Right Ventricular Mechanical Circulatory Support:
Mechanical circulatory support (MCS) in right ventricular cardiogenic shock must address the three major problems of cardiogenic shock; decreased oxygen delivery, increased oxygen consumption, and poor perfusion (Table 1).
Table 1: Major Problems of Cardiogenic Shock
The major benefit of MCS is that it can provide the support needed to increase oxygen delivery while significantly decreasing oxygen consumption. It does this by taking over the work of the heart and allowing the heart to rest. Additionally, MCS will typically improve mean arterial pressure (MAP) as well as cardiac output (CO), whereas most vasoactive medications usually can only do one at the sacrifice of the other. This is important because MAP and CO are the two components of cardiac power. It was discussed previously that cardiac power is best prognostic marker for cardiogenic shock.
Cardiac Power (CPO) = MAP x CO / 451
Normal CPO ≥ 1.0 W
Reduced CPO < 1.0 W
CPO requiring MCS ≤ 0.6
Right Ventricular Support Devices
*VA ECMO: Veno-arterial extracorporeal membrane oxygenation
1. Impella RP/RP Flex
General Information:
This device is designed to take over the work of the right ventricle (RV). This is done by placing a cannula through the RV that ends in the pulmonary artery (PA). The inlet side of the cannula is in the right atrium (RA) and the pump suctions blood from the RA and ejects it into the PA under continuous flow. The cannula sits across the tricuspid and pulmonic valve and can pump up to 4lpm of blood flow.
Placement:
The original Impella RP was inserted percutaneously into the femoral vein, advanced over a wire, and placed under fluoroscopy into the PA. The introducer is 23Fr and the Impella is a 22Fr pump on an 11Fr catheter. The new RP Flex is designed to be placed in the right internal jugular and advanced just like the original RP into the PA. The one turn into the PA allows for easier placement of the device.
Impella RP Placement
Physiological Benefits of the Device:
The right ventricle does not do well when it is overdistended. Because the wall is more prone to microvascular resistance and ischemia when the RV becomes overdistended, the overdistention will push the septum over to the LV and decrease the LV diameter and LV underfilling. The decreased stroke volume from RV failure will also prevent the LV from filling and both lead to decreased preload on the LV side and increased preload on the RV side. The Impella RP will drain the RV and decrease its radius which will decrease wall stress (afterload), decrease microvascular resistance, and allow for LV relaxation. This will increase oxygen supply and decrease oxygen demand. The outlet into the PA will increase cardiac output, increase preload to the LV, and improve MAP. This will improve oxygen delivery and cardiac power.
Figure 1: Physiological Benefits of the Impella RP Flex
Benefits of the Device:
One of the major benefits of this device is that it is the only option available with an internal cannula and pump and, therefore, has no extracorporeal blood. With no blood going outside the body, it is better tolerated and has fewer issues maintaining body temperatures.
Limitations of the device:
The major limitations of this device were with the original model where it was placed in the femoral vein and was difficult to place and had limited mobility. This decreased its use as the dual lumen RVAD cannulas were used more commonly. The new RP flex design should increase Impella RP use. The most common complications are bleeding and hemolysis.
2. Percutaneous Peripheral RVAD
General Information:
These are external devices where blood is pulled into a circuit and pumped back into the body. The blood is pulled out of the right atrium or right ventricle and pumped back into the pulmonary artery. The amount of blood flow allowed depends on the size of the cannulas. The bigger the size of the cannulas the more blood flow is achieved and typically allows up to 4-5lpm of blood flow. The cannulas are placed peripherally in either the femoral, subclavian, or internal jugular vein.
A. Dual Lumen Cannulas
A dual lumen cannula is usually inserted in the right internal jugular vein and comes in two varieties: Protek Duo and Quantum. Protek duo has two sizes, 29Fr & 31Fr, while the Quantum has 27Fr & 31Fr.
There are few differences between the Protek Duo and the Quantum Dual Lumen. The major difference is that the Quantum has drainage holes within the RV. Direct RV drainage appears to have some extra benefits compared to RA drainage. Both can be ordered separately from any pump/circuit system or insertion kit.
Percutaneous Dual Lumen RVAD Cannulation
Placement:
To place these devices, a catheter, usually balloon-tipped, must be floated into the pulmonary artery from the right internal jugular vein or left subclavian vein. A wire is then inserted and left in the pulmonary artery. The catheter is removed and the tract is dilated. Then the dual lumen cannula is inserted over the wire, under fluoroscopy, and the wire is then removed. The external motor and circuit are attached to the cannula.
Quantum Dual Lumen Cannula Placement
Protek Duo Dual Lumen Cannula Placement
B. Single Lumen Cannulas
This version involves two percutaneously placed single lumen cannulas. One is inserted into the femoral vein and the tip is placed in the right atrium. The other cannula is inserted in the other femoral vein or the internal jugular/left subclavian and the tip is placed in the pulmonary artery.
Placement:
To place this device, catheters must be floated both into the pulmonary artery and the right atrium. For the pulmonary artery cannula, a small, usually balloon-tipped, catheter is placed into the PA. Then a wire is inserted into the catheter and left in the pulmonary artery. The small catheter is removed, the tract is dilated and then the cannula is inserted over the wire and the wire removed. For the right atrial cannula, a wire is inserted through a small femoral catheter into the right atrium and left in place. The small cannula is then removed, the tract is dilated, and the cannula is inserted over the wire into the right atrium and the wire is then removed. These cannulations can be done under fluoroscopy or transesophageal echocardiography (TEE). The external motor and circuit are then attached to the cannula.
Percutaneous Single Lumen RVAD Cannulation
Physiological Benefits of the Device:
The physiological benefits of the percutaneous peripheral RVAD are the same as the Impella RP. The peripheral RVAD will drain the RV via the RA or will drain the RV itself and decrease the RV radius which will decrease wall stress (afterload), decrease microvascular resistance, and allow for LV relaxation. This will increase oxygen supply and decrease oxygen demand. The return cannula in the PA will increase cardiac output, increase preload to the LV, and improve MAP which will improve oxygen delivery and cardiac power.
Figure 2: Physiological Benefits of the Percutaneous Peripheral RVAD
Benefits of the Device:
The benefit of the peripheral RVAD is that it can offer slightly higher flows compared to the RP flex. This would be beneficial for larger patients who need the extra flow to keep their cardiac index > 2lpm/m2. Another benefit is that an oxygenator can be spliced into the circuit if the patient were to need increased oxygen support. This is called oxyRVAD to VPA ECMO.
Limitations of the device:
Peripheral RVADs have an external circuit and require blood to leave the body. This leads to issues with temperature regulation and is more likely to have an inflammatory response.
Having to use two single lumen cannulas with one in the groin also makes it less desirable. It is more time-consuming to place two cannulas and it makes the patient less mobile. This configuration is rarely used now with the increased use of the dual lumen cannulas and the Impella RP Flex.
3. Surgical Central RVAD
General Information:
This is an external device where the blood is pulled into a circuit and pumped back into the body. This is done with a sternotomy or thoracotomy, and the cannulas are directly placed in the RA and the PA. The size of the drainage cannula in the RA is typically > 30Fr and the return cannula in the PA is 22Fr to 24Fr. The blood is pulled out of the right atrium and pumped back into the pulmonary artery at up to 10lpm of flow.
Placement:
To place this device, the chest is opened by sternotomy or thoracotomy, and a cannula is sewn into the right atrium and the pulmonary artery under direct visualization.
Surgical Central RVAD Cannulation
Physiological Benefits of the Device:
The physiological benefits of central cannulation are the same as peripheral cannulation. It will drain the RV which decreases its radius which will decrease the wall tension and wall stress (afterload), decrease microvascular resistance, and allow for LV relaxation. This will increase oxygen supply and decrease oxygen demand. The return cannula in the PA will increase cardiac output, increase preload to the LV, and improve MAP which will improve oxygen delivery and cardiac power.
Figure 3: Physiological Benefits of the Surgical Central RVAD
Benefits of the Device:
The benefit of the central RVAD is that it can offer much higher flows compared to the RP flex or the peripheral RVAD, up to 10lpm. This would be beneficial for larger patients who need the extra flow. Another benefit is that an oxygenator can be spliced into the circuit if the patient were to need increased oxygen support. This is called oxyRVAD to VPA ECMO.
Limitations of the device:
One of the biggest limitations is that it is significantly more invasive and requires a thoracotomy or sternotomy. It also may require the chest to be left open temporarily or the cannulas must be tunneled through the skin. It also has an external circuit and requires blood to leave the body. This leads to issues with temperature regulation and is more likely to have an inflammatory response. This configuration is typically done when complications occur in the operating room and RV support is needed during a procedure. It is not often used as a planned RV support due to its invasiveness without being permanent.
4. VA-ECMO
VA ECMO will support the right ventricle but since it also supports the LV it is discussed under biventricular support
Table 6: Summary of Right Ventricle MCS Devices and Hemodynamic Benefits
| Impella RP Flex | Protek Duo/ Quantum | Central Cannulation |
Flow | 4lpm | 4-5lpm | 4-10lpm |
Sheath/Cannula Size | 23Fr | 27Fr, 29Fr, 31Fr | Drain: 32-40Fr Return: 22-24Fr |
Inflow/Drainage | Right Atrium | Right Atrium | Right Atrium/Ventricle |
Outflow/Return | Pulmonary Artery | Pulmonary Artery | Pulmonary Artery |
Cannula/Circuit | Internal Cannula | External Circuit | External Circuit |
Directional Flow | Concordant | Concordant | Concordant |
Perfusion | ↑ | ↑↑ | ↑↑↑ |
Preload (RVEDV) | ↓ | ↓↓ | ↓↓↓ |
RVEDP | ↓ | ↓↓ | ↓↓↓ |
Afterload (Wall Stress) | ↓ | ↓↓ | ↓↓↓ |
Oxygen Delivery | ↑ | ↑↑ | ↑↑↑ |
Oxygen Demand | ↓ | ↓↓ | ↓↓ |
Cardiac Power | ↑ | ↑↑ | ↑↑↑ |
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