Minimal Microvascular Resistance: Agreement Between Continuous and Bolus Thermodilution.

BACKGROUND

Continuous thermodilution quantifies absolute microvascular resistance (R, Wood units), a key metric of microvascular function. R is minimal during hyperemia (R) with increased R suggestive of microvascular dysfunction. Bolus thermodilution measures the index of microcirculatory resistance (IMR), a dimensionless surrogate of R.

AIMS

We compared R measured by continuous thermodilution (invasive R) with the gold standard [O]HO positron emission tomography (PET R), and assessed the correlation between invasive R and IMR.

METHODS

First, the accuracy of invasive R was assessed in a cohort of 24 patients in which both invasive R and PET R were measured in the left anterior descending (LAD) and circumflex (LCX) arteries, corresponding to 46 measurements of R in total (LAD = 24, LCX = 22). Next, agreement between invasive R and IMR was evaluated in the LAD in a cohort of 250 patients with angina and non-obstructive coronary arteries.

RESULTS

Invasive R exhibited a strong correlation with PET R (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 R and PET R. However, invasive R exhibited no significant correlation with IMR (r = 0.11 [95% CI -0.01 to 0.23], p = 0.08).

CONCLUSION

Invasive R derived from continuous thermodilution exhibited excellent agreement with noninvasive R measured by [O]HO PET, the current non-invasive standard of reference. In contrast, IMR exhibited no significant correlation with invasive R in patients with angina and non-obstructive coronary arteries.