Effect of acute myocardial infarction on the utility of fractional flow reserve for the physiologic assessment of the severity of coronary artery narrowing

Prognostic Impact of Coronary Flow Reserve in Patients With Reduced Left Ventricular Ejection Fraction

Background

Intracoronary physiologic indexes such as coronary flow reserve (CFR) and left ventricular ejection fraction (LVEF) have been regarded as prognostic indicators in patients with coronary artery disease. The current study evaluated the association between intracoronary physiologic indexes and LVEF and their differential prognostic implications in patients with coronary artery disease.

Methods and Results

A total of 1889 patients with 2492 vessels with available CFR and LVEF were selected from an international multicenter prospective registry. Baseline physiologic indexes were measured by thermodilution or Doppler methods and LVEF was recorded at the index procedure. The primary outcome was target vessel failure, which was a composite of cardiac death, target vessel myocardial infarction, or clinically driven target vessel revascularization over 5 years of follow‐up. Patients with reduced LVEF <50% (162 patients [8.6%], 202 vessels [8.1%]) showed a similar degree of epicardial coronary artery disease but lower CFR values than those with preserved LVEF (2.4±1.2 versus 2.7±1.2, P<0.001), mainly driven by the increased resting coronary flow. Conversely, hyperemic coronary flow, fractional flow reserve, and the degree of microvascular dysfunction were similar between the 2 groups. Reduced CFR (≤2.0) was seen in 613 patients (32.5%) with 771 vessels (30.9%). Reduced CFR was an independent predictor for target vessel failure (hazard ratio, 2.081 [95% CI, 1.385–3.126], P<0.001), regardless of LVEF.

Conclusions

CFR was lower in patients with reduced LVEF because of increased resting coronary flow. Patients with reduced CFR showed a significantly higher risk of target vessel failure than did those with preserved CFR, regardless of LVEF.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04485234.

Fractional Flow Reserve: Patient Selection and Perspectives

The aim of this review was to discuss the current practice and patient selection for invasive FFR, new techniques to estimate invasive FFR and future of coronary physiology tests. We elaborate on the indication and application of FFR and on the contraindications and concerns in certain patient populations.

Performing and Interpreting Fractional Flow Reserve Measurements in Clinical Practice: An Expert Consensus Document

Fractional flow reserve (FFR) measurements can determine the haemodynamic relevance of coronary artery stenoses. Current guidelines recommend their use in lesions in the absence of non-invasive proof of ischaemia. The prognostic impact of FFR has been evaluated in randomised trials, and it has been shown that revascularisation can be safely deferred if FFR is >0.80, while revascularisation of stenoses with FFR values ≤0.80 results in significantly lower event rates compared to medical treatment. Left main stenoses, aorto-ostial lesions, as well as patients with left ventricular hypertrophy and severely-impaired ejection fraction, have been excluded from large, randomised trials. While FFR measurements are relatively straightforward to perform, uncertainty about procedural logistics, as well as data acquisition and interpretation in specific situations, could explain why they are not widely used in clinical practice. We summarise the clinical data in support of FFR measurements, and provide recommendations for performing and interpreting the procedure.

Comprehensive assessment of coronary fractional flow reserve

Fractional flow reserve (FFR) is considered nowadays as the gold standard for invasive assessment of physiologic stenosis significance and an indispensable tool for decision-making in coronary revascularization. Robust studies have shown that FFR is more effective in accurately identifying which lesions should be stented, and revascularization guided by FFR improves the outcome of coronary artery disease in patients. Therefore, FFR has been upgraded to a class A recommendation in current guidelines when the ischemic potential for specific target lesions is controversial. This article reviews the laboratory practice, functional evaluation of FFR as a gold standard and its emerging clinical application. In addition, novel noninvasive technologies of FFR measurement are discussed in depth.

Influence of Variable Native Arterial Diameter and Vasculature Status on Coronary Diagnostic Parameters

In current practice, diagnostic parameters, such as fractional flow reserve (FFR) and coronary flow reserve (CFR), are used to determine the severity of a coronary artery stenosis. FFR is defined as the ratio of hyperemic pressures distal (p˜rh) and proximal (p˜ah) to a stenosis. CFR is the ratio of flow at hyperemic and basal condition. Another diagnostic parameter suggested by our group is the pressure drop coefficient (CDP). CDP is defined as the ratio of the pressure drop across the stenosis to the upstream dynamic pressure. These parameters are evaluated by invasively measuring flow (CFR), pressure (FFR), or both (CDP) in a diseased artery using guidewire tipped with a sensor. Pathologic state of artery is indicated by lower CFR (<2). Similarly, FFR lower than 0.75 leads to clinical intervention. Cutoff for CDP is under investigation. Diameter and vascular condition influence both flow and pressure drop, and thus, their effect on FFR and CDP was studied. In vitro experiment coupled with pressure-flow relationships from human clinical data was used to simulate pathophysiologic conditions in two representative arterial diameters, 2.5 mm (N1) and 3 mm (N2). With a 0.014 in. (0.35 mm) guidewire inserted, diagnostic parameters were evaluated for mild (∼64% area stenosis (AS)), intermediate (∼80% AS), and severe (∼90% AS) stenosis for both N1 and N2 arteries, and between two conditions, with and without myocardial infarction (MI). Arterial diameter did not influence FFR for clinically relevant cases of mild and intermediate stenosis (difference < 5%). Stenosis severity was underestimated due to higher FFR (mild: ∼9%, intermediate: ∼ 20%, severe: ∼ 30%) for MI condition because of lower pressure drops, and this may affect clinical decision making. CDP varied with diameter (mild: ∼20%, intermediate: ∼24%, severe: by 2.5 times), and vascular condition (mild: ∼35%, intermediate: ∼14%, severe: ∼ 9%). However, nonoverlapping range of CDP allowed better delineation of stenosis severities irrespective of diameter and vascular condition.

Coronary physiology in the cath lab: beyond the basics

The adoption of invasive coronary physiologic lesion assessment before percutaneous coronary intervention has become routine in many catheterization laboratories. In the last decade, numerous studies have demonstrated favorable outcomes for revascularization decisions based on in-lab coronary physiology in many patients. The use of coronary physiology in the laboratory has been identified as a class IIa recommendation for patients in whom the clinical presentation and supporting data are too inconclusive to make an objective decision regarding treatment. This article reviews pertinent concepts and studies of the more complex applications of translesional pressure measurements for optimal patient outcomes.

Current concepts of integrated coronary physiology in the catheterization laboratory

Over the last 15 years, the use of invasive coronary physiology in the catheterization laboratory has demonstrated favorable outcomes for decision making in patients with intermediate single-vessel stenoses, complex bifurcation and ostial branch stenoses, multivessel coronary artery disease, and left main stenoses. A recent large multicenter study (FAME [FFR versus Angiography for Multivessel Evaluation]) found that a physiologically-guided approach was superior to the standard angiographically-guided approach for percutaneous revascularization in patients with multivessel coronary artery disease. This review addresses selected pertinent concepts and studies supporting the integration of coronary physiology in the catheterization laboratory for optimal patient outcomes.

Usefulness of fractional flow reserve measurements to defer revascularization in patients with stable or unstable angina pectoris, non-ST-elevation and ST-elevation acute myocardial infarction, or atypical chest pain

This study determined the safety of deferring coronary revascularization based on a fractional flow reserve (FFR) value > or = 0.75 in a series of consecutive unselected coronary patients with moderate coronary lesions, including patients with unstable angina, myocardial infarction (MI), and/or positive noninvasive test findings. The study included 201 consecutive coronary patients (mean age 62 +/- 10 years; 65% men) with 231 lesions evaluated by FFR measurement for which revascularization was deferred based on a FFR value > or = 0.75. Lesions associated with a positive noninvasive test result were those located in an artery supplying a myocardial territory in which myocardial ischemia was demonstrated by a noninvasive test. Cardiac events (cardiac death, MI, revascularization) and Canadian Cardiovascular Society angina class were evaluated at follow-up. Indications for coronary angiography included unstable angina or MI (62%), stable angina (30%), or atypical chest pain (8%). Forty-four patients (22%) had > or = 1 coronary lesion associated with a positive noninvasive test result in which FFR was evaluated. Mean FFR value was 0.87 +/- 0.06 and mean lesion percent diameter stenosis was 41 +/- 8%. At 11 +/- 6 months of follow-up, cardiac events occurred in 20 patients (10%), and no significant differences were observed between patients with unstable angina or MI and those with stable angina (9% vs 13%, p = 0.44) or between patients with and without lesions associated with positive noninvasive test results (9% vs 10%, p = 1.00). At the end of follow-up, 88% of patients were asymptomatic in angina class 0 or I, with no differences across various groups. In conclusion, these results suggest that patients with moderate coronary lesions can be safely managed without revascularization on the basis of FFR measurements, irrespective of clinical presentation and/or presence of positive noninvasive test results.

Fractional Flow Reserve of Infarct-Related Arteries Identifies Reversible Defects on Noninvasive Myocardial Perfusion Imaging Early After Myocardial Infarction

OBJECTIVES

We hypothesized that fractional flow reserve (FFR) of an infarct-related artery (IRA) early after myocardial infarction (MI) identifies inducible ischemia on noninvasive imaging.

BACKGROUND

Early after MI, IRAs frequently have angiographically indeterminant lesions. Whether FFR can detect reversible perfusion defects early after MI when dynamic microvascular abnormalities are present is not known.

METHODS

Rest and dipyridamole (DP)-stress 99mTc sestamibi single-photon emission computed tomography (SPECT) were performed in 48 patients 3.7 +/- 1.3 days after MI, with 23 patients undergoing concurrent myocardial contrast echocardiography (MCE). Angiography, FFR, and percutaneous coronary intervention (PCI) of the IRA (as necessary) were subsequently performed. Follow-up SPECT was performed 11 weeks after PCI to identify true reversibility on baseline SPECT.

RESULTS

The sensitivity, specificity, positive and negative predictive value, and concordance of FFR < or =0.75 for detecting reversibility on SPECT were 88%, 50%, 68%, 89%, and 71% (chi-square <0.001), respectively; which improved to 88%, 93%, 88%, 93%, and 91% (chi-square <0.001), respectively, for the detection of true reversibility. The corresponding values of FFR < or =0.75 for detecting reversibility on DP-MCE were 90%, 100%, 100%, 75%, and 93% (chi-square <0.001), respectively, and on either SPECT or MCE were 88%, 93%, 91%, 91%, and 91% (chi-square <0.001), respectively. The optimal FFR value for discriminating inducible ischemia on noninvasive imaging was 0.78.

CONCLUSIONS

Fractional flow reserve of the IRA accurately identifies reversibility on noninvasive imaging early after MI. These findings support the utility of FFR early after MI.

Cardiac magnetic resonance perfusion imaging for the functional assessment of coronary artery disease: a comparison with coronary angiography and fractional flow reserve

AIMS

Cardiac magnetic resonance perfusion imaging (CMRI) is a promising technique for non-invasive measurement of myocardial perfusion reserve. Fractional flow reserve (FFR) is an established invasive method for functional assessment of coronary artery disease (CAD). To prospectively assess the diagnostic value of CMRI for the detection of haemodynamically significant coronary lesions, compared with coronary angiography (CA) and FFR.

METHODS AND RESULTS

Forty-three patients with suspected or known CAD underwent CA, CMRI, and FFR measurement. First pass magnetic resonance perfusion examination was performed during hyperaemia (140 microg/kg/min adenosine over 6 min) and at rest. One hundred and twenty-nine perfusion territories were assessed by semi-quantitative evaluation of signal intensity-time curves using the myocardial perfusion reserve index (MPRI) [upslope(stress(corrected))/upslope(rest(corrected))]. Perfusion territories were categorized as normal (coronary stenosis < or = 50%), intermediate (stenosis > 50% and FFR > 0.75), or severe (stenosis > 50% and FFR < or = 0.75 or total occlusion). MPRI values (+/-SD) were significantly different between the three categories [normal, 2.2 +/- 0.5 vs. intermediate, 1.8 +/- 0.5 (P = 0.005) and intermediate vs. severe, 1.2 +/- 0.3 (P < 0.001)]. An MPRI cut-off value of 1.5 (derived from receiver operating characteristics analysis) distinguished haemodynamically relevant (severe) from non-relevant (normal and intermediate) stenoses with a sensitivity of 88% (CI 74-100%) and a specificity of 90% (CI 84-96%).

CONCLUSION

In contrast to earlier studies that compared CMRI with morphological examination (CA) alone, the present study compared CMRI with CA plus a standard invasive functional assessment (FFR) and demonstrated that CMRI is able to distinguish haemodynamically relevant from non-relevant coronary lesions with a high sensitivity and specificity and may therefore contribute to clinical decision-making.

Coronary pressure measurements in post-myocardial infarction patients

The development of pressure monitoring guide-wires has facilitated the measurements of coronary pressures distal to a stenosis. The ratio of the distal coronary and aortic pressures (P(d)/P(a)) measured during maximal hyperaemia is a useful index for diagnosis and monitoring the treatment of patients with coronary artery disease and for guiding percutaneous coronary intervention. However, the role of coronary pressure measurements in post- myocardial infarction (MI) patients is not well established. Coronary pressure measurements should be used with caution during the acute phase of MI due to serious micro-vascular impairment. The hyperaemic pressure P(d)/P(a) ratio can identify ischaemic myocardial territories in patients with recent MI. Theoretically, coronary pressure measurements may be of value in predicting myocardial recovery after revascularization in post-MI patients with a moderate stenosis of the infarct-related artery and without angiographically evident collaterals.

Relation of myocardial perfusion defects and nonsignificant coronary lesions by angiography with insights from intravascular ultrasound and coronary pressure measurements

Several studies have demonstrated a correlation between myocardial ischemia and severity of coronary lesions as determined by intravascular ultrasound (IVUS) and fractional flow reserve (FFR) measurements. However, their value for the assessment of mild coronary stenoses that are associated with myocardial perfusion abnormalities has not been well studied. The objective of this study was to prospectively compare the results of myocardial perfusion as determined by exercise/dipyridamole myocardial single-photon emission computed tomography with IVUS and FFR measurements in patients who had angiographically mild coronary stenosis (< 50% diameter stenosis by quantitative coronary angiography). Forty-eight patients who had stable coronary disease (61 +/- 11 years of age; 6 women) were included. All had mild coronary stenosis in the proximal/middle segment of > or = 1 coronary artery and had undergone maximal exercise myocardial technetium-99m tetrofosmin single-photon emission computed tomography within 48 hours before coronary angiography. IVUS measurements included lesion lumen area, external elastic membrane area, lesion plaque burden (calculated as external elastic membrane minus lumen area, divided by external elastic membrane, and multiplied by 100), and lumen area stenosis (calculated as reference lumen area minus lesion lumen area, divided by reference lumen area, multiplied by 100). Fifty-three coronary lesions were studied, with a mean percent diameter stenosis of 34.9 +/- 7.9% on angiography. Myocardial perfusion defects were demonstrated by single-photon emission computed tomography in 11 patients (12 myocardial regions) with no differences in lesion percent diameter stenosis compared with those without perfusion defects. The presence of reversible perfusion defects was associated with a higher lesion plaque burden as evaluated by IVUS (67.4 +/- 8.1% vs 60.2 +/- 9.3%, p = 0.01). FFR values did not differ in the presence or absence of perfusion defects (0.90 +/- 0.06 vs 0.92 +/- 0.07, respectively; p = NS). In conclusion, plaque burden as determined by IVUS may partly explain the presence of myocardial perfusion defects in cases of angiographically nonsignificant coronary lesions. However, the high FFR values associated with these lesions suggest that other mechanisms, such as endothelial/microvascular dysfunction, might also account for perfusion abnormalities in these patients.