Coronary Physiology Beyond Coronary Flow Reserve in Microvascular Angina

Differentiating Macrovascular and Microvascular Ischemia Using Fractal Analysis of Dynamic Myocardial Perfusion Stress-CT

OBJECTIVES

Fractal analysis of dynamic myocardial stress computed tomography perfusion imaging (4D-CTP) has shown potential to noninvasively differentiate obstructive coronary artery disease (CAD) and coronary microvascular disease (CMD). This study validates fractal analysis of 4D-CTP in a multicenter setting and assesses its diagnostic accuracy in subgroups with ischemia and nonobstructed coronary arteries (INOCA) and with mild to moderate stenosis.

MATERIALS AND METHODS

From the AMPLIFiED multicenter trial, patients with suspected or known chronic myocardial ischemia and an indication for invasive coronary angiography were included. Patients underwent dual-source CT angiography, 4D-CTP, and CT delayed-enhancement imaging. Coronary artery disease, CMD, and normal perfusion were defined by a combined reference standard comprising invasive coronary angiography with fractional flow reserve, and absolute or relative CT-derived myocardial blood flow. Nonobstructed coronary arteries were defined as ≤25% stenosis and mild to moderate stenosis as 26%-80%.

RESULTS

In 127 patients (27% female), fractal analysis accurately differentiated CAD (n = 61, 23% female), CMD (n = 23, 30% female), and normal perfusion (n = 34, 35% female) with a multiclass area under the receiver operating characteristic curve (AUC) of 0.92 and high agreement (multiclass κ = 0.89). In patients with ischemia (n = 84), fractal analysis detected CAD (n = 61) over CMD (n = 23) with sensitivity of 95%, specificity of 74%, accuracy of 89%, and AUC of 0.83. In patients with nonobstructed coronary arteries (n = 33), INOCA (n = 15) was detected with sensitivity of 100%, specificity of 78%, accuracy of 88%, and AUC of 0.94. In patients with mild to moderate stenosis (n = 27), fractal analysis detected CAD (n = 19) over CMD with sensitivity of 84%, specificity of 100%, accuracy of 89%, and AUC of 0.95.

CONCLUSIONS

In this multicenter study, fractal analysis of 4D-CTP accurately differentiated CAD and CMD including subgroups with INOCA and with mild to moderate stenosis.

Coronary microvascular dysfunction, arrythmias, and sudden cardiac death: A literature review

The coronary vascular system has a unique structure and function that is adaptive to myocardial demand. It is composed of a continuous network of vessels receding in size from epicardial arteries to the microvascular circulation. Failure to meet myocardial demand results in ischemia, angina, and adverse myocardial outcomes. It is evident that 50 % of patients with angina have a non-obstructive coronary disease and 66 % of these patients have coronary microvascular dysfunction (CMD). The impact of CMD on the atria and ventricles is exhibited through its association with atrial fibrillation and distortion of ventricular repolarization. Ultimately, this influence increases the risk of mortality, morbidity, and sudden cardiac arrest. CMD serves as an independent risk for atrial fibrillation, increases ventricular electrical inhomogeneity, and contributes to the progression of cardiac disease. The underlying pathogenesis may be attributed to oxidative stress evident through reactive oxygen species, impaired vasoactive function, and structural disorders such as fibrotic changes. Myocardial ischemia, brought about by a demand-supply mismatch in CMD, may create a milieu for ventricular arrythmia and sudden cardiac arrest through distortion of ventricular repolarization parameters such as QT dispersion and corrected QT dispersion.

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.

Impact of cardiac history and myocardial scar on increase of myocardial perfusion after revascularization

PURPOSE

We sought to assess the impact of coronary revascularization on myocardial perfusion and fractional flow reserve (FFR) in patients without a cardiac history, with prior myocardial infarction (MI) or non-MI percutaneous coronary intervention (PCI). Furthermore, we studied the impact of scar tissue.

METHODS

Symptomatic patients underwent [15O]H2O positron emission tomography (PET) and FFR before and after revascularization. Patients with prior CAD, defined as prior MI or PCI, underwent scar quantification by magnetic resonance imaging late gadolinium enhancement.

RESULTS

Among 137 patients (87% male, age 62.2 ± 9.5 years) 84 (61%) had a prior MI or PCI. The increase in FFR and hyperemic myocardial blood flow (hMBF) was less in patients with prior MI or non-MI PCI compared to those without a cardiac history (FFR: 0.23 ± 0.14 vs. 0.20 ± 0.12 vs. 0.31 ± 0.18, p = 0.02; hMBF: 0.54 ± 0.75 vs. 0.62 ± 0.97 vs. 0.91 ± 0.96 ml/min/g, p = 0.04). Post-revascularization FFR and hMBF were similar across patients without a cardiac history or with prior MI or non-MI PCI. An increase in FFR was strongly associated to hMBF increase in patients without a cardiac history or with prior MI/non-MI PCI (r = 0.60 and r = 0.60, p < 0.01 for both). Similar results were found for coronary flow reserve. In patients with prior MI scar was negatively correlated to hMBF increase and independently predictive of an attenuated CFR increase.

CONCLUSIONS

Post revascularization FFR and perfusion were similar among patients without a cardiac history, with prior MI or non-MI PCI. In patients with prior MI scar burden was associated to an attenuated perfusion increase.

Prognostic value of positron emission tomography derived myocardial flow reserve: A systematic review and meta-analysis

BACKGROUND AND AIMS

Positron Emission Tomography (PET)-derived myocardial flow reserve (MFR) has been shown to have a role in the diagnosis and prognosis of patients with coronary artery disease (CAD). We performed a systematic review and meta-analysis to summarize the body of literature and synthesize the evidence on the prognostic role of PET-derived MFR in patients with known or suspected CAD.

METHODS

A comprehensive literature search of the Medline database from its inception to August 2023, in humans, in any language, was conducted for clinical studies examining the prognostic value of PET imaging in patients of any age, sex, and CAD status. Systematic screening and data extraction of the identified studies were followed by quantitative meta-analysis of PET-MFR's role in predicting adverse clinical events using random effect model. Studies were appraised using the modified Newcastle-Ottawa tool.

RESULTS

A total of 21 studies assessing the prognostic role of PET derived MFR in 46,815 patients with known and/or suspected CAD were included (mean (SD) age 66 (4) years, 48% women). The mean follow-up duration was 36 months (range 10-96). Cardiovascular risk factors were prevalent (73% hypertension, 35% diabetes and 67% dyslipidemia). The definition of the composite outcome varied between studies, with various combinations of mortality, non-fatal myocardial infarction, hospitalization, and coronary revascularization. Pooled impaired MFR was significantly associated with an increased risk of adverse outcomes (RR = 2.94, 95% CI 2.42-3.56, p < 0.001). Results were similar in a subgroup of patients with suspected CAD.

CONCLUSIONS

The available body of evidence shows that impaired PET-derived MFR measured using different tracers and PET systems is strongly associated with an increased risk of adverse cardiovascular events. Limitations of this review include observational nature of studies, marked heterogeneity in patient populations, inconsistency in thresholds to define abnormal MFR, and differing components for the composite outcome.

Accelerated stenotic flow in the left anterior descending coronary artery explains the causes of impaired coronary flow reserve: an integrated transthoracic enhanced Doppler study

Background

Accelerated stenotic flow (AsF) in the entire left anterior descending coronary artery (LAD), assessed by transthoracic enhanced color Doppler (E-Doppler TTE), can reveal coronary stenosis (CS) and its severity, enabling a distinction between the microcirculatory and epicardial causes of coronary flow reserve (CFR) impairment.

Methods

Eighty-four consecutive patients with a CFR <2.0 (1.5 ± 0.4), as assessed by E-Doppler TTE, scheduled for coronary angiography (CA) and eventually intracoronary ultrasounds (IVUS), were studied. CFR was calculated by the ratio of peak diastolic flow velocities: during i.v. adenosine (140 mcg/Kg/m) over resting; AsF was calculated as the percentage increase of localized maximal velocity in relation to a reference velocity.

Results

CA showed ≥50% lumen diameter narrowing of the LAD (critical CS) in 68% of patients (57/84) vs. non-critical CS in 32% (27/84). Based on the established CA/IVUS criteria, the non-critical CS subgroup was further subdivided into 2 groups: subcritical/diffuse [16/27 pts (57%)] and no atherosclerosis [11/27 pts (43%)]. CFR was similar in the three groups: 1.4 ± 0.3 in critical CS, 1.5 ± 0.4 in subcritical/diffuse CS, and 1.6 ± 0.4 in no atherosclerosis (p = ns). Overall, at least one segment of accelerated stenotic flow in the LAD was found in 73 patients (87%), while in 11 (13%) it was not. The AsF was very predictive of coronary segmental narrowing in both angio subgroups of atherosclerosis but as expected with the usage of different cutoffs. On the basis of the ROC curve, the optimal cutoff was 109% and 16% AsF % increment to successfully distinguish critical from non-critical CS (area under the curve [AUC] = 0.99, p < 0.001) and diffuse/subcritical from no CS (AUC = 0.91%, p < 0.001). Sensitivity and specificity were 96% and 100% and 82% and 100%, respectively.

Conclusion

E-Doppler TTE is highly feasible and reliable in detecting the CS of any grade of severity, distinguishing epicardial athero from microvascular causes of a severe CFR reduction.

Prognostic Value of Modified Coronary Flow Capacity Derived From [15O]H2O Positron Emission Tomography Perfusion Imaging

BACKGROUND

Coronary flow capacity (CFC) is a measure that integrates hyperemic myocardial blood flow and coronary flow reserve to quantify the pathophysiological impact of coronary artery disease on vasodilator capacity. This study explores the prognostic value of modified CFC derived from [15O]H2O positron emission tomography perfusion imaging.

METHODS

Quantitative rest/stress perfusion measurements were obtained from 1300 patients with known or suspected coronary artery disease. Patients were classified as having myocardial steal (n=38), severely reduced CFC (n=141), moderately reduced CFC (n=394), minimally reduced CFC (n=245), or normal flow (n=482) using previously defined thresholds. The end point was a composite of death and nonfatal myocardial infarction.

RESULTS

During a median follow-up of 5.5 (interquartile range, 3.7-7.8) years, the end point occurred in 153 (12%) patients. Myocardial steal (hazard ratio [HR], 6.70 [95% CI, 3.21-13.99]; P<0.001), severely reduced CFC (HR, 2.35 [95% CI, 1.16-4.78]; P=0.018), and moderately reduced CFC (HR, 1.95 [95% CI, 1.11-3.41]; P=0.020) were associated with worse prognosis compared with normal flow, after adjusting for clinical characteristics. Similarly, in the overall population, increased resting myocardial blood flow (HR, 3.05 [95% CI, 1.68-5.54]; P<0.001), decreased hyperemic myocardial blood flow (HR, 0.68 [95% CI, 0.52-0.90]; P=0.007) and decreased coronary flow reserve (HR, 0.55 [95% CI, 0.42-0.71]; P<0.001) were independently associated with adverse outcome. In a model adjusted for the combined use of perfusion metrics, modified CFC demonstrated independent prognostic value (overall P=0.017).

CONCLUSIONS

[15O]H2O positron emission tomography-derived resting myocardial blood flow, hyperemic myocardial blood flow, coronary flow reserve, and CFC are prognostic factors for death and nonfatal myocardial infarction in patients with known or suspected coronary artery disease. Importantly, after adjustment for clinical characteristics and the combined use of [15O]H2O positron emission tomography perfusion metrics, modified CFC remained independently associated with adverse outcome.

Tales from the future-nuclear cardio-oncology, from prediction to diagnosis and monitoring

Cancer and cardiovascular diseases (CVD) often share common risk factors, and patients with CVD who develop cancer are at high risk of experiencing major adverse cardiovascular events. Additionally, cancer treatment can induce short- and long-term adverse cardiovascular events. Given the improvement in oncological patients' prognosis, the burden in this vulnerable population is slowly shifting towards increased cardiovascular mortality. Consequently, the field of cardio-oncology is steadily expanding, prompting the need for new markers to stratify and monitor the cardiovascular risk in oncological patients before, during, and after the completion of treatment. Advanced non-invasive cardiac imaging has raised great interest in the early detection of CVD and cardiotoxicity in oncological patients. Nuclear medicine has long been a pivotal exam to robustly assess and monitor the cardiac function of patients undergoing potentially cardiotoxic chemotherapies. In addition, recent radiotracers have shown great interest in the early detection of cancer-treatment-related cardiotoxicity. In this review, we summarize the current and emerging nuclear cardiology tools that can help identify cardiotoxicity and assess the cardiovascular risk in patients undergoing cancer treatments and discuss the specific role of nuclear cardiology alongside other non-invasive imaging techniques.

Echocardiographic assessment of primary microvascular angina and primary coronary microvascular dysfunction

There is an increasing interest in the role of echocardiography in the evaluation of primary microvascular angina, which is attributed to primary coronary microvascular dysfunction. Valid echocardiographic techniques are expected to facilitate the diagnosis and follow-up of these patients and would be valuable for research purposes and therapy evaluation. However, adequate echocardiographic data are lacking, and the interpretation of the limited available literature is hindered by the previous addition of microvascular angina under more inclusive entities, such as cardiac syndrome X. In experienced hands, the assessment of primary coronary microvascular dysfunction in patients with suspected primary microvascular angina, using multiple echocardiographic techniques is feasible, relatively inexpensive, and safe. Exclusion of obstructive epicardial coronary artery disease is, however, a prerequisite for diagnosis. Two-dimensional transthoracic echocardiography, routine stress echocardiography, and speckle-tracking echocardiography indirectly assess primary coronary microvascular dysfunction by evaluating potential impairment in myocardial function and lack diagnostic sensitivity and specificity. Conversely, certain echocardiographic techniques, including Doppler-derived coronary flow velocity reserve and myocardial contrast echocardiography, assess some coronary microvascular dysfunction parameters and have exhibited diagnostic and prognostic potentials. Doppler-derived coronary flow velocity reserve is the best studied and only guideline-approved echocardiographic technique for documenting coronary microvascular dysfunction in patients with suspected microvascular angina. Myocardial contrast echocardiography, by comparison, can detect heterogeneous and patchy myocardial involvement by coronary microvascular dysfunction, which is an advantage over the common practice of coronary flow velocity reserve assessment in a single vessel (commonly the left anterior descending artery) which only reflects regional microvascular function. However, there is no consensus regarding the diagnostic criteria, and expertise performing this technique is limited. Echocardiography remains underexplored and inadequately utilized in the setting of microvascular angina and coronary microvascular dysfunction. Appraisal of the current echocardiographic literature regarding coronary microvascular dysfunction and microvascular angina is important to stay current with the progress in its clinical recognition and create a basis for future research and technological advancements.

Prognostic Significance of Coronary Microvascular Dysfunction in Patients With Heart Failure With Preserved Ejection Fraction

BACKGROUND

The prognostic impact of coronary microvascular dysfunction (CMD) has been scarcely addressed in heart failure with preserved ejection fraction (HFpEF). This study investigated the prevalence and prognostic significance of CMD as measured by a novel pressure wire-free coronary angiography-derived index of microcirculatory resistance (caIMR) on clinical outcomes.

METHODS

Patients diagnosed with HFpEF from 2019 to 2021 were enrolled retrospectively. caIMR was used to quantify microvascular function, and patients were categorised into 2 groups based on their caIMR. The primary end points were composite of all-cause death and heart failure rehospitalisation.

RESULTS

Of 137 HFpEF patients, CMD (defined as caIMR ≥ 25) was present in 88 patients (64.2%). Forty-five patients (32.8%) experienced composite events during a mean follow-up of 15 months. Compared with patients with caIMR < 25, those with caIMR ≥ 25 had a notably higher incidence of composite events (16.3% vs 42.0%; P = 0.002). On survival analysis, patients with caIMR ≥ 25 demonstrated a worse prognosis than those with caIMR < 25 for composite events (P = 0.006). Patients with caIMR ≥ 25 in multiple coronary arteries showed a trend to worse outcome than those with caIMR ≥ 25 in a single coronary artery (log-rank P = 0.056). In adjusted analysis, caIMR ≥ 25 was independently predictive of adverse outcomes (adjusted hazard ratio 2.93, 95% confidence interval [CI] 1.28-6.70; P = 0.010). caIMR displayed a significant predictive power for adverse event prediction (area under the receiver operating characteristic curve 0.767, 95% CI 0.677-0.858; P < 0.001).

CONCLUSIONS

CMD is highly prevalent and is an independent predictor of adverse outcomes in HFpEF patients. Assessment of CMD may identify high-risk patients early for intensified treatment and risk-factor management.

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

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

Imaging Early Life Cardiovascular Phenotype

The growing epidemics of obesity, hypertension, and diabetes, in addition to worsening environmental factors such as air pollution, water scarcity, and climate change, have fueled the continuously increasing prevalence of cardiovascular diseases (CVDs). This has caused a markedly increasing burden of CVDs that includes mortality and morbidity worldwide. Identification of subclinical CVD before overt symptoms can lead to earlier deployment of preventative pharmacological and nonpharmacologic strategies. In this regard, noninvasive imaging techniques play a significant role in identifying early CVD phenotypes. An armamentarium of imaging techniques including vascular ultrasound, echocardiography, magnetic resonance imaging, computed tomography, noninvasive computed tomography angiography, positron emission tomography, and nuclear imaging, with intrinsic strengths and limitations can be utilized to delineate incipient CVD for both clinical and research purposes. In this article, we review the various imaging modalities used for the evaluation, characterization, and quantification of early subclinical cardiovascular diseases.

Prognostic Impact of Indeterminate Diastolic Function in Patients With Functionally Insignificant Coronary Stenosis

BACKGROUND

Cardiac diastolic dysfunction is an independent predictor of mortality, regardless of left ventricular (LV) systolic function. However, the current guidelines that define cardiac diastolic dysfunction may underrate the clinical implications of those with indeterminate diastolic function.

OBJECTIVES

We sought to evaluate the prognostic implications of indeterminate diastolic function on echocardiography and its association with coronary microvascular dysfunction (CMD).

METHODS

A total of 330 patients without LV systolic dysfunction and significant epicardial coronary stenosis (fractional flow reserve > 0.80) were analyzed from a prospective registry. Cardiac diastolic dysfunction was defined according to 2 algorithms depending on the presence of myocardial disease. First, the presence of myocardial disease and evidence of elevated LV filling pressure indicated diastolic dysfunction. Second, diastolic function in those without myocardial disease was defined using echocardiographic parameters (E/e', e' velocity, tricuspid regurgitation velocity, and left atrial volume index). Patients who did not meet half of the available criteria were classified as having indeterminate diastolic function. Coronary microvascular dysfunction was defined as coronary flow reserve < 2.0 and index of microcirculatory resistance ≥ 25 U. The primary outcome was cardiovascular death or admission for heart failure at 5 years.

RESULTS

Coronary flow reserve was lower in patients with indeterminate diastolic function compared with those with no diastolic dysfunction (3.5 ± 1.6 vs 3.2 ± 1.6, P = .002). The prevalence of CMD was also higher in patients with indeterminate diastolic function than in those with no diastolic dysfunction (10.6% vs 4.9%, P < .034). Patients with indeterminate diastolic function showed significantly higher risk of cardiovascular death or admission for heart failure than those without indeterminate diastolic function but not greater than those with definite diastolic dysfunction (cumulative incidence: 12.6%, 27.2%, and 32.7%, respectively, log-rank P < .001). Presence of CMD and elevated LV filling pressure (E/e' > 14) were independent predictors for cardiovascular death or admission for heart failure in patients with indeterminate diastolic function.

CONCLUSIONS

Patients with indeterminate diastolic function on echocardiogram showed higher risk of cardiovascular death or admission for heart failure than those with no diastolic dysfunction. Presence of CMD and elevated LV filling pressure were independent predictors for cardiovascular death or admission for heart failure among patients with indeterminate diastolic function.

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

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

Heart Rate Lowering Significantly Increases Feasibility in Doppler Recording Blood Flow Velocity in Coronaries during Transthoracic Doppler Echocardiography

Background: Coronary blood flow Doppler recording by Transthoracic Doppler in convergent mode (E-Doppler TTE) might be further improved by lowering heart rate (HRL) down to <60 bpm, since low HR < 60 b/m causes a disproportional lengthening of the diastole, so the coronaries are still for a longer time, very much improving the Doppler signal/noise ratio. Methods: A group of 26 patients underwent E-Doppler TTE before and after HR lowering in four branches of the coronary tree, namely, the left main (LMCA); left anterior descending (LAD), subdivided into three segments: proximal, mid and distal; proximal left circumflex (LCx); and obtuse marginal (OM). Color and PW coronary Doppler signal was judged by two expert observers as undetectable (SCORE 1), weak or with clutter artifacts (SCORE 2), or well delineated (SCORE 3). In addition, local accelerated stenotic flow (AsF) was measured in the LAD before and after HRL. Results: Beta-blockers significantly decreased the mean HR from 76 ± 5 to 57 ± 6 bpm (p < 0.001). Before HRL, the Doppler quality was very poor in the proximal and mid-LAD segments (median score value = 1 in both), while in the distal LAD, it was significantly better but still suboptimal (median score value = 1.5, p = 0.009 vs. proximal and mid-LAD score). After HRL, blood flow Doppler recording in the three LAD segments was strikingly improved (median score value = 3, 3 and 3, p = ns), so the effect of HRL was more efficacious in the two more proximal LAD segments. In 10 patients undergoing coronary angiography (CA), no AsF as expression of transtenotic velocity was detected at baseline. After HRL, thanks to the better quality and length of color flow, ASF was detected in five patients while in five others, it was not in perfect agreement with CA (Spearman correlation coefficient = 1, p < 0.01). The color flow in the proximal LCx and OM was extremely poor at baseline (color flow length 0 and 0, median (interquartile range) mm, respectively) and improved considerably after HRL (color flow length 23 [13.5] and 25 [12.0] mm, respectively, p < 0.001). Conclusions: HRL greatly improved the success rate of blood flow Doppler recording in coronaries, not only in the LAD, but also in the LCx. Therefore, AsF for stenosis detection and coronary flow reserve assessment can have wider clinical applications. However, further studies with larger samples are needed to confirm these results.

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.

Prognostic Impact of Cardiac Diastolic Function and Coronary Microvascular Function on Cardiovascular Death

Background Coronary microvascular dysfunction (CMD) has been considered as a possible cause of cardiac diastolic dysfunction. The current study evaluated the association between cardiac diastolic dysfunction and CMD, and their prognostic implications in patients without significant left ventricular systolic dysfunction and epicardial coronary stenosis. Methods and Results A total of 330 patients without left ventricular systolic dysfunction (ejection fraction ≥50%) and significant epicardial coronary stenosis (fractional flow reserve >0.80) were analyzed. Cardiac diastolic dysfunction was defined by echocardiographic parameters (early diastolic transmitral flow velocity/early diastolic mitral annular velocity, e' velocity, tricuspid regurgitation velocity, and left atrial volume index). Overt CMD was defined as coronary flow reserve <2.0 and index of microcirculatory resistance ≥25 U. The primary end point was cardiovascular death or admission for heart failure during 5 years of follow-up. In patients without left ventricular systolic dysfunction and significant epicardial coronary stenosis, prevalence of cardiac diastolic dysfunction and overt CMD was 25.5% and 11.2%, respectively. Overt CMD was independently associated with cardiac diastolic dysfunction (adjusted odds ratio, 3.440 [95% CI, 1.599-7.401]; P=0.002). Patients with cardiac diastolic dysfunction showed significantly higher risk of the primary outcome than those without (adjusted hazard ratio [HR], 2.996 [95% CI, 1.888-4.755]; P<0.001). Patients with overt CMD also showed significantly higher risk of the primary outcome than those without (adjusted HR, 2.939 [95% CI, 1.642-5.261]; P<0.001). Presence of overt CMD was associated with significantly increased risk of cardiovascular death among the patients with cardiac diastolic dysfunction (43.8% versus 14.5%; P=0.006) but not in patients without cardiac diastolic dysfunction (interaction P<0.001). Inclusion of overt CMD into the model with cardiac diastolic dysfunction significantly improved predictive ability for cardiovascular death or heart failure admission (conconrdance index, 0.719 versus 0.737; P for comparison=0.034). Conclusions There was significant association between the presence of cardiac diastolic dysfunction and overt CMD. Both cardiac diastolic dysfunction and overt CMD were associated with increased risk of cardiovascular death or admission for heart failure. Integration of overt CMD into cardiac diastolic dysfunction showed improvement of the risk stratification in patients without significant left ventricular systolic dysfunction and epicardial coronary stenosis. Registration DIAST-CMD (Prognostic Impact of Cardiac Diastolic Function and Coronary Microvascular Function) registry; Unique identifier: NCT05058833.

Subendocardial and Transmural Myocardial Ischemia: Clinical Characteristics, Prevalence, and Outcomes With and Without Revascularization

BACKGROUND

Subendocardial ischemia is commonly diagnosed but not quantified by imaging.

OBJECTIVES

This study sought to define size and severity of subendocardial and transmural stress perfusion deficits, clinical associations, and outcomes.

METHODS

Regional rest-stress perfusion in mL/min/g, coronary flow reserve, coronary flow capacity (CFC), relative stress flow, subendocardial stress-to-rest ratio and stress subendocardial-to-subepicardial ratio as percentage of left ventricle were measured by positron emission tomography (PET) with rubidium Rb 82 and dipyridamole stress in serial 6,331 diagnostic PETs with prospective 10-year follow-up for major adverse cardiac events with and without revascularization.

RESULTS

Of 6,331 diagnostic PETs, 1,316 (20.7%) had severely reduced CFC with 41.4% having angina or ST-segment depression (STΔ) >1 mm during hyperemic stress, increasing with size. For 5,015 PETs with no severe CFC abnormality, 402 (8%) had angina or STΔ during stress, and 82% had abnormal subendocardial perfusion with 8.7% having angina or STΔ >1 mm during dipyridamole stress. Of 947 cases with stress-induced angina or STΔ >1 mm, 945 (99.8%) had reduced transmural or subendocardial perfusion reflecting sufficient microvascular function to increase coronary blood flow and reduce intracoronary pressure, causing reduced subendocardial perfusion; only 2 (0.2%) had normal subendocardial perfusion, suggesting microvascular disease as the cause of the angina. Over 10-year follow-up (mean 5 years), severely reduced CFC associated with major adverse cardiac events of 44.4% compared to 8.8% for no severe CFC (unadjusted P < 0.00001) and mortality of 15.2% without and 6.9% with revascularization (P < 0.00002) confirmed by multivariable Cox regression modeling. For no severe CFC, mortality was 3% with and without revascularization (P = 0.90).

CONCLUSIONS

Reduced subendocardial perfusion on dipyridamole PET without regional stress perfusion defects is common without angina, has low risk of major adverse cardiac events, reflecting asymptomatic nonobstructive diffuse coronary artery disease, or angina without stenosis. Severely reduced CFC causes angina in fewer than one-half of cases but incurs high mortality risk that is significantly reduced after revascularization.

Pathophysiology and Outcomes of Endothelium Function in Coronary Microvascular Diseases: A Systematic Review of Randomized Controlled Trials and Multicenter Study

BACKGROUND

Coronary macrovascular disease is a concept that has been well-studied within the literature and has long been the subject of debates surrounding coronary artery bypass grafting (CABG) vs. Percutaneous Coronary Intervention (PCI). ISCHEMIA trial reported no statistical difference in the primary clinical endpoint between initial invasive management and initial conservative management, while in the ORBITA trial PCI did not improve angina frequency score significantly more than placebo, albeit PCI resulted in more patient-reported freedom from angina than placebo. However, these results did not prove the superiority of the PCI against OMT, therefore do not indicate the benefit of PCI vs. the OMT. Please rephrase the sentence. We reviewed the role of different factors responsible for endothelial dysfunction from recent randomized clinical trials (RCTs) and multicentre studies.

METHODS

A detailed search strategy was performed using a dataset that has previously been published. Data of pooled analysis include research articles (human and animal models), CABG, and PCI randomized controlled trials (RCTs). Details of the search strategy and the methods used for data pooling have been published previously and registered with Open-Source Framework.

RESULTS

The roles of nitric oxide (NO), endothelium-derived contracting factors (EDCFs), and vasodilator prostaglandins (e.g., prostacyclin), as well as endothelium-dependent hyperpolarization (EDH) factors, are crucial for the maintenance of vasomotor tone within the coronary vasculature. These homeostatic mechanisms are affected by sheer forces and other several factors that are currently being studied, such as vaping. The role of intracoronary testing is crucial when determining the effects of therapeutic medications with further studies on the horizon.

CONCLUSION

The true impact of coronary microvascular dysfunction (CMD) is perhaps underappreciated, which supports the role of medical therapy in determining outcomes. Ongoing trials are underway to further investigate the role of therapeutic agents in secondary prevention.

The Role of Gut Microbiota and Trimethylamine N-oxide in Cardiovascular Diseases

Changes in the intestinal flora and its metabolites have been associated with cardiovascular disease (CVD). Short-chain fatty acids, bile acids, and especially trimethylamine N-oxide (TMAO), an endothelial toxic factor produced by gut microbiota from phosphatidylcholine in meat, have been identified to be closely related to endothelial cell dysfunction as well as tightly affiliated with CVD, the two main types being coronary artery disease (CAD) and coronary microvascular disease (CMVD). We discuss how changes in the gut flora and the metabolite TMAO contribute to the development of CAD and CMVD. The above insight might serve as a stepping stone for novel CAD and CMVD diagnostics and therapies centered on microbiota.

Hidden Coronary Atherosclerosis Assessment but Not Coronary Flow Reserve Helps to Explain the Slow Coronary Flow Phenomenon in Patients with Angiographically Normal Coronary Arteries

The significance of the slow coronary flow phenomenon (SCFph), as visualized in patients (pts) with angiographically normal coronary arteries, is controversial. Absolute coronary flow reserve (CFR) in the left anterior descending coronary artery (LAD), non-invasively assessed by a transthoracic color-guided pulsed-wave Doppler (E-Doppler TTE), is a reliable parameter to assess coronary microcirculatory dysfunction (CMD). Mild and angiographically hidden epicardial atherosclerosis (Hath), as visualized by intracoronary ultrasound (IVUS), which could be the clue to atherosclerotic coronary microvascular involvement, has never been investigated together with CFR in patients. This study was aimed at assessing the value of CFR and HA in explaining the SCFph. Methods. Both non-invasive assessment of CFR in the LAD and corrected TIMI frame count assessment of the coronary contrast runoff were performed in 124 pts with angiographically normal coronary arteries. Among the whole group, 32 patients also underwent intracoronary ultrasounds in the LMCA and LAD, and the maximal plaque burden was assessed (Lesion external elastic (EEM) cross sectional area (CSA)—Lesion Lumen CSA/Lesion EEM CSA * 100). We found that 24 of the 124 pts (group 1) had the SCFph and the remaining 100 had a normal runoff (group 2). CFR, evaluated in both groups, was not significantly different, being 2.79 ± 0.79 (Mean ± SD) in group 1 and 2.90 ± 0.8 in group 2 (p = ns); in the pts also examined by IVUS (32 pts), the SCFph was always associated with hidden atherosclerosis, and a plaque burden of ≥33%. On the contrary, in the normal runoff group, any grade of PB was observed (from no athero to a PB > 70%) and remarkably, 10 pts had no signs of athero or just a minimal plaque burden. This resulted in a ROC curve analysis in which PB < 33% had a high negative predictive value (100%) in ruling out the SCFph. In addition, considering a CFR value < 2.21 as an index of coronary microcirculatory dysfunction, we found CMD in 15 pts (15%) in group 1 and in 7 pts (29%) in group 2 (p = ns). In conclusion, the SCFph is strongly connected to epicardial athero to the extent that the absence of hidden coronary athero has a very high negative predictive power in ruling out SCFph. CFR that is based on an endothelium-independent mechanism remains fairly normal in this condition. An endothelium-dependent microcirculatory constriction at rest due to atherosclerotic involvement of the coronary microvascular network is a possible explanation of the SCFph.

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.

Deep Learning for Explainable Estimation of Mortality Risk From Myocardial Positron Emission Tomography Images

BACKGROUND

We aim to develop an explainable deep learning (DL) network for the prediction of all-cause mortality directly from positron emission tomography myocardial perfusion imaging flow and perfusion polar map data and evaluate it using prospective testing.

METHODS

A total of 4735 consecutive patients referred for stress and rest ⁸²Rb positron emission tomography between 2010 and 2018 were followed up for all-cause mortality for 4.15 (2.24-6.3) years. DL network utilized polar maps of stress and rest perfusion, myocardial blood flow, myocardial flow reserve, and spill-over fraction combined with cardiac volumes, singular indices, and sex. Patients scanned from 2010 to 2016 were used for training and validation. The network was tested in a set of 1135 patients scanned from 2017 to 2018 to simulate prospective clinical implementation.

RESULTS

In prospective testing, the area under the receiver operating characteristic curve for all-cause mortality prediction by DL (0.82 [95% CI, 0.77-0.86]) was higher than ischemia (0.60 [95% CI, 0.54-0.66]; P <0.001), myocardial flow reserve (0.70 [95% CI, 0.64-0.76], P <0.001) or a comprehensive logistic regression model (0.75 [95% CI, 0.69-0.80], P <0.05). The highest quartile of patients by DL had an annual all-cause mortality rate of 11.87% and had a 16.8 ([95% CI, 6.12%-46.3%]; P <0.001)-fold increase in the risk of death compared with the lowest quartile patients. DL showed a 21.6% overall reclassification improvement as compared with established measures of ischemia.

CONCLUSIONS

The DL model trained directly on polar maps allows improved patient risk stratification in comparison with established methods for positron emission tomography flow or perfusion assessments.

Robust Association Between Changes in Coronary Flow Capacity Following Percutaneous Coronary Intervention and Vessel-Oriented Outcomes and the Implication for Clinical Practice

Background

Coronary flow capacity (CFC) is a potentially important physiologic marker of ischemia for guiding percutaneous coronary intervention (PCI) indication, while the changes through PCI have not been investigated.

Objectives

To assess the determinants and prognostic implication of delta CFC, defined as the change in the CFC status following PCI.

Materials and Methods

From a single-center registry, a total of 450 patients with chronic coronary syndrome (CCS) who underwent fractional flow reserve (FFR)-guided PCI with pre-/post-PCI invasive coronary physiological assessments were included. Associations between PCI-related changes in thermodilution method-derived CFC categories and incident target vessel failure (TVF) were assessed.

Results

The mean (SD) age was 67.1 (10.0) years and there were 75 (16.7%) women. Compared with patients showing no change in CFC categories after PCI, patients with category worsened, +1, +2, and +3 category improved had the hazard ratio (95% CI) for incident TVF of 2.27 (0.95, 5.43), 0.85 (0.33, 2.22), 0.45 (0.12, 1.63), and 0.14 (0.016, 1.30), respectively (p for linear trends = 0.0051). After adjustment for confounders, one additional change in CFC status was associated with 0.61 (0.45, 0.83) times the hazard of TVF. CFC changes were largely predicted by the pre-PCI CFC status.

Conclusion

Coronary flow capacity changes following PCI, which was largely determined by the pre-PCI CFC status, were associated with the lower risk of incident TVF in patients with CCS who underwent PCI. The CFC changes provide a mechanistic explanation on potential favorable effect of PCI on reducing vessel-oriented outcome in lesions with reduced CFC and low FFR.

Differential Impact of Coronary Revascularization on Long-Term Clinical Outcome According to Coronary Flow Characteristics: Analysis of the International ILIAS Registry

BACKGROUND

Coronary pressure indices such as fractional flow reserve are the standard for guiding elective revascularization. However, considering additional coronary flow parameters could further individualize and optimize the decision on revascularization. We aimed to investigate the potentially differential prognostic associations of elective percutaneous coronary intervention (PCI) according to coronary flow properties represented by coronary flow reserve (CFR), coronary flow capacity (CFC), and baseline CFC (bCFC).

METHODS

From the ILIAS Registry (Inclusive Invasive Physiological Assessment in Angina Syndromes) composed of 16 hospitals globally from 7 countries, patients with obstructive coronary artery disease who underwent invasive coronary physiological assessment were included (N=2370 vessels). We assessed effect measure modifications of the association of PCI and 5-year target vessel failure according to CFR, CFC, and bCFC either assessed by Doppler-technique or thermodilution-method.

RESULTS

The mean age of the population was 63.3 years, and there were 1322 (73.6%) males. Median fractional flow reserve was 0.85, and PCI was performed in 600 (25.3%) vessels. Reduced CFR, CFC, and abnormal bCFC were defined in 988 (41.7%), 542 (22.9%), and 600 (25.3%) vessels, respectively. Significant effect measure modifications were observed by CFC either in odds ratio (P=0.0018), additive (P=0.029), and hazard ratio scale (P=0.0002). The absolute risk of 5-year target-vessel failure was higher if treated by PCI in vessels with normal CFC by 1.8 (-1.7 to 5.3) percent, while that was lower by -5.9 (-12 to -0.1) percent in those with reduced CFC. CFR and bCFC were not significant effect modifiers in any scales. Similar associations were observed in per-patient analyses, whereas the findings were less robust.

CONCLUSIONS

We observed qualitative effect measure modification of PCI and 5-year clinical outcomes according to CFC status in additive scale. CFR and bCFC were not robust effect modifiers. Therefore, CFC could be potentially used to optimize the patient selection for elective PCI treatment combined with fractional flow reserve.

Cardiac computed tomography-derived coronary artery volume to myocardial mass

In the absence of disease impacting the coronary arteries or myocardium, there exists a linear relationship between vessel volume and myocardial mass to ensure balanced distribution of blood supply. This balance may be disturbed in diseases of either the coronary artery tree, the myocardium, or both. However, in contemporary evaluation the coronary artery anatomy and myocardium are assessed separately. Recently the coronary lumen volume to myocardial mass ratio (V/M), measured noninvasively using coronary computed tomography angiography (CTCA), has emerged as an integrated measure of myocardial blood supply and demand in vivo. This has the potential to yield new insights into diseases where this balance is altered, thus impacting clinical diagnoses and management. In this review, we outline the scientific methodology underpinning CTCA-derived measurement of V/M. We describe recent studies describing alterations in V/M across a range of cardiovascular conditions, including coronary artery disease, cardiomyopathies and coronary microvascular dysfunction. Lastly, we highlight areas of unmet research need and future directions, where V/M may further enhance our understanding of the pathophysiology of cardiovascular disease.

Fractal analysis of 4D dynamic myocardial stress-CT perfusion imaging differentiates micro- and macrovascular ischemia in a multi-center proof-of-concept study

Fractal analysis of dynamic, four-dimensional computed tomography myocardial perfusion (4D-CTP) imaging might have potential for noninvasive differentiation of microvascular ischemia and macrovascular coronary artery disease (CAD) using fractal dimension (FD) as quantitative parameter for perfusion complexity. This multi-center proof-of-concept study included 30 rigorously characterized patients from the AMPLIFiED trial with nonoverlapping and confirmed microvascular ischemia (n_micro = 10), macrovascular CAD (n_macro = 10), or normal myocardial perfusion (n_normal = 10) with invasive coronary angiography and fractional flow reserve (FFR) measurements as reference standard. Perfusion complexity was comparatively high in normal perfusion (FD_normal = 4.49, interquartile range [IQR]:4.46-4.53), moderately reduced in microvascular ischemia (FD_micro = 4.37, IQR:4.36-4.37), and strongly reduced in macrovascular CAD (FD_macro = 4.26, IQR:4.24-4.27), which allowed to differentiate both ischemia types, p < 0.001. Fractal analysis agreed excellently with perfusion state (κ = 0.96, AUC = 0.98), whereas myocardial blood flow (MBF) showed moderate agreement (κ = 0.77, AUC = 0.78). For detecting CAD patients, fractal analysis outperformed MBF estimation with sensitivity and specificity of 100% and 85% versus 100% and 25%, p = 0.02. In conclusion, fractal analysis of 4D-CTP allows to differentiate microvascular from macrovascular ischemia and improves detection of hemodynamically significant CAD in comparison to MBF estimation.

Prevalence of Coronary Microvascular Disease and Coronary Vasospasm in Patients With Nonobstructive Coronary Artery Disease: Systematic Review and Meta-Analysis

Background

A relevant proportion of patients with suspected coronary artery disease undergo invasive coronary angiography showing normal or nonobstructive coronary arteries. However, the prevalence of coronary microvascular disease (CMD) and coronary spasm in patients with nonobstructive coronary artery disease remains to be determined. The objective of this study was to determine the prevalence of coronary CMD and coronary vasospastic angina in patients with no obstructive coronary artery disease.

Methods and Results

A systematic review and meta‐analysis of studies assessing the prevalence of CMD and vasospastic angina in patients with no obstructive coronary artery disease was performed. Random‐effects models were used to determine the prevalence of these 2 disease entities. Fifty‐six studies comprising 14 427 patients were included. The pooled prevalence of CMD was 0.41 (95% CI, 0.36–0.47), epicardial vasospasm 0.40 (95% CI, 0.34–0.46) and microvascular spasm 24% (95% CI, 0.21–0.28). The prevalence of combined CMD and vasospastic angina was 0.23 (95% CI, 0.17–0.31). Female patients had a higher risk of presenting with CMD compared with male patients (risk ratio, 1.45 [95% CI, 1.11–1.90]). CMD prevalence was similar when assessed using noninvasive or invasive diagnostic methods.

Conclusions

In patients with no obstructive coronary artery disease, approximately half of the cases were reported to have CMD and/or coronary spasm. CMD was more prevalent among female patients. Greater awareness among physicians of ischemia with no obstructive coronary arteries is urgently needed for accurate diagnosis and patient‐tailored management.

Papillary muscle ischemia on high-resolution cine imaging of nitrogen-13 ammonia positron emission tomography: Association with myocardial flow reserve and prognosis in coronary artery disease

BACKGROUND

The evaluation of papillary muscle (PM) perfusion through existing perfusion imaging, including single-photon emission computed tomography and magnetic resonance imaging, is not possible. Therefore, this study sought to investigate the detection of PM ischemia in coronary artery disease (CAD) using nitrogen-13 (N-13) ammonia positron emission tomography (NH3 PET) and its association with global myocardial flow reserve (MFR) and major adverse cardiac events (MACE).

METHODS

Data of adenosine-stress NH3 PET for 263 consecutive patients with known or suspected CAD were retrospectively analyzed. PM ischemia was defined as the absence of PM accumulation under stress conditions and PM presence at rest on high-resolution cine imaging derived from PET-computed tomography scanner with time-of-flight technology. The primary outcome was MACE.

RESULTS

Of 263 patients, 30 experienced mean follow-up period of 910 days (MACE), while 31 (11.8%) presented PM ischemia. Compared to patients without PM ischemia, those with PM ischemia reported a significantly lower global MFR and a significantly higher rate of MACE (P < .0001).

CONCLUSION

NH3 PET enables the detection of PM ischemia in approximately 10% of patients with known or suspected CAD. PM ischemia is associated with reduced global MFR and is an important sign in predicting prognosis.

Development of a dedicated 3D printed myocardial perfusion phantom: proof-of-concept in dynamic SPECT

We aim to facilitate phantom-based (ground truth) evaluation of dynamic, quantitative myocardial perfusion imaging (MPI) applications. Current MPI phantoms are static representations or lack clinical hard- and software evaluation capabilities. This proof-of-concept study demonstrates the design, realisation and testing of a dedicated cardiac flow phantom. The 3D printed phantom mimics flow through a left ventricular cavity (LVC) and three myocardial segments. In the accompanying fluid circuit, tap water is pumped through the LVC and thereafter partially directed to the segments using adjustable resistances. Regulation hereof mimics perfusion deficit, whereby flow sensors serve as reference standard. Seven phantom measurements were performed while varying injected activity of ^99mTc-tetrofosmin (330–550 MBq), cardiac output (1.5–3.0 L/min) and myocardial segmental flows (50–150 mL/min). Image data from dynamic single photon emission computed tomography was analysed with clinical software. Derived time activity curves were reproducible, showing logical trends regarding selected input variables. A promising correlation was found between software computed myocardial flows and its reference (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\rho$$\end{document}ρ= − 0.98; p = 0.003). This proof-of-concept paper demonstrates we have successfully measured first-pass LV flow and myocardial perfusion in SPECT-MPI using a novel, dedicated, myocardial perfusion phantom.

What an Interventionalist Needs to Know About INOCA

Ischaemia with non-obstructed coronary artery disease (INOCA) remains a diagnostic and therapeutic challenge. An anatomical investigationbased approach to ischaemic heart disease fails to account for disorders of vasomotion. The main INOCA endotypes are microvascular angina, vasospastic angina, mixed (both) or non-cardiac symptoms. The interventional diagnostic procedure (IDP) enables differentiation between clinical endotypes, with linked stratified medical therapy leading to a reduced symptom burden and a better quality of life. Interventionists are therefore well placed to make a positive impact with more personalised care. Despite adjunctive tests of coronary function being supported by contemporary guidelines, IDP use in daily practice remains limited. More widespread adoption should be encouraged. This article reviews a stratified approach to INOCA, describes a streamlined approach to the IDP and highlights some practical and safety considerations.

Predictors of Exercise Capacity in Dilated Cardiomyopathy with Focus on Pulmonary Venous Flow Recorded with Transesophageal Eco-Doppler

The aim of this study was to clarify the relative contribution of elevated left ventricle (LV) filling pressure (FP) estimated by pulmonary venous (PV) and mitral flow, transesophageal Doppler recording (TEE), and other extracardiac factors like obesity and renal insufficiency (KI) to exercise capacity (ExC) evaluated by cardiopulmonary exercise testing (CPX) in patients with dilated cardiomyopathy (DCM). During the CPX test, 119 patients (pts) with DCM underwent both peak VO₂ consumption and then TEE with color-guided pulsed-wave Doppler recording of PVF and transmitral flow. In 78 patients (65%), peak VO₂ was normal or mildly reduced (>14 mL/kg/min) (group 1) while it was markedly reduced (≤14 mL/kg/min) in 41 (group 2). In univariate analysis, systolic fraction (S Fract), a predictor of elevated pre-a LV diastolic FP, appeared to be the best diastolic parameter predicting a significantly reduced peak VO₂. Logistic regression analysis identified five parameters yielding a unique, statistically significant contribution in predicting reduced ExC: creatinine clearance < 52 mL/min (odds ratio (OR) = 7.4, p = 0.007); female gender (OR = 7.1, p = 0.004); BMI > 28 (OR = 5.8, p = 0.029), age > 62 years (OR = 5.5, p = 0.03), S Fract < 59% (OR = 4.9, p = 0.02). Conclusion: KI was the strongest predictor of reduced ExC. The other modifiable factors were obesity and severe LV diastolic dysfunction expressed by blunted systolic venous flow. Contrarily, LV ejection fraction was not predictive, confirming other previous studies. This has important clinical implications.

Inflammation in Coronary Microvascular Dysfunction

Chronic low-grade inflammation is involved in coronary atherosclerosis, presenting multiple clinical manifestations ranging from asymptomatic to stable angina, acute coronary syndrome, heart failure and sudden cardiac death. Coronary microvasculature consists of vessels with a diameter less than 500 μm, whose potential structural and functional abnormalities can lead to inappropriate dilatation and an inability to meet the required myocardium oxygen demands. This review focuses on the pathogenesis of coronary microvascular dysfunction and the capability of non-invasive screening methods to detect the phenomenon. Anti-inflammatory agents, such as statins and immunomodulators, including anakinra, tocilizumab, and tumor necrosis factor-alpha inhibitors, have been assessed recently and may constitute additional or alternative treatment approaches to reduce cardiovascular events in atherosclerotic heart disease characterized by coronary microvascular dysfunction.

Prognostic value of modified coronary flow capacity by 13N-ammonia myocardial perfusion positron emission tomography in patients without obstructive coronary arteries

BACKGROUND

Vasodilator capacity of coronary circulation is an important diagnostic and prognostic tool in patients with coronary artery disease (CAD). We aimed to clarify the incidence of coronary microvascular dysfunction (CMD), defined as impaired modified coronary flow capacity (mCFC) proposed by Johnson and Gould and measured by ¹³N-ammonia myocardial perfusion positron emission tomography (PET), in patients without obstructive CAD and to evaluate the risk of future cardiovascular events.

METHODS

This retrospective study recruited 407 consecutive CAD-suspected patients who underwent both pharmacological stress/rest ¹³N-ammonia PET and coronary angiography. Of the 407 patients, 137 patients (median age, 70 years; 63 women) were eligible and followed up (median, 19.8 months). Endpoints were defined as cardiovascular death or major adverse cardiovascular events (MACEs), such as cardiovascular death, nonfatal myocardial infarction, unplanned hospitalization for any cardiac reasons, and unplanned coronary revascularization. The impaired mCFC group included patients with mildly to severely reduced regional CFC in, at least, one vascular territory (n=34), while the remaining patients (n=103) were categorized as having preserved mCFC.

RESULTS

Overall, cardiovascular death and MACEs occurred in five (4%) patients. The Kaplan-Meier curve showed a significant reduction in event-free survival for cardiovascular death (p=0.004) and MACEs (p<0.0001) in the impaired mCFC group, compared to the preserved mCFC group. Impaired mCFC was independently associated with the incidence of both cardiovascular death and MACEs after propensity-score adjustments [hazard ratio (HR), 10.7; 95% confidence interval (CI), 1.0-106.0; p=0.04 and HR, 9.5; 95% CI, 2.5-36.2; p<0.001, respectively].

CONCLUSIONS

In CAD-suspected patients without obstructive coronary arteries, impaired mCFC was observed in approximately 25% and was associated with a higher risk of cardiovascular death and MACEs. The mCFC concept can help identify patients who would benefit from specific therapies or lifestyle modifications to prevent future MACEs and can clarify potential mechanisms of CMD.

Combined Pressure and Flow Measurements to Guide Treatment of Coronary Stenoses

OBJECTIVES

The aim of this study was to assess clinical outcomes after combined pressure and flow assessment of coronary lesions.

BACKGROUND

Although fractional flow reserve (FFR) remains the invasive reference standard for revascularization, approximately 40% of stenoses have discordant coronary flow reserve (CFR). Optimal treatment for these disagreements remains unclear.

METHODS

A total of 455 subjects with 668 lesions were enrolled from 12 sites in 6 countries. Only lesions with reduced FFR and CFR underwent revascularization; all other combinations received initial medical therapy.

RESULTS

Fourteen percent of lesions had FFR ≤0.8 but CFR ≥2.0 while 23% of lesions had FFR >0.8 but CFR <2.0. During 2-year follow-up, the primary endpoint of composite all-cause death, myocardial infarction, and revascularization in lesions with FFR ≤0.8 but CFR ≥2.0 (10.8% event rate) compared with lesions with FFR >0.8 and CFR ≥2.0 (6.2% event rate) exceeded the prespecified +10% noninferiority margin (P = 0.090). Target vessel failure models using both continuous FFR and continuous CFR found that only higher FFR was associated with reduced target vessel failure (Cox P = 0.007) after initial medical treatment. Central core laboratory review accepted 69.8% of all tracings with mean differences of <0.01 for FFR and <0.02 for CFR, indicating no material impact on clinical measurements or outcomes.

CONCLUSIONS

All-cause death, myocardial infarction, and revascularization after 2 years was not noninferior between lesions with FFR ≤0.8 but CFR ≥2.0 and lesions with FFR >0.8 and CFR ≥2.0. These results do not support using invasive CFR ≥2.0 to defer revascularization for lesions with reduced FFR if the patient would otherwise be a candidate on the basis of the entire clinical scenario and treatment preference.

Assessment and pathophysiology of microvascular disease: recent progress and clinical implications

The development of novel, non-invasive techniques and standardization of protocols to assess microvascular dysfunction have elucidated the key role of microvascular changes in the evolution of cardiovascular (CV) damage, and their capacity to predict an increased risk of adverse events. These technical advances parallel with the development of novel biological assays that enabled the ex vivo identification of pathways promoting microvascular dysfunction, providing novel potential treatment targets for preventing cerebral-CV disease. In this article, we provide an update of diagnostic testing strategies to detect and characterize microvascular dysfunction and suggestions on how to standardize and maximize the information obtained from each microvascular assay. We examine emerging data highlighting the significance of microvascular dysfunction in the development CV disease manifestations. Finally, we summarize the pathophysiology of microvascular dysfunction emphasizing the role of oxidative stress and its regulation by epigenetic mechanisms, which might represent potential targets for novel interventions beyond conventional approaches, representing a new frontier in CV disease reduction.

Design and rationale of the randomized trial of comprehensive lifestyle modification, optimal pharmacological treatment and utilizing PET imaging for quantifying and managing stable coronary artery disease (the CENTURY study)

BACKGROUND

The literature reports no randomized trial in chronic coronary artery disease (CAD) of a comprehensive management strategy integrating intense lifestyle management, maximal medical treatment to specific goals and high precision quantitative cardiac positron emission tomography (PET) for identifying high mortality risk patients needing essential invasive procedures. We hypothesize that this comprehensive strategy achieves greater risk factor reduction, lower major adverse cardiovascular events and fewer invasive procedures than standard practice.

METHODS

The CENTURY Study (NCT00756379) is a randomized-controlled-trial study in patients with stable or at high risk for CAD. Patients are randomized to standard of care (Standard group) or intense comprehensive lifestyle-medical treatment to targets and PET guided interventions (Comprehensive group). Comprehensive Group patients are regularly consulted by the CENTURY team implementing diet/lifestyle/exercise program and medical treatment to target risk modification. Cardiac PET at baseline, 24-, and 60-months quantify the physiologic severity of CAD and guide interventions in the Comprehensive group while patients and referring physicians of the Standard group are blinded to PET results. The primary end-point is the CENTURY risk score reduction during 5 years follow-up. The secondary endpoint is a composite of death, non-fatal myocardial infarction, stroke, and coronary revascularization.

CONCLUSIONS

The CENTURY Study is the first study in stable CAD to test the incremental benefit of a comprehensive strategy integrating intense lifestyle modification, medical treatment to specific goals, and high-precision quantitative myocardial perfusion imaging to guide revascularization. A total of 1028 patients have been randomized, and the 5 years follow-up will conclude in 2022.

The Evaluation of Left Ventricle Ischemic Extent in Patients with Significantly Suspicious Cardiovascular Disease by 99mTc-Sestamibi Dynamic SPECT/CT and Myocardial Perfusion Imaging: A Head-to-Head Comparison

Heart disease is the second most common cause of mortality in Taiwan, mainly coronary artery disease (CAD).Quantitative coronary blood flow has been collected by dynamic single-photon emission computed tomography (Dynamic SPECT/CT) for CAD diagnosis in previous studies. However, few studies defined the extent of left ventricle (LV) ischemia on Dynamic SPECT/CT for predicting significant coronary artery stenosis. This study evaluates the extent of LV ischemic blockage in patients suspected of CAD who were referred by cardiologists. A total of 181 patients with suspected CAD were enrolled. They underwent ^99mTc-Sestamibi (MIBI) Dynamic SPECT/CT survey before cardiac intervention. Dynamic SPECT/CT has better sensitivity (88%), specificity (96%), and accuracy (94%) compared with those of semi-quantitative MIBI MPI (more than 10%). Results indicated that5% of the LV ischemic extent can yield positive PCI results (>70% stenosis in coronary arteries) compared with the moderate abnormal extent of at least 15% of LV. When the percentage of combined moderate abnormal extent and ischemia extent of LV reaches 27.3%, positive PCI results may be indicated. This study revealed Dynamic SPECT/CT has greater sensitivity, specificity, and accuracy as compared with MPI. Thus, the severity of abnormal perfusion extent of LV on Dynamic SPECT/CT might be beneficial to predict positive PCI results in patients with significant suspicion CAD.