Antithrombotic Therapy in Peripheral Arterial Occlusive Disease: Percutaneous Transluminal Angioplasty
The mechanism of transluminal dilation of stenotic arteries involves overstretching of the arterial wall leading to longitudinal splits and fractures of the plaque and intima, with splits often extending into the media. Platelet-rich thrombi rapidly accumulate on areas of intimal disruption, and studies with indium-Ill-labeled platelets demonstrate marked uptake of labeled platelets at angioplasty sites. In experimental animals, platelet accumulation occurs at sites of angioplasty after 30 min, persists for hours, and is most excessive when there is increased histologic evidence of dissection. Theoretically, effective antithrombotic therapy could be expected to decrease thromboembolic complications associated with angioplasty and might reduce the incidence of recurrent stenoses. Scintigraphic studies with indium-ill-labeled platelets demonstrate that aspirin treatment prior to angioplasty in humans reduces platelet deposition at angioplasty sites. ventolin inhaler
In patients undergoing percutaneous transluminal coronary angioplasty (PTCA), data from a level III trial suggested that antiplatelet therapy with aspirin alone or aspirin combined with dipyridamole significantly reduced the incidence of angiographically detected new thrombi at the PTCA site as well as the incidence of clinically significant thrombi (defined as causing 100% occlusion or requiring emergency surgery or streptokinase therapy). The results were most striking when antiplatelet therapy was started before angioplasty. In a level I trial, antiplatelet therapy with aspirin and dipyridamole starting 24 h prior to PTCA significantly reduced the incidence of periprocedural Q-wave myocardial infarctions from 6.9% in control subjects to 1.6% (p < 0.01). The patients in this trial continued antiplatelet therapy or placebo for 6 months and underwent repeated angiography to detect recurrent stenoses. The incidence of recurrent stenoses was identical in both groups, 38%. Data from other level I trials have documented that as single agents, aspirin, warfarin, and ticlopidine have no effect in preventing recurrent stenoses after PTCA. More than 55 randomized trials have been conducted and none have clearly shown any agents to be useful in the prevention of recurrent stenoses, despite numerous experimental studies showing drug efficacy in animal models. Thus, short-term, periprocedural use of aspirin and dipyridamole is recommended because it reduces the incidence of MI during PTCA. Whether dipyridamole is a necessary adjunct to aspirin in this setting is unknown, and additional data are needed. Dextran has also been evaluated in patients undergoing PTCA (level I trial) and has been found to be without benefit. Almost all patients are heparinized during PTCA, and this is continued for variable periods after PTCA. Although there are no controlled trials to assess the benefit of this practice, data available from level II studies demonstrate a reduction in thromboembolic events, including MI, with systemic he-parinization during routine transfemoral coronary angiography and other high-risk angiographic procedures.