Mechanical Circulatory Support in the New Era: An Overview

Kiran Shekar; Shaun D. Gregory; John F. Fraser

Disclosures

Crit Care. 2016;20(66) 

In This Article

Research Priorities and Advancing the Field of Mechanical Circulatory Support

Despite an ongoing debate on the merits and demerits of a non-pulsatile circulation, which results in the setting of many of these MCS strategies based on rotary blood pumps, short-term clinical results are encouraging. Equally, more research is needed in the area of microcirculatory alterations in the presence of a non-pulsatile circulation. When it comes to MCS, the simplicity of rotary blood pumps results in less shear forces on blood cells and biotrauma as compared to displacement pumps.

Temporary Acute Mechanical Circulatory Support

Peripheral VA-ECMO is an imperfect but viable tool in patients with cardiac failure. Improvement in cannula design for ease of insertion eliminating the need for backflow cannulation will improve its risk/benefit ratio. Technological solutions to minimize the afterload increases imposed on the native heart and timed afterload reduction if possible to promote aortic valve opening and minimize LV distension may alleviate the need for invasive central strategies. Development of minimally invasive LV venting strategies is also desirable. Similarly, an advanced understanding of the biological burden of adding an extracorporeal circuit with vast surface area is poorly understood and basic science research to advance our understanding of the pathophysiology of ECMO is the first step towards optimization of hematological, inflammatory, infectious and pharmacokinetic issues that add to the morbidity of ECMO. Clinical research currently must focus on establishing best practice guidelines for use of ECMO in the clinical setting of cardiogenic shock or severe cardiorespiratory failure. Paracorporeal short-term VADs are an attractive but underutilized option for acute MCS and further research should focus on improving the durability of these devices,[46] minimizing morbidity especially ischemic limb complications and generating much needed evidence for their use.

Long-term Mechanical Circulatory Support-vads and Total Artificial Hearts

With durable and miniaturized pumps that have proven clinical success, and the upcoming evolution to even smaller devices, future development of MCS should focus on developing the system around the pump to reduce postoperative complications. The two most frequent adverse events identified in the sixth INTERMACS report[29] were bleeding and infection. Bleeding is partly due to the anticoagulation regime following VAD implantation and acquired von Willebrand syndrome.[47,48] Research will simultaneously focus on improving implantation techniques, through development of less-invasive procedures off-CPB, whilst developing a more complete understanding of the complex blood-VAD interaction. The relative lack of pulsatility seen with rotary VADs is known to at least contribute to gastrointestinal bleeding, arteriovenous malformations, hemolysis and pump thrombosis.[49] Interest in pulsing rotary blood pumps (i.e., speed modulation) has therefore increased and should be further explored, with the potential added benefits of increased aortic valve opening, coronary perfusion, baroreflex sensitivity and ventricular washout.

Early percutaneous driveline infections are a feared and catastrophic complication,[50] while late-onset driveline infections are the equal highest cause of death in VAD patients after 4 years of support.[29] Therefore, improved driveline development and implantation techniques along with clinically approved transcutaneous energy transfer systems are required. Meanwhile, right heart failure is a frequent and potentially fatal complication following LVAD implantation[51,26] and is associated with worse outcomes.[29] Further research and clinical experience with dual LVAD biventricular support configurations must be carried out, while the continued development of RVAD-specific devices and rotary total artificial heart technology should be completed in parallel to source an optimal solution. The low preload and high afterload sensitivities of these rotary VADs can result in venous congestion and ventricular suction events.[52] Physiological control systems, which actively change pump speed based on hemodynamic feedback variables, have been developed but not clinically accepted. Further research should focus on progression into clinical practice; however, this may depend on the development of a reliable, implantable sensor (pressure and/or flow) for hemodynamic feedback.

Global Databases and Registries

The diversity of MCS techniques, especially in the acute setting, adds to the challenges of performing meaningful clinical studies in the area. Preliminary understanding of global MCS practices and inherent heterogeneity in practice is a key pre-requisite. Similar to INTERMACS, establishment of a broader acute MCS registry collecting data in the acute setting using ECMO or pVAD based strategies may be an important step forward. The ELSO registry, over time, has become an invaluable tool; however, current data collection does not involve advanced temporary MCS strategies discussed in this article and some modifications to reporting structure may have to be made to ensure that all MCS runs based on an ECMO circuit are reported. It should be noted that most reporting to these global databases remains optional.

Global Trial Networks

Without global engagement, it will be impossible to drive the high quality randomized trials necessary for the safe development of these therapies. In the last few years, ELSO has developed strong regional representations with most geographical regions having their own active chapters that promote training, education and research. Networks such as the International ECMO Network (ECMONet), and the International Society for Rotary Blood Pumps have been formed to foster further research and development of best practice guidelines in the field of MCS. These existing platforms can be effectively used to design and conduct high quality MCS trials. Responsible and ethically-sound industry engagement is also paramount when designing such trials.

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