More than half a century ago, Kantrowitz et al. first described the use of an “intra-aortic cardiac assistance system” using a balloon-tipped catheter inserted into the descending thoracic aorta.1 They described two patients who developed cardiogenic shock after acute myocardial infarction. The blood pressure remained low, followed by anuria, in spite of high-dose vasopressor therapy. Following intra-aortic balloon counterpulsation, there was a perceptible improvement in the hemodynamic status in both patients. The first patient continued to improve, was weaned off balloon support, and made a complete recovery. However, the second patient developed recurrent ventricular fibrillation, rendering balloon counterpulsation ineffective. Since then, there have been major technological advances in the field of mechanical support, ranging from percutaneous left ventricular assist devices to the total artificial heart. However, from its humble beginnings, the intra-aortic balloon pump (IABP) has remained the most frequently used mechanical support device.
How does IABP work?
The IABP is a double-lumen, balloon-tipped catheter, usually inserted through a sheath placed in the femoral artery. A sheathless technique is preferred in patients with peripheral vascular disease. The catheter tip is positioned in the descending thoracic aorta immediately distal to the left subclavian artery. One lumen is connected to the balloon, allowing back and forth movement of helium gas, while the other lumen is used for flushing the catheter and transduce aortic pressure. The balloon inflates during diastole leading to augmentation of aortic root and coronary artery pressures, thus improving coronary perfusion; it rapidly deflates in systole enabling reduction of afterload with a decrease in systolic pressures. (Figure 1) The inflation-deflation sequence is timed with the arterial waveform or the EKG trace to synchronize with the cardiac cycle. Besides improving coronary blood flow and oxygen supply to the myocardium, IABP support results in a reduction of the left ventricular wall stress and afterload with a decrease in the myocardial oxygen consumption. The stroke volume and cardiac output increase, with an improvement in organ perfusion.
When is IABP support useful?
The classical indications for the use of IABP support include acute myocardial infarction with cardiogenic shock, as an adjunct to high-risk percutaneous coronary intervention, preoperative stabilization prior to coronary artery bypass surgery, and for continued support in the postoperative period. Less conventional indications include stabilization of left main disease, and as a bridge to cardiac transplantation. It may also be effective in the management of mechanical complications of myocardial infarction, such as acute mitral regurgitation and ventricular septal defect. Patients with intractable arrhythmia and heart failure refractory to medical therapy may also benefit.
IABP is generally contraindicated in the presence of aortic regurgitation as it may increase retrograde flow during balloon inflation through a leaky valve. It is also contraindicated in aortic dissection or aneurysm and in the presence of severe coagulopathy. In patients with severe peripheral vascular disease, it may lead to ischemia of the limb.
What is the evidence?
Acute myocardial infarction with cardiogenic shock
Early retrospective and registry-based studies seemed to suggest improved survival with a combination of thrombolytic therapy and IABP in patients with cardiogenic shock after acute myocardial infarction.2
The IABP-SHOCK II is the only large RCT addressing the efficacy of IABP in patients with acute myocardial infarction and cardiogenic shock who undergo early revascularization.3 In this multicentric German study, 600 patients who were planned to undergo early PCI or emergency coronary artery bypass surgery were randomized to receive IABP support either before or immediately following the intervention, based on physician judgment. More than 95% of patients in both groups underwent PCI; about 3% of patients underwent emergency coronary artery bypass surgery. No significant difference was observed in the 30-d all-cause mortality, the primary outcome. The study had several limitations, including the selection of patients with relatively mild shock, and exclusion of patients with mechanical complications of myocardial infarction. IABP was inserted after revascularization in the majority (87%) of patients, which failed to evaluate the possible benefit of early hemodynamic stabilization in cardiogenic shock. A relatively large number of patients in the control group (10%) crossed over and underwent IABP insertion, which may have masked a possible benefit from IABP support on intention-to-treat analysis. The question of IABP efficacy in more severe forms of cardiogenic shock after acute myocardial infarction remains unanswered.
A more recent meta-analysis of 13 observational and four randomized controlled trials (RCT) of patients with acute myocardial infarction complicated by cardiogenic shock revealed no overall difference in hospital mortality.4 However, mortality was significantly lower among patients who received thrombolysis combined with IABP. In contrast, patients who received PCI and IABP support had significantly increased mortality.
Acute myocardial infarction without cardiogenic shock
Considering the potential improvement in coronary perfusion resulting from aortic counterpulsation, would IABP insertion reduce infarct size and improve clinical outcomes in patients with acute myocardial infarction without cardiogenic shock? This question was addressed in an RCT involving 337 patients in a multicentric study.5 IABP was inserted prior to PCI and continued for at least 12 h in the intervention group; patients in the control group received PCI alone. The infarct size was assessed using cardiac magnetic resonance imaging and expressed as a percentage of the total mass of the left ventricle. No significant difference was noted in the infarct size between patients who received IABP compared to those who did not. Besides, there was no significant difference in secondary outcomes, including major vascular or bleeding complications, transfusion requirements, and 6 m mortality. This study clearly demonstrated the lack of benefit of balloon counterpulsation in patients with acute myocardial infarction, without cardiogenic shock.
IABP before high-risk PCI
Observational studies have revealed improvement in clinical outcomes with elective IABP insertion prior to high-risk PCI. The BCIS 1 study was carried out to address this question. This multicentre RCT was conducted across 17 tertiary cardiac centers in the UK.6 The study included 301 patients with a left ventricular ejection fraction of less than 30% and extensive coronary artery disease. IABP was inserted before PCI in the intervention group. The primary endpoint of major cardiac and cardiovascular events (MACCE) including death, acute myocardial infarction, cerebrovascular event, or requirement for repeat revascularization at hospital discharge was not significantly different between groups. The 6 m all-cause mortality was similar in both groups. At 5 y follow-up, there was significantly less mortality in the IABP group; however, the study was not powered to determine long term mortality. The mechanism of long term benefit in the absence of any difference in the short term mortality also remains unclear.
Coronary artery bypass surgery
Balloon counterpulsation is frequently used to stabilize patients before they undergo coronary artery bypass surgery, and for continued hemodynamic support in the postoperative period. Qui et al. prospectively evaluated the efficacy of pre vs. postoperative IABP insertion in patients with severe left ventricular dysfunction who underwent off-pump coronary artery.7 Patients who underwent preoperative IABP had a significantly lower in-hospital mortality, and reduced incidence of low cardiac output, malignant arrhythmias, and acute renal failure in the postoperative period.
A Cochrane meta-analysis evaluated data from 255 patients in six randomized controlled trials;8 132 patients underwent balloon counterpulsation. In-hospital mortality was significantly lower with balloon counterpulsation. A postoperative low cardiac output syndrome was more common among patients who did not receive IABP support. A high crossover rate (51%) to balloon counterpulsation was noted. A recent meta-analysis confirmed these findings.9 Considering the poor outcomes in patients who undergo IABP support as a late intervention,10 preoperative stabilization may be appropriate in high-risk patients undergoing coronary artery bypass surgery.
The bottom line
- Balloon counterpulsation remains the most frequently used device for mechanical circulatory support.
- Although the SHOCK II trial showed a lack of clinical benefit in patients with acute myocardial infarction and cardiogenic shock, IABP support may continue to play a role in patients with more severe degrees of shock.
- Mechanical support with IABP may not significantly impact infarct size or clinical outcomes in hemodynamically stable patients with acute myocardial infarction.
- The use of IABP as a supportive measure before high-risk PCI has not been shown to affect major cardiac and cardiovascular events.
- Balloon counterpulsation may have a crucial role in the stabilization of high-risk patients prior to coronary artery bypass surgery and continued support in the postoperative period.
1. Tj S, Butner N, Sherman L. Initial Clinical Experience With Intraaortic Balloon Pumping in Cardiogenic Shock. :6.
2. Sanborn TA, Sleeper LA, Bates ER, et al. Impact of thrombolysis, intra-aortic balloon pump counterpulsation, and their combination in cardiogenic shock complicating acute myocardial infarction: a report from the SHOCK Trial Registry. SHould we emergently revascularize Occluded Coronaries for cardiogenic shocK? J Am Coll Cardiol. 2000;36(3 Suppl A):1123-1129. doi:10.1016/s0735-1097(00)00875-5
3. Thiele H, Zeymer U, Neumann F-J, et al. Intraaortic Balloon Support for Myocardial Infarction with Cardiogenic Shock. N Engl J Med. 2012;367(14):1287-1296. doi:10.1056/NEJMoa1208410
4. Romeo F, Acconcia MC, Sergi D, et al. The outcome of intra-aortic balloon pump support in acute myocardial infarction complicated by cardiogenic shock according to the type of revascularization: A comprehensive meta-analysis. Am Heart J. 2013;165(5):679-692. doi:10.1016/j.ahj.2013.02.020
5. Patel MR, Smalling RW, Thiele H, et al. Intra-aortic balloon counterpulsation and infarct size in patients with acute anterior myocardial infarction without shock: the CRISP AMI randomized trial. JAMA. 2011;306(12):1329-1337. doi:10.1001/jama.2011.1280
6. Perera D. Elective Intra-aortic Balloon Counterpulsation During High-Risk Percutaneous Coronary InterventionA Randomized Controlled Trial. JAMA. 2010;304(8):867. doi:10.1001/jama.2010.1190
7. Qiu Z, Chen X, Xu M, et al. Evaluation of preoperative intra-aortic balloon pump in coronary patients with severe left ventricular dysfunction undergoing OPCAB surgery: early and mid-term outcomes. J Cardiothorac Surg. 2009;4(1):39. doi:10.1186/1749-8090-4-39
8. Theologou T, Bashir M, Rengarajan A, et al. Preoperative intra aortic balloon pumps in patients undergoing coronary artery bypass grafting. Cochrane Database Syst Rev. 2011;(1):CD004472. doi:10.1002/14651858.CD004472.pub3
9. Deppe A-C, Weber C, Liakopoulos OJ, et al. Preoperative intra-aortic balloon pump use in high-risk patients prior to coronary artery bypass graft surgery decreases the risk for morbidity and mortality-A meta-analysis of 9,212 patients. J Card Surg. 2017;32(3):177-185. doi:10.1111/jocs.13114
10. Böning A, Buschbeck S, Roth P, et al. IABP before cardiac surgery: clinical benefit compared to intraoperative implantation. Perfusion. 2013;28(2):103-108. doi:10.1177/0267659112471577