AMIHOT: No 30-day benefit from superoxygenated blood infusion after AMI stenting

New Orleans, LA - Intracoronary infusion of oxygen-supersaturated blood after stenting in patients with acute MI had no effect on infarct size or 30-day clinical outcomes in the multicenter Acute Myocardial Infarction with Hyperoxemic Therapy (AMIHOT) trial reported at the American College of Cardiology 2004 Scientific Sessions. But its investigators say there is reason to hope the novel treatment will lead to LV functional preservation at the prospectively planned three-month echocardiographic follow-up.

Dr William W O'Neill

Of the randomized trial's 252 patients who underwent primary or rescue stenting within 24 hours of an acute MI, those who received an immediate infusion of autologous blood mixed with aqueous O₂ showed no significant differences in degree of 24-hour ST-segment resolution or creatine-kinase release as compared with the control group. Nor were there differences in a composite end point of 30-day death, reinfarction, stroke, or target-vessel revascularization, said Dr William W O'Neill (William Beaumont Hospital, Royal Oak, MI) in his formal AMIHOT presentation.

"The ST-segment data trended in the right direction," O'Neill told heartwire . "And we were pleased that there was absolutely no problem with safety. That's the first hurdle in terms of approval of a device." And, he noted, there were hints of a possible benefit for some patients. In the trial's 143 patients with anterior MI, those treated with aqueous O₂ showed 25% more ST-segment resolution as compared with controls, but even in this higher-risk subgroup the difference fell short of significance.

"We're disappointed that we didn't show a benefit in the ST-segment Holter data," O'Neill told heartwire . "But we're really hanging our hat on the convalescent left-ventricular function," which he still hopes will show improvement. Those data are scheduled for release at the May 2004 Euro-PCR meeting in Paris, O'Neill said.

Dr Jack L Martin

At a press conference, Dr Jack L Martin (Main Line Health, Bryn Mawr, PA) presented preliminary data from 68 AMIHOT patients enrolled at his center, suggesting those hopes might be borne out, at least in some patients. Aqueous O₂ treatment was associated with a 60% increase in ventricular wall motion at three-month echocardiography among those with anterior MI.

In an interview, Martin described a possible mechanism for such a delayed benefit. Not only may the treatment increase O₂ delivery to jeopardized myocytes, it may also prevent permanent damage to the myocardial capillary bed. "We think that it's salvaging the ischemic cells in the microcirculation itself, the endothelial cells that have become swollen," he said. "We hope that an intact microcirculation will allow normal healing processes to happen more effectively."

The possibility of a late functional benefit is based on several pilot trials of the technique. In one of them, a published observational study, post-PCI aqueous O₂ infusion in 29 patients with acute MI was associated with significantly improved global ventricular wall-motion scores at 24 hours, with progressive improvement over three months. The benefit was largely due to functional recovery in the infarct zone.

Aqueous O₂ therapy: How it works

TherOx AO cartridge (Source: TherOx)

The TherOx^® AO System (TherOx Inc, Irvine, CA, which funded the AMIHOT trial) has been available in Europe since October 2001 but remains investigational elsewhere. The device combines physiologic saline with 100% O₂ at 25 000 psi, then mixes the superoxygenated solution with the patient's blood at a 3:72 concentration in a disposable three-chambered canister. The mixture is essentially free of microbubbles. After final retraction of the stent-delivery catheter, a proprietary infusion catheter is advanced through conventional guides to deliver the superoxygenated blood to the infarct-related artery at 75 mL/min. The procedure takes about 90 minutes.

According to AMIHOT investigator Martin, the learning curve for PCI operators is short, as the procedure involves few new skills, at least once the mixing apparatus is prepped and the superoxygenated blood ready to deliver.

AMIHOT: Patient features at baseline and acute therapy

Heartwire from Medscape © 2004 

Cite this: AMIHOT: No 30-day benefit from superoxygenated blood infusion after AMI stenting - Medscape - Mar 15, 2004.