Perivascular fatty tissue at the brachial artery is linked to insulin resistance but not to local endothelial dysfunction

AIMS/HYPOTHESIS

Different ectopic fat depots, such as visceral or hepatic fat, are known to affect whole body insulin sensitivity. It has recently been hypothesised that differences in perivascular adipose tissue (PVAT) mass around resistance vessels may also contribute to insulin resistance, possibly via direct vascular effects leading to reduced capillary cross-sectional area in the muscle, which in turn affects muscular blood flow and glucose uptake. Based on this, the aim of the present study was to test whether PVAT around conduit arteries (i.e. the brachial artery) influences NO bioavailability, expressed as flow-mediated dilation (FMD), or insulin sensitivity in humans in vivo.

METHODS

Insulin sensitivity was measured by OGTT in all 95 participants (59 women, 36 men; median age 47 years, range 19-66 years) and by the gold standard, a euglycaemic-hyperinsulinaemic clamp, in a randomly selected subgroup of 33 participants. Quantification of the different fat compartments, including PVAT around the brachial artery, was achieved by high-resolution magnetic resonance imaging (1.5 T). Blood flow and FMD were measured at the brachial artery using high-resolution (13 MHz) ultrasound, after 5 min of forearm occlusion.

RESULTS

PVAT was negatively correlated with insulin sensitivity and the post-ischaemic increase in blood flow. The association between PVAT and insulin sensitivity (r = -0.54, beta = -0.37, p = 0.009) was independent of age, sex, visceral adipose tissue, liver fat, BMI and further cardiovascular risk factors. No correlation could be detected between PVAT and local endothelial function. However, we observed an independent association between PVAT and post-ischaemic increase in blood flow (r = -0.241; beta = -1.69; p = 0.02).

CONCLUSIONS/INTERPRETATION

PVAT seems to play an independent role in the pathogenesis of insulin resistance. This may be due to direct vascular effects influencing muscular blood flow.

Sixty-four-MSCT in the characterization of porcine acute and subacute myocardial infarction: determination of transmurality in comparison to magnetic resonance imaging and histopathology

OBJECTIVE

The aim of this study was to assess the accuracy of MSCT in characterizing myocardial infarction (MI) and, thereby, determine the extent of early perfusion defect (ED), microvascular obstruction (MO) and transmural depth of late enhancement (LE) in comparison to MRI and histology.

MATERIALS AND METHODS

Seven pigs were studied with MSCT (Somatom Sensation 64) and MRI (Magnetom Sonata) a median 1 and 21 days following temporary occlusion of a diagonal branch and creation of small reperfused infarction. For depiction of ED, CT images were acquired in the early arterial phase and following 35 s; LE and MO were evaluated on images obtained at 3, 5, 10 and 15 min. Thereby, a bolus/low-flow contrast injection protocol was used. Triphenyltetrazolium-chloride (TTC) stain and histology were obtained. Volumes of enhancement patterns were assessed as percentage of the ventricle and compared by Bland-Altman analysis. Segmental co-localization and graded transmurality was evaluated with weighted-kappa-test.

RESULTS

Close spatial agreement was observed for MRI-MO and MSCT-MO (bias=0.55; CI=-1.49 to 2.60 at 5 min MSCT), TTC and MSCT-LE (bias=-1.28; CI=-3.76 to 1.19) or MRI-LE and MSCT-LE (bias=-0.79; CI=-4.19 to 2.60). There was good segmental co-localization for MO (weighted kappa=0.93) and high agreement for transmural extent of TTC, MRI-LE and MSCT-LE (weighted kappa=0.84 TTC versus MSCT; 0.86 MRI versus MSCT). Arterial and 35s ED significantly underestimated infarct size and showed poor segmental or transmural agreement (weighted kappa=0.33; 0.44).

CONCLUSIONS

MSCT late-scans not only reliably depict size of MO and LE in acute or subacute infarct phases but, moreover, allow for accurate determination of LE transmurality.

Late myocardial enhancement assessed by 64-MSCT in reperfused porcine myocardial infarction: diagnostic accuracy of low-dose CT protocols in comparison with magnetic resonance imaging

The purpose was to assess the practicability of low-dose CT imaging of late enhancement in acute infarction. Following temporary occlusion of the second diagonal branch, seven pigs were studied by multislice computed tomography (MSCT) and magnetic resonance imaging (MRI). Thus, 64-slice CT was performed at 3, 5, 10 and 15 min following the injection of contrast medium according to a bolus/low-flow protocol. Standard parameters of 120 kV and 800 mAs were compared with 80 kV and 400 mAs in various combinations. Infarct volumes were assessed as percentage of the ventricle for both MSCT and MR images. CT density values for viable and infarcted myocardium were obtained and image quality assessed. Mean infarct volume as measured by MRI was 12.33+/-7.06%. MSCT achieved best correlation of volumes at 5 and 10 min. Whilst lowering of tube current resulted in poor correlation, tube voltage did not affect accuracy of infarct measurement (r (2)=0.92 or 0.93 at 5 min, 800 mAs and 80 or 120 kV). In terms of image quality, greater image noise with 80 kV was compensated by significantly better contrast enhancement between viable and non-viable myocardium at lower voltage. Myocardial viability can accurately be assessed by MSCT at 80 kV, which ensures higher contrast for late enhancement and yields good correlation with MRI.