2.1

Study protocol

Patients were pretreated with ≥ 80 mg of aspirin daily for > 24 h, and intravenous heparin was administered during the index procedure to maintain an activated clotting time > 250 s. All anti IIb/IIIa agents use were left to the operator’s discretion with proper heparin dosage adjustments. Intracoronary nitroglycerine (> 100 μg) was given before intervention and at the end of index procedure prior to final angiogram. Patients falling within inclusion criteria were treated with the X80 laser catheter starting at 60 fluence and 40 hertz laser parameters (SLT). After the successful laser passage, adjunctive balloon angioplasty and stenting were performed to complete treatment according to the standard procedure. When the laser catheter failed to cross target lesion completely, laser parameters were increased to 60 fluence and 80 hertz and then to 80 fluence and 80 hertz (ILT) in an attempt to traverse the lesion. If still unsuccessful, the laser catheter was withdrawn, recalibrated, and reinserted, and three more laser sequences were attempted. Three successive laser sequences without catheter tip progression had to be experienced before increasing laser parameters. At least 12 laser trains were attempted before failure was declared (3 × 60 fluence/40 hertz, 3 × 60/80, 3 × 80/80, and 3 × 80/80 postrecalibration). After the procedure, sheaths were removed immediately (radial approach) or 6 h later. Creatinine kinase measurements and electrocardiogram were obtained on all patients prior to and 24 h after index procedure. No clinical follow-up was recorded after hospital discharge.

2.2

Laser procedure

The excimer laser is a pulsed xenon–chlorine-based mid ultraviolet wave length (308 nm) laser relying on absorption in the nonaqueous components of the atherosclerotic plaque, such as proteins and nucleic acids, for debulking . The new X80 catheter measures 0.9 mm in diameter with concentric fibers. It was built to deliver energy up to 80 mJ/mm ² at 80 hertz with a lasing cycle characterized by 10 s of active firing and 5 s of silence. The laser system requires a 5-min warm-up period to turn on. The catheter is prepared by flushing the central guidewire lumen and connecting the proximal end to the laser console. Calibration of the catheter is then performed, and the desired energy level is set up. The catheter is then passed over the guidewire just proximal to the lesion. The flush-and-bathe technique for blood and dye clearance from the entire system by saline infusion is mandatory prior to each lasing train. Lasing is performed by applying gentle forward pressure to the catheter in order to cross the lesion under fluoroscopy while energy is emitted from the catheter distal tip with foot pedal activation. The procedure is then finalized by laser catheter removal and the additional balloon and stent use according to the standard practice. Repeat arteriography after intracoronary nitroglycerine was recorded after laser use, before any adjunctive therapy and at the end of the procedure.

2.3

Definitions

Laser technical success was defined as the laser catheter crossing the entire length of the stenotic lesion determined by angiographic evidence of the catheter tip in the artery distal to the stenosis. Procedural success was defined as < 50% residual stenosis after laser and adjunctive therapy. Clinical success requested procedural success with absence of major adverse cardiac events at hospital discharge. Major adverse cardiac events included death of all causes, non-Q-wave and Q-wave myocardial infarction, need for target lesion revascularization, tamponade, and life-threatening arrhythmias. Q-wave myocardial infarction was defined as elevation of creatinine kinase levels > 3 times above laboratory normal values with any abnormal MB fraction and the development of new pathology Q-waves on the electrocardiogram. A non-Q-wave myocardial infarction was defined as the development of similar creatinine kinase elevation without Q-waves.

Anterograde flow was assessed by the thrombolysis in myocardial infarction (TIMI) scale . Lesion morphology was characterized by the modified American College of Cardiology/American Heart Association (ACC/AHA) score . Laser complications included dissection type C or worse according to the National Heart, Lung and Blood Institute classification , coronary spasm, thrombus formation, no reflow, embolization, perforation, loss of major side branch (> 2 mm in diameter), and acute closure. Spasm was defined as transient reduction in blood flow with vessel caliber narrowing relieved either spontaneously or by nitroglycerine. Thrombus formation was defined as the new appearance of an intraluminal filling defect, lucency, or haziness refractory to intracoronary nitroglycerine. No reflow was determined by reduction of ≥ 1 TIMI flow grade without angiographic demonstration of embolization, whereas embolization was characterized by new appearance of a distal intraluminal filling defect or loss of a distal branch. Perforation requested demonstration of a persistent extravascular collection of contrast medium beyond the vessel wall. Finally, acute closure was defined as sustained TIMI 0 to 1 flow grade caused by obstruction of the target lesion.

2.4

Data collection and analysis

Detailed in-hospital case report forms were prospectively completed for each patient. A study monitor traveled to each site for independent verification of case report form accuracy. Angiograms were evaluated by individual operators using local online quantitative coronary analysis software and visual assessment. However, all the angiograms were evaluated at the independent QCA Core Laboratory. No significant discrepancies between the online and offline analyses were seen.

Data were entered into a SAS database (software version 7.2, SAS Institute). Statistical calculations used Wilcoxon scores (rank sums) and McNemar analysis for frequency tables. A P value < 0.05 was required for statistical significance.