MUNICH, Germany—Although use of an intra-aortic balloon pump (IABP) in patients with acute myocardial infarction (AMI) complicated by cardiogenic shock appears safe, the technique does not improve short-term mortality compared with optimal medical therapy when early revascularization is planned. The findings from a randomized study were reported by Holger Thiele, MD, of the University of Leipzig-Heart Center (Leipzig, Germany), August 27, 2012, at the European Society of Cardiology (ESC) Congress and simultaneously published online ahead of print in the New England Journal of Medicine.

Dr. Thiele pointed out that while IABP has been used for almost 5 decades and carries a class I recommendation for this indication (IB from the AHA/ACC and IC from the ESC, until its very recent downgrading), the guidelines were based largely on registry data. Because cardiologists have not been convinced of the efficacy of the procedure, it is currently deployed in only about 25% to 40% of cases.

To help resolve the uncertainty, the 37-center IABP-SHOCK (Intra-aortic Balloon Pump in Cardiogenic Shock) II trial randomized 600 patients with AMI and cardiogenic shock who were expected to undergo early revascularization to optimal medical therapy with (n = 301) or without (n = 299) IABP.

Among patients in the control group, 10% subsequently underwent IABP insertion, most within the first 24 hours of randomization. On the other hand, 4.3% of patients assigned to an IABP did not receive the device, in many instances because the patient had died. Balloon insertion occurred before or immediately after revascularization, which was PCI in 95.8% of patients. The median duration of IABP support was 3.0 days (interquartile range, 2.0-4.0).

Thirty-Day Mortality Equivalent

Mortality at 30 days, the primary endpoint, was equivalent between the IABP and control groups (39.7% and 41.3%, respectively; log-rank P = 0.92).

Results were consistent in all subgroups, except for a lower mortality in the control group among patients who had had a previous MI (P = 0.04). In addition, there was no interaction between mortality and the timing of IABP insertion before (n = 37) or after (n = 240) revascularization.

Results were similar for all secondary endpoints or process-of-care measures, including time to hemodynamic stabilization, length of stay in the ICU, serum lactate levels, dose and duration of catecholamine therapy, and renal function. IAPB patients were half as likely to receive an active left ventricular assist device, although the difference did not reach statistical significance (3.7% vs. 7.4%; P = 0.053).

No Harm Done

On the other hand, IABP use appeared safe, with no higher rates of in-hospital stroke, GUSTO life-threatening/severe bleeding, peripheral ischemic complications requiring intervention, or sepsis than in the placebo group. Rates of reinfarction and stent thrombosis were also similar for the 2 arms.

In a press conference, Dr. Thiele noted that some data suggest that high-risk patients who undergo CABG may yet benefit from IABP use, but that requires further research.

Commenting on the presentation, Uta C. Hoppe, MD, of Paracelsus Medical University (Salzburg, Germany), said that the crossover rate of 10% to IABP therapy and more frequent use of left ventricular assist devices in control patients (7.4% vs. 3.7%) might to some extent have influenced the results.

Moreover, given that the IABP-SHOCK trial was also negative at 30 days and only became positive after 6 and 12 months, further follow-up of IABP-SHOCK II will be of interest, she said. 

Hemodynamic Status Does Not Predict Survival

One conclusion to be drawn from the current data, Dr. Hoppe said, is that improved hemodynamic status alone is not a surrogate marker for survival in MIs complicated by cardiogenic shock. The neutral effect of IABP use on outcome in the present study might in part be due to the fact that unlike fibrinolysis, PCI does not rely on coronary perfusion pressure to establish patency, she added.

On the other hand, the procedure’s lack of impact might also underscore the more complex pathophysiology of cardiogenic shock. In that case, the high mortality rates in cardiogenic shock are unlikely to be due to “underuse” of IABP therapy. Still, results of the IABP-SHOCK II trial do not support general IABP implantation in patients undergoing primary revascularization for MI complicated by shock.

Guidelines “Strongly Challenged”

In an editorial accompanying the study in NEJM, Christopher M. O’Connor, MD, and Joseph G. Rogers, MD, both of Duke University (Durham, NC), say the study results were “surprising,” adding that “although IABP was safe, there was no evidence that it was associated with hemodynamic improvement—a mechanistic effect of IABP that has long been considered to be critical for its clinical application.”

The study has a number of limitations, they point out. For example, the modest sample size means it is not definitive, and the fact that the cohort is only moderate risk suggests the findings may not apply to higher-risk patients. And like Dr. Hoppe, they note that patients crossing over to IABP may have influenced the final results.

But in the end, they write, “the data do not support the routine use of IABP in [AMI patients] complicated by cardiogenic shock, and the level I guideline recommendation is now strongly challenged.”

2. Thiele H, Zeymer U, Neumann F-J, et al. Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med. 2012;Epub ahead of print.

3. O’Connor CM, Rogers JG. Evidence for overturning the guidelines in cardiogenic shock. N Engl J Med. 2012:Epub ahead of print.

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