[Current percutaneous coronary intervention technology for management of coronary artery disease]

Enormous advance was obtained in the field of percutaneous coronary intervention, treatment for coronary artery disease. Drug eluting stent (DES) offers advantages over bare metal stent (BMS) such as reduction in restenosis rates. However, several concerns were proposed when compared with BMS. Currently, numerous technologies are under development to avert the complications of DES, such as stent thrombosis, or to challenge complex lesion, such as left main trunk/bifurcation. We summarized some of the development that is emerging on current management of coronary intervention.

Coronary artery stent evaluation using a vascular model at 64-detector row CT: comparison between prospective and retrospective ECG-gated axial scans

Objective

We wanted to evaluate the performance of prospective electrocardiogram (ECG)-gated axial scans for assessing coronary stents as compared with retrospective ECG-gated helical scans.

Materials and Methods

As for a vascular model of the coronary artery, a tube of approximately 2.5-mm inner diameter was adopted and as for stents, three (Bx-Velocity, Express2, and Micro Driver) different kinds of stents were inserted into the tube. Both patent and stenotic models of coronary artery were made by instillating different attenuation (396 vs. 79 Hounsfield unit [HU]) of contrast medium within the tube in tube model. The models were scanned with two types of scan methods with a simulated ECG of 60 beats per minute and using display field of views (FOVs) of 9 and 18 cm. We evaluated the in-stent stenosis visually, and we measured the attenuation values and the diameter of the patent stent lumen.

Results

The visualization of the stent lumen of the vascular models was improved with using the prospective ECG-gated axial scans and a 9-cm FOV. The inner diameters of the vascular models were underestimated with mean measurement errors of -1.10 to -1.36 mm. The measurement errors were smaller with using the prospective ECG-gated axial scans (Bx-Velocity and Express2, p < 0.0001; Micro Driver, p = 0.0004) and a 9-cm FOV (all stents: p < 0.0001), as compared with the other conditions, respectively. The luminal attenuation value was overestimated in each condition. For the luminal attenuation measurement, the use of prospective ECG-gated axial scans provided less measurement error compared with the retrospective ECG-gated helical scans (all stents: p < 0.0001), and the use of a 9-cm FOV tended to decrease the measurement error.

Conclusion

The visualization of coronary stents is improved by the use of prospective ECG-gated axial scans and using a small FOV with reduced blooming artifacts and increased spatial resolution.

Comparison of vascular response to zotarolimus-eluting stent versus sirolimus-eluting stent: intravascular ultrasound results from ENDEAVOR III

BACKGROUND

The purpose of this study was to investigate the vascular response of zotarolimus-eluting stent (ZES) and sirolimus-eluting stent (SES) using serial intravascular ultrasound (IVUS).

METHODS

Data were obtained from the Endeavor Drug-Eluting Coronary Stent System Versus the Center Siromlimus-Eluting Coronary Stent System in De Novo Native Coronary Artery Lesions (ENDEAVOR) III trial, a randomized study comparing ZES and SES for the treatment of de novo native coronary artery lesions. Serial (baseline and 8-month follow-up) IVUS was available in 258 patients (190 ZES, 68 SES).

RESULTS

At 8 months, ZES had greater percentage of neointimal volume index (ZES 1.1 +/- 0.8 mm3/mm vs SES 0.2 +/- 0.1 mm3/mm, P < .01), resulting in smaller lumen volume index (6.0 +/- 2.0 mm3/mm vs 7.0 +/- 2.1 mm3/mm, P < .05). Zotarolimus-eluting stents showed larger IVUS-detectable neointimal coverage over stent surface (50.2% vs 10.5%, P < .01) and greater mean neointimal thickness (0.19 +/- 0.07 mm vs 0.10 +/- 0.06 mm, P < .01). Zotarolimus-eluting stents had a significantly lower incidence of late-acquired incomplete stent apposition.

CONCLUSIONS

Zotarolimus-eluting stent is associated with a significantly greater amount of neointimal hyperplasia compared with SES. This amount of hyperplasia in ZES is distributed throughout the stent at 8-month follow-up.

Characterization of late incomplete stent apposition: a comparison among bare-metal stents, intracoronary radiation and sirolimus-eluting stents

BACKGROUND

Late incomplete stent apposition (LISA) develops following implantation of conventional bare-metal stents (BMS) or drug-eluting stents, or after adjunctive intracoronary radiation (IR). However, no study has systematically compared the morphology of LISA seen with various treatment modalities.

PURPOSE

To compare the morphometric features of LISA accompanying BMS, IR or sirolimus-eluting stents (SES) using serial intravascular ultrasound (IVUS).

METHODS

A query of Stanford University's IVUS database of the Cardiovascular Core Analysis Laboratory was performed to identify LISA cases. Dedicated software programs were used for volumetric IVUS analyses.

RESULTS

In 30 LISA cases (12 BMS, 6 IR and 12 SES), there was no intertreatment difference in the degree of LISA (lumen area minus stent area at follow up). Serial analyses of LISA segments showed that vessel area of SES and IR showed significant increase at follow up as compared with post procedure, while there was no significant change in plaque area. In contrast, the BMS group showed no increase in vessel area, whereas plaque area revealed significant reduction. Eight of 12 BMS cases were treated by directional atherectomy before stenting; however, there was no difference in the area change between patients with or without pre-stent atherectomy. Post-procedure plaque thickness beneath the stent struts of LISA was thinner for SES as compared with BMS.

CONCLUSIONS

Plaque reduction primarily contributes to LISA after BMS, whereas vessel expansion is the predominant factor in LISA development for IR and SES. Thus, the mechanism of LISA may vary among different interventional treatments.

Impact of gender on neointimal hyperplasia following coronary artery stenting

Whether gender affects long-term outcomes after bare metal stent implantation remains controversial. The aim of this study was to examine the impact of gender on neointimal hyperplasia in a large cohort of patients after stent implantation using 3-dimensional intravascular ultrasound. Lumen and stent areas were manually traced at 0.5-mm intervals throughout the stented segment. Using Simpson's method, lumen, stent, and neointimal (stent - lumen) volumes were calculated and standardized by stent length. Women were older, presented more often with hyperlipidemia or hypertension, and had smaller reference vessel diameter and mean stent area, compared with men. Although neointimal hyperplasia and neointimal thickness in women were similar to that in men, the percentage of neointimal hyperplasia (neointimal area divided by stent area) was higher in women due to the smaller stent area. After adjusting for stent area, the percentage of neointimal hyperplasia did not differ by gender. In conclusion, the results of this study indicate that neointimal hyperplasia after bare metal stent implantation in women is similar to that seen in men. Despite the similarity in outcome, there are several gender-specific differences in baseline characteristics.

Intracoronary nicorandil prior to reperfusion in acute myocardial infarction

BACKGROUND

A prospective, randomised, single centre study was designed to test the safety and efficacy of nicorandil infusion, a potassium channel opener, prior to reperfusion in ST-elevation acute myocardial infarction (STEMI).

METHODS AND RESULTS

Seventy STEMI patients with TIMI 0 to 2 flow were randomly assigned to nicorandil (Group N; n = 35) or control (Group C; n = 35) and underwent direct percutaneous coronary intervention (PCI). In Group N, 2 mg of nicorandil was infused directly into the infarct area prior to reperfusion. Incidence of anterior infarction was 60% in both groups. With nicorandil infusion, additional ST elevations without chest pain were observed for a few minutes in 94% of cases. However, no ventricular fibrillation or ventricular tachycardia occurred. TIMI myocardial perfusion grade 3 was significantly higher in Group N (40% vs. 17%, p<0.01). Patients were followed for up to 8 months, with similar incidence of major clinical adverse events, however left ventricular regional wall motion score significantly improved in Group N (P < 0.05). The effect of nicorandil was seen in patients without ischaemic preconditioning (P < 0.05).

CONCLUSION

This study suggests that direct infusion of nicorandil prior to revascularisation may be safe and beneficial.

Heterogeneity of neointimal distribution of in-stent restenosis in patients with diabetes mellitus

Diabetes mellitus is an independent predictor of restenosis after percutaneous coronary intervention. The pattern of restenosis after bare metal stent implantation in diabetic patients was examined with 3-dimensional intravascular ultrasound analysis. Lumen and stent were manually traced at every 0.5-mm interval in stented segments. Using Simpson's method, stent, luminal, and neointimal (stent minus lumen) volumes were calculated and average area was calculated as volume data divided by length. To measure the cross-sectional and longitudinal severities of luminal encroachment by the neointima, percent neointimal area (neointimal area divided by stent area) and neointimal hyperplasia 50 (IH50) (defined as percent stent length with percent neointimal area >50%) were calculated. In 278 patients (68 with diabetes and 210 without diabetes), there was a significantly higher percentage of maximal percent neointimal area with significantly longer percent stent length that was severely encroached by the neointima in diabetic patients. Diabetic patients showed a more heterogenous pattern of the neointima after bare metal stenting, resulting in longer high-grade obstruction segments. This may have important implications for stent design and pharmacokinetic properties of next-generation drug-eluting technology for this complex patient subset.

Novel stent system for bifurcation lesions: Examination by intravascular ultrasound

Bifurcation disease represents a mechanical and biological challenge for definitive interventional treatment. This case report discusses an experience with a novel stent system designed for the treatment of bifurcation lesions.

The impact of metallic allergy on stent implantation

BACKGROUND

Relation between metallic allergy and in-stent restenosis (ISR) has been inconclusive. We hypothesized that mechanism of restenosis is different between initial stent implantation and dilatation for ISR. Thus, we studied metallic allergy and restenosis in these two different situations separately.

METHODS AND RESULTS

We performed follow-up angiography and patch test for metallic allergy in a total of 174 stented consecutive patients, 109 patients (63%) for restudy of initial stent implantation and 65 patients (37%) for restudy of treatment following ISR. The positive rate of patch test in initial stent implantation was not significantly different between with or without restenosis (10% vs. 9%; p=ns). Whereas, following dilatation of ISR, the incidence of positive patch test was significantly higher in patients with recurrence of restenosis than those without the recurrence (39% vs. 12%; p=0.02). Multivariate analysis revealed that the positive patch test (Odd Ratio 4.39, p=0.02) and diffuse typed ISR (Odd Ratio 3.68, p=0.03) were significant predictors of recurrent restenosis.

CONCLUSIONS

Metal allergy does not have any correlation with the restenosis after initial stent implantation. However, metal allergy is frequently observed in patients with recurrence of ISR. Metal allergy may contribute to a mechanism in the repeat recurrence of ISR, but not to restenosis after initial stent implantation.

Effect of lumen narrowing within coronary stents on proximal and distal vessel segments following bare metal stent implantation

Adjacent reference vessel response to smaller lumens at stented segments was examined with 3-dimensional intravascular ultrasound analysis. In 128 patients after bare metal stent implantation, minimal lumen area (MLA) within the stent and average lumen area at distal/proximal adjacent reference segments (5 mm) were obtained at baseline and follow-up. In the smaller in-stent MLA group (MLA <3 mm2), lumen area decreased significantly at the distal edge compared with the larger in-stent MLA group (MLA > or =3 mm2), although no significant difference was seen at the proximal edge. In-stent lumen patency may influence vascular responses at adjacent reference segments after bare metal stent implantation.

Initial characterization of Ikari Guide catheter for transradial coronary intervention

Ikari is a new guide catheter for transradial intervention (TRI) that produces stronger back-up force by utilizing an unfavorable angle between the subclavian and brachiocephalic arteries. We report the initial results of the Ikari guide catheter based on the experience of a single center. Six operators performed a total of 102 coronary interventions for 91 patients using the Ikari guide catheter, while 101 interventions were performed with the transfemoral approach (TFI) during the same period. A left Ikari catheter was used in 63 procedures, and a right Ikari catheter was used in 39. The success rate for the procedure was 97% with a 6 French Ikari catheter. All failures were due to tortuous brachiocephalic arteries. For the Ikari procedure, the average fluorescence time was 14.5 9.5 minutes and the dye volume used was 153 53 ml; these results were equal to or better than those of TFI during the same period (20.1 12.2 minutes and 184 61 ml, respectively). These preliminary data suggest that an acceptable success rate can be achieved in TRI using appropriate guides, such as an Ikari catheter.

Activation of the nicotinic acetylcholine receptor involves a switch in conformation of the alpha subunits

The nicotinic acetylcholine (ACh) receptor belongs to a superfamily of synaptic ion channels that open in response to the binding of chemical transmitters. Their mechanism of activation is not known in detail, but a time-resolved electron microscopic study of the muscle-type ACh receptor had suggested that a local disturbance in the ligand-binding region and consequent rotations in the ligand-binding alpha subunits, connecting to the transmembrane portion, are involved. A more precise interpretation of this structural change is given here, based on comparison of the extracellular domain of the ACh receptor with an ACh-binding protein (AChBP) to which a putative agonist is bound. We find that, to a good approximation, there are two alternative extended conformations of the ACh receptor subunits, one characteristic of either alpha subunit before activation, and the other characteristic of all three non-alpha subunits and the protomer of AChBP. Substitution in the three-dimensional maps of alpha by non-alpha subunits mimics the changes seen on activation, suggesting that the structures of the alpha subunits are modified initially by their interactions with neighbouring subunits and switch to the non-alpha form when ACh binds. This structural change, which entails 15-16 degrees rotations of the inner pore-facing parts of the alpha subunits, most likely acts as the trigger that opens the gate in the membrane-spanning pore.

The effect of heat conditioning of the primary area before and after induction of hyperalgesia by topical/intradermal capsaicin or by controlled heat injury

The aim of the present study was to test the effect of heat conditioning before and after the induction of hyperalgesia. Three different methods were used for induction of hyperalgesia, topical capsaicin, intradermal capsaicin injection, and a controlled heat injury. The vascular (blood flow and skin temperature) and sensory changes (area of secondary hyperalgesia and ongoing pain) associated with the cutaneous hyperalgesia were compared. Each experiment consisted of two randomized sessions separated by at least 2 days. In one session, pre-conditioning of the skin by heat was performed 30 min before the induction of hyperalgesia using a probe at 45 degrees C for 5 min in the center of the expected primary hyperalgesic area. After the induction of hyperalgesia, heat conditioning was performed twice in the center of the primary hyperalgesic area using a temperature of 2 degrees C above the present individual pain threshold. On the contra-lateral arm, no heat conditioning was applied while hyperalgesia was induced using the same method. This session was evaluated as a control. The pre-conditioning induced an increased skin temperature in the primary area for both topical capsaicin and the controlled heat injury. Post-conditioning caused increased blood flow in the secondary hyperalgesic area for the topical capsaicin method and increased blood flow in the primary hyperalgesic area for the controlled heat injury method. However, conditioning with heat in an attempt to increase the C-fiber input did not have any effect on the ongoing pain ratings and sensory test results in any of the methods. The results of the present study suggest that there is still a need for a better experimental model with more stable allodynia both between sessions and between subjects while at the same time minimizing discomfort to the volunteer.

Dominant distribution of mitochondrial DNA from recipient oocytes in bovine embryos and offspring after nuclear transfer

In the process of nuclear transfer, heteroplasmic sources of mitochondrial DNA from a donor cell and a recipient oocyte are mixed in the cytoplasm of the reconstituted embryo. The distribution of mitochondrial DNA heteroplasmy in nuclear transfer bovine embryos and resultant offspring was investigated by measuring polymorphism in the displacement loop region of mitochondrial DNA using PCR-mediated single-strand conformation polymorphism. Most offspring (20 of 21 calves) from recipient oocytes of undefined mitochondrial DNA genotypes showed different genotypes from the mitochondrial DNA of donor cells. The single calf that was an exception showed heteroplasmy, including the donor mitochondrial DNA genotype. Six cloned calves were produced from oocytes of a defined mitochondrial DNA genotype. All of these clonal members and various tissues showed only the mitochondrial DNA genotype derived from the oocyte. The mitochondrial DNA from donor cells appeared to be eliminated during early embryonic development; it gradually decreased at the early cleavage stages and was hardly detectable by the blastocyst stage. These results indicate that the genotype of mitochondrial DNA from recipient oocytes may become the dominant category of mitochondrial DNA in calves resulting from nuclear transfer.

Nicotinic acetylcholine receptor at 4.6 A resolution: transverse tunnels in the channel wall

The nicotinic acetylcholine (ACh) receptor is the neurotransmitter-gated ion channel responsible for the rapid propagation of electrical signals between cells at the nerve/muscle synapse. We report here the 4.6 A structure of this channel in the closed conformation, determined by electron microscopy of tubular crystals of Torpedo postsynaptic membranes embedded in amorphous ice. The analysis was conducted on images recorded at 4 K with a 300 kV field emission source, by combining data from four helical families of tubes (-16,6; -18,6; -15,7; -17,5), and applying three-dimensional corrections for lattice distortions. The study extends earlier work on the same specimen at 9 A resolution. Several features having functional implications now appear with better definition. The gate of the channel forms a narrow bridge, consisting of no more than one or two rings of side-chains, across the middle portion of the membrane-spanning pore. Tunnels, framed by twisted beta-sheet strands, are resolved in the extracellular wall of the channel connecting the water-filled vestibule to the putative ACh-binding pockets. A set of narrow openings through which ions can flow are resolved between alpha-helical segments forming part of the cytoplasmic wall of the channel. It is suggested that the extracellular tunnels are access routes to the binding pockets for ACh, and that the cytoplasmic openings serve as filters to exclude anions and other impermeant species from the vicinity of the pore. Both transverse pathways are likely to be important in achieving a rapid postsynaptic response.

The structure of bacteriorhodopsin at 3.0 A resolution based on electron crystallography: implication of the charge distribution

Electron crystallography has the potential to visualise the charge status of atoms. This is due to the significantly different scattering factors of neutral and ionised atoms for electrons in the low-resolution range (typically less than 5 A). In previous work, we observed two different types of densities around acidic residues in the experimental (|Fo|) map of bacteriorhodopsin (bR), a light-driven proton pump. We suggested that these might reflect different states of the acidic residues; namely, the protonated (neutral) and the deprotonated (negatively charged) state. To evaluate the observed charge more quantitatively, we refined the atomic model for bR and eight surrounding lipids using our electron crystallographic data set between 8.0 and 3.0 A resolution, where the charge effect is small. The refined model yielded an R-factor of 23.7% and a free R-factor of 33.0%. To evaluate the effect of charges on the density map, we calculated a difference (|Fo|-|Fc|) map including data of a resolution lower than 8.0 A resolution, where the charge effect is significant. We found strong peaks in the difference map mainly in the backbone region of the transmembrane helices. We interpreted these peaks to come from the polarisation of the polar groups in the main chain of the alpha-helices and we examined this by assuming a partial charge of 0.5 for the peptide carbonyl groups. The resulting R and free R-factors dropped from 0.250 and 0.341 to 0.246 and 0.336, respectively. Furthermore, we also observed some strong peaks around some side-chains, which could be assigned to positively charged atoms. Thus, we could show that Asp36 and Asp102 are likely to interact with cations nearby. In addition, peaks found around the acidic residues Glu74, Glu194 and Glu212 have different features and might represent positive charges on polarised water molecules or hydroxonium ions.

Macromolecular structure determination by electron microscopy: new advances and recent results

Electron microscopy is undergoing a mini-renaissance, as a number of biological systems are yielding to higher resolution analysis as a result of advances in instrumentation, specimen preparation and image-processing technology. The atomic structure of tubulin has now been solved, crucial elements of secondary structure have recently been revealed in several membrane proteins (rhodopsin, gap junctions, aquaporin, and Ca2+ and H+ ATPases) and in a virus particle, and macromolecular complexes are being seen in increasingly fine detail. This growth has been enhanced further by the ability to combine structures of macromolecular complexes derived by electron microscopy with X-ray structures of their components, in order to reconstruct molecular machines and large multiprotein complexes in immense detail.