Autonomic Innervation and MIBG Imaging

Inclusion Criteria: * Age 18-80 years. * Symptoms including one or more of the following: palpitations, shortness of breath, dizziness, presyncope or syncope, chest pain, tiredness or lack of energy. * Failure of beta-blockers or at least one antiarrhythmic agent other than Amiodarone to prevent AF. In those patients who are not eligible to antiarrhythmic agents other than Amiodarone, patients may choose to undergo catheter ablation rather than starting Amiodarone. * Paroxysmal (self-terminating AF within 7 days) or persistent AF (requiring an intervention to terminate or lasting more than 7 days). Exclusion Criteria: * Intracardiac thrombus as determined by transesophageal echocardiography * Class III or IV congestive heart failure * Persistent AF duration of more than 3 years * Myocardial infarction within the last 6 months * Left atrial size of greater than 55 mm determined by 2D echocardiogram * Inability to undergo a transesophageal echocardiogram or cardiac CT * Inability to undergo D-SPECT™ imaging * Inability to take Warfarin or the new oral anticoagulants * Previously received 123I-mIBG or 131I-mIBG * History or suspicion of significant allergic reaction or anaphylaxis to iodine or iodinated imaging agents * Use of medications for non-cardiac medical conditions that are known to interfere with 123I-mIBG uptake and these medications cannot be safely withheld for at least 24 hours before study procedures * Diagnosis of or signs or symptoms of a neurologic disease such as Parkinson's disease, multiple systems atrophy or Parkinsonian syndromes, or other diseases known to affect the sympathetic nervous system * Pregnancy as determined by a pre-procedure pregnancy tests