ECMO and the Intraaortic Balloon Pump: In Search of the Ideal Mechanical Circulatory Support Device

Cardiogenic shock is a state of profound hemodynamic compromise that results in death for at least one-third of patients.¹ Many patients – with time, supportive therapy, and revascularization as appropriate – will survive the initial hemodynamic insult and have a good long-term prognosis. Therefore, temporary therapies are needed to bridge patients to myocardial recovery or long-term cardiac replacement options such as left ventricular assist device or transplantation. Available medical therapies, including vasopressors and inotrope/vasodilators, have not been proven to reduce mortality and are associated with negative hemodynamic effects such as increased left ventricular afterload and tachycardia. A mechanical device for temporary circulatory support is an attractive alternative.

The ideal mechanical circulatory support (MCS) device could be placed rapidly at bedside with few serious complications and fully restore systemic circulation, normalize end-organ perfusion, increase myocardial blood flow, and decrease myocardial oxygen demand. The search for this ideal device began in the 1960s with the development of the intraaortic balloon pump (IABP), still the most frequently used MCS device.² Clinicians may also choose from axial flow pumps (Impella; Abiomed), percutaneous cardiac bypass (TandemHeart; CardiacAssist), and bypass with extracorporeal membrane oxygenation (ECMO). Unfortunately, none of these devices meet all of the criteria for the ideal MCS device, and clinical trials have failed to show a definitive mortality benefit of any existing device for the treatment of cardiogenic shock. Simultaneous use of two MCS devices is possible and may be considered when shock persists despite the use of a single device or when the advantages of one device compensate for limitations of the other. 

In this month’s issue of the Journal of Invasive Cardiology, Cheng and colleagues report on one such combination, the simultaneous use of ECMO and IABP.³ This meta-analysis of observational studies comparing use of ECMO and IABP vs ECMO alone for treatment of cardiogenic shock showed no difference in overall mortality, both in the full cohort and when examining subgroups by etiology of shock and relative timing of device deployment. In theory, the combined hemodynamic effects of these two devices approach the ideal MCS device, since the putative benefits of the IABP seem well suited to compensate for the limitations of ECMO. Percutaneous veno-arterial ECMO can provide full cardiopulmonary support for days or weeks but may increase left ventricular (LV) afterload and myocardial oxygen demand because oxygenated blood is returned to the femoral or axillary artery, thereby increasing aortic pressure. Percutaneous ECMO does not decompress the LV. LV ballooning and respiratory failure may result. The IABP reduces afterload and decreases myocardial oxygen demand. Similarly, ECMO may not improve coronary oxygen delivery. Oxygenated blood from the arterial cannula must travel retrograde to perfuse the coronaries. Patients may also expel blood anterograde across the aortic valve, and in the setting of concomitant respiratory failure, this anterograde flow may be relatively deoxygenated. IABP has been shown to improve coronary flow, at least in normal coronary arteries. Nonetheless, Cheng et al find no benefit of this combination compared with ECMO alone.

The negative results of this study fit with recent observational and randomized studies of IABP for patients with myocardial infarction and cardiogenic shock. The IABP SHOCK II study randomized 600 patients with ST-segment elevation myocardial infarction and cardiogenic shock to IABP or medical therapy at the time of primary percutaneous coronary intervention (PCI). There was no difference in mortality between the two groups at 30 days or 1 year.⁴ A meta-analysis of observational studies reported that IABP was not associated with a survival benefit among patients with cardiogenic shock treated with PCI.⁵ Why doesn’t the IABP show a survival benefit in trials, despite over four decades of clinical use and encouraging hemodynamic studies? The effects of IABP may be insufficient to improve survival for patients with severe hemodynamic compromise, whether or not ECMO is used. Or, the increased rate of complications associated with the IABP could counterbalance any hemodynamic benefit. Alternatively, the IABP may provide a clinical benefit that, to date, has not been accurately assessed by clinical trials. Observational studies are limited by selection bias. Patients receiving IABP (or the combination of ECMO and IABP) may be sicker at baseline than patients used for comparison. Randomized trials of patients in cardiogenic shock are challenging to perform and may enroll patients who differ from the broader cardiogenic shock population. All of these caveats may also be applied to studies of ECMO. No randomized studies of ECMO for cardiogenic shock have been performed, and observational studies have not provided convincing proof of efficacy. Neither ECMO nor IABP have independently demonstrated a mortality benefit; perhaps it is unsurprising that the combination also fares poorly in the current meta-analysis. 

We remain in search of the ideal MCS device. Only randomized controlled trials can provide definitive answers about when to use MCS and which device to select. In the absence of these trials (which may never occur), physicians will likely continue to reach for MCS for their sickest patients. The various available percutaneous MCS devices can be viewed on a spectrum of increasing hemodynamic support and concomitant risk of complications. Combination therapy with percutaneous ECMO and IABP is near the invasive extreme of this spectrum, providing full hemodynamic support at the expense of multiple large vascular cannulae with resultant risk of bleeding, infection, hemolysis, and embolization. Other options exist. Central cannulation for ECMO provides more stable vascular access and can include a vent to unload the LV. Alternative MCS devices, such as TandemHeart and Impella, have been incompletely studied but appear to offer significant hemodynamic support with fewer complications than ECMO. A recent consensus document offers guidance on the use of MCS,⁶ but ultimately device selection will be determined by clinician and institutional experience. MCS decision-making can benefit from the “heart team” model, using multidisciplinary teams including interventional cardiologists, heart failure specialists, and cardiothoracic surgeons to best deploy and manage support devices.

When possible, clinicians should attempt to match a patient’s hemodynamic deficits to the appropriate support modality (Figure 1). If an initial treatment fails, escalation of hemodynamic support may be required. Simultaneous use of ECMO and IABP may be a viable option, but this remains speculative, absent any randomized data. Ultimately, new technologies are needed to achieve optimal hemodynamic support with minimal complications.

References

1. Kunadian V, Qiu W, Ludman P, et al. Outcomes in patients with cardiogenic shock following percutaneous coronary intervention in the contemporary era: an analysis from the BCIS database (British Cardiovascular Intervention Society). JACC Cardiovasc Interv. 2014;7:1374-1385. Epub 2014 Dec 20.
2. Stretch R, Sauer CM, Yuh DD, Bonde P. National trends in the utilization of short-term mechanical circulatory support: incidence, outcomes, and cost analysis. J Am Coll Cardiol. 2014;64:1407-1415. Epub 2014 Oct 04.
3. Cheng R, Hachamovitch R, Makkar R, et al. Lack of survival benefit found with use of intraaortic balloon pump in extracorporeal membrane oxygenation: a pooled experience of 1517 patients. J Invasive Cardiol. 2015;27:453-458. Epub 2015 Jul 15.
4. Thiele H, Zeymer U, Neumann FJ, et al. Intraaortic balloon counterpulsation in acute myocardial infarction complicated by cardiogenic shock (IABP-SHOCK II): final 12 month results of a randomised, open-label trial. Lancet. 2013;382:1638-1645. Epub 2013 Sep 10. 
5. Sjauw KD, Engstrom AE, Vis MM, et al. A systematic review and meta-analysis of intraaortic balloon pump therapy in ST-elevation myocardial infarction: should we change the guidelines? Eur Heart J. 2009;30:459-468. Epub 2009 Jan 27. 
6. Rihal CS, Naidu SS, Givertz MM, et al. 2015 SCAI/ACC/HFSA/STS clinical expert consensus statement on the use of percutaneous mechanical circulatory support devices in cardiovascular care: endorsed by the American Heart Association, the Cardiological Society of India, and Sociedad Latino Americana de Cardiologia Intervencion; Affirmation of Value by the Canadian Association of Interventional Cardiology-Association Canadienne de Cardiologie d’intervention. J Am Coll Cardiol. 2015;65:e7-e26. Epub 2015 Apr 12.

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From Duke University Medical Center, Department of Cardiology, Durham, North Carolina.

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.

Address for correspondence: Michael Sketch Jr, MD, Duke University Medical Center, Cardiology, 7430 Hospital North, Box 3157, Durham, NC 27710. Email: michael.sketch@duke.edu