Coronary Microvascular Dysfunction (CMD)

Go Beyond the Angiogram to Get to the Root Cause of Persistent Angina

Assessing for Coronary Microvascular Dysfunction (CMD)

CATH CMD is a global algorithm that captures the essential details of performing the bolus thermodilution workflow and assists in decision-making in a simple and stepwise manner. In summary, CATH captures the how to perform bolus thermodilution and CMD captures the what to do with the Index of Microcirculatory Resistance (IMR) and Coronary Flow Reserve (CFR) measurements to provide a diagnosis of Coronary Microvascular Dysfunction (CMD).

A full physiology assessment (with Resting full-cycle Ratio (RFR), Fractional Flow Reserve (FFR), IMR and CFR) of the epicardial arteries and the microvasculature can provide patients with persistent angina an accurate diagnosis to improve outcomes.1

Learn more from the experts

Now Published in JSCAI

Did you know a standardized approach to CMD assessment can enhance your workflow in the cath lab? Learn how the CATH CMD algorithm can help streamline the assessment of CMD and improve patient outcomes.

CATH CMD Algorithm


Catheter Engagement

  • Flush thoroughly2
  • Coaxial guide engagement2
  • Ensure no damping2
CATH CMD Catheter Engagement


Advance Wire

  • Interrogate LAD unless there is a specific territory of interest1
  • Advance wire sensor 2/3 distally in vessel3
  • Administer GTN/NTG2
CATH CMD Wire Advancement

Transit Time at Rest

  • Flush/purge pre-Tmnrest to clear any blood and contrast3
  • Room temperature saline3
  • Brisk 3 mL x 3 injections3
  • Address outliers (± 0.25s) before proceeding*4

*Repeat measurement of Tmnrest

CATH CMD Transit Time

Hyperemic Transit Time

  • Induce hyperemia5
  • Confirm hyperemia*6
  • Flush/purge pre-Tmnhyp to clear any blood and contrast6
  • Room temperature saline6
  • Brisk 3 mL x 3 injections6
  • Address outliers (± 0.15s) before proceeding**4

*Decrease in pressure, patient symptoms, FFR drop
**Repeat measurement of Tmnhyp

CATH CMD Hyperemic Transit Time


Coronary Flow Reserve (CFR)

  • CFR <2.5*4
  • CFR gray zone 2.0-2.4*

*Evolving concensus

CATH CMD Coronary Flow Reserve (CFR)


Index of Microcirculatory Resistance (IMR)

  • IMR ≥251
  • Use IMRcorr if FFR ≤0.807
CATH CMD Index of Microcirculatory Resistance (IMR)



  • Diagnosis of CMD based on IMR ≥25 and CFR <2.5*1,4
  • CFR gray zone 2.0-2.4*
  • Refer to guidelines and consensus document1,4,8,9

*Evolving consensus

CATH CMD Coronary Microvascular Dysfunction Diagnosis

GTN (glyceryl trinitrate) | NTG (nitroglycerin) | LAD (left anterior descending) | FFR (fractional flow reserve) | IMRcorr (IMR corrected) | CMD (coronary microvascular dysfunction) | Tmnrest (resting transit mean time) | Tmnhyp (hyperemic transit mean time)


  1. Kunadian V, et al. EAPCI Expert Consensus Document on Ischaemia with Non-Obstructive Coronary Arteries. EHJ. 2020; 0, 1-21.
  2. Berry C. Fractional Flow Reserve, Coronary Flow Reserve and the Index of Microvascular Resistance in Clinical Practice. Radcliffe Cardiology. 2014, 1-6.
  3. Fearon W, et al. Invasive Assessment of the Coronary Microvasculature: The Index of Microcirculatory Resistance. Circ Cardiovasc Interv. 2017; 10:e005361
  4. Perera D, et al. Invasive coronary physiology in patients with angina and non-obstructive coronary artery disease. Heart. 2022; 0, 1-8.
  5. Ford T, et al. Stratified Medical Therapy Using Invasive Coronary Function Testing in Angina: The CorMicA Trial. JACC. 2018, 72, 2841-55.
  6. Ang D, et al. Interventional Diagnostic Procedure: a Practical Guide for the Assessment of Coronary Vascular Function. JOVE 2022; 181, e2265.
  7. Yong A, et al. Calculation of the Index of Microcirculatory Resistance Without Coronary Wedge Pressure Measurement in the Presence of Epicardial Stenosis. JACC: Cardiovasc Interv. 2013; 6, 53-8.
  8. Knuuti J, et al. ESC guidelines. EHJ. 2020; 41, 407-477.
  9. Gulati M, et al. 2021 Chest Pain Guideline, Circulation. 2021; 144, e368-e454.

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