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

Impact of coronary computed tomography angiography-derived fractional flow reserve based on deep learning on clinical management

Background

To examine the value of coronary computed tomography angiography (CCTA)-derived fractional flow reserve based on deep learning (DL-FFRCT) on clinical practice and analyze the limitations of the application of DL-FFRCT.

Methods

This is an observational, retrospective, single-center study. Patients with suspected coronary artery disease (CAD) were enrolled. The patients underwent invasive coronary angiography (ICA) examination within 1 months after CCTA examination. And quantitative coronary angiography (QCA) was performed to evaluate the area stenosis rate. The CCTA data of these patients were retrospectively analyzed to calculate the FFRCT value.

Results

A total of 485 lesions of coronary arteries in 229 patients were included in the analysis. Of the lesions, 275 (56.7%) were ICA-positive, and 210 (43.3%) were FFRCT-positive. The discordance rate of the risk stratification of FFRCT for ICA-positive lesions was 33.1% (91) and that for ICA-negative lesions was 12.4% (26). 14.6% (7/48) patients with mild to moderate coronary stenosis in ICA have functional ischemia according to FFRCT positive indications. In addition, hemodynamic analysis of severely calcified, occluded, or small (< 2 mm in diameter) coronary arteries by DL-FFRCT is not so reliable.

Conclusion

This study revealed that most patients with ICA negative did not require further invasive FFR. Besides, some patients with mild to moderate coronary stenosis in ICA may also have functional ischemia. However, for severely calcified, occluded, or small coronary arteries, treatment strategy should be selected based on ICA in combination with clinical practice.

Linear concentration-response relationship of serum caffeine with adenosine-induced fractional flow reserve overestimation: a comparison with papaverine

BACKGROUND

Caffeine intake from one cup of coffee one hour before adenosine stress tests, corresponding to serum caffeine levels of 3-4 mg/L, is thought to be acceptable for non-invasive imaging.

AIMS

We aimed to elucidate whether serum caffeine is independently associated with adenosine-induced fractional flow reserve (FFR) overestimation and their concentration-response relationship.

METHODS

FFR was measured using adenosine (FFRADN) and papaverine (FFRPAP) in 209 patients. FFRADN overestimation was defined as FFRADN - FFRPAP. The locally weighted scatterplot smoothing (LOWESS) approach was applied to evaluate the relationship between serum caffeine level and FFRADN overestimation. Multiple regression analysis was used to determine independent factors associated with FFRADN overestimation.

RESULTS

Caffeine was ingested at <12 hours in 85 patients, at 12-24 hours in 35 patients, and at >24 hours in 89 patients. Multiple regression analysis identified serum caffeine level as the strongest factor associated with FFRADN overestimation (p<0.001). The LOWESS curve demonstrated that FFRADN overestimation started from just above the lower detection limit of serum caffeine and increased approximately 0.01 FFR unit per 1 mg/L increase in serum caffeine level with a linear relationship. The 90th percentile of serum caffeine levels for the ≤12-hour, the 12-24-hour, and the >24-hour groups corresponded to FFRADN overestimations by 0.06, 0.03, and 0.02, respectively.

CONCLUSIONS

Serum caffeine overestimates FFRADN values in a linear concentration-response manner. FFRADN overestimation occurs at much lower serum caffeine levels than those that were previously believed. Our results highlight that standardised caffeine control is required for reliable adenosine-induced FFR measurements.

Respiration-related variations in Pd/Pa ratio and fractional flow reserve in resting conditions and during intravenous adenosine administration

Aims

We evaluated the occurrence and physiology of respiration‐related beat‐to‐beat variations in resting Pd/Pa and FFR during intravenous adenosine administration, and its impact on clinical decision‐making.

Methods and Results

Coronary pressure tracings in rest and at plateau hyperemia were analyzed in a total of 39 stenosis from 37 patients, and respiratory rate was calculated with ECG‐derived respiration (EDR) in 26 stenoses from 26 patients. Beat‐to‐beat variations in FFR occurred in a cyclical fashion and were strongly correlated with respiratory rate (R² = 0.757, p < 0.001). There was no correlation between respiratory rate and variations in resting Pd/Pa. When single‐beat averages were used to calculate FFR, mean ΔFFR was 0.04 ± 0.02. With averaging of FFR over three or five cardiac cycles, mean ΔFFR decreased to 0.02 ± 0.02, and 0.01 ± 0.01, respectively. Using a FFR ≤ 0.80 threshold, stenosis classification changed in 20.5% (8/39), 12.8% (5/39) and 5.1% (2/39) for single‐beat, three‐beat and five‐beat averaged FFR. The impact of respiration was more pronounced in patients with pulmonary disease (ΔFFR 0.05 ± 0.02 vs 0.03 ± 0.02, p = 0.021).

Conclusion

Beat‐to‐beat variations in FFR during plateau hyperemia related to respiration are common, of clinically relevant magnitude, and frequently lead FFR to cross treatment thresholds. A five‐beat averaged FFR, overcomes clinically relevant impact of FFR variation.

Comparing invasive hemodynamic responses in adenosine hyperemia versus physical exercise stress in chronic coronary syndromes

OBJECTIVES

Adenosine hyperemia is an integral component of the physiological assessment of obstructive coronary artery disease in patients with chronic coronary syndrome (CCS). The aim of this study was to compare systemic, coronary and microcirculatory hemodynamics between intravenous (IV) adenosine hyperemia versus physical exercise stress in patients with CCS and coronary stenosis.

METHODS

Twenty-three patients (mean age, 60.6 ± 8.1 years) with CCS and single-vessel coronary stenosis underwent cardiac catheterization. Continuous trans-stenotic coronary pressure-flow measurements were performed during: i) IV adenosine hyperemia, and ii) physical exercise using a catheter-table-mounted supine ergometer. Systemic, coronary and microcirculatory hemodynamic responses were compared between IV adenosine and exercise stimuli.

RESULTS

Mean stenosis diameter was 74.6% ± 10.4. Median (interquartile range) FFR was 0.54 (0.44-0.72). At adenosine hyperemia versus exercise stress, mean aortic pressure (Pa, 91 ± 16 mmHg vs 99 ± 15 mmHg, p < 0.0001), distal coronary pressure (Pd, 58 ± 21 mmHg vs 69 ± 24 mmHg, p < 0.0001), trans-stenotic pressure ratio (Pd/Pa, 0.63 ± 0.18 vs 0.69 ± 0.19, p < 0.0001), microvascular resistance (MR, 2.9 ± 2.2 mmHg.cm-1.sec-1 vs 4.2 ± 1.7 mmHg.cm-1.sec-1, p = 0.001), heart rate (HR, 80 ± 15 bpm vs 85 ± 21 bpm, p = 0.02) and rate-pressure product (RPP, 7522 ± 2335 vs 9077 ± 3200, p = 0.0001) were all lower. Conversely, coronary flow velocity (APV, 23.7 ± 9.5 cm/s vs 18.5 ± 6.8 cm/s, p = 0.02) was higher. Additionally, temporal changes in Pa, Pd, Pd/Pa, MR, HR, RPP and APV during IV adenosine hyperemia versus exercise were all significantly different (p < 0.05 for all).

CONCLUSIONS

In patients with CCS and coronary stenosis, invasive hemodynamic responses differed markedly between IV adenosine hyperemia versus physical exercise stress. These differences were observed across systemic, coronary and microcirculatory hemodynamics.

Simplified Assessment of the Index of Microvascular Resistance

Background

To validate a simplified invasive method for the calculation of the index of microvascular resistance (IMR).

Methods

This is a prospective, single-center study of patients with chronic coronary syndromes presenting with nonobstructive coronary artery disease. IMR was obtained using both intravenous (IV) adenosine and intracoronary (IC) papaverine. Each IMR measurement was obtained in duplicate. The primary objective was the agreement between IMR acquired using adenosine and papaverine. Secondary objectives include reproducibility of IMR and time required for the IMR measurement.

Results

One hundred and sixteen IMR measurements were performed in 29 patients. The mean age was 68.8 ± 7.24 years, and 27.6% was diabetics. IMR values were similar between papaverine and adenosine (17.7 ± 7.26 and 20.1 ± 8.6, p=0.25; Passing-Bablok coefficient A 0.58, 95% CI −2.42 to 3.53; coefficient B 0.90, 95% CI −0.74 to 1.07). The reproducibility of IMR was excellent with both adenosine and papaverine (ICC 0.78, 95% CI 0.63 to 0.88 and ICC 0.93, 95% CI 0.87 to 0.97). The time needed for microvascular assessment was significantly shortened by the use of IC papaverine (3.23 (2.84, 3.78) mins vs. 5.48 (4.94, 7.09) mins, p < 0.0001).

Conclusion

IMR can be reliably measured using IC papaverine with similar results compared to intravenous infusion of adenosine with increased reproducibility and reduced procedural time. This approach simplifies the invasive assessment of the coronary microcirculation in the catheterization laboratory.

Temporal Changes in Coronary Hyperemic and Resting Hemodynamic Indices in Nonculprit Vessels of Patients With ST-Segment Elevation Myocardial Infarction

Importance

Percutaneous coronary intervention (PCI) of nonculprit vessels among patients with ST-segment elevation myocardial infarction (STEMI) is associated with improved clinical outcome compared with culprit vessel-only PCI. Fractional flow reserve (FFR) and coronary flow reserve are hyperemic indices used to guide revascularization. Recently, instantaneous wave-free ratio was introduced as a nonhyperemic alternative to FFR. Whether these indices can be used in the acute setting of STEMI continues to be investigated.

Objective

To assess the value of hemodynamic indices in nonculprit vessels of patients with STEMI from the index event to 1-month follow-up.

Design, Setting, and Participants

This substudy of the Reducing Micro Vascular Dysfunction in Revascularized STEMI Patients by Off-target Properties of Ticagrelor (REDUCE-MVI) randomized clinical trial enrolled 98 patients with STEMI who had an angiographic intermediate stenosis in at least 1 nonculprit vessel. Patient enrollment was between May 1, 2015, and September 19, 2017. After successful primary PCI, nonculprit intracoronary hemodynamic measurements were performed and repeated at 1-month follow-up. Cardiac magnetic resonance imaging was performed from 2 to 7 days and 1 month after primary PCI.

Main Outcomes and Measures

The value of nonculprit instantaneous wave-free ratio, FFR, coronary flow reserve, hyperemic index of microcirculatory resistance, and resting microcirculatory resistance from the index event to 1-month follow-up.

Results

Of 73 patients with STEMI included in the final analysis, 59 (80.8%) were male, with a mean (SD) age of 60.8 (9.9) years. Instantaneous wave-free ratio (SD) did not change significantly (0.93 [0.07] vs 0.94 [0.06]; P = .12) and there was no change in resting distal pressure/aortic pressure (mean [SD], 0.94 [0.06] vs 0.95 [0.06]; P = .25) from the acute moment to 1-month follow-up. The FFR decreased (mean [SD], 0.88 [0.07] vs 0.86 [0.09]; P = .001) whereas coronary flow reserve increased (mean [SD], 2.9 [1.4] vs 4.1 [2.2]; P < .001). Hyperemic index of microcirculatory resistance decreased and resting microcirculatory resistance increased from the acute moment to follow-up. The decrease in distal pressure from rest to hyperemia was smaller at the acute moment vs follow-up (mean [SD], 10.6 [11.2] mm Hg vs 14.1 [14.2] mm Hg; P = .05). This blunted acute hyperemic response correlated with final infarct size (ρ, -0.29; P = .02). The resistive reserve ratio was lower at the acute moment vs follow-up (mean [SD], 3.4 [1.7] vs 5.0 [2.7]; P < .001).

Conclusions and Relevance

In the acute setting of STEMI, nonculprit coronary flow reserve was reduced and FFR was augmented, whereas instantaneous wave-free ratio was not altered. These results may be explained by an increased hyperemic microvascular resistance and a blunted adenosine responsiveness at the acute moment that was associated with infarct size.

Long-Term Effects of Transcatheter Aortic Valve Implantation on Coronary Hemodynamics in Patients With Concomitant Coronary Artery Disease and Severe Aortic Stenosis

Background As younger patients are being considered for transcatheter aortic valve implantation (TAVI), the assessment and treatment of concomitant coronary artery disease is taking on increased importance. Methods and Results Thirteen contemporary lower-risk patients with TAVI with severe aortic stenosis (AS) and moderate-severe coronary lesions were included. Patients underwent assessment of coronary hemodynamics in the presence of severe AS (pre-TAVI), in the absence of severe AS (immediately post-TAVI), and at longer-term follow-up (6 months post-TAVI). Fractional flow reserve decreased from 0.85 (0.76-0.88) pre-TAVI to 0.79 (0.74-0.83) post-TAVI, and then to 0.71 (0.65-0.77) at 6-month follow-up (P<0.001 for all comparisons). Conversely, instantaneous wave-free ratio was not significantly different: 0.82 (0.80-0.90) pre-TAVI, 0.83 (0.77-0.88) post-TAVI, and 0.83 (0.73-0.89) at 6 months (P=0.735). These changes are explained by the underlying coronary flow. Hyperemic whole-cycle coronary flow (fractional flow reserve flow) increased from 26.36 cm/s (23.82-31.82 cm/s) pre-TAVI to 30.78 cm/s (29.70-34.68 cm/s) post-TAVI (P=0.012), to 40.20 cm/s (32.14-50.00 cm/s) at 6-month follow-up (P<0.001 for both comparisons). Resting flow during the wave-free period of diastole was not significantly different: 25.48 cm/s (21.12-33.65 cm/s) pre-TAVI, 24.54 cm/s (20.74-27.88 cm/s) post-TAVI, and 25.89 cm/s (22.57-28.96 cm/s) at 6 months (P=0.500). Conclusions TAVI acutely improves whole-cycle hyperemic coronary flow, with ongoing sustained improvements at longer-term follow-up. This enhanced response to hyperemic stimuli appears to make fractional flow reserve assessment less suitable for patients with severe AS. Conversely, resting diastolic flow is not significantly influenced by the presence of severe AS. Resting indices of coronary stenosis severity, therefore, appear to be more appropriate for this patient population, although large-scale prospective randomized trials will be required to determine the role of coronary physiology in patients with severe AS.

Instantaneous wave-free ratio (iFR®) to determine hemodynamically significant coronary stenosis: A comprehensive review

Coronary angiography is considered to be the gold standard in the morphological evaluation of coronary artery stenosis. The morphological assessment of the severity of a coronary lesion is very subjective. Thus, the invasive fractional flow reserve (FFR) measurement represents the current standard for estimation of the hemodynamic significance of coronary artery stenosis. The FFR-guided revascularization strategy was initially classified as a Class-IA-recommendation in the 2014 European Society of Cardiology/European Association for Cardio-Thoracic Surgery guidelines on myocardial revascularization. Both the Deferral vs Performance of Percutaneous Coronary Intervention of Functionally Non-Significant Coronary Stenosis and Flow Reserve vs Angiography for Multivessel Evaluation studies showed no treatment advantage for hemodynamically insignificant stenoses. With the help of FFR (and targeted interventions), clinical results could be improved; however, the use in clinical practice is still limited due to the need of adenosine administration and a significant prolongation of the length of the procedure. Instantaneous wave-free ratio (iFR®) is a new innovative approach for the determination of the hemodynamic significance of coronary stenosis, which can be obtained at rest without the use of vasodilators. Regarding the periprocedural complications as well as prognosis, iFR® showed non-inferiority to FFR in the SWEDEHEART and DEFINE-FLAIR trials. Furthermore, iFR®, enhanced by iFR®-pullback, provides the possibility to display the iFR®-change over the course of the vessel to create a hemodynamic map.

Coronary Hemodynamics in Patients With Severe Aortic Stenosis and Coronary Artery Disease Undergoing Transcatheter Aortic Valve Replacement: Implications for Clinical Indices of Coronary Stenosis Severity

OBJECTIVES

In this study, a systematic analysis was conducted of phasic intracoronary pressure and flow velocity in patients with severe aortic stenosis (AS) and coronary artery disease, undergoing transcatheter aortic valve replacement (TAVR), to determine how AS affects: 1) phasic coronary flow; 2) hyperemic coronary flow; and 3) the most common clinically used indices of coronary stenosis severity, instantaneous wave-free ratio and fractional flow reserve.

BACKGROUND

A significant proportion of patients with severe aortic stenosis (AS) have concomitant coronary artery disease. The effect of the valve on coronary pressure, flow, and the established invasive clinical indices of stenosis severity have not been studied.

METHODS

Twenty-eight patients (30 lesions, 50.0% men, mean age 82.1 ± 6.5 years) with severe AS and coronary artery disease were included. Intracoronary pressure and flow assessments were performed at rest and during hyperemia immediately before and after TAVR.

RESULTS

Flow during the wave-free period of diastole did not change post-TAVR (29.78 ± 14.9 cm/s vs. 30.81 ± 19.6 cm/s; p = 0.64). Whole-cycle hyperemic flow increased significantly post-TAVR (33.44 ± 13.4 cm/s pre-TAVR vs. 40.33 ± 17.4 cm/s post-TAVR; p = 0.006); this was secondary to significant increases in systolic hyperemic flow post-TAVR (27.67 ± 12.1 cm/s pre-TAVR vs. 34.15 ± 17.5 cm/s post-TAVR; p = 0.02). Instantaneous wave-free ratio values did not change post-TAVR (0.88 ± 0.09 pre-TAVR vs. 0.88 ± 0.09 post-TAVR; p = 0.73), whereas fractional flow reserve decreased significantly post-TAVR (0.87 ± 0.08 pre-TAVR vs. 0.85 ± 0.09 post-TAVR; p = 0.001).

CONCLUSIONS

Systolic and hyperemic coronary flow increased significantly post-TAVR; consequently, hyperemic indices that include systole underestimated coronary stenosis severity in patients with severe AS. Flow during the wave-free period of diastole did not change post-TAVR, suggesting that indices calculated during this period are not vulnerable to the confounding effect of the stenotic aortic valve.

The impact of Objective Mathematical Analysis during Fractional Flow Reserve measurement: results from the OMA-FFR study

AIMS

Fractional flow reserve (FFR), the reference standard for guiding coronary revascularisation, is most commonly acquired during intravenous adenosine infusion. Results may be sensitive to system- and operator-dependent variability in how pressure data are analysed and interpreted. To quantify FFR objectively, we developed a computational protocol to process the recorded pressure signals in a consistent manner. We studied the impact on lesion (re)classification and compared this with the operator-selected FFR obtained during cardiac catheterisation.

METHODS AND RESULTS

The algorithm used a moving average and Fourier transformation to identify the Pd/Pa ratio at its nadir (FFRmin) and during the stable hyperaemic period (FFRstable) in <2 s with 100% repeatability, in 163 coronary stenoses (93 patients). The mean operator-selected FFR (FFRCL) was higher than FFRmin and lower than FFRstable (0.779 vs. 0.762 vs. 0.806, p=<0.01). Compared with FFRmin, FFRstable resulted in 16.5% of all lesions being reclassified, all from significant to non-significant (p<0.01). FFRCL classified lesion significance differently from both FFRstable and FFRmin (11.7% and 6.1% lesions reclassified, respectively, p<0.01).

CONCLUSIONS

Subtle differences in how pressure data are analysed and interpreted by the operator during adenosine infusion result in significant differences in the classification of physiological lesion significance. An algorithmic analysis may be helpful in standardising FFR analysis, providing an objective and repeatable result.

Past, Present and Future of Coronary Physiology

It is well known that the apparent significant coronary stenosis on angiography sometimes does not cause significant ischemia, and vice versa. For this reason, decision-making based on coronary physiology is becoming more and more important. Fractional flow reserve (FFR), which has emerged as a useful tool to determine which lesions need revascularization in the catheterization laboratory, now has a class IA indication in the European Society of Cardiology guidelines. More recently, the instantaneous wave-free ratio, which is considered easier to use than FFR, has been graded as equivalent to FFR. This review discusses the concepts of FFR and instantaneous wave-free ratio, current evidence supporting their use, and future directions in coronary physiology.

The relationship between the basal coronary translesional pressure ratio and fractional flow reserve

AIM

Fractional flow reserve (FFR) allows for physiological definition of coronary lesion severity but requires induction of maximal coronary circulation hyperemia with administration of adenosine leading to coronary resistive vessel vasodilatation. However, the hyperemic response to adenosine, and therefore the calculation of FFR, may be affected by dysfunction of the coronary microvasculature. The aim was to define the relationship between basal P_d /P_a and FFR and identify lesion-independent predictors of the change in P_d /P_a with hyperemia.

METHODS AND RESULTS

One hundred and sixty-six consecutive patients undergoing FFR measurement were prospectively enrolled (mean age 62.6 ± 10.3 years, 27% females). Basal P_d /P_a , FFR, and delta P_d /P_a (difference between basal P_d /P_a and FFR) were recorded. Independent predictors of delta P_d /P_a included angiographic lesion severity, lesion length, gender, body mass index, and total cholesterol:HDL cholesterol ratio. The best basal P_d /P_a cutoff value to predict lesion physiological significance was 0.87 (positive predictive value of 100% for an FFR value ≤0.80) and the best cutoff for nonsignificance was 0.93 (negative predictive value of 98% for an FFR value >0.80).

CONCLUSION

The delta P_d /P_a may be affected by patient gender, body mass index, and cholesterol profile. A basal P_d /P_a value of ≥0.93 is highly predictive of an FFR >0.80. Conversely, a basal P_d /P_a value of ≤0.87 is highly predictive of an FFR ≤0.80. © 2017 Wiley Periodicals, Inc.

Hybrid Instantaneous Wave-Free Ratio-Fractional Flow Reserve versus Fractional Flow Reserve in the Real World

BACKGROUND

The instantaneous wave-free ratio (iFR) is a novel method to assess the ischemic potential of coronary artery stenoses. Clinical trial data have shown that iFR has acceptable diagnostic agreement with fractional flow reserve (FFR), the reference standard for the functional assessment of coronary stenoses. This study compares iFR measurements with FFR measurements in a real world, single-center setting.

METHODS AND RESULTS

Instantaneous wave-free ratio and FFR were measured in 50 coronary artery lesions in 42 patients, with FFR ≤ 0.8 classified as functionally significant. An iFR-only technique, using a treatment cut-off value, iFR ≤ 0.89, provided a classification agreement of 84% with FFR ≤ 0.80. Use of a hybrid iFR-FFR technique, incorporating FFR measurement for lesions within the iFR gray zone of 0.86-0.93, would improve classification agreement with FFR to 94%, with diagnosis achieved without the need for hyperemia in 57% patients.

CONCLUSION

This study in a real-world setting demonstrated good classification agreement between iFR and FFR. Use of a hybrid iFR-FFR technique would achieve high diagnostic accuracy while minimizing adenosine use, compared with routine FFR.

Fractional flow reserve: a clinical perspective

Fractional flow reserve (FFR) is a reference invasive diagnostic test to assess the physiological significance of an epicardial coronary artery stenosis. FFR-guided percutaneous coronary intervention in stable coronary artery disease has been assessed in three seminal clinical trials and the indications for FFR assessment are expanding into other clinical scenarios. In this article we review the theoretical, experimental and clinical basis for FFR measurement. We place FFR measurement in the context of the comprehensive invasive assessment of coronary physiology in patients presenting with known or suspected angina pectoris in daily clinical practice, and review the recent developments in FFR assessment.

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.

Validation of the "smart" minimum FFR Algorithm in an unselected all comer population of patients with intermediate coronary stenoses

Using data from a commercial pressure wire system (St. Jude Medical) we previously developed an automated "smart" algorithm to determine a reproducible value for minimum FFR (smFFR) and confirmed that it correlated very closely with measurements made off-line by experienced coronary physiology core laboratories. In this study we used the same "smart" minimum algorithm to analyze data derived from a different, commercial pressure wire system (Philips Volcano) and compared the values obtained to both operator-defined steady state FFR and the online automated minimum FFR reported by the pressure wire analyser. For this analysis, we used the data collected during the VERIFY 2 study (Hennigan et al. in Circ Cardiovasc Interv, doi: 10.1161/CIRCINTERVENTIONS.116.004016 ) in which we measured FFR in 257 intermediate coronary stenoses (mean DS 48%) in 197 patients. Maximal hyperaemia was induced using intravenous adenosine (140 mcg/kg/min). We recorded both the online minimum FFR generated by the analyser and the operator-reported steady state FFR. Subsequently, the raw pressure tracings were coded, anonymised and 256/257 were subjected to further off-line analysis using the smart minimum FFR (smFFR) algorithm. The operator-defined steady state FFR correlated well with smFFR: r = 0.988 (p < 0.001), average bias 0.008 (SD 0.014), 95% limits of agreement -0.020 to 0.036. The online automated minimum FFR also correlated well with the smFFR: r = 0.998 (p < 0.001), average bias 0.004 (SD 0.006), 95% limits of agreement -0.016 to 0.008. Finally, the online automated minimum FFR correlated well the operator-reported steady state FFR: r = 0.988 (p < 0.001), average bias 0.012 (SD 0.014), 95% limits of agreement -0.039 to 0.015. In 95% of lesions studied (244/256), the operator reported steady-state FFR, smFFR, and online automated minimum FFR agreed with each other to within 0.04, which is within the previously reported test/retest limits of agreement of FFR reported by an experienced core lab. Disagreements >0.05 among methods were rare but in these cases the two automated algorithms almost always agreed with each other rather than with the operator-reported value. Within the VERIFY 2 dataset, experienced operators reported a similar FFR value to both an online automated minimum (Philips Volcano) and off-line "smart" minimum computer algorithm. Thus, treatment decisions and clinical studies using either method will produce nearly identical results.

Effects of caffeine on fractional flow reserve values measured using intravenous adenosine triphosphate

We investigated the effects of caffeine intake on fractional flow reserve (FFR) values measured using intravenous adenosine triphosphate (ATP) before cardiac catheterization. Caffeine is a competitive antagonist for adenosine receptors; however, it is unclear whether this antagonism affects FFR values. Patients were evenly randomized into 2 groups preceding the FFR study. In the caffeine group (n = 15), participants were given coffee containing 222 mg of caffeine 2 h before the catheterization. In the non-caffeine group (n = 15), participants were instructed not to take any caffeine-containing drinks or foods for at least 12 h before the catheterization. FFR was performed in patients with more than intermediate coronary stenosis using the intravenous infusion of ATP at 140 μg/kg/min (normal dose) and 170 μg/kg/min (high dose), and the intracoronary infusion of papaverine. FFR was followed for 30 s after maximal hyperemia. In the non-caffeine group, the FFR values measured with ATP infusion were not significantly different from those measured with papaverine infusion. However, in the caffeine group, the FFR values were significantly higher after ATP infusion than after papaverine infusion (P = 0.002 and P = 0.007, at normal and high dose ATP vs. papaverine, respectively). FFR values with ATP infusion were significantly increased 30 s after maximal hyperemia (P = 0.001 and P < 0.001 for normal and high dose ATP, respectively). The stability of the FFR values using papaverine showed no significant difference between the 2 groups. Caffeine intake before the FFR study affected FFR values and their stability. These effects could not be reversed by an increased ATP dose.

Comparative Study between Perfusion Changes and Positive Findings on Coronary Flow Reserve

BACKGROUND

Functional assessment of coronary artery obstruction is used in cardiology practice to correlate anatomic obstructions with flow decrease. Among such assessments, the study of the coronary fractional flow reserve (FFR) has become the most widely used.

OBJECTIVE

To evaluate the correlation between FFR and findings of ischemia obtained by noninvasive methods including stress echocardiography and nuclear medicine and the presence of critical coronary artery obstruction.

METHODS

Retrospective study of cases treated with systematized and standardized procedures for coronary disease between March 2011 and August 2014. We included 96 patients with 107 critical coronary obstructions (> 50% in the coronary trunk and/or ≥ 70% in other segments) estimated by quantitative coronary angiography (QCA) and intracoronary ultrasound (ICUS). All cases presented ischemia in one of the noninvasive studies.

RESULTS

All 96 patients presented ischemia (100%) in one of the functional tests. On FFR study with adenosine 140 g/kg/min, 52% of the cases had values ≤ 0.80. On correlation analysis for FFR ≤ 0.80, the evaluation of sensitivity, specificity, positive and negative predictive values, accuracy, and ROC curve in relation to the stenosis degree and length, and presence of ischemia, no significant values or strong correlation were observed.

CONCLUSION

Coronary FFR using a cut-off value of 0.80 showed no correlation with noninvasive ischemia tests in patients with severe coronary artery obstructions on QCA and ICUS.

Quantification of the Effect of Pressure Wire Drift on the Diagnostic Performance of Fractional Flow Reserve, Instantaneous Wave-Free Ratio, and Whole-Cycle Pd/Pa

Background—

Small drifts in intracoronary pressure measurements (±2 mm Hg) can affect stenosis categorization using pressure indices. This has not previously been assessed for fractional flow reserve (FFR), instantaneous wave-free ratio (iFR), and whole-cycle distal pressure/proximal pressure (Pd/Pa) indices.

Methods and Results—Four hundred forty-seven

stenoses were assessed with FFR, iFR, and whole-cycle Pd/Pa. Cut point values for significance were predefined as ≤0.8, <0.90, and <0.93, respectively. Pressure wire drift was simulated by offsetting the distal coronary pressure trace by ±2 mm Hg. FFR, iFR, and whole-cycle Pd/Pa indices were recalculated and stenosis misclassification quantified. Median (±median absolute deviation) values for FFR, iFR, and whole-cycle Pd/Pa were 0.81 (±0.11), 0.90 (±0.07), and 0.93 (±0.06), respectively. For the cut point of FFR, iFR, and whole-cycle Pd/Pa, 34.6% (155), 50.1% (224), and 62.2% (278) of values, respectively, lay within ±0.05 U. With ±2 mm Hg pressure wire drift, 21% (94), 25% (110), and 33% (148) of the study population were misclassified with FFR, iFR, and whole-cycle Pd/Pa, respectively. Both FFR and iFR had significantly lower misclassification than whole-cycle Pd/Pa (P<0.001). There was no statistically significant difference between the diagnostic performance of FFR and iFR (P=0.125).

Conclusions—

In a substantial proportion of cases, small amounts of pressure wire drift are enough to cause stenoses to change classification. Whole-cycle Pd/Pa is more vulnerable to such reclassification than FFR and iFR.

Effect of High (200 μg/kg per Minute) Adenosine Dose Infusion on Fractional Flow Reserve Variability

BACKGROUND

Variations in distal coronary pressure (Pd)/aortic pressure (Pa) ratio during steady-state hyperemia with standard (140 μg/kg per minute) adenosine dose may hamper accurate fractional flow reserve assessment. This study investigated to what extent an increased adenosine dose can overcome Pd/Pa variation.

METHODS AND RESULTS

In a prospective, single-arm study, out of 95 prospectively screened patients, 38 (40.0%) exhibited significant (≥0.05 difference of max Pd/Pa minus min Pd/Pa) variations in Pd/Pa from 15 s post Pd/Pa dip and until the end of a 3-minute adenosine (140 μg/kg per minute) infusion. Thirty patients agreed to participate in a post 5-minute repeat fractional flow reserve assessment using 200 μg/kg per minute 3-minute adenosine infusion. The study's co-primary end point of Pd/Pa coefficient of dispersion was lower for the high versus standard adenosine dose: 1.31 (1.13-2.72) versus 2.76 (2.38-5.60), P=0.002. The study's co-primary end point of ΔPd/Pa was also lower for the high versus standard adenosine dose: 0.065 (0.038-0.10) versus 0.08 (0.06-0.11), P=0.002. This difference was mainly driven by the lowering effect of the high adenosine dose on the maximum Pd/Pa compared to the standard dose: 0.84 (0.81-0.93) versus 0.90 (0.83-0.95), P=0.007, while minimum Pd/Pa remained unaffected. High adenosine dose was adequately tolerated by all patients, without requiring infusion discontinuation in any case.

CONCLUSIONS

Pd/Pa variability is frequently observed during standard adenosine infusion and is significantly decreased following a high (200 μg/kg per minute) adenosine dose. This is achieved without a significant difference in the minimum Pd/Pa.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02350439.

Assessment of left anterior descending artery stenosis of intermediate severity by fractional flow reserve, instantaneous wave-free ratio, and non-invasive coronary flow reserve

To test the usefulness of non-invasive coronary flow reserve (CFR) by transthoracic Doppler echocardiography by comparison to invasive fractional flow reserve (FFR) and instantaneous wave-free ratio (IFR), a new vasodilator-free index of coronary stenosis severity, in patients with left anterior descending artery (LAD) stenosis of intermediate severity (IS) and stable coronary artery disease. 94 consecutive patients (mean age 68 ± 10 years) with angiographic LAD stenosis of IS (50-70 % diameter stenosis), were prospectively studied. IFR was calculated as a trans-lesion pressure ratio during the wave-free period in diastole; FFR as distal pressure divided by mean aortic pressure during maximal hyperemia (using 180 μg intracoronary adenosine); and CFR as hyperemic peak LAD flow velocity divided by baseline flow velocity using intravenous adenosine (140 μg/kg/min over 2 min). The mean values of IFR, FFR, and CFR were 0.88 ± 0.07, 0.81 ± 0.09, and 2.4 ± 0.6 respectively. A significant correlation was found between CFR and FFR (r = 0. 68), FFR and IFR (r = 0.6), and between CFR and IFR (r = 0.5) (all, p < 0.01). Using a ROC curve analysis, the best cut-off to detect a significant lesion based on FFR assessment (FFR ≤ 0.8, n = 31) was IFR ≤ 0.88 with a sensitivity (Se) of 74 %, specificity (Sp) of 73 %, AUC 0.81 ± 0.04, accuracy 72 %; and CFR ≤ 2 with a Se = 77 %, Sp = 89 %, AUC 0.88 ± 0.04, accuracy 85 % (all, p < 0.001). In stable patients with LAD stenosis of IS, non-invasive CFR is a useful tool to detect a significant lesion based on FFR. Furthermore, there was a better correlation between CFR and FFR than between CFR and IFR, and a trend to a better diagnostic performance for CFR versus IFR.

Diagnostic performance of instantaneous wave-free ratio for the evaluation of coronary stenosis severity confirmed by fractional flow reserve: A PRISMA-compliant meta-analysis of randomized studies

BACKGROUND

The instantaneous wave-free ratio (iFR) is a new vasodilator-free index of coronary stenosis severity. The aim of this meta-analysis is to assess the diagnostic performance of iFR for the evaluation of coronary stenosis severity with fractional flow reserve as standard reference.

METHODS

We searched PubMed, EMBASE, CENTRAL, ProQuest, Web of Science, and International Clinical Trials Registry Platform (ICTRP) for publications concerning the diagnostic value of iFR. We used a random-effects covariate to synthesize the available data of sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), and diagnostic odds ratio (DOR). Overall test performance was summarized by the summary receiver operating characteristic curve (sROC) and the area under the curve (AUC).

RESULTS

Eight studies with 1611 subjects were included in the meta-analysis. The pooled sensitivity, specificity, LR+, LR-, and DOR for iFR were respectively 73.3% (70.1-76.2%), 86.4% (84.3-88.3%), 5.71 (4.43-7.37), 0.29 (0.22-0.38), and 20.54 (16.11-26.20). The area under the summary receiver operating characteristic curves for iFR was 0.8786. No publication bias was identified.

CONCLUSION

The available evidence suggests that iFR may be a new, simple, and promising technology for coronary stenosis physiological assessment.

Effect of Varying Hemodynamic and Vascular Conditions on Fractional Flow Reserve: An In Vitro Study

Background

The aim of this study was to investigate the impact of varying hemodynamic conditions on fractional flow reserve (ratio of pressure distal [P_d] and proximal [P_a] to stenosis under hyperemia) in an in vitro setting. Failure to achieve maximal hyperemia and the choice of hyperemic agents may have differential effects on coronary hemodynamics and, consequently, on the determination of fractional flow reserve.

Methods and Results

An in vitro flow system was developed to experimentally model the physiological coronary circulation as flow‐dependent stenosis resistance in series with variable downstream resistance. Five idealized models with 30% to 70% diameter stenosis severity were fabricated using VeroClear rigid material in an Objet260 Connex printer. Mean aortic pressure was maintained at 7 levels (60–140 mm Hg) from hypotension to hypertension using a needle valve that mimicked adjustable microcirculatory resistance. A range of physiological flow rates was applied by a steady flow pump and titrated by a flow sensor. The pressure drop and the pressure ratio (P_d/P_a) were assessed for the 7 levels of aortic pressure and differing flow rates. The in vitro experimental data were coupled with pressure–flow relationships from clinical data for populations with and without myocardial infarction, respectively, to evaluate fractional flow reserve. The curve for pressure ratio and flow rate demonstrated a quadratic relationship with a decreasing slope. The absolute decrease in fractional flow reserve in the group without myocardial infarction (with myocardial infarction) was on the order of 0.03 (0.02), 0.05 (0.02), 0.07 (0.05), 0.17 (0.13) and 0.20 (0.24), respectively, for 30%, 40%, 50%, 60%, and 70% diameter stenosis, for an increase in aortic pressure from 60 to 140 mm Hg.

Conclusions

The fractional flow reserve value, an index of physiological stenosis significance, was observed to decrease with increasing aortic pressure for a given stenosis in this idealized in vitro experiment for vascular groups with and without myocardial infarction.

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.

Comparison of Ticagrelor Versus Thienopyridine Loading Effect on Fractional Flow Reserve in Patients With Coronary Artery Disease

Ticagrelor loading dose (LD) increases adenosine plasma levels, which might interfere with fractional flow reserve (FFR) assessment because the latter is based on adenosine-induced hyperemia. In a prospective study, consecutive patients who underwent coronary angiography with at least 1 de novo stenosis >50% and <90% in severity amenable to intervention underwent FFR assessment using intravenous adenosine 140 μg/kg/min for 3 minutes. Patients were subsequently randomized to either ticagrelor 180 mg (n = 38) or control thienopyridine (n = 38) (prasugrel 60 mg [n = 28] or clopidogrel 600 mg [n = 10]), followed by a second FFR assessment of the target lesion 2 hours after drug. Pre-drug, steady hyperemia FFR (sFFR, median, first to third quartiles) was 0.82 (0.75 to 0.88) and 0.81 (0.75 to 0.88), p = 0.9, whereas post-drug, 0.82 (0.72 to 0.87) and 0.79 (0.73 to 0.86), p = 0.5, in thienopyridine and ticagrelor-treated patients, respectively. The primary end point of percent relative change in sFFR between pre- and post-drug periods was greater in ticagrelor- than thienopyridine-treated patients, -1.24 (-5.54 to 0.0) versus -0.51 (-3.68 to 3.21), p = 0.03, respectively. Absolute change in sFFR between pre- and post-drug periods was marginally higher in ticagrelor- than thienopyridine-treated patients -0.01 (-0.04 to 0.0) versus -0.005 (-0.03 to 0.02), p = 0.048, respectively. Reclassification of treatment decision at the sFFR ≤ 0.80 cutoff post-drug occurred in 6 (15.8%) versus 5 (13.2%) of ticagrelor- and thienopyridine-treated patients, respectively. In conclusion, after ticagrelor LD, an absolute and relative reduction in sFFR compared with thienopyridine LD is observed. Administration of ticagrelor should be considered as a potential source, albeit minor, of FFR variability.

Fractional flow reserve-guided management in stable coronary disease and acute myocardial infarction: recent developments

Coronary artery disease (CAD) is a leading global cause of morbidity and mortality, and improvements in the diagnosis and treatment of CAD can reduce the health and economic burden of this condition. Fractional flow reserve (FFR) is an evidence-based diagnostic test of the physiological significance of a coronary artery stenosis. Fractional flow reserve is a pressure-derived index of the maximal achievable myocardial blood flow in the presence of an epicardial coronary stenosis as a ratio to maximum achievable flow if that artery were normal. When compared with standard angiography-guided management, FFR disclosure is impactful on the decision for revascularization and clinical outcomes. In this article, we review recent developments with FFR in patients with stable CAD and recent myocardial infarction. Specifically, we review novel developments in our understanding of CAD pathophysiology, diagnostic applications, prognostic studies, clinical trials, and clinical guidelines.

Limitations and Pitfalls of Fractional Flow Reserve Measurements and Adenosine-Induced Hyperemia

Coronary hemodynamic measurements provide a critical tool to assess the ischemic potential of coronary stenoses. Fractional flow reserve (FFR) is a reliable method to relate translesional coronary pressures to hyperemic myocardial blood flow. Although a basic understanding in FFR can be quickly achieved, many of the nuances and potential pitfalls require special attention. The authors discuss the practical setup of coronary pressure measurement, the most common pitfalls in technique and ways to avoid them, and the limitations of available pharmacologic hyperemic methods.

Evaluation of Microvascular Disease and Clinical Outcomes

Although coronary microcirculatory dysfunction occurs in numerous cardiac conditions and influences prognosis, it has been largely ignored in clinical practice due to the lack of adequate methods for its assessment. Microcirculatory dysfuntion may result from a variety of causes, including structural remodelling (arterioles or capillaries), dysregulation (paradoxical arteriolar vasoconstriction), hypersensitivity to vasoactive factors or adrenergic drive, and extravascular compression of collapsable elements. Thus, the selection of a method to interrogate coronary microcirculation should be based on the suspected cause of dysfunction. This article reviews such assessment tools and their prognostic information.

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.

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.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Pre-angioplasty instantaneous wave-free ratio pullback provides virtual intervention and predicts hemodynamic outcome for serial lesions and diffuse coronary artery disease

OBJECTIVES

The aim of this study was to perform hemodynamic mapping of the entire vessel using motorized pullback of a pressure guidewire with continuous instantaneous wave-free ratio (iFR) measurement.

BACKGROUND

Serial stenoses or diffuse vessel narrowing hamper pressure wire-guided management of coronary stenoses. Characterization of functional relevance of individual stenoses or narrowed segments constitutes an unmet need in ischemia-driven percutaneous revascularization.

METHODS

The study was performed in 32 coronary arteries with tandem and/or diffusely diseased vessels. An automated iFR physiological map, integrating pullback speed and physiological information, was built using dedicated software to calculate physiological stenosis severity, length, and intensity (ΔiFR/mm). This map was used to predict the best-case post-percutaneous coronary intervention (PCI) iFR (iFRexp) according to the stented location, and this was compared with the observed iFR post-PCI (iFRobs).

RESULTS

After successful PCI, the mean difference between iFRexp and iFRobs was small (mean difference: 0.016 ± 0.004) with a strong relationship between ΔiFRexp and ΔiFRobs (r = 0.97, p < 0.001). By identifying differing iFR intensities, it was possible to identify functional stenosis length and quantify the contribution of each individual stenosis or narrowed segment to overall vessel stenotic burden. Physiological lesion length was shorter than anatomic length (12.6 ± 1.5 vs. 23.3 ± 1.3, p < 0.001), and targeting regions with the highest iFR intensity predicted significant improvement post-PCI (r = 0.86, p < 0.001).

CONCLUSIONS

iFR measurements during continuous resting pressure wire pullback provide a physiological map of the entire coronary vessel. Before a PCI, the iFR pullback can predict the hemodynamic consequences of stenting specific stenoses and thereby may facilitate the intervention and stenting strategy.

Wave speed in human coronary arteries is not influenced by microvascular vasodilation: implications for wave intensity analysis

Wave intensity analysis and wave separation are powerful tools for interrogating coronary, myocardial and microvascular physiology. Wave speed is integral to these calculations and is usually estimated by the single-point technique (SPc), a feasible but as yet unvalidated approach in coronary vessels. We aimed to directly measure wave speed in human coronary arteries and assess the impact of adenosine and nitrate administration. In 14 patients, the transit time Δt between two pressure signals was measured in angiographically normal coronary arteries using a microcatheter equipped with two high-fidelity pressure sensors located Δs = 5 cm apart. Simultaneously, intracoronary pressure and flow velocity were measured with a dual-sensor wire to derive SPc. Actual wave speed was calculated as DNc = Δs/Δt. Hemodynamic signals were recorded at baseline and during adenosine-induced hyperemia, before and after nitroglycerin administration. The energy of separated wave intensity components was assessed using SPc and DNc. At baseline, DNc equaled SPc (15.9 ± 1.8 vs. 16.6 ± 1.5 m/s). Adenosine-induced hyperemia lowered SPc by 40 % (p < 0.005), while DNc remained unchanged, leading to marked differences in respective separated wave energies. Nitroglycerin did not affect DNc, whereas SPc transiently fell to 12.0 ± 1.2 m/s (p < 0.02). Human coronary wave speed is reliably estimated by SPc under resting conditions but not during adenosine-induced vasodilation. Since coronary wave speed is unaffected by microvascular dilation, the SPc estimate at rest can serve as surrogate for separating wave intensity signals obtained during hyperemia, thus greatly extending the scope of WIA to study coronary physiology in humans.