CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 4, September/October 2023 AFRICA 253 A good correlation between FFR and iFR values or resting full-cycle ratio (RFR) in both diabetic and non-diabetic patients was found in a study investigating the relationship of DM and insulin treatment with FFR and the non-hyperaemic indices iFR and RFR. Amismatch between FFR and iFR or RFRwas found in approximately 20% of cases, and the frequency of mismatch was not associated with the presence of diabetes. This mismatch has been associated with microvascular dysfunction.25 In a trial evaluating the safety and efficacy of deferred revascularisation compared with complete revascularisation using an FFR-guided revascularisation strategy in patients with DM, major adverse cardiovascular events were more common after deferred revascularisation, especially in patients with a history of MI.26 A study investigating the safety of a delayed revascularisation strategy (FFR > 0.80) in patients with diabetes showed a higher rate of target lesion failure in patients with diabetes than in non-diabetic patients.23 On the basis of the above-mentioned studies, differences in the baseline values of Pd/Pa can be expected in patients with DM in comparison to the normal population as a result of microvascular dysfunction. However, in our study, we did not find a different predictive value for baseline Pd/Pa in patients with DM. We concluded that the previous default values can be used in patients with DM. Of course, it is important to remember that a vulnerable plaque leading to acute coronary syndrome is not always associated with anatomically severe stenosis and that FFR measurement does not provide sufficient information about the content of the plaque. The bottom line is that even if the FFR value of patients with DM is not in the critical zone, either at baseline or with adenosine infusion, it is essential to ensure good long-term follow up, strict glycaemic control and lifestyle modification. In a study evaluating the association between moderate CKD and FFR after stent implantation, moderate CKD was associated with insufficient improvement in FFR after stent implantation. The pre-procedure FFR values in the different eGFR groups were not significantly different.27 Another study, conducted to determine whether CKD (creatinine clearance < 45 ml/min) affected FFR in patients with moderate (50–70%) coronary stenosis, found that microcirculatory resistance was higher in patients with CKD, whereas a positive FFR value, defined as FFR < 0.80, was less frequent in the CKD group.28 Again, it is important to remember that people with CKD may have microvascular dysfunction and impaired coronary vasodilator capacity.29 In addition, GFR is an important indicator of kidney function, but changes in FFR measurements and different cardiovascular outcomes can also occur, for instance, in the presence of protein and albumin excretion in the urine. In a study conducted in a group of hypertensive patients, it was reported that there was a difference between normotensive and hypertensive individuals during the FFR procedure, and the FFR value was significantly lower in the hypertensive group. So, to avoid unnecessary interventions, it is important to perform measurements under conditions where blood pressure is regulated.30 Therefore, it can be considered that baseline Pd/ Pa values may also be affected by fluctuating blood pressure. We found no differences in baseline Pd/Pa values between different clinical conditions. Considering this with the data in the literature, we can conclude that the adopted thresholds for the baseline Pd/Pa value can be used in different clinical groups. Clearly, more relevant data and studies are needed. Study limitations There are a number of limitations in the interpretation of the study results, which should be taken into account. First, this is a single-centre, retrospective study with a relatively small number of patients. Prospective, multicentre, randomised trials with larger numbers of patients may provide more detailed results. Second, the use of additional intravascular imaging modalities in some patient groups, such as diabetic patients, may alter clinical decisions and outcomes. Third, it is important to obtain and carefully analyse patients’ follow-up results after FFR in the medium and long term. Our study did not evaluate these data. Fourth, some of the stenoses found to be anatomically non-critical on CAG may develop into acute coronary syndrome in the future. Therefore, it is unclear whether FFR or another intravascular imaging modality should be applied to some of these non-critical stenoses. Further investigation is warranted. Beyond these limitations, our study provides important information regarding the applicability of baseline FFR cut-off values to all populations. Conclusion In our study, baseline Pd/Pa correlated with FFR values during hyperaemia at certain cut-off values. No significant difference was found between baseline Pd/Pa as a reference value for lesion assessment in different clinical conditions. Therefore, baseline Pd/Pa is a parameter that does not require hyperaemia to be used in the assessment of lesion severity. In addition, the same default values for Pd/Pa can be used in different subgroups. References 1. Kwon TG, Matsuzawa Y, Li J, et al. Clinical usefulness of nonhyperemic baseline Pd/Pa as a hybrid baseline Pd/Pa-fractional flow reserve strategy. Coron Artery Dis 2015; 26(1): 49–55. 2. Jeremias A, Maehara A, Généreux P, et al. Multicenter core laboratory comparison of the instantaneous wave-free ratio and resting Pd/Pa with fractional flow reserve: the RESOLVE study. J Am Coll Cardiol 2014; 63(13): 1253–1261. 3. Echavarría-Pinto M, van de Hoef TP, Garcia-Garcia HM, et al. Diagnostic accuracy of baseline distal-to-aortic pressure ratio to assess coronary stenosis severity: a post-hoc analysis of the ADVISE II Study. J Am Coll Cardiol Cardiovasc Interv 2015; 8(6): 834–836. 4. Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018) [published correction appears in Circulation 2018; 138(20): e652]. Circulation 2018; 138(20): e618–e651. 5. Chapter 1: Definition and classification of CKD. Kidney Int Suppl (2011) 2013; 3(1): 19–62. 6. De Bruyne B, Pijls NH, Barbato E, Bartunek J, Bech JW, Wijns W, Heyndrickx GR. Intracoronary and intravenous adenosine 5’-triphosphate, adenosine, papaverine, and contrast medium to assess fractional flow reserve in humans. Circulation 2003; 107(14): 1877–1883. 7. Tonino PA, De Bruyne B, Pijls NH, et al. Fractional flow reserve versus angiography for guiding percutaneous coronary intervention. N Engl J Med 2009; 360(3): 213–224.
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