CARDIOVASCULAR
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IMR and CFR

INDEX OF MICROVASCULAR RESISTANCE (IMR) & CORONARY FLOW RESERVE (CFR)

Patients with persistent angina—but no obstructive coronary artery disease (NOCAD) on angiography—may have coronary microvascular dysfunction (CMD). As a group these patients are underdiagnosed. In fact among patients assessed for angina, the majority (59%) have little or no angiographic abnormality, as shown in the visual.1 Yet the majority have symptoms of a coronary disorder.2

Two physiological indices— index of microvascular resistance (IMR) and coronary flow reserve (CFR)—are needed to diagnose CMD.2

When patients are assessed for angina, 59% have little or no angiographic abnormality.

IMR and CFR are calculated from the 2 temperature sensors located in proximal and distal positions on the PressureWire™ X Guidewire. These sensors allow physicians to capture the measurements using thermodilution.

Proximal and distal temperature sensors on PressureWire™ X Guidewire calculate the index of microvascular resistance (IMR) and coronary flow reserve (CFR)

Using thermodilution to evaluate IMR and CFR

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. (Get details about the PressureWire™ X Guidewire features and function.

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).

Thermodilution is used to evaluate IMR and CFR

Measuring IMR and CFR

Measuring IMR and CFR is straightforward, requiring just a few minutes.

 

After being recorded, measurements are then displayed for review.

IMR = Blood Flow in Microvasculature
CFR = Blood Flow in Epicardial Vessels + Microvasculature

Touchscreen showing IMR and CFR values to assess coronary microvascular dysfunction

Microvascular Dysfunction

IMR and CFR cutoffs in population of ischemia with no obstructive coronary artery disease (INOCA) patients, CorMicA trial.2

Microvascular disease correlates with these values: IMR ≥ 25   CFR < 2.0

Why treat coronary microvascular dysfunction?

NOCAD patients with ischemia and CMD are at higher risk of major adverse cardiac events (MACE).4 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.5-7

MACE
+
⇧ Healthcare Costs

As the CorMicA study reveals, patients may benefit when coronary microvascular dysfunction is accurately diagnosed and properly treated.3

27% Improvement in Angina Severity†3,8

18% Improvement in Quality of Life3,8

When coronary microvascular disease is treated, patients benefit from improved angina severity and improved quality of life

 

† According to the Seattle Angina Questionnaire score.

Proper assessment, diagnosis, and treatment of CMD is the only way to improve outcomes in CMD patients at high risk for MACE.4,9

Following society guidelines for IMR and CFR

ESC guidelines recommend measuring IMR and CFR using a guidewire-based approach for symptomatic patients who exhibit no significant evidence of epicardial stenosis.

hemodynamic system’s coronary flow reserve identifies CMD

a Class of recommendation. b Level of evidence.
CFR = coronary flow reserve; iwFR = instantaneous wave-free ratio; FFR = fractional flow reserve

The PressureWire™ X Guidewire has the capability to wirelessly measure both temperature (IMR, CFR) and pressure (FFR, RFR) values.

References

  1. Patel MR , Peterson ED , Dai D , et al. Low diagnostic yield of elective coronary angiography. N Engl J Med. 2010;362:886-895. doi:10.1056/NEJMoa0907272.
  2. Ford TJ, Berry C. How to diagnose and manage angina without obstructive coronary artery disease: lessons from the British Heart Foundation CorMicA Trial. Interv Cardiol Rev. 2019;14(2):76-82.
  3. Ford TJ, Stanley B, Sidik N, et al. 1-year outcomes of angina management guided by invasive coronary function testing (CorMicA). J Am Coll Cardiol Intv. 2020;13:33-45.
  4. Taqueti VR, Di Carli MF. Coronary microvascular disease pathogenic mechanisms and therapeutic options: JACC state-of-the-art review. J Am Coll Cardiol. 2018;72:2625–2641. doi:10.1016/j.jacc.2018.09.042.
  5. Rahman H, Corcoran D, Rahman M, et al. Diagnosis of patients with angina and non-obstructive coronary disease in the catheter laboratory. Heart. 2019;105:1536-1542.
  6. Lee B, Lim H, Fearon WF, et al. Invasive evaluation of patients with angina in the absence of obstructive coronary artery disease. Circulation. 2015;131:1054–1060.
  7. Reriani M, Flammer AJ, Duhé J, et al. Coronary endothelial function testing may improve long-term quality of life in subjects with microvascular coronary endothelial dysfunction. Open Heart. 2019;6:e000870. doi: 10.1136/openhrt-2018-000870.
  8. Ford TJ, Stanley B, Good R, et al. Stratified medical therapy using invasive coronary function testing in angina: the CorMicA trial. J Am Coll Cardiol. 2018;72:2841-2855.
  9. Jespersen L, Hvelplund A, Abildstrøm SZ, et al. Stable angina pectoris with no obstructive coronary artery disease is associated with increased risks of major adverse cardiovascular events. Eur Heart J. 2012;33:734-744. doi:10.1093/eurheartj/ehr331.
  10. Knuuti J, Wijns W, Saraste A, et al. 2019 ESC Guidelines for the diagnosis and management of chronic coronary syndromes: the Task Force for the diagnosis and management of chronic coronary syndromes of the European Society of Cardiology (ESC). Eur Heart J. 2020;41(3);407-477. doi: 10.1093/eurheartj/ehz425.

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DO YOU WISH TO CONTINUE AND EXIT CARDIOVASCULAR.ABBOTT?

CONTENTS OF THE SITE ARE NOT UNDER THE CONTROL OF ABBOTT.