During intravenous microbubble infusion, high mechanical index (HMI) impulses from a diagnostic ultrasound transducer helped prevent microvascular obstruction and improved functional outcomes at one-month follow-up in patients with STEMI who underwent PCI.
Lead researcher Wilson Mathias, Jr., MD, of the University of São Paulo Medical School in Brazil, and colleagues published their results online in the Journal of the American College of Cardiology on May 23.
The researchers said that an estimated 1.1 million patients in the U.S. were discharged from hospitals in 2010 with a diagnosis of acute coronary syndrome, including 813,000 with acute MI. Patients with acute STEMI typically receive pharmacological thrombolysis or PCI, which the researchers said improves patients’ prognosis.
This study included 30 patients who had their first STEMI and arrived at the Heart Institute (InCor) University of São Paulo emergency department from May 2014 through September 2015. They were randomized to diagnostic ultrasound HMI impulses before emergent PCI and for an additional 30 minutes after PCI or to low mechanical index (LMI) imaging for perfusion assessments before and after PCI. When applying HMI impulses, the researchers used the 5 percent Definity microbubble infusion (Lantheus Medical Imaging, Inc.) running at 3 to 5 ml/min.
An additional 70 STEMI patients who arrived during times when ultrasound was available served as a control group. Each of the 100 patients received 300 mg of aspirin, 600 mg of clopidogrel, heparin and emergent PCI protocols.
The mean age was 59 years old in the diagnostic ultrasound groups and 60 in the PCI only group. In addition, 37 percent and 59 percent of patients, respectively, had a history of hypertension, while 57 percent and 36 percent of patients, respectively, had a history of smoking.
There were no differences in the groups with regards to the prevalence of diabetes, hyperlipidemia, blood pressure, heart rate or oxygen saturation before or after PCI.
The median door-to-dilation times were 82 minutes in the LMI plus PCI group, 72 minutes in the HMI plus PCI group and 103 minutes in the PCI only group. In addition, 60 percent of patients in the HMI plus PCI group had angiographic recanalization compared with 10 percent of LMI plus PCI patients and 23 percent of PCI only patients.
“This is the first human study to demonstrate a therapeutic effect of [diagnostic ultrasound]-guided cavitation of intravenously administered, commercially available ultrasound contrast agents during acute STEMI,” the researchers wrote. “Early epicardial recanalization rates were significantly higher with the intermittent brief application of HMI impulses to the microcirculation through the apical windows. More importantly, these beneficial effects were evident at the microvascular level, with improved capillary flow already observed immediately following PCI.”
The researchers cited a few limitations of the study, including that they could not obtain one-month follow-up contrast echocardiographic data on PCI-only patients because of financial reasons.
“By acutely improving microvascular flow in acute STEMI, [diagnostic ultrasound] also may play a critical supplemental role in preventing the remodeling that leads to further reductions in ejection fraction and increased risk for arrhythmic and heart failure complications,” the researchers wrote. “Our initial study was too small to examine these differences, but larger trials are warranted to study whether this improvement in microvascular outcome with [diagnostic ultrasound] translates into reduced morbidity and mortality at longer-term follow-up.”