Diagnostic accuracy of Instantaneous Wave-Free Ratio (iFR) for the assessment of myocardial ischaemia: a comparison with non-invasive stress imaging

Background

Instantaneous Wave-Free Ratio (iFR) allows for the assessment of the haemodynamic effects of epicardial coronary stenoses without the need for hyperaemia; iFR is currently recommended as a means to evaluate myocardial ischaemia.

Purpose

To assess the diagnostic accuracy of iFR with respect to the identification of coronary epicardial stenoses causing ischemia. Therefore, we combined anatomical (% stenosis at invasive coronary angiography, ICA) and functional (non-invasive imaging stress test, NIST) information to obtain a “gold standard” for the identification of stenoses causing ischaemia.

Methods

We enrolled 71 patients (52 male, 19 female; age mean 68.4±8.1 years) with chronic coronary syndrome or low-risk acute coronary syndrome without ST segment elevation who had at least a NIST and who had at least one vessel with a 50%-85% stenosis at ICA. iFR was measured in all coronary arteries with stenosis >50% and categorised according to the 0.89 threshold for ischaemia.

Results

iFR was assessed in 122 vessels. In a per-vessel analysis, in 56.7% ischaemia was present both at iFR and NIST, in 21.3% ischaemia was absent in both, while in 23.0% ischaemia was found at NIST but not confirmed by iFR. The overall accuracy of iFR with respect to NIST was 90.1%. However, when considering as the “gold standard” for coronary disease causing ischaemia the contemporary presence of an epicardial stenosis >70% at ICA and a positive NIST, the diagnostic accuracy of iFR greatly improved. The sensibility, specificity, PPV, NPV and accuracy were 96.5%, 75.0%, 73.3%, 96.7% and 84.4%, respectively. In case of discordance between NIST and iFR, revascularization was based on iFR. At a mean follow-up of 23±18 months, the composite endpoint of MACE (major adverse cardiac events, defined as the composite of all-cause death, nonfatal MI and unplanned coronary revascularization) occurred in 16.4%, while death/MI occurred in 11.9%. Stratification according to the per-patient concordance between iFR and NIST showed no significant differences in rates of MACE (p=0.50) and death/MI (p=0.20). Stratification based on iFR showed a higher death/MI rate in iFR-positive patients (11.9% vs. 0%, p=0.047) and a trend to higher MACE rate (11.9% vs. 4.47% p=0.14),

Conclusions

The diagnostic accuracy of iFR is low when compared with NIST as the reference for myocardial ischaemia, but it is very high when compared with the combined presence of epicardial stenosis and positive NIST. Therefore, iFR can accurately guide the decision to treat or defer revascularization of intermediate coronary stenoses, being most useful in patients with multivessel CAD and when non-invasive functional data are lacking or discordant with anatomy.

Funding Acknowledgement

Type of funding source: None

P2538Arterial stiffness and remodeling from large to small arteries in patients with spontaneous coronary artery dissection: evidence for a systemic subclinical involvement

Background and aim

Spontaneous coronary artery dissection (SCAD) is a major cause of acute coronary syndrome in women aged 50 years or less (22–43%). Its etiology is still unknown, though an association with systemic diseases such as fibromuscular dysplasia and collagenopathies has been found. This study is aimed at investigating the presence of subclinical structural and functional alterations in extracoronary districts in SCAD patients.

Methods

The design was a case-control study. Carotid, radial and digital arteries were scanned by standard or ultrahigh frequency ultrasound; clips were analyzed by automated image analysis software for diameter, intima-media thickness (IMT) and local distensibility. Applanation tonometry was used to obtain carotid-femoral pulse wave velocity, a measure of regional, aortic stiffness, and carotid pressure waveform.

Results

30 patients previously diagnosed with SCAD (27 women, age 51±10 years, 8 treated hypertensives, 4 smokers, mean BP 83±11mmHg, BMI 25±5kg/mq) and 30 controls, matched for age, sex and CV risk factors by propensity score, were enrolled. 18 SCAD patients underwent PTCA and 6 had a diagnosis of extracoronary fibromuscular dysplasia. In the left radial artery, wall thickness, cross-sectional area (2.96±1.07 vs 1.79±1.41mm2, p=0.008), and wall inhomogeneity were increased, especially in the outer layer, whereas diameter, wall/lumen ratio and distensibility were comparable to controls. In the left common carotid artery, an increased carotid stiffness was shown in SCAD (5.99±0.89 m/s vs 5.6±0.85, 0.03), while IMT tended to be increased bilaterally (0.63±0.12 vs 0.59±0.10mm, p=0.08). Aortic stiffness was similar in the two groups (7.0±1.9 vs 6.7±1.7m/s, p=0.60). Carotid (20.4±14.2 vs 11.9±15.0%, p=0.03), but not aortic augmentation index, was increased bilaterally.

Conclusions

SCAD patients showed a peculiar pattern of alterations in vascular remodeling and stiffness in extracoronary arterial segments such as the carotid and radial arteries, supporting the hypothesis that a systemic susceptibility is present even in the absence of systemic diseases.