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

Abstract

SummaryPrevious 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 mFRR ), as well as to achieving maximal cardiac output (CO), SV, SVV, and SVRI (time which is determined as the ratio of distal to proximal pressure (Pd/Pa) under conditions of maximal hyperemia, represents a reproducible indicator of physiologically significant coronary stenosis.1,2) FFR-guided percutaneous coronary intervention (PCI) has significantly better clinical outcomes than PCI guided by angiography.3,4) Therefore, therapy guided by FFR is a key part of clinical management in patients with coronary artery disease (CAD).Although maximal hyperemia is a crucial factor for the assessment of FFR, 5) it is not always easy to obtain confirmatory evidence of reaching the maximal point of hyperemia in clinical practice. Intravenous adenosine administration is considered the gold standard for elicitation of maximal hyperemia, 3) but there is no clear evidence indicating the point of maximal hyperemia. Moreover, heart rate and blood pressure fluctuate because of respiration and are influenced by intravenous adenosine administration itself, which may lead to an inaccurate FFR. Intravenous adenosine administration is known to increase myocardial blood flow, cardiac output (CO), and stroke volume (SV) and to reduce systemic vascular resistance index (SVRI).6,7) Maximal hyperemia is a condition of maximal vasodilatation with the highest SV and the lowest SVRI. Accordingly, the monitoring of SV and SVRI may be used to verify whether maximal hyperemia has been achieved. Although pulmonary artery catheterization (PAC) is a reliable and reproducible method for assessing circulatory dynamics, 8) CO and SV measured with non-invasive electrical velocimetry (EV) were recently shown to be a viable alternative.9,10) Noninvasive EV is based on impedance cardiography, which can measure fluctuations in aortic blood volume during the cardiac cycle. EV additionally traces the direction and changes in the mechanical characteristics of erythrocytes for circulatory dynamics calculation. In the beginning of systole, this orientation changes into an alignment that leads to an acceleration of the erythrocytes, causing a maximum rate of change in electrical impedance. The general condition during FFR assessment is relative...

Agreement between single plane and biplane derived angiographic fractional flow reserve in patients with intermediate coronary artery stenosis

“…Reasons for underutilization include additional procedure time, technical challenges, a residual risk of vessel injury by pressure catheters, pressure wire drift effects [6] as well as side effects and lack of availability of adenosine at some institutions [7]. Furthermore, subjective assessments have to be used to evaluate whether maximal hyperemia is achieved [7][8][9]. To overcome these problems, image-based methods that do not need pressure wires or the induction of hyperemia have been introduced to compute coronary angiography-derived FFR [10][11][12][13].…”