Among stable patients undergoing cardiac catheterization, the majority (59%) have little or no angiographic abnormality, as shown in the visual1 in spite of the fact that the majority have symptoms of a coronary disorder.2 Patients with ischemia and no obstructive artery disease (INOCA) may have coronary microvascular dysfunction (CMD). As a group, these patients are underdiagnosed.
The index of microcirculatory resistance (IMR) and coronary flow reserve (CFR) are used to assess the microvasculature to help provide a diagnosis of CMD.
When an interventional cardiologist (IC) injects saline flush at ambient temperature into the artery, the PressureWire™ X Guidewire detects temperature changes as the saline passes the proximal and distal sensors.
Coronary flow is estimated based on the time it takes the saline to pass between proximal and distal sensors. This time (in seconds) is known as the Mean Transit Time (Tmn).
The CoroFlow‡ Cardiovascular System can be used to review physiology measurements.7
IMR = measures the blood flow in microvasculature
CFR = measures the blood flow in the epicardial arteries and the microvasculature
IMR and CFR cutoffs in a population of INOCA patients are shown on the right (based on CorMicA trial).8
INOCA patients may be suffering from persistent angina due to CMD and are at higher risk of major adverse cardiac events (MACE).9 Until such symptomatic patients receive proper treatment, they are frequent consumers of healthcare resources due to repeat evaluations, cath lab tests, emergency room visits, and hospitalizations.10-12
As the CorMicA study reveals, patients may benefit when coronary microvascular dysfunction is accurately diagnosed and properly treated.8,13
In addition, a comprehensive physiology assessment was demonstrated to be highly cost-effective at £4,500 per QALY. This is well below the accepted cost-effectiveness threshold of £20,000 per QALY for NICE (UK).14-16
Proper assessment, diagnosis, and treatment of CMD can improve outcomes in CMD patients at high risk for MACE and reduce healthcare burden.3,9,17
ESC and ACC/AHA guidelines recommend measuring IMR and CFR using a guidewire-based approach for symptomatic patients who exhibit no significant evidence of epicardial stenosis.
The ESC guidelines18 2019 were updated accordingly to include an increased focus on microvascular dysfunction.
|Guidewire-based CFR and/or microcirculatory resistance measurements should be considered in patients with persistent symptoms, but coronary arteries that are either angiographically normal or have moderate stenosis with preserved iwFR/FFR||IIa||B|
The AHA/ACC Clinical Practice Guideline on chest pain includes Class IIa recommendation for guidewire-based assessment for INOCA patients.19
|Recommendations for Patients With INOCA||Classa||Levelb|
|For patients with persistent stable chest pain and non-obstructive CAD and at least mild myocardial ischemia on imaging, it is reasonable to consider invasive coronary function testing to improve the diagnosis of coronary microvascular dysfunction and to enhance risk stratification.||IIa||B-NR|
CFR = coronary flow reserve; CMR = cardiac magnetic resonance; ECG = electrocardiogram;
FFR = fractional flow reserve; iwFR = instantaneous wave-free ratio; LAD = left anterior descending; PET = positron emission tomography.
a Class of recommendation.
b Level of evidence.
Level-NR: Level (Quality) of Evidence Level B-NR (non-randomized): moderate-quality evidence from 1 or more well designed, well executed non-randomized studies, observational studies or registry studies. RCTs. Meta-analyses of such studies.
The PressureWire™ X Guidewire with CoroFlow‡ Cardiovascular System has the capability to wirelessly measure comprehensive physiology indices to assess for epicardial disease (FFR, RFR) and microvascular dysfunction (IMR, CFR).4,7
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