Contrast Fractional Flow Reserve (cFFR): A pragmatic response to the call for simplification of invasive functional assessment

Coronary functional assessment in non-obstructive coronary artery disease: Present situation and future direction

Non-obstructive coronary artery disease (CAD), which is defined as coronary stenosis <50%, has been increasingly recognized as an emerging entity in clinical practice. Vasomotion abnormality and coronary microvascular dysfunction are two major mechanisms contributing to the occur of angina with non-obstructive CAD. Although routine coronary functional assessment is limited due to several disadvantages, functional evaluation can help to understand the pathophysiological mechanism and/or to exclude specific etiologies. In this review, we summarized the potential mechanisms involved in ischemia with non-obstructive coronary arteries (INOCA) and myocardial infarction with non-obstructive coronary arteries (MINOCA), the two major form of non-obstructive CAD. Additionally, we reviewed currently available functional assessment indices and their use in non-obstructive CAD. Furthermore, we speculated that novel technique combined anatomic and physiologic parameters might provide more individualized therapeutic choice for patients with non-obstructive CAD.

Functional Coronary Artery Assessment: a Systematic Literature Review

Cardiovascular diseases represent the number one cause of death in the world, including the most common disorders in the heart's health, namely coronary artery disease (CAD). CAD is mainly caused by fat accumulated in the arteries' internal walls, creating an atherosclerotic plaque that impacts the blood flow functional behavior. Anatomical plaque characteristics are essential but not sufficient for a complete functional assessment of CAD. In fact, plaque analysis and visual inspection alone have proven insufficient to determine the lesion severity and hemodynamic repercussion. Furthermore, the fractional flow reserve (FFR) exam, which is considered the gold standard for stenosis functional impair determination, is invasive and contains several limitations. Such a panorama evidences the need for new techniques applied to image exams to improve CAD functional assessment. In this article, we perform a systematic literature review on emerging methods determining CAD significance, thus delivering a unique base for comparing these methods, qualitatively and quantitatively. Our goal is to guide further studies with evidence from the most promising methods, highlighting the benefits from both areas. We summarize benchmarks, metrics for evaluation, and challenges already faced, thus shedding light on the requirements for a valid, meaningful, and accepted technique for functional assessment evaluation. We create a base of comparison based on quantitative and qualitative indicators and highlight the most relevant geometrical metrics that correlate with lesion significance. Finally, we point out future benchmarks based on recent literature.

Prognostic impact of FFR/contrast FFR discordance

BACKGROUND

Contrast fractional flow reserve (cFFR) is a relatively new tool for the assessment of intermediate coronary artery stenosis and represents a reliable surrogate of FFR with the advantage of potentially simplifying functional evaluation. We aimed to compare the incidence of major adverse cardiac events (MACE) in patients undergoing functional evaluation with both FFR and cFFR based on the results of the two indexes.

METHOD AND RESULT

We retrospectively analyzed outcomes in 488 patients who underwent functional evaluation with FFR and cFFR. Patients were divided into four groups using the cutoff values of 0.80 for FFR and 0.85 for cFFR: -/- (n = 298), +/+ (n = 134), -/+(n = 31) and +/- (n = 25). All patients were treated according to FFR value. MACE rate was assessed in each group, including death, myocardial infarction and urgent target vessel revascularization (TVR). Mean follow-up time was 22 ± 15 months. Incidence of MACE at follow-up was 8.3% in FFR-/cFFR-, 14.0% in FFR+/cFFR+, 16.0% in FFR-/cFFR+ and 8.0% in FFR+/cFFR- without a significant difference amongst the 4 groups (p = 0.2). Nevertheless, a significant difference in the rate of TVR comparing FFR-/cFFR- (n = 17) and FFR-/cFFR+ (n = 5) was found at 24 months (5.7% vs 16.0%; p = 0.027).

CONCLUSION

cFFR is accurate in predicting FFR and consequently reliable in guiding coronary revascularization. In the rare case of discordance, while FFR+/cFFR- patients show a prognosis similar to FFR-/cFFR- patients, FFR-/cFFR+ patients show a prognosis similar to FFR+/cFFR+ patients.

Comparison of resting and adenosine-free pressure indices with adenosine-induced hyperemic fractional flow reserve in intermediate coronary lesions

OBJECTIVE

Fractional flow reserve (FFR) using adenosine has been the gold standard in the functional assessment of intermediate coronary stenoses in the catheterization laboratory. We aim to study the correlation of adenosine-free indices such as whole cycle Pd/Pa [the ratio of mean distal coronary pressure (Pd) to the mean pressure observed in the aorta (Pa)], instantaneous wave-free ratio (iFR), and contrast-induced submaximal hyperemia (cFFR) with FFR.

METHODS

This multicenter, prospective, observational study included patients with stable angina or acute coronary syndrome (>48 h since onset) with discrete intermediate coronary lesions (40-70% diameter stenosis). All patients underwent assessment of whole cycle Pd/Pa, iFR, cFFR, and FFR. We then evaluated the correlation of these indices with FFR and assessed the diagnostic efficiencies of them against FFR ≤0.80.

RESULTS

Of the 103 patients from three different centers, 83 lesions were included for analysis. The correlation coefficient (r value) of whole cycle Pd/Pa, iFR, and cFFR in relation to FFR were +0.84, +0.77, and +0.70 (all p values < 0.001), respectively, and the c-statistic against FFR ≤0.80 were 0.92 (0.86-0.98), 0.89(0.81-0.97), and 0.91 (0.85-0.97) (all p values < 0.001), respectively. The best cut-off values identified by receiver-operator characteristic curve for whole cycle Pd/Pa, iFR, and cFFR were 0.94, 0.90, and 0.88, respectively, for an FFR ≤0.80. By the concept of "adenosine-free zone" (iFR = 0.86-0.93), 59% lesions in this study would not require adenosine.

CONCLUSION

All the three adenosine-free indices had good correlation with FFR. There is no difference in the diagnostic accuracies among the indices in functional evaluation of discrete intermediate coronary stenoses. However, further validation is needed before adoption of adenosine-free pressure parameters into clinical practice.