Abstract
BVS polymeric struts are transparent to the light so that the vessel wall contour can be easily visualized using optical coherence tomography (OCT). Therefore OCT represents a unique tool for both the evaluation of the resorption process and for the assessment of acute BVS mechanical failure. Similarly, the metal-free struts allow unrestricted coronary computed tomography angiography (CCTA), thus this non invasive method might become the gold standard for a non invasive assessment of BVS. In this case we show the ability of CCTA, performed with a low X-Ray dose, to provide a good evaluation of scaffold expansion. The quantitative measurements were in agreement with those obtained with OCT.
Scaffold underexpansion and acute recoil is one of the major drawbacks of the promising ABSORB Bioresorbable Vascular Scaffolds (BVS) (Abbott Vascular, Santa Clara, CA, USA). BVSs have a different appearance from metallic stents when imaged with optical coherence tomography (OCT). Unlike metallic stents which are powerful light reflectors and induce posterior shadowing and blooming artifacts on the surface and edges, BVS polymeric struts are transparent to the light so that the vessel wall contour can be easily visualized . Therefore OCT represents a unique tool for both the evaluation of the resorption process and for the assessment of acute BVS mechanical failure. Similarly, the metal-free struts allow unrestricted coronary computed tomography angiography (CCTA) thus this non invasive method might become the gold standard for a non invasive assessment of BVSs especially if an accurate examination can be performed with low radiation dose acquisition protocols.
A 62 years-old lady affected with hypertension and diabetes presented with stable angina. The coronary angiogram showed two long critical lesions of the mid and proximal left anterior descending coronary artery (LAD). Despite the presence of calcific spots at the proximal LAD we considered the PCI with BVS to be feasible. Lesions predilatation was performed using non compliant balloons (diameter: 2.5 mm for the distal lesion and 3.0 mm for the proximal). Since the balloons were properly expanded we did not performed lesion debulking with rotational atherectomy. A 2.5 × 28 mm Absorb was deployed at the mid LAD, and adequate scaffold expansion was confirmed with OCT. On the other hand, both angiogram and OCT showed focal asymmetric scaffold expansion of the 3 × 28 mm BVS deployed at the proximal LAD (minimal lumen area [MLA] = 6.14 mm 2 , minimal lumen diameter [MLD] = 1.65 mm, maximal lumen diameter = 3.88 mm). We were not able to expand correctly the scaffold despite of multiple aggressive post dilatations with a non compliant high pressure balloon (OPN, SIS Medical AG; Winterthur, Switzerland) inflated up to 35 atm.
A CCTA low radiation dose scan protocol on a multi slice computed tomography (MSCT) system (Somatom Definition FLASH, Siemens Healthcare, Forchheim, Germany) was performed before the discharge in order to rule out further lumen shrinkage due to sub-acute scaffold recoil.
This MSCT system differs from previous-generation instruments by a higher temporal resolution with a gantry rotation time of up to 0.28 s, enabling high-pitch FLASH acquisition. The CCTA dataset was acquired using a prospectively ECG-triggered high-pitch spiral acquisition protocol which allowed the scan of the entire cardiac volume in a single breath-hold and within one cardiac cycle during the diastolic phase. An automated injector was used to administer 50 ml of contrast medium (Iomeprol; Iomeron 400, Bracco, Milan, Italy) at a rate of 5 ml/s followed by a saline chaser bolus 40 ml. CCTA acquisition was performed with a slice thickness of 0.60 mm.
In our case the patient’s heart rate was reduced to a target of 55 bpm with the administration of 10 mg of intravenous metoprolol. The final cumulative radiation dose exposure was 0.46 mSv. The CCTA scans were evaluated using all conventional visualization techniques (axial images, multiplanar images, curved multiplanar images, maximum intensity projection, volume rendering) on a dedicated workstation with a cardiac software platform (SyngoVia, Siemens, Germany).
The MLA computed on CCTA was 6.33 mm 2 ( Fig. 1 , panel B minimal lumen diameter [MLD] = 1.68 mm, maximal lumen diameter = 3.92 mm). Since there was agreement between the MLA as assessed with OCT and vessel analysis on CCTA, we were able to rule out sub-acute scaffold recoil. The patient was discharged the day after. At one month follow-up the patient was asymptomatic.
