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       Transducer height: The transducer should be at the level of the aortic root, since when it is above the heart, the aortic pressure trace will be below that of the coronary pressure trace. This error is easily recognized. If, however, the transducer is below the heart, then the aortic pressure trace is above the distal coronary pressure to give the appearance of an apparent trans‐stenotic pressure gradient. This is more challenging to recognize and if missed can lead to erroneously positive results. However, it is readily resolved by performing normalization at the beginning of the case and checking for equalization of pressures whenever the sensor is returned to the vessel ostium.

       Pressure signal drift: Iterations of pressure wire technology have reduced pressure wire drift, but it remains a recognized issue. This can be identified at the end of the distal pressure recording when the sensor is returned to the ostium. Provided there is no drift, the Pd/Pa ratio should remain at 1.0. If the value differs from 1.0, then drift has occurred – a result of electrical charge developing on the pressure sensor. Drift may also be identified when the wire is distal to a stenosis since the pressure waveform may take on the appearance of the aortic trace. Measurements should be repeated if drift exceeds 2 mmHg, especially if the measured physiology value is close to the ischemic cut‐off point. Drift is a dynamic problem as a result of electrical phenomenon and is more likely if the wire is used rapidly after activation. To avoid this, early activation of the wire with a heparinized saline flush is recommended. Allowing a longer period of inactivity between activation and clinical usage should minimize early wire drift. It is recommended that in cases in which a pressure wire is known to be needed, to have the wire activated and ready on the table, well before it is needed.

       Guide catheter damping: All guiding catheters will produce a degree of ostial stenosis for the vessel. This is particularly problematic for 8 Fr and 7 Fr catheters and may be observed as damping of the aortic pressure signal with loss of the dicrotic notch. 5 Fr and 6 Fr catheters are less likely to cause significant damping, but if it occurs, the wire should be normalized in the aortic root and then the catheter should be disengaged once the wire is passed distal to the stenosis. Caution is also required during intravenous adenosine infusion since the increase in intracoronary flow and altered aortic hemodynamics mean that the guiding catheter can be drawn into the vessel: this will cause damping with a reduction of flow and under‐estimation of distal stenosis significance. Catheters with side‐holes should be avoided since they appear to generate a normal aortic pressure waveform, while the catheter pressure is not truly representative of aortic pressure.

       Whipping artifact: Whipping may be observed if the pressure sensor is against the vessel wall or is repeatedly striking it. This can be overcome by withdrawing the wire slightly.

       Erroneous console determination of indices: It is common for pressure wire consoles to compute FFR values when the pressure ratio is at its lowest. However, FFR should be calculated when there is stable hyperemia, and this may not be the lowest ratio. This issue is accentuated when using intracoronary adenosine injections where recording or calculation during the injection phase can give an artefactual aortic pressure trace and therefore an erroneous FFR value. Manual adjustment of the recorded ratio will resolve this. During iFR recording, ectopy or erroneous ECG tracings may affect iFR calculation. Errors can be identified by assessing when the wave‐free period has been calculated and making a repeat measure.

       Large hemodynamic changes: Caution is required when there are large hemodynamic shifts in aortic pressures caused by central adenosine infusions. Large falls in proximal aortic pressure cannot account for a significant proportion of the change in distal coronary pressure and may alter the FFR results [46]. Caution should be taken to ensure ratios are calculated during stable hyperemia to match the original validation work. In some situations, the lowest FFR value can occur during the initial peak hyperemic phase causing a change in classification of stenosis significance [47,48]. Prolonged intravenous infusions of adenosine can cause paradoxical vasoconstriction of the microcirculation and the whole trace should be observed for a reliable value [49].