Excimer Laser Revascularization of Saphenous Vein Grafts in Acute Myocardial Infarction

ABSTRACT: Patients who develop acute myocardial infarction due to occlusion in a saphenous vein graft (SVG) constitute a revascularization challenge. Excimer laser angioplasty may have a potential advantage in the treatment of SVGs, since its 308 nanometer wavelength is avidly absorbed by both atherosclerotic plaque and thrombus. The data presented herein support the notion that excimer laser angioplasty is a technology that has a potential role in achieving adequate revascularization outcomes in this selected, high-risk patient population. J INVAS CARDIOL 2004;16:177–180 Key words: revascularization, saphenous vein graft Reperfusion therapy with catheter intervention is a mainstay treatment strategy for acute myocardial infarction (AMI).^1–4 However, patients who develop AMI due to occlusion in a saphenous vein graft (SVG) constitute a revascularization challenge. Even in elective settings, percutaneous intervention in degenerated SVGs is commonly associated with complications, especially distal embolization, no reflow and CPK elevation.^5–12 This is a major reason leading to the exclusion of SVG lesions from most AMI trials. Recent experience with excimer laser angioplasty in symptomatic patients with either preserved or depressed left ventricular function has demonstrated its efficacy and safety in native coronary arteries and old grafts alike.^13–15 Excimer laser angioplasty may have a potential advantage in the treatment of SVGs, since its 308 nanometer wavelength is avidly absorbed by both atherosclerotic plaque and thrombus.^16–18 Hence, the purpose of this communication is to report our experience with the application of excimer laser angioplasty for revascularization of old SVGs in the setting of AMI. Methods The multicenter, international Cohort of Acute Revascularization in Myocardial Infarction with Excimer Laser (CARMEL) registry consisted of 151 AMI patients who received excimer laser angioplasty. These patients were enrolled between 1998 and 2002 at 8 participating medical centers. Patients were eligible for enrollment if they had an AMI within 24 hours and required percutaneous interventions for ongoing symptoms and/or ischemia. Patients presenting to the cardiac catheterization suite with cardiogenic shock were eligible for inclusion. Exclusion criteria included use of warfarin, child-bearing potential and known contraindications to aspirin, heparin, ticlopidine or clopidogrel. The present report concerns the group of 31 patients within this study whose infarct-related vessel was an SVG. All patients were treated with 325 mg oral aspirin before angioplasty and daily thereafter. Intravenous heparin was given to achieve an activated clotting time of between 250 and 300 seconds. A pulsed-wave xenon chloride laser (Spectranetics CVX-300; Spectranetics, Colorado Springs, Colorado) was utilized. This laser operates within a wavelength of 308 nanometers, with a pulse duration of 135 nanoseconds, and produces an output of 165 millijoules per pulse. The size of the laser catheter used (0.9 mm, 1.4 mm, 1.7 mm or 2.0 mm) was left at the discretion of the interventionalist based on reference vessel diameter, target lesion morphology and degree of lesion obstruction. Routine lasing techniques were applied.^16,17 The laser catheter was slowly advanced at a speed of 0.2–0.5 mm/second. Retrograde lasing was performed as deemed necessary by the interventionalist. Adjunct balloon angioplasty and stenting were then performed and final angiograms were taken. Definitions. Laser success was defined as complete crossing of the target lesion by the laser catheter, a decrease in the diameter stenosis > 20% after lasing application¹⁹ and achievement of TIMI 2 or 3 flow. Procedural success was defined as a final reduction of lumen diameter stenosis to 20 Dissection was considered to be major if associated with death, myocardial infarction or the need for bypass surgery, and was considered minor if it led to no clinical complications.²¹ Angiographic thrombi were subclassified based on TIMI thrombus grading scale,²² whereby grade 1 was small ( 1.5 times normal diameter) and grade 4 was extensive (> 3.0 times normal diameter). Q-wave myocardial infarction was diagnosed as elevation of creatine kinase-MB above laboratory normal values and the development of Q-waves on the electrocardiogram. Non-Q wave myocardial infarction was defined as creatine kinase determination of > 1.5 times normal with a positive MB with or without persistent ST-segment or T-wave changes on the post-procedural electrocardiogram. Groin site complications included the need for blood transfusion or surgical intervention. Quantitative coronary angiography (QCA) was performed by an independent core angiographic laboratory at Stanford University, Palo Alto, California. This laboratory was blinded to the clinical data and procedure outcomes. Statistical analysis was performed at the Clinical Research Institute of Duke University in Durham, North Carolina. Categorical factors are described using percentages and frequency of characteristics or events. Continuous measures are described using means with standard deviations. A p-value of 23 Patients presenting with AMI with a culprit lesion in an SVG constitute a high-risk group for revascularization. Balloon angioplasty in these lesions is often associated with complications, especially distal embolization. The rationale for excimer laser application in this setting stems from recent clinical reports documenting its efficient plaque debulking and thrombus dissolution in acute coronary syndromes.^15,24 The device success rate in the present series is 87%. Early observations on the yield of excimer laser in old SVGs reported a 94% success rate,²⁵ relatively higher than the 77% and 79% success rates for balloon angioplasty in the Heparin Registry Study²⁶ and in the Coronary Angioplasty versus Excisional Atherectomy Trial (CAVEAT) II study,²⁷ respectively. Comparing laser with other technologies, the Washington Hospital Center group has reported application of transluminal extraction catheter (TEC) and adjunct stenting versus ELCA and adjunct stenting in SVGs.²⁸ While the angiographic success rates were 100% in each group, the complication rates were higher in the TEC/stent group versus the ELCA/stent group: non-Q wave MI 15.6% versus 8.7%, acute vessel closure 2.9% versus 0% and no-reflow 2.2% versus 0%, respectively. They also reported 6-month follow-up data on a large group of patients (n = 131 with 196 lesions).29 The ELCA/stent group had a 6-month target lesion revascularization (TLR) of only 6.9%. However, the 6-month event-free survival rate was only 67% due to a high mortality (9%) and frequent need for revascularization of non-target lesions. The group at Lakeland Regional Medical Center presented their experience with the excimer laser in SVG lesions.³⁰ A total of 119 consecutive patients who underwent ELCA in old SVGs (mean age, 10.8 years) were included in a cohort. The success rate was 98.2%, with a non-Q wave MI rate (CPK-MB > 3x upper limit of normal) of 0.8% and a Q-wave MI rate of 1.7%. These rates appear to be lower than the recent SAFER trial, which documented an MI rate of 8.4% despite the use of distal protection devices.³¹ It should be noted that the target lesions treated in our series were considerably long and complex. The acceptable success rate reported herein was obtained without distal protection technology. Indeed, the role of protection devices in the setting of AMI has not yet been established. In fact, the unique interaction of excimer laser energy with thrombus and atherosclerotic material appears to account for a considerable revascularization gain. Absorption of this wavelength induces vaporization of atherosclerotic material and formation of acoustic shock waves, which propagate along the irradiated plaque and disrupt the fibrin fibers within the thrombus. The excimer laser energy is capable as well of suppression of platelet aggregation.³² The latter effect is termed the “stunned platelet phenomenon.” Furthermore, the in vitro by-products of laser thrombolysis have been shown to be small particles of less than 10 microns in size.³³ Conceivably, this effective debulking accounts for low rates of distal embolization and no-reflow phenomenon, as reported herein and in similar experiences pertaining to excimer laser utilization in AMI.^13,15,24 Study limitations. Our analysis is a retrospective study of prospectively collected data as entered into a cohort. As an observational study, this cohort was not designed to identify the most successful technology for revascularization of old SVGs in the setting of AMI. There is no evidence that similar or improved results could not have been obtained by a different technology. Conclusion. The management of patients sustaining AMI who need revascularization of an old SVG remains challenging. The data presented herein support the notion that excimer laser angioplasty is a technology that has a potential role in achieving adequate revascularization outcomes in this selected, high-risk patient population.