Pronto‚Ñ¢ Catheter Thrombectomy in Acute ST-Segment Myocardial Infarction: A Case Series

The aim in the treatment of patients with myocardial infarction is the early restoration of TIMI 3 blood flow in the infarct related artery.¹ Primary angioplasty during an acute myocardial infarction achieves this objective but is associated with increased procedural risk because of the probability of dealing with a high thrombus burden.² Although TIMI 3 flow is achieved in > 90% of patients with primary angioplasty/stenting in acute myocardial infarction, up to 15–20% of patients continue to have impaired myocardial perfusion. This is evident angiographically as the “no reflow” phenomenon, and its occurrence independently portends a poor prognosis.³ The etiology of the “no-reflow” phenomenon is thought to be multifactorial. Microvascular spasm, myocardial edema, endothelial dysfunction, and embolization of thrombus and plaque have all been incriminated in its etiology.⁴ The right coronary artery (RCA) has been reported to have a greater susceptibility to larger thrombi and a higher incidence of “no-reflow” when compared to the left coronary arteries.5 In this case series, the successful use of the new Pronto™ thrombectomy catheter (Vascular Solutions, Inc., Minneapolis, Minnesota) in the treatment of RCA ST-elevation infarction is described. Case Reports Case #1. A 58-year-old female with no prior cardiac history presented with 4 hours of crushing retrosternal chest pain. ST-elevation of 3 mm in the inferior leads with reciprocal ST-depression in the anterior leads was noted on her ECG at presentation. She was treated in the emergency room with 325 mg of aspirin; 300 mg of clopidogrel; 1 mg/kg subcuateous enoxaparin, and 180 µg/kg bolus and 2 µg/kg/minute intravenous infusion of eptifibatide. Emergent angiography documented single-vessel coronary artery disease, with the culprit vessel being a dominant RCA that was occluded with TIMI 0 flow and no collaterals. Case #2. A 68-year-old male presented within 2 hours of onset of chest pain to the emergency room. ST-elevation in the inferior leads was noted in the ECG on presentation. Urgent angiography documented the culprit vessel to be the dominant RCA. No collaterals were noted. The left anterior descending was noted to have an 80% mid-segment stenosis. Discussion In the setting of acute myocardial infarction, one of the major factors limiting successful myocardial salvage is distal embolization and the “no-reflow” phenomenon. A variety of interventional approaches and useful clinical investigation has been completed in this subgroup of patients but definitive and conclusive data remains elusive. The relative roles of aggressive antiplatelet pharmacotherapy; mechanical thrombectomy and distal embolic protection in the setting of acute myocardial infarction are not clearly defined. One thing that has emerged consistently has been the need for an endpoint beyond TIMI 3 flow as a measure of myocardial salvage. Myocardial blush grade; corrected TIMI frame counts and ST-segment resolution have all been shown to add incremental prognostic value above and beyond TIMI 3 flow restoration in the setting of acute myocardial infarctions.^6,7 After excluding visible macrothrombus and dissection, pharmacological treatment of the “no-reflow” phenomenon includes subselective administration of nitroglycerin, thrombolytic agents, intracoronary vasodilators (papaverine, adenosine, diltiazem, verapamil), nitric oxide donors like nitroprusside, glycoprotein IIb/IIIa inhibitors or even epinephrine.^8–16 Current and developing approaches to thrombectomy include direct atherectomy devices like TEC and excimer laser; coronary ultrasound thrombolysis; rheolytic thrombectomy and intracoronary aspiration thrombectomy with the Rescue (Boston Scientific Corp., Natick, Massachusetts) catheter and, most recently, the Pronto catheter.^17–24 In addition home made devices like guiding catheters/diagnostic catheters and the Export catheter (Percusurge/Medtronic, Santa Rosa, California) have all been innovatively used by operators in attempts to treat angiographically visible thrombus in proximal vessels. Excimer laser coronary angioplasty, coronary ultrasound thrombolysis and the AngioJet device (Possis Medical, Minneapolis, Minnesota) are handicapped by their lack of universal availability and time consuming set up. These disadvantages make them less useful in the setting of an acute MI where time is of essence. Guiding catheters and diagnostic catheters when used as thrombectomy devices are limited by their potential for causing proximal vessel dissection or plaque disruption. In addition their large size can make them difficult to deliver in tortuous and calcified vessels. The Pronto catheter attempts to overcome some of the shortcomings of the available thrombectomy devices. Its simple, one-operator deployment provides easy deliverability; large sloped, atraumatic extraction lumen; predictable force of extraction and a self-centering wire lumen. The cross sectional area of the extraction lumen is 0.94 mm². The extraction force when studied in vitro was -95 k Pa and remained constant for 15 seconds, after which the force decayed as the vacuum in the syringe was replaced by aspirated fluid.²⁵ In the two cases described, ST-segment resolution was used as a surrogate marker for myocardial salvage. ST-segments returned to near normal after the thrombectomy with the Pronto catheter. The device can also be used in the setting of NSTEMI with angiographically visible thrombus and also in the treatment of acute coronary syndromes involving saphenous vein grafts. Angiographic flow through the infarct related artery was TIMI 3 and myocardial blush grade (MBG) was grade III at the completion of the procedure. This case highlights the successful use of a new, simple, user friendly thrombectomy device in the setting of an acute myocardial infarction. Respect for the microvasculature and striving for more than just TIMI 3 flow has emerged as the new paradigm in the treatment of myocardial infarction. Thrombectomy and distal protection devices are probably necessary in concert to provide complete protection from both macro and micro-embolization. The use of these devices together will need to be tested rigorously in randomized control trials before their use becomes uniform and the standard of care. Until such time, case reports like this one provide speculative and intellectually provocative scientific information that adds to the body of data supporting use of these devices in acute myocardial infarctions.

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