Effect of Diffuse Subendocardial Hypoperfusion on Left Ventricular Cavity Size by 13N-Ammonia Perfusion PET in Patients With Hypertrophic Cardiomyopathy

Vasodilator-induced transient left ventricular (LV) cavity dilation by positron emission tomography (PET) is common in patients with hypertrophic cardiomyopathy (HC). Because most patients with PET-LV cavity dilation lack obstructive epicardial coronary artery disease, we hypothesized that vasodilator-induced subendocardial hypoperfusion resulting from microvascular dysfunction underlies this result. To test this hypothesis, we quantified myocardial blood flow (MBF) (subepicardial, subendocardial, and global MBF) and left ventricular ejection fraction (LVEF) in 104 patients with HC without significant coronary artery disease, using ¹³NH₃-PET. Patients with HC were divided into 2 groups, based on the presence/absence of LV cavity dilation (LVvolume_stress/LVvolume_rest >1.13). Transient PET-LV cavity dilation was evident in 52% of patients with HC. LV mass, stress left ventricular outflow tract gradient, mitral E/E', late gadolinium enhancement, and prevalence of ischemic ST-T changes after vasodilator were significantly higher in patients with HC with LV cavity dilation. Baseline LVEF was similar in the 2 groups, but LV cavity dilation⁺ patients had lower stress-LVEF (43 ± 11 vs 53 ± 10; p <0.001), lower stress-MBF in the subendocardial region (1.6 ± 0.7 vs 2.3 ± 1.0 ml/min/g; p <0.001), and greater regional perfusion abnormalities (summed difference score: 7.0 ± 6.1 vs 3.9 ± 4.3; p = 0.004). The transmural perfusion gradient, an indicator of subendocardial perfusion, was similar at rest in the 2 groups. Notably, LV cavity dilation⁺ patients had lower stress-transmural perfusion gradients (0.85 ± 0.22, LV cavity dilation⁺ vs 1.09 ± 0.39, LV cavity dilation^-; p <0.001), indicating vasodilator-induced subendocardial hypoperfusion. The stress-transmural perfusion gradient, global myocardial flow reserve, and stress-LVEF were associated with LV cavity dilation. In conclusion, diffuse subendocardial hypoperfusion and myocardial ischemia resulting from microvascular dysfunction contribute to development of transient LV cavity dilation in HC.

Potential Role of Cardiovascular Imaging in Improving Cardiovascular Outcome in Coronary Artery Disease

BACKGROUND

There is increasing interest in cardiovascular imaging modalities in the detection of subclinical and clinically-manifested coronary artery disease (CAD) to improve cardiovascular outcome in these patients.

METHODS

SPECT/CT and PET/CT can be applied for the assessment of myocardial perfusion and myocardial blood flow (MBF) quantification in CAD detection and characterization, while CT is predominantly used to identify coronary plaque burden and epicardial narrowing. In addition, PET/CT plays an increasing role in the detection of the "vulnerable" plaque in the epicardial artery.

RESULTS

Imaging of myocardial perfusion with SPECT, SPECT/CT and PET/CT is a mainstay in clinical practice for the identification of flow-limiting epicardial lesions and risk stratification of patients with suspected or known CAD. In this direction, the concurrent ability of PET/CT to determine regional myocardial blood flow (MBF) in ml/g/min at rest and during pharmacologically- induced hyperemic flows allows the calculation of the myocardial flow reserve (MFR) that may unravel reductions in coronary vasodilator capacity, as functional precursor of the CAD process, monitor its response to preventive medical intervention, yield important prognostic information in subclinical - and clinically-manifested CAD, and contributes to identify the flow-limiting effect of single lesions in multivessel CAD. Adding noncontrast computed-tomography (CT) measurements of coronary artery calcifications has further improved the reclassification of cardiovascular risk in asymptomatic individuals with intermediate probability of the presence of CAD. With contrast CT, the non-invasive visualization of coronary vessels, CAD-related plaque burden and stenosis has become feasible. Yet, a definite identification of the &quot;vulnerable plaque&quot; is still a matter of ongoing research. PET/CT in conjunction with various positron-emitting radiotracer yields promise in the detection of the &quot;vulnerable plaque," that, however, needs further clinical evaluation in CAD patients.

CONCLUSION

Multimodality imaging in cardiovascular disease is likely to further advances and refine the identification and characterization of cardiovascular pathology in the near future.

Impact of incomplete revascularization of coronary artery disease on long-term cardiac outcomes. Retrospective comparison of angiographic and myocardial perfusion imaging criteria for completeness

BACKGROUND

Coronary revascularization in patients with coronary artery disease may be guided by coronary angiography (CA) or alternatively by ischemia on stress myocardial perfusion imaging (MPI). Which strategy leads to optimal cardiac outcomes is uncertain.

METHODS

We performed a retrospective analysis of 170 patients with MPI ischemia and percutaneous coronary intervention. The primary endpoint was all-cause mortality at a mean follow-up of 47 ± 21 months; the secondary end point was the composite of deaths, nonfatal myocardial infarction, and repeat coronary revascularization (MACE). The coronary revascularization was defined as complete (CCR) or incomplete (ICR) as judged by CA criteria and by MPI ischemia matched with CA criteria.

RESULTS

Nighty-two patients (54%) had ICR by CA criteria (ICR-CA) and 84 (49%) had ICR by MPI criteria (ICR-MPI). Mortality and MACE were lower in patients with CCR-MPI than with ICR-MPI (P = .048, and P = .025). Survival of patients with CCR-CA and ICR-CA was not different (P = .081). Patients with both ICR-MPI and ICR-CA had the worst survival, whereas patients with CCR-MPI and CCR-CA had the best survival (P = .047). By multivariate analysis, ICR-MPI + ICR-CA was an independent predictor of death (P = .025).

CONCLUSION

Patients with ICR by MPI were at higher risk than those with CCR. Patients with both ICR by MPI and CA were at the highest risk, while patients with CCR by both MPI and CA had the best long-term event-free survival.

Role of risk stratification by SPECT, PET, and hybrid imaging in guiding management of stable patients with ischaemic heart disease: expert panel of the EANM cardiovascular committee and EACVI

Risk stratification has become increasingly important in the management of patients with suspected or known ischaemic heart disease (IHD). Recent guidelines recommend that these patients have their care driven by risk assessment. The purpose of this position statement is to summarize current evidence on the value of cardiac single-photon emission computed tomography, positron emission tomography, and hybrid imaging in risk stratifying asymptomatic or symptomatic patients with suspected IHD, patients with stable disease, patients after coronary revascularization, heart failure patients, and specific patient population. In addition, this position statement evaluates the impact of imaging results on clinical decision-making and thereby its role in patient management. The document represents the opinion of the European Association of Nuclear Medicine (EANM) Cardiovascular Committee and of the European Association of Cardiovascular Imaging (EACVI) and intends to stimulate future research in this field.

Positron-emitting myocardial blood flow tracers and clinical potential

Positron-emitting myocardial flow radiotracers such as (15)O-water, (13)N-ammonia and (82)Rubidium in conjunction with positron-emission-tomography (PET) are increasingly applied in clinical routine for coronary artery disease (CAD) detection, yielding high diagnostic accuracy, while providing valuable information on cardiovascular (CV) outcome. Owing to a cyclotron dependency of (15)O-water and (13)N-ammonia, their clinical use for PET myocardial perfusion imaging is limited to a few centers. This limitation could be overcome by the increasing use of (82)Rubidium as it can be eluted from a commercially available (82)Strontium generator and, thus, is independent of a nearby cyclotron. Another novel F-18-labeled myocardial flow radiotracer is flurpiridaz which has attracted increasing interest due to its excellent radiotracer characteristics for perfusion and flow imaging with PET. In particular, the relatively long half-life of 109 minutes of flurpiridaz may afford a general application of this radiotracer for PET perfusion imaging comparable to technetium-99m-labeled single-photon emission computed tomography (SPECT). The ability of PET in conjunction with several radiotracers to assess myocardial blood flow (MBF) in ml/g/min at rest and during vasomotor stress has contributed to unravel pathophysiological mechanisms underlying coronary artery disease (CAD), to improve the detection and characterization of CAD burden in multivessel disease, and to provide incremental prognostic information in individuals with subclinical and clinically-manifest CAD. The concurrent evaluation of myocardial perfusion and MBF may lead to a new era of a personalized, image-guided therapy approach that may offer potential to further improve clinical outcome in CV disease patients but needing validation in large-scale clinical trials.

The impacts of severe perfusion defects, akinetic/dyskinetic segments, and viable myocardium on the accuracy of volumes and LVEF measured by gated ⁹⁹mTc-MIBI SPECT and gated ¹⁸F-FDG PET in patients with left ventricular aneurysm: cardiac magnetic resonance imaging as the reference

BACKGROUND

To compare the accuracy of end-diastolic and end-systolic volumes (EDV, ESV) and LV ejection fraction (LVEF) measured by both GSPECT and GPET, using cardiac magnetic resonance imaging (CMR) as a reference. Furthermore, the impacts of severe perfusion defects, akinetic/dyskinetic segments, and residual viable myocardium on the accuracy of LV functional parameters were investigated.

METHODS

Ninety-six consecutive patients with LV aneurysm and LV dysfunction (LVEF 32 ± 9%) diagnosed by CMR were studied with GSPECT and GPET. EDV, ESV, and LVEF were calculated using QGS software.

RESULTS

Correlations of volumes were excellent (r 0.81-0.86) and correlation of LVEF was moderate (r 0.65-0.76) between GSPECT vs CMR and between GPET vs CMR. Compared with CMR, ESV was overestimated by GSPECT (P < .01) and underestimated by GPET (P < .0001); EDV was underestimated by GPET (P < .001); LVEF was underestimated by GSPECT but overestimated by GPET (both P < .001). Multivariate regression analysis revealed that the number of segments with severe perfusion defects (P < .001) was the only independent factor which was correlated to the EDV difference between GSPECT and CMR, the number of akinetic/dyskinetic segments with absent wall thickening (WT) was the only independent factor which was significantly correlated to the differences of ESV and LVEF measurements between GSPECT vs CMR and between GPET vs CMR (P < .0001), respectively. Neither the mismatch score nor the segments with viable myocardium were correlated to the differences of LV volumes and LVEF measurements between different imaging modalities.

CONCLUSIONS

In LV aneurysm patients, LV volumes and LVEF measured by both GSPECT and GPET imaging correlated well with those determined by CMR, but should not be interchangeable in individual patients. The accuracy of LVEF measured by GSPECT and GPET was affected by the akinetic/dyskinetic segments with absent WT.

Impact of obesity and bariatric surgery on metabolism and coronary circulatory function

Increases in intra-abdominal visceral adipose tissue have been widely appreciated as a risk factor for metabolic disorders such as dyslipidemia, hypertension, insulin resistance, and type 2 diabetes, whereas this is not the case for peripheral or subcutaneous obesity. While the underlying mechanisms that contribute to these differences in adipose tissue activity remain uncertain, increases in visceral fat commonly induce metabolic dysregulation, in part because of increased venous effluent of fatty acids and/or adipokines/cytokines to the liver. Increased body weight, paralleled by an increase in plasma markers of the insulin-resistance syndrome and chronic inflammation, is independently associated with coronary circulatory dysfunction. Recent data suggest that plasma proteins originating from the adipose tissue, such as endocannabinoids (EC), leptin, and adiponectin (termed adipocytes) play a central role in the regulation and control of coronary circulatory function in obesity. Positron emission tomography (PET) in concert with tracer kinetic modeling is a well established technique for quantifying regional myocardial blood flow at rest and in response to various forms of vasomotor stress. Myocardial flow reserve assessed by PET provides a noninvasive surrogate of coronary circulatory function. PET also enables the monitoring and characterization of coronary circulatory function in response to gastric bypass-induced weight loss in initially morbidly obese individuals, to medication and/or behavioral interventions related to weight, diet, and physical activity. Whether the observed improvement in coronary circulatory dysfunction via weight loss may translate to diminution in cardiovascular events awaits clinical confirmation.

Anatomic versus physiologic assessment of coronary artery disease. Role of coronary flow reserve, fractional flow reserve, and positron emission tomography imaging in revascularization decision-making

Angiographic severity of coronary artery stenosis has historically been the primary guide to revascularization or medical management of coronary artery disease. However, physiologic severity defined by coronary pressure and/or flow has resurged into clinical prominence as a potential, fundamental change from anatomically to physiologically guided management. This review addresses clinical coronary physiology-pressure and flow-as clinical tools for treating patients. We clarify the basic concepts that hold true for whatever technology measures coronary physiology directly and reliably, here focusing on positron emission tomography and its interplay with intracoronary measurements.