Do Electrophysiological Interventions Confer a Prothrombotic State?

(RF) catheter ablation, or modulation, and implantation of devices, such as permanent pacemakers or atrioverters, are investigations or interventions that are being used much more liberally than ever before in the management of various cardiac arrhythmias, such as atrial fibrillation (AF). Whereas antiarrhythmics only suppress the arrhythmia and not cure them, these procedures offer a hope of a ‘cure’ of the arrhythmia. If anything, the use of nonpharmacological investigations and interventions for cardiac arrhythmias is likely to increase, rather than decrease, in the future. These interventions are invasive and require manipulation of mapping electrodes, the positioning of ablation catheters, delivery of ablation energy, and the positioning of pacemaker electrodes and, therefore, complications do occur. For example, Hindricks et al. reported that procedure related complications of RF catheter ablation occur in approximately 5.1% of patients. Importantly, thromboembolic complications commonly occur in RF catheter ablation (in 0.6%–1.3% of cases) with the risk being higher when the ablation procedure is performed in the left heart (1.8%–2%) and for ventricular tachycardia (2.8%). However, it is still not clear whether the increased risk of thromboembolism is due to the RF catheter ablation (or other electrophysiological procedure) itself, the procedure duration or if activation of coagulation pathways contributes to the risk of subsequent thromboembolism. If the use of antiplatelet and antithrombotic agents results in significant suppression of the coagulation system, does this translate into a decrease in thromboembolic risk, and do the benefits of the prolonged use of anticoagulation therapy outweigh the thromboembolic risk of the procedure. These outstanding issues need to be addressed. It has been well recognized for over 150 years that abnormalities in the blood vessel wall, blood flow, and blood constituents may result in an increased propensity towards thrombus formation (Virchow’s triad). The first two of Virchow’s basic postulates for thrombogenesis, namely, abnormalities of blood flow and vessels, may be altered by the presence of “foreign” material, such as the mapping/pacing/atrioverter electrodes. Furthermore, the heating of tissue and/or blood during RF catheter ablation current delivery, or defibrillation energy with an atrioverter, may leave a damaged endocardial/endothelial surface that activates the coagulation system. Indeed, tissue overheating during RF catheter ablation current delivery may even result in gas formation with audible “popping. ” RF catheter ablation of chronic atrial flutter has been associated with significant left atrial stunning and the development of spontaneous echo contrast, perhaps indicating more stasis within the left atrium. Perhaps the implantation of devices, such as permanent pacemakers, may actually predispose to thromboembolic events, as observed by Seeger and Scherer, who found a 15% incidence of asymptomatic pulmonary embolism among patients undergoing pacemaker implantation who were not receiving heparin therapy, compared to no embolism in patients who received low dose heparin prophylactically. In particular, altered atrioventricular synchrony causes flow disturbance, which may also predispose to thromboembolism by the activation of the coagulation system. For example, a higher incidence of thromboembolism is observed in patients undergoing ventricular pacing when compared to atrioventricular sequential pacing, or atrial pacing, for sick sinus syndrome. Indeed, Sparks et al. demonstrated that chronic loss of atrioventricular synchrony induced by VVI pacing was associated with a significant decrease in left atrial appendage (LAA) velocity, LAA fractional area change, and the GUEST EDITORIAL