Physiologic Testing
The use of invasive coronary artery physiological testing has been increasing in the catheterization lab. There are various types of physiological testing available in the contemporary era.
Overview of Coronary Wire-Based Assessment
Index of Microcirculatory Resistance (IMR)
IMR represents minimal microcirculatory resistance measured during conditions of hyperemia. IMR is calculated from the average pressure in the distal part of the coronary artery and the coronary blood flow measured by thermodilution using a specific pressure wire. An IMR higher than 25 is considered abnormal.
- Specific for the microvasculature
- Quantitative and reproducible
- Predictive of outcomes
Coronary Flow Reserve (CFR) [FFR + IMR]
CFR is defined as the ratio between coronary blood flow at maximal hyperemia and baseline condition. It expresses the capacity of the coronary circulation to respond to a physiological increase in oxygen demands with a corresponding increase in blood flow.
- Not microvascular specific
- Affected by resting hemodynamic
Resting Full-cycle Ratio (RFR) (Abbott)
- RFR non-hyperemic index is based on the largest drop in pressure throughout the cardiac cycle
- RFR has shown to have similar diagnostic performance as compared with other non-hyperemic pressure indices (IRIS-FFR, VALIDATE RFR)
- The RFR index studies indicate a threshold of ≤ 0.89 for consideration of PCI
PressureWire X guidewire (Abbott) is a new wireless physiology pressure wire that enables to measure pressure and temperature to calculate:
- Resting Full-Cycle Ratio (RFR)
- Fractional Flow Reserve (FFR)
- Index of Microvascular Resistance (IMR)
- Coronary Flow Reserve (CFR)
Compatible with OPTIS™ Imaging System for integrated imaging and physiology approach during PCI.
What is DFR?
Diastolic Hyperemia-free ratio (DFR) (Boston Scientific) is a resting diastolic index based on 2 criteria: identifying portion of cardiac cycle below the average aortic pressure, and selecting samples with negative slope. It is equivalent diagnostic and prognostic performance as the instantaneous wave-free ratio (iFR). The cut-off value for DFR is ≤ 0.89.
COMET II wire (Boston Scientific) is designed by ASAHI technology to be used as a workhorse pressure guidewire to measure all physiological indices – FFR, DFR and Pd/Pa. The wire possesses tip shapeability, better shape retention, and 1:1 torque and can be integrated with POLARIS system for multi-modality IVUS and physiology-guided PCI.
COMET II wire (Boston Scientific) is designed by ASAHI technology to be used as a workhorse pressure guidewire to measure all physiological indices – FFR, DFR and Pd/Pa. The wire possesses tip shapeability, better shape retention, and 1:1 torque and can be integrated with POLARIS system for multi-modality IVUS and physiology-guided PCI.
What is iFR?
Instant Wave-free Ratio (iFR) (Philips) is a non-hyperemic index based on the principle of measuring Pd/Pa ratio during “wave-free” period of cardiac cycle. Wave free period is a portion of diastole when resistance is constant.
- iFR has shown similar outcomes to FFR when used for guiding coronary revascularization in 2 large RCTs (iFR-SWEDEHEART and DEFINE-FLAIR)
- Proven cut-point to defer PCI is >0.89
- iFR pullback allows physiologic interrogation of entire vessel in case of serial or diffuse coronary lesions
- iFR co-registration onto angiogram allows accurate physiologic guidance to assist in treatment decisions
OmniWire (Philips)
- Combines workhorse design with advantage of iFR measurement throughout the case
- Nitinol distal core to increase durability and shape recovery
- Solid proximal core improves torque, pushability and kink resistance
Figure. Physiology pressure ratios. [FFR = fractional flow reserve, iFR = instantaneous wave-free ratio (Philips), RFR = resting full-cycle ratio (Abbott)]
