The impact of revascularization on myocardial blood flow as assessed by positron emission tomography

A computational study of the connection between coronary revascularization and cardio-cerebral hemodynamics

BACKGROUND AND OBJECTIVE

Some patients experience life-threatening strokes during coronary revascularization. Despite its clinical importance, few numerical studies have investigated the impact of coronary revascularization on cardio-cerebral hemodynamics. This study aims to address this gap by evaluating the effects of eliminating coronary stenosis on both coronary and cerebral blood flow using patient-specific simulations.

METHODS

A patient-specific cardio-cerebral arterial network with a 70% stenosis in the left main coronary artery was reconstructed, and computational fluid dynamics were employed to evaluate the effects of eliminating coronary stenosis. The three-dimensional time-dependent incompressible Navier-Stokes equations were discretized using a stabilized P1-P1 Galerkin finite element method and an implicit second-order backward differentiation formula. A regional blood flow distribution model, coupled with a lumped Windkessel model, was applied at the outlet boundaries. The 3D pulsatile blood flow was solved using a parallel solver based on a scalable Newton-Krylov-Schwarz algorithm, enabling fast and efficient simulations.

RESULTS

Coronary revascularization significantly improved myocardial blood flow, increasing the coronary fractional flow reserve from 0.742 to 0.904, indicating enhanced myocardial perfusion. However, cerebral hemodynamics were negatively affected, with a 2.49% reduction in blood flow through the main cerebral artery, suggesting an elevated risk of cerebral ischemia. The proposed computational framework demonstrated good parallel scalability across thousands of processor cores.

CONCLUSIONS

This study highlights the dual impact of coronary revascularization, improving myocardial perfusion while potentially elevating the risk of cerebral ischemic complications. The efficient computational approach provides a valuable tool for evaluating cardio-cerebral hemodynamics in patient-specific settings, making it suitable for complex and time-intensive simulations.

Peak myocardial work assessment to detect coronary ischemia during dobutamine stress echocardiography

Introduction

Peak global myocardial work efficiency (GWE), a measure of peak global myocardial constructive to wasted work ratio, has been shown to discriminate coronary ischemia during treadmill stress echocardiography (SE). We wanted to assess additive utility of peak global longitudinal strain (GLS), global work index (GWI), and GWE in improving positive predictive value (PPV) of an abnormal dobutamine stress echocardiography (DSE) and calculate cost-savings by avoiding secondary tests.

Methods

We prospectively enrolled patients with abnormal DSE who underwent secondary confirmatory tests to confirm significant CAD as our primary cohort, and measured baseline and peak GLS, GWI, and GWE. We also included a control group with normal DSE results and similar measurements. The cost of secondary testing was used to calculate potential savings.

Results

Among the 45 patients (71% females, mean age 60 ± 12 yrs.), 9 had significant CAD, 11 had non-significant CAD, and 25 were controls (N). Patients with significant CAD had significantly lower peak GLS [-15 (-17, -12.5) vs. -20 (-22, -19.5)%, p < 0.001], peak GWI [1,057 (810.5, 1,057) vs. 2,245 (1,928.5, 2,961) mmHg%, p = 0.02], peak GWE [82 (74.5, 86.5) vs. 89 [(86, 93.5)%, p = 0.001], and peak GCW [1,618 (1,153.5, 2,003) vs. 2,585 (2,262.5, 3,262) mmHg%, p = 0.02] compared to control. ROC analysis demonstrated peak GWE [AUC 0.76 (0.55, 0.97) p = 0.01] to discriminate coronary ischemia. Incorporating peak GWE of <87% into abnormal DSE interpretation improved PPV from 45% to 81%, resulting in an estimated cost savings of $8,274.00 per screened patient.

Conclusions

Incorporating peak GWE into standard DSE interpretation enhanced diagnostic accuracy and reduced the cost of downstream testing.

Nuclear Cardiology Surrogate Biomarkers in Clinical Trials

Nuclear cardiology offers a diverse range of imaging tools that provide valuable insights into myocardial perfusion, inflammation, metabolism, neuroregulation, thrombosis, and microcalcification. These techniques are crucial not only for diagnosing and managing cardiovascular conditions but also for gaining pathophysiologic insights. Surrogate biomarkers in nuclear cardiology, represented by detectable imaging changes, correlate with disease processes or therapeutic responses and can serve as endpoints in clinical trials when they demonstrate a clear link with these processes. By providing early indicators of therapeutic efficacy-often before clinical outcomes manifest-surrogate biomarkers can accelerate treatment development. This disease-focused review will highlight key nuclear cardiology surrogate biomarkers, emphasizing the importance of standardized imaging protocols and robust quantitative techniques to ensure accuracy and reproducibility. We will also explore the challenges to the broader adoption of imaging biomarkers, including the need for well-defined pathophysiologic correlations, greater data diversity in clinical research, and overcoming regulatory barriers. Addressing these challenges will improve the utility of imaging biomarkers in clinical trials, enabling more precise cardiovascular care through early diagnosis and therapeutic monitoring, ultimately accelerating the development of novel cardiovascular therapies.

Impact of coronary revascularization on coronary flow capacity measured by transthoracic Doppler echocardiography in patients with chronic coronary syndrome

Coronary flow capacity (CFC) integrates quantitative assessment of hyperemic myocardial blood flow and coronary flow reserve. We aimed to evaluate the effect of elective percutaneous coronary revascularization (PCI) on CFC using serial stress transthoracic Doppler echocardiography (STDE). Overall, 148 stable patients underwent STDE of the left anterior descending arteries (LAD), before and after elective PCI. Coronary flow velocity reserve (CFVR) was measured using basal and hyperemic diastolic peak velocity (hDPV). Vessels were classified into four CFC categories: severely, moderately, or mildly reduced CFC, and normal flow. Changes in hDPV and CFC status post-PCI, as well as predictors of hDPV increase, were assessed. Despite improvements in fractional flow reserve (FFR) in all cases, 31 cases (20.9%) showed a decrease in hDPV following PCI. Vessels with ischemic CFC, defined as moderately or severely reduced CFC, decreased from 46.6% (69/148) to 19.6% (29/148) post-PCI. Conversely, CFC worsened in 15.5% of patients. Multivariable analysis showed lower pre-PCI hDPV and ischemic CFC were independently predictive of higher-level (> 50%) hDPV increase after PCI. Approximately 20% of FFR-guided LAD PCI resulted in decreased hDPV. CFC deterioration was not uncommon despite FFR improvement. Preprocedural non-invasive STDE may help identify lesions that benefit from revascularization.

Fast vs slow rubidium-82 infusion profiles and test-retest precision of myocardial perfusion using contemporary 3D cardiac analog positron emission tomography-computed tomography imaging

BACKGROUND

On legacy 2D positron emission tomography (PET) systems utilizing a 50 mL/min Rb-82 profile, test-retest precision of quantitative perfusion is ∼10%. It is unclear whether Rb-82 infusion rate significantly impacts quantitative perfusion and/or image quality on modern analog 3D PET-CT systems. We aimed to determine whether the Rb-82 infusion profile significantly impacts test-retest precision of quantitative perfusion, perfusion metrics, and/or image quality on a modern analog 3D PET-CT scanner.

METHODS

Ninety-eight volunteers from 3 distinct groups: healthy volunteers (Normals), patients with risk factors, and/or coronary disease (Clinicals) and patients with prior transmural myocardial infarctions (Infarcts), underwent cardiac stress testing on an analog 3D PET-CT. Participants received 3 consecutive resting scans and 2 consecutive stress scans, minutes apart, with two randomly assigned Rb-82 infusion profiles: 50 mL/min (fast [F]) and 20 mL/min (slow [S]). Perfusion metrics (resting (rMBF) and stress myocardial blood flow (sMBF)) were calculated using HeartSee software. Coefficients of variance (COV), repeatability (RC), MBF, and image quality metrics were compared.

RESULTS

rMBF correlated well between F and S profiles, with intraclass correlation coefficients (ICC) ranging .91-.93. sMBF was highly correlated between F and S profiles (ICC = .97). Fast and slow profiles were associated with similar same-day test-retest precision (COV 11.5% vs 11.3% (P = .77); RC 21.5% vs 22.6%, for F-F vs S-S). There were no clinically significant differences in MBF values between F and S profiles. Image quality metrics were similar between the 2 profiles.

CONCLUSIONS

There are no clinically significant differences in precision, perfusion metrics, or image quality between Rb-82 fast and slow infusions using a contemporary analog 3D PET-CT.

PET myocardial perfusion imaging: Trends, challenges, and opportunities

Various non-invasive images are used in clinical practice for the diagnosis and prognostication of chronic coronary syndromes. Notably, quantitative myocardial perfusion imaging (MPI) through positron emission tomography (PET) has seen significant technical advancements and a substantial increase in its use over the past two decades. This progress has generated an unprecedented wealth of clinical information, which, when properly applied, can diagnose and fine-tune the management of patients with different types of ischemic syndromes. This state-of-art review focuses on quantitative PET MPI, its integration into clinical practice, and how it holds up at the eyes of modern cardiac imaging and revascularization clinical trials, along with future perspectives.

Quantitative analysis of myocardial blood flow in surgically revascularized and not revascularized myocardial segments. A pilot PET study

PURPOSE

To prospectively compare changes in myocardial blood flow (MBF) and myocardial flow reserve (MFR) in multivessel coronary artery disease (MVCAD) patients undergoing incomplete revascularization (IR) versus complete revascularization (CR) by coronary artery bypass grafting (CABG).

METHODS

Seven male patients (age 68 ± 9 years) with MVCAD underwent myocardial perfusion PET/CT with [13N]ammonia before and at least 4 months after CABG. Segmental resting and stress MBF as well as MFR were measured. Resting and during stress left ventricle ejection fraction (LVEF) were also calculated.

RESULTS

Three patients (43%) underwent CR and four (57%) IR. Among 119 myocardial segments, 101 (85%) were revascularized, and 18 (15%) were not. After CABG, stress MBF (mL/min/gr) and MFR are significantly increased in all myocardial segments, with a greater increase in the revascularized segments (p = 0.013). In both groups, LVEF significantly decreased during stress at baseline PET (p = 0.04), but not after CABG.

CONCLUSION

Stress MBF and MFR significantly improve after CABG in both revascularized and not directly revascularized myocardial segments. IR strategy may be considered in patients with high surgical risk for CR.

Coronary flow capacity and survival prediction after revascularization: physiological basis and clinical implications

BACKGROUND AND AIMS

Coronary flow capacity (CFC) is associated with an observed 10-year survival probability for individual patients before and after actual revascularization for comparison to virtual hypothetical ideal complete revascularization.

METHODS

Stress myocardial perfusion (mL/min/g) and coronary flow reserve (CFR) per pixel were quantified in 6979 coronary artery disease (CAD) subjects using Rb-82 positron emission tomography (PET) for CFC maps of artery-specific size-severity abnormalities expressed as percent left ventricle with prospective follow-up to define survival probability per-decade as fraction of 1.0.

RESULTS

Severely reduced CFC in 6979 subjects predicted low survival probability that improved by 42% after revascularization compared with no revascularization for comparable severity (P = .0015). For 283 pre-and-post-procedure PET pairs, severely reduced regional CFC-associated survival probability improved heterogeneously after revascularization (P < .001), more so after bypass surgery than percutaneous coronary interventions (P < .001) but normalized in only 5.7%; non-severe baseline CFC or survival probability did not improve compared with severe CFC (P = .00001). Observed CFC-associated survival probability after actual revascularization was lower than virtual ideal hypothetical complete post-revascularization survival probability due to residual CAD or failed revascularization (P < .001) unrelated to gender or microvascular dysfunction. Severely reduced CFC in 2552 post-revascularization subjects associated with low survival probability also improved after repeat revascularization compared with no repeat procedures (P = .025).

CONCLUSIONS

Severely reduced CFC and associated observed survival probability improved after first and repeat revascularization compared with no revascularization for comparable CFC severity. Non-severe CFC showed no benefit. Discordance between observed actual and virtual hypothetical post-revascularization survival probability revealed residual CAD or failed revascularization.

Prognostic value of global myocardial flow reserve in patients with history of coronary artery bypass grafting

AIMS

It is not well understood whether positron emission tomography (PET)-derived myocardial flow reserve (MFR) is prognostic among patients with prior coronary artery bypass grafting (CABG).

METHODS AND RESULTS

Consecutive patients with a clinical indication for PET were enrolled in the Houston Methodist DeBakey Heart and Vascular Center PET registry and followed prospectively for incident outcomes. The primary outcome was a composite of all-cause death, myocardial infarction (MI)/unplanned revascularization, and heart failure admissions. Cox proportional hazards models were used to study the association between MFR (<2 vs. ≥2) and incident events adjusting for clinical and myocardial perfusion imaging variables. The study population consisted of 836 patients with prior CABG; mean (SD) age 68 (10) years, 53% females, 79% Caucasian, 36% non-Hispanic, and 66% with MFR <2. Over a median (interquartile range [IQR]) follow-up time of 12 (4-24) months, there were 122 incident events (46 HF admissions, 28 all-cause deaths, 23 MI, 22 PCI/3 repeat CABG 90 days after imaging). In adjusted analyses, patients with impaired MFR had a higher risk of the primary outcome [hazard ratio (HR) 2.06; 95% CI 1.23-3.44]. Results were significant for admission for heart failure admissions (HR 2.92; 95% CI 1.11-7.67) but not for all-cause death (HR 2.01, 95% CI 0.85-4.79), or MI/UR (HR 1.93, 95% CI 0.92-4.05).

CONCLUSION

Among patients with a history of CABG, PET-derived global MFR <2 may identify those with a high risk of subsequent cardiovascular events, especially heart failure, independent of cardiovascular risk factors and perfusion data.

Assessment of resting myocardial blood flow in regions of known transmural scar to confirm accuracy and precision of 3D cardiac positron emission tomography

BACKGROUND

Composite invasive and non-invasive data consistently demonstrate that resting myocardial blood flow (rMBF) in regions of known transmural myocardial scar (TMS) converge on a value of ~ 0.30 mL/min/g or lower. This value has been confirmed using the 3 most common myocardial perfusion agents (13N, 15O-H2O and 82Rb) incorporating various kinetic models on older 2D positron emission tomography (PET) systems. Thus, rMBF in regions of TMS can serve as a reference "truth" to evaluate low-end accuracy of various PET systems and software packages (SWPs). Using 82Rb on a contemporary 3D-PET-CT system, we sought to determine whether currently available SWP can accurately and precisely measure rMBF in regions of known TMS.

RESULTS

Median rMBF (in mL/min/g) and COV in regions of TMS were 0.71 [IQR 0.52-1.02] and 0.16 with 4DM; 0.41 [0.34-0.54] and 0.10 with 4DM-FVD; 0.66 [0.51-0.85] and 0.11 with Cedars; 0.51 [0.43-0.61] and 0.08 with Emory-Votaw; 0.37 [0.30-0.42], 0.07 with Emory-Ottawa, and 0.26 [0.23-0.32], COV 0.07 with HeartSee.

CONCLUSIONS

SWPs varied widely in low end accuracy based on measurement of rMBF in regions of known TMS. 3D PET using 82Rb and HeartSee software accurately (0.26 mL/min/g, consistent with established values) and precisely (COV = 0.07) quantified rMBF in regions of TMS. The Emory-Ottawa software yielded the next-best accuracy (0.37 mL/min/g), though rMBF was higher than established gold-standard values in ~ 5% of the resting scans. 4DM, 4DM-FDV, Cedars and Emory-Votaw SWP consistently resulted values higher than the established gold standard (0.71, 0.41, 0.66, 0.51 mL/min/g, respectively), with higher interscan variability (0.16, 0.11, 0.11, and 0.09, respectively).

TRIAL REGISTRATION

clinicaltrial.gov, NCT05286593, Registered December 28, 2021, https://clinicaltrials.gov/ct2/show/NCT05286593 .

Myocardial perfusion imaging by 15O-H2O positron emission tomography predicts clinical revascularization procedures in symptomatic patients with previous coronary artery bypass graft

Aims

We wanted to assess if ¹⁵O-H₂O myocardial perfusion imaging (MPI) in a clinical setting can predict referral to coronary artery catheterization [coronary angiography (CAG)], execution of percutaneous coronary intervention (PCI), and post-PCI angina relief for patients with angina and previous coronary artery bypass graft (CABG).

Methods and results

We analysed 172 symptomatic CABG patients referred for ¹⁵O-H₂O positron emission tomography (PET) MPI at Aarhus University Hospital Department of Nuclear Medicine & PET Centre, of which five did not complete the scan. In total, 145 (87%) enrolled patients had an abnormal MPI. Of these, 86/145 (59%) underwent CAG within 3 months; however, no PET parameters predicted referral to CAG. During the CAG, 25/86 (29%) patients were revascularized by PCI. Relative flow reserve (RFR) (0.49 vs. 0.54 P = 0.03), vessel-specific myocardial blood flow (MBF) (1.53 vs. 1.88 mL/g/min, P < 0.01), and vessel-specific myocardial flow reserve (MFR) (1.73 vs. 2.13, P < 0.01) were significantly lower in patients revascularized by PCI. Receiver operating characteristic analysis of the vessel-specific parameters yielded optimal cutoffs of 1.36 mL/g/min (MBF) and 1.28 (MFR) to predict PCI. Angina relief was experienced by 18/24 (75%) of the patients who underwent PCI. Myocardial blood flow was an excellent predictor of angina relief on both a global [area under the curve (AUC) = 0.85, P < 0.01] and vessel-specific (AUC = 0.90, P < 0.01) level with optimal cutoff levels of 1.99 mL/g/min and 1.85 mL/g/min, respectively.

Conclusion

For CABG patients, RFR, vessel-specific MBF, and vessel-specific MFR measured by ¹⁵O-H₂O PET MPI predict whether subsequent CAG will result in PCI. Additionally, global and vessel-specific MBF values predict post-PCI angina relief.

Indicators of abnormal PET coronary flow capacity in detecting cardiac ischemia

Coronary flow capacity (CFC) categorizes severity of left ventricular (LV) ischemia by PET myocardial blood flow (MBF). Our objective was to correlate abnormal CFC with other indicators of regional ischemia. Data were examined retrospectively for 231 patients evaluated for known/suspected CAD who underwent rest and regadenoson-stress ⁸²Rb PET/CT. MBF and myocardial flow reserve (MFR) were quantified, from which CFC was categorized as Normal CFC (1), Minimally reduced (2), Mildly reduced (3), Moderately reduced (4), and Severely reduced (5) for the three main arterial territories as well as globally. Relative perfusion summed stress score (SSS) and systolic phase contraction bandwidth (BW) were assessed. Accuracy to detect arteries with CFC ≥ 4 was highest for a Regional Index combining SSS and BW (88 ± 3%). A Global Index formed from stress ejection fraction, SSS and BW was the most accurate means of identifying patients with global CFC ≥ 4 (84 ± 3%). Arteries with abnormal CFC derived from absolute myocardial blood flow measurements are accurately identified by composite parameters combining regionally aberrant relative perfusion patterns and asynchrony.

Quantification of Resting Myocardial Blood Flow Using Rubidum82 Positron Emission Tomography in Regions with MRI-Confirmed Myocardial Scar

Background: Resting myocardial blood flow (rMBF) within regions of myocardial scar as measured by positron emission tomography (PET) has not yet been assessed with the radiotracer Rubidium⁸² (Rb⁸²) or correlated with scar thickness. Cardiac magnetic resonance imaging (cMRI) offers high spatial resolution and identifies myocardial scar with late gadolinium enhancement (LGE). Using Rb⁸² PET, we sought to characterize rMBF in regions of myocardial scar of varying thicknesses determined by cMRI. Methods/Results: Patients with a history of myocardial infarction, a resting Rb⁸² PET study and a cMRI were identified. On cMRI, regions of infarction, defined as >50% LGE with akinesis, were sub-categorized as 50-75% LGE or >75% LGE, corresponding with increasing transmural scar thickness. PET zones of infarct based on size and %LGE by cMRI were quantified for mean and minimum rMBF. Mean rMBF (cc/min/g) in infarct zones with >75% LGE was 0.32±0.07 with a minimum rMBF of 0.19±0.03. In infarct zones with 50-75% LGE, rMBF was 0.45±0.14 (50-75% vs. >75%, p=0.002). Conclusions: We identified rMBF within cMRI confirmed regions of myocardial scar of varying thicknesses. rMBF has an inverse relationship with the extent of LGE on cMRI, with the most severe regions (>75% LGE) having mean and minimal rMBF (cc/min/g) of 0.32±0.07 and 0.19±0.03, respectively.

Insights into Myocardial Perfusion PET Imaging: the Coronary Flow Capacity

Purpose of Review

The present work summarizes the clinical relevance of coronary flow capacity (CFC) with an eye on future perspectives.

Recent findings

CFC concept has been recently introduced providing a comprehensive framework for coronary physiology evaluation.

Summary

It has been widely demonstrated that coronary artery disease (CAD) is a complex disease with a multifactorial etiology resulting from different pathogenic mechanisms. Cardiac positron emission tomography (PET) currently represents the gold standard for CAD assessment, providing absolute myocardial perfusion data including coronary flow reserve (CFR), calculated as the ratio of hyperemic to rest absolute myocardial blood flows. CFC can be obtained from dynamic PET images by plotting the primary stress perfusion data and CFR values for each pixel on a graph of predefined exact ranges. The routine evaluation of this parameter may add diagnostic and prognostic value to clinical and conventional imaging data.

Development of an approach to extracting coronary arteries and detecting stenosis in invasive coronary angiograms

Purpose: In stable coronary artery disease (CAD), reduction in mortality and/or myocardial infarction with revascularization over medical therapy has not been reliably achieved. Coronary arteries are usually extracted to perform stenosis detection. As such, developing accurate segmentation of vascular structures and quantification of coronary arterial stenosis in invasive coronary angiograms (ICA) is necessary. Approach: A multi-input and multiscale (MIMS) U-Net with a two-stage recurrent training strategy was proposed for the automatic vessel segmentation. The proposed model generated a refined prediction map with the following two training stages: (i) stage I coarsely segmented the major coronary arteries from preprocessed single-channel ICAs and generated the probability map of arteries; and (ii) during the stage II, a three-channel image consisting of the original preprocessed image, a generated probability map, and an edge-enhanced image generated from the preprocessed image was fed to the proposed MIMS U-Net to produce the final segmentation result. After segmentation, an arterial stenosis detection algorithm was developed to extract vascular centerlines and calculate arterial diameters to evaluate stenotic level. Results: Experimental results demonstrated that the proposed method achieved an average Dice similarity coefficient of 0.8329, an average sensitivity of 0.8281, and an average specificity of 0.9979 in our dataset with 294 ICAs obtained from 73 patients. Moreover, our stenosis detection algorithm achieved a true positive rate of 0.6668 and a positive predictive value of 0.7043. Conclusions: Our proposed approach has great promise for clinical use and could help physicians improve diagnosis and therapeutic decisions for CAD.

The impact of coronary revascularization on vessel-specific coronary flow capacity and long-term outcomes: a serial [15O]H2O positron emission tomography perfusion imaging study

AIMS

Coronary flow capacity (CFC) integrates quantitative hyperaemic myocardial blood flow (hMBF) and coronary flow reserve (CFR) to comprehensively assess physiological severity of coronary artery disease (CAD). This study evaluated the effects of revascularization on CFC as assessed by serial [15O]H2O positron emission tomography (PET) perfusion imaging.

METHODS AND RESULTS

A total of 314 patients with stable CAD underwent [15O]H2O PET imaging at baseline and after myocardial revascularization to assess changes in hMBF, CFR, and CFC in 415 revascularized vessels. Using thresholds for ischaemia and normal perfusion, vessels were stratified in five CFC categories: myocardial steal, severely reduced CFC, moderately reduced CFC, minimally reduced CFC, and normal flow. Additionally, the association between CFC increase and the composite endpoint of death and non-fatal myocardial infarction (MI) was studied. Vessel-specific CFC improved after revascularization (P < 0.01). Furthermore, baseline CFC was an independent predictor of CFC increase (P < 0.01). The largest changes in ΔhMBF (0.90 ± 0.74, 0.93 ± 0.65, 0.79 ± 0.74, 0.48 ± 0.61, and 0.29 ± 0.66 mL/min/g) and ΔCFR (1.01 ± 0.88, 0.99 ± 0.69, 0.87 ± 0.88, 0.66 ± 0.91, and -0.01 ± 1.06) were observed in vessels with lower baseline CFC (P < 0.01 for both). During a median follow-up of 3.5 (95% CI 3.1-3.9) years, an increase in CFC was independently associated with lower rates of death and non-fatal MI (HR 0.43, 95% CI 0.19-0.98, P = 0.04).

CONCLUSION

Successful revascularization results in an increase in CFC. Furthermore, baseline CFC was an independent predictor of change in hMBF, CFR, and subsequently CFC. In addition, an increase in CFC was associated with a favourable outcome in terms of death and non-fatal MI.

Improved regional myocardial blood flow and flow reserve after coronary revascularization as assessed by serial 15O-water positron emission tomography/computed tomography

AIMS

Myocardial perfusion imaging without and with quantitative myocardial blood flow (MBF) and myocardial flow reserve (MFR) plays an important role in the diagnosis and risk stratification of patients with stable coronary artery disease (CAD). We aimed to quantify the effects of coronary revascularization on regional stress MBF and MFR and to determine whether the presence of subendocardial infarction was associated with these changes.

METHODS AND RESULTS

Forty-seven patients with stable CAD were prospectively enrolled. They underwent 15O-water positron emission tomography at baseline and 6 months after optimal medical therapy alone (n = 16), percutaneous coronary intervention (PCI) (n = 18), or coronary artery bypass grafting (CABG) (n = 13). Stenosis of ≥50% diameter was detected in 98/141 vessels (70%). The regional MFR was significantly increased from baseline to follow-up [1.84 (interquartile range, IQR 1.28-2.17) vs. 2.12 (IQR 1.69-2.63), P < 0.001] in vessel territories following PCI or CABG due to an increase in the stress MBF [1.33 (IQR 0.97-1.67) mL/g/min vs. 1.64 (IQR 1.38-2.17) mL/g/min, P < 0.001], whereas there was no significant change in the regional stress MBF or MFR in vessel territories without revascularization. A multilevel mixed-effects models adjusted for baseline characteristics, subendocardial infarction assessed by cardiovascular magnetic resonance imaging, and intra-patient correlation showed that the degree of angiographic improvement after coronary revascularization was significantly associated with increased regional stress MBF and MFR (P < 0.05 for all).

CONCLUSION

Coronary revascularization improved the regional stress MBF and MFR in patients with stable CAD. The magnitude of these changes was associated with the extent of revascularization independent of subendocardial infarction.

PET Stress Testing with Coronary Flow Capacity in the Evaluation of Patients with Coronary Artery Disease and Left Ventricular Dysfunction: Rethinking the Current Paradigm

PURPOSE OF REVIEW

Cardiomyopathy with underlying left ventricular (LV) dysfunction is a heterogenous group of disorders that may be present with, and/or secondary to, coronary artery disease (CAD). The purpose of this review is to demonstrate, via case illustrations, the benefits offered by cardiac positron-emission tomography (PET) stress testing with coronary flow capacity (CFC) in the evaluation and treatment of patients with left ventricular (LV) dysfunction and CAD.

RECENT FINDINGS

CFC, a metric that is increasing in prominence, represents the integration of several absolute perfusion metrics into clinical strata of CAD severity. Our prior work has demonstrated improvement in regional perfusion metrics as a result of revascularization to territories with severe reduction in CFC. Conversely, when CFC is adequate, there is no change in regional perfusion metrics following revascularization, despite angiographically severe stenosis. Furthermore, Gould et al. demonstrated decreased rates of myocardial infarction and death following revascularization of myocardium with severely reduced CFC, with no clinical benefit observed following revascularization of patients with preserved CFC. In a series of cases, we present pre-revascularization and post-revascularization PET scans with perfusion metrics in patients with LV dysfunction and CAD. In these examples, we demonstrate improvement in LV function and perfusion metrics following revascularization only in cases where baseline CFC is severely reduced. PET with CFC offers unique guidance regarding revascularization in patients with reduced LV function and CAD.

Reliability and Reproducibility of Absolute Myocardial Blood Flow: Does It Depend on the PET/CT Technology, the Vasodilator, and/or the Software?

PURPOSE OF REVIEW

The COURAGE and ISCHEMIA trials showed no reduced mortality after revascularization compared to medical treatment. Is this lack of benefit due to revascularization having no benefit regardless of CAD severity or to suboptimal patient selection due to non-quantitative cardiac imaging?

RECENT FINDINGS

Comprehensive, integrated, myocardial perfusion quantified by regional pixel distribution of coronary flow capacity (CFC) is the final common expression of objective CAD severity for which revascularization reduces mortality. Current lack of revascularization benefit derives from narrow thinking focused on measuring one isolated aspect of coronary characteristics, such as angiogram stenosis, its fractional flow reserve (FFR), anatomic FFR simulations, relative stress imaging, absolute stress ml/min/g or coronary flow reserve (CFR) alone, or even more narrowly on global CFR or fixed regions of interest in assumed coronary artery distributions, or in arbitrary 17 segments on bull's-eye displays, rather than regional pixel distribution of perfusion metrics as they actually are in an individual. Comprehensive integration of all quantitative perfusion metrics per regional pixel into coronary flow capacity guides artery-specific interventions for reduced mortality in non-acute CAD but requires addressing the methodologic questions in the title.

Mortality Prediction by Quantitative PET Perfusion Expressed as Coronary Flow Capacity With and Without Revascularization

OBJECTIVES

This study sought to determine the relationship between the severity of reduced quantitative perfusion parameters and mortality with and without revascularization.

BACKGROUND

The physiological mechanisms for differential mortality risk of coronary flow reserve (CFR) and coronary flow capacity (CFC) before and after revascularization are unknown.

METHODS

Global and regional rest-stress (ml/min/g), CFR, their regional per-pixel combination as CFC, and relative stress in ml/min/g were measured as percent of LV in all serial routine 5,274 diagnostic PET scans with systematic follow-up over 10 years (mean 4.2 ± 2.5 years) for all-cause mortality with and without revascularization.

RESULTS

Severely reduced CFR of 1.0 to 1.5 and stress perfusion ≤1.0 cc/min/g incurred increasing size-dependent risks that were additive because regional severely reduced CFC (CFCsevere) was associated with the highest major adverse cardiac event rate of 80% (p < 0.0001 vs. either alone) and a mortality risk of 14% (vs. 2.3% for no CFCsevere; p = 0.001). Small regions of CFCsevere ≤0.5% predicted high risk (p < 0.0001 vs. no CFCsevere) related to a wave front of border zones at risk around the small most severe center. By receiver-operating characteristic analysis, relative stress topogram maps of stress (ml/min/g) as a fraction of LV defined these border zones at risk or for mildly reduced CFC (area under the curve [AUC]: 0.69) with a reduced relative tomographic subendocardial-to-subepicardial ratio. CFCsevere incurred the highest mortality risk that was reduced by revascularization (p = 0.005 vs. no revascularization) for artery-specific stenosis not defined by global CFR or stress perfusion alone.

CONCLUSIONS

CFC is associated with the size-dependent highest mortality risk resulting from the additive risk of CFR and stress (ml/min/g) that is significantly reduced after revascularization, a finding not seen for global CFR. Small regions of CFCsevere ≤0.5% of LV also carry a high risk because of the surrounding border zones at risk defined by relative stress perfusion and a reduced relative subendocardial-to-subepicardial ratio.