Identification of the State of Maximal Hyperemia in the Assessment of Coronary Fractional Flow Reserve Using Non-Invasive Electrical Velocimetry.

Previous research revealed that, in patients with coronary pressure-derived fractional flow reserve (FFR) in the 'grey zone' (0.75-0.85), repeated FFR assessments sometimes yield conflicting results. One of the causes of the fluctuations in FFR values around the grey zone may be imprecise identification of the point where maximal hyperemia is achieved. Identification of the state of maximal hyperemia during assessment of FFR can be challenging. This study aimed to determine whether non-invasive electrical velocimetry (EV) can be used to identify the state of maximal hyperemia.Stroke volume (SV), SV variation (SVV), and systemic vascular resistance index (SVRI) were determined by EV in 15 patients who underwent FFR assessment. Time intervals from initiation of adenosine infusion to achieving maximal hyperemia (time), as well as to achieving maximal cardiac output (CO), SV, SVV, and SVRI (time, time, time, and time, respectively), were determined. Time and time were closer to time than other values (time/time versus time/time = 1.03 ± 0.2 versus 1.36 ± 0.4, P < 0.05). The maximum of SV was difficult to determine owing to considerable variations, but the maximum of SVV was clearly recognized. Time and time were significantly correlated with time, with time showing a stronger correlation than time (time: r = 0.92, P < 0.01; time: r = 0.80, P < 0.01).Maximal SVV is reached close to maximal hyperemia. Monitoring of SVV with non-invasive EV during FFR assessment can help identify the state of maximal hyperemia.