EP Highlights of 2003

What advancements were seen in 2003? What can we expect this year? In this article, Drs. Link and Phang discuss what the biggest EP topics were, including the new treatments for atrial fibrillation and congestive heart failure, ICD therapy options, and the results from last year s clinical trials. Cardiac electrophysiology in 2003 has continued to advance and expand in many areas. Increasing experience and clinical trial data have further refined the rapidly growing arena of ablation for atrial fibrillation (AF). Several important clinical trials were completed and presented at this year s major scientific sessions, including the use of a new anticoagulant, increasing data supporting the benefit of cardiac resynchronization therapy (CRT), and an expanded study of implantable cardioverter defibrillator (ICD) therapy in different patient populations. Atrial Fibrillation Initial techniques described by Dr. Haissaguerre for radiofrequency (RF) ablation of atrial fibrillation involved the mapping and segmental isolation of pulmonary veins, guided by pulmonary vein potentials.¹ This electrophysiologic approach carries a significant recurrence rate, often leading to repeat ablation procedures. Pappone and colleagues described a new, anatomic approach with circumferential ablation around all of the pulmonary veins, not guided by pulmonary vein potentials,² with a success rate of up to 85% in paroxysmal AF patients and up to 68% in permanent AF patients. Morady and colleagues compared these two electrophysiologic and anatomic approaches in a randomized fashion.³ The anatomic method was shown by these investigators to have a superior cure rate, and may prove to be the superior method as we enter 2004. Younger patients with paroxysmal AF and no structural heart disease have a significantly higher cure rate than older patients with structural heart disease and longstanding chronic AF. While young paroxysmal AF patients may have cure rates approaching 70-80%, the older chronic atrial fibrillation patients may only expect a 30% cure rate. Complication rates have been relatively low, and notably, pulmonary vein stenosis has been markedly reduced by a variety of methods. The circumferential decapolar catheter, used in conjunction with electro-anatomical mapping, helps to guide the electrophysiologist s ablation catheter on the atrial side of the pulmonary vein ostia. Reconstructed, three-dimensional images of the left atrium and pulmonary vein anatomy by CT or MRI has become the standard in providing a map prior to performing the ablation, as well as providing a method of monitoring for pulmonary vein stenosis. Intracardiac echocardiography is used in some centers for visualization of the ablation catheter tip and is useful for real-time adjustment of ablation energy according to appearance of the type of microbubbles visualized.⁴ The SPORTIF V (Stroke Prevention using an Oral Direct Thrombin Inhibitor in Patients with Atrial Fibrillation) trial, presented at the AHA Scientific Sessions in November 2003, showed that the new oral direct thrombin inhibitor, ximelagatran, is well-tolerated and compares favorably with warfarin in this randomized, double-blind trial. The primary endpoint of any stroke or systemic embolic event was 1.6% per year for ximelagatran and 1.2% per year for warfarin. Important to note was the fact that INRs were maintained in the therapeutic range for about 80% of the study period, under the setting of close follow-up in a large clinical trial. This likely exceeds real world conditions of accurate warfarin dosing. Physicians, patients, and coumadin clinics everywhere will be eagerly awaiting the FDA approval and release of this new medication. Congestive Heart Failure While prior clinical trials with cardiac resynchronization therapy showed significant improvements in symptoms, functional status, and quality of life, the COMPANION (Comparison of Medical Therapy, Pacing and Defibrillation in Chronic Heart Failure) trial (presented at both the ACC and AHA Scientific Sessions in 2003) showed that CRT + ICD therapy significantly reduced all-cause mortality (HR 0.64; p = 0.003, secondary endpoint), making this the first CRT trial to show a survival benefit. The primary endpoint of the composite of all-cause mortality and hospitalizations was significantly improved with both CRT and CRT + ICD therapies, compared to optimal medical treatment. Echocardiographic evaluation by pulsed-wave and tissue Doppler for interventricular and intraventricular dyssynchrony is being increasingly investigated and appears to be a potentially helpful predictor of responders to CRT. Ongoing studies will also compare conventional biventricular pacing to left ventricular (LV)-only pacing and LV-RV (right ventricular) offset pacing, and will help to refine our ability to select patients who will benefit from CRT. ICD Therapy The AMIOVIRT (Amiodarone Vs. Implantable Defibrillator in Patients with Nonischemic Cardiomyopathy and Asymptomatic Non-sustained Ventricular Tachycardia) trial studied 103 patients with nonischemic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of 5 The DEFINITE (Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation) trial, presented at this November s AHA Scientific Sessions, demonstrated that in 458 patients with nonischemic dilated cardiomyopathy, LVEF p = 0.06). The potential mortality benefit of ICD therapy in nonischemic dilated cardiomyopathy patients will be further clarified by the upcoming SCD-HeFT (Sudden Cardiac Death in Heart Failure) trial. In other news… The Public Access Defibrillation (PAD) study, also presented at the AHA Scientific Sessions in November 2003, showed that trained laypersons using automated external defibrillators (AEDs) could double the survival rates in cardiac arrest victims compared to conventional CPR alone. CMS (Medicare) narrowed the interpretation of the MADIT II results using a QRS width qualifier (greater than 120 ms), based on substudy data and not the original entry criteria of the randomized control trial. The FDA banned ephedra due to its significant and unreasonable risk of illness and injury, marking the first ever FDA ban on an herbal medication. Conclusion Like other areas of medicine in which technology plays such an important role, the availability of new devices and technologies sometimes outpaces our understanding of underlying mechanisms. Despite the ability of these new technologies to increase the success of our therapies, patient selection and risk stratification remains a challenging goal for the future. The cost of these therapies to patients and the health care system in general remains an ongoing future challenge.