Measurement from arteriograms of regional myocardial bed size distal to any point in the coronary vascular tree for assessing anatomic area at risk

Research on individualized distribution approach of coronary resting blood flow for noninvasive calculation of fractional flow reserve

BACKGROUND AND OBJECTIVES

The distribution of coronary resting blood flow is critical for accurately calculating the computed tomography (CT) angiography-derived fractional flow reserve (FFRCT). However, the diagnostic accuracy of FFRCT calculated by the fixed exponents between two risk factors and coronary resting blood flow, including myocardial mass and diameter of the coronary artery branch, was insufficient compared with invasive fractional flow reserve (FFR). In this study, we proposed the individualized distribution of coronary resting blood flow based on coronary ultrasound blood flow measurement, to improve the diagnostic accuracy of FFRCT calculation.

METHODS

Five risk factors and an unknown coefficient K were integrated to calculate the individualized distribution of coronary resting blood flow. The K value was fit using the least square method based on coronary ultrasound blood flow measurement results of 30 volunteers. We developed a novel approach for calculating the individualized distribution of coronary resting blood flow and applied it to calculate FFRCT (FFRCTI). Then, we tested the performance of the individualized distribution approach by comparing it with the approach proposed by Taylor based on coronary ultrasound blood flow measurement results of 13 volunteers. Finally, we tested the diagnostic accuracy of FFRCT calculated by two approaches in invasive FFR of 121 vessels with coronary stenosis.

RESULTS

We identified five risk factors and 6.83×10-5 for K value, including cardiac output, mean arterial pressure, myocardial mass, coronary artery volume, and diameter of the coronary artery branch, to calculate the individualized distribution of coronary resting blood flow. The mean square error of the individualized distribution approach (0.0088) was significantly less than that of the approach proposed by Taylor (0.0799). The diagnostic accuracy of FFRCTI calculated by the individualized distribution approach (91.74%) was higher than that of the approach proposed by Taylor (FFRCTT) (82.64%).

CONCLUSIONS

The individualized distribution approach of coronary resting blood flow can significantly improve the diagnostic accuracy of FFRCT calculation compared with invasive FFR, and support its wide clinical application for diagnosing myocardial ischemia caused by coronary stenosis.

Vessel-Specific Outcomes of Deferred Revascularization Following Negative Fractional Flow Reserve

Variations in myocardial supply area and hydrostatic pressure gradients result in greater likelihood of positive fractional flow reserve (FFR) in the left anterior descending (LAD) compared with the circumflex (Cx) and right coronary artery (RCA). However, the same FFR threshold for deferral of revascularization is applied to all arteries, without evidence that this results in equivalent outcomes. We assessed vessel-specific outcomes of deferred revascularization for the 3 major coronary arteries based on FFR > 0.8. In this retrospective study, data were obtained on consecutive patients who underwent indicated FFR assessment across 2 tertiary institutions. Patients with deferred revascularization were followed for 36 months for the primary end point of vessel-specific target lesion failure (TLF). Of 1,916 major coronary arteries (1,579 patients), the odds ratio of positive FFR was highest in the LAD (odds ratio 3.36, p <0.001). In total, 867 vessels (733 patients) with FFR > 0.8 had complete 3-year medical record follow-ups. The TLF rate for deferred vessels was 10.21%, 11.52%, and 10.96% for the LAD, Cx, and RCA respectively. In a multivariate analysis, there was no significant difference in the odds of TLF for the 0.84 (0.53 to 1.33, p = 0.459), 1.17 (0.68 to 2.01, p = 0.582), and 1.11 (0.62 to 2.00, p = 0.715) in the LAD, Cx, and RCA, respectively. In a multivariate analysis, diabetes mellitus was the only baseline characteristic significantly associated at risk of TLF (1.43 [1.01 to 2.02], p = 0.043). In conclusion, despite greater likelihood of positive FFR in the LAD, the FFR threshold for deferred revascularization resulted in equivalent outcomes in all 3 major coronary arteries, and patients with diabetes mellitus may represent a group that requires aggressive surveillance and risk factor modification after deferred revascularization.

Impact of coronary disease patterns, anatomical factors, micro-vascular disease and non-coronary cardiac factors on invasive coronary physiology

Invasive coronary physiology has been applied by interventional cardiologists to guide the management of coronary artery disease (CAD), with well-defined thresholds applied to determine whether CAD should be managed with optimal medical therapy (OMT) alone or OMT and percutaneous coronary intervention (PCI). There are multiple modalities in clinical use, including hyperaemic and non-hyperaemic indices. Despite endorsement in the major guidelines, there are various factors which impact and confound the readings of invasive coronary physiology, both within the coronary tree and beyond. This review article aims to summarise the mechanisms by which these factors impact invasive coronary physiology, and distinguish factors that contribute to ischaemia from confounding factors. The potential for mis-classification of ischaemic status is highlighted. Lastly, the authors identify targets for future research to improve the precision of physiology-guided management of CAD.

Recombinant Klotho Protein Ameliorates Myocardial Ischemia/Reperfusion Injury by Attenuating Sterile Inflammation

Currently, no effective therapy and potential target have been elucidated for preventing myocardial ischemia and reperfusion injury (I/R). We hypothesized that the administration of recombinant klotho (rKL) protein could attenuate the sterile inflammation in peri-infarct regions by inhibiting the extracellular release of high mobility group box-1 (HMGB1). This hypothesis was examined using a rat coronary artery ligation model. Rats were divided into sham, sham+ rKL, I/R, and I/R+ rKL groups (n = 5/group). Administration of rKL protein reduced infarct volume and attenuated extracellular release of HMGB1 from peri-infarct tissue after myocardial I/R injury. The administration of rKL protein inhibited the expression of pro-inflammatory cytokines in the peri-infarct regions and significantly attenuated apoptosis and production of intracellular reactive oxygen species by myocardial I/R injury. Klotho treatment significantly reduced the increase in the levels of circulating HMGB1 in blood at 4 h after myocardial ischemia. rKL regulated the levels of inflammation-related proteins. This is the first study to suggest that exogenous administration of rKL exerts myocardial protection effects after I/R injury and provides new mechanistic insights into rKL that can provide the theoretical basis for clinical application of new adjunctive modality for critical care of acute myocardial infarction.

Early Hyperdynamic Sepsis Alters Coronary Blood Flow Regulation in Porcine Fecal Peritonitis

Background: Sepsis is a common condition known to impair blood flow regulation and microcirculation, which can ultimately lead to organ dysfunction but such contribution of the coronary circulation remains to be clarified. We investigated coronary blood flow regulatory mechanisms, including autoregulation, metabolic regulation, and endothelial vasodilatory response, in an experimental porcine model of early hyperdynamic sepsis.

Methods: Fourteen pigs were randomized to sham (n = 7) or fecal peritonitis-induced sepsis (n = 7) procedures. At baseline, 6 and 12 h after peritonitis induction, the animals underwent general and coronary hemodynamic evaluation, including determination of autoregulatory breakpoint pressure and adenosine-induced maximal coronary vasodilation for coronary flow reserve and hyperemic microvascular resistance calculation. Endothelial-derived vasodilatory response was assessed both in vivo and ex vivo using bradykinin. Coronary arteries were sampled for pathobiological evaluation.

Results: Sepsis resulted in a right shift of the autoregulatory breakpoint pressure, decreased coronary blood flow reserve and increased hyperemic microvascular resistance from the 6th h after peritonitis induction. In vivo and ex vivo endothelial vasomotor function was preserved. Sepsis increased coronary arteries expressions of nitric oxide synthases, prostaglandin I₂ receptor, and prostaglandin F_2α receptor.

Conclusion: Autoregulation and metabolic blood flow regulation were both impaired in the coronary circulation during experimental hyperdynamic sepsis, although endothelial vasodilatory response was preserved.

Branch flow distribution approach and its application in the calculation of fractional flow reserve in stenotic coronary artery

OBJECTIVE

To calculate fractional flow reserve (FFR) based on computed tomography angiography (i.e., FFRCT) by considering the branch flow distribution in the coronary arteries.

BACKGROUND

FFR is the gold standard to diagnose myocardial ischemia caused by coronary stenosis. An accurate and noninvasive method for obtaining total coronary blood flow is needed for the calculation of FFRCT.

METHODS

A mathematical model for estimating the coronary blood flow rate and two approaches for setting the patient-specific flow boundary condition were proposed. Coronary branch flow distribution methods based on a volume-flow approach and a diameter-flow approach were employed for the numerical simulation of FFRCT. The values of simulated FFRCT for 16 patients were compared with their clinically measured FFR.

RESULTS

The ratio of total coronary blood flow to cardiac output and the myocardial blood flow under the condition of hyperemia were 16.97% and 4.07 mL/min/g, respectively. The errors of FFRCT compared with clinical data under the volume-flow approach and diameter-flow approach were 10.47% and 11.76%, respectively, the diagnostic accuracies of FFRCT were 65% and 85%, and the consistencies were 95% and 90%.

CONCLUSIONS

The mathematical model for estimating the coronary blood flow rate and the coronary branch flow distribution method can be applied to calculate the value of clinical noninvasive FFRCT.

Allometric scaling patterns among the human coronary artery tree, myocardial mass, and coronary artery flow

Human coronary artery tree is a physiological transport system for oxygen and vital materials through a hierarchical vascular network to match the energy demands of myocardium, which has the highest oxygen extraction ratio among body organs and heavily depends on the blood flow for its energy supply. Therefore, it would be reasonable to expect that the key design principle of this arterial network is to minimize energy expenditure, which can be described by allometric scaling law. We enrolled patients who underwent coronary computed tomography angiography without obstructive lesion. The cumulative arterial length (L), volume (V), and diameter (D) in relation to the artery-specific myocardial mass (M) were assessed. Flow rate (Q) was computed using quantitative flow ratio (QFR) measurement in patients who underwent invasive angiography. A total of 638 arteries from 43 patients (mean age 61 years, male gender 65%) were analyzed. A significant power-law relationship was found among L-M, V-M, D-M, V-L, D-L, and V-D, and also among Q-M, Q-L, Q-V, and Q-D in 106 arteries interrogated with QFR (p < .001, all). Our results suggest that the fundamental design principle of the human coronary arterial network may follow allometric scaling law.

Computed tomographic myocardial mass compared with invasive myocardial perfusion measurement

Objective

The prognostic importance of a coronary stenosis depends on its functional severity and its depending myocardial mass. Functional severity can be assessed by fractional flow reserve (FFR), estimated non-invasively by a specific validated CT algorithm (FFR_CT). Calculation of myocardial mass at risk by that same set of CT data (CTmass), however, has not been prospectively validated so far. The aim of the present study was to compare relative territorial-based CTmass assessment with relative flow distribution, which is closely linked to true myocardial mass.

Methods

In this exploratory study, 35 patients with (near) normal coronary arteries underwent CT scanning for computed flow-based CTmass assessment and underwent invasive myocardial perfusion measurement in all 3 major coronary arteries by continuous thermodilution. Next, the mass and flows were calculated as relative percentages of total mass and perfusion.

Results

The mean difference between CTmass per territory and invasively measured myocardial perfusion, both expressed as percentage of total mass and perfusion, was 5.3±6.2% for the left anterior descending territory, −2.0±7.4% for the left circumflex territory and −3.2±3.4% for the right coronary artery territory. The intraclass correlation between the two techniques was 0.90.

Conclusions

Our study shows a close relationship between the relative mass of the perfusion territory calculated by the specific CT algorithm and invasively measured myocardial perfusion. As such, these data support the use of CTmass to estimate territorial myocardium-at-risk in proximal coronary arteries.

Quantification of Myocardial Mass Subtended by a Coronary Stenosis Using Intracoronary Physiology

Background:

In patients with stable coronary artery disease, the amount of myocardium subtended by coronary stenoses constitutes a major determinant of prognosis, as well as of the benefit of coronary revascularization. We devised a novel method to estimate partial myocardial mass (PMM; ie, the amount of myocardium subtended by a stenosis) during physiological stenosis interrogation. Subsequently, we validated the index against equivalent PMM values derived from applying the Voronoi algorithm on coronary computed tomography angiography.

Methods:

Based on the myocardial metabolic demand and blood supply, PMM was calculated as follows: PMM (g)=APV×D 2 ×π/(1.24×10 − 3 ×HR×sBP+1.6), where APV indicates average peak blood flow velocity; D, vessel diameter; HR, heart rate; and sBP, systolic blood pressure. We calculated PMM to 43 coronary vessels (32 patients) interrogated with pressure and Doppler guidewires, and compared it with computed tomography–based PMM.

Results:

Median PMM was 15.8 g (Q1, Q3: 11.7, 28.4 g) for physiology-based PMM, and 17.0 g (Q1, Q3: 12.5, 25.9 g) for computed tomography–based PMM ( P =0.84). Spearman rank correlation coefficient was 0.916 ( P <0.001), and Passing-Bablok analysis revealed absence of both constant and proportional differences (coefficient A: −0.9; 95% CI, −4.5 to 0.9; and coefficient B, 1.00; 95% CI, 0.91 to 1.25]. Bland-Altman analysis documented a mean bias of 0.5 g (limit of agreement: −9.1 to 10.2 g).

Conclusions:

Physiology-based calculation of PMM in the catheterization laboratory is feasible and can be accurately performed as part of functional stenosis assessment.

Time-Dependent Myocardial Necrosis in Patients With ST-Segment-Elevation Myocardial Infarction Without Angiographic Collateral Flow Visualized by Cardiac Magnetic Resonance Imaging: Results From the Multicenter STEMI-SCAR Project

Background Acute complete occlusion of a coronary artery results in progressive ischemia, moving from the endocardium to the epicardium (ie, wavefront). Dependent on time to reperfusion and collateral flow, myocardial infarction ( MI ) will manifest, with transmural MI portending poor prognosis. Late gadolinium enhancement cardiac magnetic resonance imaging can detect MI with  high diagnostic accuracy. Primary percutaneous coronary intervention is the preferred reperfusion strategy in patients with ST -segment-elevation MI with <12 hours of symptom onset. We sought to visualize time-dependent necrosis in a population with ST -segment-elevation MI by using late gadolinium enhancement cardiac magnetic resonance imaging (STEMI-SCAR project). Methods and Results ST -segment-elevation MI patients with single-vessel disease, complete occlusion with TIMI (Thrombolysis in Myocardial Infarction) score 0, absence of collateral flow (Rentrop score 0), and symptom onset <12 hours were consecutively enrolled. Using late gadolinium enhancement cardiac magnetic resonance imaging, the area at risk and infarct size, myocardial salvage index, transmurality index, and transmurality grade (0-50%, 51-75%, 76-100%) were determined. In total, 164 patients (aged 54±11 years, 80% male) were included. A receiver operating characteristic curve (area under the curve: 0.81) indicating transmural necrosis revealed the best diagnostic cutoff for a symptom-to-balloon time of 121 minutes: patients with >121 minutes demonstrated increased infarct size, transmurality index, and transmurality grade (all P<0.01) and decreased myocardial salvage index ( P<0.001) versus patients with symptom-to-balloon times ≤121 minutes. Conclusions In MI with no residual antegrade and no collateral flow, immediate reperfusion is vital. A symptom-to-balloon time of >121 minutes causes a high grade of transmural necrosis. In this pure ST -segment-elevation MI population, time to reperfusion to salvage myocardium was less than suggested by current guidelines.

Diagnostic performance of the quantification of myocardium at risk from MPI SPECT/CTA 2G fusion for detecting obstructive coronary disease: A multicenter trial

BACKGROUND

The effective non-invasive identification of coronary artery disease (CAD) and its proper referral for invasive treatment are still unresolved issues. We evaluated our quantification of myocardium at risk (MAR) from our second generation 3D MPI/CTA fusion framework for the detection and localization of obstructive coronary disease.

METHODS

Studies from 48 patients who had rest/stress MPI, CTA, and ICA were analyzed from 3 different institutions. From the CTA, a 3D biventricular surface of the myocardium with superimposed coronaries was extracted and fused to the perfusion distribution. Significant lesions were identified from CTA readings and positioned on the fused display. Three estimates of MAR were computed on the 3D LV surface on the basis of the MPI alone (MARp), the CTA alone (MARa), and the fused information (MARf). The extents of areas at risk were used to generate ROC curves using ICA anatomical findings as reference standard.

RESULTS

Areas under the ROC curve (AUC) for CAD detection using MARf was 0.88 (CI = 0.75-0.95) and for MARp and MARa were, respectively 0.82 (CI = 0.69-0.92) and 0.75 (CI = 0.60-0.86) using the ≥70% stenosis criterion. AUCs for CAD localization (all vessels) using MARf showed significantly higher performance than either MARa or MARp or both.

CONCLUSIONS

Using ICA as the reference standard, MAR as the quantitative parameter, and AUC to measure diagnostic performance, MPI-CTA fusion imaging provided incremental diagnostic information compared to MPI or CTA alone for the diagnosis and localization of CAD.

Comparison of Computed Tomography derived Fractional Flow Reserve to invasive Fractional Flow Reserve in Diagnosis of Functional Coronary Stenosis: A Meta-Analysis

Computed Tomography derived Fractional Flow Reserve (CTFFR) is an emerging non-invasive imaging modality to assess functional significance of coronary stenosis. We performed a meta-analysis to compare the diagnostic performance of CTFFR to invasive Fractional Flow reserve (FFR). Electronic search was performed to identify relevant articles. Pooled Estimates of sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-) and diagnostic odds ratio (DOR) with corresponding 95% confidence intervals (CI) were calculated at the patient level as well as the individual vessel level using hierarchical logistic regression, summary receiver operating characteristic (SROC) curve and area under the curve were estimated. Our search yielded 559 articles and of these 17 studies was included in the analysis. A total of 2,191 vessels in 1294 patients were analyzed. Pooled estimates of sensitivity, specificity, LR+, LR- and DOR with corresponding 95% CI at per-patient level were 83% (79-87), 72% (68-76), 3.0 (2.6-3.5), 0.23 (0.18-0.29) and 13 (9-18) respectively. Pooled estimates of sensitivity, specificity, LR+, LR- and DOR with corresponding 95% CI at per-vessel level were 85% (83-88), 76% (74-79), 3.6 (3.3-4.0), 0.19 (0.16-0.22) and 19 (15-24). The area under the SROC curve was 0.89 for both per patient level and at the per vessel level. In our meta-analysis, CTFFR demonstrated good diagnostic performance in identifying functionally significant coronary artery stenosis compared to the FFR.

Quantification of vessel-specific coronary perfusion territories using minimum-cost path assignment and computed tomography angiography: Validation in a swine model

BACKGROUND

As combined morphological and physiological assessment of coronary artery disease (CAD) is necessary to reliably resolve CAD severity, the objective of this study was to validate an automated minimum-cost path assignment (MCP) technique which enables accurate, vessel-specific assignment of the left (LCA) and right (RCA) coronary perfusion territories using computed tomography (CT) angiography data for both left and right ventricles.

METHODS

Six swine were used to validate the MCP technique. In each swine, a dynamic acquisition comprised of twenty consecutive volume scans was acquired with a 320-slice CT scanner following peripheral injection of contrast material. From this acquisition the MCP technique was used to automatically assign LCA and RCA perfusion territories for the left and right ventricles, independently. Each animal underwent another dynamic CT acquisition following direct injection of contrast material into the LCA or RCA. Using this acquisition, reference standard LCA and RCA perfusion territories were isolated from the myocardial blush. The accuracy of the MCP technique was evaluated by quantitatively comparing the MCP-derived LCA and RCA perfusion territories to these reference standard territories.

RESULTS

All MCP perfusion territory masses (Mass_MCP) and all reference standard perfusion territory masses (Mass_RS) in the left ventricle were related by Mass_MCP = 0.99Mass_RS+0.35 g (r = 1.00). Mass_MCP and Mass_RS in the right ventricle were related by Mass_MCP = 0.94Mass_RS+0.39 g (r = 0.96).

CONCLUSION

The MCP technique was validated in a swine animal model and has the potential to be used for accurate, vessel-specific assignment of LCA and RCA perfusion territories in both the left and right ventricular myocardium using CT angiography data.

Fractional Flow Reserve or Coronary Flow Reserve for the Assessment of Myocardial Perfusion : Implications of FFR as an Imperfect Reference Standard for Myocardial Ischemia

Purpose of Review

Accumulating evidence exists for the value of coronary physiology for clinical decision-making in ischemic heart disease (IHD). The most frequently used pressure-derived index to assess stenosis severity, the fractional flow reserve (FFR), has long been considered the gold standard for this purpose, despite the fact that the FFR assesses solely epicardial stenosis severity and aims to estimate coronary flow impairment in the coronary circulation. The coronary flow reserve (CFR) directly assesses coronary blood flow in the coronary circulation, including both the epicardial coronary artery and the coronary microvasculature, but is nowadays less established than FFR. It is now recognized that both tools may provide insight into the pathophysiological substrate of ischemic heart disease, and that particularly combined FFR and CFR measurements provide a comprehensive insight into the multilevel involvement of IHD. This review discusses the diagnostic and prognostic characteristics, as well as future implications of combined assessment of FFR and CFR pressure and flow measurements as parameters for inducible ischemia.

Recent Findings

FFR and CFR disagree in up to 40% of all cases, giving rise to fundamental questions regarding the role of FFR in contemporary ischemic heart disease management, and implying a renewed approach in clinical management of these patients using combined coronary pressure and flow measurement to allow appropriate identification of patients at risk for cardiovascular events.

Summary

This review emphasizes the value of comprehensive coronary physiology measurements in assessing the pathophysiological substrate of IHD, and the importance of acknowledging the broad spectrum of epicardial and microcirculatory involvement in IHD. Increasing interest and large clinical trials are expected to further strengthen the potential of advanced coronary physiology in interventional cardiology, consequently inducing reconsideration of current clinical guidelines.

Diagnostic performance of two corrected transluminal attenuation gradient metrics in coronary CT angiography for the evaluation of significant in-stent restenosis by dual-source CT: a validation study with invasive coronary angiography

AIM

To determine the diagnostic potential of transluminal attenuation gradients (TAG) with exclusion of stented coronary segments (TAG-ExS) and TAG-corrected contrast opacification (CCO) excluding stented coronary segments (TAG-CCO-ExS) for the assessment of in-stent restenosis (ISR).

MATERIALS AND METHODS

TAG-ExS and TAG-CCO-ExS were calculated in 93 coronary arteries with 190 stents. The diagnostic performances and the incremental values of the two metrics to coronary computed tomography angiography (CCTA) were analysed and compared.

RESULTS

For all stents and stents >3 mm in diameter, TAG-ExS and TAG-CCO-ExS were significantly lower in ≥50% than that in <50% of ISR (both p<0.05). For stent diameters ≤3 mm, significantly lower TAG-CCO-ExS (p=0.000), but not TAG-ExS (p=0.059), was found in ≥50% than in <50% of ISR. Addition of TAG-ExS or TAG-CCO-ExS to CCTA, did not improve the diagnostic accuracy of CCTA significantly (all p>0.05). Only TAG-CCO-ExS had a significant impact on CCTA for the reclassifications of ISR (p=0.046) in stent diameters ≤3 mm.

CONCLUSIONS

TAG-ExS and TAG-CCO-ExS did not provide incremental diagnostic value over CCTA in assessing ISR. TAG-CCO-ExS slightly enhanced the reclassifications of ISR for stents ≤3 mm in diameter.

Myocardial Mass Contributes to the Discrepancy Between Anatomic Stenosis Severity Assessed by Intravascular Ultrasound and Fractional Flow Reserve in Intermediate Lesions of the Coronary Artery

OBJECTIVES

The present study investigated the major contributors to the discrepancy between the minimal lumen area (MLA) and fractional flow reserve (FFR).

BACKGROUND

There was considerable discrepancy between MLA or diameter stenosis (DS) and FFR.

METHODS

We enrolled 744 patients with intermediate stenoses of the left anterior descending artery (LAD). Summed epicardial coronary artery length distal to the target stenosis was obtained from each longest view of the vessels on the coronary angiograms. Mismatching was defined as a lesion with FFR of >0.80 and MLA smaller than the best cut-off value (BCV) for predicting FFR of ≤0.80. Reverse mismatching was defined as a lesion with FFR of ≤0.80 and MLA larger than the BCV.

RESULTS

Summed epicardial coronary artery length was longer at the lesions of proximal LAD than that of middle LAD (380 mm ± 82 mm vs. 341 mm ± 80 mm, P < 0.001). Reverse mismatching was found more frequently in the proximal than middle LAD (28.3% vs. 5.5%, P < 0.001). Independent predictors of FFR ≤ 0.80 were age, male, multi-vessel disease, proximal LAD lesion, MLA, DS, plaque burden at distal reference, lesion length and summed epicardial coronary artery length. Proximal LAD lesion was an independent predictor of reverse mismatching (hazard ratio 3.162, 1.858-5.382, P < 0.001).

CONCLUSIONS

Myocardial mass subtended by a lesion is an important factor predicting FFR ≤0.80 and discrepancy between FFR and MLA. Myocardial mass subtended by a lesion should be considered when determining the revascularization therapy by intravascular ultrasound parameters. © 2017 Wiley Periodicals, Inc.

Targeting the dominant mechanism of coronary microvascular dysfunction with intracoronary physiology tests

The coronary microcirculation plays a key role in modulating blood supply to the myocardium. Several factors like myocardial oxygen demands, endothelial and neurogenic conditions determine its function. Although there is available evidence supporting microvascular dysfunction as an important cause of myocardial ischaemia, with both prognostic and symptomatic implications, its diagnosis and management in clinical practice is still relegated to a second plane. Both diagnostic and therapeutic approaches are hampered by the broadness of the concept of microvascular dysfunction, which fails addressing the plurality of mechanisms leading to dysfunction. Normal microcirculatory function requires both structural integrity of the microcirculatory vascular network and preserved signalling pathways ensuring adequate and brisk arteriolar resistance shifts in response to myocardial oxygen demands. Pathological mechanisms affecting these requirements include structural remodelling of microvessels, intraluminal plugging, extravascular compression or vasomotor dysregulation. Importantly, not every diagnostic technique provides evidence on which of these pathophysiological mechanisms is present or predominates in the microcirculation. In this paper we discuss the mechanisms of coronary microvascular dysfunction and the intracoronary tools currently available to detect it, as well as the potential role of each one to unmask the main underlying mechanism.

Coronary flow capacity: concept, promises, and challenges

The vasodilator capacity of the coronary circulation is an important diagnostic and prognostic characteristic, and its accurate assessment is therefore an important frontier. The coronary flow capacity (CFC) concept was introduced to overcome the limitations associated with the use of coronary flow reserve (CFR) for this purpose, which are related to the sensitivity of CFR to physiological alterations in systemic and coronary hemodynamics. CFC was developed from positron emission tomography, and was subsequently extrapolated to invasive coronary physiology. These studies suggest that CFC is a robust framework for the identification of clinically relevant coronary flow abnormalities, and improves identification of patients at risk for adverse events over the use of CFR alone. This Review will discuss the concept of CFC, its promises in the setting of ischaemic heart disease, and its challenges both in theoretical and practical terms.

Noninvasive FFR derived from coronary CT angiography in the management of coronary artery disease: technology and clinical update

After a decade of clinical use of coronary computed tomographic angiography (CCTA) to evaluate the anatomic severity of coronary artery disease, new methods of deriving functional information from CCTA have been developed. These methods utilize the anatomic information provided by CCTA in conjunction with computational fluid dynamics to calculate fractional flow reserve (FFR) values from CCTA image data sets. Computed tomography-derived FFR (CT-FFR) enables the identification of lesion-specific drop noninvasively. A three-dimensional CT-FFR modeling technique, which provides FFR values throughout the coronary tree (HeartFlow FFR_CT analysis), has been validated against measured FFR and is now approved by the US Food and Drug Administration for clinical use. This technique requires off-site supercomputer analysis. More recently, a one-dimensional computational analysis technique (Siemens cFFR), which can be performed on on-site workstations, has been developed and is currently under investigation. This article reviews CT-FFR technology and clinical evidence for its use in stable patients with suspected coronary artery disease.

Better Diagnosis of Functionally Significant Intermediate Sized Narrowings Using Intravascular Ultrasound-Minimal Lumen Area and Coronary Computed Tomographic Angiography-Based Myocardial Segmentation

Lesion morphology poorly predicts functional significance of intermediate coronary artery stenosis. The aim of this study was to determine whether a coronary artery-based myocardial segmentation method that quantifies subtended myocardium can improve the diagnostic accuracy of intravascular ultrasound (IVUS)-derived parameters for detecting ischemia-producing lesions. Coronary computed tomography angiography, IVUS, and fractional flow reserve (FFR) data were analyzed in 101 non-left main lesions (20% to 80% angiographic stenosis). Using the coronary artery-based myocardial segmentation method, total left ventricular myocardial volume (Vtotal), myocardial volume subtended by the stenotic coronary segment (Vsub), and Vratio (the ratio of the Vsub to the Vtotal) were assessed. Both Vsub >30.7 cm(3) and Vratio >25.4% were determinants of FFR ≤0.75 (area under the curve = 0.696 and 0.744). Overall, an IVUS-measured minimum lumen area (IVUS-MLA) ≤2.83 mm(2) predicted FFR ≤0.75 with a sensitivity 88% and specificity 73%. Among lesions with IVUS-MLA ≤2.83 mm(2) and FFR >0.75, 89% showed Vsub <30.7 cm(3). In 50 lesions with Vsub >30.7 cm(3), an IVUS-MLA ≤2.85 mm(2) predicted FFR ≤0.75 with sensitivity 85%, specificity 92%, positive predictive value 92%, and negative predictive value 85%. Conversely, in 51 lesions with a Vsub ≤30.7 cm(3), IVUS-MLA ≤2.67 mm(2) showed sensitivity 100%, specificity 69%, positive predictive value 38%, and negative predictive value 100% for predicting FFR ≤0.75. Body surface area, reference lumen diameter, and vessel area had modest correlations with Vsub. In those lesion subsets, IVUS-MLA ≈2.8 mm(2) accurately predicted an FFR ≤0.75, whereas the clinical relevance of assessing and treating lesions with a smaller myocardial territory may be limited (ClinicalTrials.gov number NCT1696006).

Reproducibility and clinical potential of myocardial mass at risk calculated by a novel software utilizing cardiac computed tomography information

To select the best revascularization strategy a correct understanding of the ischemic territory and the coronary anatomy is crucial. Stress myocardial perfusion single photon emission computed tomography (SPECT) is the gold standard to assess ischemia, however, SPECT has important limitations such as lack of coronary anatomical information or false negative results due to balanced ischemia in multi-vessel disease. Angiographic scores are based on anatomical characteristics of coronary arteries but they lack information on the extent of jeopardized myocardium. Cardiac computed tomography (CCT) has the ability to evaluate the coronary anatomy and myocardium in one sequence, which is theoretically the ideal method to assess the myocardial mass at risk (MMAR) for any target lesion located at any point in the coronary tree. In this study we analyzed MMAR of the three main coronary arteries and three major side branches; diagonal (Dx), obtuse marginal (OM), and posterior descending artery (PDA) in 42 patients with normal coronary arteries using an algorithm based on the Voronoi method. The distribution of MMAR among the three main coronary arteries was 44.3 ± 5.6 % for the left anterior descending artery, 28.2 ± 7.3 % for the left circumflex artery, and 26.8 ± 8.6 % for the right coronary artery. MMAR of the three major side branches was 11.3 ± 3.9 % for the Dx, 12.6 ± 5.2 % for the OM and 10.2 ± 3.4 % for the PDA. Intra- and inter-observer analysis showed excellent correlation (r = 0.97; p < 0.0001 and r = 0.95; p < 0.0001, respectively). In conclusion, CCT-based MMAR assessment is reliable and may offer important information for selection of the optimal revascularization procedure.

Growth, ageing and scaling laws of coronary arterial trees

Despite the well-known design principles of vascular systems, it is unclear whether the vascular arterial tree obeys some scaling constraints during normal growth and ageing in a given species. Based on the micro-computed tomography measurements of coronary arterial trees in mice at different ages (one week to more than eight months), we show a constant exponent of 3/4, but age-dependent scaling coefficients in a length-volume scaling law (Lc=K(length-volume) · Vc³/⁴; Lc is the crown length, Vc is the crown volume, K(length-volume) is the age-dependent scaling coefficient) during normal growth and ageing. The constant 3/4 exponent represents the self-similar fractal-like branching pattern (i.e. basic mechanism to regulate the development of vascular trees within a species), whereas the age-dependent scaling coefficients characterize the structural growth or resorption of vascular trees during normal growth or ageing, respectively. This study enhances the understanding of age-associated changes in vascular structure and function.

Fundamentals in clinical coronary physiology: why coronary flow is more important than coronary pressure

Wide attention for the appropriateness of coronary stenting in stable ischaemic heart disease (IHD) has increased interest in coronary physiology to guide decision making. For many, coronary physiology equals the measurement of coronary pressure to calculate the fractional flow reserve (FFR). While accumulating evidence supports the contention that FFR-guided revascularization is superior to revascularization based on coronary angiography, it is frequently overlooked that FFR is a coronary pressure-derived estimate of coronary flow impairment. It is not the same as the direct measures of coronary flow from which it was derived, and which are critical determinants of myocardial ischaemia. This review describes why coronary flow is physiologically and clinically more important than coronary pressure, details the resulting limitations and clinical consequences of FFR-guided clinical decision making, describes the scientific consequences of using FFR as a gold standard reference test, and discusses the potential of coronary flow to improve risk stratification and decision making in IHD.

CT-based diagnosis of diffuse coronary artery disease on the basis of scaling power laws

PURPOSE

To provide proof of concept for a diagnostic method to assess diffuse coronary artery disease (CAD) on the basis of coronary computed tomography (CT) angiography.

MATERIALS AND METHODS

The study was approved by the Cleveland Clinic Institutional Review Board, and all subjects gave informed consent. Morphometric data from the epicardial coronary artery tree, determined with CT angiography in 120 subjects (89 patients with metabolic syndrome and 31 age- and sex-matched control subjects) were analyzed on the basis of the scaling power law. Results obtained in patients with metabolic syndrome and control subjects were compared statistically.

RESULTS

The mean lumen cross-sectional area (ie, lumen cross-sectional area averaged over each vessel of an epicardial coronary artery tree) and sum of intravascular volume in patients with metabolic syndrome (0.039 cm(2) ± 0.015 [standard deviation] and 2.71 cm(3) ± 1.75, respectively) were significantly less than those in control subjects (0.054 cm(2)± 0.015 and 3.29 cm(3)± 1.77, respectively; P < .05). The length-volume power law showed coefficients of 27.0 cm(-4/3) ± 9.0 (R(2) = 0.91 ± 0.08) for patients with metabolic syndrome and 19.9 cm(-4/3) ± 4.3 (R(2) = 0.92 ± 0.07) for control subjects (P < .05). The probability frequency shows that more than 65% of patients with metabolic syndrome had a coefficient of 23 or more for the length-volume scaling power law, whereas approximately 90% of the control subjects had a coefficient of less than 23.

CONCLUSION

The retrospective scaling analysis provides a quantitative rationale for diagnosis of diffuse CAD.

Quantification of myocardial area at risk in the absence of collateral flow: the validation of angiographic scores by myocardial perfusion single-photon emission computed tomography

OBJECTIVES

Our study aimed to compare the area at risk (AAR) determined by single-photon emission computed tomography (SPECT) with the Bypass Angioplasty Revascularization Investigation (BARI) and modified Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH) angiographic scores in the setting of patients undergoing coronary angioplasty for either unstable angina or an STEMI.

BACKGROUND

Radionuclide myocardial perfusion imaging prior to reperfusion has classically been the most widely practised technique for assessing the AAR and has been successfully used to compare the efficacy of various reperfusion strategies in patients with an ST-segment elevation myocardial infarction (STEMI). The BARI and modified APPROACH scores are angiographic methods widely used to provide a rapid estimation of the AAR; however, they have not been directly validated with myocardial perfusion single-photon emission computed tomography (SPECT).

METHODS

Fifty-five patients with no previous myocardial infarction who underwent coronary angioplasty for single-vessel disease (unstable angina: n = 25 or an STEMI: n = 30) with no evidence of collaterals (Rentrop Collateral Score <2) were included in a prospective study. In STEMI patients, the (99m)Tc-tetrofosmin was injected prior to opening of the occluded vessel and, in patients with unstable angina after 10-15 seconds of balloon inflation. Acquisition was performed with a dual-head gammacamera with a low-energy and high-resolution collimator. A total of 60 projections were acquired using a non-circular orbit. No attenuation or scatter correction was used. Maximal contours of hypoperfusion regions corresponding to each coronary artery occlusion were delineated over a polar map of 17 segments and compared with the estimated AAR determined by two experienced interventional cardiologists using both angiographic scores.

RESULTS

Mean AAR percentage in SPECT was 35.0 (10.0%-56.0%). A high correlation was found between BARI and APPROACH scores (r = 0.9, P < .001). Furthermore, a high correlation was also observed between BARI versus SPECT and APPROACH versus SPECT to estimate the AAR (r = 0.9, P < .001 and r = 0.8, P < .001, respectively). Better correlations were observed when the left anterior descending artery (LAD) was revascularized (r = 0.8, P < 0.001 with BARI; r = 0.8, P = .001 with APPROACH) compared to other territories (r = 0.8, P = .001 with BARI; r = 0.7, P = .001 with APPROACH). Also, better correlations were observed in patients who underwent an elective rather than a primary percutaneous revascularization procedure.

CONCLUSIONS

In the absence of collateral flow, BARI and APPROACH scores constitute valid methods for AAR estimation in current clinical practice, with more accurate results when used for the LAD territory; both are useful not only in STEMI patients but also in patients with unstable angina.

3D Imaging of vascular networks for biophysical modeling of perfusion distribution within the heart

One of the main determinants of perfusion distribution within an organ is the structure of its vascular network. Past studies were based on angiography or corrosion casting and lacked quantitative three dimensional, 3D, representation. Based on branching rules and other properties derived from such imaging, 3D vascular tree models were generated which were rather useful for generating and testing hypotheses on perfusion distribution in organs. Progress in advanced computational models for prediction of perfusion distribution has raised the need for more realistic representations of vascular trees with higher resolution. This paper presents an overview of the different methods developed over time for imaging and modeling the structure of vascular networks and perfusion distribution, with a focus on the heart. The strengths and limitations of these different techniques are discussed. Episcopic fluorescent imaging using a cryomicrotome is presently being developed in different laboratories. This technique is discussed in more detail, since it provides high-resolution 3D structural information that is important for the development and validation of biophysical models but also for studying the adaptations of vascular networks to diseases. An added advantage of this method being is the ability to measure local tissue perfusion. Clinically, indices for patient-specific coronary stenosis evaluation derived from vascular networks have been proposed and high-resolution noninvasive methods for perfusion distribution are in development. All these techniques depend on a proper representation of the relevant vascular network structures.

Estimation of Myocardial Volume at Risk from CT Angiography

The determination of myocardial volume at risk distal to coronary stenosis provides important information for prognosis and treatment of coronary artery disease. In this paper, we present a novel computational framework for estimating the myocardial volume at risk in computed tomography angiography (CTA) imagery. Initially, epicardial and endocardial surfaces, and coronary arteries are extracted using an active contour method. Then, the extracted coronary arteries are projected onto the epicardial surface, and each point on this surface is associated with its closest coronary artery using the geodesic distance measurement. The likely myocardial region at risk on the epicardial surface caused by a stenosis is approximated by the region in which all its inner points are associated with the sub-branches distal to the stenosis on the coronary artery tree. Finally, the likely myocardial volume at risk is approximated by the volume in between the region at risk on the epicardial surface and its projection on the endocardial surface, which is expected to yield computational savings over risk volume estimation using the entire image volume. Furthermore, we expect increased accuracy since, as compared to prior work using the Euclidean distance, we employ the geodesic distance in this work. The experimental results demonstrate the effectiveness of the proposed approach on pig heart CTA datasets.

Estimation of coronary artery hyperemic blood flow based on arterial lumen volume using angiographic images

The purpose of this study is to develop a method to estimate the hyperemic blood flow in a coronary artery using the sum of the distal lumen volumes in a swine animal model. The limitations of visually assessing coronary artery disease are well known. These limitations are particularly important in intermediate coronary lesions where it is difficult to determine whether a particular lesion is the cause of ischemia. Therefore, a functional measure of stenosis severity is needed using angiographic image data. Coronary arteriography was performed in 10 swine (Yorkshire, 25-35 kg) after power injection of contrast material into the left main coronary artery. A densitometry technique was used to quantify regional flow and lumen volume in vivo after inducing hyperemia. Additionally, 3 swine hearts were casted and imaged post-mortem using cone-beam CT to obtain the lumen volume and the arterial length of corresponding coronary arteries. Using densitometry, the results showed that the stem hyperemic flow (Q) and the associated crown lumen volume (V) were related by Q = 159.08 V(3/4) (r = 0.98, SEE = 10.59 ml/min). The stem hyperemic flow and the associated crown length (L) using cone-beam CT were related by Q = 2.89 L (r = 0.99, SEE = 8.72 ml/min). These results indicate that measured arterial branch lengths or lumen volumes can potentially be used to predict the expected hyperemic flow in an arterial tree. This, in conjunction with measured hyperemic flow in the presence of a stenosis, could be used to predict fractional flow reserve based entirely on angiographic data.

Coronary pressure measurement based decision making for percutaneous coronary intervention

The fractional flow reserve (FFR) is a simple, reliable, and reproducible physiologic index of lesion severity. In patients with intermediate stenosis, FFR≥0.75 can be used to safely defer percutaneous coronary intervention (PCI), and patients with FFR≥0.75 have a very low cardiac event rate. Coronary pressure measurement can determine which lesion should be treated with PCI in patients with tandem lesions, and PCI on the basis of FFR has been demonstrated to result in an acceptably low repeat PCI rate. FFR can identify patients with equivocal left main coronary artery disease who benefit from coronary bypass surgery. Coronary pressure measurement distinguishes patients with an abrupt pressure drop pattern from those with a gradual pressure drop pattern, and the former group of patients benefit from PCI. Coronary pressure measurement is clinically useful in evaluating sufficient recruitable coronary collateral blood flow for prevention of ischemia, which affects future cardiac events. FFR is useful for the prediction of restenosis after PCI. As an end-point of PCI, FFR ≥0.95 and ≥0.90 would be appropriate for coronary stenting and coronary angioplasty, respectively. In summary, if you encounter a coronary stenosis in doubt you should measure pressure rather than dilate it.

Extraction of morphometry and branching angles of porcine coronary arterial tree from CT images

The morphometry (diameters, length, and angles) of coronary arteries is related to their function. A simple, easy, and accurate image-based method to seamlessly extract the morphometry for coronary arteries is of significant value for understanding the structure-function relation. Here, the morphometry of large (> or = 1 mm in diameter) coronary arteries was extracted from computed tomography (CT) images using a recently validated segmentation algorithm. The coronary arteries of seven pigs were filled with Microfil, and the cast hearts were imaged with CT. The centerlines of the extracted vessels, the vessel radii, and the vessel lengths were identified for over 700 vessel segments. The extraction algorithm was based on a topological analysis of a vector field generated by normal vectors of the extracted vessel wall. The diameters, lengths, and angles of the right coronary artery, left anterior descending coronary artery, and left circumflex artery of all vessels > or = 1 mm in diameter were tabulated for the respective orders. It was found that bifurcations at orders 9-11 are planar ( approximately 90%). The relations between volume and length and area and length were also examined and found to scale as power laws. Furthermore, the bifurcation angles follow the minimum energy hypothesis but with significant scatter. Some of the applications of the semiautomated extraction of morphometric data in applications to coronary physiology and pathophysiology are highlighted.

Differences in cardiac microcirculatory wave patterns between the proximal left mainstem and proximal right coronary artery

Despite having almost identical origins and similar perfusion pressures, the flow-velocity waveforms in the left and right coronary arteries are strikingly different. We hypothesized that pressure differences originating from the distal (microcirculatory) bed would account for the differences in the flow-velocity waveform. We used wave intensity analysis to separate and quantify proximal- and distal-originating pressures to study the differences in velocity waveforms. In 20 subjects with unobstructed coronary arteries, sensor-tipped intra-arterial wires were used to measure simultaneous pressure and Doppler velocity in the proximal left main stem (LMS) and proximal right coronary artery (RCA). Proximal- and distal-originating waves were separated using wave intensity analysis, and differences in waves were examined in relation to structural and anatomic differences between the two arteries. Diastolic flow velocity was lower in the RCA than in the LMS (35.1 +/- 21.4 vs. 56.4 +/- 32.5 cm/s, P < 0.002), and, consequently, the diastolic-to-systolic ratio of peak flow velocity in the RCA was significantly less than in the LMS (1.00 +/- 0.32 vs. 1.79 +/- 0.48, P < 0.001). This was due to a lower distal-originating suction wave (8.2 +/- 6.6 x 10(3) vs. 16.0 +/- 12.2 x 10(3) W.m(-2).s(-1), P < 0.01). The suction wave in the LMS correlated positively with left ventricular pressure (r = 0.6, P < 0.01) and in the RCA with estimated right ventricular systolic pressure (r = 0.7, P = 0.05) but not with the respective diameter in these arteries. In contrast to the LMS, where coronary flow velocity was predominantly diastolic, in the proximal RCA coronary flow velocity was similar in systole and diastole. This difference was due to a smaller distal-originating suction wave in the RCA, which can be explained by differences in elastance and pressure generated between right and left ventricles.

Determination of fractional flow reserve (FFR) based on scaling laws: a simulation study

Fractional flow reserve (FFR) provides an objective physiological evaluation of stenosis severity. A technique that can measure FFR using only angiographic images would be a valuable tool in the cardiac catheterization laboratory. To perform this, the diseased blood flow can be measured with a first pass distribution analysis and the theoretical normal blood flow can be estimated from the total coronary arterial volume based on scaling laws. A computer simulation of the coronary arterial network was used to gain a better understanding of how hemodynamic conditions and coronary artery disease can affect blood flow, arterial volume and FFR estimation. Changes in coronary arterial flow and volume due to coronary stenosis, aortic pressure and venous pressure were examined to evaluate the potential use of flow and volume for FFR determination. This study showed that FFR can be estimated using arterial volume and a scaling coefficient corrected for aortic pressure. However, variations in venous pressure were found to introduce some error in FFR estimation. A relative form of FFR was introduced and was found to cancel out the influence of pressure on coronary flow, arterial volume and FFR estimation. The use of coronary flow and arterial volume for FFR determination appears promising.

Estimation of regional myocardial mass at risk based on distal arterial lumen volume and length using 3D micro-CT images

The determination of regional myocardial mass at risk distal to a coronary occlusion provides valuable prognostic information for a patient with coronary artery disease. The coronary arterial system follows a design rule which allows for the use of arterial branch length and lumen volume to estimate regional myocardial mass at risk. Image processing techniques, such as segmentation, skeletonization and arterial network tracking, are presented for extracting anatomical details of the coronary arterial system using micro-computed tomography (micro-CT). Moreover, a method of assigning tissue voxels to their corresponding arterial branches is presented to determine the dependent myocardial region. The proposed micro-CT technique was utilized to investigate the relationship between the sum of the distal coronary arterial branch lengths and volumes to the dependent regional myocardial mass using a polymer cast of a porcine heart. The correlations of the logarithm of the total distal arterial lengths (L) to the logarithm of the regional myocardial mass (M) for the left anterior descending (LAD), left circumflex (LCX) and right coronary (RCA) arteries were log(L)=0.73log(M)+0.09 (R=0.78), log(L)=0.82log(M)+0.05 (R=0.77) and log(L)=0.85log(M)+0.05 (R=0.87), respectively. The correlation of the logarithm of the total distal arterial lumen volumes (V) to the logarithm of the regional myocardial mass for the LAD, LCX and RCA were log(V)=0.93log(M)-1.65 (R=0.81), log(V)=1.02log(M)-1.79 (R=0.78) and log(V)=1.17log(M)-2.10 (R=0.82), respectively. These morphological relations did not change appreciably for diameter truncations of 600-1400microm. The results indicate that the image processing procedures successfully extracted information from a large 3D dataset of the coronary arterial tree to provide prognostic indications in the form of arterial tree parameters and anatomical area at risk.