IVUS and Endovascular Interventions
Literature regarding use of IVUS for endovascular interventions is scarce. Wada et al.60 reported a small case series of patients undergoing IVUS guided stent placement for subclavian artery disease. Short term results were good and long term outcomes were remarkable for absence of ISR over a 51 month median follow up. Contrast minimising strategies like the use of carbon dioxide digital subtraction and IVUS to guide interventions have been described for renal artery interventions,61 and for iliac artery CTO interventions.62
In addition to providing measurements and precisely locate key landmarks and venous branches, IVUS can identify important abnormalities (e.g. external compression, acute and chronic thrombus, fibrosis, mural wall thickening, spurs and trabeculations) that aid in the adequate execution of strategies to treat venous obstruction and bedside placement of vena cava filters.63 IVUSguided bedside placement of inferior vena cava (IVC) filters using a single puncture technique eliminates the risk of transportation, is safe, efficient and cost effective. It may be used in conjunction with pre-procedure computed tomography (CT) derived measurements to minimise filter malposition.64 IVUS has been used for direct and transjugular intrahepatic portosystemic shunt placement, transcaval liver biopsy, transcaval puncture of type II endoleaks and for cardiac mass biopsies.65
Safety and Complications
Strategies to prevent contrast induced nephropathy include adequate hydration and use of IVUS to guide interventions.61 IVUS has the potential to reduce radiation dose and increase procedure safety as previously discussed. As with any vessel instrumentation, IVUS carries the risk of vessel dissection, injury, perforation or total occlusion, air embolism, unstable angina, MI, haemodynamic instability, arrhythmias, limb ischaemia and death. Studies evaluating coronary IVUS have shown major complication rates ranging from 0.1 % including dissection, thrombus and ventricular arrhythmias66 to 1.1 % if spasm and guidewire entrapment are accounted for.67 Spasm has been described as frequently as in 2.9 % of cases,66 but is rarely refractory to vasodilators and device retrieval.
Future Directions
Similar to Volcano’s automatised lesion assessment software (Target Assist), Boston Scientific is working on advanced lesion assessment software that will allow for automatised bookmarks and measurements for the healthier proximal and distal portions as well as the tightest portion of a lesion immediately following pullback. Hybrid IVUS and optical coherence tomography (OCT) catheters are on the horizon.68 Co-registration of 3D coronary angiography and IVUS or OCT will improve our understanding of complex lesions and improve our ability to deliver optimal interventional results.69 Sync Vision™ (Volcano Corporation) will use a built-in device motion indicator and combine anatomical and functional assessment using IVUS and instantaneous Wave-Free Ratio (iFR) co-registration. New transducer technology will offer advancements like increased image resolution, multi-frequency devices, real-time volumetric ultrasound imaging capability,70 and software improvements to facilitate image interpretation and increase ease of use. IVUS on guide-wires and forward-looking IVUS for use in CTOs are attractive options that may soon complement our current interventional armamentarium.