Frequency and clinical implications of fluid dynamically significant diffuse coronary artery disease manifest as graded, longitudinal, base-to-apex myocardial perfusion abnormalities by noninvasive positron emission tomography

Prognostic value of myocardial flow reserve measured with CZT cardiac-dedicated SPECT low-dose dynamic myocardial perfusion imaging in patients with INOCA

BACKGROUND

Clinical use of dynamic myocardial perfusion imaging (D-MPI) of cadmium-zinc-telluride (CZT) cardiac-dedicated SPECT is growing, showing a higher application value than conventional SPECT. The prognostic value of ischemia in patients with non-obstructive coronary arteries (INOCA) remains an important challenge for investigation. The primary objective of this study was to investigate the prognostic value of myocardial flow reserve (MFR) measured with low-dose D-MPI of CZT cardiac-dedicated SPECT in the assessment of patients with INOCA.

METHODS

Consecutive screening of patients with INOCA and obstructive coronary artery disease (OCAD) who had coronary angiography (CAG) data was performed within three months before or after D-MPI imaging. The patients who met the inclusion criteria were retrospectively analyzed and follow-up by telephone was performed. The enrolled patients were then divided into the INOCA and OCAD groups. INOCA was defined as signs and/or symptoms of myocardial ischemia but with < 50% epicardial stenosis. OCAD was defined as obstructive stenosis (≥ 50% stenosis) of epicardial coronary arteries or their major branches on the CAG. Medical treatments, Seattle Angina Questionnaire (SAQ) scores, and major adverse cardiac events (MACEs) were studied. The Kaplan-Meier survival curve, Log-rank test, and univariable COX regression analysis were used to evaluate the prognosis of patients and associated predictors, with P < 0.05 being considered statistically significant.

RESULTS

A total of 303 patients (159 males and 144 females) were enrolled for the final analysis after excluding 24 patients who were lost to follow-up. The mean age of the included cases was 61.94 ± 8.59 years, of which 203 (67.0%) cases were OCAD and 100 (33.0%) cases were INOCA, respectively. The median follow-up was 16 months (14-21 months). Kaplan-Meier survival curves showed that the incidence of MACE was similar in the INOCA and OCAD groups (log-rank P = 0.2645), while those with reduced MFR showed a higher incidence of MACE than those with normal MFR (log-rank P = 0.0019). The subgroup analysis in the OCAD group revealed that 105 patients with reduced MFR had a higher incidence of MACE than those with normal MFR (log-rank P = 0.0226). The subgroup analysis in the INOCA group showed that 37 patients with reduced MFR had a higher incidence of MACE than those with normal MFR in the INOCA group (log-rank P = 0.0186). Univariable Cox regression analysis showed for every 1 unit increase in MFR, the risk of MACE for INOCA was reduced by 66.1% and that for OCAD by 64.2%. For each 1 mL·g-1·min-1 increase in LV-sMBF, the risk of MACE was reduced by 72.4% in INOCA patients and 63.6% in OCAD patients.

CONCLUSIONS

MFR measured with low-dose D-MPI CZT SPECT provides incremental prognostic value in patients with INOCA. Patients with reduced MFR show an increased risk of MACE, increased symptom burdens, and impaired quality of life. INOCA patients with reduced MFR experienced higher rate of MACE than OCAD patients with normal MFR.

Quantitative flow ratio derived pullback pressure gradient and CZT-SPECT measured longitudinal flow gradient for hemodynamically significant coronary artery disease

BACKGROUND

Whether physiological coronary diffuseness assessed by quantitative flow reserve (QFR) pullback pressure gradient (PPG) correlates with longitudinal myocardial blood flow (MBF) gradient and improves diagnostic performances for myocardial ischemia remains unknown.

METHODS AND RESULTS

MBF was measured in mL g-1 min-1 with 99mTc-MIBI CZT-SPECT at rest and stress, corresponding myocardial flow reserve (MFR = MBF stress/MBF rest) and relative flow reserve (RFR = MBF stenotic area/MBF reference) were calculated. Longitudinal MBF gradient was defined as apical and basal left ventricle MBF gradient. △longitudinal MBF gradient was calculated by longitudinal MBF gradient at stress and rest. QFR-PPG was acquired from virtual QFR pullback curve. QFR-PPG significantly correlated with hyperemic longitudinal MBF gradient (r = 0.45, P = 0.007) and △longitudinal MBF gradient (stress-rest) (r = 0.41, P = 0.016). Vessels with lower RFR had lower QFR-PPG (0.72 vs. 0.82, P = 0.002), hyperemic longitudinal MBF gradient (1.14 vs. 2.22, P = 0.003) and △longitudinal MBF gradient (0.50 vs. 1.02, P = 0.003). QFR-PPG, hyperemic longitudinal MBF gradient and △longitudinal MBF gradient showed comparable diagnostic performances for predicting decreased RFR (area under curve [AUC]: 0.82 vs. 0.81 vs. 0.75, P = NS) or QFR (AUC: 0.83 vs. 0.72 vs. 0.80, P = NS). In addition, QFR-PPG and QFR in combination showed incremental value compared with QFR for predicting RFR (AUC = 0.83 vs. 0.73, P = 0.046, net reclassification index = 0.508, P = 0.001).

CONCLUSION

QFR-PPG significantly correlated with longitudinal MBF gradient and △longitudinal MBF gradient when used for physiological coronary diffuseness assessment. All three parameters had high accuracy in predicting RFR or QFR. Adding physiological diffuseness assessment increased accuracy for predicting myocardial ischemia.

Diagnostic performance of exercise stress tests for detection of epicardial and microvascular coronary artery disease: the UZ Clear study

BACKGROUND

Cardiac stress tests remain the cornerstone for evaluating patients suspected of having obstructive coronary artery disease (CAD). Coronary microvascular dysfunction (CMD) can lead to abnormal non-invasive tests.

AIMS

We sought to assess the diagnostic performance of exercise stress tests with indexes of epicardial and microvascular resistance as reference.

METHODS

This was a prospective, single-arm, multicentre study of patients with an intermediate pretest probability of CAD and positive exercise stress tests who were referred for invasive angiography. Patients underwent an invasive diagnostic procedure (IDP) with measurement of fractional flow reserve (FFR) and index of microvascular resistance (IMR) in at least one coronary vessel. Obstructive CAD was defined as diameter stenosis (DS) >50% by quantitative coronary angiography (QCA). The objective was to determine the false discovery rate (FDR) of cardiac exercise stress tests with both FFR and IMR as references.

RESULTS

One hundred and seven patients (137 vessels) were studied. The mean age was 62.1±8.7, and 27.1% were female. The mean diameter stenosis was 37.2±27.5%, FFR was 0.84±0.10, coronary flow reserve was 2.74±2.07, and IMR 20.3±11.9. Obstructive CAD was present in 39.3%, whereas CMD was detected in 20.6%. The FDR was 60.7% and 62.6% with QCA and FFR as references (p-value=0.803). The combination of FFR and IMR as clinical reference reduced the FDR by 25% compared to QCA (45.8% vs 60.7%; p-value=0.006).

CONCLUSIONS

In patients with evidence of ischaemia, an invasive functional assessment accounting for the epicardial and microvascular compartments led to an improvement in the diagnostic performance of exercise tests, driven by a significant FDR reduction.

Incorporating coronary artery calcium scoring in the prediction of obstructive coronary artery disease with myocardial ischemia: a study with sequential use of coronary computed tomography angiography and positron emission tomography imaging

BACKGROUND

Additional strategies are needed to refine the referral for diagnostic testing of symptomatic patients with suspected coronary artery disease (CAD). We aimed to compare various models to predict hemodynamically obstructive CAD.

METHODS AND RESULTS

Symptomatic patients with suspected CAD who underwent coronary artery calcium scoring (CACS) and sequential coronary computed tomography angiography (CCTA) and [15O]H2O positron emission tomography (PET) myocardial perfusion imaging were analyzed. Obstructive CAD was defined as a suspected coronary artery stenosis on CCTA with myocardial ischemia on PET (absolute stress myocardial perfusion ≤ 2.4 mL/g/min in ≥ 1 segment). Three models were developed to predict obstructive CAD-induced myocardial ischemia using logistic regression analysis: (1) basic model: including age, sex and cardiac symptoms, (2) risk factor model: adding number of risk factors to the basic model, and (3) CACS model: adding CACS to the risk factor model. Model performance was evaluated using discriminatory ability with area under the receiver-operating characteristic curves (AUC). A total of 647 patients (mean age 62 ± 9 years, 45% men) underwent CACS and sequential CCTA and PET myocardial perfusion imaging. Obstructive CAD with myocardial ischemia on PET was present in 151 (23%) patients. CACS was independently associated with myocardial ischemia (P < .001). AUC for the discrimination of ischemia for the CACS model was superior over the basic model and risk factor model (P < .001).

CONCLUSIONS

Adding CACS to the model including age, sex, cardiac symptoms and number of risk factors increases the accuracy to predict obstructive CAD with myocardial ischemia on PET in symptomatic patients with suspected CAD.

Post COVID-19 syndrome with impairment of flow-mediated epicardial vasodilation and flow reserve

AIMS

The aim of this study is to evaluate whether post-acute sequelae of COVID-19 cardiovascular syndrome (PASC-CVS) is associated with alterations in coronary circulatory function.

MATERIALS AND METHODS

In individuals with PASC-CVS but without known cardiovascular risk factors (n = 23) and in healthy controls (CON, n = 23), myocardial blood flow (MBF) was assessed with ¹³ N-ammonia and PET/CT in mL/g/min during regadenoson-stimulated hyperemia, at rest, and the global myocardial flow reserve (MFR) was calculated. MBF was also measured in the mid and mid-distal myocardium of the left ventricle (LV). The Δ longitudinal MBF gradient (hyperemia minus rest) as a reflection of an impairment of flow-mediated epicardial vasodilation, was calculated.

RESULTS

Resting MBF was significantly higher in PASC-CVS than in CON (1.29 ± 0.27 vs. 1.08 ± 0.20 ml/g/min, p ≤ .024), while hyperemic MBFs did not differ significantly among groups (2.46 ± 0.53 and 2.40 ± 0.34 ml/g/min, p = .621). The MFR was significantly less in PASC-CVS than in CON (1.97 ± 0.54 vs. 2.27 ± 0.43, p ≤ .031). In addition, there was a Δ longitudinal MBF gradient in PASC-CVS, not observed in CON (-0.17 ± 0.18 vs. 0.04 ± 0.11 ml/g/min, p < .0001).

CONCLUSIONS

Post-acute sequelae of COVID-19 cardiovascular syndrome may be associated with an impairment of flow-mediated epicardial vasodilation, while reductions in coronary vasodilator capacity appear predominantly related to increases in resting flow in women deserving further investigations.

18F-flurpiridaz positron emission tomography segmental and territory myocardial blood flow metrics: incremental value beyond perfusion for coronary artery disease categorization

AIMS

We determined the feasibility and diagnostic performance of segmental 18F-flurpiridaz myocardial blood flow (MBF) measurement by positron emission tomography (PET) compared with the standard territory method, and assessed whether flow metrics provide incremental diagnostic value beyond relative perfusion quantitation (PQ).

METHODS AND RESULTS

All evaluable pharmacological stress patients from the Phase III trial of 18F-flurpiridaz were included (n = 245) and blinded flow metrics obtained. For each coronary territory, the segmental flow metric was defined as the lowest 17-segment stress MBF (SMBF), myocardial flow reserve (MFR), or relative flow reserve (RFR) value. Diagnostic performances of segmental and territory MBF metrics were compared by receiver operating characteristic (ROC) areas under the curve (AUC). A multiple logistic model was used to evaluate whether flow metrics provided incremental diagnostic value beyond PQ alone. The diagnostic performances of segmental flow metrics were higher than their territory counterparts; SMBF AUC = 0.761 vs. 0.737; MFR AUC = 0.699 vs. 0.676; and RFR AUC = 0.716 vs. 0.635, respectively (P < 0.001 for all). Similar results were obtained for per-vessel coronary artery disease (CAD) ≥70% stenosis categorization and per-patient analyses. Combinatorial analyses revealed that only SMBF significantly improved the diagnostic performance of PQ in CAD ≥50% stenoses, with PQ AUC = 0.730, PQ + segmental SMBF AUC = 0.782 (P < 0.01), and PQ + territory SMBF AUC = 0.771 (P < 0.05). No flow metric improved diagnostic performance when combined with PQ in CAD ≥70% stenoses.

CONCLUSION

Assessment of segmental MBF metrics with 18F-flurpiridaz is feasible and improves flow-based epicardial CAD detection. When combined with PQ, only SMBF provides additive diagnostic performance in moderate CAD.

Nomogram based on multimodal echocardiography for assessing the evolution of diabetic cardiomyopathy in diabetic patients with normal cardiac function

Background

Diabetic cardiomyopathy (DCM) remains asymptomatic for many years until progression to asymptomatic left ventricular diastolic dysfunction (ALVDD), a subclinical cardiac abnormality present in early-stage DCM. Because LV function in patients with type 2 diabetes mellitus (T2DM) may be subtly altered long before the onset of ALVDD, quantitative assessment of the risk of progression to early-stage DCM in T2DM patients with normal hearts is critical for delaying or even reversing DCM.

Objective

This study aimed to establish a nomogram with the aid of DCM characteristics revealed by multimodal echocardiography to assess the likelihood of the progression to early-stage DCM in T2DM patients with normal cardiac function.

Methods

Of the 423 T2DM patients enrolled, 302 were included in the training cohort and 121 in the validation cohort. The clinical characteristics, biochemical data, and multimodal echocardiographic parameters were collected. In the training cohort, the screened correlates of ALVDD were utilized to develop a nomogram for estimating the risk coefficient for early-stage DCM. This model was validated both in the training and validation cohorts.

Results

ALVDD was independently correlated with the number of comorbidities [with one comorbidity: odds ratio (OR) = 3.009; with two comorbidities: OR = 4.026], HbA1c (OR = 1.773), myocardial blood flow (OR = 0.841), and global longitudinal strain (OR = 0.856) (all P < 0.05). They constituted a nomogram to visualize the likelihood of DCM development in T2DM patients with normal cardiac function. The model was validated to present strong discrimination and calibration, and obtained clinical net benefits both in the training and validation cohorts.

Conclusion

We constructed and validated a nomogram to estimate the likelihood of developing early-stage DCM in T2DM patients with normal cardiac function. The alteration of the nomogram-predicted risk coefficient is expected to be proposed as a therapeutic target to slow or stop DCM progression.

Impact of overestimation of fractional flow reserve by adenosine on anatomical-functional mismatch

Adenosine occasionally results in overestimation of fractional flow reserve (FFR) values, compared with other hyperemic stimuli. We aimed to elucidate the association of overestimation of FFR by adenosine with anatomically significant but functionally non-significant lesions (anatomical-functional mismatch) and its influence on reclassification of functional significance. Distal-to-aortic pressure ratio (Pd/Pa) was measured using adenosine (Pd/PaADN) and papaverine (Pd/PaPAP) in 326 patients (326 vessels). The overestimation of FFR was calculated as Pd/PaADN-Pd/PaPAP. The anatomical-functional mismatch was defined as diameter stenosis > 50% and Pd/PaADN > 0.80. Reclassification was indicated by Pd/PaADN > 0.80 and Pd/PaPAP ≤ 0.80. The mismatch (n = 72) had a greater overestimation of FFR than the non-mismatch (n = 99): median 0.02 (interquartile range 0.01-0.05) versus 0.01 (0.00-0.04), p = 0.014. Multivariable analysis identified the overestimation of FFR (p = 0.003), minimal luminal diameter (p = 0.001), and non-left anterior descending artery (LAD) location (p < 0.001) as determinants of the mismatch. Reclassification was indicated in 29% of the mismatch and was more frequent in the LAD than in the non-LAD (52% vs. 20%, p = 0.005). The overestimation of FFR is an independent determinant of anatomical-functional mismatch. Anatomical-functional mismatch, specifically in the LAD, may suggest a false-negative result.

Importance of plaque volume and composition for the prediction of myocardial ischaemia using sequential coronary computed tomography angiography/positron emission tomography imaging

AIMS

Coronary atherosclerosis with a large necrotic core has been postulated to reduce the vasodilatory capacity of vascular tissue. In the present analysis, we explored whether total plaque volume and necrotic core volume on coronary computed tomography angiography (CCTA) are independently associated with myocardial ischaemia on positron emission tomography (PET).

METHODS AND RESULTS

From a registry of symptomatic patients with suspected coronary artery disease and clinically indicated CCTA with sequential [15O]H2O PET myocardial perfusion imaging, we quantitatively measured diameter stenosis, total and compositional plaque volumes on CCTA. Primary endpoint was myocardial ischaemia on PET, defined as an absolute stress myocardial blood flow ≤2.4 mL/g/min in ≥1 segment. Multivariable prediction models for myocardial ischaemia were consecutively created using logistic regression analysis (stenosis model: diameter stenosis ≥50%; plaque volume model: +total plaque volume; plaque composition model: +necrotic core volume). A total of 493 patients (mean age 63 ± 8 years, 54% men) underwent sequential CCTA/PET imaging. In 153 (31%) patients, myocardial ischaemia was detected on PET. Diameter stenosis ≥50% (P < 0.001) and necrotic core volume (P = 0.029) were independently associated with myocardial ischaemia, while total plaque volume showed borderline significance (P = 0.052). The plaque composition model (χ2 = 169) provided incremental value for the prediction of ischaemia when compared with the stenosis model (χ2 = 138, P < 0.001) and plaque volume model (χ2 = 164, P = 0.021).

CONCLUSION

The volume of necrotic core on CCTA independently and incrementally predicts myocardial ischaemia on PET, beyond diameter stenosis alone.

Clinically viable myocardial CCTA segmentation for measuring vessel-specific myocardial blood flow from dynamic PET/CCTA hybrid fusion

Background

Positron emission tomography (PET)-derived LV MBF quantification is usually measured in standard anatomical vascular territories potentially averaging flow from normally perfused tissue with those from areas with abnormal flow supply. Previously we reported on an image-based tool to noninvasively measure absolute myocardial blood flow at locations just below individual epicardial vessel to help guide revascularization. The aim of this work is to determine the robustness of vessel-specific flow measurements (MBF^vs) extracted from the fusion of dynamic PET (dPET) with coronary computed tomography angiography (CCTA) myocardial segmentations, using flow measured from the fusion with CCTA manual segmentation as the reference standard.

Methods

Forty-three patients’ ¹³NH₃ dPET, CCTA image datasets were used to measure the agreement of the MBF^vs profiles after the fusion of dPET data with three CCTA anatomical models: (1) a manual model, (2) a fully automated segmented model and (3) a corrected model, where major inaccuracies in the automated segmentation were briefly edited. Pairwise accuracy of the normality/abnormality agreement of flow values along differently extracted vessels was determined by comparing, on a point-by-point basis, each vessel’s flow to corresponding vessels’ normal limits using Dice coefficients (DC) as the metric.

Results

Of the 43 patients CCTA fully automated mask models, 27 patients’ borders required manual correction before dPET/CCTA image fusion, but this editing process was brief (2–3 min) allowing a 100% success rate of extracting MBF^vs in clinically acceptable times. In total, 124 vessels were analyzed after dPET fusion with the manual and corrected CCTA mask models yielding 2225 stress and 2122 rest flow values. Forty-seven vessels were analyzed after fusion with the fully automatic masks producing 840 stress and 825 rest flow samples. All DC coefficients computed globally or by territory were ≥ 0.93. No statistical differences were found in the normal/abnormal flow classifications between manual and corrected or manual and fully automated CCTA masks.

Conclusion

Fully automated and manually corrected myocardial CCTA segmentation provides anatomical masks in clinically acceptable times for vessel-specific myocardial blood flow measurements using dynamic PET/CCTA image fusion which are not significantly different in flow accuracy and within clinically acceptable processing times compared to fully manually segmented CCTA myocardial masks.

Characteristics of Myocardial Perfusion in Type 2 Diabetes Mellitus and Its Association with Left Ventricular Diastolic Dysfunction: A Study of Myocardial Contrast Echocardiography

Background

Diabetic cardiomyopathy (DCM) will gradually progress to heart failure without intervention. The timely identification of left ventricular diastolic dysfunction (LVDD) in the early stage and active intervention helps delay the onset of heart failure. Although myocardial contrast echocardiography (MCE) allows an accurate evaluation of myocardial perfusion (MP), the characteristics of MP in early-stage or even sub-clinical LVDD are still unclear.

Objective

This study aims to reveal the characteristics of MP in asymptomatic and normotensive patients with type 2 diabetes mellitus (T2DM) using MCE and investigate its association with LVDD development.

Methods

A total of 327 T2DM patients were retrospectively analyzed. Patients diagnosed with LVDD were included in the LVDD+ group (n = 76), and those with normal left ventricular diastolic function were included in the LVDD- group (n = 251). The clinical characteristics, general echocardiographic findings, and MCE parameters were compared between the two groups. The accuracy of MCE parameters in the diagnosis of LVDD and their correlations with characteristics of T2DM were evaluated.

Results

In the LVDD+ group, the A×β (derived from the replenishment curve of MCE, presenting myocardial blood flow) was significantly lower, and the HbA1c and diabetes duration were significantly higher compared to the LVDD- group (all P < 0.05). The decrease of A×β helped warn the occurrence of LVDD although it was not suitable for the independent diagnosis of LVDD (AUC = 0.745). A×β was negatively correlated with diabetes duration and HbA1c (r = -0.350 and -0.226, both P < 0.001).

Conclusion

MCE was feasible for detecting MP abnormalities in asymptomatic T2DM patients. Although the A×β values of T2DM patients with subclinical LVDD were better than those with diagnosed LVDD, it impaired with the increase of HbA1c and diabetes duration. It suggested that MCE might be useful for monitoring glycemic control in T2DM patients with DCM.

Relation of Obstructive Sleep Apnea in Patients With a Coronary Chronic Total Occlusion to Coronary Collaterals and Mortality

A chronic total occlusion (CTO) is frequently identified in patients undergoing coronary angiography. The prognostic implications of intermittent hypoxia from obstructive sleep apnea (OSA) on patients with a CTO, and effects on collateral recruitment are unknown. The aim of this study was to determine the prevalence, vascular effects, and prognostic implications of the presence of OSA in patients with a CTO. Patients with a CTO between July 2010 and December 2019 were reviewed. Electronic medical records were accessed to determine documented patient history of OSA, demographics, and clinical course. Patients with robust collateral recruitment were defined as Rentrop grade 2 or 3. A total of 948 patients were included in the study, of which 127 (13.4%) had a documented history of OSA. These patients were younger (67.0 years vs 70.6 years, p < 0.01), had a higher body mass index (29.6 kg/m² vs 26.7 kg/m², p < 0.0001), higher rates of hypertension (91.3% vs 83.2%, p < 0.05), higher rates of smokers (63.3% vs 49.0%, p < 0.01) and more use of β-blockers (79% vs 68.5%, p < 0.05) and statins (92.7% vs 82.1%, p < 0.01). A documented history of OSA was independently associated with robust collaterals (OR 3.0 95%CI 1.5 to 5.8, p < 0.01) and lower mortality (HR 0.3 95% CI 0.1 to 0.7, p < 0.01) with a mean survival of 10.8 years, as compared to 8.1 years (log rank p < 0.0001). In conclusion, in patients with a CTO, documented OSA is independently associated with more robust coronary collaterals and lower mortality. The possible cardioprotective implications of intermittent hypoxia in OSA, as well as treatment effect requires further investigation.

Early onset of left ventricular regional asynchrony in arteries with sub-clinical stenosis

BACKGROUND

Asynchrony has been reported to be a marker of ischemic-induced left ventricular dysfunction, the magnitude of which correlates with extent of epicardial coronary disease. We wished to determine whether normal-appearing arterial territories with mild degrees of asynchrony have lower 82Rb PET absolute myocardial blood flow (MBF) and/or lower myocardial flow reserve (MFR).

METHODS AND RESULTS

Data were examined retrospectively for 105 patients evaluated for known/suspected CAD who underwent rest/regadenoson-stress 82Rb PET/CT and quantitative coronary angiography. Rest and stress absolute MBF and MFR were quantified from first-pass 82Rb PET curves. Regional relative myocardial perfusion summed stress score (SSS), summed rest score (SRS), regional phase bandwidth (BW), and regional semi-quantitative asynchrony visual scores of (Asynch) were assessed. We found that in apparently normal arteries (SSS < 4, SRS < 4 and stenosis < 70%), those with abnormally low MFR < 2.0 compared to those with MFR ≥ 2.0 had larger phase BW (186 ± 79° vs 158 ± 67°, P = .02), and more visually apparent Asynch (5.7 ± 4.2 vs 3.9 ± 3.6, P = .02), which was associated with increasing stenosis values (ρ = 0.44, P < .0001).

CONCLUSION

A subgroup of coronary territories with normal relative perfusion and normal or non-obstructive coronary disease may have reduced MFR, which is signaled physiologically by a mild degree of left ventricular asynchrony.

Global Fractional Flow Reserve Value Predicts 5-Year Outcomes in Patients With Coronary Atherosclerosis But Without Ischemia

Background

Global fractional flow reserve (FFR) (ie, the sum of the FFR values in the 3 major coronary arteries) is a physiologic correlate of global atherosclerotic burden. The objective of the present study was to investigate the value of global FFR in predicting long‐term clinical outcome of patients with stable coronary artery disease but no ischemia‐inducing stenosis.

Methods and Results

We studied major adverse cardiovascular events (MACEs: all‐cause death, myocardial infarction, and any revascularization) after 5 years in 1122 patients without significant stenosis (all FFR >0.80; n=275) or with at least 1 significant stenosis successfully treated by percutaneous coronary intervention (ie, post–percutaneous coronary intervention FFR >0.80; n=847). The patients were stratified into low, mid, or high tertiles of global FFR (≤2.80, 2.80–2.88, and ≥2.88). Patients in the lowest tertile of global FFR showed the highest 5‐year MACE rate compared with those in the mid or high tertile of global FFR (27.5% versus 22.0% and 20.9%, respectively; log‐rank P=0.040). The higher 5‐year MACE rate was mainly driven by a higher rate of revascularization in the low global FFR group (16.4% versus 11.3% and 11.8%, respectively; log‐rank P=0.038). In a multivariable model, an increase in global FFR of 0.1 unit was associated with a significant reduction in the rates of MACE (hazard ratio [HR], 0.988; 95% CI, 0.977–0.998; P=0.023), myocardial infarction (HR, 0.982; 95% CI, 0.966–0.998; P=0.032), and revascularization (HR, 0.985; 95% CI, 0.972–0.999; P=0.040).

Conclusions

Even in the absence of ischemia‐producing stenoses, patients with a low global FFR, physiologic correlate of global atherosclerotic burden, present a higher risk of MACE at 5‐year follow‐up.

Coronary microvascular dysfunction in stable ischaemic heart disease (non-obstructive coronary artery disease and obstructive coronary artery disease)

Diffuse and focal epicardial coronary disease and coronary microvascular abnormalities may exist side-by-side. Identifying the contributions of each of these three players in the coronary circulation is a difficult task. Yet identifying coronary microvascular dysfunction (CMD) as an additional player in patients with coronary artery disease (CAD) may provide explanations of why symptoms may persist frequently following and why global coronary flow reserve may be more prognostically important than fractional flow reserve measured in a single vessel before percutaneous coronary intervention. This review focuses on the challenges of identifying the presence of CMD in the context of diffuse non-obstructive CAD and obstructive CAD. Furthermore, it is going to discuss the pathophysiology in this complex situation, examine the clinical context in which the interaction of the three components of disease takes place and finally look at non-invasive diagnostic methods relevant for addressing this question.

Vessel-specific quantification of absolute myocardial blood flow, myocardial flow reserve and relative flow reserve by means of fused dynamic 13NH3 PET and CCTA: Ranges in a low-risk population and abnormality criteria

OBJECTIVES

The goal of the present work is to present a novel methodology for the extraction of MBF, MFR and RFR along coronary arteries by means of multimodality image fusion of dynamic PET and CCTA images.

BACKGROUND

FFR is the reference standard to identify flow-limiting lesions, but its invasiveness limits broad application. New noninvasive methodologies are warranted to stratify patients and guide treatment.

METHODS

A group of 16 low-risk CAD subjects who underwent both 13NH3 PET and CCTA were analyzed. Image fusion techniques were employed to align the studies and CCTA-derived anatomy used to identify coronaries trajectories. MBF was calculated by means of a 1-tissue compartmental model for the standard vascular territories and along patient-specific vessel paths from the base to the apex of the heart.

RESULTS

Low-risk ranges for MBF. MFR and RFR for LAD, LCX and rPDA were computed for the entire cohort and separated by gender. Computed low-risk ranges were used to assess a prospective patient with suspected CAD.

CONCLUSIONS

Our vessel-specific functional indexes and 3D displays offer promise to more closely replicate what is commonly performed during a catheterization session and have the potential of providing effective noninvasive tools for the identification of flow-limiting lesions and image-guided therapy.

Reduced effects of cardiac extracorporeal shock wave therapy on angiogenesis and myocardial function recovery in patients with end-stage coronary artery and renal diseases

Background

Growing evidence have shown cardiac extracorporeal shock wave therapy (ESWT) improve clinical symptoms and left ventricular ejection fraction (LVEF) for patients with end-stage diffuse coronary artery disease (EnD-CAD) unsuitable for coronary interventions. However, little is known whether cardiac ESWT remains effective on symptomatic relief and improvement of LVEF for the EnD-CAD patients with end-stage renal disease (ESRD).

Methods

This was a small-scale prospective study. Between August 2016 and January 2019, a total of 16 subjects received cardiac ESWT for their EnD-CAD. They were divided into two groups according to ESRD or not, i.e., EnD-CAD group (n = 8) and EnD-CAD/ESRD group (n = 8). Clinical symptoms including angina and dyspnea, levels of circulating endothelial progenitor cells (EPC), LVEF, and adverse events were regularly followed up for one year to compare safety and efficacy of cardiac ESWT between the EnD-CAD patients with or without ESRD.

Results

All participants tolerated cardiac ESWT without any relevant side effects such as skin allergic reaction, local redness/tenderness or cardiac arrhythmia. There were similar baseline comorbidities and clinical features between two groups, but the EnD-CAD/ESRD group had significantly higher serum potassium level as well as lower renal function and lipid profile (all p-values <0.03). After cardiac ESWT, the patients in both groups had significant improvement in angina and dyspnea at 1 year (all p-values <0.03). However, the EnD-CAD/ESRD group did not have increase in either circulating EPC levels or LVEF at 6 months (mean change in LVEF: −4.00% ± 8.32%, p = 1.000). In contrast, the EnD-CAD group had gradually improving levels of circulating EPC surface markers and increased LV systolic function (mean change in LVEF: +4.87% ± 8.76%, p = 0.092). Notably, patients in the EnD-CAD/ESRD group suffered from high incidental clinical adverse events before and after enrollment into the ESWT study (75% vs. 25%, p = 0.132).

Conclusion

Although cardiac ESWT provided improvement of clinical symptoms in the EnD-CAD patients, its long-term effects on the angiogenesis and LVEF were reduced for those high-risk patients with concomitant EnD-CAD and ESRD.

Trial registration

none.

SPECT Versus PET Myocardial Perfusion Imaging in Patients with Equivocal CT

PURPOSE OF REVIEW

The most pertinent clinical question in post-coronary computed tomography angiography (CCTA) patients is the assessment of the physiological significance of an anatomically identified stenosis. The clinical application of radionuclide MPI using single-photon emission computed tomography (SPECT) versus positron emission tomography (PET) in the evaluation and management of patients with an inconclusive CCTA is reviewed using a case-based approach.

RECENT FINDINGS

Recent evidence suggests that CCTA is the most sensitive non-invasive test to exclude angiographic CAD and may be an effective first-line test especially among symptomatic low-intermediate risk patients. However, in the presence of angiographic atherosclerosis, its specificity and positive predictive value for identifying flow-limiting stenosis are modest. Radionuclide myocardial perfusion imaging offers accurate quantitative assessment of myocardial ischemia, which helps with risk stratification and patient management especially the potential need for revascularization. Routine accurate quantifications of myocardial blood flow and flow reserve are major advantages of PET MPI, which are especially useful when used in patients at intermediate-high clinical risk.

"Apical thinning": Relations between myocardial wall thickness and apical left ventricular tracer uptake as assessed with positron emission tomography myocardial perfusion imaging

BACKGROUND

A reduction in left ventricular apical tracer uptake (apical thinning) is frequently observed in myocardial perfusion imaging (MPI), yet its cause remains a matter of debate, particularly in perfusion emission tomography (PET). This analysis sought to determine whether apical thinning in PET-MPI is attributable to true anatomical thinning of the left ventricular apical myocardium.

METHODS AND RESULTS

We retrospectively analyzed 57 patients without any history or signs of apical myocardial infarction who underwent rest PET-MPI with 13N-ammonia and contrast-enhanced cardiac computed tomography (CT). Semi-quantitative normalized percent apical 13N-ammonia uptake at rest, myocardial blood flow (MBF), and k2 wash-out rate constants were compared to apical myocardial wall thickness measurements derived from CT and base-to-apex gradients were calculated. Apical thinning was found in 93% of patients and in 74% when analysis of normalized apical tracer uptake was confined to end-systole. No significant correlation was found between apical myocardial thickness and apical tracer uptake (r = - 0.080, P = .553), MBF (r = - 0.211, P = .115), or k2 wash-out rate (r = - 0.023, P = .872), nor between apical myocardial thickness and any gradients. A statistically significant but small difference in apical myocardial thickness was observed in patients with moderately to severely reduced apical tracer uptake vs patients with normal to mildly reduced uptake (4.3 ± 0.7 mm vs 4.7 ± 0.7 mm; P = .043).

CONCLUSIONS

Apical thinning is a highly prevalent finding during 13N-ammonia PET-MPI that is not solely attributable to true anatomical apical wall thickness or the partial volume effect. Other factors that yet need to be identified seem to have a more prominent impact.

PET Perfusion and Flow Assessment: Tomorrows' Technology Today

Quantitative myocardial perfusion PET/CT imaging is one of the most accurate tests for diagnosis and risk stratification of patients with suspected or known CAD. The test provides a comprehensive evaluation of patients with ischemic heart disease including quantitative assessments of regional myocardial perfusion, LV volumes and ejection fraction, calcified atherosclerotic burden, and myocardial blood flow and flow reserve (MFR). A normal stress myocardial blood flow and MFR (>2.0) has a very high negative predictive value and reliably excludes high-risk obstructive CAD. A global normal MFR (>2.0) identifies patients at consistently lower clinical risk. Conversely, a severely reduced MFR (<1.5) identifies patients at high clinical risk for adverse events regardless of whether this is due to obstructive CAD, microvascular dysfunction, or a combination of the 2. On the other hand, the delineation of atherosclerotic burden with either a formal quantitative coronary calcium score or by a semiquantitative assessment of the CT transmission scan is very helpful to guide the need for intensive preventive therapies. Recent evidence suggests that patients with angiographically obstructive CAD and a severe reduction in flow reserve (<1.6) may have a prognostic advantage from revascularization. This finding awaits confirmation by randomized clinical trials.

Diagnostic value of peak filling rate derived from ECG-gated myocardial perfusion SPECT for detecting myocardial ischaemia in patients with non-obstructive coronary artery disease

Background: Left ventricular (LV) diastolic dysfunction represents an earlier step of the ischaemic cascade. We tested the hypothesis that the index of LV diastolic function from electrocardiogram (ECG)-gated single photon emission computed tomography (SPECT) is useful in detecting myocardial ischaemia in patients with non-obstructive coronary artery disease (CAD).Methods: One-hundred-ten patients with non-obstructive CAD and summed redistribution score of zero were enrolled. Summed difference score (SDS) of ≥2 was considered as the presence of myocardial ischaemia. Peak filling rate (PFR) defined as the maximum dV/dt divided by LV end-diastolic volume was obtained as the index of LV diastolic function.Results: Of 110 patients with non-obstructive CAD, 51 patients had myocardial ischaemia. SDSs in patients with myocardial ischaemia and those without were 3.5 ± 1.8 and 0.4 ± 0.5, respectively (p < 0.001). PFRs after stress (r = -0.22, p = 0.02) and at redistribution (r = -0.24, p = 0.01) were inversely correlated with SDS. Multivariate logistic regression analysis showed that PFR at redistribution was an independent predictor of the presence of myocardial ischaemia in patients with non-obstructive CAD (odds ratio: 0.15, 95% confidence interval: 0.04-0.51, p = 0.002).Conclusion: Our data suggest that PFR, the index of LV diastolic function from ECG-gated SPECT, helps to find myocardial ischaemia in patients with non-obstructive CAD.

Clinical implications of three-vessel fractional flow reserve measurement in patients with coronary artery disease

Aims

There are limited data on the clinical implications of total physiologic atherosclerotic burden assessed by invasive physiologic studies in patients with coronary artery disease. We investigated the prognostic implications of total physiologic atherosclerotic burden assessed by total sum of fractional flow reserve (FFR) in three vessels (3V-FFR).

Methods and results

A total of 1136 patients underwent FFR measurement in three vessels (3V FFR-FRIENDS study, NCT01621438). The patients were classified into high and low 3V-FFR groups according to the median value of 3V-FFR (2.72). The primary endpoint was major adverse cardiac events (MACE, a composite of cardiac death, myocardial infarction and ischaemia-driven revascularization) at 2 years. Mean angiographic percent diameter stenosis and FFR were 43.7 ± 19.3% and 0.90 ± 0.08, respectively. There was a negative correlation between 3V-FFR and estimated 2-year MACE rate (P < 0.001). The patients in low 3V-FFR group showed a higher risk of 2-year MACE than those in the high 3V-FFR group [(7.1% vs. 3.8%, hazard ratio (HR) 2.205, 95% confidence interval (CI) 1.201-4.048, P = 0.011]. The higher 2-year MACE rate was mainly driven by the higher rate of ischaemia-driven revascularization in the low 3V-FFR group (6.2% vs. 2.7%, HR 2.568, 95% CI 1.283-5.140, P = 0.008). In a multivariable adjusted model, low 3V-FFR was an independent predictor of MACE (HR 2.031, 95% CI 1.078-3.830, P = 0.029).

Conclusion

Patients with high total physiologic atherosclerotic burden assessed by 3V-FFR showed higher risk of 2-year clinical events than those with low total physiologic atherosclerotic burden. The difference was mainly driven by ischaemia-driven revascularization for both functionally significant and insignificant lesions at baseline. Three-vessel FFR might be used as a prognostic indicator in patients with coronary artery disease.

Clinical trial registration

3V FFR-FRIENDS study (https://clinicaltrials.gov/ct2/show/NCT01621438, NCT01621438).

Coronary Microvascular Dysfunction: Clinical Considerations and Noninvasive Diagnosis

Chest pain in patients without obstructive coronary artery disease has been realized as a frequent problem encountered in clinical practice. Invasive flow investigations have suggested that up to two-thirds of patients with nonobstructive coronary atherosclerosis may have microvascular dysfunction (MVD). Positron emission tomography myocardial perfusion imaging in conjunction with tracer-kinetic modeling enables the concurrent quantification of myocardial blood flow (MBF) in milliliters per minute per gram of tissue. This allows the assessment of hyperemic MBFs and myocardial flow reserve for the noninvasive identification and characterization of MVD as an important functional substrate for angina symptoms amenable to intensified and individualized medical intervention with nitrates, calcium-channel blockers, statins, angiotensin-converting enzyme inhibitors, and/or angiotensin II type 1 receptor blockers. Recent investigations suggest that cardiac magnetic resonance and computed tomography may also be suitable for the noninvasive detection of MVD. Whether intensified and individualized treatment related improvement or even normalization of hyperemic MBF and/or myocardial flow reserve may lead to a persistent reduction in angina symptoms and/or improved cardiovascular outcome as compared to standard care, deserves further testing in large-scale randomized clinical trials.

Coronary Microvascular Disease Pathogenic Mechanisms and Therapeutic Options: JACC State-of-the-Art Review

Coronary microvascular disease (CMD) refers to the subset of disorders affecting the structure and function of the coronary microcirculation, is prevalent in patients across a broad spectrum of cardiovascular risk factors, and is associated with an increased risk of adverse events. Contemporary evidence supports that most patients with CMD also have macrovessel atherosclerosis, which has important implications for their prognosis and management. In this state-of-the-art review, the authors summarize the pathophysiology of CMD, provide an update of diagnostic testing strategies, and classify CMD into phenotypes according to severity and coexistence with atherosclerosis. They examine emerging data highlighting the significance of CMD in specific populations, including obesity and insulin resistance, myocardial injury and heart failure with preserved ejection fraction, and nonobstructive and obstructive coronary artery disease. Finally, they discuss the role of CMD as a potential target for novel interventions beyond conventional approaches, representing a new frontier in cardiovascular disease reduction.

PET-measured longitudinal flow gradient correlates with invasive fractional flow reserve in CAD patients

Aims

We aimed to evaluate whether a PET-determined longitudinal decrease in myocardial blood flow (MBF) or gradient, assumed as a more specific flow parameter for epicardial resistance, correlates with invasively measured fractional flow reserve (FFR) in coronary artery disease (CAD) patients.

Methods and Results

In 29 patients with suspected or known CAD, myocardial perfusion and MBF in mL/g/min was determined with 13N-ammonia PET/CT during regadenoson stimulation and at rest, and corresponding myocardial flow reserve (MFR = MBF stress/MBF rest) was calculated. MBF parameters were assessed in the myocardial region with stress-related perfusion defect and with stenosis ≥50% (Region 1), without defect but with stenosis ≥50% (Region 2), or without stenosis ≥50% (Region 3). Hyperaemic MBFs were significantly lower in the mid-distal than in the mid-left ventricular myocardium in Regions 1-3 [median and IQ range: 1.57 (1.24, 1.84) vs. 1.87 (1.61, 2.00), and 1.23 (1.11, 1.86) vs. 1.89 (1.80, 1.97), and 1.78 (1.48, 2.00) vs. 1.94 (1.84, 2.05) mL/g/min, P < 0.0001]. Resulting longitudinal MBF gradient during hyperaemic flows was more pronounced in Region 2 than in Regions 1 and 3, respectively [-0.46 (-0.70, -0.10) vs. -0.17 (-0.29, -0.11) and -0.15 (-0.25, -0.09) mL/g/min, respectively, P < 0.01]. There was a significant correlation between the hyperaemic longitudinal MBF gradient and FFR (r = 0.95; P < 0.0001), while this association was less pronounced for corresponding MFR (r = 0.50; P = 0.006).

Conclusion

The observed close correlation between a longitudinal MBF gradient during hyperaemic flows and invasively measured FFR suggests the longitudinal flow gradient as an emerging non-invasive index of flow-limiting CAD.

Myocardial ischemia in the absence of obstructive coronary lesion: The role of post-stress diastolic dysfunction in detecting early coronary atherosclerosis

BACKGROUND

The interactions between non-obstructive coronary atherosclerosis (<50% stenosis) and myocardial perfusion and functional parameters on myocardial perfusion imaging (MPI) have never been evaluated.

METHODS AND RESULTS

One-hundred and ninety-five patients were submitted to stress-rest MPI and invasive coronary angiography. The presence of obstructive coronary lesions (>50% stenosis) was excluded. The summed stress score (SSS) was calculated in every patient. Moreover, the left ventricular (LV) ejection fraction (EF) and peak filling rate (PFR) were computed from gated MPI images as measures of systolic and diastolic functions. Sixty/195 patients (31%) showed the presence of non-obstructive atherosclerosis (>20% and <50% diameter reduction). Interestingly, they presented a higher SSS than those with normal coronary arteries (P < 0.001) despite a similar myocardial scar burden. If compared to patients with normal coronary arteries, those with non-obstructive atherosclerosis showed more abnormal post-stress PFR values (2.5 ± 0.9 vs 2.9 ± 0.8, P = 0.004), despite a similar EF. On multivariate analysis, the presence non-obstructive atherosclerosis was the only significant predictor (P = 0.026) of post-stress LV diastolic impairment, independently from perfusion parameters.

CONCLUSIONS

In patients without anatomically significant coronary lesions, the development of post-stress LV diastolic dysfunction on MPI associates with the presence of non-obstructive atherosclerosis on coronary angiography.

Positron Emission Tomography-Determined Hyperemic Flow, Myocardial Flow Reserve, and Flow Gradient-Quo Vadis?

Positron emission tomography/computed tomography (PET/CT) applied with positron-emitting flow tracers such as ¹³N-ammonia and ⁸²Rubidium enables the quantification of both myocardial perfusion and myocardial blood flow (MBF) in milliliters per gram per minute for coronary artery disease (CAD) detection and characterization. The detection of a regional myocardial perfusion defect during vasomotor stress commonly identifies the culprit lesion or most severe epicardial narrowing, whereas adding regional hyperemic MBFs, myocardial flow reserve (MFR), and/or longitudinal flow decrease may also signify less severe but flow-limiting stenosis in multivessel CAD. The addition of regional hyperemic flow parameters, therefore, may afford a comprehensive identification and characterization of flow-limiting effects of multivessel CAD. The non-specific origin of decreases in hyperemic MBFs and MFR, however, prompts an evaluation and interpretation of regional flow in the appropriate context with the presence of obstructive CAD. Conversely, initial results of the assessment of a longitudinal hyperemic flow gradient suggest this novel flow parameter to be specifically related to increases in CAD caused epicardial resistance. The concurrent assessment of myocardial perfusion and several hyperemic flow parameters with PET/CT may indeed open novel avenues of precision medicine to guide coronary revascularization procedures that may potentially lead to a further improvement in cardiovascular outcomes in CAD patients.

The effect of coronary revascularization on regional myocardial blood flow as assessed by stress positron emission tomography

OBJECTIVES

We examined whether regional improvement in stress myocardial blood flow (sMBF) following angiography-guided coronary revascularization depends on the existence of a perfusion defect on positron emission tomography (PET).

BACKGROUND

Percent stenosis on coronary angiography often is the main factor when deciding whether to perform revascularization, but it does not reliably relate to maximum sMBF. PET is a validated method of assessing sMBF.

METHODS

19 patients (79% M, 65 ± 12 years) underwent PET stress before and after revascularization (17 PCI, 2 CABG). Pre- and post-revascularization sMBF for each left ventricular quadrant (anterior, septal, lateral, and inferior) was stratified by the presence or absence of a baseline perfusion defect on PET and whether that region was revascularized.

RESULTS

Intervention was performed on 40 of 76 quadrants. When a baseline perfusion defect existed in a region that was revascularized (n = 26), post-revascularization flow increased by 0.6 ± 0.7 cc/min/g (1.2 ± 0.4 vs 1.7 ± 0.8, P < 0.001). When no defect existed but revascularization was performed (n = 14), sMBF did not change significantly (1.7 ± 0.3 vs 1.5 ± 0.4 cc/min/g, P = 0.16). In regions without a defect that were not revascularized (n = 29), sMBF did not significantly change (2.0 ± 0.6 vs 1.9 ± 0.7, P = 0.7).

CONCLUSIONS

When a stress-induced perfusion defect exists on PET, revascularization improves sMBF in that region. When there is no such defect, sMBF shows no net change, whether or not intervention is performed in that area. PET stress may be useful for identifying areas of myocardium that could benefit from revascularization, and also areas in which intervention is unlikely to yield improvement in myocardial blood flow.

Diffuse coronary artery disease among other atherosclerotic plaque characteristics by coronary computed tomography angiography for predicting coronary vessel-specific ischemia by fractional flow reserve

BACKGROUND AND AIMS

Coronary computed tomography angiography (CCTA) permits effective identification of diffuse CAD and atherosclerotic plaque characteristics (APCs). We sought to examine the usefulness of diffuse CAD beyond luminal narrowing and APCs by CCTA to detect vessel-specific ischemia.

METHODS

407 vessels (n = 252 patients) from the DeFACTO diagnostic accuracy study were retrospectively analyzed for percent plaque diffuseness (PD). Percent plaque diffuseness (PD) was obtained on per-vessel level by summation of all contiguous lesion lengths and divided by total vessel length, and was logarithmically transformed (log percent PD). Additional CCTA measures of stenosis severity including minimal lumen diameter (MLD), and APCs, such as positive remodeling (PR) and low attenuation plaque (LAP), were also included. Vessel-specific ischemia was defined as fractional flow reserve (FFR) ≤0.80. Multivariable regression, discrimination by area under the receiver operating characteristic curve (AUC), and category-free net reclassification improvement (cNRI) were assessed.

RESULTS

Backward stepwise logistic regression revealed that for every unit increase in log percent PD, there was a 58% (95% CI: 1.01-2.48, p = 0.048) rise in the odds of having an abnormal FFR, independent of stenosis severity and APCs. The AUC indicated no further improvement in discriminatory ability after adding log percent PD to the final parsimonious model of MLD, PR, and LAP (AUC difference: 0.003, 95% CI: -0.003-0.010, p = 0.33). Conversely, adding log percent PD to the base model of MLD, PR, and LAP improved cNRI by 0.21 (95% CI: 0.01-0.41, p < 0.001).

CONCLUSIONS

Accounting for diffuse CAD may help improve the accuracy of CCTA for detecting vessel-specific ischemia.

Visualization of the improvement of myocardial perfusion after coronary intervention using motorized fractional flow reserve pullback curve

This study aimed to evaluate the feasibility and utility of using motorized pullback of the pressure guidewire to provide a graphic assessment and prediction of the benefits of coronary intervention. Fractional flow reserve (FFR) measurements were performed with motorized pullback imaging in 20 patients who underwent successful percutaneous coronary intervention (PCI) of the left anterior descending artery. Physiological lesion length (PLL) was calculated using frame counts to determine stent length. FFR area was calculated by integrating the FFR values recorded during pullback tracing (FFRarea). The percentage increase in FFR area (%FFRarea) was defined as the ratio of the difference between the pre- and post-intervention FFRarea to the total frame count. The average FFR values were enhanced following PCI, from 0.64 to 0.82, and the median value of the difference between pre- and post-interventional FFR values (D-FFR) and %FFRarea were 0.13 and 10.6%, respectively. The %FFRarea demonstrated a significant positive correlation with D-FFR (R², 0.61; p < 0.01). PLL tended to be longer and the %FFRarea was smaller in lesions with a gradual pressure-drop pattern than those with an abrupt pressure-drop pattern (35.37 vs. 20.40 mm, p = 0.07; 5.78 vs. 16.21%, p < 0.05, respectively). Motorized pullback tracing was able to identify the extent and location of stenosis and help in appropriate stent implantation, in addition to visualizing and quantifying the improvement in FFR following PCI.

Myocardial blood flow: Putting it into clinical perspective

In recent years, positron emission tomography/computed tomography (PET/CT)-determined myocardial perfusion in conjunction with myocardial blood flow (MBF) quantification in mL·g(-1)·min(-1) has emerged from mere research application to initial clinical use in the detection and characterization of the coronary artery disease (CAD) process. The concurrent evaluation of MBF during vasomotor stress and at rest with the resulting myocardial flow reserve (MFR = MBF during stress/MBF at rest) expands the scope of conventional myocardial perfusion imaging not only to the detection of the most advanced and culprit CAD, as evidenced by the stress-related regional myocardial perfusion defect, but also to the less severe or intermediate stenosis in patients with multivessel CAD. Due to the non-specific nature of the hyperemic MBF and MFR, the interpretation of hyperemic flow increases with PET/CT necessitates an appropriate placement in the context with microvascular function, wall motion analysis, and eventually underlying coronary morphology in CAD patients. This review aims to provide a comprehensive overview of various diagnostic scenarios of PET/CT-determined myocardial perfusion and flow quantification in the detection and characterization of clinically manifest CAD.

Normal stress-only myocardial single photon emission computed tomography predicts good outcome in patients with coronary artery stenoses between 40 and 70

OBJECTIVE

Normal stress myocardial single photon emission computed tomography (SPECT) usually indicates good physiologic function of all coronary lesions, and also indicates a good outcome. We hypothesize that it can still predict good outcome in patients with coronary stenoses between 40 and 70%.

METHODS

A group of patients who underwent stress myocardial SPECT after coronary angiography were consecutively recruited in our center. Patients were eligible if they had one or more coronary stenoses between 40 and 70%. Patients with coronary stenoses greater than 50% diameter of left main or greater than 70% diameter of nonleft main epicardial vessels, and left ventricular ejection fraction less than 50% were excluded. The outcome was defined as major adverse events, including cardiac death, nonfatal myocardial infarction, and revascularization. Patients' survival curves were constructed accorded to the method of Kaplan and Meier and compared using the log-rank test.

RESULTS

A study cohort of 77 patients was enrolled. According to the summed stress score, 43 patients were assigned to the perfusion defect group and 34 patients were assigned to the perfusion normal group. The follow-up duration was 6.4±0.3 years. In the perfusion normal group, only one of 34 (2.9%) patients developed major adverse events. In the perfusion defect group, six of 43 (14%) developed major adverse events, P-value of 0.041.

CONCLUSION

It is safe to defer a percutaneous coronary intervention in patients with coronary stenoses between 40 and 70% and normal stress myocardial SPECT.

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

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

Quantitative myocardial perfusion PET parametric imaging at the voxel-level

Quantitative myocardial perfusion (MP) PET has the potential to enhance detection of early stages of atherosclerosis or microvascular dysfunction, characterization of flow-limiting effects of coronary artery disease (CAD), and identification of balanced reduction of flow due to multivessel stenosis. We aim to enable quantitative MP-PET at the individual voxel level, which has the potential to allow enhanced visualization and quantification of myocardial blood flow (MBF) and flow reserve (MFR) as computed from uptake parametric images. This framework is especially challenging for the (82)Rb radiotracer. The short half-life enables fast serial imaging and high patient throughput; yet, the acquired dynamic PET images suffer from high noise-levels introducing large variability in uptake parametric images and, therefore, in the estimates of MBF and MFR. Robust estimation requires substantial post-smoothing of noisy data, degrading valuable functional information of physiological and pathological importance. We present a feasible and robust approach to generate parametric images at the voxel-level that substantially reduces noise without significant loss of spatial resolution. The proposed methodology, denoted physiological clustering, makes use of the functional similarity of voxels to penalize deviation of voxel kinetics from physiological partners. The results were validated using extensive simulations (with transmural and non-transmural perfusion defects) and clinical studies. Compared to post-smoothing, physiological clustering depicted enhanced quantitative noise versus bias performance as well as superior recovery of perfusion defects (as quantified by CNR) with minimal increase in bias. Overall, parametric images obtained from the proposed methodology were robust in the presence of high-noise levels as manifested in the voxel time-activity-curves.

Quantification of myocardial blood flow using non-electrocardiogram-triggered MRI with three-slice coverage

PURPOSE

Accurate quantification of myocardial perfusion is dependent on reliable electrocardiogram (ECG) triggering. Measuring myocardial blood flow (MBF) in patients with arrhythmias or poor ECGs is currently infeasible with MR. The purpose of this study was to demonstrate the feasibility of a non-ECG-triggered method with clinically useful three-slice ventricular coverage for measurement of MBF in healthy volunteers.

METHODS

A saturation recovery magnetization-prepared gradient recalled echo acquisition was continuously repeated during first-pass imaging. A slice-interleaved radial trajectory was employed to enable image-based retrospective triggering. The arterial input function was generated using a beat-by-beat T1 estimation method. The proposed technique was validated against a conventional ECG-triggered dual-bolus technique in 10 healthy volunteers. The technique was further demonstrated under adenosine stress in 12 healthy volunteers.

RESULTS

The proposed method produced MBF with no significant difference compared with the ECG-triggered technique. The proposed method yielded mean myocardial perfusion reserve comparable to published literature.

CONCLUSION

We have developed a non-ECG-triggered quantitative perfusion imaging method. In this preliminary study, our results demonstrate that our method yields comparable MBF compared with the conventional ECG-triggered method and that it is feasible for stress imaging.

Quantification of coronary flow reserve in patients with ischaemic and non-ischaemic cardiomyopathy and its association with clinical outcomes

AIMS

Patients with left ventricular systolic dysfunction frequently show abnormal coronary vascular function, even in the absence of overt coronary artery disease. Moreover, the severity of vascular dysfunction might be related to the aetiology of cardiomyopathy.We sought to determine the incremental value of assessing coronary vascular dysfunction among patients with ischaemic (ICM) and non-ischaemic (NICM) cardiomyopathy at risk for adverse cardiovascular outcomes.

METHODS AND RESULTS

Coronary flow reserve (CFR, stress/rest myocardial blood flow) was quantified in 510 consecutive patients with rest left ventricular ejection fraction (LVEF) ≤45% referred for rest/stress myocardial perfusion PET imaging. The primary end point was a composite of major adverse cardiovascular events (MACE) including cardiac death, heart failure hospitalization, late revascularization, and aborted sudden cardiac death.Median follow-up was 8.2 months. Cox proportional hazards model was used to adjust for clinical variables. The annualized MACE rate was 26.3%. Patients in the lowest two tertiles of CFR (CFR ≤ 1.65) experienced higher MACE rates than those in the highest tertile (32.6 vs. 15.5% per year, respectively, P = 0.004), irrespective of aetiology of cardiomyopathy.

CONCLUSION

Impaired coronary vascular function, as assessed by reduced CFR by PET imaging, is common in patients with both ischaemic and non-ischaemic cardiomyopathy and is associated with MACE.