Minimal Microvascular Resistance: Agreement Between Continuous and Bolus Thermodilution
ABSTRACT
Background
Continuous thermodilution quantifies absolute microvascular resistance (Rμ, Wood units), a key metric of microvascular function. Rμ is minimal during hyperemia (Rμ,hyper) with increased Rμ,hyper suggestive of microvascular dysfunction. Bolus thermodilution measures the index of microcirculatory resistance (IMR), a dimensionless surrogate of Rμ,hyper.
Aims
We compared Rμ,hyper measured by continuous thermodilution (invasive Rμ,hyper) with the gold standard [15O]H2O positron emission tomography (PET Rμ,hyper), and assessed the correlation between invasive Rμ,hyper and IMR.
Methods
First, the accuracy of invasive Rμ,hyper was assessed in a cohort of 24 patients in which both invasive Rμ,hyper and PET Rμ,hyper were measured in the left anterior descending (LAD) and circumflex (LCX) arteries, corresponding to 46 measurements of Rμ,hyper in total (LAD = 24, LCX = 22). Next, agreement between invasive Rμ,hyper and IMR was evaluated in the LAD in a cohort of 250 patients with angina and non-obstructive coronary arteries.
Results
Invasive Rμ,hyper exhibited a strong correlation with PET Rμ,hyper (r = 0.86 [95% CI 0.76–0.92], p < 0.001), with good absolute agreement (ICC 0.82 [95% CI 0.70–0.90], p < 0.001). Passing-Bablok regression analysis found no significant systematic (intercept A: 54.53 [95% CI -18.95 to 120.96]) or proportional (slope B: 0.90 [95% CI 0.71–1.15]) bias between invasive Rμ,hyper and PET Rμ,hyper. However, invasive Rμ,hyper exhibited no significant correlation with IMR (r = 0.11 [95% CI -0.01 to 0.23], p = 0.08).
Conclusion
Invasive Rμ,hyper derived from continuous thermodilution exhibited excellent agreement with noninvasive Rμ,hyper measured by [15O]H2O PET, the current non-invasive standard of reference. In contrast, IMR exhibited no significant correlation with invasive Rμ,hyper in patients with angina and non-obstructive coronary arteries.
Conflicts of Interest
T.M. is supported by a grant from the Swiss National Science Foundation (SNSF). D.B., M.V., and A.W. report receiving research grants provided by the Cardiopath Ph.D. program. C.C. reports receiving research grants from Biosensor, Coroventis Research, Medis Medical Imaging, Pie Medical Imaging, CathWorks, Boston Scientific, Siemens, HeartFlow Inc, Abbott Vascular, and consultancy fees from HeartFlow Inc, Abbott Vascular, and Philips Volcano. NHJP received institutional research grants from Abbott, has consulting relationships with and receives fees from Abbott and Coroventis, has equity in ASML, General Electric, HeartFlow, and Philips, is member of the Scientific Advisory Board (SAB) of Heartflow, and has patents pending in the field of the coronary microcirculation and aortic valve stenosis. B.D.B. has a consulting relationship with Boston Scientific, Abbott Vascular, CathWorks, Siemens, and Coroventis Research; receives research grants from Abbott Vascular, Coroventis Research, Cathworks, Boston Scientific; and holds minor equities in Philips-Volcano, Siemens, GE Healthcare, Edwards Life Sciences, HeartFlow, Sanofi, and Celyad.
Open Research
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
