Pitfalls & Practical Tips

Name: Pitfalls & Practical Tips
Uploaded: 2017-07-10T17:49:00+00:00
Duration: PTM26S52
Channel: Hugh Jenkins
Description: Pitfalls & Practical Tips

Pitfalls & Practical Tips
As with every new technique, when you start performing coronary pressure measurements using PressureWire™ you will face some potential pitfalls, which may lead to erroneous results or misinterpretation of data. Many of these pitfalls are easily recognized, a few are more tricky but most are easily avoided once people are aware of them. The aim of this presentation is to highlight the most common ones and prepare you to deal with them if they arise.

Transducer Height and AO Pressure Equalization Guidewire Introducer Needles Guide Catheter (wedging, damping & side holes) PressureWire™ Drift Artifacts Mean-beat Setting Sensor Element Against Vessel Wall Suboptimal Hyperemia

Importance of Transducer Height and AO Pressure
Position the AO transducer at patient’s heart level (midaxillary line) Correct height AO transducer 10 cm (4 inches) too high = AO 8 mmHg too low 10 cm (4 inches) too low = AO 8 mmHg too high

Effect of Moving the Aortic Transducer
This pressure recording illustrates what is happening to the pressure from the fluid-filled transducer (Pa) when the transducer is moved up or down in relation to the level of the patient’s aortic root. If there is a difference between the two pressures that is > +/- 5 mmHg, this should be corrected by moving the fluid-filled transducer to the correct level. If the difference is less, electronic equalization is performed using the button on the RadiAnalyzer™ /RadiAnalyzer™ Xpress. Verification of two equal pressures is very important for the upcoming pressure recordings. If the baseline recordings here are off, a systematic error will be created throughout the FFR calculations.

AO and the ACIST™ Contrast Injector
Important: These instructions do not replace the ACIST instructions for use. Always refer to the complete instructions for use when operating the ACIST device. The following slides describe pitfalls associated with use of the ACIST contrast injector. ACIST CVI is an advanced contrast delivery device (ACIST Medical Systems, USA) used in catheterization laboratories to automate and simplify contrast and saline injection.

AO and the ACIST Contrast Injector
Contrast injector syringe Saline bag 3-way stopcock To patient Movable pressure transducer with disposable dome Peristatic saline pump with closing mechanism Contrast and saline is injected using a remote-controlled injector that is positioned next to the catheterization lab table. The system is loaded with single-use sets of tubing that connect the injector to the guide catheter. A disposable AO pressure dome is also included in the set and is mounted on a pressure transducer on the ACIST device itself.

Aortic root, stopcock and transducer at same level
AO and the ACIST Contrast Injector The following steps should be performed each time you: - calibrate AO - equalize pressures before FFR measurement - measure FFR - verify equal pressures at the end of the measurement Flush tubing with saline Place the transducer at the same level as the patient’s heart (midaxillary) Place the 3-way stopcock at the same level as the transducer Aortic root, stopcock and transducer at same level

Aortic root, stopcock and transducer at same level
AO and the ACIST Contrast Injector Calibrating the AO Transducer Open 3-way stopcock to zero AO Aortic root, stopcock and transducer at same level When calibrating the AO transducer, you must open the transducer to air, usually with a stopcock on the transducer itself. On the ACIST device, however, the stopcock is located at the end of the disposable set with 180 cm (71 inches) of tubing between valve and transducer. The tubing is filled with contrast fluid or saline. Whenever calibrating the AO transducer, the height of the 3-way stopcock as well as the transducer itself becomes very important. Any difference in height will offset AO pressure from atmospheric pressure so they must both be at the height of the aortic root. A difference in height of 5 cm (2 inches) = 4 mmHg Incorrect AO pressure may lead to incorrect FFR calculation, and also the false impression that there is a problem with PressureWire = drift or large equalization values.

Transducer Height and AO Pressure Equalization Guidewire Introducer Needles Guide Catheter (wedging, damping & side holes) PressureWire Drift Artifacts Mean-beat Setting Sensor Element Against Vessel Wall Suboptimal Hyperemia

Equalization PressureWire sensor just outside tip of guide catheter
Equalization between the aortic pressure transducer and PressureWire sensor must always take place with the PressureWire sensor just outside the tip of the guide catheter. Flush the guide catheter in order to obtain perfect phasic tracings. Equalizing is performed by pressing the Equalize button for 3 seconds. The equalization value (e.g., “EQ 3”) will appear in green above the Pd/Pa ratio (yellow). The wave forms should be superimposed and the Pd/Pa should be 1.0. With the PressureWire sensor in this position, the Pd/Pa ratio should remain stable, confirming that there is no drift. Verification of equal pressures is always performed after FFR measurement to ensure there has been no drift. Verification is performed with the guide catheter tip and PressureWire sensor in the same position as during equalization. Equalization between the aortic pressure transducer and PressureWire sensor must always take place with PressureWire sensor just outside the tip of the guide catheter.

Guidewire Introducer Needles
A guidewire introducer needle is often put into the Y-connector to facilitate wire manipulations in the coronary artery. The introducer needle may leak blood and decrease aortic pressure (Pa) by 0–10 mmHg and result in a falsely high FFR. There is more leakage from larger bore needles (shown in yellow) than small ones (clear). There is more leakage from larger bore needles (shown in yellow) than small ones (clear).

Effect of Large Needle Introduction of a ”large needle” in the valve of the Y-connector In this example, using a large bore, yellow needle causes a drop in aortic pressure of approximately 10 mmHg. To avoid loss of AO pressure, the introducer needle should be removed and the hemostatic valve closed tightly: - during equalization - when FFR is measured - during verification of pressures During pullback of PressureWire, the hemostatic valve may be relaxed slightly to facilitate movement. If the needle is removed during equalization but not during FFR measurement or verification, the Pd/Pa ratio will be incorrect since the Pa pressure may not be the same due to leakage of blood (FFR would be falsely high and at verification it will look like there was drift). If for some reason the needle was not removed during equalization, then do not remove it during FFR measurement and verification either. This will at least ensure the Pa pressure is the same throughout. In this example, using a large bore, the yellow needle causes a drop in aortic pressure of approximately 10 mmHg.

Effect of Thin Needle Introduction of a ”thin needle” in the valve of the Y-connector In this case the introducer needle has a small lumen, which creates minimal pressure leakage. In this case, the introducer needle has a small lumen, which creates minimal pressure leakage.

Wedging of Guide Catheter
7 Fr Guide Catheter The presence of a guide catheter in the coronary ostium induces some degree of “stenosis” depending on the relative size of the guide and the coronary ostium. Damping aortic pressure can result in a falsely high FFR. It is important to detect wedging of the guide catheter because otherwise the Pa value will be falsely low and the FFR value falsely high. When wedging is anticipated, the guide catheter should be pulled back slightly into the aorta so as not to impede blood flow during: - equalization - FFR measurements - verification of equal pressures The presence of a guide catheter in the coronary ostium induces some degree of “stenosis” depending on the relative size of the guide and the coronary ostium.

1 2 Deep-Seated (Wedged) Guide Catheter
A deep-seated (wedged) guide catheter in the ostium of the right or left main vessels can cause damping of the aortic waveform. Waveform 1 shows the effect with the catheter inserted and waveform 2 shows the effect when the catheter is withdrawn into the aorta, revealing an immediate pressure gradient. When the aortic pressure signal becomes “ventricularized” (a U-shaped rather than V-shaped diastolic waveform), this means that the guide catheter is wedged in the vessel, impeding flow. Often, the presence of the guide catheter does not induce any gradient at rest. However, when flow increases over the ostial segment, the mere presence of the guide catheter may induce a pressure drop which can be recognized by paying attention to the appearance of the AO pressure (Pa) waveform. In summary, if a dampened aortic waveform is observed for whatever reason (large guide, normal size guide in small vessel or ostial disease), it is strongly advisable to use I.V. hyperemia and to withdraw the guide catheter during: equalization - FFR measurement - verification of pressures. A deep-seated (wedged) guide catheter in the ostium of the right or left main vessels can cause damping of the aortic waveform. Waveform 1 shows the effect with the catheter inserted and waveform 2 shows the effect when the catheter is withdrawn into the aorta, revealing an immediate pressure gradient.

Guide Catheter in Ostium = Stenosis
This is a schematic representation of the space occupied by different sizes of guide catheters in an ostium 3 mm in diameter (radius = 1.5 mm). The formula for calculating the area of a circle is: A=π r2, therefore: π x = 7 mm2 The area of the ostium is approximately 7 mm2 An 8 Fr guide catheter has a diameter of 2.4 mm (radius is 1.2 mm): π x = 4.5 mm2 The area of an 8 F catheter is 4.5 mm2 . So, an 8 Fr guide catheter creates a simulated stenosis of approximately 64% (4.5/7.0 ~ 0.64). This is a schematic representation of the space occupied by different sizes of guide catheters in an ostium 3 mm in diameter (radius = 1.5 mm).

Effect of Guide Catheter with Side Holes
If a guide catheter with side holes is used, one should realize that the pressure signal recorded through the catheter does not necessarily correspond to the pressure in the proximal segment of the coronary artery since it is influenced by both coronary pressure (through the distal end of the catheter) and by aortic pressure (through the side holes). Because of the presence of the catheter, the actual proximal coronary pressure is often lower than the value recorded by the catheter. If a guide catheter with side holes is used, it is mandatory to pull it back out of the coronary ostium before FFR calculations are performed. This emphasizes the fact that an intracoronary hyperemic stimulus cannot be used since part of the drug will be delivered into the aorta and one can never be sure that true maximum hyperemia is achieved. If a guide catheter with side holes is used, the pressure signal recorded through the catheter does not necessarily correspond to the pressure in the proximal segment of the coronary artery since it is influenced by both coronary pressure (through the distal end of the catheter) and by aortic pressure (through the side holes).

Drift Waveform Drift After a long procedure, differences may sometimes occur between aortic and distal pressures even if this difference does not correspond to a true pressure gradient. Drift can be distinguished from a true pressure gradient by paying attention to the shape of the distal (PressureWire) tracing. When a true gradient is present, the PressureWire diastolic waveform is somewhat “ventricularized” (U-shaped rather than V-shaped). When the difference is due to drift, the two pressure tracings have exactly the same form. If pressure waveforms look suspicious, pull back PressureWire to the guide catheter tip to verify equal pressures. If at this point pressures are not equal: - flush the guide catheter - check the height of the AO transducer - check that the guidewire introducer needle has been removed - manipulate PressureWire to ensure the sensor is not against the vessel wall. If pressures still do not become equal, then “re-equalize” using the Equalize button on the interface (pressing once to remove the previous equalization and once more to perform a new equalization). After a long procedure, differences may sometimes occur between aortic and distal pressures even if this difference does not correspond to a true pressure gradient.

Drift Waveform Drift in right coronary artery: aortic notch maintained
When performing pressure measurements in the right coronary artery, recognizing drift by the shape of the curve is more difficult. However, one should suspect drift if the aortic notch is maintained in the distal pressure waveform in the presence of a considerable gradient.

Flush Artifact RadiAnalyzer Xpress selects artifact Actual FFR is 0.83
After FFR measurement, the Stop button is pressed and a static screen is displayed, delineating the lowest FFR gradient. This is shown by the yellow vertical line, which corresponds to the yellow numbers (Pd/Pa ratio) on the right-hand side. RadiAnalyzer Xpress sometimes inadvertently picks up incorrect values due to artifacts, as seen here. During intracoronary flushing, Pa pressure is affected, resulting in an artifact. In the example on the left, the FFR is incorrect because the Pd/Pa ratio is based on the artifact. When this happens, it is important to move the cursor (found in the menu) away from the artifact to the spot where the gradient is greatest. The correct FFR value is shown on the right, in this case 0.83 (a big difference from 0.59!) RadiAnalyzer Xpress selects artifact Actual FFR is 0.83

Blunted Flush Artifact
No red phasic signal but mean signal remains For a correct FFR one needs to have 2 accurate waveforms present. In this example, the FFR value was calculated at a spot where there is no red/aortic phasic signal. In this case, the cursor should also be moved to a better location.

One-Beat Artifact This is an example of a one-beat artifact.

Move Cursor to Show Correct FFR
In the case of artifacts, one needs to move the cursor (vertical FFR line) to the appropriate place on the waveform using the cursor button.

Changing Mean-beat The default Mean-beat setting is 3. Changing the beat setting allows you to vary the number of heart beats over which the data is collected to calculate the FFR. The default value is 3, and this is adequate in most situations. If a hyperemic drug with short duration is used, the beat setting should be no higher than 3.

FFR Procedure Mean Pa Mean Pd FFR=Pd/Pa
FFR is calculated at the location of the greatest difference between Pa and Pd mean pressures during maximum hyperemia.

Pitfalls Slow Mean Pressure
Caused by a mean pressure setting that is too slow and a short-lasting hyperemic agent May overestimate lowest Pd and thus underestimate functional significance Avoid by using long-lasting hyperemic agent or changing RadiAnalyzer Xpress setting to a maximum of 3 beats True lowest Pdmean False lowest Pdmean This slide shows an example of FFR overestimation (which will cause a significant lesion to be missed). When the RadiAnalyzer Xpress is set to calculate mean pressure over several beats, the changes in the mean pressure signals lag behind the changes in the phasic pressure signals. You can see in this image how changes in the mean distal pressure curve do not match the changes in the phasic distal pressure curve. The mean distal pressure curves should be more separated at the spot where the phasic distal pressure is lowest. This is important when using a hyperemic drug with short peak. It takes too long for the mean pressure to catch up with the changes in phasic pressure and the hyperemic plateau (true FFR) is therefore missed. NOTE: The problem can be avoided by using a long-lasting hyperemic agent (IV) to allow mean pressure enough time to stabilize at maximum hyperemia. When calculating FFR manually (e.g., using Aeris without upgraded software) use of a long-lasting hyperemic drug (IV) is mandatory. Ref: Coronary pressure (2nd edition), Pijls, NHJ and De Bruyne, B. Kluwer Academic Publishers 2000.

Pitfalls Recognizing Slow Mean Pressure
Balance point: divides the pressure curve into two equally weighted halves Balanced Too high Too low Mean curve is too high Mean curve is at the balance point of the phasic curve This error can be discovered by checking whether the mean distal pressure curve is correct by comparing it to the phasic distal pressure curve. If the mean pressure curve is not located at the balance point of the phasic pressure curve, then the FFR value will not be correct. Here you see where the distal phasic pressure is lowest, the distal mean curve has not changed as quickly and its position is abnormally high on the phasic curve. If this is the case, change the RadiAnalzyer Xpress settings to calculate mean pressure over max. 3 beats (this is the default setting).

Sensor in Contact with Vessel Wall
When the PressureWire sensor element itself is against the vessel wall, an artifact can be seen in the form of a brief but pronounced increase (“spike”) in the pressure signal measured by the wire. If not recognized, this artifact will tend to falsely elevate the Pd value. To correct this artifact, the wire should simply be manipulated to avoid contact with the vessel wall. When the PressureWire sensor element itself is against the vessel wall, an artifact can be seen in the form of a brief but pronounced increase (“spike”) in the pressure signal measured by the wire.

Suboptimal Maximal Hyperemia
Fluctuating Pd/Pa line = steady state NOT achieved and likely sub-optimal maximal hyperemia Fluctuating Pd/Pa line = steady state NOT achieved and likely suboptimal maximal hyperemia. Suboptimal hyperemia is commonly seen when the drug of choice is administered via a peripheral vein or when the patient is holding his/her breath, causing a Valsalva effect.

Steady-State Maximal Hyperemia
Horizontal Pd/Pa line = steady state and likely maximum hyperemia Steady state hyperemia is commonly achieved using an I.V. hyperemic agent administered via a femoral sheath. The mean Pd/Pa line is only seen during recording and a smooth, non-fluctuating line should be observed.

Rx Only Please review the Instructions for Use prior to using these devices for a complete listing of indications, contraindications, warnings, precautions, potential adverse events and directions for use. Product referenced is approved for CE Mark. PressureWire is designed, developed and manufactured by St. Jude Medical Systems AB. PressureWire, RADI, ST.JUDE MEDICAL, the nine-squares symbol and MORE CONTROL. LESS RISK. are registered and unregistered trademarks and service marks of St. Jude Medical, Inc. and its related companies. ©2011 St. Jude Medical, Inc. All rights reserved. Acist is a registered trademark of ACIST Medical Systems, Inc.

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