12.1
When should coronary physiology be used?
12.1.1
Before PCI
- 1.
Determine significance of intermediate coronary lesions.
Several studies have shown that PCI of lesions with adenosine fractional flow reserve (FFR)>0.80 (FFR>0.75 was used in earlier studies ) or lesions with nonhyperemic indices that do not show ischemia (such as instantaneous wave free ratio—iFR>0.89 ) can be safely deferred without increasing the incidence of adverse outcomes. This also applies to left main lesions . In addition to iFR, several other nonhyperemic indices have been developed (such as the resting full cycle ratio [RFR], the diastolic hyperemia-free ratio [DFR], and the diastolic pressure ratio [DPR]) and provide nearly identical measurements with the iFR.
- 2.
Determine which lesions require revascularization in patients with multivessel CAD.
Use of adenosine FFR (usually in lesions with <90% angiographic diameter stenosis) during multivessel PCI is associated with treatment of fewer lesions and better clinical outcomes as compared with angiography-guided PCI . Physiologic assessment should not be performed for clinical decision making in culprit or suspected culprit lesions in patients presenting with an acute coronary syndrome (ACS). Intracoronary imaging should be used to assess ACS culprit lesions .
12.1.2
During PCI
- 1.
Post-PCI adenosine FFR is emerging as a tool to determine functionally optimal PCI results . Post-PCI adenosine FFR>0.91 has been associated with optimal outcomes.
Causes of suboptimal post-PCI adenosine FFR ( Fig. 12.1 ) :
- •
Geographic miss of culprit lesion.
- •
Inadequate lesion coverage (not covering from healthy to healthy segment).
- •
Suboptimal stent selection and deployment (undersized—underexpanded).
- •
Diffuse disease.
- •
Stent edge dissection.
- •
Serial lesions (another intermediate lesion becoming hemodynamically manifest after treating the culprit lesion).
- •
Coronary vasospasm.
- •
Extreme vessel tortuosity (causing wire bias and accordioning effect).
- •
Large collateral supply by the treated vessel to a CTO-supplied territory.
- •
Myocardial bridging.
- •
Pressure wire-related technical issues (such as drift or wire malfunction).
Figure 12.1
Use of post-PCI FFR to optimize PCI results.
- •
- 2.
To assess the side branch during provisional bifurcation stenting.
Angiographic assessment of jailed side branches during bifurcation stenting can be challenging. Intracoronary nitroglycerin may help reverse coronary spasm. Adenosine FFR of the jailed side branch can help guide further treatment :
FFR≤0.80 : further treatment of the side branch is needed (assuming that the vessel diameter is ≥2 mm), as there is increased risk of subsequent adverse events.
FFR>0.80 : no further treatment of the side branch is needed.
12.2
How to do coronary physiologic assessment?
Starting point : The guide catheter is engaged in the target coronary vessel. The guide pressure waveform should not be dampened, as this can result in underestimation of the lesion severity (artificially increasing the FFR or nonhyperemic indices) .
12.2.1
Step 1: Flush and zero pressure guidewire outside the body
12.2.1.1
Goals
To prepare the pressure guidewire for use.
12.2.1.2
How?
Flush the pressure guidewire container with normal saline, connect to the patient interface module (PIM), and zero it. The wire is shaped as described in Chapter 8 (Wiring), paying attention to not damage the pressure sensor (that is usually located 3 cm from the tip).
12.2.1.3
Challenges
- 1.
Unable to zero pressure wire.
Causes:
- •
Poor pressure wire connection.
- •
Defective pressure wire.
- •
Prevention:
- •
Check all connections prior to connecting guidewire.
- •
Treatment:
- •
Check all connections.
- •
Replace pressure wire with a new one.
- •
12.2.1.4
What can go wrong?
- 2.
Inadequate calibration: if this is not appreciated prior to insertion of the guidewire in the guide catheter, it will delay the procedure, as it will require removal of the guidewire and recalibration.
- 3.
Wire damage that may require discarding the pressure wire and using a new one.
12.2.2
Step 2: Insert pressure guidewire in the guide catheter through the Y-connector and advance to the tip of the guide catheter ( Fig. 12.2 )
12.2.2.1
Goals
To deliver the pressure guidewire to the guide catheter tip.
12.2.2.2
How?
Insert the pressure guidewire using an introducer through the hemostatic valve of the catheter-connector and advance it until it reaches the tip of the guide catheter. Partially advance the pressure wire into the coronary artery until the proximal end of the radiopaque portion of the wire is at the tip of the guide catheter ( Fig. 12.2 ).
12.2.2.3
Challenges
- 1.
Inability to advance the pressure wire within the target vessel
Causes:
- •
Suboptimal guide catheter engagement.
- •
Suboptimal guide catheter choice (for example using a too large EBU guide catheter may result in the wire preferentially entering the circumflex instead of the LAD and vice versa).
- •
Suboptimal shape of the guidewire tip.
- •
Prevention:
- •
Ensure excellent guide catheter engagement using an appropriately sized guide catheter as outlined in Chapter 5 , Coronary and Graft Engagement.
- •
Appropriate shaping of the guidewire tip.
- •
Treatment:
- •
Change guide catheter for a better fitting guide catheter.
- •
Modify the shape of the guidewire tip.
- •
12.2.2.4
What can go wrong?
- 2.
Wire deformation
Causes:
- •
Suboptimal wire shaping prior to insertion into the guide catheter.
- •
Wire protruding through the introducer tip while being inserted.
- •
Other equipment (such as guide catheter extensions, balloons, and stents) present inside the guide catheter.
- •
Prevention:
- •
Ensure the guidewire is fully retracted within the introducer while inserting through the hemostatic valve of the Y-connector.
- •
If there is resistance to wire advancement, do NOT push hard!
- •
If additional equipment is present within the guide catheter, either remove it prior to inserting the pressure guidewire, or advance thepressure guidewire under fluoroscopy.
- •
Treatment:
- •
Reshape pressure guidewire if feasible, or use a new one.
- •
Follow all precautions outlined under “Prevention” above.
- •
12.2.3
Step 3: Remove introducer, flush guide catheter with normal saline, and equalize pressures ( Fig. 12.3 )
12.2.3.1
Goals
To ensure that the pressure read by the pressure guidewire matches the guide catheter pressure.
12.2.3.2
How?
The introducer is removed, the guide catheter flushed with normal saline, and the guide catheter-derived and pressure wire-derived pressures are equalized.
12.2.3.3
Challenges
- 1.
Unable to perform pressure equalization (sometimes the system may equalize the mean pressures, but the pressure waveforms may not overlap introducing error in the measurement of the hyperemic FFR).
Causes:
- •
Failure to remove the wire introducer.
- •
Failure to flush the guide catheter.
- •
Pressure guidewire failure.
- •
Suboptimal guidewire tip position (too deep into the target vessel).
- •
Air in the aortic pressure line.
- •
Prevention:
- •
Ensure that the introducer is removed from the tuohy.
- •
Ensure that the guide catheter is flushed.
- •
Ensure that the systemic pressure line is flushed and properly zeroed.
- •
Ensure that the proximal portion of the radiopaque segment of the pressure guidewire is at the guide catheter tip.
- •
Treatment:
- •
Perform steps described under “Prevention” above.
- •
If pressure equalization still fails, change pressure guidewire.
- •
12.2.4
Step 4: Advance pressure wire distal to the target lesion(s) ( Fig. 12.4 )
12.2.4.1
Goal
To advance the pressure guidewire distal to the target lesion(s).
12.2.4.2
How?
The introducer is reinserted (optional) and the guidewire is advanced through and distal to the target lesion(s) and ideally as distal in the coronary artery as possible to assess flow through the entire artery .
12.2.4.3
Challenges
- 1.
Unable to advance guidewire past lesion.
See Section 8.6, Section 8.7, Section 8.8 .
12.2.4.4
What can go wrong?
12.2.4.4.1
Target vessel injury
See Section 8.7 .
12.2.4.4.2
Pressure drift
Causes:
- •
Technical problem with the pressure wire.
- •
Loose or malfunctioning pressure transducer.
Prevention:
- •
Ensure that pressures are equalized prior to advancing the pressure guidewire through the lesion.
- •
Avoid disconnecting the pressure guidewire connection during wire manipulations.
Treatment:
- •
Retract pressure guidewire so that the proximal end of the radiopaque portion of the pressure guidewire is at the tip of the guide catheter, reequalize pressures, readvance the pressure guidewire through the lesion, and repeat physiologic assessment.
12.2.5
Step 5: Measure a resting physiologic index ( Fig. 12.5 )
