Thrombus aspiration in STEMI revisited: impact on coronary microcirculation?

Correspondence to Dr Georg M Fröhlich; [email protected] In this issue of Open Heart, Hoole et al present the IMPACT trial. The authors investigate the effect of thrombus aspiration (TA) on changes in microvascular function during primary percutaneous coronary intervention (PPCI) for ST elevation myocardial infarction (STEMI). However, no difference between the TA group and the control group receiving balloon angioplasty first line could be verified. This is a timely topic indeed, since the impact of TA on coronary microcirculation was an important rationale to suggest prognostic benefits in patients with STEMI in the past. Early data from smaller and medium-sized randomised controlled trials (RCT) fuelled substantial enthusiasm about the concept of coronary thrombectomy with a view to reduce the thrombus burden, and avoid distal embolisation and consecutive ‘no reflow’ in PPCI. 3 Of note, ‘no reflow’ following PPCI has been observed frequently in this patient cohort. This phenomenon has been closely associated with microvascular obstruction and increased myocardial infarct size, with worse adverse clinical outcome. Similarly, dislodged debris from the culprit lesion, consisting of conglomerates of platelets and neutrophil granulocytes, may congest the microvasculature and deteriorate the ‘no reflow’. This is also a feature of the reperfusion injury (RI), which occurs after restoration of blood flow in the infarcted vessel. Notably, this RI has been estimated to account for up to 50% of the final infarct size, and efforts to mitigate the RI and ‘no reflow’ appear therefore as an appealing therapeutic approach. Unfortunately, more recent larger RCTs investigating manual thrombectomy in the setting of PPCI yielded rather disappointing results. Earlier this year, the largest RCT in this field was published. More than 10 000 patients referred for PPCI were randomised to receive TA or balloon angioplasty followed by stenting. Neither the primary composite end point of cardiovascular death, cardiogenic shock, New York Heart Association (NYHA) class IV or recurrent myocardial infarction nor cardiovascular death after 6 months were improved by TA. Notably, 87% of patients had a significant thrombus burden. Some concern was raised over a slightly increased stroke rate in the TA group, however, very few events were observed in this patient cohort. Thrombectomy was also tested on top of intracoronary abciximab (glycoprotein, GPIIb/IIIa inhibition) administration in the INFUSE-AMI trial. While abciximab reduced the infarct size as assessed by cardiac MRI, this was not confirmed for thrombectomy. Several other strategies to reduce distal embolisation and microvascular obstruction were investigated, mostly in smaller pilot trials. Sezer et al suggested applying low-dose streptokinase after PPCI to open the microvasculature and improve microvascular function. They repeated coronary angiography 2 days after the index event, and reassessed the coronary flow reserve and the index of microvascular resistance. Importantly, all outcome measures of microvascular function were significantly improved in the streptokinase group as compared to the control group. After 6 months, there was no difference in left ventricular function between the study groups. However, this was a pilot study with a limited sample size of 40 patients, so no definitive conclusions could be drawn. The evaluation of the microvasculature by measuring the index of microvascular resistance and coronary flow are well established surrogate parameters to assess microvascular function, and are closely associated to outcome. Cuculi et al assessed microvascular resistance and coronary flow reserve as well as microvascular obstruction on cardiac MRI in patients undergoing primary PCI. The authors observed a severely dysfunctional microvasculature in those patients with