Conclusion: Novel Approaches to Managing Bradycardia during Coronary Rheolytic Thrombectomy

The AngioJet device has been shown to be a safe and effective device for mechanical thrombectomy, yet its association with severe bradyarrhythmia has impeded its broad acceptance and widespread use. This “brady effect” has forced physicians to temper the established benefits of rheolytic thrombectomy (RT) with the inconvenience of temporary pacing in this patient population. For some clinicians, the potential risks of temporary pacing may have outweighed the known benefits of mechanical thrombectomy. Complicating the picture is the fact that the mechanisms of bradyarrhythmia in this setting remain unknown. In fact, their development seems paradoxical, in that the conditions appear to favor the genesis of tachyarrhythmias instead. The cellular hemolysis produced during RT is associated with adenosine, which has a variety of known cardiac effects, among them a delay in conduction time across the atrioventricular node. Such conduction delays may explain heart block, but they do not illuminate sinus bradycardia. In order to make the important benefits of mechanical thrombectomy available to a broader base of patients, interventional cardiologists on the leading edge of this technology have proposed and tested a variety of approaches to obviate the need for temporary transvenous pacing. These may be grouped roughly into two categories: electrical therapy and pharmacological therapy. In terms of electrical management of RT-mediated bradyarrhythmias, the use of temporary pacing via a coronary guidewire appears to hold great promise. In this supplement, contributors report a 96.2% effectiveness rate with no apparent adverse effects. For physicians comfortable with pacing in this context, guidewire pacing appears to be an important alternative. Pharmacological approaches have considerable appeal and we report on successful, albeit small, studies using glycopyrrolate and aminophylline, an adenosine antagonist. In the case of glycopyrrolate, the study (n = 10) found no episodes of symptomatic bradycardia, no adverse events and no need for temporary pacing. Glycopyrrolate offers the considerable appeal of being a drug that need only be administered during the actual procedure; it can be discontinued when the thrombectomy is completed. Aminophylline, an adenosine antagonist, has been shown effective in reducing high-degree heart block post-myocardial infarction. Thorough animal studies in the porcine model have demonstrated the effectiveness of adenosine antagonists in preventing heart block caused by RT, but human studies have been limited to date. Our contributors found that bradyarrhythmias requiring pacing occurred in less than 1% of cases when aminophylline was administered prior to RT, versus 20% of cases when aminophylline was withheld. Aminophylline is an imperfect but intriguing solution. This drug has other cardiovascular effects; among them, it acts as a vasodilator and it has certain pro-arrhythmic effects relating to atrial fibrillation. The variety of novel alternatives to temporary pacing during RT offers the benefits of mechanical thrombectomy to many more patients who need it, not just to those who may be able to tolerate concomitant temporary pacing. It is not hard to imagine how such novel approaches may one day make it possible for tertiary care facilities to offer RT procedures or for primary and secondary care facilities to offer RT procedures to a broader range of patients. What is most gratifying to us as medical scientists, however, is the new knowledge and new questions that these novel approaches have caused us to ponder. We do not fully understand how these bradyarrhythmias occur, but in learning to combat them, we have advanced our understanding of both the electrical management of cardiac rhythm disorders and the pharmacological effects on electrophysiological properties of the heart in this critically ill patient population.