Patients who experience cardiogenic shock after acute myocardial infarction (AMI) have alarmingly high mortality rates, and judging from a new study, one current recommended treatment may make little difference in terms of 30-day survival. Treatment guidelines for AMI patients in whom early revascularization is planned include mechanical hemodynamic support-most commonly in the form of an intraaortic balloon pump (IABP)-a class I recommendation in the United States and in international guidelines. The treatment has been credited with enhanced coronary blood flow, increased perfusion of vital organs, maintenance of infarct artery patency, and decreased systemic inflammation. Evidence supporting these assertions, however, has so far been limited; support for IABP use has been based mainly on registry data and few adequately powered randomized trials. Thiele and colleagues at the Leipzig Heart Center (University of Leipzig, Leipzig, Germany) noted this paucity of clinical trials and set out to compare the efficacy of IABP counterpulsation with that of standard therapy.
Between June 2009 and March 2012, the team studied 600 patients from 37 medical centers in Germany, randomly assigning them either to an IABP treatment group (301 patients) or a non-IABP treatment group (controls, 299 patients). At 30 days, all-cause mortality was similar among patients in the two groups-39.7% in the IABP group and 41.3% in the control group. Although the authors make it clear that the use of an IABP proved safe, with no significant differences between the groups in rates of stroke, bleeding, sepsis, or peripheral ischemic complications, they found no real benefit to its use.
In an accompanying editorial, O'Connor and Rogers write that the patients represented a moderate-risk cohort, with a 30-day mortality rate of 40%-lower than that in other trials involving patients with cardiogenic shock-so the results may not apply to patients at highest risk. Despite this fact and the small study size, they conclude that the data don't support the routine use of an IABP in AMI patients with cardiogenic shock, and they express hope that the study will galvanize interest in exploring new and innovative solutions to this devastating clinical problem.
Clinicians, however, shouldn't necessarily expect a sea change in the treatment of AMI patients, but rather a more carefully focused look at the treatment and its applications. "Many critical care nurses could share that they have seen patients improve hemodynamically with the use of IABPs and argue that there is benefit with its use in cardiogenic shock, based on case-specific data," says Rochelle Armola, director of trauma services at ProMedica Toledo Hospital in Toledo, Ohio. However, she added, it should also give nurses pause when a guideline recommendation is made at a high level, such as class I, despite insufficient research to support it. "That recommendation needs to be reexamined," she says.
"What the trial really emphasizes is the need to revascularize the patients as soon as possible," says Gordon Tomaselli, immediate past president of the American Heart Association and chief of the Division of Cardiology at the Johns Hopkins Hospital in Baltimore, Maryland. He notes that although the IABP offers no mortality benefit early on, at least one study has indicated that it might do so at six months or further out.
"With future randomized trials," says Armola, "we may find the results of this research to be confirmed, challenged, or population specific. Until then, we will probably begin to see some practitioners giving more careful consideration to IABP use."-Laura Wallis
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