Epicardial COronary STIFfness (ECOStif:) represents a new paradigm for caring patients in the cathlab; it can be assessed by measuring coronary pulse wave velocity (PWV) with a regular pressure wire (Harbaoui et al., JAHA 2017); Yet, the basic physiology of ECOStif: is mostly unknown while it should be critical for its interpretation. This study aimed at determining the impact on ECOStif: of 1) mean blood pressure (MBP) and heart rate (HR) variations and of, 2) various degrees of luminal stenosis (St).

Ten female pigs weighting 48±3kg were included. Coronary angiography was performed under general anesthesia via the right carotid artery (6F). ECOStif: was measured in the left anterior artery with 2 pressure wires (Abbott) positioned at the proximal and at the distal part of the artery. ECOStif: was measured in 3 MBP conditions (60, 80, 100mmHg) and in 3 HR conditions (90, 110, 130 bpm). One condition was repeated for assessing repeatability. At 80mmHg and 110 bpm, 2 different stenosis were produced by inflating balloons of increasing size (St1, St2) and assessed by measuring fractional flow reserve (FFR).

In basal conditions ECOStif 8.12±2,82m/s. ECOStif: increased significantly with increasing MBP (P<0.05) but not with HR (2-way-ANOVA repeated measurements). The average increase was from 0.08 to 0.1m/s/mmHg for MBP. The repeatability was fair around 6%. ECOStif: decreased with stenosis severity: 6,55±0,95, 5,67±1.63, 4,87±0,76m/s for basal, St1, and St2, respectively (P<0.05) corresponding to FFR at 0.93±0.07, 0.82±0.11, 0.7±0.14, respectively.

ECOStif: has a reasonable repeatability. As expected from basic physiology, it is influenced by large MBP variations and at a lesser extent by HR changes. It is also slightly influenced by coronary stenosis. The present study is critical to better understand this new parameter and to address its robustness in the prospect of its clinical use.