[Skip to Content]
Access to paid content on this site is currently suspended due to excessive activity being detected from your IP address 54.158.98.119. Please contact the publisher to request reinstatement.
[Skip to Content Landing]
Download PDF
Figure 1.
Search Strategy and Source of Included Studies
Search Strategy and Source of Included Studies
Figure 2.
Randomized Controlled Trials Comparing Intra-Aortic Balloon Pump (IABP) Therapy With Control for the Outcome of Mortality in Patients With Acute Myocardial Infarction, Stratified by the Presence or Absence of Cardiogenic Shock
Randomized Controlled Trials Comparing Intra-Aortic Balloon Pump (IABP) Therapy With Control for the Outcome of Mortality in Patients With Acute Myocardial Infarction, Stratified by the Presence or Absence of Cardiogenic Shock

Odds ratios are calculated by random-effects Mantel-Haenszel analysis.

Figure 3.
Observational Studies Reporting on Intra-Aortic Balloon Pump (IABP) Therapy and the Outcome of Mortality in Patients With Acute Myocardial Infarction
Observational Studies Reporting on Intra-Aortic Balloon Pump (IABP) Therapy and the Outcome of Mortality in Patients With Acute Myocardial Infarction

Odds ratios are calculated by random-effects Mantel-Haenszel analysis.

Figure 4.
Observational Studies Reporting on Intra-Aortic Balloon Pump (IABP) Therapy and the Outcome of Mortality in Patients With Acute Myocardial Infarction, Stratified by Mode of Reperfusion (Primary Percutaneous Coronary Intervention, Fibrinolysis, or No Reperfusion)
Observational Studies Reporting on Intra-Aortic Balloon Pump (IABP) Therapy and the Outcome of Mortality in Patients With Acute Myocardial Infarction, Stratified by Mode of Reperfusion (Primary Percutaneous Coronary Intervention, Fibrinolysis, or No Reperfusion)

Odds ratios are calculated by random-effects Mantel-Haenszel analysis.

Figure 5.
Metaregression Analysis of the Relationship Between the Baseline Inequality Index and Odds Ratio (OR) of Mortality Between Intra-Aortic Balloon Pump (IABP) and Control in Observational Studies
Metaregression Analysis of the Relationship Between the Baseline Inequality Index and Odds Ratio (OR) of Mortality Between Intra-Aortic Balloon Pump (IABP) and Control in Observational Studies

The baseline inequality index explains almost half of the variance between included studies. The index was also significantly associated with mortality (P = .002). Notably, when the difference in the baseline inequality index was zero (y-intercept, red circle) there was no difference in mortality between the IABP and control groups (OR, 0.02 [95% CI, −0.53 to 0.56]; P = .96). Meta-regression analysis was performed using restricted maximum likelihood estimation. Symbols indicate ORs, and error bars, 95% CIs. Gray shading indicates the 95% CIs around the regression line. Blue and orange symbols indicate patients with and without cardiogenic shock, respectively. Size of data markers indicates study weight.

1.
Goldberg  RJ, Spencer  FA, Gore  JM, Lessard  D, Yarzebski  J.  Thirty-year trends (1975 to 2005) in the magnitude of, management of, and hospital death rates associated with cardiogenic shock in patients with acute myocardial infarction: a population-based perspective. Circulation. 2009;119(9):1211-1219.
PubMedArticle
2.
Thiele  H, Zeymer  U, Neumann  FJ,  et al; IABP-SHOCK II Trial Investigators.  Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med. 2012;367(14):1287-1296.
PubMedArticle
3.
Fuchs  RM, Brin  KP, Brinker  JA, Guzman  PA, Heuser  RR, Yin  FC.  Augmentation of regional coronary blood flow by intra-aortic balloon counterpulsation in patients with unstable angina. Circulation. 1983;68(1):117-123.
PubMedArticle
4.
Gold  HK, Leinbach  RC, Sanders  CA, Buckley  MJ, Mundth  ED, Austen  WG.  Intraaortic balloon pumping for control of recurrent myocardial ischemia. Circulation. 1973;47(6):1197-1203.
PubMedArticle
5.
Awad  HH, Anderson  FA  Jr, Gore  JM, Goodman  SG, Goldberg  RJ.  Cardiogenic shock complicating acute coronary syndromes: insights from the Global Registry of Acute Coronary Events. Am Heart J. 2012;163(6):963-971.
PubMedArticle
6.
Van de Werf  F, Bax  J, Betriu  A,  et al; ESC Committee for Practice Guidelines (CPG).  Management of acute myocardial infarction in patients presenting with persistent ST-segment elevation: the Task Force on the Management of ST-Segment Elevation Acute Myocardial Infarction of the European Society of Cardiology. Eur Heart J. 2008;29(23):2909-2945.
PubMedArticle
7.
Kushner  FG, Hand  M, Smith  SC  Jr,  et al.  2009 focused updates: ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction (updating the 2004 guideline and 2007 focused update) and ACC/AHA/SCAI guidelines on percutaneous coronary intervention (updating the 2005 guideline and 2007 focused update): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines [published correction appears in J Am Coll Cardiol. 2010;55(6):612]. J Am Coll Cardiol. 2009;54(23):2205-2241.
PubMedArticle
8.
Thiele  H, Zeymer  U, Neumann  FJ,  et al; Intraaortic Balloon Pump in Cardiogenic Shock II (IABP-SHOCK II) trial investigators.  Intra-aortic balloon counterpulsation in acute myocardial infarction complicated by cardiogenic shock (IABP-SHOCK II): final 12 month results of a randomised, open-label trial. Lancet. 2013;382(9905):1638-1645.
PubMedArticle
9.
O’Gara  PT, Kushner  FG, Ascheim  DD,  et al; American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.  2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2013;127(4):e362-e425.
PubMedArticle
10.
Windecker  S, Kolh  P, Alfonso  F,  et al; Authors/Task Force Members.  2014 ESC/EACTS Guidelines on myocardial revascularization: the Task Force on Myocardial Revascularization of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS)—developed with the special contribution of the European Association of Percutaneous Cardiovascular Interventions (EAPCI). Eur Heart J. 2014;35(37):2541-2619.
PubMedArticle
11.
Moher  D, Liberati  A, Tetzlaff  J, Altman  DG; PRISMA Group.  Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med. 2009;151(4):264-269, W64.
PubMedArticle
12.
Higgins  JP, Altman  DG, Gøtzsche  PC,  et al; Cochrane Bias Methods Group; Cochrane Statistical Methods Group.  The Cochrane Collaboration’s tool for assessing risk of bias in randomised trials. BMJ. 2011;343:d5928.
PubMedArticle
13.
Stroup  DF, Berlin  JA, Morton  SC,  et al; Meta-analysis of Observational Studies in Epidemiology (MOOSE) group.  Meta-analysis of observational studies in epidemiology: a proposal for reporting. JAMA. 2000;283(15):2008-2012.
PubMedArticle
14.
Review Manager (RevMan), Version 5.0. Copenhagen, Denmark: The Nordic Cochrane Centre, The Cochrane Collaboration; 2008.
15.
Higgins  JP, Thompson  SG.  Quantifying heterogeneity in a meta-analysis. Stat Med. 2002;21(11):1539-1558.
PubMedArticle
16.
R Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2013.
17.
Viechtbauer  W.  Conducting meta-analyses in R with the metafor package. J Stat Softw. 2010;36(3):1-48.
18.
Ohman  EM, Nanas  J, Stomel  RJ,  et al; TACTICS Trial.  Thrombolysis and counterpulsation to improve survival in myocardial infarction complicated by hypotension and suspected cardiogenic shock or heart failure: results of the TACTICS Trial. J Thromb Thrombolysis. 2005;19(1):33-39.
PubMedArticle
19.
Prondzinsky  R, Lemm  H, Swyter  M,  et al.  Intra-aortic balloon counterpulsation in patients with acute myocardial infarction complicated by cardiogenic shock: the prospective, randomized IABP SHOCK Trial for attenuation of multiorgan dysfunction syndrome. Crit Care Med. 2010;38(1):152-160.
PubMedArticle
20.
Flaherty  JT, Becker  LC, Weiss  JL,  et al.  Results of a randomized prospective trial of intraaortic balloon counterpulsation and intravenous nitroglycerin in patients with acute myocardial infarction. J Am Coll Cardiol. 1985;6(2):434-446.
PubMedArticle
21.
Gu  J, Hu  W, Xiao  H, Feng  X, Chen  Y, Zhang  D.  Intra-aortic balloon pump improves clinical prognosis and attenuates C-reactive protein level in acute STEMI complicated by cardiogenic shock. Cardiology. 2010;117(1):75-80.
PubMedArticle
22.
Kono  T, Morita  H, Nishina  T,  et al.  Aortic counterpulsation may improve late patency of the occluded coronary artery in patients with early failure of thrombolytic therapy. J Am Coll Cardiol. 1996;28(4):876-881.
PubMedArticle
23.
O’Rourke  MF, Norris  RM, Campbell  TJ, Chang  VP, Sammel  NL.  Randomized controlled trial of intraaortic balloon counterpulsation in early myocardial infarction with acute heart failure. Am J Cardiol. 1981;47(4):815-820.
PubMedArticle
24.
Ohman  EM, George  BS, White  CJ,  et al; Randomized IABP Study Group.  Use of aortic counterpulsation to improve sustained coronary artery patency during acute myocardial infarction: results of a randomized trial. Circulation. 1994;90(2):792-799.
PubMedArticle
25.
Stone  GW, Marsalese  D, Brodie  BR,  et al; Second Primary Angioplasty in Myocardial Infarction (PAMI-II) Trial Investigators.  A prospective, randomized evaluation of prophylactic intraaortic balloon counterpulsation in high risk patients with acute myocardial infarction treated with primary angioplasty. J Am Coll Cardiol. 1997;29(7):1459-1467.
PubMedArticle
26.
van ’t Hof  AW, Liem  AL, de Boer  MJ, Hoorntje  JC, Suryapranata  H, Zijlstra  F.  A randomized comparison of intra-aortic balloon pumping after primary coronary angioplasty in high risk patients with acute myocardial infarction. Eur Heart J. 1999;20(9):659-665.
PubMedArticle
27.
Vijayalakshmi  K, Kunadian  B, Whittaker  VJ,  et al.  Intra-aortic counterpulsation does not improve coronary flow early after PCI in a high-risk group of patients: observations from a randomized trial to explore its mode of action. J Invasive Cardiol. 2007;19(8):339-346.
PubMed
28.
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.
PubMedArticle
29.
Anderson  RD, Ohman  EM, Holmes  DR  Jr,  et al.  Use of intraaortic balloon counterpulsation in patients presenting with cardiogenic shock: observations from the GUSTO-I Study—Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries. J Am Coll Cardiol. 1997;30(3):708-715.
PubMedArticle
30.
Barron  HV, Every  NR, Parsons  LS,  et al; Investigators in the National Registry of Myocardial Infarction 2.  The use of intra-aortic balloon counterpulsation in patients with cardiogenic shock complicating acute myocardial infarction: data from the National Registry of Myocardial Infarction 2. Am Heart J. 2001;141(6):933-939.
PubMedArticle
31.
Bengtson  JR, Kaplan  AJ, Pieper  KS,  et al.  Prognosis in cardiogenic shock after acute myocardial infarction in the interventional era. J Am Coll Cardiol. 1992;20(7):1482-1489.
PubMedArticle
32.
Gu  J, Hu  W, Xiao  H,  et al.  Prophylactic intra-aortic balloon pump reduces C-reactive protein levels and early mortality in high-risk patients undergoing percutaneous coronary intervention. Acta Cardiol. 2011;66(4):499-504.
PubMed
33.
Kovack  PJ, Rasak  MA, Bates  ER, Ohman  EM, Stomel  RJ.  Thrombolysis plus aortic counterpulsation: improved survival in patients who present to community hospitals with cardiogenic shock. J Am Coll Cardiol. 1997;29(7):1454-1458.
PubMedArticle
34.
Moulopoulos  S, Stamatelopoulos  S, Petrou  P.  Intraaortic balloon assistance in intractable cardiogenic shock. Eur Heart J. 1986;7(5):396-403.
PubMed
35.
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.
PubMedArticle
36.
Sjauw  KD, Engström  AE, Vis  MM,  et al.  Efficacy and timing of intra-aortic counterpulsation in patients with ST-elevation myocardial infarction complicated by cardiogenic shock. Neth Heart J. 2012;20(10):402-409.
PubMedArticle
37.
Stomel  RJ, Rasak  M, Bates  ER.  Treatment strategies for acute myocardial infarction complicated by cardiogenic shock in a community hospital. Chest. 1994;105(4):997-1002.
PubMedArticle
38.
Waksman  R, Weiss  AT, Gotsman  MS, Hasin  Y.  Intra-aortic balloon counterpulsation improves survival in cardiogenic shock complicating acute myocardial infarction. Eur Heart J. 1993;14(1):71-74.
PubMedArticle
39.
Zeymer  U, Bauer  T, Hamm  C,  et al.  Use and impact of intra-aortic balloon pump on mortality in patients with acute myocardial infarction complicated by cardiogenic shock: results of the Euro Heart Survey on PCI. EuroIntervention. 2011;7(4):437-441.
PubMedArticle
40.
Zeymer  U, Hochadel  M, Hauptmann  KE,  et al.  Intra-aortic balloon pump in patients with acute myocardial infarction complicated by cardiogenic shock: results of the ALKK-PCI registry. Clin Res Cardiol. 2013;102(3):223-227.
PubMedArticle
41.
Brodie  BR, Stuckey  TD, Hansen  C, Muncy  D.  Intra-aortic balloon counterpulsation before primary percutaneous transluminal coronary angioplasty reduces catheterization laboratory events in high-risk patients with acute myocardial infarction. Am J Cardiol. 1999;84(1):18-23.
PubMedArticle
42.
Kumbasar  SD, Semiz  E, Sancaktar  O, Yalçinkaya  S, Ermiş  C, Değer  N.  Concomitant use of intraaortic balloon counterpulsation and streptokinase in acute anterior myocardial infarction. Angiology. 1999;50(6):465-471.
PubMedArticle
43.
Ohman  EM, Califf  RM, George  BS,  et al; Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) Study Group.  The use of intraaortic balloon pumping as an adjunct to reperfusion therapy in acute myocardial infarction. Am Heart J. 1991;121(3, pt 1):895-901.
PubMedArticle
44.
Sjauw  KD, Engström  AE, Vis  MM,  et al.  A systematic review and meta-analysis of intra-aortic balloon pump therapy in ST-elevation myocardial infarction: should we change the guidelines? Eur Heart J. 2009;30(4):459-468.
PubMedArticle
45.
Ayanian  JZ, Berwick  DM.  Do physicians have a bias toward action? a classic study revisited. Med Decis Making. 1991;11(3):154-158.
PubMedArticle
46.
Shahzad  A, Kemp  I, Mars  C,  et al; HEAT-PPCI trial investigators.  Unfractionated heparin versus bivalirudin in primary percutaneous coronary intervention (HEAT-PPCI): an open-label, single centre, randomised controlled trial. Lancet. 2014;384(9957):1849-1858.
PubMedArticle
47.
Wood  S. HEAT-PPCI: heparin bests bivalirudin in STEMI, amid heated debate. http://www.medscape.com/viewarticle/822927. Accessed December 14, 2014.
48.
Jabbour  RJ, Shun-Shin  MJ, Finegold  JA,  et al.  Effect of study design on the reported effect of cardiac resynchronization therapy (CRT) on quantitative physiological measures: stratified meta-analysis in narrow-QRS heart failure and implications for planning future studies. J Am Heart Assoc. 2015;4(1):e000896.
PubMedArticle
49.
Howard  JP, Francis  DP.  Overcoming the three biases obscuring the science of renal denervation in humans: big-day bias, check-once-more bias and I-will-take-it-now bias [published online ahead of print October 31, 2014]. Trends Cardiovasc Med. doi: 10.1016/j.tcm.2014.10.011.
PubMed
50.
Sen  S, Davies  JE, Malik  IS,  et al.  Why does primary angioplasty not work in registries? quantifying the susceptibility of real-world comparative effectiveness data to allocation bias. Circ Cardiovasc Qual Outcomes. 2012;5(6):759-766.
PubMedArticle
51.
Lawlor  DA, Davey Smith  G, Ebrahim  S.  Commentary: the hormone replacement-coronary heart disease conundrum: is this the death of observational epidemiology? Int J Epidemiol. 2004;33(3):464-467.
PubMedArticle
Original Investigation
June 2015

Intra-aortic Balloon Pump Therapy for Acute Myocardial InfarctionA Meta-analysis

Author Affiliations
  • 1International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, London, United Kingdom
JAMA Intern Med. 2015;175(6):931-939. doi:10.1001/jamainternmed.2015.0569
Abstract

Importance  Intra-aortic balloon pump (IABP) therapy is a widely used intervention for acute myocardial infarction with cardiogenic shock. Guidelines, which previously strongly recommended it, have recently undergone substantial change.

Objective  To assess IABP efficacy in acute myocardial infarction.

Data Sources  Human studies found in Pubmed, Embase, and Cochrane libraries through December 2014 and in reference lists of selected articles. Search strings were “myocardial infarction” or “acute coronary syndrome” and “intra-aortic balloon pump” or “counterpulsation.”

Study Selection  Randomized clinical trials (RCTs) and observational studies comparing use of IABP with no IABP in patients with acute myocardial infarction.

Data Extraction and Synthesis  Two reviewers independently extracted the data, and risk of bias in RCTs was assessed using the Cochrane risk of bias tool. We conducted separate meta-analyses of the RCTs and observational studies. Data were quantitatively synthesized using random-effects meta-analysis.

Main Outcomes and Measures  Thirty-day mortality.

Results  There were 12 eligible RCTs randomizing 2123 patients. In the RCTs, IABP use had no statistically significant effect on mortality (odds ratio [OR], 0.96 [95% CI, 0.74-1.24]), with no significant heterogeneity among trials (I2 = 0%; P = .52). This result was consistent when studies were stratified by the presence (OR, 0.94 [95% CI, 0.69-1.28]; P = .69, I2 = 0%) or absence (OR, 0.98 [95% CI, 0.57-1.69]; P = .95, I2 = 17%) of cardiogenic shock. There were 15 eligible observational studies totaling 15 530 patients. Their results were mutually conflicting (heterogeneity I2 = 97%; P < .001), causing wide uncertainty in the summary estimate for the association with mortality (OR, 0.96 [95% CI, 0.54-1.70]). A simple index of baseline risk marker imbalance in the observational studies appeared to explain much of the heterogeneity in the observational data (R2meta = 46.2%; P < .001).

Conclusions and Relevance  Use of IABP was not found to improve mortality among patients with acute myocardial infarction in the RCTs, regardless of whether patients had cardiogenic shock. The observational studies showed a variety of mutually contradictory associations between IABP therapy and mortality, much of which was explained by the differences between studies in the balance of risk factors between IABP and non-IABP groups.

Introduction

Acute myocardial infarction complicated by cardiogenic shock has a mortality of more than 50%.1,2 In this challenging clinical scenario, one therapeutic option is insertion of an intra-aortic balloon pump (IABP). The IABP, inserted via the femoral artery and positioned in the descending aorta, assists circulation. In systole, its deflation reduces ventricular workload and helps the ventricle push blood into the aorta. In diastole, its inflation enhances coronary artery perfusion and promotes flow to systemic organs.3,4 Half of all patients with acute myocardial infarction and cardiogenic shock undergoing cardiac catheterization receive an IABP.5

Some observational studies had reported much better outcomes in patients receiving IABP therapy than in those not receiving it. The 2008 European6 and 2009 American guidelines7 issued class I recommendations for the use of IABP in acute myocardial infarction with cardiogenic shock. Within the past 5 years, however, new randomized clinical trial (RCT) data from the IABP-SHOCK II trial2,8 prompted these guideline systems to soften their recommendations. The 2013 US guidelines reduced it to class IIa.9 The 2014 European guidelines went farther, designating it as class III, which is reserved for therapies that are neutral or harmful.10

We conducted an updated meta-analysis examining all available observational and RCT evidence for the use of IABP in acute myocardial infarction, including the recent landmark RCT.2 We address studies of patients with cardiogenic shock and those without, and patients treated either by no reperfusion, fibrinolysis (sometimes called thrombolysis), or primary percutaneous coronary intervention (PCI). Because of the potential for heterogeneity, it was important to consider a random-effects analysis approach. Because of the wide variation in event rate in the control groups, we used odds ratios (ORs) as the expression of the results of each study.

Studies have been reported to display a range of associations between IABP therapy and mortality. To make this easy to visualize, we devised a simple index of baseline risk marker imbalance in observational studies. This could be displayed as a metaregression plot, allowing the reader to infer from a group of observational studies the likely result of an observational study that had balanced risk markers in the treatment and control groups.

Methods

We carried out a meta-analysis of studies that evaluated IABP in acute myocardial infarction. We conducted the meta-analysis in accordance with published guidance.11

Search Strategy

We searched the MEDLINE, Cochrane, and Embase databases (1950 to December 2014) for all trials of IABPs. Our search strings were “myocardial infarction” or “acute coronary syndrome” and “intra-aortic balloon pump” or “counterpulsation.” We excluded nonhuman studies.

Inclusion and Exclusion Criteria

Studies were eligible if they compared IABP recipients with a control group in the setting of acute myocardial infarction. Both observational studies and RCTs were separately identified. Studies of IABP therapy in elective PCI were not eligible.

Data Abstraction

Abstracts were reviewed by 2 authors (Y.A. and J.O.) to determine suitability for inclusion and full-text articles retrieved. Any disagreements were resolved by a third author (D.P.F.). Reference lists of retrieved articles, reviews, and meta-analyses were hand searched to identify additional studies.

Assessment of Risk of Bias

The RCTs were assessed using the Cochrane risk of bias tool,12 which considers the quality of randomization, allocation concealment, blinding, incomplete outcome data, and the completeness of reporting of outcomes. The meta-analysis of observational studies was performed in accordance with published guidance.13 In addition, we assessed baseline differences and considered methodological issues. Publication bias was investigated by means of a funnel plot.

Data Analysis

We conducted separate random-effects meta-analyses for the RCTs and the observational studies. The primary end point was 30-day mortality. We used Review Manager, version 5.2.1.14 Heterogeneity15 was assessed using the I2 and τ2 statistics.

Baseline Inequality Index

To assess the baseline inequality between treatment and control groups in observational studies, and its relationship with apparent benefit, we devised a simple baseline inequality index. It needed to be a method that could be applied across all studies even when data presentation was parsimonious, lacking standard deviation information.

To do this, we prepared a list of baseline characteristics that are recognized markers of risk, as follows: age, prior myocardial infarction, history of diabetes mellitus, heart failure, peripheral arterial disease, hypertension, presence of pulmonary edema, systolic blood pressure, and treatment with angioplasty (in which the lack of treatment would confer increased risk).

Within each study, and for each marker, we assessed whether the published central estimate (mean or median, whichever was reported) was higher in the IABP group than the control group (which we scored as +1) or lower (which we scored −1). If the values of a marker were equal or not given, we scored 0. For each study, we totaled this score.

For the observational studies, we devised a simple index of baseline inequality in risk factors between treatment and control groups. We then performed a random-effects metaregression using the baseline inequality index as a moderator using the statistical programming environment R16 and its “metafor” package.17 We generated a scatter plot showing the relationship between the log OR of death and the baseline inequality index, overlaid with the metaregression.

Results
Search Results

There were 12 eligible RCTs (3 in patients with2,18,19 and 9 in patients without cardiogenic shock2028) randomizing 2123 patients. There were 15 eligible observational studies2943 totaling 15 530 patients. The search strategy is outlined in Figure 1.

Characteristics of Studies and Risk of Bias

The study characteristics are shown in eTable 1 and eTable 2 in the Supplement. Two RCTs included patients who did not receive reperfusion therapy20,23; 2 included patients reperfused by fibrinolysis18,22; and the remaining 8 included patients receiving PCI.2,19,21,2428 In total, there were 1050 patients in the IABP groups and 1073 in the control groups in the RCTs. One observational study included patients who did not receive reperfusion therapy34; 8 included patients reperfused by fibrinolysis29,31,33,35,37,38,42,43; 1 included patients reperfused by either fibrinolysis or PCI30; and the remaining 5 included patients receiving PCI.32,36,3941 Eight of the 15 observational studies were single center,3032,3638,41,42 whereas the remaining 7 were multicenter studies.29,30,33,35,39,40,43

Although none used a sham device and therefore all were unblinded, we believe that the use of mortality as the primary outcome would prevent the lack of blinding from contributing substantial bias. The summary table for risk of bias is shown in eTable 3 in the Supplement. Publication bias was assessed using a funnel plot, which did not show significant asymmetry (eFigure in the Supplement).

Randomized Clinical Trials

In the 12 RCTs (2123 patients) (Figure 2), there was no significant effect on mortality overall (OR, 0.96 [95% CI, 0.74-1.24]; P = .74). There was no significant evidence of heterogeneity (τ2 = 0.00, I2 = 0%; P = .52). There were 177 deaths in the 1050 patients randomized to IABP and 184 in the 1073 randomized to control.

In the patients with cardiogenic shock, the odds ratio was 0.94 (95% CI, 0.69-1.28; P = .69), whereas in those without shock it was 0.98 (95% CI, 0.57-1.69; P = .95). Three-quarters of deaths were in patients with cardiogenic shock: 134 of 177 (75.7%) in the IABP groups and 138 of 184 (75.0%) in the control groups.

Observational Studies

In contrast, there was significant heterogeneity among the 15 nonrandomized studies (τ2 = 1.04, I2 = 97%; P < .001 [15 530 patients]). Assembled as a single group (Figure 3), they showed a neutral outcome (OR, 0.96 [95% CI, 0.54-1.70]; P = .89). There were 2904 deaths in the 6161 IABP recipients and 4147 in the 9369 patients who did not receive IABP.

The observational data can be considered in categories of patient status: with or without cardiogenic shock; or in categories of reperfusion strategy: no reperfusion, fibrinolysis, or primary PCI. The observational data in patients with cardiogenic shock showed statistically nonsignificant lower mortality in the IABP group (OR, 0.70 [95% CI, 0.47-1.05]; P = .09) albeit with significant heterogeneity (I2 = 92%, τ2 = 0.36; P < .001). In contrast, the studies addressing patients without cardiogenic shock showed a significant opposite association (OR, 7.73 [95% CI, 2.64-22.63]; P < .001), again with significant heterogeneity (I2 = 82%, τ2 = 0.60; P = .003). Almost all deaths occurred in patients with cardiogenic shock: 2803 of the 2904 deaths (96.5%) in IABP recipients and 4068 of 4147 deaths (98.1%) in those who did not receive IABP.

The observational data in patients treated with primary PCI (Figure 4) showed higher mortality in the IABP recipients (OR, 1.96 [95% CI, 1.01-3.83]; P = .05) with significant heterogeneity (I2 = 96%, τ2 = 0.64; P < .001). In contrast, the studies addressing patients treated with fibrinolysis showed statistically nonsignificant lower mortality in the IABP recipients (OR, 0.64 [95% CI, 0.34-1.21]; P = .17), again with significant heterogeneity (I2 = 93%, τ2 = 0.72; P < .001). In the 1 study with neither fibrinolysis nor primary PCI, there was a finding of statistically nonsignificant lower mortality with IABP (OR, 0.08 [95% CI, 0.00-1.38]; P = .08). In patients receiving IABP therapy, mortality was equal in the fibrinolysis and primary PCI groups: 1440 of 2904 (49.6%). In patients not receiving IABP therapy, the majority of deaths were in the fibrinolysis group: 2922 of 4147 deaths (70.5%) occurred in the fibrinolysis group and 1210 of 4147 deaths (29.2%) in the PCI group.

Relationship Between Between-Group Difference in Mortality and Baseline Inequality in Risk Factors

A univariate metaregression analysis found a significant association between the baseline inequality score and the between-group difference in mortality (P = .002) (Figure 5). Whereas in the RCTs, the OR for mortality was uniform across trials (I2 = 0%), in the observational studies it was extremely heterogeneous between the studies (I2 = 97%). On metaregression analysis, much of this heterogeneity was explained by baseline imbalance in risk markers (R2meta = 46.2%; P < .001).

The metaregression analysis allows estimation from the observational studies of what the OR would be when the baseline inequality index is zero (ie, baseline risk markers balanced between study groups). This is the intercept of the regression line at the point where the baseline inequality index is zero. At this point, lnOR was 0.02 (95% CI, −0.53 to 0.56), which in terms of OR is 1.02 (95% CI, 0.59 to 1.76; P = .96).

Discussion

Despite 3 decades of research, there is no prospectively specifiable group of patients with acute myocardial infarction whose mortality is reduced by the insertion of an IABP. The evidence covers more than 17 000 patients and spans the eras during which the concomitant therapy has been no reperfusion, fibrinolysis, and primary PCI. This neutral finding is consistent in patients with and without cardiogenic shock.

The results of the RCTs are extraordinarily uniform, with no statistically detectable heterogeneity. In contrast, in the larger and more representative populations addressed by the observational studies, there is very high heterogeneity. In these observational studies, there at first appear to be differences in outcome between patients with and without cardiogenic shock, with a trend toward lower mortality for patients with cardiogenic shock if they receive an IABP. However, these findings may result from the clear inequality of baseline risk factors, with the IABP recipients having a better baseline risk profile (Figure 3).

Such study-specific inequalities in baseline risk factors between therapy groups also appear to be responsible for the differing outcome associations between observational studies with no reperfusion, those with fibrinolysis, and those with primary PCI (Figure 3). In the majority of these studies, there was a clear tendency for the IABP recipients to have lower risk characteristics during the no-reperfusion and fibrinolysis eras (8 of 9 studies). The metaregression analysis (Figure 5) indicates baseline inequality to be a powerful driver of outcome differences between patient groups in observational studies. More importantly, this method of analyzing the observational studies highlights that an observational study with no baseline inequality would be expected to have equal mortality in the 2 study groups, a finding consistent with the RCT data where it can be observed more simply.

Our analysis extends the 2009 meta-analysis in several ways.44 First, it incorporates important recent data sets including the large IABP SHOCK II RCT2 and several large observational studies.39,40 Second, it applies random-effects meta-analysis (rather than fixed effect) because there is severe heterogeneity among the observational studies (I2 = 97%). Third, it includes 3 separate analyses of the observational studies: meta-analysis stratified by the presence or absence of cardiogenic shock, meta-analysis stratified by modality of reperfusion, and a metaregression analysis adjusting for baseline inequality index. Fourth, our analysis used OR as the summary statistic instead of risk difference. We chose OR because it allows fairer comparison of studies with different background risk levels. This may be important here because control group mortality varied among studies from 3.8%41 to 80.9%.38

The Era of Appropriate Use

It can be difficult to change established clinical practice. In patients with cardiogenic shock, the prognosis is bleak, with few therapeutic options. A very large registry30 showing better outcomes in patients with cardiogenic shock who receive IABP is frequently discussed, yet the extent of baseline patient inequality is rarely mentioned, perhaps because its importance is not universally realized. Charts such as Figure 4 and Figure 5 may assist clinicians in recognizing this.

In the challenging clinical situation of acute myocardial infarction complicated by cardiogenic shock, there is an understandable desire to do something rather than appear to do nothing. This natural human tendency is established in the behavioral literature as “action bias.”45 With the greater data set now available, and the increasing focus on judicious use of limited resources, it is our duty to be continually reassessing the net utility of interventions.

Limitations

We only examined results of published studies and cannot exclude the possibility that there are studies with other results that have not been published. Furthermore, the lack of statistically significant evidence of publication bias on the funnel plot does not give complete reassurance.

The RCTs have provided a very consistent result in terms of low heterogeneity between trials; the observational studies, in contrast, have shown intense heterogeneity. However, it should be remembered that RCTs can only cover the subset of patients who agree to be randomized. With few exceptions,2 RCT entrance criteria are restrictive, which may limit their representativeness. The requirement for prior written informed consent limits the patients who could even be considered for an RCT, a limitation that is only now being addressed by new trial designs,46 which are controversial.47 Randomized clinical trials also often require a complex series of follow-up assessments, which can affect who will agree to be enrolled. Moreover, the intensely supervised environment of RCTs can deliver different concomitant care than that experienced by the general patient population to whom the results will eventually be applied.

The outcome assessed in this study was 30-day mortality, chosen because the ultimate motivation for IABP use is to improve the high mortality in these patients. Moreover, it can be assessed without bias, which is important because all the studies were unblinded. There may be other benefits of IABP, but there are challenges to using them for guiding recommendations for therapy. For example, hemodynamic aspects such as cardiac output and blood pressure are consistently increased by IABP therapy, but this has not translated into a beneficial effect on mortality. Other clinical end points are available, but measuring the effect of IABP without bias in an unblinded study is challenging, even with randomization. Length of stay, for example, is decided by physicians. Better ventricular function or quality of life are desirable, but relying on them as end points requires elaborate steps to deliver blinding. Without blinding, there can be inadvertent assessment bias, and the magnitude of this can be surprisingly large.48,49

In contrast to RCTs, observational studies can cover more comprehensive cohorts of patients and provide larger data sets. They can provide important data on the magnitude of health care problems and identify cohorts with particularly bad outcomes. The challenge in interpreting the outcome associations of therapy in an individual observational study is that there may be baseline imbalance between study groups.50 This can cause the results to not point in the same direction as RCTs, a lesson painfully learned with estrogen therapy for prevention of ischemic heart disease.51 It is important that well-conducted observational studies provide baseline information because this allows analyses such as those in Figures 3, 4, and 5, which may help reconcile results of observational studies with those of RCTs.

The baseline inequality index is a nonparametric score. In attempting to quantify unequal baseline allocation of high-risk patients, we used an approach that readers can understand and reproduce easily. Although more advanced scores might be more desirable in principle, many studies do not report information that would be necessary, for example presenting the mean without the standard deviation.

Conclusions

Intra-aortic balloon pump therapy has now been studied for 30 years, in the context of no reperfusion, fibrinolysis, and primary PCI. Intra-aortic balloon pump therapy does not improve mortality in acute myocardial infarction in the populations studied in RCTs, regardless of the presence or absence of cardiogenic shock. Overall, the observational studies also did not show better outcomes for patients treated with IABP. There was, however, substantial heterogeneity among the observational studies with IABP. These differences may be explained by the different baseline inequalities in the different observational studies.

Back to top
Article Information

Accepted for Publication: February 7, 2015.

Corresponding Author: Sayan Sen, PhD, International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London, 59-61 N Wharf Rd, London W2 1LA, United Kingdom (sayan.sen@imperial.ac.uk).

Conflict of Interest Disclosures: None reported.

Published Online: March 30, 2015. doi:10.1001/jamainternmed.2015.0569.

Author Contributions: Dr Ahmad had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Ahmad, Sen, Shun-Shin, Davies, Cole, Francis.

Acquisition, analysis, or interpretation of data: Ahmad, Sen, Shun-Shin, Ouyang, Finegold, Al-Lamee, Davies, Cole.

Drafting of the manuscript: Ahmad, Sen, Shun-Shin, Ouyang, Finegold, Davies, Cole, Francis.

Critical revision of the manuscript for important intellectual content: Ahmad, Sen, Shun-Shin, Finegold, Al-Lamee, Cole, Francis.

Statistical analysis: Ahmad, Sen, Shun-Shin, Al-Lamee, Cole.

Obtained funding: Francis.

Administrative, technical, or material support: Ahmad, Finegold, Al-Lamee, Cole.

Study supervision: Ahmad, Sen, Shun-Shin, Al-Lamee, Davies, Cole, Francis.

Funding/Support: This research was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Imperial College Healthcare National Health Service (NHS) Trust and Imperial College London. Dr Sen (G1000357) is a Medical Research Council Fellow. Dr Shun-Shin (FS/14/27/30752), Dr Finegold (FS/14/25/30676), Dr Davies (FS/05/006), Dr Cole (FS/12/12/29294), and Dr Francis (FS/10/038) are British Heart Foundation Fellows.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health.

References
1.
Goldberg  RJ, Spencer  FA, Gore  JM, Lessard  D, Yarzebski  J.  Thirty-year trends (1975 to 2005) in the magnitude of, management of, and hospital death rates associated with cardiogenic shock in patients with acute myocardial infarction: a population-based perspective. Circulation. 2009;119(9):1211-1219.
PubMedArticle
2.
Thiele  H, Zeymer  U, Neumann  FJ,  et al; IABP-SHOCK II Trial Investigators.  Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med. 2012;367(14):1287-1296.
PubMedArticle
3.
Fuchs  RM, Brin  KP, Brinker  JA, Guzman  PA, Heuser  RR, Yin  FC.  Augmentation of regional coronary blood flow by intra-aortic balloon counterpulsation in patients with unstable angina. Circulation. 1983;68(1):117-123.
PubMedArticle
4.
Gold  HK, Leinbach  RC, Sanders  CA, Buckley  MJ, Mundth  ED, Austen  WG.  Intraaortic balloon pumping for control of recurrent myocardial ischemia. Circulation. 1973;47(6):1197-1203.
PubMedArticle
5.
Awad  HH, Anderson  FA  Jr, Gore  JM, Goodman  SG, Goldberg  RJ.  Cardiogenic shock complicating acute coronary syndromes: insights from the Global Registry of Acute Coronary Events. Am Heart J. 2012;163(6):963-971.
PubMedArticle
6.
Van de Werf  F, Bax  J, Betriu  A,  et al; ESC Committee for Practice Guidelines (CPG).  Management of acute myocardial infarction in patients presenting with persistent ST-segment elevation: the Task Force on the Management of ST-Segment Elevation Acute Myocardial Infarction of the European Society of Cardiology. Eur Heart J. 2008;29(23):2909-2945.
PubMedArticle
7.
Kushner  FG, Hand  M, Smith  SC  Jr,  et al.  2009 focused updates: ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction (updating the 2004 guideline and 2007 focused update) and ACC/AHA/SCAI guidelines on percutaneous coronary intervention (updating the 2005 guideline and 2007 focused update): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines [published correction appears in J Am Coll Cardiol. 2010;55(6):612]. J Am Coll Cardiol. 2009;54(23):2205-2241.
PubMedArticle
8.
Thiele  H, Zeymer  U, Neumann  FJ,  et al; Intraaortic Balloon Pump in Cardiogenic Shock II (IABP-SHOCK II) trial investigators.  Intra-aortic balloon counterpulsation in acute myocardial infarction complicated by cardiogenic shock (IABP-SHOCK II): final 12 month results of a randomised, open-label trial. Lancet. 2013;382(9905):1638-1645.
PubMedArticle
9.
O’Gara  PT, Kushner  FG, Ascheim  DD,  et al; American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.  2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2013;127(4):e362-e425.
PubMedArticle
10.
Windecker  S, Kolh  P, Alfonso  F,  et al; Authors/Task Force Members.  2014 ESC/EACTS Guidelines on myocardial revascularization: the Task Force on Myocardial Revascularization of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS)—developed with the special contribution of the European Association of Percutaneous Cardiovascular Interventions (EAPCI). Eur Heart J. 2014;35(37):2541-2619.
PubMedArticle
11.
Moher  D, Liberati  A, Tetzlaff  J, Altman  DG; PRISMA Group.  Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med. 2009;151(4):264-269, W64.
PubMedArticle
12.
Higgins  JP, Altman  DG, Gøtzsche  PC,  et al; Cochrane Bias Methods Group; Cochrane Statistical Methods Group.  The Cochrane Collaboration’s tool for assessing risk of bias in randomised trials. BMJ. 2011;343:d5928.
PubMedArticle
13.
Stroup  DF, Berlin  JA, Morton  SC,  et al; Meta-analysis of Observational Studies in Epidemiology (MOOSE) group.  Meta-analysis of observational studies in epidemiology: a proposal for reporting. JAMA. 2000;283(15):2008-2012.
PubMedArticle
14.
Review Manager (RevMan), Version 5.0. Copenhagen, Denmark: The Nordic Cochrane Centre, The Cochrane Collaboration; 2008.
15.
Higgins  JP, Thompson  SG.  Quantifying heterogeneity in a meta-analysis. Stat Med. 2002;21(11):1539-1558.
PubMedArticle
16.
R Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2013.
17.
Viechtbauer  W.  Conducting meta-analyses in R with the metafor package. J Stat Softw. 2010;36(3):1-48.
18.
Ohman  EM, Nanas  J, Stomel  RJ,  et al; TACTICS Trial.  Thrombolysis and counterpulsation to improve survival in myocardial infarction complicated by hypotension and suspected cardiogenic shock or heart failure: results of the TACTICS Trial. J Thromb Thrombolysis. 2005;19(1):33-39.
PubMedArticle
19.
Prondzinsky  R, Lemm  H, Swyter  M,  et al.  Intra-aortic balloon counterpulsation in patients with acute myocardial infarction complicated by cardiogenic shock: the prospective, randomized IABP SHOCK Trial for attenuation of multiorgan dysfunction syndrome. Crit Care Med. 2010;38(1):152-160.
PubMedArticle
20.
Flaherty  JT, Becker  LC, Weiss  JL,  et al.  Results of a randomized prospective trial of intraaortic balloon counterpulsation and intravenous nitroglycerin in patients with acute myocardial infarction. J Am Coll Cardiol. 1985;6(2):434-446.
PubMedArticle
21.
Gu  J, Hu  W, Xiao  H, Feng  X, Chen  Y, Zhang  D.  Intra-aortic balloon pump improves clinical prognosis and attenuates C-reactive protein level in acute STEMI complicated by cardiogenic shock. Cardiology. 2010;117(1):75-80.
PubMedArticle
22.
Kono  T, Morita  H, Nishina  T,  et al.  Aortic counterpulsation may improve late patency of the occluded coronary artery in patients with early failure of thrombolytic therapy. J Am Coll Cardiol. 1996;28(4):876-881.
PubMedArticle
23.
O’Rourke  MF, Norris  RM, Campbell  TJ, Chang  VP, Sammel  NL.  Randomized controlled trial of intraaortic balloon counterpulsation in early myocardial infarction with acute heart failure. Am J Cardiol. 1981;47(4):815-820.
PubMedArticle
24.
Ohman  EM, George  BS, White  CJ,  et al; Randomized IABP Study Group.  Use of aortic counterpulsation to improve sustained coronary artery patency during acute myocardial infarction: results of a randomized trial. Circulation. 1994;90(2):792-799.
PubMedArticle
25.
Stone  GW, Marsalese  D, Brodie  BR,  et al; Second Primary Angioplasty in Myocardial Infarction (PAMI-II) Trial Investigators.  A prospective, randomized evaluation of prophylactic intraaortic balloon counterpulsation in high risk patients with acute myocardial infarction treated with primary angioplasty. J Am Coll Cardiol. 1997;29(7):1459-1467.
PubMedArticle
26.
van ’t Hof  AW, Liem  AL, de Boer  MJ, Hoorntje  JC, Suryapranata  H, Zijlstra  F.  A randomized comparison of intra-aortic balloon pumping after primary coronary angioplasty in high risk patients with acute myocardial infarction. Eur Heart J. 1999;20(9):659-665.
PubMedArticle
27.
Vijayalakshmi  K, Kunadian  B, Whittaker  VJ,  et al.  Intra-aortic counterpulsation does not improve coronary flow early after PCI in a high-risk group of patients: observations from a randomized trial to explore its mode of action. J Invasive Cardiol. 2007;19(8):339-346.
PubMed
28.
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.
PubMedArticle
29.
Anderson  RD, Ohman  EM, Holmes  DR  Jr,  et al.  Use of intraaortic balloon counterpulsation in patients presenting with cardiogenic shock: observations from the GUSTO-I Study—Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries. J Am Coll Cardiol. 1997;30(3):708-715.
PubMedArticle
30.
Barron  HV, Every  NR, Parsons  LS,  et al; Investigators in the National Registry of Myocardial Infarction 2.  The use of intra-aortic balloon counterpulsation in patients with cardiogenic shock complicating acute myocardial infarction: data from the National Registry of Myocardial Infarction 2. Am Heart J. 2001;141(6):933-939.
PubMedArticle
31.
Bengtson  JR, Kaplan  AJ, Pieper  KS,  et al.  Prognosis in cardiogenic shock after acute myocardial infarction in the interventional era. J Am Coll Cardiol. 1992;20(7):1482-1489.
PubMedArticle
32.
Gu  J, Hu  W, Xiao  H,  et al.  Prophylactic intra-aortic balloon pump reduces C-reactive protein levels and early mortality in high-risk patients undergoing percutaneous coronary intervention. Acta Cardiol. 2011;66(4):499-504.
PubMed
33.
Kovack  PJ, Rasak  MA, Bates  ER, Ohman  EM, Stomel  RJ.  Thrombolysis plus aortic counterpulsation: improved survival in patients who present to community hospitals with cardiogenic shock. J Am Coll Cardiol. 1997;29(7):1454-1458.
PubMedArticle
34.
Moulopoulos  S, Stamatelopoulos  S, Petrou  P.  Intraaortic balloon assistance in intractable cardiogenic shock. Eur Heart J. 1986;7(5):396-403.
PubMed
35.
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.
PubMedArticle
36.
Sjauw  KD, Engström  AE, Vis  MM,  et al.  Efficacy and timing of intra-aortic counterpulsation in patients with ST-elevation myocardial infarction complicated by cardiogenic shock. Neth Heart J. 2012;20(10):402-409.
PubMedArticle
37.
Stomel  RJ, Rasak  M, Bates  ER.  Treatment strategies for acute myocardial infarction complicated by cardiogenic shock in a community hospital. Chest. 1994;105(4):997-1002.
PubMedArticle
38.
Waksman  R, Weiss  AT, Gotsman  MS, Hasin  Y.  Intra-aortic balloon counterpulsation improves survival in cardiogenic shock complicating acute myocardial infarction. Eur Heart J. 1993;14(1):71-74.
PubMedArticle
39.
Zeymer  U, Bauer  T, Hamm  C,  et al.  Use and impact of intra-aortic balloon pump on mortality in patients with acute myocardial infarction complicated by cardiogenic shock: results of the Euro Heart Survey on PCI. EuroIntervention. 2011;7(4):437-441.
PubMedArticle
40.
Zeymer  U, Hochadel  M, Hauptmann  KE,  et al.  Intra-aortic balloon pump in patients with acute myocardial infarction complicated by cardiogenic shock: results of the ALKK-PCI registry. Clin Res Cardiol. 2013;102(3):223-227.
PubMedArticle
41.
Brodie  BR, Stuckey  TD, Hansen  C, Muncy  D.  Intra-aortic balloon counterpulsation before primary percutaneous transluminal coronary angioplasty reduces catheterization laboratory events in high-risk patients with acute myocardial infarction. Am J Cardiol. 1999;84(1):18-23.
PubMedArticle
42.
Kumbasar  SD, Semiz  E, Sancaktar  O, Yalçinkaya  S, Ermiş  C, Değer  N.  Concomitant use of intraaortic balloon counterpulsation and streptokinase in acute anterior myocardial infarction. Angiology. 1999;50(6):465-471.
PubMedArticle
43.
Ohman  EM, Califf  RM, George  BS,  et al; Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) Study Group.  The use of intraaortic balloon pumping as an adjunct to reperfusion therapy in acute myocardial infarction. Am Heart J. 1991;121(3, pt 1):895-901.
PubMedArticle
44.
Sjauw  KD, Engström  AE, Vis  MM,  et al.  A systematic review and meta-analysis of intra-aortic balloon pump therapy in ST-elevation myocardial infarction: should we change the guidelines? Eur Heart J. 2009;30(4):459-468.
PubMedArticle
45.
Ayanian  JZ, Berwick  DM.  Do physicians have a bias toward action? a classic study revisited. Med Decis Making. 1991;11(3):154-158.
PubMedArticle
46.
Shahzad  A, Kemp  I, Mars  C,  et al; HEAT-PPCI trial investigators.  Unfractionated heparin versus bivalirudin in primary percutaneous coronary intervention (HEAT-PPCI): an open-label, single centre, randomised controlled trial. Lancet. 2014;384(9957):1849-1858.
PubMedArticle
47.
Wood  S. HEAT-PPCI: heparin bests bivalirudin in STEMI, amid heated debate. http://www.medscape.com/viewarticle/822927. Accessed December 14, 2014.
48.
Jabbour  RJ, Shun-Shin  MJ, Finegold  JA,  et al.  Effect of study design on the reported effect of cardiac resynchronization therapy (CRT) on quantitative physiological measures: stratified meta-analysis in narrow-QRS heart failure and implications for planning future studies. J Am Heart Assoc. 2015;4(1):e000896.
PubMedArticle
49.
Howard  JP, Francis  DP.  Overcoming the three biases obscuring the science of renal denervation in humans: big-day bias, check-once-more bias and I-will-take-it-now bias [published online ahead of print October 31, 2014]. Trends Cardiovasc Med. doi: 10.1016/j.tcm.2014.10.011.
PubMed
50.
Sen  S, Davies  JE, Malik  IS,  et al.  Why does primary angioplasty not work in registries? quantifying the susceptibility of real-world comparative effectiveness data to allocation bias. Circ Cardiovasc Qual Outcomes. 2012;5(6):759-766.
PubMedArticle
51.
Lawlor  DA, Davey Smith  G, Ebrahim  S.  Commentary: the hormone replacement-coronary heart disease conundrum: is this the death of observational epidemiology? Int J Epidemiol. 2004;33(3):464-467.
PubMedArticle
×