  Aims: The presence of coronary tandem lesions poses a significant challenge
for the accurate diagnosis and management of coronary artery diseases. This
study set out to provide a deeper understanding of the haemodynamic
interactions between tandem obstructive coronary lesions and their impact on
different haemodynamic diagnostic parameters. Methods and Results: Using a
computational fluid dynamic model, validated against in vitro laboratory
experiments, we investigated the various combinations of moderate and severe
stenoses interchangeably located in the proximal and distal segments of the
artery. The investigation was conducted using two diagnostic parameters: one
hyperaemic-based, i.e., FFR, and one rest-based, i.e., iFR, technique, both of
which are commonly used to assess the physiological significance of coronary
stenoses. The three main findings of this work are: (a) the recovery distance
(the immediate local distance affected by the presence of stenosis) is much
shorter for the rest-measured diagnostic parameter compared with the
hyperaemic-measured diagnostic parameter; (b) pressure drop measurements
immediately downstream of the stenotic sections overestimate the significance
of stenoses, and (c) the presence of a moderate stenosis downstream of a severe
stenosis increases FFR value (faster FFR recovery). Conclusion: These findings
enhance our understanding of the diagnostic accuracy of hyperaemic-based and
rest-based physiological diagnostic coronary assessments and the nuances of
using these different techniques when assessing tandem coronary stenoses. This
understanding can help inform tailored therapeutic approaches for the
management of coronary artery disease.
