• Methods and Procedures Subjects for this study will be enrolled from the ICD clinic at Pocono Medical Center. The ICD clinic at Pocono Medical Center is located in the cardiology office 2.4 miles from the main hospital building where patients undergo interrogation of their ICD under the direction of the principal investigator.~During a routine ICD interrogation, the patient is attached to a 3 lead surface ECG. The ICD is then checked to assess sensing and pacing parameters and impedance for leads in all cardiac chambers. Battery voltage is assessed, and any stored events which include data from any appropriate or inappropriate therapies, are examined. Appropriate therapies consist of either an ICD shock or anti-tachycardia pacing for ventricular tachyarrhythmias. Inappropriate therapies consist of either an ICD shock or anti-tachycardia pacing for an event other than ventricular tachyarrhythmias, and may be triggered by supraventricular tachyarrhythmias or electronic noise.~Once the subjects are enrolled in the study, a 12-lead ECG will be performed (instead of a 3 lead ECG) before ICD interrogation (baseline ECG). A 12 lead ECG will then be repeated while performing right ventricular pacing through the programmer at 100 beats per minute at the time of pacing threshold testing (paced ECG). QRS durations from the baseline and paced ECG will be measured electronically in leads V3-V6. The measured QRS complexes should not be preceded by an atrial or ventricular premature complex.~All subjects will then continue to be followed every three months in the ICD clinic for routine ICD interrogation as clinically indicated for the duration of the study. Data for any appropriate and inappropriate ICD therapies will be retrieved and documented in the case report form. Subjects will be considered to have suffered SCD if they meet one of the following criteria.~An appropriate ICD therapy (shock or anti-tachycardia pacing)~Death occurring within one hour of onset of cardiac symptoms~Death during sleep~Unwitnessed death in a formerly stable patient~Death during attempted resuscitation Data regarding mortality will be obtained from patient's family, family physician and hospital records.~Project Plan Based on the current patient volume in the ICD clinic, and the rate of new ICD implants, it is estimated that enrolling 250 patients will take 3 years. The study will conclude when the last enrolled patient has been followed for 2 years. The follow-up period will, therefore, be 2-5 years for patients enrolled in the study. The total study duration is therefore expected to be 5 years.~Data Analysis and Data Monitoring At enrollment and at each subsequent visit, the following data will be collected.~Demographic data: age, gender and racial and ethnic origin, height, weight and vital signs including heart rate and blood pressure~Co-morbid conditions: coronary artery disease, congestive heart failure, diabetes, hypertension, smoking, dyslipidemia, family history of sudden cardiac death in a first degree relative, renal failure, and others~Medical regimen: all medications being taken at the time of visit~Testing of Cardiac substrate: reports of most recent 24 hour ambulatory electrocardiography, echocardiogram, stress test, multigated acquisition scan,, cardiac catheterization and revascularization, coronary artery bypass surgery, and electrophysiological evaluation~Details of ICD implantation: indication for ICD implantation (primary versus secondary prevention), type of ICD implanted (single chamber, dual chamber or biventricular) as well as the manufacturer, and the position of the right ventricular lead (apical versus septal)~Prolonged paced QRS duration will be defined as ≥150 ms, narrow paced QRS duration will be defined as <150 ms. All baseline characteristics of patient population will be expressed as percentages. Relative risk of SCD with prolonged paced QRS duration will be determined. Kaplan-Meier analysis will be done using the end-point of appropriate ICD therapy used as a surrogate marker of SCD, and clinical SCD to generate survival curves for each subgroup .
The purpose of the study is to determine whether prolonged paced QRS duration is a marker of sudden cardiac death in subjects with implantable cardioverter-defibrillators (ICD).