Circulatory Support for Shock Complicating Myocardial Infarction

ABSTRACT: We discuss a patient with acute myocardial infarction complicated by cardiogenic shock (AMI-CS) who underwent percutaneous coronary intervention and hemodynamic support with a new short-term percutaneously inserted device, the Impella CP (Abiomed). We also review the evidence for mechanical circulatory support and management strategies in patients with AMI-CS.

J INVASIVE CARDIOL 2014;26(8):E109-E114

Key words: Impella CP, cardiogenic shock, AMI

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Cardiogenic shock complicating acute myocardial infarction (AMI-CS) continues to have a high mortality of 40%-50% despite early revascularization and adjunctive therapies. AMI-CS is predominantly due to left ventricular pump failure, complicates 5%-7% of cases of ST-elevation myocardial infarction (STEMI), and is a leading cause of hospital death after myocardial infarction.

 Patients who have AMI-CS shock have a high prevalence of risk factors such as diabetes, hypertension, and hyperlipidemia, but have a lower prevalence of preexisting renal dysfunction and heart failure of approximately 5%-10%. The patients that survive acute cardiogenic shock have good long-term outcomes, with a 6-year survival rate of 62.4% in the revascularization arm of the SHOCK trial.¹ Thus, improved early management in these acutely ill patients without preexisting end-organ dysfunction has the potential to substantially affect quantity and quality of life.

We discuss a patient with AMI-CS who underwent percutaneous coronary intervention (PCI) and hemodynamic support with the Impella CP (Abiomed), a new, short-term, percutaneously inserted device, and review the evidence for mechanical circulatory support and management strategies in patients with AMI-CS.

Case Report. The patient was a 71-year-old man with hypertension, hyperlipidemia, and cerebrovascular disease. He presented to his local hospital with chest and epigastric discomfort for 7 days. Electrocardiogram showed left bundle branch block. Initial transthoracic echocardiogram (TTE) showed left ventricular ejection fraction (LVEF) of 40% with anterior and anteroseptal hypokinesis. Coronary angiogram showed 90% distal left main (LMCA) stenosis, proximal 70% mid left anterior descending (LAD) stenosis with occlusion in the mid segment, 70% first diagonal (D1) stenosis, 70% proximal circumflex (LCX) stenosis, 70% proximal right coronary artery (RCA) stenosis, and 80% mid RCA stenosis. Left ventricular end-diastolic pressure (LVEDP) was 35 mm Hg.  He was taken to the operating room for emergent coronary artery bypass graft (CABG) surgery. In the operating room, transesophageal echocardiogram demonstrated LVEF of 10%, with moderate mitral regurgitation. Swan-Ganz catheterization pressures showed pulmonary artery systolic pressure (PASP) of 80 mm Hg, and cardiac index (CI) of 1.7 L/min/m². The surgery was aborted, an intra-aortic balloon pump (IABP) was placed, and he was started on milrinone; the patient was then transferred to our institution for further management.

Admission hemodynamics revealed right atrial pressure (RAP) of 18 mm Hg, pulmonary artery pressure (PAP) of 72/36 mm Hg, and CI of 1.59 L/min/m ². Chest x-ray showed pulmonary edema and the patient required bilevel positive airway pressure. He was also in renal failure, with creatinine 2.1 mg/dL. His operative risk for CABG was felt to be excessive. He was not a candidate for transplant or durable left ventricular assist device (LVAD) because of age and other comorbidities. He thus underwent high-risk multivessel PCI and hemodynamic support with an Impella CP device. 

The patient underwent PCI of the proximal and mid RCA with 3.0 x 38 mm and 3.0 x 18 mm Xience Xpedition drug-eluting stent (DES) implantation (Figures 1A and 1B), PCI of the diagonal (D1) with a 2.25 x 18 mm Xience Xpedition DES, PCI of the LMCA into the LAD with a 3.0 x 18 mm Xience Xpedition DES, and PCI of the LMCA into the LCX with a 3.0 x 24 mm Promus Element DES (Figures 2A and 2B). The LAD was not intervened upon, given occlusion for 7 days. An Impella CP was inserted prior to the PCI and was left in for hemodynamic support. His hemodynamics immediately prior to the intervention revealed a RAP of 16 mm Hg, PAP of 62/24 (38) mm Hg, CI of 2.3 L/min/m², and systemic vascular resistance (SVR) of 3339 dyn·s/cm⁵ despite intravenous milrinone at 0.5 µg/kg/min, nitroglycerin, and IABP. Hemodynamics immediately after the procedure were unchanged, but by the next morning, they had improved, with RAP of 8 mm Hg, PAP of 46/11 mm Hg, CI of 2.8 L/min/m², and SVR of 1683 dyn.s/cm⁵. Attempts to wean the Impella 2 days later were not tolerated, with dyspnea and increased filling pressures. Oral and intravenous afterload reduction was initiated, and the Impella was weaned after 5 days. The device was removed and hemostasis was obtained with manual compression for 40 minutes without complications. There was no clinically significant hemolysis on support. Peak LDH was 661 U/L, plasma hemoglobin was <30 mg/dL, and he did not require transfusion. His creatinine improved to 1.3 mg/dL within 1 week after revascularization. Milrinone was gradually weaned over the subsequent 10 days. Repeat echocardiogram 3 weeks after revascularization revealed LVEF of 30%. The patient was discharged home with close follow-up in the clinic.

Discussion. Cardiogenic shock is a common and devastating complication of AMI, yet relatively little information exists on risk stratification and management strategies. The most important development in the last decade has been a standard of early revascularization after results of the SHOCK trial in 2002 showed a survival difference at 6 months. However, despite early revascularization, early mortality remains in excess of 40% in contemporary series.^2,3

The primary problem caused by AMI-CS is low cardiac output, which may or may not improve shortly after revascularization. During this early period, multisystem organ failure can lead to significant morbidity and mortality. Mechanical circulatory support may prevent or sometimes reverse this end-organ dysfunction. There is extensive experience showing improved survival and quality of life with mechanical circulatory support in patients with advanced chronic heart failure as well as patients with chronic heart failure who progress to cardiogenic shock in the absence of MI. In contrast, there are limited data on mechanical circulatory support with patients with AMI-CS, and management is usually center specific.  A variety of support devices are available for AMI-CS, including the IABP, percutaneous and surgically implanted LVADs, and extracorporeal membrane oxygenation (ECMO). The studies for many of these devices are single center and retrospective, and the randomized trials are small and not powered to detect survival differences. Therefore, the 2013 American College of Cardiology/American Heart Association ST-elevation MI guidelines provide a IIb recommendation with level of evidence C for LVADs in AMI-CS and a IIa recommendation for IABP.⁴

The IABP is the most widely-used device for AMI-CS. Studies in the thrombolytic era showed survival benefit in this setting with IABP.⁵ It has also been shown to improve survival in high-risk cardiac surgery^6-8 and to be useful for mechanical complications after AMI.⁹  However, several recent meta-analyses have shown no survival benefit from IABP when used with PCI.^10-12 The IABP was studied most rigorously in a 600-patient multicenter trial of patients with AMI-CS who underwent early revascularization, and did not show a difference in 30-day mortality.¹³ The 2013 STEMI guidelines have thus downgraded IABP in AMI-CS from a I to a IIa recommendation.⁴ IABP support may be useful in mild degrees of cardiogenic shock by decreasing afterload, but in moderate and severe shock with profound low output, it may not provide adequate active support.

The Impella 2.5 is a catheter-mounted device percutaneously inserted through a 13 Fr sheath through the femoral artery, and can provide up to 2.5 L of flow. The ISAR-SHOCK trial randomized 26 patients with AMI-CS to IABP or Impella 2.5. The cardiac index was higher at 30 minutes in the Impella group, but 30-day survival was similar between the groups.¹⁴ A multicenter registry of 120 patients who received the Impella 2.5 showed a high 30-day mortality of 64%. Many of these patients had severe shock and were placed on support as a last resort after failed conventional therapy, and 41% had cardiopulmonary resuscitation (CPR) prior to device implantation.  The Impella 2.5 device may not provide adequate support in patients with profound shock, and an early switch to higher-level support may be necessary.¹⁵

The Impella 5.0 is a more powerful device that can provide up to 5 L/min of flow. It has a 21 Fr sheath that requires insertion through the axillary artery or via femoral cutdown, limiting widespread emergency use in catheterization laboratories. Published AMI-CS experience is extremely limited.  A review of 34 patients with AMI-CS had 9 patients who received early Impella 5.0 support and 25 patients who received Impella 2.5 support. Eight of 25 patients in the Impella 2.5 group were upgraded to Impella 5.0 based on clinical criteria. At 30 days, 6 out of 25 patients in the Impella 2.5 group were alive, 3 of whom had been upgraded to Impella 5.0. In the Impella 5.0 group, 3 out of 9 patients were alive at 30 days.¹⁶  

The Impella CP is a similar device that received United States Food and Drug Administration approval in September of 2012. It can be placed percutaneously through a 14 Fr sheath, and provides 3-3.3 L/min of flow, approximately 1 L/min higher than the Impella 2.5.^17,18 There are no reports yet in AMI-CS patients, but in our case, it provided adequate hemodynamic support and ease of implantation in a patient with moderate shock.

The TandemHeart is another percutaneously inserted LVAD, with the in-flow cannula placed transseptally into the left atrium and the outflow cannula into the femoral artery. It can provide up to 5 L/min of flow with 17 Fr arterial cannulae. A randomized controlled trial of 33 patients presenting within 24 hours of developing CS who received TandemHeart vs IABP showed higher cardiac index, mean arterial pressure, and lower pulmonary capillary wedge pressure in the TandemHeart group.  No survival difference was observed at 30 days. The study was stopped early in part due to low recruitment, and was not powered to investigate mortality benefit.¹⁹ A second randomized controlled trial of 41 patients with AMI-CS randomized to TandemHeart vs IABP  showed similar hemodynamic results. There was more bleeding and limb ischemia in the TandemHeart group.²⁰  Kar et al reviewed 117 patients at a single center who received TandemHeart for refractory cardiogenic shock (ischemic and non-ischemic) despite inotropes and IABP. Fifty-six of these patients underwent CPR just prior to device implantation. The mean time from onset of shock to placement of TandemHeart was 2.6 days. Hemodynamic parameters were significantly improved, and survival at 30 days was 59.8%. Hemodynamic improvement without clinical improvement in the non-survivors suggests other mechanisms, such as inflammation, complications, and established multisystem organ failure, that may have led to mortality. Furthermore, patients who were not candidates for long-term LVAD therapy or transplant, but could not be weaned off the Tandemheart, had poor survival.²¹

Several generations of surgical LVADs have been used in AMI-CS (Table 1). Hill and colleagues reported  a case of postinfarction shock supported with a Thoratec Pierce-Donachy LVAD until transplant in 1986.²² In 1990, a multicenter study of 72 patients receiving the Thoratec Pierce-Donachy device included 17 patients with AMI-CS. Of these patients, 76% survived to heart transplant.²³ A report of  25 patients with AMI-CS supported with the ThermoCardioSystems, Inc LVADs early (<2 weeks) or late (>2 weeks) after MI showed a survival to transplant of 67% and 60%, respectively. An additional 7% in the early group were explanted.²⁴ These studies also established the safety of apical cannulation in recently infarcted friable myocardium.  Park reported on 7 patients with AMI-CS supported by the Heartmate 1000 IP LVAD. Six of these patients (86%) survived to transplant.²⁵ A review of 17 patients with AMI-CS supported with the pulsatile paracorporeal Abiomed BVS 5000 between 1994 and 2002 showed a 54% survival rate in patients receiving LVADs, and very poor prognosis with patients requiring BI-VAD support.²⁶ The Abiomed BVS registry reported on 44 patients with AMI-CS who had a survival to discharge rate of 36%.²⁷ The Abiomed AB 5000 registry of 100 patients with AMI-CS revealed 40% cumulative survival or discharge at 30 days.²⁸ Investigators at the University of Pennsylvania compared 49 patients who received LVADs for AMI-CS to 66 patients who received LVADs for chronic ischemic cardiomyopathy.  Seventy-four percent of the AMI-CS group were successfully bridged to transplant, compared to 61% of the chronic ischemic patients. The in-hospital mortality rate was 33% for the AMI-CS patients and 41% for the chronic ischemic patients.²⁹  A recent report of 13 patients who received durable LVADs for AMI-CS reported 92% survival to hospital discharge, and 86% 1-year survival.³⁰ Though the small size of these studies makes achieving statistical significance difficult, their consistency suggests that in selected patients with AMI-CS, mechanical circulatory support has the potential to dramatically improve survival.

Veno-arterial ECMO for cardiogenic shock can be placed centrally, typically for postcardiotomy shock in the operating room, or peripherally through the femoral artery and vein for shock and cardiac arrest. It can be instituted quickly and provide full support, but it does not decompress the left ventricle and has a relatively high incidence of complications. High mortality and frequent bleeding complications limited use in the 1970s and 1980s, but there has been a recent resurgence in interest with the advent of new pumps, oxygenators, and smaller portable devices. A review of 10 patients with acute MI and cardiovascular collapse supported with ECMO showed a 40% long-term survival.³¹ The University of Pittsburgh experience of 33 patients with AMI-CS showed a 1-year survival rate of 64%.³² In another series of 27 patients with AMI-CS supported with ECMO, 59% survived to discharge.³³ A study of 20 patients with AMI-CS who had ECMO instituted during cardiopulmonary resuscitation had a 50% survival to discharge.³⁴  ECMO can also be used to successfully provide support during PCI³⁵  and as a bridge to LVAD therapy.³⁶

Patients can have AMI-CS of varying severity, requiring different levels of support and management, creating challenges in designing randomized controlled trials and formulating guideline recommendations for particular devices. One strategy in the management of patients with AMI-CS is to ensure adequate perfusion and end-organ function using various mechanisms, including pressors, inotropes, percutaneous VADs, surgical VADs, or ECMO.  Implicit in this approach is the concept of escalating therapy until goals are met before irreversible end-organ dysfunction occurs. A retrospective study analyzed 138 patients with AMI-CS, all of whom who received intensive medical therapy and IABP. Forty-three of these patients were treated with intensive medical therapy, 77 were treated with PCI or CABG, and 18 were treated with circulatory support with VAD/ECMO or transplant. The circulatory support/transplant group had a lower in-hospital mortality (33%) compared with the revascularization group (63%) and the medical therapy group (81%). Five-year survival for the VAD/ECMO/heart transplant group was 63% compared with 21% in the revascularization group and 6% in the intensive therapy group.³⁷ The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) is a multicenter registry of surgical LVADs in the United States. The sickest subgroup of patients receiving surgical LVADs is classified as INTERMACS level I, critical cardiogenic shock. These patients, who include some with AMI-CS, are “crashing and burning,” with life-threatening hypotension and rapidly escalating inotrope requirements. In these patients, 1-year survival is 70%.³⁸ Thus, adequate support of the circulation by mechanical circulatory support may have the capability to normalize cardiac output and reverse end-organ dysfunction in critically ill patients.

The optimal care of these complicated patients requires individualized care and multidisciplinary collaboration. Close communication and a coordinated approach among intensive care and transplant physicians, interventional cardiologists, and cardiac surgeons with well-defined goals and management approaches will provide the best care for these patients (Figure 3).  A patient with a first MI with early revascularization, whose hemodynamics are expected to improve after myocardial stunning improves, may be better served by a short-term, easily removable percutaneous device  in the catheterization laboratory. The degree of shock and assessment of right ventricular function dictates the level of support required. TandemHeart has more published experience for profound shock in this setting. A patient with a mechanical complication from AMI may also be bridged with a percutaneous device until definitive intervention. A sicker patient with recent resuscitation from cardiac arrest and biventricular failure may be appropriate for ECMO in the intensive care unit while neurologic status is assessed and further options contemplated. A shock patient with known ischemic cardiomyopathy who suffers a new infarction or a patient with a large-territory infarction that either is completed or cannot be revascularized is unlikely to recover, and may need a surgical LVAD as either a bridge to transplant or long-term therapy. A percutaneous LVAD may be useful in this situation to stabilize the patient, but is unlikely to provide definitive therapy. Patients with other comorbidities, such as severe underlying disease of other organ systems, advanced malignancy, significant neurologic insult, or a very late presentation with established severe multisystem organ failure is unlikely to recover, and may need a palliative care approach. There is not enough evidence currently to recommend standardized approaches, analogous to the door-to-balloon time in ST-elevation MI or early goal-directed therapy in sepsis, but as more data become available, similar standards and algorithms for cardiogenic shock may provide the most efficient management that maximizes survival.

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From the Division of Cardiovascular Diseases, University of Alabama at Birmingham, Birmingham, Alabama.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted September 3, 2013, provisional acceptance given November 7, 2013, final version accepted December 11, 2013.

Address for correspondence: Deepak Acharya, MD, Division of Cardiovascular Diseases, THT 321, 1900 University Blvd, Birmingham, AL 35294. Email: dacharya@uab.edu