IABP-SHOCK II: IABP in Myocardial Infarction with Cardiogenic Shock (2012)

“Intra-aortic balloon counterpulsation did not significantly reduce 30-day mortality in patients with cardiogenic shock complicating acute myocardial infarction for whom an early revascularization strategy was planned.”

  • The IABP-SHOCK II Trial Investigators

1. Publication Details

  • Trial Title: Intraaortic Balloon Support for Myocardial Infarction with Cardiogenic Shock
  • Citation: Thiele H, Zeymer U, Neumann FJ, et al. Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med. 2012;367(14):1287-1296. DOI: 10.1056/NEJMoa1208410
  • Published: October 4, 2012, in The New England Journal of Medicine
  • Author: Holger Thiele, M.D.
  • Funding: German Research Foundation; German Cardiac Society; and others.

2. Keywords

  • Myocardial Infarction, Cardiogenic Shock, Intra-Aortic Balloon Pump (IABP), Percutaneous Coronary Intervention (PCI), Mechanical Circulatory Support, Randomized Controlled Trial

3. The Clinical Question

  • In adult patients with acute myocardial infarction (AMI) complicated by cardiogenic shock (Population), does the addition of an intra-aortic balloon pump (IABP) to early revascularization (Intervention) compared to early revascularization alone (Comparison) reduce 30-day all-cause mortality (Outcome)?

4. Background and Rationale

  • Existing Knowledge: Cardiogenic shock complicating AMI has a very high mortality rate. The intra-aortic balloon pump (IABP) was the most widely used form of mechanical circulatory support. It was thought to improve outcomes by increasing coronary blood flow and reducing cardiac afterload. For decades, its use was recommended in guidelines based on physiological principles and observational data.
  • Knowledge Gap: Despite its widespread use and guideline recommendations, there was no high-quality evidence from a large, multicenter randomized controlled trial to determine if IABP therapy actually improved survival in the modern era of early revascularization with PCI.
  • Proposed Hypothesis: The authors hypothesized that the addition of IABP support to early revascularization would be superior to early revascularization alone in reducing 30-day mortality.

5. Study Design and Methods

  • Design: A multicenter, prospective, open-label, randomized, controlled trial (used to test the effectiveness of interventions).
  • Setting: 37 tertiary care centers in Germany.
  • Trial Period: Enrollment ran from June 2009 to March 2012.
  • Population:
    • Inclusion Criteria: Adult patients with AMI complicated by cardiogenic shock, for whom early revascularization (either PCI or CABG) was planned.
    • Exclusion Criteria: Included cardiac arrest with a duration of resuscitation >30 minutes, mechanical causes of shock (e.g., valve rupture), and contraindications to IABP insertion.
  • Intervention: Patients were randomized to receive an intra-aortic balloon pump (IABP) in addition to standard medical therapy and planned early revascularization.
  • Control: Patients were randomized to receive standard medical therapy and planned early revascularization alone, without an IABP.
  • Management Common to Both Groups: All patients were intended to receive early and complete coronary revascularization and best medical therapy for cardiogenic shock.
  • Power and Sample Size: The authors calculated that a sample size of 600 patients would provide 80% power to detect an 8% absolute risk reduction in 30-day mortality. (Power is a study’s ability to find a real difference between treatments if one truly exists; 80% is the standard accepted level for clinical trials).
  • Outcomes:
    • Primary Outcome: All-cause mortality at 30 days.
    • Secondary Outcomes: Included measures of hemodynamic stability, organ perfusion, and rates of complications such as bleeding and stroke.

6. Key Results

  • Enrollment and Baseline: 600 patients were randomized (301 to the IABP group and 299 to the control group). The groups were well-matched at baseline.
  • Trial Status: The trial was completed as planned.
  • Primary Outcome: There was no significant difference in 30-day mortality. 119 of 300 patients (39.7%) in the IABP group died, compared with 123 of 298 patients (41.3%) in the control group (p=0.91).
  • Secondary Outcomes: There were no significant differences between the groups in any of the secondary outcomes, including time to hemodynamic stabilization or organ perfusion markers.
  • Adverse Events: The incidence of major bleeding and peripheral ischemic complications was similar in both groups.

7. Medical Statistics

  • Analysis Principle: The trial was analyzed using an intention-to-treat principle.
  • Statistical Tests Used: The primary outcome was analyzed using a chi-square test.
  • Primary Outcome Analysis: The primary outcome was a comparison of the proportions of death between the two groups.
  • Key Statistic(s) Reported: The key statistics were the absolute mortality rates and the associated P-value.
  • Interpretation of Key Statistic(s):
    • P-value: The p-value of 0.91 for the primary outcome is much higher than the 0.05 threshold, indicating that the result was not statistically significant and very likely due to chance (a result is conventionally considered statistically significant if the p-value is less than 0.05).
  • Clinical Impact Measures: As the trial was neutral, ARR and NNT are not applicable.
  • Subgroup Analyses: No significant differences were found in any of the pre-specified subgroups.

8. Strengths of the Study

  • Study Design and Conduct: The large, multicenter, randomized, controlled design provided high-quality evidence on a critical clinical question.
  • Generalizability: The pragmatic design and inclusion of 37 diverse centers make the findings highly generalizable to real-world practice in similar healthcare systems.
  • Statistical Power: The study was large and adequately powered to confidently rule out a modest but clinically important mortality benefit.
  • Patient-Centered Outcomes: The primary outcome of 30-day mortality is a robust and patient-centered endpoint.

9. Limitations and Weaknesses

  • Internal Validity (Bias): The study was open-label (unblinded), which introduces a risk of performance bias.
  • External Validity (Generalizability): The study population was from a high-income European setting with rapid access to PCI.
  • Other: A small proportion of patients in the control group (10%) crossed over to receive a rescue IABP, which could have diluted the difference between the groups, biasing the result towards the null.

10. Conclusion of the Authors

  • The authors concluded that in patients with AMI complicated by cardiogenic shock who are undergoing early revascularization, the use of an IABP does not reduce 30-day mortality.

11. To Summarize

  • Impact on Current Practice: This was a profoundly practice-changing trial. It provided definitive evidence that a therapy recommended in guidelines for decades was not beneficial. It led to the immediate de-adoption of the routine use of IABP in this population.
  • Specific Recommendations:
    • Patient Selection: For the broad population of adult patients with AMI and cardiogenic shock undergoing early revascularization.
    • Actionable Intervention: Do not routinely place an intra-aortic balloon pump.
  • What This Trial Does NOT Mean: This trial does NOT mean that IABP has no role in the ICU. It may still be considered for specific mechanical complications of MI (e.g., acute mitral regurgitation) or as a bridge in other forms of cardiogenic shock.
  • Implementation Caveats: The key takeaway is that for the most common cause of cardiogenic shock (AMI), routine IABP use is not supported by evidence.

12. Context and Related Studies

  • Building on Previous Evidence: The IABP-SHOCK II trial (2012) was designed to provide a definitive answer to a question that was based on decades of physiological reasoning and observational data but lacked high-quality RCT support.
  • Influence on Subsequent Research: The definitive neutral result of this trial was a major factor in the revision of international cardiology guidelines, which downgraded the recommendation for routine IABP use. It also spurred a great deal of research into other, more powerful forms of mechanical circulatory support, such as Impella and VA-ECMO (e.g., the ECLS-SHOCK trial (2023)).

13. Unresolved Questions & Future Directions

  • Unresolved Questions: The role of IABP in specific subgroups or for other indications (like high-risk PCI without shock) remains an area of investigation.
  • Future Directions: The failure of IABP to improve survival in this trial has shifted the focus of research towards more advanced mechanical circulatory support devices to determine if they can improve the dismal prognosis of cardiogenic shock.

14. External Links

15. Framework for Critical Appraisal

  • Clinical Question: The research question was highly relevant, testing a universally recommended and widely used intervention for a deadly condition.
  • Methods: The large, multicenter, randomized controlled trial design was of high quality. The main methodological weakness is the open-label design, though the primary outcome of mortality is objective and unlikely to be biased.
  • Results: The study reported a clear neutral finding for its primary outcome, with a narrow confidence interval centered on the null value. This provides strong evidence against a meaningful clinical benefit of routine IABP use in this population.
  • Conclusions and Applicability: The authors’ conclusion is a direct and fair reflection of the data. The high external validity of this pragmatic trial means its findings are broadly applicable. This is a classic example of a high-quality “negative” trial that was profoundly practice-changing by providing strong evidence to stop a common but ineffective therapy.

16. Disclaimer and Contact

  • This summary is provided by the Academic Committee of ESBICM (ACE) to facilitate the understanding of this study; readers are advised to refer to the original trial document for a deeper understanding. If you find any information incorrect, or missing, or it needs an update or have a request for a specific critical care trial summary, kindly write to us at academics[at]esbicm.org.
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