Comparative analysis of instantaneous wave-free ratio and quantitative real-time myocardial contrast echocardiography for the assessment of myocardial perfusion

Background and hypothesis

The field of coronary artery physiology is developing rapidly and changing the practice of interventional cardiology. A new functional evaluation technique using the instantaneous wave-free ratio (iFR) has become an alternative to fractional flow reserve. Future research studies need to determine whether physiological indicators play a role in evaluating myocardial perfusion in the catheter room.

Materials and methods

Thirty-eight patients scheduled for coronary angiography and iFR evaluation underwent a real-time myocardial contrast echocardiography (RT-MCE) examination at rest. The myocardial perfusion parameters (A, β, and A × β) on the myocardial perfusion curve were quantitatively analyzed using Q-Lab software. Coronary angiography and iFR assessment were completed within 1 week after the RT-MCE examination in all patients. Correlation analysis was used to identify iFR- and MCE-related indicators. The sensitivity and specificity of iFR in the quantitative detection of coronary microcirculation were obtained.

Results

The correlation coefficients between iFR and A, β, and A × β were 0.81, 0.66, and 0.82, respectively. The cut-off value for iFR was 0.85 for microvascular ischemia detection, while the sensitivity and specificity for the diagnosis of myocardial perfusion were 90.7 and 89.9%, respectively. The receiver operating characteristic (ROC) curve area for iFR was 0.946 in the segments related to myocardial blood flow.

Conclusion

The iFR is an effective tool for detecting myocardial microcirculation perfusion, with satisfactory diagnostic performance and a demonstrated role in physiological indices used for the perfusion assessment.

Calculation of Intracoronary Pressure-Based Indexes with JLabChart

The Fractional Flow Reserve (FFR) and instantaneous wave-Free Ratio (iFR) have been proposed and clinically validated to measure the pressure gradient across coronary stenoses. They provide quantitative information on stenosis severity. Both are used in coronary revascularization procedures to measure intracoronary pressure giving quantitative information to evaluate coronary diseases during angiographic procedures. We designed and implemented a tool able to acquire and measure iFR and FFR supporting the physicians studying and treating patients in interventional cardiology laboratories. We designed an extensive case study to assess the performance of the tool in (i) acquiring pressure signals from blood pressure measurement systems; (ii) calculating FFR and iFR; and (iii) filtering out extra-beats signals during realtime signal analysis phases. The tool, named JLabChart, is available online. We tested it on two sets of data for a total of 600 cycles from 201 pressure measurements performed on 65 patients, from the Interventional Cardiology Unit of Magna Graecia University. The recognition of cardiac cycles and keypoint of the pressure curve was effective in 100% of cases for proximal (aortic) pressure and in 99.2% for distal pressure. The FFR calculated by JLabChart had an excellent correlation (Rp=0.960; p<0.001) with the FFR values obtained through the commercial systems. Similar results were obtained with iFR (Rp=0.998; p<0.001). Finally, the tool measurement results were compared with a commercial tool proving JLabChart’s efficiency with real cases. It was also compared with measurements performed on synthetic vessels and stenosis designed using the Comsol commercial tool. JLabChart is able to provide reliable measurements of FFR and iFR indexes used to support decisions on interventional procedures. It represents a valuable open source support system that can be used in an interventional cardiology laboratory.

Correlation between fractional flow reserve and instantaneous wave-free ratio with morphometric assessment by optical coherence tomography in diabetic patients

Currently there is lack of data regarding the use of optical coherence tomography (OCT) to depict the hemodynamic relevance of coronary stenoses in diabetic patients. We sought to assess the diagnostic accuracy of OCT-derived morphologic assessment in identifying hemodynamically significant coronary lesions as determined by both, the resting instantaneous wave-free ratio (iFR) and the hyperemic fractional flow reserve (FFR) in diabetic patients. Diabetic patients presenting with at least one intermediate coronary lesion were prospectively and consecutively enrolled. All lesions were systematically assessed by iFR, FFR and OCT. A total of 41 intermediate lesions were analysed. Mean iFR and FFR values were 0.90 ± 0.04 and 0.81 ± 0.06, respectively (intra-class correlation coefficient 0.49; 95% CI 0.22-0.79). A moderate correlation between iFR and OCT derived minimal lumen diameter (MLD, r = 0.49) and minimal lumen area (MLA, r = 0.50) was found. Conversely, there was a poor correlation between FFR and OCT-derived MLD (r = 0.34) and MLA (r = 0.32). The diagnostic efficiency of MLA and MLD to identify iFR significant stenoses showed an AUC of 0.82 (95% CI 0.69-0.95) for MLD and 0.83 (95% CI 0.71-0.96) for MLA. A worse diagnostic efficiency was found when FFR was used as the reference with an AUC of 0.71 (95% CI 0.54-0.87) for MLD and 0.70 (95% CI 0.53-0.87). OCT-derived MLA and MLD were the strongest independent anatomic predictors of abnormal iFR and FFR values. In diabetic patients, OCT-derived MLA and MLD showed a moderate diagnostic efficiency in identifying functionally significant coronary stenoses by FFR or iFR. In diabetics, anatomic OCT measurements better predicted resting than FFR-determined physiologically significant lesions.

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.

Invasive physiological indices to determine the functional significance of coronary stenosis

Physiological measurements are now commonly used to assess coronary lesions in the cardiac catheterisation laboratory, and this practice is evidence-based and supported by clinical guidelines. Fractional flow reserve is currently the gold standard method to determine whether coronary lesions are functionally significant, and is used to guide revascularization. There are however several other physiological measurements that have been proposed as alternatives to the fractional flow reserve. This review aims to comprehensively discuss physiological indices that can be used in the cardiac catheterisation laboratory to determine the functional significance of coronary lesions. We will focus on their advantages and disadvantages, and the current evidence supporting their use.