Dr. Navin Kapur and the Physiology of IABP and VA-ECMO 

Navin Kapur, M.D., FAHA, FACC, FSCAI, FHFSA, chief medical & scientific officer at J&J MedTech, discusses the physiology of mechanical circulatory support (MCS) with the intra-aortic balloon pump (IABP) and veno-arterial extracorporeal membrane oxygenation (VA-ECMO).

IABP

The IABP sits in the descending aorta, providing diastolic augmentation by inflating during diastole and infusing the coronary arteries, and then deflating during systole. Dr. Kapur explains that IABP is also known as an intra-aortic counterpulsation pump (IACP), because when the balloon deflates, it reduces afterload, theoretically facilitating ejection of blood into systemic circulation.

“It has to be timed to systole and diastole,” Dr. Kapur emphasizes, which can be challenging in patients with arrhythmias. In addition, the device’s counterpulsation relies heavily on stroke volume. Therefore, the IABP may not be a good choice for patients with very low stroke volume and minimal pulsation since the device can’t produce as much counterpulsation and thus is not as effective at reducing afterload or augmenting cardiac output.

Dr. Kapur explains that the IABP is most commonly used in patients who have critical aortic stenosis, who have preserved or normal heart function, or who have severe mitral regurgitation plus heart failure. “Where you don’t want to see balloon pump, for example, is in AMI cardiogenic shock,” Kapur states, “because in cardiogenic shock, you have that severely reduced native stroke volume. You have minimal pulsation. As a result, you don’t get the benefits of counterpulsation. And so that’s where the balloon pump starts to find its limitations in terms of its application.”

VA-ECMO

VA-ECMO drains blood from the venous system, pumps it through a rotary flow pump and oxygenator, and returns the blood to the arterial system, reversing flow up the aorta and increasing afterload. As a result of the mechanism of action of VA-ECMO, the native heart has to pump against the VA-ECMO pump.

VA-ECMO is primarily used for ECMO-assisted cardiopulmonary resuscitation (ECPR) as it is most effective when there is no cardiac function, such as in patients in cardiac arrest. Dr. Kapur notes, however, that the fundamental clinical mantra for VA-ECMO is: “As soon as you go on VA-ECMO, you want to come off VA-ECMO.” He emphasizes that there is a short window for using VA-ECMO to stabilize a patient in cardiac arrest, but then you need to transition that patient to something else.

Due to its afterload increasing physiology, VA-ECMO may be less appropriate for patients with AMI cardiogenic shock, in whom an increase in afterload can increase infarct size and subsequent damage to the heart. In addition, the oxygenator in the VA-ECMO system can create hyperoxemia, which can lead to increased reactive oxygen species (ROS) and oxidative damage.

Another concern regarding the use of VA-ECMO—a topic of current debate—is whether VA-ECMO actually reduces cardiac preload and pressure since VA-ECMO is draining volume from the system. Dr. Kapur explains that with less volume and pressure in the heart, the aortic valve may stop opening and closing, facilitating clot formation and potential clot ejection when heart function resumes.