Coronary physiological assessment combining fractional flow reserve and index of microcirculatory resistance in patients undergoing elective percutaneous coronary intervention with grey zone fractional flow reserve

Physiology-Based Revascularization of Left Main Coronary Artery Disease

It is of critical importance to correctly assess the significance of a left main lesion. Underestimation of significance beholds the risk of inappropriate deferral of revascularization, whereas overestimation may trigger major but unnecessary interventions. This article addresses the invasive physiological assessment of left main disease and its role in deciding upon revascularization. It mainly focuses on the available evidence for fractional flow reserve and instantaneous wave-free ratio, their interpretation, and limitations. We also discuss alternative invasive physiological indices and imaging, as well as the link between physiology, ischemia, and prognosis.

Effect of microcirculatory resistance on coronary blood flow and instantaneous wave-free ratio: A computational study

BACKGROUND AND OBJECTIVE

The instantaneous wave-free ratio (iFR) has been proposed to estimate the hemodynamic severity of atherosclerotic stenosis in coronary arteries. The atherosclerotic stenosis in a proximal coronary artery could change its distal microcirculatory resistance (MR). However, there is a lack of investigation about the effect of MR variation on the blood flow and iFR of stenotic coronary arteries. We aim to investigate the changes of blood flow and iFR caused by distal MR variation.

METHODS

Four three-dimensional models of coronary arteries were reconstructed from the computed tomography images of two normal cases and two cases with 74.9% and 96.4% (in area) stenoses in a large branch of left anterior descending artery (LAD). Computational fluid dynamics simulation was performed on each model under 6 MR situations: hyperemia as the reference situation, resting when MR was multiplied by 8/3 in all outlet branches, h-one-1.5 and h-one-2 when MR was multiplied by 1.5 and 2.0 in one branch (the stenotic, or the corresponding branch in normal case) of LAD, h-branches-1.5 and h-branches-2 when MR was multiplied by 1.5 and 2.0 in the stenotic/corresponding and its cognate branches. Flow rate and iFR of each outlet branch were then calculated and compared between different MR situations to investigate the effect of MR variation on flow rate and iFR.

RESULTS

In the 74.9% stenosed and normal cases, referring to the hyperemia situation, the increase of MR in any branch significantly decreased its flow rate and increased its iFR, with limited effect on the flow rate (<3%) and iFR (<0.01) of other branches. However, in the 96.4% stenosed case, the doubled MR in the stenosed branch (h-one-2) significantly increased the flow rate (>10%) and iFR (>0.05) of its cognate branches.

CONCLUSION

The increase of MR in a normal or mildly stenosed branch of coronary artery decreases its blood flow and increases its iFR, with limited effect on other branches. Whereas, the increase of MR in a severely stenotic large branch could significantly increase the flow velocity and iFR of its cognate branches.

Caution! You're approaching a gray zone: FFR outcomes and the role of CFR and IMR

This study demonstrates that compared with low- fractional flow reserve (FFR) lesions (<0.75), those in the gray-zone FFR (0.75-0.80) are less likely to have improvement or more likely to have impairment in flow after percutaneous coronary intervention. The findings suggest index of microcirculatory resistance measurement may help identify lesions in the FFR gray zone that are most likely to improve. The study reinforces that FFR measurements represent a continuum of ischemic values and that a single dichotomous threshold oversimplifies the answer to whether a lesion should be revascularized.

Optimal Treatment Strategy for Coronary Artery Stenoses with Grey Zone Fractional Flow Reserve Values. A Systematic Review and Meta-Analysis

OBJECTIVES

We conducted a review and meta-analysis of published data to compare revascularization to deferral strategy for coronary lesions with grey zone fractional flow reserve (FFR).

BACKGROUND

Optimal treatment for coronary stenoses with FFR values between 0.75 and 0.80, the so-called grey zone, remains a matter of debate.

METHODS

We included all studies evaluating revascularization versus deferral for lesions with grey zone FFR. The primary outcome was study-defined major adverse cardiac events (MACE). Secondary outcomes were the composite of death or MI and target vessel revascularization (TVR). A total of 2362 patients were included, of whom 1181 underwent revascularization (revascularization group) and 1181 received medical treatment only (deferral group).

RESULTS

After a mean follow-up period of 2.4 years, no difference was found for the primary outcome of the study-defined MACE between the two groups [RR = 1.33 (0.73-2.44), p = 0.35]. In addition, there was no difference for the secondary outcomes of death or MI and TVR between the two groups [RR = 1.39 (0.56-3.47), p = 0.48 and RR = 1.49 (0.89-2.51), p = 0.13, respectively].

CONCLUSIONS

In this meta-analysis revascularization of coronary stenoses with grey zone FFR showed no advantage over a deferral strategy in terms of study-defined MACE. Case by case judgment should be implemented to guide treatment in this special subset of patients.

Comparison of myocardial microcirculatory perfusion after catheter-administered intracoronary thrombolysis with anisodamine versus standard thrombus aspiration in patients with ST-elevation myocardial infarction

OBJECTIVE

To evaluate efficacy, safety and feasibility of targeted intracoronary injection using pro-urokinase combined with anisodamine (TCA) versus thrombus aspiration (TA) in ST-elevation myocardial infarction (STEMI) patients with high thrombus loads.

BACKGROUND

The best method of avoiding thrombus detachment and stroke in PCI patients with high thrombus loads has not yet been established.

METHODS

STEMI patients receiving coronary artery angiography or percutaneous coronary intervention (CAG/PCI) with thrombus grade ≥ 3 from January 1, 2017 to June 30, 2018 were randomly assigned to targeted intracoronary thrombolysis (pro-urokinase and anisodamine via catheter (TCA) group), or the TA group which followed the standard thrombus aspiration procedure. Parameters compared included thrombus grade, index of microcirculatory resistance (IMR), postoperative myocardial SPECT, thrombosis in myocardial infarction (TIMI) scores including flow grade, corrected TIMI frame counts (CTFCs), and TIMI myocardial perfusion grade (TMPG). Adverse events were followed up within 3 months.

RESULTS

Thirty-nine patients were finally enrolled. In primary CAG/PCI, the TCA group had higher percentages of TIMI 3 flow and lower IMR values compared with the TA group. The ratio of TMPG 3 grade in the TCA group was higher in repeat CAG, and the perfusion descending area (PDA) presented by SPECT was lower than in the TA group. No significant difference was seen in major adverse coronary events (MACEs) or bleeding events at follow-up.

CONCLUSIONS

TCA appears to be effective, safe, and feasible for repatency and reduction of high thrombus burden in primary PCI and may protect myocardial microcirculation with improved outcomes.

Optimal Revascularization Threshold of Fractional Flow Reserve and its Effect on Outcomes: Perspectives From a High-Volume Center in China

This study aimed to investigate the favorable revascularization threshold for fractional flow reserve (FFR) in daily practice. Between March 2013 and March 2017 in a high-volume center in China, 903 patients with 1210 lesions underwent coronary intervention with adjunctive FFR and were consecutively enrolled. The mean FFR was 0.80 ± 0.11, revascularization was deferred for 68% of lesions, and the median follow-up period was 21 months. For lesions with an FFR > 0.80, deferral of revascularization appeared safe. In contrast, for lesions with an FFR ≤ 0.80, deferral of revascularization was associated with a greater risk of target lesion failure (TLF) than revascularization (hazard ratio [HR] 4.63, 95% confidence interval [CI] 2.02-10.06, P < .001). For lesions with an FFR value in the gray-zone (0.76-0.80), medical treatment alone was less effective than revascularization ( P = .020). For deferred lesions, FFR was an independent predictor for the future risk of TLF, when data were categorized (HR [FFR ≤ 0.75 vs FFR ≥ 0.86] 3.35, 95% CI 1.13-9.97, P = .030; HR [FFR 0.76-0.80 vs FFR ≥ 0.86] 4.01, 95% CI 1.73-9.31, P = .001) or continuous (HR 0.004, 95% CI 0.00-0.13, P = .002). Thus, an FFR value of 0.80 appears to be the optimal threshold for decision-making regarding revascularization and risk stratification.