Your patient is in trouble. He has just suffered a myocardial infarction; now his systolic blood pressure is below 90, his skin is clammy, his urine output is minimal, and he is in respiratory distress. What should you do?
Recognizing that he is in cardiogenic shock, you consider using an intraaortic balloon pump (IABP). International guidelines recommend IABP as a class I treatment; it’s thought to improve coronary blood flow and reduce afterload.
But does the use of IABP actually extend life? Previous studies have been inconclusive. And according to the results of the IABP-SHOCK II Trial, published in this week’s NEJM, the answer may be no.
This prospective study enrolled 600 patients with acute myocardial infarction complicated by cardiogenic shock, all of whom were expected to undergo early revascularization by coronary artery bypass surgery or percutaneous coronary intervention. Patients were randomized to either receive (intervention group) or not receive (control group) intraaortic balloon counterpulsation. The primary outcome of interest was 30-day all-cause mortality.
At 30 days, the mortality rate was 39.7% for the intervention group (119 out of 300 patients) and 41.3% for the control group (123 out of 298 patients). The difference between groups was not statistically significant (95% CI: 0.79 to 1.17, P=0.69). There was also no statistically significant difference along a number of secondary dimensions.
While no clear benefit was observed, the use of IABP didn’t appear to be harmful: complication rates were similar between the intervention and control groups, although this may be a reflection of the participation of highly experienced centers.
It is possible that by enrolling patients of moderate risk, the study failed to capture mortality benefits conferred by IABP for higher risk patients. Still, the results may give one pause. Current clinical practice guidelines endorsing the use of IABP have little outcomes data to support them. Particularly in light of these new study findings, it may be time to reevaluate the recommendation to use IABP.
More generally, the study highlights the need to rigorously evaluate any assumptions that may influence how clinical trials are designed. In an accompanying editorial, Drs. Christopher O’Connor and Joseph Rogers write, “In an era of rapid intervention in the catheterization laboratory and a pervasive perception of lack of equipoise, the IABP-SHOCK II investigators should be commended for completing a moderate-sized trial in 3 years at 37 sites.” They add: “We hope that the results of this trial will galvanize a broadly based mandate to address this devastating clinical problem by reestablishing equipoise and international engagement in research on novel devices and pharmacologic therapies.”
In your current practice, what influences your decision to either use or not use IABP to treat cardiogenic shock in the setting of acute myocardial infarction? What is the relative importance of published treatment guidelines?