This study will look at the effects of standardised balloon inflation times, pressure and balloon types and atherosclerotic plaque morphology on the procedural results of percutaneous coronary intervention (PCI).

Patients presenting with symptoms of coronary artery disease (e.g. chest pain - angina) are often treated with stents (referred to as percutaneous coronary intervention, PCI). Stents treat the cause of symptoms by improving blood flow to the heart muscle through expanding a narrowed, or diseased segment within a coronary artery. The procedure involves the inflation of a balloon to expand the stent inside the artery. As part of standard clinical care multiple balloon inflations are required during the procedure. Deficiencies in the expansion of the stent at the time of the procedure are associated serious complications such as stent blockages or re-narrowing of the artery, either of which may not occur until much later.

Improvements to the technique of stent expansion are therefore highly desirable to improve outcomes for patients. A number of factors are thought to influence the success of the procedure, including: the type of balloon used to inflate the stent, the pressure used and the duration of balloon inflation. Another important factor may be the mechanical properties of the narrowed segment of the artery (plaque) and how they interact with the stent. At present however, there is no consensus view and the practise of individual cardiologists consequently remains highly variable.

The aim of this study is better characterise relationship between pressure and duration of balloon inflation, type of balloon used and plaque properties during stent procedures using state-of-the-art imaging. Although assessment of each of these factors by a cardiologist is already included as part of standard care, our research protocol will focus the analysis into a systematic framework to allow conclusions to be drawn. The findings will used better inform cardiologists of the technical modifications that can help improve stenting procedures and translate to better outcomes for patients.

Inclusion Criteria:

• Patients with symptomatic coronary artery disease (stable angina, non-ST elevation acute coronary syndromes) undergoing percutaneous coronary intervention with intracoronary ultrasound (IVUS) guidance
• Patients > 18 years
• De novo coronary stenoses in native coronary arteries
• Written informed consent

Exclusion Criteria:

• ST-elevation acute coronary syndrome
• Haemodynamic instability
• Cardiogenic shock
• Severe renal dysfunction (eGFR < 30 ml/min/1.73m2)
• In-stent restenosis
• Chronic total occlusions
• Saphenous vein and arterial bypass grafts
• Patients who are currently enrolled in any other study where involvement in this study would involve significant deviation from either protocol

Patients with symptomatic coronary artery disease (stable angina, non-ST elevation acute coronary syndromes) already referred for coronary intervention will be prospectively enrolled sequentially as they attend the St Thomas' Cardiac Catheterisation Laboratories.