Complementary Imaging as Solution to Challenges
Unlike in the US and Japan complementary imaging is still unpopular in Europe firstly because the predominant philosophy is to keep procedures simple and secondly because of restricted reimbursement. No wonder that up until 2010 IVUS and Multislice Computed Tomography (MSCT) were used in 1.5 % (IVUS) and 4.0 % (MSCT) of cases only by the members of the EuroCTO club. With a redoubling of the retrograde approach in 2012 the use of IVUS increased to a still modest 12.5 %. No doubt IVUS appears helpful to identify the take-off of the occluded vessel when no stump is discernible, to facilitate re-entry after having created a large false channel and to identify the position of the retrograde wire in the dissection channel as well as to measure the vessel diameter and safely select the proper balloon size. MSCT is used to depict long and tortuous occlusions and to locate calcifications not visible angiographically29, 30 - definitely helpful information if the first attempt to recanalise failed. Since only a few studies with small numbers are reported so far, the importance of MSCT with its adverse additional X-ray exposure and additional costs remains unsolved.
Retrograde Approach
If a vigorous antegrade attempt to open the vessel failed a second attempt then mostly a retrogradely approach is recommendable in most patients. Until recently, it was strongly suggested to schedule the retrograde attempt a few weeks after the antegrade failure.31 Many operators, including me, nowadays favour to switch ad hoc after 10-15 min of unsuccessful antegrade wiring with different wires and wiring techniques well before the distal vessel gets affected by enlarged false channels. The first report of retrograde recanalisation of a CTO was published by a French group in 1996.32 In 2005, Katoh opened an important new window, pioneering the modern era of retrograde CTO recanalisation with the CART technique.33 The novelties introduced in this procedure were the targeted septal collateral crossing and the connection of an antegrade and retrograde subintimal channel.
To facilitate this approach several tools were newly developed like the channel dilator Corsair, a long wire for externalisation (ASAHI RG3®), Short (90-95 centimetres [cm]) or shortened guiding catheters (GCs) are sometimes necessary especially in long epicardial connections. Monitoring of anticoagulation during the procedure is very important.
An ACT should be measured every 30 min and should be maintained over 300 sec until the end of the procedure is foreseeable, to avoid any thrombotic complications in the donor artery, which are potentially lethal. Septal collaterals are most often used (about 75 % of cases) followed by epicardial collaterals that are in general larger but more tortuous and more difficult to traverse. Stronger and straight collaterals are easier to be crossed than invisible and tortuous connections, but it is not rare to discover that the collateral that appeared less favourable was quite easy to cross.
There are three main techniques to cross and dilate the occlusion:
1. Retrograde marker wire at the distal end of occlusion as a targetfor the antegrade stiff and tapered wire.
2. Retrograde penetration of occlusion with wire and Corsair and externalisation of a long wire like Rotablator Wire or ASAHI RG3 via guiding catheter exiting the antegrade sheath followed by antegrade stenting.
3. Connecting both false wire channels either via retrograde subintimaldilation (CART technique) or antegrade subintimal dilation (reverse-CART technique) followed by antegrade stenting.
Since the retrograde approach is generally more difficult and time consuming all CTO procedures should be started in an antegrade way with very few exceptions. The more complex nature is documented by the EuroCTO club registry 2008-2010 with a procedural time of antegrade approach 87 min, dye consumption 268 millilitres (ml) in 4,299 patients versus 154 min and 383 ml dye consumption in 501 patients with retrograde approach. As patients selected for retrograde approach are generally more awkward and the procedure is more tricky, the current success rate is roughly 15 % lower than antegrade. To make matters worse the retrograde approach is handicapped by a 2-3 fold higher rate incidence of severe in-hospital complications.
Retrograde Challenges
The most difficult part is the successful transition of collaterals, which might only be possible in 60-70 % of CTO patients. The most favourable collaterals are the well visible straight interseptals and the worst are the tiny cork screw like epicardials. Although collaterals may be successful even if the vessel course is not clearly depicted angiographically, it is recommendable to take advantage of superselective dye injection via the retrograde Corsair. This is best done by a 3 ml syringe with Luer-lock and forceful injection. To prove proper position in the vessel and avoid detrimental forceful intramural injection one should be able to aspirate blood before injecting dye. Connecting an antegrade and retrograde dissection again should aim at limiting the extension of a subintimal track to avoid long subintimal stenting. Antegrade IVUS is very helpful to identify the optimal balloon size for retrograde CART and the optimal position for re-entry (where both wires are closest).
Complications
In-hospital complications are rare, but not negligible - quite similar to PCI of non-occluded vessels in the EuroCTO online registry 2008-2010 (N=4,820 patients) death occurred in 0.30 %, any MI in 2.70 %, emergency CABG in 0.21 % and cardiac tamponade in 0.45 % of cases. As mentioned earlier the complication rate with retrograde approach exceeds that of antegrade by at least 2-3 times (major adverse cardiac events [MACE] 4.5 %)34 and according to G. Werner infarctions defined as CK rise to >3 times upper limit were 3.1 % following antegrade and 7.1-20.0 % following retrograde approach via septal or epicardial collaterals.35
Some of the complications of retrograde approach are quite unusual like collateral perforation, septum haematoma, aortic dissection, dissection and thrombotic occlusion of the collateral donating vessel or severe wire entrapment. In general I assume that complications after retrograde approach do occur more often than reported in registries and I strongly recommend adopting this technique only after extensive proctoring. In summary CTO PCI is probably the most challenging percutaneous intervention, but almost every vehement assignment in CTO may nowadays be mastered with high success rates, low complication rates and good long-term results, provided that indication, operator experience and strategy are ­fit and proper.