Impact of stenosis resistance and coronary flow capacity on fractional flow reserve and instantaneous wave-free ratio discordance: a combined analysis of DEFINE-FLOW and IDEAL

BACKGROUND

The pressure-derived parameters fractional flow reserve (FFR) and the emerging instantaneous wave-free ratio (iFR) are the most widely applied invasive coronary physiology indices to guide revascularisation. However, approximately 15-20% of intermediate stenoses show discordant FFR and iFR, and therapeutical consensus is lacking.

AIMS

We sought to associate hyperaemic stenosis resistance index, coronary flow reserve (CFR) and coronary flow capacity (CFC) to FFR/iFR discordance.

METHODS

We assessed pressure and flow measurements of 647 intermediate lesions (593 patients) of two multi-centre international studies.

RESULTS

FFR and iFR were discordant in 15% of all lesions (97 out of 647). FFR+/iFR- lesions had similar hyperaemic average peak velocity (hAPV), CFR and CFC as FFR-/iFR- lesions, whereas FFR-/iFR+ lesions had similar hAPV, CFR and CFC as FFR+/iFR+ lesions (p > 0.05 for all). FFR+/iFR- lesions were associated with lower baseline stenosis resistance, but not hyperaemic stenosis resistance, compared with FFR-/iFR+ lesions (p < 0.001).

CONCLUSIONS

Discordance with FFR+/iFR- is characterised by maximal flow values, CFR, and CFC patterns similar to FFR-/iFR- concordance that justifies conservative therapy. Discordance with FFR-/iFR+ on the other hand, is characterised by low flow values, CFR, and CFC patterns similar to iFR+/FFR+ concordance that may benefit from percutaneous coronary intervention.

Indicators of abnormal PET coronary flow capacity in detecting cardiac ischemia

Coronary flow capacity (CFC) categorizes severity of left ventricular (LV) ischemia by PET myocardial blood flow (MBF). Our objective was to correlate abnormal CFC with other indicators of regional ischemia. Data were examined retrospectively for 231 patients evaluated for known/suspected CAD who underwent rest and regadenoson-stress ⁸²Rb PET/CT. MBF and myocardial flow reserve (MFR) were quantified, from which CFC was categorized as Normal CFC (1), Minimally reduced (2), Mildly reduced (3), Moderately reduced (4), and Severely reduced (5) for the three main arterial territories as well as globally. Relative perfusion summed stress score (SSS) and systolic phase contraction bandwidth (BW) were assessed. Accuracy to detect arteries with CFC ≥ 4 was highest for a Regional Index combining SSS and BW (88 ± 3%). A Global Index formed from stress ejection fraction, SSS and BW was the most accurate means of identifying patients with global CFC ≥ 4 (84 ± 3%). Arteries with abnormal CFC derived from absolute myocardial blood flow measurements are accurately identified by composite parameters combining regionally aberrant relative perfusion patterns and asynchrony.

Prognostic value of modified coronary flow capacity by 13N-ammonia myocardial perfusion positron emission tomography in patients without obstructive coronary arteries

BACKGROUND

Vasodilator capacity of coronary circulation is an important diagnostic and prognostic tool in patients with coronary artery disease (CAD). We aimed to clarify the incidence of coronary microvascular dysfunction (CMD), defined as impaired modified coronary flow capacity (mCFC) proposed by Johnson and Gould and measured by ¹³N-ammonia myocardial perfusion positron emission tomography (PET), in patients without obstructive CAD and to evaluate the risk of future cardiovascular events.

METHODS

This retrospective study recruited 407 consecutive CAD-suspected patients who underwent both pharmacological stress/rest ¹³N-ammonia PET and coronary angiography. Of the 407 patients, 137 patients (median age, 70 years; 63 women) were eligible and followed up (median, 19.8 months). Endpoints were defined as cardiovascular death or major adverse cardiovascular events (MACEs), such as cardiovascular death, nonfatal myocardial infarction, unplanned hospitalization for any cardiac reasons, and unplanned coronary revascularization. The impaired mCFC group included patients with mildly to severely reduced regional CFC in, at least, one vascular territory (n=34), while the remaining patients (n=103) were categorized as having preserved mCFC.

RESULTS

Overall, cardiovascular death and MACEs occurred in five (4%) patients. The Kaplan-Meier curve showed a significant reduction in event-free survival for cardiovascular death (p=0.004) and MACEs (p<0.0001) in the impaired mCFC group, compared to the preserved mCFC group. Impaired mCFC was independently associated with the incidence of both cardiovascular death and MACEs after propensity-score adjustments [hazard ratio (HR), 10.7; 95% confidence interval (CI), 1.0-106.0; p=0.04 and HR, 9.5; 95% CI, 2.5-36.2; p<0.001, respectively].

CONCLUSIONS

In CAD-suspected patients without obstructive coronary arteries, impaired mCFC was observed in approximately 25% and was associated with a higher risk of cardiovascular death and MACEs. The mCFC concept can help identify patients who would benefit from specific therapies or lifestyle modifications to prevent future MACEs and can clarify potential mechanisms of CMD.

PET Stress Testing with Coronary Flow Capacity in the Evaluation of Patients with Coronary Artery Disease and Left Ventricular Dysfunction: Rethinking the Current Paradigm

PURPOSE OF REVIEW

Cardiomyopathy with underlying left ventricular (LV) dysfunction is a heterogenous group of disorders that may be present with, and/or secondary to, coronary artery disease (CAD). The purpose of this review is to demonstrate, via case illustrations, the benefits offered by cardiac positron-emission tomography (PET) stress testing with coronary flow capacity (CFC) in the evaluation and treatment of patients with left ventricular (LV) dysfunction and CAD.

RECENT FINDINGS

CFC, a metric that is increasing in prominence, represents the integration of several absolute perfusion metrics into clinical strata of CAD severity. Our prior work has demonstrated improvement in regional perfusion metrics as a result of revascularization to territories with severe reduction in CFC. Conversely, when CFC is adequate, there is no change in regional perfusion metrics following revascularization, despite angiographically severe stenosis. Furthermore, Gould et al. demonstrated decreased rates of myocardial infarction and death following revascularization of myocardium with severely reduced CFC, with no clinical benefit observed following revascularization of patients with preserved CFC. In a series of cases, we present pre-revascularization and post-revascularization PET scans with perfusion metrics in patients with LV dysfunction and CAD. In these examples, we demonstrate improvement in LV function and perfusion metrics following revascularization only in cases where baseline CFC is severely reduced. PET with CFC offers unique guidance regarding revascularization in patients with reduced LV function and CAD.

Reliability and Reproducibility of Absolute Myocardial Blood Flow: Does It Depend on the PET/CT Technology, the Vasodilator, and/or the Software?

PURPOSE OF REVIEW

The COURAGE and ISCHEMIA trials showed no reduced mortality after revascularization compared to medical treatment. Is this lack of benefit due to revascularization having no benefit regardless of CAD severity or to suboptimal patient selection due to non-quantitative cardiac imaging?

RECENT FINDINGS

Comprehensive, integrated, myocardial perfusion quantified by regional pixel distribution of coronary flow capacity (CFC) is the final common expression of objective CAD severity for which revascularization reduces mortality. Current lack of revascularization benefit derives from narrow thinking focused on measuring one isolated aspect of coronary characteristics, such as angiogram stenosis, its fractional flow reserve (FFR), anatomic FFR simulations, relative stress imaging, absolute stress ml/min/g or coronary flow reserve (CFR) alone, or even more narrowly on global CFR or fixed regions of interest in assumed coronary artery distributions, or in arbitrary 17 segments on bull's-eye displays, rather than regional pixel distribution of perfusion metrics as they actually are in an individual. Comprehensive integration of all quantitative perfusion metrics per regional pixel into coronary flow capacity guides artery-specific interventions for reduced mortality in non-acute CAD but requires addressing the methodologic questions in the title.

Invasive coronary physiology: a Dutch tradition

Invasive coronary physiology has been applied since the early days of percutaneous transluminal coronary angioplasty, and has become a rapidly emerging field of research. Many physiology indices have been developed, tested in clinical studies, and are now applied in daily clinical practice. Recent clinical practice guidelines further support the use of advanced invasive physiology methods to optimise the diagnosis and treatment of patients with acute and chronic coronary syndromes. This article provides a succinct review of the history of invasive coronary physiology, the basic concepts of currently available physiological parameters, and will particularly highlight the Dutch contribution to this field of invasive coronary physiology.

The impact of revascularization on myocardial blood flow as assessed by positron emission tomography

Purpose

Revascularization aims to improve myocardial perfusion. However, changes in regional artery-specific quantitative perfusion after revascularization have not been systematically investigated. It is unclear whether artery-specific thresholds for coronary flow capacity (CFC) and/or relative perfusion predict improved stress perfusion after revascularization. We sought to determine the impact of revascularization based on predefined, artery-specific, severity size thresholds for CFC and/or relative perfusion defects.

Methods

Fifty patients underwent PET imaging before revascularization and then prospectively within 90 days after revascularization. Changes in regional myocardial blood flow (MBF) were stratified based on baseline perfusion abnormalities, baseline reduced CFC, and whether revascularization was performed in that region.

Results

Following angiographic stenosis-directed revascularization, in regions with relative perfusion abnormalities and decreased CFC, stress MBF (sMBF) increased by 0.51 cm³/min/g (59%) from baseline (p < 0.001). In regions without baseline perfusion abnormalities and yet decreased CFC, sMBF increased by 0.35 cm³/min/g (40%) from baseline (p < 0.001). In regions without perfusion abnormalities and normal CFC, sMBF did not increase significantly (+0.07 cm³/min/g, p = 0.56). Patients in whom revascularization was concordant with abnormal PET findings showed increased whole-heart sMBF (+0.22 cm³/min/g, p < 0.001), but in patients in whom revascularization was targeted only to regions without perfusion abnormalities or low CFC, sMBF did not change significantly (−0.06 cm³/min/g, p = 0.38).

Conclusion

Revascularization targeted to regions with reduced CFC and relative perfusion abnormalities on baseline PET yielded significant improvements in sMBF. When revascularization was performed in regions without reduced CFC, sMBF did not improve.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04278-8) contains supplementary material, which is available to authorized users.

Coronary flow capacity: concept, promises, and challenges

The vasodilator capacity of the coronary circulation is an important diagnostic and prognostic characteristic, and its accurate assessment is therefore an important frontier. The coronary flow capacity (CFC) concept was introduced to overcome the limitations associated with the use of coronary flow reserve (CFR) for this purpose, which are related to the sensitivity of CFR to physiological alterations in systemic and coronary hemodynamics. CFC was developed from positron emission tomography, and was subsequently extrapolated to invasive coronary physiology. These studies suggest that CFC is a robust framework for the identification of clinically relevant coronary flow abnormalities, and improves identification of patients at risk for adverse events over the use of CFR alone. This Review will discuss the concept of CFC, its promises in the setting of ischaemic heart disease, and its challenges both in theoretical and practical terms.