Cardiovascular Imaging in Obesity

Obesity represents one of the most challenging public health problems of our century. It accounts for approximately 5% of deaths worldwide, mostly owing to cardiovascular disease and its associated complications. Cardiovascular noninvasive imaging may provide early accurate information about hypertrophy and ischemia/fibrosis in obese subjects. Echocardiography and nuclear cardiology have serious limitations in obese subjects owing to poor acoustic window and attenuation artifacts, respectively. Coronary computed tomography angiography can provide information about obstructive coronary disease; however, the use of radiation is a serious disadvantage. Finally, cardiac magnetic resonance (CMR) holds the promise of an “all in one” examination by combining evaluation of function, wall motion/thickness, stress rest/perfusion, replacement and diffuse fibrosis without radiation. Future studies are required to document the cost/benefit ratio of the CMR in the evaluation of cardiovascular risk in overweight/obese children and adolescents.

Combining perfusion and angiography with a low-dose cardiac CT technique: a preliminary investigation in a swine model

Morphological and physiological assessment of coronary artery disease (CAD) is necessary for proper stratification of CAD risk. The objective was to evaluate a low-dose cardiac CT technique that combines morphological and physiological assessment of CAD. The low-dose technique was evaluated in twelve swine, where three of the twelve had coronary balloon stenosis. The technique consisted of rest perfusion measurement combined with angiography followed by stress perfusion measurement, where the ratio of stress to rest was used to derive coronary flow reserve (CFR). The technique only required two volume scans for perfusion measurement in mL/min/g; hence, four volume scans were acquired in total; two for rest with angiography and two for stress. All rest, stress, and CFR measurements were compared to a previously validated reference technique that employed 20 consecutive volume scans for rest perfusion measurement combined with angiography, and stress perfusion measurement, respectively. The 32 cm diameter volumetric CT dose index ($${\text{CTDI}}_{\text{vol}}^{32}$$ CTDI vol 32 ) and size-specific dose estimate (SSDE) of the low-dose technique were also recorded. All low-dose perfusion measurements (PLOW) in mL/min/g were related to reference perfusion measurements (PREF) through regression by PLOW = 1.04 PREF − 0.08 (r = 0.94, RMSE = 0.32 mL/min/g). The $${\text{CTDI}}_{\text{vol}}^{32}$$ CTDI vol 32 and SSDE of the low-dose cardiac CT technique were 8.05 mGy and 12.80 mGy respectively, corresponding to an estimated effective dose and size-specific effective dose of 1.8 and 2.87 mSv, respectively. Combined morphological and physiological assessment of coronary artery disease is feasible using a low-dose cardiac CT technique.

Influences on myocardial perfusion in non-obstructive coronary disease: an observational quantitative perfusion mapping study

Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): This study was supported by a Clinical Training Research Fellowship (K. Knott) from the British Heart Foundation and directly and indirectly from the Biomedical Research Centre at University College London Hospitals and Barts Heart Centre. Background Cardiovascular magnetic resonance (CMR) with automated inline perfusion mapping permits rapid fully automated non-invasive myocardial blood flow (MBF, ml/g/min). Understanding the microvascular component of MBF would help optimize epicardial coronary artery disease detection and potentially serve as an independent diagnostic / therapeutic target. Purpose To explore MBF influences at stress and rest in patients with unobstructed epicardial coronary arteries. Methods 242 participants (mean age 56.9 years) from 5 European centers with unobstructed epicardial coronary arteries and no myocardial scar underwent adenosine vasodilator perfusion mapping at stress and rest. The factors influencing MBF were determined using univariate and multivariate linear regression analyses. Results Mean rest perfusion was 0.91+/-0.24ml/g/min. Rest perfusion was higher in females (0.97+/-0.22ml/g/min vs 0.83 +/- 0.24ml/g/min) and lower in patients on beta blockers. Mean stress MBF was 2.53+/-0.82ml/g/min. Factors independently associated with reduced stress MBF were increasing age, diabetes, increasing left ventricular mass (LVMi) and the use of beta blockers. The predicted stress MBF can be obtained from the equation MBF = 2.66–0.015(age-60)–0.013(LVMi-57)-0.405(diabetes)–0.365(beta blocker). This means stress MBF falls 10% over 19 years and that diabetes drops the MBF by the equivalent of being 27 years older. These changes are large: for example, a 70-year-old diabetic would have 30% lower stress MBF than a 35 year-old non-diabetic. Conclusions In the absence of obstructive epicardial coronary disease, stress MBF falls with age, diabetes, increased LV mass and beta-blockers. These data may help develop normal reference ranges, input to other modelling (eg CT FFR), and they advance perfusion mapping as a measure of microvascular function. Abstract Figure. Summary of the determinants of perfusion

P707 Positive rest and negative adenosine stress perfusion in typical angina

Clinical Presentation A 45 year old gentleman seen in Rapid Access Chest Pain Clinic with typical angina (exertional chest pain). No risk factors for CAD. Normal ECG. Pre-test probability of significant CAD 51% . Diagnostic techniques and findings The patient was referred for adenosine stress CMR. CMR was performed on a 1.5 Tesla scanner. Cine was performed first, followed by stress perfusion, gadolinium enhance images and finally rest perfusion images. LV systolic function was normal. A significant perfusion defect of the LAD territory was noted on the rest but not on the stress perfusion images. The radiographers confirmed that stress and rest perfusion images were performed normally (stress first). A good physiological response was obtained during the assumed vasodilator stress with > 20% in the HR (from 65-75bpm to 91-107bpm respectively). During the presumed rest perfusion acquisition, HR was similar to the previously recorded resting HR. The spleen was not adequately visible to comment on splenic switch off. This type of perfusion defect (normal stress/abnormal rest) had not been described before, and there is no evidence that it was due to acquisition error. A coronary CT was advised to assess the LAD. CT coronary angiogram showed mild coronary calcification. A severe (80%), focal, non-calcified mid LAD stenosis was identified. A mild proximal OM1 stenosis was also noted. The patient subsequently underwent an invasive angiogram which confirmed the presence of a severe mid LAD stenosis. PCI was performed in the same setting with deployment of a single 4x18mm XIENCE drug eluting stent. The successful procedure was optimised with OCT guidance. Learning points Resting perfusion is often considered an integral part of adenosine perfusion imaging in order to overcome dark ring artefact, but it requires an additional contrast injection, prolongs imaging time and adds to cost. Some experts suggest that resting perfusion does not add to clinical interpretation and is not required. Our case is interesting, showing a previously unreported phenomenon. We cannot explain the reason for it but do not believe that the stress/rest order was reversed (as this would require two radiographers to go off protocol, and they and the supervising physician to be lying) and the physiological response is as expected. It therefore suggests that a rest study may occasionally provide helpful diagnostic information. Abstract P707 Figure.

P4469Reduced myocardial perfusion reserve in type 2 diabetes is caused by increased rest perfusion as well as decreased maximal perfusion during stress

Background Reduced myocardial perfusion reserve is a well-known complication in patients with type 2 diabetes mellitus (T2DM). Furthermore, reduced myocardial perfusion reserve has been linked to the development of diastolic dysfunction, a key characteristic in diabetic cardiomyopathy. However, it is not fully explored whether a decrease in perfusion during stress or an increase in perfusion during rest is responsible for this reduction in myocardial perfusion reserve, nor is it clear what causes these changes. Purpose The purpose of this study was to examine differences in myocardial perfusion in rest and during stress in patients with T2DM compared to healthy control subjects, and to identify potential predictors for changes in perfusion during rest and stress among patients with T2DM. Methods 200 patients with T2DM and 25 healthy volunteers matched for age and sex underwent a comprehensive cardiac MRI protocol including gadolinium first-pass perfusion during rest and stress (adenosine infusion 140 mg/min–1/kg–1). Perfusion was measured on a per-segment basis based on the AHA model and averaged to calculate global perfusion index both during rest and stress. Any areas with infarctions and/or significant perfusion defects were excluded from the analysis. Backwards stepwise multiple linear regression was performed to identify predictors for perfusion changes during rest and stress in patients with T2DM. Variables with P<0.1 in a univariate analysis were included into the models. Results Patients with T2DM had significantly higher rest perfusion index (0.135±0.024 vs. 0.120±0.016; P=0.001) and significantly lower stress perfusion index (0.174±0.041 vs. 0.225±0.027; P<0.001) compared to healthy volunteers. In a multiple linear regression model among patients with T2DM female sex (P<0.001) was associated with increased rest perfusion. In a similar analysis for stress perfusion, diabetes duration (P=0.01), albuminuria (P<0.001) and the presence of ischaemic heart disease (P<0.001) were associated with reduced myocardial stress perfusion index in patients with T2DM. Conclusion In patients with T2DM reductions in myocardial perfusion reserve is caused by a combination of increased basal myocardial blood flow and a decrease in maximal blood flow during stress. Decreased stress perfusion is associated with coronary vascular disease and the diabetic complication albuminuria related to renal microvascular disease. Stress perfusion also decreased with increasing duration of T2DM. This suggest that the coronary microcirculation is gradually damaged in patients with T2DM and that the mechanism responsible is similar to that causing renal microvascular damage. Acknowledgement/Funding Local science committee of Region Zealand, Regional science committee of Region Zealand, The Danish Heart Association