Adequacy of intracoronary versus intravenous adenosine-induced maximal coronary hyperemia for fractional flow reserve measurements

Factors Predicting 150 and 200 Microgram Adenosine Requirement during Four Increasing Doses of Intracoronary Adenosine Bolus Fractional Flow Reserve Assessment

Direct intracoronary adenosine bolus is an excellent alternative to intravenous adenosine fractional flow reserve (FFR) measurement. This study, during four increasing adenosine boluses (50, 100, 150, and 200 mcg), aimed to explore clinical and angiographic predictors of coronary stenotic lesions for which the significant ischemic FFR (FFR ≤ 0.8) occurred at 150 and 200 mcg adenosine doses. Data from 1055 coronary lesions that underwent FFR measurement at the Central Chest Institute of Thailand from August 2011 to July 2021 were included. Baseline clinical and angiographic characteristics were analyzed. The FFR ≤ 0.8 occurred at adenosine 150 and 200 mcg boluses in 47 coronary lesions, while the FFR ≤ 0.8 occurred at adenosine 50 and 100 mcg boluses in 186 coronary lesions. After univariable and multivariable logistic regression analyses, four characteristics, including male sex, younger age, non-smoking status, and FFR procedure of RCA, were predictors of the occurrence of FFR ≤ 0.8 at adenosine 150 and 200 mcg doses. Combining all four predictors as a predictive model resulted in an AuROC of 0.72 (95% CI: 0.68–0.76), an 86% negative predictive value. Comparing these four predictors, the FFR procedure of RCA gave the most predictive power, with the AuROC of 0.60 (95% CI: 0.56–0.63).

Comparison of efficacy and safety of intracoronary nicardipine and adenosine for fractional flow reserve assessment of coronary stenosis

BACKGROUND

Administration of intracoronary (IC) adenosine allows an easily feasible, inexpensive, and more rapid alternative method for fractional flow reserve (FFR). It is common practice in many centers worldwide. Nicardipine is a strong coronary vasodilator but its efficacy and safety for assessing FFR is not established. The purpose of present study was to compare the efficacy and safety of IC nicardipine and adenosine for assessing FFR.

METHODS

One hundred and fifty-nine patients with a total of 193 vessels undergoing clinically indicated FFR assessment of intermediate coronary stenoses were included. For the initial assessment of FFR, hyperemia was induced by an IC adenosine. After a washout period of 3 min, FFR was reassessed using 200 μg of IC nicardipine.

RESULTS

Hyperemic efficacy among two different stimuli was compared. The mean FFR with IC adenosine was 0.83 ± 0.09 and that with an IC nicardipine was 0.84 ± 0.09. The median FFR with an IC adenosine was 0.83 (0.78-0.91) and that with an IC nicardipine was 0.85 (0.79-0.91) (p-value 0.246). Both FFR values showed an excellent correlation (R² = 0.982, p < 0.001). Nicardipine produced fewer changes in heart rate, less chest pain and less flushing than adenosine. Transient atrioventricular block occurred in 29 patients with IC adenosine and none with IC nicardipine.

CONCLUSIONS

IC bolus injection of nicardipine could be introduced as a safe and practical alternative method of inducing hyperemia during FFR measurements. Compared to IC adenosine, IC nicardipine has a similar hyperemic efficacy and excellent side-effect profile.

High dose escalation of intracoronary adenosine in the assessment of fractional flow reserve: A retrospective cohort study

Maximal hyperaemia for fractional flow reserve (FFR) may not be achieved with the current recommended doses of intracoronary adenosine. Higher doses (up to 720 μg) have been reported to optimize hyperaemic stimuli in small dose-response studies. Real-world data from a large cohort of patients is needed to evaluate FFR results and the safety of high-dose escalation. This is a retrospective study aimed to evaluate the safety and frequency of FFR ≤0.8 after high-dose escalation of intracoronary adenosine. Data were extracted from the medical databases of two university hospitals. Increasing doses (100, 200, 400, 600, and 800 μg) of adenosine were administered as intracoronary boluses until FFR ≤0.8 was achieved or heart block developed. The percentage of FFR ≤0.8 after higher-dose escalation was compared with those at conventional doses, and the predictors for FFR ≤0.8 after higher doses were analysed. In the 1163 vessels of 878 patients, 402 vessels (34.6%) achieved FFR ≤0.8 at conventional doses and 623 vessels (53.6%) received high-dose escalation. An additional 84 vessels (13.5%) achieved FFR ≤0.8 after high-dose escalation. No major complications developed during high-dose escalation. Borderline FFR (0.81-0.85) at the conventional dose, stenosis >60%, and triple-vessel disease increased the likelihood of FFR ≤0.8 after high-dose escalation, but chronic kidney disease decreased it. For vessels of borderline FFR at conventional doses, 46% achieved FFR ≤0.8 after high-dose escalation. In conclusion, High-dose escalation of intracoronary adenosine increases the frequency of FFR ≤0.8 without major complications. It could be especially feasible for borderline FFR values near the 0.8 diagnostic threshold.

Continuous intracoronary versus standard intravenous infusion of adenosine for fractional flow reserve assessment: the HYPEREMIC trial

AIMS

The aim of this study was to evaluate the accuracy of a continuous intracoronary (IC) adenosine infusion, administered through the novel HYPEREM™IC over-the-wire microcatheter, to measure fractional flow reserve (FFR).

METHODS AND RESULTS

The HYPEREMIC trial was a randomised, non-inferiority, crossover study in which patients with intermediate coronary lesions were enrolled for sequential pressure wire studies. FFR was measured using intravenous (IV) (140-180 mcg/kg/min) versus continuous non-weight-adjusted IC (360 mcg/min) adenosine. Patients were randomised and blinded to the order in which they received the adenosine, separated by a washout period. The primary endpoint was the mean hyperaemic FFR. Forty-one patients were enrolled at three UK sites between June and November 2016. The mean (standard deviation) FFR was 0.82 (±0.09) after IC versus 0.84 (±0.09) after IV adenosine. The difference of -0.02 (95% confidence interval [CI]: -0.03 to -0.01) confirmed the non-inferiority (margin <0.05) of IC to IV adenosine. Intracoronary adenosine was associated with a shorter mean time to maximal hyperaemia (difference -44 [95% CI: -59 to -29] seconds; p<0.0001). Chest discomfort was reported in 32/41 (78.0%) patients during IV adenosine versus 12/41 (29.3%) patients during IC adenosine.

CONCLUSIONS

Continuous IC adenosine was a reliable, faster and better tolerated method of achieving maximal hyperaemia compared to IV adenosine.

End-stage renal failure is associated with impaired coronary microvascular function

BACKGROUND

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease. Studies investigating the disproportionate burden of cardiovascular disease have occurred predominantly in the peripheral vasculature, often used noninvasive imaging modalities, and infrequently recruited patients receiving dialysis. This study sought to evaluate invasive coronary dynamic vascular function in patients with end-stage renal failure (ESRF).

PATIENTS AND METHODS

Patients referred for invasive coronary angiography prior to renal transplantation were invited to participate. Control patients were recruited in parallel. Baseline characteristics were obtained. Coronary diameter (via quantitative coronary angiography) and coronary blood flow (via Doppler Flowire) were measured; macrovascular endothelial-dependent and independent effects were evaluated in response to intracoronary acetylcholine infusion (10 and 10 mol/l) and intracoronary glyceryl trinitrate, respectively. Microvascular function was evaluated by response to adenosine and expressed as coronary flow velocity reserve. Mean values were compared.

RESULTS

Thirty patients were evaluated: 15 patients with ESRF (mean age 52.1 ± 9, male 73%) and 15 control patients (mean age 53.3 ± 13, male 60%). Comorbidity profile, aside from ESRF, was well matched. Baseline coronary blood flow was similar between groups (101.6 ± 10.3 vs. 103.4 ± 9.1 ml/min, P = 0.71), as was endothelial-dependent response to acetylcholine (159.1 ± 16.9 vs. 171.1 ± 16.8 ml/min, P = 0.41). Endothelial-independent response to glyceryl trinitrate was no different between groups (14.3 ± 3.1 vs. 13.1 ± 2.3%, P = 0.73. A significantly reduced coronary flow velocity reserve was observed in the ESRF cohort compared to controls (2.34 ± 0.4 vs. 3.05 ± 0.3, P = 0.003).

CONCLUSION

Patients with ESRF had preserved endothelial-dependent function however compared to controls, demonstrated significantly attenuated microvascular reserve. An impaired response to adenosine may not only represent a component of the pathophysiological milieu in patients with ESRF but may also provide a basis for the suboptimal diagnostic performance of vasodilatory stress in this population.

Impact of Age on the Functional Evaluation of Intermediate Coronary Stenoses With Instantaneous Wave-Free Ratio and Fractional Flow Reserve

The optimal strategy for assessing the ischemic significance of intermediate coronary stenoses with adenosine-induced fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) is still debated. Few studies have previously assessed the impact of age on FFR and iFR, which was the aim of our study. Patients undergoing FFR and iFR evaluation for intermediate (40%-70%) coronary lesions were included and divided according to age. Fractional flow reserve was performed by intracoronary boluses of adenosine (60-1440 μg). Instantaneous wave-free ratio was automatically calculated. Among 148 patients undergoing FFR measurement of 166 lesions, 45.3% were ≥70 years. Elderly patients had higher minimal lumen diameter (P = .03). We also observed a linear relationship between iFR and FFR independently of age. Fractional flow reserve values were higher in the elderly patients, whereas iFR was not related to age. A total of 33 lesions had a positive iFR with no difference for age (17.3% vs 22%, P = .56), while FFR <0.80 was more infrequent in the elderly patients (17.1% vs 34.8%, P = .02). In intermediate coronary stenoses, iFR and FFR correlation is unaffected by age. Fractional flow reserve is higher in the elderly patients, whereas iFR is less affected by age. Future large-scale studies are needed to define whether iFR should be the preferred choice in elderly patients.

Influence of caffeine intake on intravenous adenosine-induced fractional flow reserve

BACKGROUND

This study evaluated whether caffeine abstention is required before fractional flow reserve (FFR) measurement by intravenous adenosine triphosphate (ATP) administration in Japanese patients.

METHODS

This study was a subanalysis of a previously published study and a total of 208 intermediate lesions that underwent FFR measurements were enrolled for this analysis. Hyperemia was induced by continuous intravenous ATP infusion at 150 μg/kg/min (IVATP150) and 210 μg/kg/min (IVATP210), and by intracoronary administration of nicorandil 2 mg (ICNIC2mg) as a reference standard.

RESULTS

The degree of change in the FFR value after ICNIC2mg and IVATP210 was similar between the caffeine and non-caffeine groups (0.00 ± 0.02 vs. 0.01 ± 0.02). In patients who consumed caffeine before the FFR measurement, the degree of FFR change was independent of the time interval (<12 h, 12-24 h, and 24-48 h) between caffeine intake and catheterization both after IVATP150 and ICNIC2mg and after IVATP210 and ICNIC2mg.

CONCLUSION

When compared with the FFR value after ICNIC2mg, the degree of change in the FFR value after IVATP210 were similar regardless of caffeine intake. Strict caffeine abstention before intravenous ATP-induced FFR measurement may not be required in clinical practice.

Relationship between adenosine A2a receptor polymorphism rs5751876 and fractional flow reserve during percutaneous coronary intervention

Fractional flow reserve (FFR) assessed during adenosine-induced maximal hyperemia has emerged as a useful tool for the guidance of percutaneous coronary interventions (PCI). However, interindividual variability in the response to adenosine has been claimed as a major limitation to the use of adenosine for the measurement of FFR, carrying the risk of underestimating the severity of coronary stenoses, with potential negative prognostic consequences. Genetic variants of the adenosine receptor A2a (ADORA2A gene), located in the coronary circulation, have been involved in the modulation of the hyperemic response to adenosine. However, no study has so far evaluated the impact of the single nucleotide polymorphism rs5751876 of ADORA2A on the measurement of FFR in patients undergoing percutaneous coronary intervention that was, therefore, the aim of our study. We included patients undergoing coronary angiography and FFR assessment for intermediate (40-70%) coronary lesions. FFR measurement was performed by pressure-recording guidewire (Prime Wire, Volcano), after induction of hyperemia with intracoronary boli of adenosine (from 60 to 1440 μg, with dose doubling at each step). Restriction fragment length polymorphism (RFLP) analysis was performed to assess the presence of rs5751876 C>T polymorphism of ADORA2a receptor. We included 204 patients undergoing FFR measurement of 231 coronary lesions. A total of 134 patients carried the polymorphism (T allele), of whom 41 (30.6%) in homozygosis (T/T).Main clinical and angiographic features did not differ according to ADORA2A genotype. The rs5751876 C>T polymorphism did not affect mean FFR values (p = 0.91), the percentage of positive FFR (p = 0.54) and the duration of maximal hyperemia. However, the time to recovery to baseline FFR values was more prolonged among the T-allele carriers as compared to wild-type patients (p = 0.04). Based on these results, in patients with intermediate coronary stenoses undergoing FFR assessment with adenosine, the polymorphism rs5751876 of ADORA2A does not affect the peak hyperemic response to adenosine and the results of FFR. However, a more prolonged effect of adenosine was observed in T-carriers.

Individual Lesion-Level Meta-Analysis Comparing Various Doses of Intracoronary Bolus Injection of Adenosine With Intravenous Administration of Adenosine for Fractional Flow Reserve Assessment

BACKGROUND

Intravenous infusion of adenosine is considered standard practice for fractional flow reserve (FFR) assessment but is associated with adverse side-effects and is time-consuming. Intracoronary bolus injection of adenosine is better tolerated by patients, cheaper, and less time-consuming. However, current literature remains fragmented and modestly sized regarding the equivalence of intracoronary versus intravenous adenosine. We aim to investigate the relationship between intracoronary adenosine and intravenous adenosine to determine FFR.

METHODS

We performed a lesion-level meta-analysis to compare intracoronary adenosine with intravenous adenosine (140 µg/kg per minute) for FFR assessment. The search was conducted in accordance to the Preferred Reporting for Systematic Reviews and Meta-Analysis statement. Lesion-level data were obtained by contacting the respective authors or by digitization of scatterplots using custom-made software. Intracoronary adenosine dose was defined as; low: <40 µg, intermediate: 40 to 99 µg, and high: ≥100 µg.

RESULTS

We collected 1972 FFR measurements (1413 lesions) comparing intracoronary with intravenous adenosine from 16 studies. There was a strong correlation (correlation coefficient =0.915; P<0.001) between intracoronary-FFR and intravenous-FFR. Mean FFR was 0.81±0.11 for intracoronary adenosine and 0.81±0.11 for intravenous adenosine (P<0.001). We documented a nonclinically relevant mean difference of 0.006 (limits of agreement: -0.066 to 0.078) between the methods. When stratified by the intracoronary adenosine dose, mean differences between intracoronary and intravenous-FFR amounted to 0.004, 0.011, or 0.000 FFR units for low-dose, intermediate-dose, and high-dose intracoronary adenosine, respectively.

CONCLUSIONS

The present study documents clinically irrelevant differences in FFR values obtained with intracoronary versus intravenous adenosine. Intracoronary adenosine hence confers a practical and patient-friendly alternative for intravenous adenosine for FFR assessment.

A simplified formula to calculate fractional flow reserve in sequential lesions circumventing the measurement of coronary wedge pressure: The APIS-S pilot study

BACKGROUND

A simplified formula to calculate the predicted fractional flow reserve (FFR) in sequen-tial coronary stenosis without balloon inflation is hereby proposed.

METHODS

In patients with an indication for FFR and sequential coronary stenosis, FFR was recorded distally and between the lesions. The predicted FFR for each stenosis was calculated with a novel formu-la. While treating one of the lesions, wedge pressure was measured during balloon inflation to calculate Pijls' formula. FFR of the remaining lesion was finally recorded (measured FFR).

RESULTS

Forty patients were enrolled in the study, 4 (10.0%) had a distal FFR > 0.80 and were excluded from the main analysis. In the remaining 36 patients, the novel formula and Pijls' formula showed virtually absolute agreement (ICCa 0.999, R2 = 0.997 for the proximal lesion, R2 = 0.999 for the distal lesion, kappa 1.000, Se 100%, Sp 100%). The agreement between predicted and measured FFR was good (ICCa 0.820; 0.640-0.909, R2 = 0.717, intercept = 0.05, slope = 0.92, kappa 0.748, Se 75%, Sp 96%). In 19 (47.5%) cases the use of the formula enabled the operator to freely decide which lesion should be treated first, an option not available if the percutaneous coronary intervention (PCI) were guided by the largest pressure drop across each lesion.

CONCLUSIONS

The predicted FFR for each lesion in sequential coronary stenosis can be accurately calculated by a simplified formula circumventing the need for balloon inflation. This approach provides the operator upfront, with detailed information on physiology, thus having a potentially high impact on the corresponding PCI strategy.

Comparison of hyperemic efficacy between femoral and antecubital fossa vein adenosine infusion for fractional flow reserve assessment

Introduction

Intravenous infusion of adenosine via the femoral vein is commonly used to achieve maximum hyperemia for fractional flow reserve (FFR) assessment in the catheterization laboratory. In the era of transradial access for coronary interventions, obtaining additional venous access with sheath insertion in the groin is unpractical and may be associated with a higher risk of bleeding complications. In a vast majority of cases, patients scheduled for the catheterization laboratory are already equipped with peripheral vein access in antecubital fossa vein. However, only limited data exist to support non-central vein infusion of adenosine instead of the femoral vein for FFR assessment.

Aim

To compare infusion of adenosine via a central versus a peripheral vein for the assessment of peak FFR.

Material and methods

We enrolled 50 consecutive patients with 125 borderline coronary lesions that were assessed by FFR using adenosine femoral and antecubital vein infusion of 140 µg/kg/min.

Results

Physiological severity assessed with femoral vein adenosine infusion at 140 µg/kg/min was mean 0.82 ±0.09, and with antecubital vein adenosine infusion at 140 µg/kg/min was 0.82 ±0.09. The mean time from initiation of adenosine infusion to maximal stable hyperemia was significantly shorter for 140 µg/kg/min femoral vein infusion as compared to antecubital vein infusion (49 ±19 s vs. 68 ±23 s; p < 0.001). There was a strong correlation between FFR values obtained from 140 µg/kg/min femoral and antecubital vein infusion (r = 0.99; p < 0.001).

Conclusions

Antecubital vein adenosine infusion achieved FFR values are very similar to those obtained using femoral vein adenosine administration. However, time to maximal hyperemia is longer with infusion via the antecubital vein.

Intracoronary versus intravenous adenosine to assess fractional flow reserve: a systematic review and meta-analysis

AIMS

Intravenous infusion of adenosine is the reference method to measure fractional flow reserve (FFR). Intracoronary boluses are often used because of time and convenience, but their effectiveness has yet to be assessed.

METHODS

We conducted a systematic review and meta-analysis of prospective studies directly comparing intravenous and intracoronary adenosine administration for FFR measurement. FFR values and prevalence of functionally critical lesions obtained with the different methods of adenosine administration were compared.

RESULTS

Twelve studies evaluating 781 lesions from 731 patients were included (63.7 years, 25.5% women, median FFR 0.82). FFR values were significantly lower with intravenous adenosine than with intracoronary adenosine [mean difference 0.01, 95% confidence interval (CI) 0.00-0.02, P = 0.005], even if no significant differences were observed when only high doses of intracoronary adenosine (≥150 μg) were considered. The prevalence of functionally critical lesions did not significantly differ between intracoronary and intravenous adenosine. Concerning the use of different doses of intracoronary adenosine, low doses (≤60 μg) were associated with higher FFR values (mean difference 0.02, 95% CI 0.01-0.03, P < 0.001) and fewer functionally critical lesions (OR 0.57, 95% CI 0.40-0.81, P = 0.002) compared with high doses. Meta-regression analysis did not show any significant interaction between the way of adenosine administration and main clinical features. Intracoronary adenosine was associated with a higher incidence of atrioventricular blocks, whereas angina and/or systemic symptoms were more frequent with intravenous adenosine.

CONCLUSION

Intracoronary adenosine might be as effective as intravenous adenosine to measure FFR, provided that adequate doses are used. Intracoronary adenosine represents a valuable alternative to intravenous adenosine whenever appropriately administered.

Impact of increasing dose of intracoronary adenosine on peak hyperemia duration during fractional flow reserve assessment

BACKGROUND

Fractional Flow Reserve (FFR) is currently indicated as a first line strategy for the functional assessment of intermediate coronary stenoses. However, the protocol for inducing hyperemia still lacks standardization. Intracoronary adenosine boli, with a progressive increase to high-dosage, have been proposed as a sensitive and accurate strategy for the classification of coronary stenoses, although being potentially affected by the achievement of plateau of the effect and by a less prolonged and stable hyperemia as compared to intravenous administration. Therefore, the aim of the present study was to define the conditioning parameters and assess the impact of increasing-dose intracoronary adenosine on peak hyperemia duration in patients undergoing FFR for intermediate coronary stenoses.

METHODS

FFR was assessed in patients with intermediate (40 to 70%) lesions by pressure-recording guidewire (Prime Wire, Volcano), after induction of hyperemia with intracoronary boli of adenosine (from 60 to 1440 μg, with dose doubling at each step). Hyperemic duration was defined as the time for the variation form minimum FFR ± 0.02 and time to recovery till baseline values.

RESULTS

We included 87 patients, undergoing FFR evaluation of 101 lesions. Mean peak hyperemia duration and time to recovery significantly increased with adenosine doses escalation (p = 0.02 and p < 0.001). Peak hyperemia duration and time to recovery with 1440 μg adenosine were 14.5 ± 12.6 s and 45.2 ± 30.7 s, respectively. Hyperemia duration was not related to Quantitative Coronary Angiography (QCA) parameters or FFR values. In fact, a similar increase in the time of hyperemic peak was noted when comparing patients with positive or negative FFR (p_between = 0.87) or patients with lesions < or ≥20 mm (p_between = 0.92) and lesions involving left main coronary or proximal left anterior descending artery (LAD) (p_between = 0.07). A linear relationship was observed between time to recovery and FFR variations, with a greater time to baseline required in patients with FFR ≤ 0.80 (p = 0.003) and in lesions ≥ 20 mm (p = 0.006), but not in LAD/LM lesions (p = 0.55).

CONCLUSIONS

The present study shows a progressive raise in the duration of peak hyperemia and time to recovery, after the administration of increasing doses of intracoronary adenosine for the assessment of FFR. Therefore, considering the potential advantages of a high-dose adenosine protocol, allowing a more prolonged hyperemia and a more precise and reliable measurement of FFR, further larger studies with such FFR strategy should certainly be advocated to confirm its safety and benefits, before its routinely use recommendation.

Meta-Analysis of Head-to-Head Comparison of Intracoronary Versus Intravenous Adenosine for the Assessment of Fractional Flow Reserve

Intravenous (IV) infusion of adenosine represents the gold standard for measuring fractional flow reserve (FFR). However, IV adenosine is more expensive and time-consuming compared with intracoronary (IC) boluses of adenosine. We conducted a meta-analysis of studies comparing IC with IV adenosine for FFR assessment in the same coronary lesions. We searched for studies comparing IC with IV adenosine and reporting absolute FFR values or rate of abnormal FFR for both routes. Prespecified subgroup analysis was performed to appraise studies using low-dose (<100 μg) or high-dose IC adenosine (≥100 μg). We retrieved 11 studies amounting to 587 patients and 621 lesions. Six studies evaluated low-dose IC boluses (15 to 80 μg) and 5 studies high-dose boluses (120 to 600 μg). Absolute FFR values were slightly, yet significantly lower with IV adenosine compared with IC adenosine (mean difference 0.02, 95% confidence interval [CI] 0.00 to 0.03, p = 0.02). This difference, however, did not translate into a significant difference in the rate of abnormal FFR between IC and IV adenosine (hazard ratio 0.93, 95% CI 0.76 to 1.13, p = 0.57); moreover, no statistically significant difference was observed between low-dose and high-dose IC adenosine subgroups. Adverse events were less frequent with IC adenosine compared with IV adenosine (risk ratio 0.17, 95% CI 0.07 to 0.43, p <0.001). In conclusion, IC administration of adenosine, although inducing a slightly lower amount of hyperemia compared with IV infusion of adenosine, yields a similar diagnostic accuracy in identifying hemodynamically significant coronary stenosis and is better tolerated by the patients.

A Test in Context: Fractional Flow Reserve: Accuracy, Prognostic Implications, and Limitations

Fractional flow reserve (FFR) is an invasive procedure used during coronary angiography to determine the functional significance of coronary stenoses. Its use is particularly helpful in intermediate or angiographically ambiguous lesions in the absence of noninvasive functional studies. Randomized clinical trials have reported improved clinical outcomes with the use of FFR to guide coronary revascularization, including a reduction in cardiac death or myocardial infarction, as well as costs, with an FFR-based strategy compared with a conventional angiography-based approach. Current societal guidelines provide a Class II, Level of Evidence: A recommendation to perform FFR in angiographically intermediate stenoses in the absence of stress testing or in the presence of discordant stress test results and angiographic findings. However, despite the relative ease of use of FFR, multiple technical factors can impair its accuracy, and attention to detail is critical when performing the test. This review focuses on the fundamental basics of FFR testing, clinical evidence, and limitations.

Temporal dissociation between the minimal distal-to-aortic pressure ratio and peak hyperemia during intravenous adenosine infusion

The present study sought to compare the temporal relation between maximal coronary flow (peak hyperemia) and minimal coronary-to-aortic pressure ratio (Pd/Pa) for intracoronary (IC) and intravenous (IV) adenosine administration. Peak hyperemia is assumed to coincide with the minimal Pd/Pa value. However, this has not been confirmed for systemic hemodynamic variations during IV adenosine infusion. Hemodynamic responses to IV and IC adenosine administration were obtained in 12 patients (14 lesions) using combined IC pressure and flow velocity measurements. A fluid dynamic model was used to predict the change in Pd/Pa for different stenosis severities and varying Pa. Hemodynamic variability during IV adenosine hyperemia was greater than during IC adenosine, as assessed by the coefficient of variation. During IV adenosine, flow velocity peaked 28 ± 4 (SE) s after the onset of hyperemia, while Pd/Pa reached a minimum (0.82 ± 0.01) 22 ± 7 s later ( P < 0.05), when Pa had declined by 6.1% and hyperemic velocity by 4.5% ( P < 0.01). Model outcomes corroborated the role of variable Pa in this dissociation. In contrast, maximal flow and minimal Pd/Pa coincided for IC adenosine, with IV-equivalent peak velocities and a higher Pd/Pa ratio (0.86 ± 0.01, P < 0.01). Hemodynamic variability during continuous IV adenosine infusion can lead to temporal dissociation of minimal Pd/Pa and peak hyperemia, in contrast to IC adenosine injection, where maximal velocity and minimal Pd/Pa coincide. Despite this variability, stenosis hemodynamics remained stable with both ways of adenosine administration. Our findings suggest advantages of IC over IV adenosine to identify maximal hyperemia from pressure-only measurements.

NEW & NOTEWORTHY Systemic hemodynamic variability during intravenous adenosine infusion produces substantial temporal dissociation between peak hyperemia appraised by coronary flow velocity and the minimal distal-to-aortic pressure ratio commonly used to determine functional stenosis severity. This dissociation was absent for intracoronary adenosine administration and tended to be mitigated in patients receiving Ca2+ antagonists.

Assessment of increasing intravenous adenosine dose in fractional flow reserve

Background

Effects of increased adenosine dose in the assessment of fractional flow reserve (FFR) were studied in relation to FFR results, hemodynamic effects and patient discomfort. FFR require maximal hyperemia mediated by adenosine. Standard dose is 140 μg/kg/min administrated intravenously. Higher doses are commonly used in clinical practice, but an extensive comparison between standard intravenous dose and a high dose (220 μg/kg/min) has previously not been performed.

Methods

Seventy-five patients undergoing FFR received standard dose adenosine, followed by high dose adenosine. FFR, mean arterial pressure (MAP) and heart rate (HR) were analyzed. Patient discomfort measured by Visual Analogue Scale (VAS) was assessed.

Results

No significant difference was found between the doses in FFR value (0.85 [0.79–0.90] vs 0.85 [0.79–0.89], p = 0.24). The two doses correlated well irrespective of lesion severity (r = 0.86, slope = 0.89, p = <0.001). There were no differences in MAP or HR. Patient discomfort was more pronounced using high dose adenosine (8.0 [5.0–9.0]) versus standard dose (5.0 [2.0–7.0]), p = <0.001.

Conclusions

Increased dose adenosine does not improve hyperemia and is associated with increased patient discomfort. Our findings do not support the use of high dose adenosine.

Trial registration

Retrospective Trial registration: Current Controlled Trials ISRCTN14618196. Registered 15 December 2016.

Clinical and angiographic predictors of persistently ischemic fractional flow reserve after percutaneous revascularization

AIMS

Despite optimal angiographic results after percutaneous coronary intervention (PCI), some lesions may continue to produce ischemia under maximal hyperemia. We evaluated the factors associated with persistently ischemic fractional flow reserve (FFR) after angiographically successful PCI.

METHODS AND RESULTS

A total of 574 consecutive patients with 664 lesions undergoing PCI who had FFR pre- and post-PCI were analyzed. Percutaneous coronary intervention led to effective ischemia reduction from pre-FFR (0.65±0.14) to post-FFR (0.87±0.08; ∆FFR 0.22±0.16, P<.001). There were 63 (9.5%) lesions with a persistently ischemic FFR of ≤0.80 despite optimal angiographic PCI results. Multivariate analysis revealed the presence of diffuse disease (odds ratio [OR] 3.54, 95% CI 1.80-6.94, P<.01), left anterior descending artery PCI (OR 8.35, 95% CI 3.82-18.27, P<.01), use of intravenous adenosine for inducing hyperemia (OR 3.95, 95% CI 2.0-7.84, P<.01), and pre-PCI FFR (OR 0.03, 95% CI 0.004-0.23, P<.01) as independent predictors of persistently ischemic FFR (≤0.80) after PCI. The predictive accuracy of this model was robust, with an area under the curve of 0.85 (95% CI 0.82-0.88).

CONCLUSION

Multiple factors are associated with persistently ischemic FFR after angiographically optimal PCI. It is recommended that in lesions with the above-identified factors, FFR should be remeasured after PCI, and if abnormal, further measures should be undertaken for functional optimization.

Invasive FFR — Current Applications and New Developments

Myocardial ischemia caused by coronary atherosclerosis is the main cause of cardiovascular mortality, which is the first cause of death in developed countries. Inducible myocardial ischemia is a negative prognostic factor for coronary artery disease patients, and it represents a major risk stratification marker for predicting mortality. The evolution of these patients depends largely on the extension of the ischemic myocardial mass and the severity of the inducible ischemia. Most patients do not show angiographically significant coronary stenosis. Therefore, such patients do not undergo coronary revascularization therapies, even though they present functional stenoses that trigger myocardial ischemia under stress conditions, which subsequently lead to a high risk for major adverse cardiovascular events. We performed a review that aims to pinpoint invasive techniques used for evaluating the functional impact of a coronary lesion that is considered non-significant upon angiographic examination, but which triggers episodes of myocardial ischemia under stress conditions, and to describe the functional markers that show the highest specificity for predicting ischemic risk, in order to recommend invasive coronary revascularization.

Intracoronary Adenosine: Dose-Response Relationship With Hyperemia

OBJECTIVES

The present study sought to establish the dosage of intracoronary (IC) adenosine associated with minimal side effects and above which no further increase in flow can be expected.

BACKGROUND

Despite the widespread adoption of IC adenosine in clinical practice, no wide-ranging, dose-response study has been conducted. A recurring debate still exists regarding its optimal dose.

METHODS

In 30 patients, Doppler-derived flow velocity measurements were obtained in 10 right coronary arteries (RCAs) and 20 left coronary arteries (LCAs) free of stenoses >20% in diameter. Flow velocity was measured at baseline and after 8 ml bolus administrations of arterial blood, saline, contrast medium, and 9 escalating doses of adenosine (4 to 500 μg). The hyperemic value was expressed in percent of the maximum flow velocity reached in a given artery (Q/Qmax, %).

RESULTS

Q/Qmax did not increase significantly beyond dosages of 60 μg for the RCA and 160 μg for LCA. Heart rate did not change, whereas mean arterial blood pressure decreased by a maximum of 7% (p < 0.05) after bolus injections of IC adenosine. The incidence of transient A-V blocks was 40% after injection of 100 μg in the RCA and was 15% after injection of 200 μg in the LCA. The duration of the plateau reached 12 ± 13 s after injection of 100 μg in the RCA and 21 ± 6 s after the injection of 200 μg in the LCA. A progressive prolongation of the time needed to return to baseline was observed. Hyperemic response after injection of 8 ml of contrast medium reached 65 ± 36% of that achieved after injection of 200 μg of adenosine.

CONCLUSIONS

This wide-ranging, dose-response study indicates that an IC adenosine bolus injection of 100 μg in the RCA and 200 μg in the LCA induces maximum hyperemia while being associated with minimal side effects.

Fractional Flow Reserve: Does a Cut-off Value add Value?

Fractional flow reserve (FFR) has been shown to improve outcomes when used to guide percutaneous coronary intervention (PCI). There have been two proposed cut-off points for FFR. The first was derived by comparing FFR against a series of non-invasive tests, with a value of ≤0.75 shown to predict a positive ischaemia test. It was then shown in the DEFER study that a vessel FFR value of ≥0.75 was associated with safe deferral of PCI. During the validation phase, a 'grey zone' for FFR values of between 0.76 and 0.80 was demonstrated, where a positive non-invasive test may still occur, but sensitivity and specificity were sub-optimal. Clinical judgement was therefore advised for values in this range. The FAME studies then moved the FFR cut-off point to ≤0.80, with a view to predicting outcomes. The ≤0.80 cut-off point has been adopted into clinical practice guidelines, whereas the lower value of ≤0.75 is no longer widely used. Here, the authors discuss the data underpinning these cut-off values and the practical implications for their use when using FFR guidance in PCI.

Physiologic Assessment of Coronary Artery Disease: Focus on Fractional Flow Reserve

The presence of myocardial ischemia is the most important prognostic factor in patients with ischemic heart disease. Fractional flow reserve (FFR) is a gold standard invasive method used to detect the stenosis-specific myocardial ischemia. FFR-guided revascularization strategy is superior to angiography-guided strategy. The recently developed hyperemia-free index, instantaneous wave free ratio is being actively investigated. A non-invasive FFR derived from coronary CT angiography is now used in clinical practice. Due to rapid expansion of invasive and non-invasive physiologic assessment, comprehensive understanding of the role and potential pitfalls of each modality are required for its application. In this review, we focus on the basic and clinical aspects of physiologic assessment in ischemic heart disease.

Fractional flow reserve-guided percutaneous coronary intervention: where to after FAME 2?

Fractional flow reserve (FFR) is a well-validated clinical coronary physiological parameter derived from the measurement of coronary pressures and has drastically changed revascularization decision-making in clinical practice. Nonetheless, it is important to realize that FFR is a coronary pressure-derived estimate of coronary blood flow impairment. It is thereby not the same as direct measures of coronary flow impairment that determine the occurrence of signs and symptoms of myocardial ischemia. This consideration is important, since the FAME 2 study documented a limited discriminatory power of FFR to identify stenoses that require revascularization to prevent adverse events. The physiological difference between FFR and direct measures of coronary flow impairment may well explain the findings in FAME 2. This review aims to address the physiological background of FFR, its ambiguities, and its consequences for the application of FFR in clinical practice, as well as to reinterpret the diagnostic and prognostic characteristics of FFR in the light of the recent FAME 2 trial outcomes.

Fractional Flow Reserve for the Evaluation of Tandem and Bifurcation Lesions, Left Main, and Acute Coronary Syndromes

Fractional flow reserve (FFR) is a well-established invasive tool to assess the physiologic significance of a coronary stenosis. Several randomized trials proved the safety of deferring revascularization based on FFR in subjects with stable coronary artery disease with single or multivessel disease. Subjects with tandem or bifurcations lesions, left main disease, and acute coronary syndromes were not included in these trials. Unique hemodynamic changes occur in each of these situations, making the measurement and interpretation of FFR challenging. This article reviews the technical aspects of assessing FFR and literature supporting FFR-guided revascularization in each of these situations.

Differences between automatically detected and steady-state fractional flow reserve

BACKGROUND

Measurement of fractional flow reserve (FFR) has become a standard diagnostic tool in the catheterization laboratory. FFR evaluation studies were based on pressure recordings during steady-state maximum hyperemia. Commercially available computer systems detect the lowest Pd/Pa ratio automatically, which might not always be measured during steady-state hyperemia. We sought to compare the automatically detected FFR and true steady-state FFR.

METHODS AND RESULTS

Pressure measurement traces of 105 coronary lesions from 77 patients with intermediate coronary lesions or multivessel disease were reviewed. In all patients, hyperemia had been achieved by intravenous adenosine administration using a dosage of 140 µg/kg/min. In 42 lesions (40%) automatically detected FFR was lower than true steady-state FFR. Mean bias was 0.009 (standard deviation 0.015, limits of agreement -0.02, 0.037). In 4 lesions (3.8%) both methods lead to different treatment recommendations, in all 4 cases instantaneous wave-free ratio confirmed steady-state FFR.

CONCLUSIONS

Automatically detected FFR was slightly lower than steady-state FFR in more than one-third of cases. Consequently, interpretation of automatically detected FFR values closely below the cutoff value requires special attention.

Pooled comparison of regadenoson versus adenosine for measuring fractional flow reserve and coronary flow in the catheterization laboratory

BACKGROUND

Adenosine is the gold standard for augmenting coronary flow during fractional flow reserve (FFR) testing of intermediate coronary stenoses. However, intravenous infusion is time-consuming and intracoronary injection is subject to variability. Regadenoson is a newer adenosine alternative administered as a single intravenous bolus during nuclear stress testing, but its efficacy and safety during FFR testing have been evaluated only in small, single-center studies.

METHODS

We pooled data from 5 academic hospitals, in which patients undergoing clinically-indicated FFR prospectively underwent comparison of intravenous adenosine infusion (140-175mcg/kg/min) versus regadenoson bolus (400mcg). Hemodynamics and symptoms with adenosine were recorded until maximal hyperemia occurred, and after returning to baseline hemodynamics, regadenoson was administered and monitoring was repeated. In a subset of patients with coronary flow data, average peak velocity (APV) at the distal flow sensor was recorded.

RESULTS

Of 149 patients enrolled, mean age was 59±9years, 76% were male, and 54% underwent testing of the left anterior descending artery. Mean adenosine-FFR and regadenoson-FFR were identical (0.82±0.10) with excellent correlation of individual values (r=0.96, p<0.001) and no difference in patient-reported symptoms. Four patients (2.6%) had discrepancies between the 2 drugs for the clinical decision-making cutoff of FFR≤0.80. Coronary flow responses to adenosine and regadenoson were similar (APV at maximal hyperemia 36cm/s for both, p=0.81).

CONCLUSIONS

Regadenoson single-bolus administration has comparable FFR, symptoms, and coronary flow augmentation when compared with standard intravenous adenosine infusion. With its greater ease of administration, regadenoson may be a more "user-friendly" option for invasive ischemic testing.

Advances in coronary physiology

Pressure-wire technology, most typically fractional flow reserve (FFR), has provided interventional cardiologists with a means of determining the physiological importance of a stenosis during angiography. There has been renewed interest in coronary physiology in the light of guideline recognition, ongoing clinical research and new technologies changing the paradigm of how assessment is performed in the catheter laboratory. We reflect on FFR, with regards the potential effects of changing hemodynamics on FFR and the latest evidence with regards to outcomes. We also review the instantaneous wave-free ratio (iFR), a new pressure-only index, measured at rest, that is under active evaluation in several international randomized controlled trials. We review the accumulated evidence and discuss the important physiological concepts between pressure and flow that underlie the approach to using resting indices. Finally we investigate future developments, including physiological mapping with iFR-Pullback and the potential to predict the hemodynamic effect of stenting.

Coronary fractional flow reserve

OBJECTIVE. This article presents the basic definitions and concepts of fractional flow reserve (FFR), a focused understanding of the need for hyperemia during assessment, key clinical studies supporting its use, and an introduction to newer noninvasive methods using FFR CT. CONCLUSION. Although it is still a new procedure, FFR CT may prove to be of tremendous use as the computational processing improves to reduce calculation times and enhance accuracy.

Effects of intravenous caffeine on fractional flow reserve measurements in coronary artery disease

BACKGROUND

Intravenous adenosine is used to minimise the coronary micro-resistance to achieve maximal hyperaemia along with nitrates for optimal fractional flow reserve (FFR) measurements. We hypothesise that caffeine, being a competitive inhibitor of adenosine, would influence adenosine-mediated FFR readings.

METHODS

Consecutive patients undergoing angiogram and FFR measurements were enrolled after abstaining from caffeine for 24 h. Patients with any contraindications to intravenous adenosine or caffeine were excluded. FFR measurements were taken using nitrates and adenosine pre and post 4 mg/kg intravenous caffeine administration and results were compared.

RESULTS

10 patients were analysed (80% men, age 59.9±9.4, weight 87.5±15.6). Baseline caffeine levels were undetectable in all patients and increased significantly postintravenous caffeine administration (16.4±5.5 μg/mL). Baseline preadenosine FFR values were similar before and after caffeine administration (0.91±0.06 vs 0.91±0.07; p=0.41). Postadenosine FFR readings were 0.79±0.07, which increased non-significantly to 0.82±0.11 postcaffeine (p=0.15). Two significant FFR readings (≤0.8) changed to non-significant after caffeine administration (0.77-0.93 and 0.8-0.91).

CONCLUSIONS

Caffeine may affect FFR results in some patients. Larger studies are warranted to clarify the extent and magnitude of caffeine/adenosine interaction particularly due to ubiquitous nature of caffeine and increasing importance of FFR in clinical practice.

Outcomes of coronary stenoses deferred revascularization for borderline versus nonborderline fractional flow reserve values

Current evidence supports deferral of revascularization for lesions with fractional flow reserve (FFR) values >0.80. The natural history after deferral of revascularization of lesions with borderline FFR values is unknown. This study evaluated the outcomes of patients after deferred revascularization of coronary stenoses based on a borderline FFR value. We retrospectively studied 720 patients with 881 intermediate-severity coronary stenoses who underwent FFR assessment from October 2002 to July 2010 and were deferred revascularization. Patients were divided into gray zone (0.75 to 0.80), borderline (0.81 to 0.85), and nonborderline (>0.85) FFR groups. Any subsequent percutaneous coronary intervention or coronary artery bypass grafting of a deferred stenosis during follow-up was classified as a deferred lesion intervention (DLI). Patient and/or lesion characteristics and clinical outcomes were compared between the FFR groups using univariate and propensity score-adjusted inverse probability of weighting Cox proportional hazards analyses. During a mean follow-up of 4.5 ± 2.1 years, 157 deferred lesions (18%) underwent DLI by percutaneous coronary intervention (n = 117) or coronary artery bypass grafting (n = 40). No statistically significant differences were observed in clinical outcomes between the gray zone and borderline FFR groups. Lesions with a borderline FFR were associated with a significantly higher risk of DLI compared with lesions with nonborderline FFR values (hazard ratio 1.63, 95% confidence interval 1.14 to 2.33, p = 0.007). Lesions deferred revascularization because of a borderline FFR (0.81 to 0.85) were associated with a higher risk of DLI compared with lesions with a nonborderline FFR (>0.85). Further study is needed to determine the optimal management of coronary stenoses with a borderline FFR value.

Assessment of coronary blood flow in the cardiac catheterization laboratory

Coronary blood flow is tightly autoregulated but is subject to epicardial and microvascular obstruction, primarily owing to coronary atherosclerosis. Because coronary flow limitation underlies ischemic heart disease, an understanding of coronary physiology is paramount. Measurement of coronary blood flow, once relegated to the research laboratory is now easily performed in the cardiac catheterization laboratory. In particular, the measurement of fractional flow reserve has been extensively studied and is an important adjunct to clinical decision making. Measurement of coronary flow informs clinicians of prognosis, guides revascularization therapy, and forms the basis of ongoing research in treatment of complex myocardial disease processes. Newer methods of assessing coronary flow measurements are undergoing validation for clinical use and should further enhance our ability to assess the importance of coronary flow in clinical disease.

Hyperemia-free delineation of epicardial and microvascular impairments using a basal index

The assessment of functional coronary lesion severity using intracoronary hemodynamic parameters like the pressure-derived fractional flow reserve and the flow-derived coronary flow reserve are known to rely critically on the establishment of maximal hyperemia. We evaluated a hyperemia-free index, basal pressure drop coefficient (bCDP), that combines pressure and velocity for simultaneous assessment of the status of both epicardial and microvascular circulations. In 23 pigs, simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual-sensor tipped guidewire in the settings of both normal and abnormal microcirculation with the presence of epicardial lesions of area stenosis (AS) < 50% and AS > 50%. The bCDP, a parameter based on fundamental fluid dynamics principles, was calculated as the transtenotic pressure-drop divided by the dynamic pressure in the distal vessel, measured under baseline (without hyperemia) conditions. The group mean values of bCDP for normal (84 ± 18) and abnormal (124.5 ± 15.6) microcirculation were significantly different. Similarly, the mean values of bCDP from AS < 50% (72.5 ± 16.1) and AS > 50% (136 ± 17.2) were also significantly different (p < 0.05). The bCDP could significantly distinguish between lesions of AS < 50% to AS > 50% under normal microcirculation (52.1 vs. 85.8; p < 0.05) and abnormal microcirculation (84.9 vs. 172; p < 0.05). Further, the bCDP correlated linearly and significantly with the hyperemic parameters FFR (r = 0.42, p < 0.05) and CDP (r = 0.50, p < 0.05). The bCDP is a promising clinical diagnostic parameter that can independently assess the severity of epicardial stenosis and microvascular impairment. We believe that it has an immediate appeal for detection of coronary artery disease if validated clinically.

ST elevation after intracoronary administration of Papaverine for fractional flow reserve estimation

INTRODUCTION

Intracoronary (IC) papaverine which is one of the commonly used agents for Fractional Flow Reserve (FFR) estimation has been reported to cause transient ST elevation in some patients. This phenomenon has not been systematically studied.

MATERIAL AND METHODS

This is a prospective, observational study. Consecutive patients, who underwent FFR at our institute using IC papaverine from May 2012 to April 2013, were included. FFR was done when clinically indicated. The procedure involved administration of 20 mg papaverine (Paparin)--Troikaa, Ahmedabad) as a fast bolus by intracoronary route followed by a 10 cc contrast flush, following which pressure measurements were made. Continuous ECG recording by Philips Hemodynamic Laboratory was obtained for all patients throughout the procedure. Post procedure, they were observed for any delayed effects and eventual outcome was documented. Fischer's mid-p test was used for statistical analysis.

RESULT

Twenty-five patients (18 males, 7 females, mean age 57.9 ± 20 years) underwent FFR using Papaverine. The mean LVEF was (51 ± 15%). Fourteen patients (56%) developed transient ST elevation ≥0.5 mm in one or more leads which resolved spontaneously in all cases without any sequelae. The presence of a significant lesion either in the coronary artery being evaluated or in a remote coronary artery did not predict the ST elevation. 70.5% of diabetics (p = 0.02), 75% of hypertensives (p = 0.008) and 75% of patients with LVH (p = 0.008) had ST elevation. None of the 5 patients without any one of these comorbidities showed ST elevation.

CONCLUSION

Transient ST elevation occurs in a significant proportion of cases receiving IC papaverine which is not associated with any adverse clinical outcomes. Micro vascular dysfunction is the most likely mechanism of this phenomenon.

Fractional flow reserve: an updated review

Revascularization of ischemia-producing coronary lesions is widely used in the management of coronary artery disease. However, some coronary lesions appear significant on the conventional angiogram when they are truly non-flow limiting. For this reason, it is becoming increasingly important to determine the coronary physiology. Fractional flow reserve (FFR) has emerged as a useful tool to determine the lesions that require revascularization. Measurement of FFR during invasive coronary angiography now has a class IA indication from the European Society of Cardiology for identifying hemodynamically significant coronary lesions when noninvasive evidence of myocardial ischemia is unavailable. Current data on FFR can be broadly classified into studies that compare the diagnostic accuracy of FFR measurement compared with other noninvasive modalities and studies that test treatment strategies of patients with intermediate coronary stenoses using a threshold value for FFR and that have clinical outcomes as endpoints. In this review, we will discuss the concept of FFR, current evidence supporting its usage, and future perspectives.

Intracoronary versus intravenous adenosine-induced maximal coronary hyperemia for fractional flow reserve measurements

BACKGROUND

Maximal hyperemia is the critical prerequisite for fractional flow reserve (FFR) assessment. Despite intravenous (IV) adenosine currently being the recommended approach, intracoronary (IC) administration of adenosine constitutes a valuable alternative in everyday practice. However, it is surprisingly unclear which IC strategy allows the achievement of FFR values that are comparable to IV adenosine.

OBJECTIVES

This study sought to compare increasing doses of IC adenosine versus IV adenosine for FFR.

METHODS

30 intermediate coronary stenoses undergoing FFR measurement were prospectively and consecutively enrolled. Hyperemia was sequentially induced by bolus of IC adenosine (ADN; 150 μg) followed by IV adenosine (IVADN) infusion over 3 minutes at dose of (140 μg/kg/min). FFR values, symptoms, and development of atrioventricular block were recorded.

RESULTS

150 μg doses of IC adenosine were well tolerated and associated with fewer symptoms than IV adenosine. Intracoronary adenosine doses induced a significant decrease of FFR compared with baseline levels (P < 0.01). Among the 6 patients with FFR values less than 0.80 identified by IVADN, 4 were correctly identified also by 150 μg bolus IC adenosine. Larger randomized studies with cross-over design are necessary to verify the results.

CONCLUSIONS

This small pilot study suggests that IC adenosine might be an alternative to IV adenosine. Larger randomized studies with a cross-over design are necessary.

Hemodynamic response to intravenous adenosine and its effect on fractional flow reserve assessment: results of the Adenosine for the Functional Evaluation of Coronary Stenosis Severity (AFFECTS) study

BACKGROUND

We studied the hemodynamic response to intravenous adenosine on calculation of fractional flow reserve (FFR). Intravenous adenosine is widely used to achieve conditions of stable hyperemia for measurement of FFR. However, intravenous adenosine affects both systemic and coronary vascular beds differentially.

METHODS AND RESULTS

A total of 283 patients (310 coronary stenoses) underwent coronary angiography with FFR using intravenous adenosine 140 mcg/kg per minute via a central femoral vein. Offline analysis was performed to calculate aortic (Pa), distal intracoronary (Pd), and reservoir (Pr) pressure at baseline, peak, and stable hyperemia. Seven different hemodynamic patterns were observed according to Pa and Pd change at peak and stable hyperemia. The average time from baseline to stable hyperemia was 68.2±38.5 seconds, when both ΔPa and ΔPd were decreased (ΔPa, -10.2±10.5 mm Hg; ΔPd, -18.2±10.8 mm Hg; P<0.001 for both). The fall in Pa closely correlated with the reduction in peripheral Pr (ΔPr, -12.9±15.7 mm Hg; P<0.001; r=0.9; P<0.001). ΔPa and ΔPd were closely related under conditions of peak (r=0.75; P<0.001) and stable hyperemia (r=0.83; P<0.001). On average, 56% (10.2 mm Hg) of the reduction in Pd was because of fall in Pa. FFR lesion classification changed in 9% using an FFR threshold of ≤0.80 and 5.2% with FFR threshold <0.75 when comparing Pd/Pa at peak and stable hyperemia.

CONCLUSIONS

Intravenous adenosine results in variable changes in systemic blood pressure, which can lead to alterations in FFR lesion classification. Attention is required to ensure FFR is measured under conditions of stable hyperemia, although the FFR value at this point may be numerically higher.

Whole-body recruitment of glycocalyx volume during intravenous adenosine infusion

Adenosine-mediated recruitment of microvascular volume in heart and muscle has been suggested to include, in addition to vasodilation of resistance vessels, an increased accessibility of the endothelial glycocalyx for flowing plasma as a result of an impairment of its barrier properties. The aim of the current study was to investigate the effect of systemic intravenous administration of adenosine on the glycocalyx-dependent exclusion of circulating blood at a whole-body level. In anesthetized goats (N = 6), systemic blood-excluded glycocalyx volume was measured by comparing the intravascular distribution volume of the suggested glycocalyx accessible tracer dextrans with a molecular weight of 40 kDa (Dex-40) to that of circulating plasma, derived from the dilution of labeled red blood cells and large vessel hematocrit. Systemic glycocalyx volume was determined at baseline and during intravenous infusion of adenosine (157 ± 11.6 μg/kg min⁻¹). Blood-inaccessible glycocalyx volume decreased from 458.1 ± 95.5 to 18.1 ± 62.2 mL (P < 0.01) during adenosine administration. While circulating plasma volume did not change significantly (617.1 ± 48.5 vs. 759.2 ± 47.9 mL, NS), the decrease in blood-excluded glycocalyx volume was associated with a decrease in Dex-40 distribution volume (from 1075.2 ± 71.0 to 777.3 ± 60.0 mL, P < 0.01). Intravenous administration of adenosine is associated with a robust impairment of whole-body glycocalyx barrier properties, reflected by a greatly reduced exclusion of circulating blood compared to small dextrans. The observed decrease in Dex-40 distribution volume suggests that the reduction in glycocalyx volume coincides with a reduction in tracer-accessible vascular volume.

Vasoactive and Antiarrhythmic Drugs During Percutaneous Coronary Intervention

The objective in percutaneous coronary intervention (PCI) is to treat flow-limiting atherothrombotic coronary plaques mechanically. Many types of antithrombotic drugs are used to prevent ischemic complications during manipulation of catheters, guidewires, balloons, and stents in coronary arteries while minimizing the risk of bleeding. However, many other types of pharmacologic agents are also used to facilitate PCI. This review focuses on the most commonly used adjunct drugs during PCI. In addition, a recommendation of which drugs should be stopped or interrupted in patients undergoing PCI is provided.

Improvement in coronary haemodynamics after percutaneous coronary intervention: assessment using instantaneous wave-free ratio

Objective

To determine whether the instantaneous wave-free ratio (iFR) can detect improvement in stenosis significance after percutaneous coronary intervention (PCI) and compare this with fractional flow reserve (FFR) and whole cycle Pd/Pa.

Design

A prospective observational study was undertaken in elective patients scheduled for PCI with FFR ≤0.80. Intracoronary pressures were measured at rest and during adenosine-mediated vasodilatation, before and after PCI. iFR, Pd/Pa and FFR values were calculated using the validated fully automated algorithms.

Setting

Coronary catheter laboratories in two UK centres and one in the USA.

Patients

120 coronary stenoses in 112 patients were assessed. The mean age was 63±10 years, while 84% were male; 39% smokers; 33% with diabetes. Mean diameter stenosis was 68±16% by quantitative coronary angiography.

Results

Pre-PCI, mean FFR was 0.66±0.14, mean iFR was 0.75±0.21 and mean Pd/Pa 0.83±0.16. PCI increased all indices significantly (FFR 0.89±0.07, p<0.001; iFR 0.94±0.05, p<0.001; Pd/Pa 0.96±0.04, p<0.001). The change in iFR after intervention (0.20±0.21) was similar to ΔFFR 0.22±0.15 (p=0.25). ΔFFR and ΔiFR were significantly larger than resting ΔPd/Pa (0.13±0.16, both p<0.001). Similar incremental changes occurred in patients with a higher prevalence of risk factors for microcirculatory disease such as diabetes and hypertension.

Conclusions

iFR and FFR detect the changes in coronary haemodynamics elicited by PCI. FFR and iFR have a significantly larger dynamic range than resting Pd/Pa. iFR might be used to objectively document improvement in coronary haemodynamics following PCI in a similar manner to FFR.

Optical coherence tomography criteria for defining functional severity of intermediate lesions: a comparative study with FFR

Fractional flow reserve (FFR) is the gold standard in the assessment of severity of the coronary stenosis. The aim of the study was to compare optical coherence tomography (OCT) obtained intermediate coronary lesions lumen areas measurements with FFR assessments, with the goal to develop an OCT threshold to identify significant coronary stenosis. 48 patients (mean age 65 ± 10 years) was enrolled for the study. Within this population, 71 intermediate coronary lesions were investigated using both FFR and OCT. High dose bolus of Adenosine (120 μg) was used to obtain coronary hyperemia. OCT imaging was performed using non-occlusive technique to assess minimal lumen area (MLA) and diameter. The OCT cut-off value that showed the best correlation with the FFR cut-off of 0.80 was the MLA less than 2.05 mm2 (accuracy 87%, sensitivity 75%, specificity 90%, p < 0.001). The study did not disclose any relationship between FFR value and the lesion length. Vessel size influenced the OCT cut-off values, with greater values being found in presence of arteries with a reference diameter greater than 3.0 mm. OCT derived minimal lumen area might be complementary to FFR measurement in identifying ischemia related lesions. Further studies are warranted to assess threshold values in relation to vessel size and location.

Use of regadenoson for measurement of fractional flow reserve

OBJECTIVE

To compare the use of regadenoson to adenosine for measurement of fractional flow reserve (FFR).

BACKGROUND

FFR is an accepted method to assess the functional significance of intermediate coronary artery stenoses and uses adenosine to induce maximal hyperemia. The use of the selective A2a receptor agonist regadenoson for FFR is not established.

METHODS

Fifty-seven patients undergoing clinically indicated FFR assessment of intermediate coronary stenoses were included. For the initial assessment of FFR, hyperemia was achieved by a standard intravenous adenosine infusion (140 mcg/kg/min). After a washout period of 10 min, FFR was reassessed using regadenoson as a single 0.4 mg intravenous bolus. FFR measurements were recorded at baseline and following maximal hyperemia with both agents.

RESULTS

Mean age was 57 ± 8 years and 47 were male. Sixty coronary lesions were evaluated and were located in the left anterior descending in 34, the left circumflex in 9, right coronary in 15, and left main coronary artery in 2. Mean ( ± SD) FFR following adenosine and regadenoson was 0.79 ( ± 0.09) and 0.79 (±0.09), respectively, P = NS. Time to FFR nadir was shorter with regadenoson compared to adenosine, 36.6 ± 24 versus 66 ± 0.19 sec, P < 0.0001, respectively. No patients experienced any significant side effects related to regadenoson.

CONCLUSIONS

Regadenoson is a viable alternative to intravenous adenosine for achieving maximal hyperemia during FFR assessment. Compared to adenosine, regadenoson has a similar hemodynamic response, achieves more rapid hyperemia, is easier to use, and has an excellent side-effect profile.