Cardiogenic Shock Complicating Acute Myocardial Infarction

Results of a randomized, prospective, open-label, multicenter trial [N Engl J Med. 2012; DOI:10.1056/NEJMoa1208410] showed no significant reduction in 30-day mortality in patients with cardiogenic shock complicating acute myocardial infarction who underwent intra-aortic balloon counterpulsation compared with those who did not. In addition, use of intra-aortic balloon counterpulsation was not associated with any significant differences in time to hemodynamic stabilization, length of stay in the intensive care unit, serum lactate levels, dose and duration of catecholamine therapy, or renal function.

Based largely on registry data, current US and European guidelines recommend the use of an intra-aortic balloon to treat patients in cardiogenic shock complicating myocardial infarction. However, recent randomized data from a small trial of 45 patients found no difference in the severity of illness between patients assigned to intra-aortic balloon counterpulsation and those assigned to a control group of standard care.

In an effort to provide stronger evidence on the efficacy and safety of using intra-aortic balloon counterpulsation in patients with cardiogenic shock complicating acute myocardial infarction, the IABP-SHOCK (Intra-aortic Balloon Pump in Cardiogenic Shock) trial assessed reduction in 30-day all-cause mortality in patients with cardiogenic shock complicating myocardial infarction randomized to intra-aortic balloon counterpulsation (treatment group; n=300) or no intra-aortic balloon counterpulsation (control group; n=298).

Patients with acute myocardial infarction complicated by cardiogenic shock for whom early revascularization was planned were eligible for the study. Cardiogenic shock was defined as having a systolic blood pressure of <90 mm Hg for >30 minutes or the need to maintain a systolic pressure >90 mm Hg by infusion of catecholamine, clinical signs of pulmonary congestion, and impaired end-organ perfusion.

Patients excluded from the study were those >90 years of age; those who had undergone resuscitation for >30 minutes; had no intrinsic heart action; were in a coma; had mechanical cause of cardiogenic shock; had onset of shock >12 hours prior to screening; had a massive pulmonary embolism, severe peripheral arterial disease, or aortic regurgitation >grade II in severity; were in shock; or had a life expectancy of <6 months due to a severe concomitant disease.

The study found no difference in a reduction in 30-day all-cause mortality between the 2 groups. Of the patients in the treatment group, 119 (39.7%) died compared with 123 (41.3%) of patients in the control group, representing a relative risk of 0.96 (95% confidence interval, 0.79-1.17; P=.69).

The study also found no differences between the treatment and control groups in secondary end points, including the time to hemodynamic stabilization, length of intensive care unit stay, serum lactate levels, dose and duration of catecholamine therapy, and renal function.

The lack of significant differences between the 2 groups in these multiple secondary end points, according to the authors, reinforces the main finding of the study that found no significant 30-day mortality reduction.

No differences were found between the treatment and control groups with rates of major bleeding in 3.3% and 4.4%, respectively (P=.51), rates of ischemic complications in 4.3% and 3.4% (P=.53), sepsis in 15.7% and 20.5% (P=.15), and stroke in 0.7% and 1.7% (P=.28).

Limitations of the study included lack of blinding, inclusion of only blood pressure, heart rate, and C-reactive measurements and no other hemodynamic measurements or laboratory inflammatory markers, the possibility that the slightly lower mortality rate may have been due to selection bias of including a higher percentage of patients with mild or moderately severe cardiogenic shock, and lack of data on longer-term outcomes.