ECMO and Ventricular Assist Devices as a Bridge to Transplant

Heart Failure Management

Many cardiac diseases, like coronary artery disease and some viral cardiomyopathy over a period of time, give rise to the condition called heart failure (HF). More than 2 million Indians suffer from HF today. The first line of management includes lifestyle modifications, as well as medical therapy. The latter uses drugs such as beta blockers, angiotensin-converting enzyme inhibitors, angiotensin receptors/blockers aldosterone antagonists, diuretics, digoxin, and many others keep getting added with more research and research and development today. Salt and fluid restriction too plays a pivotal role. Patients with a wide QRS complex in their electrocardiogram and those having a moderate to severe symptoms of HF need to have a cardiac resynchronization therapy and a patient with fatal arrhythmias needs an implantable defibrillator inserted as therapy. So, use of advanced mechanical therapies is a necessity in HF patient.

Most HF Indians have class III or class IV symptoms of dyspnea at rest of some duration or a recent origin. In this scenario of advanced mechanical support in HF patient, the two definitive therapies of nearly 6,000 in number and still on the increase are the use of ventricular assist devices (VAD) and heart transplant, which have met with some success (Box 1). This editorial briefly revises extracorporeal membrane oxygenation (ECMO) as a bridge to transplant (Figs. 1 and 2).

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Fig. 1

Mechanical assist devices in heart failure patients. (Adapted with permission and courtesy to Jaypee Publishers, New Delhi, Manual of ECMO in ICU 2018, 2^nd ed.) ECMO, extracorporeal membrane oxygenation; IABP, intra-aortic balloon pump; LVAD, left ventricular assist device.

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Fig. 2

The typical extracorporeal membrane oxygenation (ECMO) circuit.

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Extracorporeal Membrane Oxygenation

ECMO is used in cardiac or pulmonary failure in moribund patients, wherein supraoptimal medical therapy does not work at all (Figs. 3A and B). Venovenous ECMO provides adequate oxygenation and carbon dioxide removal in isolated refractory respiratory failure, while venoarterial (VA) ECMO when support is required for cardiac and/or respiratory failure.¹

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Fig. 3

Choice of extracorporeal membrane oxygenation (ECMO) in different clinical scenarios.

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Understanding the CHOICE of ECMO

Patient on VA ECMO Severe Systolic and Diastolic MR

ECMO Complications

While on ECMO one needs to worry of its complications as well, which may vary from sepsis to thrombosis. Echocardiography (ECHO) aids in helping delineate ECMO complications. Multiple views of ECHO (both two- and three-dimensional) help in ECMO success (Figs. 4A and B).², ³

ECMO Complications—Flow Obstruction

Obstruction of the inferior vena cava has been seen on a transesophageal echocardiography in the lower hepatic view (Fig. 5).

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Fig. 4

Intraventricular thrombosis is a well-known complication of myocardial infraction. Extracorporeal membrane oxygenation (ECMO) and left ventricular akinesis can increase this risk (A) seen in an ECHO picture as thrombus or cast embolus or cause flow obstruction to superior vena cava/inferior vena cava (B). Complications of ECMO may vary from and result from rupture or dysfunction of any ECMO circuit component.

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Fig. 5

Obstruction of the inferior vena cava.

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The use of integrated ECMO circuit benefits the patients well as shown in Box 1.⁴

Whenever using ECMO as a bridge to transplant or a bridge to recovery or a bridge to VAD or a bridge to nowhere important to remember that ECMO is a transient and not the definitive therapy, thus it is used as a bridge. ECMO helps as a therapeutic option while awaiting an organ for transplant or a VAD for definitive therapy.

When weaning from ECMO thus though no definitive weaning guidelines exist we clinical judgement, hemodynamic parameters and ECHO variables are useful. Monitoring on ECMO is important (Box 2) and knowledge of ECMO advantages in HF patients is very useful (Box 3 and 4).

Box 2

Objective parameters to target in cardiogenic shock on ECMO

• ScVO2 >70% • MAP >60 mm Hg (in case of full support with nonpulsatile flow) • MAP >70 mm Hg (in case of partial support with pulsatile flow) • Avoid full flow and give partial flow about 2/3 through ECMO • Maintain oxygen saturation of 90% or PaO2 of >50 mm Hg (in young patient) and >60 (in elderly and with CAD or CVA) • Maintain coronary saturation of >70%

Abbreviations: CAD, coronary artery disease; CVA, cardiovascular accident; ECMO, extracorporeal membrane oxygenation; MAP, mean arterial pressure; PaO_2, partial oxygen pressure; ScVO₂, central venous oxygen saturation.

Box 3

Advantages of ECMO in ADHF patients

• ECMO can be inserted at the bedside • It is relatively cheap (as compared to the implantable LVAD) • Gives the treating physicians some time to wait for recovery or a more stable condition • Portable, can be inserted in Cath lab using 17-21Fr cannulas • IABP to reduce afterload • Centrifugal pump at 2–4L/min • Bridge to surgical VAD, transplant or recovery

Abbreviations: ECMO, extracorporeal membrane oxygenation; IABP, intra-aortic balloon pump; LVAD, left ventricular assist device.

Box 4

ECMO pump assisted protection for transplant

▪ Possible fields of application: Respiratory failure, such as ARDS, ALI, VILI ▪ Patient and user values: Extracorporeal CO2 removal enables protective ventilation ▪ Special feature: Support of gas exchange for up to 30 days without exchanging components with focus on low flow and CO2 removal instead of oxygenation ▪ Cannulation: Percutaneous cannulation of either jugular, subclavian, or femoral vein

Abbreviations: ALI, acute lung injury; ARDS, acute respiratory distress syndrome; ECMO, extracorporeal membrane oxygenation; VILI, ventilator-induced lung injury.

Future of ECMO

Applications for ECMO have expanded today, which also include percutaneous temporary left ventricular assistance and low-flow ECMO for CO₂ removal. With new equipment of ECMO machinery, like oxygenators, pump and surface coatings, there is improvement in ECMO procedure, both by becoming more simple and more safe (Fig. 6).⁵, ⁶, ⁷

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Fig. 6

The Cardiohelp. (Adapted with permission and courtesy to Jaypee Publishers, New Delhi, Manual of ECMO in ICU 2018, 2nd ed.)

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Ventricular Assist Devices as a Bridge to Transplant

VAD is a mechanical pump that is surgically attached to one of the heart's ventricles to augment or replace native ventricular function. It can be used for the left ventricular assist device (LVAD), right VAD), or both ventricles. They are provided with external power sources that connect to the implanted pump via a percutaneous lead (driveline) that exits the body on the right abdomen. Pump output flow can be pulsatile or nonpulsatile. The need for a VAD in heart disease patients is felt even more acutely, today in 2021, than ever before as the number of patients with heart disease rises. Heart disease is the leading cause of death in the Western world. Approximately five million people in the United States have congestive heart failure.

Left Ventricular Assist Devices

LVADs are increasingly used as a bridge to transplantation. It remains unclear whether the use of pre transplant LVADs adversely affects short-term survival after cardiac transplantation (Fig. 7).

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Fig. 7

Impella and HeartMate I, two VADS in Global use.

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Components of an LVAD

The LVAD consists of a pump with controller, cannulas, and power source as explained in Box 8. Each component has its own sets on complications (Box 4 5 6 7 8).

LVAD versus Transplant

Malignancy is typically a contraindication for heart transplantation, but LVAD may be a consideration. There are no strict age limit for LVAD and no immunosuppressive therapy for LVAD. If there are psychosocial factors that make the patient ineligible for transplant, it is unlikely that the patient will be an LVAD candidate.

Summary

Advances in ECMO and VAD technology have made durable mechanical assist therapy available for select severely symptomatic HF patients. These pumps are surgically implanted at some tertiary care centers. Demonstrate mortality and quality of Life benefit patients must be undergo selection similar to heart transplant evaluation. Devices may become an important component in the management of acute HF. Although devices improve hemodynamic and metabolic parameters, there is currently no proven mortality benefit. These devices are not without complication; therefore selection of patient and device is key, requiring an integrated stepwise approach. ECMO in ADHF serves as a bridge to LVAD.