A randomised controlled clinical trial of prolonged balloon inflation during stent deployment strategy in primary percutaneous coronary intervention for ST-segment elevation myocardial infarction: a pilot study

Primary percutaneous coronary intervention (PPCI) is the standard procedure for reperfusion for ST-segment elevation myocardial infarction (STEMI). However, coronary no-reflow, a phenomenon in which the cardiac tissue fails to perfuse normally despite the use of PPCI, remains common and is associated with adverse outcomes.

The purpose of this study was to investigate whether prolonged balloon inflation in stent deployment vs. conventional rapid inflation/deflation technique may result in lower incidence of the no-reflow phenomenon in PPCI.

This proof-of-concept pilot trial was the first to investigate the effect of prolonged balloon inflation during stent deployment strategy in PPCI and to determine whether prolonged or rapid balloon inflation strategies could provide more short- and long-term benefits for patients with STEMI.

In patients with STEMI, prolonged balloon inflation during stent deployment strategy during PPCI lowered the incidence of the no-reflow phenomenon and improved the myocardial microcirculation perfusion.

This was a single centre, randomised, single blinded, parallel pilot trial (NCT03199014). Patients were randomly assigned in a 1:1 ratio to either the prolonged balloon inflation in stent deployment group (PBSG; single balloon inflation, low-pressure inflation sustained for > 30 s after the target balloon inflation pressure had been reached) or conventional deployment strategy group (CDSG; as a control group, stent balloon inflation time < 10 s). A subset of patients was included in the cardiac magnetic resonance (CMR) assessment.

• Incidence of the no-reflow phenomenon according to thrombolysis in MI (TIMI) flow grade, a grading system used to evaluate blood flow

• Major adverse cardiovascular events (any events of target vessel revascularisation, recurrent myocardial infarction [MI], or cardiovascular mortality)

• Age ≥ 18 years
• Patients with STEMI who were referred to PPCI within 12 h after the onset of symptoms and with ST-segment elevation ≥ 1 mm in ≥ 2 contiguous leads or a presumed new left bundle branch block or a true posterior MI
• Admission within 12 h of symptom onset or admission between 12 and 24 h if there was evidence of continuing ischemia

• Cardiogenic shock, an intra-aortic balloon pump implant, or extracorporeal membrane oxygenation
• Thrombolysis
• Previous myocardial infarction (MI)
• Severe valvular disease
• Coronary artery bypass grafting
• Renal dysfunction (glomerular filtration rate of < 30 mL/min/1.73 m2)
• Cardiomyopathy
• Congenital heart disease
• Malignant arrhythmia
• Chronic obstructive pulmonary disease

• Between November 2016 and May 2018, 156 patients with STEMI were assessed, of which 120 were enrolled according to the eligibility criteria
• About 96.7% and 63.3% of the patients (n=120) in PBSG and CDSG respectively experienced TIMI flow grade 3 (p = 0.005).
• Patients in the PBSG and CDSG achieved 0% vs. 30% no-reflow or slow flow (p = 0.002); 90% vs. 66.7% ST-segment resolution ≥ 50% (p = 0.028); 35.6 ± 14.5 frames vs. 49.18 ± 25.2 frames on corrected TIMI frame count (p = 0.014); and 60% vs. 20% myocardial blush grade 3 (p = 0.001) respectively
• The rate of major cardiovascular adverse event at 1 month was 3.3% in both groups, but 3.3% and 6.7%, at 1 year, for the PBSG and CDSG, respectively (p = 1.00)
•  There was no significant difference in the procedure time, radiation exposure time, or contrast volume, number of bleeding events and clinical endpoints between the two groups
• According to the subgroup analysis, male patients (relative risk [RR], 1.46; 95% confidence interval [CI], 1.09–1.94), non-thrombectomy (RR, 1.40; 95% CI, 1.05–1.86), high thrombus burden (RR, 1.52; 95% CI, 1.07–2.16), door-to-balloon time < 90 min (RR, 1.81; 95% CI, 1.24–2.64), and nonanterior wall infarction (RR, 2.53; 95% CI, 1.60–4.02) were presented with lower risk for no-reflow phenomenon, which favours PBSG (p for interaction = 0.07)
• The presence of microvascular obstruction (MVO) in the CMR subset of cases was detected in PBSG (6.7%) and CDSG (50%) (p = 0.023)

During stent deployment strategy in PPCI, prolonged balloon inflation reduced the incidence of coronary no-reflow and improved the myocardial microcirculation with no significant difference between 30-day and 1-year clinical outcomes. While there were no differences between the two groups in terms of the procedure time, radiation exposure time, and number of bleeding events, the prolonged balloon inflation strategy was more effective in male participants and those with previous thrombectomy, heavy thrombosis burden, and non-anterior wall infraction. According to the CMR subset, the prolonged balloon inflation strategy was also beneficial in reducing the MVO incidence and improving cardiac function.   

• This study was performed in a single centre with a small sample that was underpowered to detect significant differences in clinical endpoints
• Patients with higher risks, more complex lesions and unstable haemodynamics were excluded, hence the results cannot be applied to all patients with STEMI
• Due to funding limitations, randomisation between the groups was not performed, hence selection bias may have occurred in the CMR subset group
• The lack of detailed description of antiplatelet strategies in baseline characteristics and post-PCI follow-up, may be a confounding factor for 1-year clinical outcomes
• This study did not disclose whether this treatment strategy could have an impact on no-reflow phenomenon