Vascular Resistance

AimsCoronary microvascular dysfunction and/or vasospasm are potential causes of ischaemia in patients with no obstructive coronary artery disease (INOCA). We tested the hypothesis that these patients also have functional abnormalities in peripheral small arteries.Methods and resultsPatients were prospectively enrolled and categorised as having microvascular angina (MVA), vasospastic angina (VSA) or normal control based on invasive coronary artery function tests incorporating probes of endothelial and endothelial-independent function (acetylcholine and adenosine). Gluteal biopsies of subcutaneous fat were performed in 81 subjects (62 years, 69% female, 59 MVA, 11 VSA, and 11 controls). Resistance arteries were dissected enabling study using wire myography. Maximum relaxation to ACh (endothelial function) was reduced in MVA vs. controls [median 77.6 vs. 98.7%; 95% confidence interval (CI) of difference 2.3-38%; P = 0.0047]. Endothelium-independent relaxation [sodium nitroprusside (SNP)] was similar between all groups. The maximum contractile response to endothelin-1 (ET-1) was greater in MVA (median 121%) vs. controls (100%; 95% CI of median difference 4.7-45%, P = 0.015). Response to the thromboxane agonist, U46619, was also greater in MVA (143%) vs. controls (109%; 95% CI of difference 13-57%, P = 0.003). Patients with VSA had similar abnormal patterns of peripheral vascular reactivity including reduced maximum relaxation to ACh (median 79.0% vs. 98.7%; P = 0.03) and increased response to constrictor agonists including ET-1 (median 125% vs. 100%; P = 0.02). In all groups, resistance arteries were ≈50-fold more sensitive to the constrictor effects of ET-1 compared with U46619.ConclusionsSystemic microvascular abnormalities are common in patients with MVA and VSA. These mechanisms may involve ET-1 and were characterized by endothelial dysfunction and enhanced vasoconstriction.Clinical trial registrationClinicalTrials.gov registration is NCT03193294.

Immediate assessment of coronary microcirculation during treatment of ST elevation myocardial infarction (STEMI) may facilitate patient stratification for targeted treatment algorithms. Use of pressure-wire to measure the index of microcirculatory resistance (IMR) is possible but has inevitable practical restrictions. We aimed to develop and validate angiography-derived index of microcirculatory resistance (IMRangio) as a novel and pressure-wire-free index to facilitate assessment of the coronary microcirculation. 45 STEMI patients treated with primary percutaneous coronary intervention (pPCI) were enrolled. Immediately before stenting and at completion of pPCI, IMR was measured within the infarct related artery (IRA). At the same time points, 2 angiographic views were acquired during hyperaemia to measure quantitative flow ratio (QFR) from which IMRangio was derived. In a subset of 15 patients both IMR and IMRangio were also measured in the non-IRA. Patients underwent cardiovascular magnetic resonance imaging (CMR) at 48 h for assessment of microvascular obstruction (MVO). IMRangio and IMR were significantly correlated (ρ: 0.85, p angio were higher in the IRA rather than in the non-IRA (p = 0.01 and p = 0.006, respectively) and were higher in patients with evidence of clinically significant MVO (> 1.55% of left ventricular mass) (p = 0.03 and p = 0.005, respectively). Post-pPCI IMRangio presented and area under the curve (AUC) of 0.96 (CI95% 0.92-1.00, p 40U and of 0.81 (CI95% 0.65-0.97, p 1.55%. IMRangio is a promising tool for the assessment of coronary microcirculation. Assessment of IMR without the use of a pressure-wire may enable more rapid, convenient and cost-effective assessment of coronary microvascular function.

Coronary microvascular resistance is increasingly measured as a predictor of clinical outcomes, but there is no accepted gold-standard measurement. We compared the diagnostic accuracy of 2 invasive indices of microvascular resistance, Doppler-derived hyperemic microvascular resistance (hMR) and thermodilution-derived index of microcirculatory resistance (IMR), at predicting microvascular dysfunction. A total of 54 patients (61 ± 10 years) who underwent cardiac catheterization for stable coronary artery disease (n = 10) or acute myocardial infarction (n = 44) had simultaneous intracoronary pressure, Doppler flow velocity and thermodilution flow data acquired from 74 unobstructed vessels, at rest and during hyperemia. Three independent measurements of microvascular function were assessed, using predefined dichotomous thresholds: (1) coronary flow reserve (CFR), the average value of Doppler- and thermodilution-derived CFR; (2) cardiovascular magnetic resonance (CMR) derived myocardial perfusion reserve index; and (3) CMR-derived microvascular obstruction. hMR correlated with IMR (rho = 0.41, p <0.0001). hMR had better diagnostic accuracy than IMR to predict CFR (area under curve [AUC] 0.82 vs 0.58, p <0.001, sensitivity and specificity 77% and 77% vs 51% and 71%) and myocardial perfusion reserve index (AUC 0.85 vs 0.72, p = 0.19, sensitivity and specificity 82% and 80% vs 64% and 75%). In patients with acute myocardial infarction, the AUCs of hMR and IMR at predicting extensive microvascular obstruction were 0.83 and 0.72, respectively (p = 0.22, sensitivity and specificity 78% and 74% vs 44% and 91%). We conclude that these 2 invasive indices of coronary microvascular resistance only correlate modestly and so cannot be considered equivalent. In our study, the correlation between independent invasive and noninvasive measurements of microvascular function was better with hMR than with IMR.

Coronary microvascular dysfunction (CMD) represent a crucial and often underdiagnosed cause of myocardial ischemia and dysfunction. It is closely linked to the prognosis of patients with coronary artery disease. Increased microvascular resistance (whether due to CMD or vascular rarefaction) is more frequent in the setting of coronary chronic total occlusions (CTO). Whether recanalization contributes to the recovery of microvascular function and whether measures of microvascular resistance can potentially be used as prognostic parameter to predict long-term success of CTO recanalization remains unknown. The aim of this study was to investigate CMD in patients with CTO and the effect of successful CTO recanalization. As well, we investigate whether CMD can be identified as a risk factor for restenosis after CTO recanalization. 119 patients underwent successful CTO recanalization at the University Medical Center in Mainz. After a follow-up period of 6 months, invasive control was carried out, in which 79 patients continued to have sufficient revascularization and 40 presented with restenosis. Angiography-based microvascular resistance (Angio-IMR) measurements were performed directly after successful CTO recanalization and at 6 months follow-up offline using a software package (QAngio XA 3D; Medis Medical Imaging Systems). 64% of the patients were male with an average age of 62 ± 9 years. The mean follow-up period was 191 ± 80 days. Median J-CTO Score was 1.8 ± 0.7. The CTO was localized at the RCA in 60%, at the LAD in 20% and at the LCX in 24% of the patients. All included patients had a good result after CTO recanalization confirmed by Quantitative flow ratio (QFR) of 0.94 ± 0.04 directly after PCI. Angio-IMR values immediately after CTO recanalization were pathological (> 25) in 78% of the patients and showed a significant decrease at 6 months follow-up (31.7 ± 7.1 vs. 28.6 ± 5.3¸ p = 0.0024). Post-procedural angio-IMR values did not predict restenosis at 6-month follow-up (31.7 ± 8 vs. 29.8 ± 7.5, p = 0.173). CMD can be detected in a majority of patients after successful CTO PCI. At 6 months follow-up we found significant improved angio-IMR values; CMD was not a predictor of restenosis.