Major calcifications are of great concern when performing percutaneous coronary intervention (PCI) because they can hinder stent deployment. Approximately 700,000 PCIs are performed each year, and many involve the use of stents to open up obstructed coronary arteries.¹ Calcified plaques are found in 17% to 35% of patients undergoing PCI.^{2 – 4} Calcifications can lead to stent underexpansion and strut malapposition, which in turn can lead to increased risk of thrombosis and in-stent restenosis.^{5 – 10} A cardiologist has several options when confronting a calcified lesion: high balloon pressures (up to 30 atm) to fracture the calcification, scoring balloon, Shockwave^TM intravascular lithotripsy (IVL), rotational atherectomy, etc. In some cases, the lesion may not be treatable.

The computational fluid dynamic method has been widely used to quantify the hemodynamic alterations in a diseased artery and investigate surgery outcomes. The artery model reconstructed based on optical coherence tomography (OCT) images generally does not include the side branches. However, the side branches may significantly affect the hemodynamic assessment in a clinical setting, i.e., the fractional flow reserve (FFR), defined as the ratio of mean distal coronary pressure to mean aortic pressure. In this work, the effect of the side branches on FFR estimation was inspected with both idealized and optical coherence tomography (OCT)-reconstructed coronary artery models. The electrical analogy of blood flow was further used to understand the impact of the side branches (diameter and location) on FFR estimation. Results have shown that the side branches decrease the total resistance of the vessel tree, resulting in a higher inlet flowrate. The side branches located at the downstream of the stenosis led to a lower FFR value, while the ones at the upstream had a minimal impact on the FFR estimation. Side branches with a diameter larger than one third of the main vessel diameter are suggested to be considered for a proper FFR estimation. The findings in this study could be extended to other coronary artery imaging modalities and facilitate treatment planning.