Percutaneous Intervention on the LIMA: Tackling the Tortuosity

The left internal mammary artery (LIMA) is an elastic or elasto-muscular artery with a diameter of 2–3 mm. It is preferred as a surgical conduit because of better flow and less risk of atherosclerosis and intimal hyperplasia, which results in higher patency rates (90–95% at 10 years), with fewer cardiac events and longer survival.1 Failure of the LIMA as a conduit occurs as a result of several possible factors: 1) intraoperative damage during mobilization, preparation and construction of anastomosis (the most common cause of failure); 2) inadequate conduit size; 3) post-operative stretching of the graft by hyperinflated lungs; 4) anastomosis to a rigid and thickened vessel; 5) insertion into a marginally stenotic vessel with competitive flow; 6) a large pectoral branch arising from the IMA; 7) proximal subclavian/LIMA stenosis; and finally 8) exposure to undiluted papaverine during surgery. Percutaneous coronary intervention (PCI) of the LIMA or through the LIMA has a success rate of 80–100% in various series.2–5 There is a low incidence of abrupt closure, distal embolization, acute myocardial infarction or emergency coronary artery bypass graft surgery.2–5 Procedural failure is related to technical challenges, failure to cross the lesion with the guidewire or balloon, inability to reach the stenosis due to vessel tortuosity or redundancy of the graft.6 Percutaneous intervention on a tortuous LIMA graft, especially with redundancy in length, is a challenge. Various modifications of the interventional technique are required in order to negotiate the tortuosity of the subclavian and the LIMA graft. We describe a technique that involves meticulous exchange of the balloon angioplasty catheter for a Transit catheter and facilitates intervention on or through a very tortuous and redundant LIMA graft. Case Report. The patient was a 49-year-old male with history of coronary artery bypass graft surgery who had recurrence of angina (Canadian Cardiovascular Society class III symptoms) a few months after surgery. Coronary and bypass angiography performed at an outside institution showed a lesion in the left anterior descending (LAD) artery, distal to the anastomosis of the LIMA graft to the LAD. Angioplasty of the lesion was attempted at that institution, but was not successful because of inability to reach the lesion with a balloon. The patient was referred to our institution for the intervention. Left radial access with a 6 French (Fr) sheath was used for the interventional procedure. Heparin 5,000 units and nitroglycerin 300 µg were administered through the radial arterial sheath to prevent radial artery vasospasm. The LIMA was engaged selectively through the left radial approach using a 90 cm, 6 Fr IMA guiding catheter. (A 90 cm guide was chosen to reach the lesion at the anastomotic site, allowing for the LIMA tortuosity). An additional 5,000 units of heparin were administered intravenously. Nitroglycerin 300 µg and verapamil 100 µg were administered through the guiding catheter into the LIMA graft to prevent vasospasm of the LIMA before starting the intervention. An angiogram was obtained before starting the intervention, which showed the tortuosity of the LIMA (Figure 1). The lesion at the anastomosis was crossed with an ACS Hi Torque Balance 0.014´´ guidewire (Guidant Corporation, Temecula, California) which was loaded with a 3 Fr over-the-wire Transit catheter (Cordis Corporation, Miami, Florida). The Transit catheter has a very flexible shaft and follows the tortuosity of the LIMA graft without causing any “accordioning” of the vessel. The radiographic landmarks (vascular clips from the bypass surgery) were used to mark the site of the lesion at the anastomotic site to facilitate the positioning of the angioplasty balloon. The Transit catheter was exchanged for an over-the-wire Coyote 2.5 x 15 mm angioplasty balloon. However, this resulted in a straightening of the vessel, leading to “accordioning” of the LIMA and “no flow” through the LIMA with the guidewire and Coyote angioplasty balloon in place. Therefore, the positioning of the Coyote angioplasty balloon was carried out using the radiographic landmarks as described above (Figure 2). Balloon angioplasty was performed at 6 atmospheres (atm) for 19 seconds followed by another dilatation at 6 atm for 23 seconds. As there was no flow through the LIMA, angiographic assessment of the angioplasty result was accomplished by a unique technique. This technique involves a 3 step process of achieving the normal LIMA tortuosity with resolution of the “accordioning” of the vessel, thus permitting flow of contrast though the vessel on contrast injection and angiographic assessment, while maintaining an access for guidewire placement. The 3 steps of this technique, outlined below, were accomplished in succession. The first step involved exchange of the Coyote angioplasty catheter for the flexible-shaft Transit catheter. The Transit catheter was advanced past the lesion. Second, the guidewire was removed from the lumen of the Transit catheter. Once the guidewire was removed from the Transit catheter, the LIMA assumed its normal tortuous contour, thus leading to resolution of the “accordioning” of the vessel. Third, injection of contrast though the guiding catheter (with the Transit catheter in place inside the LIMA in order to maintain a channel for guidewire access) now permitted visualization of the entire LIMA and allowed angiographic assessment of the angioplasty lesion site (Figure 3). Additional and longer balloon dilatations were performed using another Coyote 2.5 x 20 mm balloon angioplasty catheter. Placement of the balloon angioplasty catheter requires a two-step process. First, placement of the guidewire through the Transit catheter lumen, and second, exchange of the Transit catheter for the angioplasty balloon catheter over the guidewire. Balloon dilatation of the lesion was carried out at 6 atm for 65 seconds followed by another dilatation at 6 atm for 85 seconds with a Coyote 2.5 x 20 mm balloon (using radiographic landmarks). Finally, an assessment of the angiographic result was accomplished with the 3 step process outlined above. Successful dilatation and a good angiographic result (with less than 20% residual stenosis) were achieved (Figure 4) and the angioplasty procedure was completed without complications. Discussion. The technical considerations of the procedure of LIMA PCI include the following issues. 1) Tortuosity of the subclavian artery often makes cannulation of the LIMA difficult. When difficulty is encountered in cannulating the LIMA due to left subclavian tortuosity, it is easier to enter in the 60° left anterior oblique projection (as it elongates the arch), using a R Judkins guiding catheter, or using the ipsilateral brachial approach. 2) Engagement of the IMA should be carried out very gently as forceful engagement may dissect the vessel. Pretreatment with nitroglycerin or verapamil may facilitate engagement of the graft. If the IMA is small, a 7 Fr guide may be useful. 3) Proper equipment selection is essential. Low-profile balloons are preferred, given the size of the conduit and its tortuosity. Due to length, tortuosity and redundancy of the IMA vessel, longer shaft balloons (150 cm), or short guides (90 cm) are required. Sometimes a guide can be fashioned by cutting the proximal end and replacing the hub with an introducer sheath. 4) Straightening of the tortuous LIMA after crossing with the guidewire can result in “pseudolesions” and “accordioning” of the IMA graft and significant reduction in flow. This makes the positioning of the balloon difficult, without use of some other radiographic landmarks, and assessment of the angioplasty result is almost impossible unless the guidewire is removed. Our new technique with the 3-step approach overcomes this problem. The 3-step technique involves exchanging the angioplasty balloon for a Transit catheter. The Transit catheter has a very flexible shaft and conforms to the tortuosity of the LIMA much better than a conventional angioplasty balloon. It does not cause any straightening of a tortuous LIMA and prevents any accordioning, spasm or decreased flow through the graft. This allows angiographic assessment when the Transit catheter is in place (Figure 3). It also maintains a port for guidewire access. We believe this new technique shall find utility in performing PCI on or through very tortuous LIMA grafts. Since this technique involves extra steps to maintain guidewire access and allow angiographic assessment, it is likely to be of use in situations where the LIMA is very tortuous and redundant. In such situations, simple placement of the guidewire causes straightening of the tortuous vessel, resulting in guidewire-induced “accordioning” and “pseudolesions”, often with no flow through the straightened LIMA vessel. This situation causes anxiety and concern during the intervention as the operator is often left unsure of whether an actual dissection or acute closure of the LIMA vessel has occurred. Using different guidewires may influence performance in situations of severe tortuosity. The guidewires are made of 3 basic components: 1) a central core or shaft (of stainless-steel or nitinol); 2) a distal flexible spring coil (usually platinum or tungsten); and 3) a lubricious coating (silicone, polytetrafluoroethylene or another hydrophilic coating). The central core is made of a proximal main body and a tapered core segment. The tapered core segment of guidewires is usually 30–35 cm in length and is the more flexible portion of the guidewire. Although guidewire construction does influence performance in situations of severe tortuosity, this may not obviate the problem of guidewire-induced “pseudolesions” and slow flow in LIMA interventions, because the tortuosity in a LIMA graft is often more pronounced than in a native coronary artery and the LIMA graft is often redundant in length. This makes the tapered core (flexible) segment of the guidewire fall short of the whole length of the LIMA graft. In tortuous vessels such as the LIMA graft, steerablility and tip response may often be lost as the wire passes through multiple curves. Partial advancement of a transport catheter (like the Transit Catheter) or balloon catheter may improve guidewire support, torque control and steerability.7 Use of a stiffer, heavy-duty guidewire may straighten the vessel curves, but will accentuate the pseudolesions and hence are not suited for LIMA interventions. Guidewires with single-core construction provide a smoother transition, enhanced torque response and less prolapse compared to shaping ribbon construction guidewires in tortuous vessels. Guidewires with nitinol cores (like the Guidant Balance family) are virtually kink resistant, while those with stainless-steel cores may be more susceptible to kinking in tortuous vessels. Hydrophilic and nitinol core guidewires, which are more flexible and kink resistant, are likely to be more suitable for wiring a LIMA graft. This technique has the benefit of maintaining access for guidewire placement and allows angiographic assessment of the result of the intervention by maintaining the contour of the LIMA while the Transit catheter is in place. Alternate endeavors with other equipment that could conceivably achieve the same goals would involve an over-the-wire balloon angioplasty catheter. However, the shaft of the Transit catheter is much more flexible than a balloon angioplasty catheter; therefore, we used the Transit catheter. The issue of guidewire-induced pseudolesions is much more pronounced in the LIMA graft than in the native coronary arteries. This has to do with the redundancy of the LIMA graft as well as its tortuosity, as opposed to tortuous coronary arteries where redundancy is hardly ever an issue. We used the radial approach in this given patient, since we were unable to cannulate the LIMA from the femoral approach secondary to the tortuosity of the left subclavian. We also overcame the problem of redundancy of the LIMA graft by using a shorter (90 cm) guiding catheter. In summary, percutaneous intervention on a tortuous LIMA graft, especially with redundancy in length, becomes a challenge. Various modifications of the interventional technique are required in order to negotiate the tortuosity of the subclavian and the LIMA graft and to accomplish the intervention while maintaining guidewire access and visualization, at the same time overcoming the problem of “pseudolesions”. Our technique involves meticulous exchange of the balloon angioplasty catheter for the Transit catheter. It obviously adds to the total procedure time and fluoroscopy time; however, there does not appear to be any other major down-side to the technique. We hope that this technique may find utility in situations of performing intervention on or through a very tortuous and redundant LIMA graft.

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