CALCIFIED CORONARY LESION: IS IT STILL THE ACHILLES’ HEAL OF PERCUTANEOUS CORONARY INTERVENTIONS?

摘要

Percutaneous Coronary Intervention of heavily calcified coronary lesions still represent a great challenge for interventional cardiologist, resulting in an increased risk of immediate and long term complications due to stent under expansion and malapposition. 2 Multi-modality imaging can help understand the characteristics of calcium, and along with that the use of new armamentarium specifically designed for dealing with moderate to heavy calcification, in making optimal lesion preparation before stent implantation. Coronary artery calcification (CAC) is seen in patients mostly with advanced age, renal disease and diabetes. Severe CAC is seen in patients between 6% and 20% treated with PCI. 3 Conventional angiography usually misses and has low sensitivity for CAC. Intravascular ultrasound (IVUS) have shown that CAC is missed in nearly half of the cases undergoing angiography. 4 IVUS helps in semiquantitative grading of calcium distribution, localisation length, but deep calcium is hidden by acoustic shadowing. OCT (Optimal Coherence Tomography) provides much better resolution than IVUS, with the additional ability of seeing the depth of calcium and seeing microcalcifications. However, unlike IVUS it requires contrast dye and has limited depth penetration. A lot of patients also have had a coronary CT before their procedure. This can also serve as useful tool to better define CAC characteristics to better plan for lesion intervention. Proper assessment of CAC is important in making a strategic plan for use of different tools of ablation in lesion preparation. Optimal lesion preparation helps in appropriate stent deployment. The first tool used for dilating coronary lesions is with plain old balloon angioplasty (POBA). Non-Compliant (NC balloons) are meant for more uniform balloon expansion and applying high pressure in a focal segment of a coronary vessel that prevent dumbbell deformation resulting in high pressure at the edges as a resulting edge dissection/perforation. NC balloon has twin-layer technology which permits very high pressures with minimal diameter increase. From limited experience they have been shown to have treated 90% of undilatable lesions compared to a conventional NC balloon with a 0.9% rate of coronary perforation. 5 The chances of unsuccessful expansion with NC balloons with moderate to heavy calcifications can be high. Further modification in balloon developed in 1991 as cutting balloon dilation device. The structure consisted of blades mounted longitudinally on a noncompliant balloon. It causes three or four endovascular radial incisions through fibrocalcific tissue without balloon slippage and results in large luminal gain. The results were more effective in aorto-ostial lesions. 6 The CAPAS trial 7 and Cutting Balloon Global Randomized trial 8 showed no difference in outcomes at six months between cutting balloon angioplasty (CBA) and POBA, except that there was an increase in rate of perforation with CBA. This high rate of perforation led to the development of the scoring balloon. It is basically a semi-complaint nylon balloon surrounded by external nitinol spiral scoring wires, which provides focal force concentration without balloon slippage. The feasibility trial 9 showed an increase in rate of dissection with no device related perforation. This balloon was used in ISR and calcified lesions. For lesion preparation to address undilatable stenosis, specially calcified lesion dilating strategy can be adopted resulting in plaque modification. The advantages of primary atherectomy are multiple and includes decrease procedural and fluoroscopy time, contrast volume and number of predilation balloon catheter used. 10 There are two form of atherectomy i.e. rotational and orbital. Rotational provides differential cutting and orbital differential sanding. Atherectomy alters plaque morphology, creates fractures in calcified lesions and causes an increase in luminal gain. All these parameters help in dilating and optimal stent expansion. Mechanical debulking of atherosclerotic plaque was introduced in 1988 by David Auth as Percutaneous Transluminal Rotational Atherectomy (PTRA). The mechanistic effect is differential cutting causing ablation of inelastic fibrocalcific plaques while sparing adjacent elastic tissue that deflects away from the ablating burr. The study by Fourier showed an increase in TLR with PTRA vs. balloon. 11,12 STRATAS and CARAT trials used debulking strategy based on the burr to artery ratio lower or higher than 0.7. 13,14 The SARS study showed impact of reducing burr speed during rotation to 140-160 K revolution per minutes (rpm) and avoiding deceleration 3,000 rpm. 15 To reduce effective ablation time and contact of the burr with the plaque i.e. pecking motion. 16 Other tools for plaque modification is Orbital Atherectomy (OA). Its advantages over RA of having a single size burr, less likelihood of crown entrapment, transient heart block, and no-reflow phenome