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Prophylactic Intra-aortic Balloon Counterpulsation—Still Searching for Answers

Published:March 08, 2018DOI:https://doi.org/10.1053/j.jvca.2018.01.051
      SINCE IT WAS FIRST introduced into clinical practice by Dr. Adrian Kantrowitz in the late 1960s, the intra-aortic balloon pump (IABP) has remained an important therapy in the management of patients with coronary artery disease (CAD). The device itself is a long narrow balloon mounted to a flexible intravascular catheter. It is inserted, usually percutaneously, into the descending thoracic aorta just distal to the origin of the left subclavian artery. Timing of balloon counterpulsation (ie, inflation and deflation) to achieve maximal hemodynamic benefit is accomplished via a pneumatic console synchronized to the cardiac cycle. Utilizing this counterpulsation mechanism, the IABP aids in optimizing the critical balance between oxygen supply and demand in the ischemic myocardium. Balloon inflation during early diastole (just after the closure of the aortic valve) improves myocardial oxygen supply by augmenting diastolic coronary blood flow and subendocardial perfusion, whereas balloon deflation at end diastole (just prior to opening of the aortic valve) decreases oxygen demand via a reduction left ventricular afterload. The ability of this minimally invasive device to increase cardiac output, with a simultaneous reduction in myocardial workload, has made the IABP one of the most effective and frequently utilized forms of temporary mechanical circulatory support in current practice.
      Guidelines from the American College of Cardiology/American Heart Association assign Class IIa recommendations (Level of Evidence: B) for preoperative IABP insertion to reduce mortality rate in coronary artery bypass grafting (CABG) patients who are considered to be at high risk (ie, left ventricular ejection fraction [LVEF] <30%, left main CAD [LMCAD], reoperations).
      • Hillis L.D.
      • Smith P.D.
      • Anderson J.L.
      • et al.
      2011 ACCF/AHA guideline for coronary artery bypass graft surgery: A report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines.
      However, the issue of whether IABP prophylaxis in high-risk CABG patients is truly beneficial remains a difficult question to resolve despite several meta-analyses and observational studies, with some studies suggesting a benefit, others demonstrating no benefit, and some even suggesting harm with its use.
      • Zaky A.
      Pro: Prophylactic preoperative use of an intra-aortic balloon pump is indicated in high-risk coronary patients undergoing coronary artery bypass grafting.
      In this edition of Journal of Cardiothoracic and Vascular Anesthesia, Litton et al.
      • Litton E.
      • Bass F.
      • Delaney A.
      • et al.
      Six-month outcomes after high-risk coronary artery bypass graft surgery and preoperative intra-aortic balloon counter pulsation use: an inception cohort study.
      present findings from an inception cohort study examining the prophylactic role of intra-aortic balloon counterpulsation (IABC) in patients at high risk for low cardiac output syndrome undergoing CABG. A total of 13 cardiac centers in Australia, Canada, New Zealand, and the United Kingdom participated in this prospective study aimed at describing 6-month mortality and quality of life among enrolled patients. In particular, a major goal was to assess a potentially valid composite incorporating potential risks and benefits of preoperative IABC use, with the ultimate hope that these end points could be measured in a large-scale randomized controlled trial (RCT). The study included 136 participants over a 29-month period, with 39 patients (29%) receiving preoperative IABC. Overall, in-hospital and 6-month mortality occurred in 7 (5%) and 11 (8%) of participants, respectively. The authors identified a composite end point that included perioperative morbidity (acute myocardial infarction, acute kidney injury, stroke), which occurred in nearly half (44%) of participants. Quality of life was measured with data from a EuroQol 5-dimensional questionnaire (EQ-5D-3L) obtained pre- and postsurgery. Although CABG surgery was found to be associated with a significant improvement in quality of life at 6 months in patients who did not experience perioperative morbidity, this benefit was lost in those who did.
      There are limited prospective, randomized studies exploring the outcomes of high-risk patients undergoing cardiac surgery with preoperative IABP versus without this intervention. One of the most notable, and frequently cited, trials was performed by Ranucci et al.
      • Ranucci M.
      • Castelvecchio S.
      • Biondi A.
      • et al.
      A randomized controlled trial of preoperative intra-aortic balloon pump in coronary patients with poor left ventricular function undergoing coronary artery bypass surgery.
      This single-center RCT attempted to assess the benefit of preoperative IABP insertion by randomly assigning high-risk (LVEF < 0.35), hemodynamically stable patients undergoing nonemergent CABG surgery to one of 2 groups: a group receiving preoperative IABP placement versus a control group that did not. Of note, the study was halted for futility after an interim analysis (including 110 participants) demonstrated no significant differences in composite end points of stroke, acute kidney injury, prolonged mechanical ventilation, deep wound infection, need for reoperation, and operative mortality between study groups. The authors concluded that prophylactic, preoperative IABP use in stable patients undergoing nonemergent CABG provided no benefit and is not justified.
      On the flip side, Christenson et al. have conducted several RCTs evaluating the effects of preoperative IABP insertion and outcomes.
      • Zaky A.
      Pro: Prophylactic preoperative use of an intra-aortic balloon pump is indicated in high-risk coronary patients undergoing coronary artery bypass grafting.
      • Christenson J.T.
      • Badel P.
      • Simonet F.
      • et al.
      Preoperative intraaortic balloon pump enhances cardiac performance and improves the outcome of redo CABG.
      • Christenson J.T.
      • Simonet F.
      • Badel P.
      • et al.
      The effect of preoperative intra-aortic balloon pump support in patients with coronary artery disease, poor left-ventricular function (LVEF <40%), and hypertensive LV hypertrophy.
      • Christenson J.T.
      • Simonet F.
      • Badel P.
      • et al.
      Optimal timing of preoperative intraaortic balloon pump support in high-risk coronary patients.
      • Christenson J.T.
      • Licker M.
      • Kalangos A.
      • et al.
      The role of intra-aortic counterpulsation in high-risk OPCAB surgery: A prospective randomized study.
      These trials demonstrated benefit in patients assigned to receive an IABP preoperatively compared to control groups, including a reduction in mortality. Many have criticized these studies, however, citing limitations of heterogeneity of patient populations and the enrollment of relatively “sicker” patient populations (ie, those with active coronary syndromes) that argue for a more therapeutic, rather than prophylactic, utilization of IABC. Although not a prospective or randomized trial, Gatti et al. recently presented findings from retrospective, observational study reviewing outcomes from 588 consecutive patients who received IABP before cardiac surgery in a single Italian university hospital setting from 1999 to 2016.
      • Gatti G.
      • Morra L.
      • Castaldi G.
      • et al.
      Preoperative intra-aortic counterpulsation in cardiac surgery: Insights from a retrospective series of 588 consecutive high-risk patients.
      This review of the more recent experience of the authors in the use of preoperative IABP demonstrated an increased rate of preoperative use of IABP for prophylaxis and unstable angina, despite a reduction in patient surgical risk throughout the study time period. Early period of surgery, rapid worsening of hemodynamics in the operating room, renal impairment, and ventilation before surgery were all predictors of in-hospital mortality, which was found to be 10.9% (64 of 588 study participants). Additionally, the study compared outcomes between 74 patients receiving preoperative IABP because of LMCAD (stenosis ≥50%) and a new cohort of 1,360 patients experiencing LMCAD but not receiving a preoperative IABP using propensity-score matching. No significant outcomes differences were observed among these 2 groups, leading the authors to state that the prophylactic use of IABP for all patients with severe LMCAD undergoing CABG was not supported by the results of their supplementary comparative analysis. In their discussion, the authors note that, in addition to a generic perception of improved immediate results using prophylactic IABP for high-risk patients undergoing CABG (ie, LMCAD with stenosis ≥50%, left ventricular dysfunction, or those undergoing redo or off-pump CABG), no definitive conclusions can be drawn from all of the evidence that has been reported in the literature.
      This is not to suggest, however, that many experts do not continue to acknowledge the potential utility of prophylactic IABP use. An international consensus conference on mortality reduction in cardiac anesthesia and intensive care has recently published findings from its “democratic” consensus process.
      • Landoni G.
      • Lomivorotov V.
      • Silvietti S.
      • et al.
      Nonsurgical strategies to reduce mortality in patients undergoing cardiac surgery: An updated consensus process.
      Recognizing that there is a lack of general agreement regarding which nonsurgical interventions can reduce mortality in cardiac surgery, the authors sought to address this issue with a consensus-based approach. Utilizing a “novel approach to consensus building,” all nonsurgical interventions (drugs, techniques, and strategies) with literature evidence of a significant effect on mortality were identified systematically, assessed, and described by a group of 458 clinicians from around the world. Clinicians included cardiac anesthesiologists, cardiac surgeons, intensivists, and cardiologists. Identified studies were all discussed during a consensus meeting and voted on by this diverse group of physicians, ultimately identifying 11 nonsurgical interventions with possible survival implications for patients undergoing cardiac surgery. Among these interventions, the conference identified prophylactic IABP placement as one of these interventions, suggesting its use in high-risk patients undergoing CABG might reduce mortality. Interestingly, the authors reported the incidence of a significant gap between the medical literature and clinical practice, which they believed confirmed that clinical practice is frequently slow to adapt to evidence. They concluded that their findings point to the continuous need for high-quality studies focused on major outcomes (ie, mortality) to update beliefs and modify practice patterns accordingly.
      It is clear that there remains a significant lack of evidence related to the topic of prophylactic, preoperative IABP use for high-risk CABG patients that can only be resolved with a definitive RCT. Litton et al.
      • Litton E.
      • Bass F.
      • Delaney A.
      • et al.
      Six-month outcomes after high-risk coronary artery bypass graft surgery and preoperative intra-aortic balloon counter pulsation use: an inception cohort study.
      specifically describe how this lack of evidence has resulted in the continued variation of prophylactic IABC use in high-risk patients undergoing CABG. They believe that their findings have identified a group who may benefit from this therapy, providing new information describing the in-hospital and medium-term outcomes of a group of high-risk patients at risk for low cardiac output syndrome that supports the feasibility and may aid in the design of a future RCT. A large, multicenter RCT is certainly required to take the next step toward uncovering more definitive evidence, either for or against, the prophylactic use of IABP in high-risk CABG patients that has remained so elusive. Until then, the unanswered questions regarding this topic will remain.

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