The Intra-aortic balloon pump (IABP)
is a mechanical device that is used to decrease myocardial oxygen demand while at the same time increasing cardiac output
. By increasing cardiac output it also increases coronary blood flow and therefore myocardial oxygen delivery. It consists of a cylindrical balloon that sits in the aorta
and counterpulsates. That is, it actively deflates in systole
increasing forward blood flow by reducing afterload
thus, and actively inflates in diastole
increasing blood flow to the coronary arteries
. These actions have the combined result of decreasing myocardial oxygen demand and increasing myocardial oxygen supply.
The balloon is inflated during diastole by a computer controlled mechanism, usually linked to either an ECG or a pressure transducer at the distal tip of the catheter; some IABPs, such as the Datascope System 98XT, allow for asynchronous counterpulsation at a set rate, though this setting is rarely used. The computer controls the flow of helium from a cylinder into and out of the balloon. Helium is used because its low viscosity allows it to travel quickly through the long connecting tubes, and has a lower risk of causing a harmful embolism should the balloon rupture while in use.
The IABP device was pioneered at the Grace-Sinai Hospital
in Detroit during the early 1960s by
Dr. Adrian Kantrowitz.
Use of counterpulsation
Intraaortic balloon counterpulsation is used in situations when the heart's own cardiac output is insufficient to meet the oxygenation demands of the body. These situations could include cardiogenic shock, severe septic shock, post cardiac surgery and numerous other situations.
The following situations may benefit from this device.
- Cardiogenic shock when used alone as treatment for myocardial infarction 9-22% survive the first year.
- Reversible intracardial mechanical defects complicating infarction, i.e. acute mitral regurgitation and septal perforation.
- Unstable angina pectoris benefits from counterpulsation.
- Post cardiothoracic surgery most common and useful is the use of counterpulsation in weaning patients from cardiopulmonary bypass after continued perioperative injury to myocardial tissue.
- Preoperative use has been suggested for high-risk patients such as those with unstable angina with stenosis greater than 70% of main coronary artery, in ventricaular dysfunction with an ejection fraction less than 35%.
- Bridge to heart transplant for those patients with left ventricular failure.
- Percutaneous coronary angioplasty
The following conditions will always exclude patients for treatment:
The following conditions could, under very pressing circumstances, be allowed to be included for therapy:
- Prosthetic vascular grafts in the aorta
- Aortic aneurysm
- Aortofemoral grafts
Since the device is placed in the femoral artery
and aorta it could provoke ischemia
, and compartment syndrome
. At highest risk is the leg which is supplied by the femoral artery may become ischemic, but also placing the balloon too distal from the arcus aortae
may induce occlusion of the renal artery
and subsequent renal failure
. Other possible complications are cerebral embolism during insertion, infection, dissection
of the aorta or iliac artery
, perforation of the artery and hemorrhage in the mediastinum
. Mechanical failure of the balloon itself is also a risk which entails vascular surgery to remove under that circumstance. After balloon removal there is also a risk of 'embolic shower' from micro clots that have formed on the surface of the balloon, and can lead to peripheral thrombosis, myocardial ischemia, hemodynamic decompensation, and late pseudoaneurysm.
The IABP's developers thought that private insurance companies would not stand for such a radical new therapy, and approached the military, asking them to keep an eye out for IABP candidates in military hospitals. One day, the call came. A retired general was hospitalized in Walter Reed Army Medical Center. He had a history of multiple infarcts and was now end-stage heart failure. The IABP scientists were all ready to go, until they found out the general was former President Dwight D. Eisenhower
. They declined the opportunity because they worried that if the IABP failed in him, it would permanently ruin the future prospects of the device.