Intra-aortic Balloon Counterpulsation and Infarct Size. Part 2
The methods used in the Counterpulsation to Reduce Infarct Size Pre-PCI Acute Myocardial Infarction (CRISP AMI) trial have been previously reported. In brief, CRISP AMI was a prospective, open, international, multicenter (N = 30) randomized controlled trial to determine if a routine strategy of IABC insertion prior to primary PCI reduced infarct size in patients with acute anterior STEMI without cardiogenic shock. Patients in the standard of care group of the trial received primary PCI without planned IABC support.
Institutional review boards and ethics committees approved the trial, and each enrolled patient provided written informed consent. The Duke Clinical Research Institute (Durham, North Carolina) coordinated the trial and carried out the data management and analyses with oversight from the steering committee. An independent data and safety monitoring board monitored the study and oversaw the safety and efficacy of the trial. Members of the steering committee were involved in study design, provided oversight during the conduct of the study, and had full access to the data after data lock and unblinding.
Study Population
To determine if IABC reduces infarct size, a population of adult patients within 6 hours of chest pain onset and planned primary PCI for acute anterior STEMI with significant myocardium at risk were sought for inclusion into the study. A 12-lead electrocardiogram demonstrating ST-segment elevation of 2 mm or higher in 2 contiguous anterior leads or a total elevation of 4 mm or higher in anterior leads was required for inclusion demonstrating significant at-risk myocardium. Patients with indications for planned IABC insertion such as cardiogenic shock, inability to undergo IABC implantation, fibrinolysis within 72 hours of presentation, or known contraindication for cardiac magnetic resonance imaging (MRI) for end point assessment were excluded. Because the primary end point was infarct size, patients with known prior myocardial infarction (MI) or coronary artery bypass graft surgery also were excluded.
Interventions and Procedures
Patients were randomized to prereperfusion initiation of IABC and mechanical reperfusion with PCI (IABC plus PCI) or primary PCI alone. Patients randomized to receive counterpulsation therapy were required to have the intra-aortic balloon inserted and pumping prior to PCI (defined by insertion of the guidewire into the infarct-related artery). Patients randomized to PCI alone may have had subsequent insertion of IABC if there was clinical deterioration. Criteria provided to investigators considering rescue IABC and crossover to counterpulsation included sustained hypotension or cardiogenic shock, uncontrolled arrhythmias, and acute mitral regurgitation or ventricular septal defect.
To ensure rapid reperfusion, sites with demonstrated ability to meet guideline standards were chosen (median door-to-device time <90 minutes). A 24-hour interactive voice response system was used for stratified block randomization, which was based on a computer-generated algorithm. Allocation occurred in random blocks and was stratified by region. In addition, data regarding the timing of first medical contact, randomization, IABC insertion, and first device were captured and monitored by the steering committee and the data and safety monitoring board during the conduct of the trial to ensure continued high-quality care.
Intra-aortic Balloon Counterpulsation and Infarct Size
Primary percutaneous reperfusion for patients with acute ST-segment elevation myocardial infarction (STEMI) has been shown to reduce mortality and is considered the standard of care when available. The benchmarked standards for time to reperfusion have shortened over time; despite significant reductions in door-to-balloon times over the past few years in the United States, the STEMI mortality rate has not significantly improved.
Patients with acute STEMI, representing 30% to 45% of approximately 1.5 million hospitalizations for acute coronary syndromes annually in the United States, are still at substantial acute mortality risk with 1-year mortality estimated to be between 6% and 15%. This may be related to microvascular obstruction resulting in no reflow at the time of mechanical reperfusion and infarct expansion over time. Additionally, this increase in infarct size is associated with adverse remodeling and decreased left ventricular (LV) function leading to heart failure and long-term morbidity following STEMI.
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Intra-aortic balloon counterpulsation (IABC) mechanically augments coronary blood flow, unloads the left ventricle, and reduces myocardial oxygen demand. These favorable hemodynamic effects have led to demonstrated improvements in outcomes, and the recommendation that patients with acute MI and cardiogenic shock be treated with IABC support and reperfusion. Although an older randomized trial of IABC in patients undergoing percutaneous transluminal coronary angioplasty for high-risk STEMI showed a modest potential effect on recurrent ischemia, more recent observational studies suggest a possible clinical benefit in patients with high-risk STEMI receiving IABC prior to reperfusion with percutaneous coronary intervention (PCI) and stenting, with increased clinical use at an early stage in the United States.16 Preclinical animal studies have demonstrated that unloading of the left ventricle with IABC prior to reperfusion reduces infarct size and myocardial salvage.
Therefore, we performed a randomized controlled trial to determine if IABC inserted prior to primary PCI compared with primary PCI alone (standard of care) reduced infarct size in patients with acute anterior STEMI without cardiogenic shock. In addition, a 6-month follow-up for clinical events including all-cause mortality, repeat infarction, and new congestive heart failure was planned.