IABP for MI with Cardiogenic Shock?
Abstract & Commentary
By Andrew J. Boyle, MBBS, PhD
Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco
Source: Thiele H, et al. Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med 2012; Aug 26. [Epub ahead of print.]
Patients who present with acute myocardial infarction (MI) complicated by cardiogenic shock represent a group at high risk for early mortality. Current guidelines recommend the use of intra-aortic balloon pump (IABP) for these patients, but there are few randomized, controlled trial data to support this. Thiele and colleagues studied the effects of IABP in 600 patients presenting with MI and cardiogenic shock. Patients were eligible for the study if they presented with acute MI (with or without ST elevation) and cardiogenic shock, defined as a systolic blood pressure (BP) lower than 90 mmHg for ≥ 30 minutes, or the requirement for catecholamine infusion to maintain BP > 90 mmHg, plus signs of pulmonary congestion and end-organ hypoperfusion (altered mental status, oliguria, cold clammy skin, or elevated serum lactate). Exclusion criteria included age ≥ 90 years, resuscitation from cardiac arrest for > 30 minutes, severe peripheral arterial disease precluding IABP, aortic regurgitation ≥ grade II, shock for > 12 hours, mechanical cause for shock (e.g., ruptured papillary muscle), or life expectancy < 6 months. Patients were randomized to receive IABP (n = 301) vs no IABP (n = 299) in an open-label fashion. All patients were expected to undergo early revascularization. The IABP could be inserted before or after percutaneous coronary intervention (PCI) and the mode of revascularizaton was left to the discretion of the operator. The primary endpoint was 30-day, all-cause mortality.
The baseline characteristics were similar between groups. The median age was 70 years; two-thirds were male and one-third were diabetic. The median systolic BP was 89 mmHg at study entry. There was no difference between groups in the primary endpoint of death at 30 days (39.7% in the IABP group vs 41.3% in the control group; P = 0.69). The authors performed intention-to-treat and per-protocol analyses of the primary outcome, as well as a multivariable analysis, and there were no differences between groups by any of these methods. There was no difference in mortality when the IABP was placed before or after PCI. Subgroup analysis revealed no difference in mortality between the IABP group and the control group when stratified by gender, diabetic status, STEMI vs non-STEMI, anterior MI vs non-anterior MI, BP above or below 80 mmHg, or first vs subsequent MI. When stratified by age, those younger than 50 years appeared to have a mortality benefit with IABP (19.4% in IABP group vs 44.1% in control group), but there was no difference in the 50-75 years group or the > 75 years group and the P-value for interaction with age did not reach statistical significance.
There were no differences in the rates of in-hospital stroke, recurrent MI, stent thrombosis, bleeding, sepsis, or peripheral arterial complications requiring intervention. There were no differences in the secondary endpoints of serum creatinine, C-reactive protein, and lactate levels. The authors conclude that the use of IABP did not significantly reduce 30-day mortality in patients with cardiogenic shock, complicating acute MI in those who undergo early revascularization.
This is a resoundingly negative study. Not only was the primary endpoint of all-cause mortality negative, the secondary endpoints were also all negative. Importantly, there were no differences whether the patient was experiencing a STEMI or non-STEMI. There was some suggestion that young patients may benefit from IABP, but this did not reach statistical significance. This study calls into question the routine use of IABP in patients with cardiogenic shock complicating MI. Should we abandon IABP completely in this setting? Or are there some patients who may still benefit from IABP in cardiogenic shock complicating MI? I think there are still some patients who may benefit from selective use of IABP in this setting. First, there may be benefit for IABP in patients with impaired coronary flow after PCI, as IABP counterpulsation augments coronary perfusion. Second, the use of IABP may allow lower doses of inotropes/pressors. In some patients, such as those with arrhythmias caused by inotropes, there may be a benefit to ceasing the inotropes and IABP may be the only way this is possible. In this paper, we are not told about adequacy of coronary flow after PCI or about arrhythmias.
Some limitations of the study should be acknowledged. First, we are not told of the effect of IABP on other meaningful endpoints, such as heart failure and ejection fraction. If there is improvement in these parameters, there may be an indication for using IABP despite a lack of mortality benefit. Second, subjects were not blinded to which group they were in; however, the clinical events committee was blinded to the treatment group of each subject. Third, we are not told details of PCI, in particular, how many patients underwent culprit-only vs multivessel stenting. This is important as it may affect overall mortality.
This study reaffirms that the mortality associated with cardiogenic shock complicating acute MI remains very high, despite early revascularization and modern intensive medical therapy. There is a need for better treatment in this group of patients. Perhaps newer percutaneously placed left ventricular assist devices may take over from IABP in the treatment of cardiogenic shock, but this remains to be tested in adequately powered clinical trials.