ECMO (Extracorporeal Membrane Oxygenation) is a temporary, life-saving treatment used to provide cardiopulmonary support for patients experiencing severe heart and/or lung failure. When both the heart and lungs are failing, ECMO can be used as a bridge to heart and lung transplant for patients who need both organ transplants but are not stable enough to survive without mechanical support while awaiting donor organs.

This situation often arises in patients with severe, end-stage heart failure and respiratory failure, where the heart and lungs are both failing to provide sufficient oxygenation to vital organs. ECMO can provide crucial support, allowing the patient time to stabilize, undergo evaluation for transplantation, and wait for a donor heart and lung.

What is ECMO?

ECMO is a machine that temporarily takes over the function of the heart and/or lungs, depending on the type of ECMO being used:

1. VA-ECMO (Veno-Arterial ECMO):
• Provides support for both cardiac and pulmonary function.
• Blood is drawn from a vein (usually the femoral vein or jugular vein), oxygenated in the ECMO machine, and then returned to the body through an artery (typically the femoral artery or carotid artery).
• This is the most commonly used type of ECMO in cases where both heart and lung support are required, such as for heart and lung transplant candidates.
2. VV-ECMO (Veno-Venous ECMO):
• Primarily used for lung support, but not typically used alone for heart and lung transplants.
• Blood is drawn from a vein, oxygenated in the ECMO machine, and then returned to the body via another vein. This type of ECMO is mainly used when lung support is the primary concern.

For patients needing both heart and lung support, VA-ECMO is typically used to maintain adequate circulation and oxygenation while they await a suitable donor heart and lungs.

Indications for ECMO as a Bridge to Heart and Lung Transplant

ECMO is employed for patients in acute or end-stage heart and lung failure who are not stable enough to wait for a heart and lung transplant without mechanical support. Common indications include:

1. End-Stage Heart Failure and Respiratory Failure:
• Patients with severe cardiogenic shock or end-stage heart failure who also experience severe respiratory failure may require ECMO support until a donor heart and lung are available.
• This could result from conditions like dilated cardiomyopathy, heart valve disease, or pulmonary hypertension.
2. Acute Myocardial Infarction (Heart Attack) and ARDS (Acute Respiratory Distress Syndrome):
• Patients who suffer a massive heart attack (myocardial infarction) along with ARDS, a condition in which the lungs fail to provide adequate oxygen exchange, can benefit from ECMO as they await a heart and lung transplant.
3. Post-Cardiopulmonary Bypass:
• After a complex heart surgery, such as coronary artery bypass grafting (CABG), valve replacement, or heart surgery complications, ECMO may be required if the patient develops severe heart failure and respiratory failure.
4. Pulmonary Hypertension with Right Heart Failure:
• Severe pulmonary hypertension can lead to right heart failure, causing low blood oxygen levels and requiring ECMO support to prevent organ damage until a transplant can be performed.
5. Complex Pulmonary Conditions:
• Patients with chronic lung diseases (such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, or emphysema) who also develop heart failure may need ECMO to provide adequate oxygenation while waiting for both a heart and lung transplant.
6. Multisystem Organ Failure:
• Patients with multisystem organ failure, where both the heart and lungs fail simultaneously, may require ECMO to support both organs until a combined heart-lung transplant becomes feasible.

How ECMO Works for Heart and Lung Transplantation

For patients needing a combined heart-lung transplant, ECMO acts as a temporary life-support system, ensuring adequate blood circulation and oxygenation while the patient is awaiting a donor organ. The process works as follows:

1. Vascular Access:
• Cannulas are inserted into large veins and arteries, typically the femoral vein, femoral artery, or jugular vein.
• These cannulas are used to draw blood out of the body, oxygenate it, and then return the oxygenated blood back into the circulatory system.
2. ECMO Circuit:
• Blood is pumped through the ECMO circuit, which includes a pump and an oxygenator (which adds oxygen and removes carbon dioxide).
• In the case of VA-ECMO, the machine provides both cardiac and pulmonary support, circulating oxygenated blood back to the body, bypassing the heart and lungs temporarily.
3. Heart and Lung Support:
• The VA-ECMO system ensures that the heart and lungs are temporarily bypassed, and it provides oxygenation to the body. The heart may be resting if it is severely damaged, and the lungs are able to rest if they are not functioning properly.
• This allows the organs to recover (if possible) and provides time for the patient to stabilize while awaiting a donor heart and lungs.
4. Monitoring and Adjustments:
• The ECMO machine needs constant monitoring and adjustments to ensure proper oxygenation, blood pressure, and circulation. The team will also manage anticoagulation therapy (to prevent blood clots) and monitor for complications like infection or bleeding.
5. Anticoagulation Therapy:
• Patients on ECMO typically receive anticoagulants (blood thinners) to prevent clotting in the ECMO circuit. However, this increases the risk of bleeding and requires careful management.

Benefits of ECMO as a Bridge to Heart and Lung Transplant

1. Life Support:
• ECMO provides essential circulatory and respiratory support, keeping patients alive who would otherwise not survive until a donor organ becomes available.
2. Time for Stabilization:
• ECMO allows time for the patient's condition to stabilize, making them more suitable for heart-lung transplantation and improving their chances of survival post-transplant.
3. Organ Protection:
• ECMO helps protect vital organs such as the brain, kidneys, and liver by ensuring that they receive adequate oxygen and blood flow despite heart and lung failure.
4. Lung and Heart Rest:
• The machine provides rest for both the heart and lungs, reducing stress on the organs and allowing them to recover temporarily, if possible.
5. Bridge to Transplant:
• ECMO can serve as a bridge for patients awaiting a combined heart and lung transplant, improving their survival chances during the waiting period.

Risks and Complications of ECMO

Although ECMO can save lives, it comes with significant risks and complications:

1. Infection:
• Invasive procedures to insert cannulas and the need for long-term monitoring increase the risk of infection (such as bloodstream infections or pneumonia).
2. Bleeding:
• Anticoagulation therapy is required to prevent clotting in the ECMO circuit, but this increases the risk of bleeding. Patients may experience internal bleeding or bleeding at the cannulation site.
3. Organ Dysfunction:
• Prolonged ECMO support can lead to kidney failure, liver dysfunction, or neurological complications due to decreased perfusion or complications from the ECMO machine.
4. Blood Clots:
• Clotting within the ECMO circuit can block blood flow and cause significant complications, such as stroke, organ failure, or loss of ECMO support.
5. Vascular Complications:
• There is a risk of vascular injury at the cannulation sites or dislodgement of the cannulas, which could lead to bleeding or loss of ECMO support.
6. Right Heart Failure:
• In some cases, ECMO can place a significant load on the right heart, leading to right heart failure or other circulatory issues.
7. Mechanical Complications:
• The ECMO machine is a complex system that can experience failure or mechanical issues that need to be addressed immediately.

Post-ECMO and Heart-Lung Transplant Surgery

Once a suitable donor heart and lungs are found, the patient will undergo heart-lung transplant surgery. The process typically follows these steps:

1. Lung and Heart Transplant Surgery:
• The patient undergoes surgery to remove the diseased heart and lungs and implant the donor organs. The transplant team works to ensure that both organs are properly connected and functioning.
2. ECMO Removal:
• ECMO is gradually discontinued as the transplanted organs begin functioning. Once the transplanted heart and lungs are working adequately, ECMO support is stopped.
3. Post-Transplant Care:
• After surgery, the patient will be closely monitored for complications like rejection, infection, or issues with the transplanted organs. Immunosuppressive medications are started to prevent rejection.
4. Rehabilitation:
• Following a heart-lung transplant, the patient will undergo rehabilitation to regain strength and improve their cardiovascular and respiratory function.

Prognosis and Survival Rates

Survival rates for patients on ECMO as a bridge to heart-lung transplant can vary, but the overall outcomes are promising when ECMO is used appropriately:

• Survival to transplant: Many patients who are placed on ECMO for a heart-lung transplant survive to receive a donor organ. However, long-term survival after receiving both a heart and lung transplant can depend on several factors, such as the patient’s age, the underlying condition, and how well the organs function after transplant.
• One-year survival rate after heart-lung transplant is around 70-80%.
• Five-year survival rate after heart-lung transplant can range from 50-60%.

Conclusion

ECMO is a critical tool used as a bridge to heart-lung transplant for patients with severe heart and lung failure. It offers life-saving support by temporarily taking over both heart and lung function, allowing patients to survive the wait for a donor organ. Although ECMO is effective, it carries significant risks, including infection, bleeding, and organ dysfunction, and requires careful monitoring and management. When used appropriately, ECMO provides essential time for stabilization and improves outcomes for patients awaiting heart and lung transplantation.