings on a quarterly basis to review processes of care and outcomes.
Figure 1Treatment algorithm highlighting key considerations in the initial diagnosis and management of acute STEMI and CS. CA, cardiac arrest; CPR, cardiopulmonary resuscitation; CS, cardiogenic shock; CVL, cardiovascular laboratory; Echo, echocardiography; ED, emergency department; EMS, emergency medical services; IRA, infarct related artery; LHC, left heart catheterisation; MAP, mean arterial pressure; MCS, mechanical circulatory support; PCI, percutaneous coronary intervention; RHC, right heart catheterisation; ROSC, return of spontaneous circulation; SCAI, Society for Cardiovascular Angiography and Interventions; ShiP, single access for high risk PCI; STEMI, ST segment elevation myocardial infarction.
Initial facility-based care
Patients with STEMI-CS will be directly transferred by EMS/aeromedical transport from the field or level III facility to the emergency department (ED). The primary goals of initial facility-based care for STEMI-CS patients are to conduct initial evaluation and screening to confirm ischaemic symptoms, ECG evidence of STEMI and stage of CS. The STEMI-CS team will implement all measures to expedite care, reduce redundancy, minimise time in the ED and facilitate transfer to CVL. The STEMI shock team will follow the RESCUE (Respiratory, Echo, SCAI Shock Class, Circulation, Unloading Ventricle, Early Reperfusion) algorithm as outlined in figure 1 for initial management of STEMI-CS in patients with a favourable prognosis for neurological recovery. The RESCUE algorithm provides a simple systematic guideline for initial management and stabilisation in STEMI-CS. When clinically necessary, continuous or bilevel positive pressure ventilation (CPAP or BiPAP) or endotracheal intubation will be performed in the ED. A limited bedside echocardiogram will be completed to assess left and right ventricular (RV) systolic function, screen for acute mechanical complications, the presence and severity of aortic stenosis or insufficiency and left ventricular mural thrombus. The initial management in the ED will follow established guidelines for the management of patients with AMI-CS. Intravenous inotropic therapy will be initiated in the ED with norepinephrine infusion, initial rate 5 μg/min, titrated to maintain mean arterial blood pressure greater than 60 mm Hg, maximal infusion 80 μg/min.10 11 Intravenous epinephrine infusion may be used as an alternative to or in combination with norepinephrine, initial rate 1 μg/min, maximal rate 15 μg/min. In general, the goal is to minimise use of multiple vasoactive drugs and to facilitate prompt transfer to the CVL for placement of MCS.12 The evaluation and management in the ED will be completed in a timely manner to avoid delay in transportation to the CVL. STEMI-CS patients who present with high probability of poor neurological recovery (initial asystole, unwitnessed cardiac arrest, no bystander cardiopulmonary resuscitation (CPR), ineffective or prolonged CPR >30 min, absence of ROSC, age ≥80, initial pH ≤7.0) requires careful consideration for termination of resuscitation or palliative care without escalation to MCS.
Procedural care
Patients with AMI-CS will be transported promptly to the CVL to enable invasive haemodynamic assessment, implementation of MCS, coronary angiography and primary PCI. The goal is to achieve FMC to MCS time less than 90 min in patients with stages C, D or E CS (figure 2). An intravascular microaxial LVAD, Impella CP (Abiomed, Danvers, Massachusetts, USA), will be inserted in the left ventricular cavity via ultrasound and fluoroscopic guided placement of a 14 French femoral arterial sheath with established techniques. Heparin anticoagulation will be administered using an intravenous weight adjusted bolus (70 units/kg) to achieve an activated clotting time (ACT) greater than 250–300 s. The patients will undergo periodic assessment of anticoagulation with ACT, additional heparin bolus dosing will be administered to maintain ACT 250–300 s during PCI. Diagnostic coronary angiography and PCI will be conducted using the single access for high-risk PCI technique.13 Culprit vessel-only PCI is recommended as the revascularisation strategy for patients with STEMI complicated by CS who have multivessel disease. This recommendation is based on findings from observational data and one randomised trial that showed no advantage for immediate multivessel PCI in AMI-CS.14–16 Non-culprit lesion PCI will be deferred except in cases of specific angiographic scenarios such as subtotal nonculprit lesions with reduced TIMI (thrombolysis in myocardial infarction) flow or multiple possible culprit lesions.5 17 18 The interventional cardiologist will establish central venous access and conduct right heart catheterisation after completion of culprit lesion PCI. Therapeutic hypothermia will be initiated in patients following out of hospital cardiac arrest.
Figure 2Procedural care and transition phase algorithm highlighting key considerations in the initial and early management of acute ST segment elevation myocardial infarction and CS. CO, cardiac output; CPO, cardiac power output; CS, cardiogenic shock; CVL, cardiovascular laboratory; CVP, central venous pressure; ICU, intensive care unit; LHC, left heart catheterisation; MAP, mean arterial pressure; PAP, pulmonary artery pressure; PaPi, pulmonary artery pulsatility index; PCI, percutaneous coronary intervention; RHC, right heart catheterisation; RAP, mean right atrial pressure; SCAI, Society for Cardiovascular Angiography and Interventions; ShiP, single access for high risk PCI; VIS, Vasoactive Inotropic Score.
Postprocedural care
The phases of postprocedural care following MCS for patients with STEMI-CS are defined based on temporal aspects of clinical management and patient hemodynamics. The phases are divided into three distinct critical aspects of management as defined by transition, recovery and de-escalation/explant of MCS. The transition care phase is defined as the first 60 min following transfer from the cardiovascular laboratory to the medical intensive care unit (ICU). The recovery phase is defined as the interval of MCS post-transition care to criteria for de-escalation or weaning from the intravascular microaxial LVAD. The de-escalation/explant phase is defined by invasive haemodynamic and clinical data suitable for weaning and discontinuation of MCS. Patient management will be guided by a clinical decision algorithm (figures 2 and 3) to triage patients for ongoing recovery in facility, transfer to a higher level of care or futility.
Figure 3Recovery phase algorithm highlighting key considerations in the management of acute ST segment elevation myocardial infarction and CS. CO, cardiac output; CPO, cardiac power output; CS, cardiogenic shock; CVL, cardiovascular laboratory; CVP, central venous pressure; EF, ejection fraction; GDMT, guideline-directed medical therapy; LHC, left heart catheterisation; MAP, mean arterial pressure; MCS, mechanical circulatory support; PAP, pulmonary artery pressure; PaPi, Pulmonary Artery Pulsatility Index; PCI, percutaneous coronary intervention; PT, physical therapy; OT, occupational therapy; RHC, right heart catheterisation; RAP, mean right atrial pressure; SCAI, Society for Cardiovascular Angiography and Interventions; ShiP, single access for high risk PCI; TTE, transthoracic echocardiogram; VAD, ventricular assist device; VIS, Vasoactive Inotropic Score.
Transition phase
The transition phase is focused on optimising MCS, intravenous inotropic therapy, cardiac rhythm management, mechanical ventilation, anticoagulation and early identification of bleeding or vascular access site complications. The first 60 min after transfer from CVL to ICU represents a critical phase in the management of patients following successful PCI in the setting of STEMI-CS. The primary management goals are to document optimal position, performance of MCS, obtain baseline invasive haemodynamic data from pulmonary artery catheter (PAC) to include the calculated haemodynamic parameters (cardiac index (CI), cardiac power output (CPO) and Pulmonary Artery Pulsatility Index (PAPI), confirm adequate mechanical ventilatory support and screen for bleeding or vascular access site complication (limb ischaemia). The early assessment of the clinical response to percutaneous revascularisation and MCS is crucial for decision-making regarding therapeutic strategies, recovery in facility, transfer to a higher level for escalation of support or futility.
The initial ICU patient management will include standard facility-based critical care protocols, invasive haemodynamic monitoring (MAP, CPO and PAPI), implementation of pLVAD orders, assessment for vascular access site bleeding/limb ischaemia and laboratory testing (ABG, arterial lactate).19–21 The goal is to achieve MAP >60 mm Hg, CPO >0.6 and PAPI >1.0 within the first 60 min of care in the ICU. A bedside echocardiogram will be completed to document the position of the pLVAD. The Impella CP catheter inlet should be positioned 3–4 cm below the aortic valve in the left ventricular cavity and the outlet 1.5–2.0 cm above the sinuses of Valsalva in the aorta. The initial invasive assessment of end-organ perfusion and haemodynamics will include measurement of mean RA pressure, PA SBP and diastolic pressure, mean PCWP, cardiac output, PA saturation and arterial lactate. The vasoactive inotropic score (VIS) will be calculated manually with the recorded infusion rate of vasoactive drugs, including dopamine, dobutamine, epinephrine, milrinone, vasopressin and norepinephrine using the following formula suggested by Gaies et al.12 22 Patients with venous lactate <5 mmol/L, VIS ≤30, CPO >0.6, PAPI >0.9 and adequate mechanical ventilation without acute limb ischaemia or indication for continuous veno-venous haemofiltration (CVVH) may be candidates for recovery infacility. Patients with acute limb ischaemia, unfavourable initial haemodynamic response (venous lactate >5 mmol/L, VIS ≥30, CPO ≤0.6, frequent diastolic suction alerts with CVP >12 mm Hg and PAPI <0.9) or acute renal failure requiring CVVH are at greatest risk for in-hospital mortality and may benefit from other forms of haemodynamic support (Impella RP, ECMO) or subspecialty care (advanced heart failure, vascular surgery).18–22 This subset of patients will be evaluated for suitability to transfer to a higher level of care or palliative care due to futility. Patients with successful PCI of infarct-related artery with restoration of TIMI-3 flow, stable intrinsic or ventricular paced cardiac rhythm, adequate oxygenation on mechanical ventilation and favourable neurologic prognosis without severe cerebral deficit will be transferred to a level I heart attack centre. Patients with unsuccessful PCI of the infarct related artery with TIMI flow <3, unstable cardiac rhythm (recurrent ventricular arrhymias, inadequate capture with RV pacing), unfavourable neurologic prognosis or with severe cerebral deficit, declining CPO, VIS ≥90, left ventricular ejection fraction less than 20% with or without other mechanical complications (severe mitral insufficiency, papillary muscle rupture, VSD) despite MCS will be evaluated for palliative care.
Recovery phase
The recovery phase is defined as the period care (1–48 hours) after initial stabilisation of CS with MCS to the point of de-escalation/explant, transfer to a higher level of care due to deterioration in haemodynamic status or palliative care for refractory CS with multiorgan system failure. The primary goals of this phase of care are to identify optimal CVP, dosing of inotropic and/or pressor therapy, maintenance of optimal position and function of Impella CP catheter, effective management of cardiac arrhythmias (VT, atrial fibrillation) and prevention of bleeding/vascular access site complications.
The continuous haemodynamic data (CI, CPO, PAPI), VIS and venous lactate levels will be used to assess myocardial recovery, suitability for de-escalation of MCS. The goal is to aggressively down titrate intravenous inotropic therapy based on invasive haemodynamic parameters. Myocardial recovery is defined as CPO >0.8 without intravenous inotropic or pressor therapy, and venous lactate <2 mmol/L. Patients with CPO >0.8 on low doses of pressor therapy (ie, norepinephrine <5 μg/min or VIS <10) with venous lactate <2 mmol/L may be considered for de-escalation of MCS. Patients with CPO <0.6, PAPI <0.9, development of RV failure or frequent diastolic suctions with CVP greater than 12, escalating requirement for inotropes/pressures and persistent venous lactate >3 mmol/L at 8 hours after initiation of MCS should be considered for escalation of therapy, transfer to a Level one heart attack centre.
De-escalation and explant phase
The de-escalation phase is identified by signs of improving intrinsic cardiac contractility manifested by increased arterial pulsatility with MAP ≥65 mm Hg, improvement in CI/CPO, echocardiographic parameters of left ventricular systolic function, declining inotrope requirement, adequate ventilation and oxygenation, less than moderate use of vasoactive agents, venous lactate less than 2 mmol/L. These patients are candidates for a ramp test to determine suitability to wean/discontinue MCS. The ramp test can be conducted using ‘rapid’ or ‘slow’ weaning protocols for de-escalation of MCS.23 The Impella CP support can be reduced in a stepwise manner from full to low levels of support (P9–P2) by 2P levels every 1–2 hours (rapid) or by more gradual pump speed reduction by 1–2 P levels every 4 hours (slow) while assessing readiness to explant criteria. Patients who maintain SBP >90 mm Hg, CI >2.2 L/min/m2 and CPO >0.8 without intravenous inotropic or pressor therapy with a ramp test will likely tolerate termination of MCS. Patients who fail the ramp test should undergo further evaluation, consideration for transfer to a higher level of care for escalation of therapy. Patients who fail to demonstrate recovery in 48 hours should be evaluated for transfer to a higher-level care for VAD/transplant.
Anticoagulation protocol
A bicarbonate-based purge solution will be used to maintain pump purge performance to simplify the postprocedural systemic anticoagulation regimen and reduce bleeding risk.24 Postprocedure, heparin anticoagulation will be guided by ACT, sample every hour for 4–6 hours (target ACT ≥180 s) then anti-Xa levels. Heparin anti-Xa assay will be initiated when ACT is <180 s, then every 6 hours after each dosage change, until two consecutive therapeutic levels are achieved at a constant rate of infusion, then once daily. The patients will remain on intravenous heparin infusion to maintain anti-Xa level 0.2–0.4 IU/mL until de-escalation and explant of Impella CP.25