COMMENTARY: Bugs and Clots: The Value of Transesophageal Echocardiography in Defining Permanent Pacemaker Lead Infections

The number of patients receiving pacemaker and implantable cardioverter-defibrillator (ICD) implants is rapidly increasing. The number of permanent pacemaker implants in the United States increased from about 95,000 in 1990 to 250,000 in 2002, while the number of ICD implants increased from 10,000 in 1990 to 100,000 in 2002.¹ Improvements in resolution and greater utilization of transesophageal echocardiography (TEE) in clinical practice have led to increased detection of abnormalities on implanted leads. The reported incidence of such masses is highly variable, but fortunately appears to be relatively low. Of the other available imaging modalities, cardiac catheterization is invasive and unlikely to pick up small masses. Magnetic resonance imaging has relative contraindication in patients with implanted devices, and the movement and metal create artifact. Multidetector computed tomography (CT) scanning also picks up a lot of artifact from the metal as well as the movement of the lead. However, improvements in the next generation of CT scanners allowing even faster acquisition of data may result in improvements in detecting masses on implanted leads. Meanwhile, ultrasound remains the best modality in defining such masses. Earlier monoplane TEE,² and more recently, multiplane TEE3,⁴ with probe frequencies of 5 to 10 MHz as well as harmonic imaging, allows for excellent resolution. However, TEE visualization of leads is limited to mostly the intracardiac portion of the leads, and acoustic shadowing may mask the presence of a small mass. Thus far, none of the available imaging modalities provide excellent tissue characterization. Obtaining samples for gross or histologic examination for diagnosis is impractical. In this issue of the Journal,⁵ Lo and colleagues report a retrospective review of all TEE examinations performed at a single institution to evaluate the role of TEE in defining masses on permanent pacemaker leads and their subsequent management. As the authors point out, clinical suspicion, together with blood cultures, generally guide clinicians as to how to manage these patients with echocardiographic abnormalities. Incidental findings with low suspicion for endocarditis may be treated conservatively or with anticoagulation, while high suspicion for endocarditis may lead to explantation of the system in addition to systemic antibiotics. An echocardiographically detected mass on an implanted lead is almost always a thrombus or vegetation. Despite excellent resolution, it is difficult and often impossible to distinguish between the two. Obviously, management of the two etiologies differs completely. Since echocardiographic imaging may not entirely determine the etiology of a mass, clinical presentation plays a vital role in interpretation and management. If endocarditis is highly suspected, then the presence of a mass is more likely to be related to that. Additionally, if the tricuspid valve leaflets show a mass or masses, it is more likely to be endocarditis. On the other hand, if the patient is at low clinical suspicion for endocarditis, it is more likely to be a thrombus. If the mass extends into the superior vena cava and is relatively linear, that also favors thrombus. Pulmonary embolism by itself does not distinguish one from the other, but lung abscess or pneumonia resulting from such embolism does favor an infectious etiology. Infection is more likely to occur in patients with diabetes mellitus, advanced age, steroid use, intravenous indwelling catheters and other infectious foci. Management of masses on leads can be complicated due to several factors. Uncertainty about the nature of the mass is an important factor that could lead to empiric treatment decisions. Other important factors may include comorbid conditions, contraindications to anticoagulation and unsuitability for cardiac surgery. Patients who are pacemaker-dependent pose a very challenging subset in cases where removal of a lead or leads is recommended. An interval of several days is recommended between the removal of an infected system and replacement with a new system for fear of infecting the new system. Supporting patients with temporary transvenous pacemakers in the interim poses problems such as prolonged stay on an intensive care unit, loss of capture and risk of infection. Extraction of chronically implanted leads requires special equipment and expertise and can lead to complications. The two surgical procedures (explantation and re-implantation), along with the cost of the devices and leads, are expensive. Hospital stay in an intensive care unit and intravenous antibiotic therapy further add to the tremendous cost of such a strategy. The increasing number of implants and the increasing utilization of echocardiography will probably lead to a greater incidence of finding masses on implanted leads. Continued improvements in imaging technology may further improve detection as well as characterization of these masses. Once recognized, careful consideration of clinical circumstances generally leads to the correct diagnosis. Patient management needs to be individualized. Pacemaker explantation is generally recommended in patients with systemic infection, pacemaker pocket infection and/or pacemaker lead infection seen on TEE.^6–8 However, one should be mindful of the high complication rate and cost associated with such a management strategy.

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