Introduction Recent clinical studies have demonstrated the efficacy and safety of the Metrix (InControl/ Guidant, Inc., Redmond and St Paul, MN, USA) implantable atrial defibrillator (IAD) in patients with recurrent atrial fibrillation (AF). 1–4 The ini- tial concern about the potential ventricular proar- rhythmic risk of such a device without backup ventricular defibrillation has limited clinical tri- als to a low risk patient population without coex- isting cardiovascular diseases. 2–4 However, AF occurs more frequently and carries a worse prog- nosis in patients with cardiovascular diseases. 5 Therefore, the long-term efficacy and safety of the IAD in patients with coexisting cardiovascular disease become critical considerations for a wider use of this new therapy in patients with AF. The aim of this study was to evaluate the effect of co- existing cardiovascular diseases on the long-term efficacy and safety of the Metrix IAD. Patients and Methods Patients The study population included 115 patients with drug refractory symptomatic, recurrent AF who received an IAD. They had previous episodes of AF that had spontaneously terminated or had been electrically cardioverted to sinus rhythm with intervals of recurrence of AF episodes . 2 weeks. Previous ineffective treatment with at least a Class I or III antiarrhythmic drug was required. Effect of Coexisting Cardiovascular Disease on the Long-Term Efficacy and Safety of the Implantable Atrial Defibrillator HUNG-FAT TSE,* CHU-PAK LAU,* LUZ-MARIA RODRIGUEZ,† CARL TIMMERMANS,† EMILE G. DAOUD, GREGORY M. AYERS,§ and HEIN J.J. WELLENS† ON BEHALF OF THE METRIX INVESTIGATORS From the *Queen Mary Hospital, the University of Hong Kong, Hong Kong, China, †Academic Hospital Maastricht, Maastricht, the Netherlands, ‡Mid-Ohio Cardiology Research, Columbus, Ohio, and §InControl/Guidant, Inc., Redmond, Washington TSE, H.-F., ET AL.: Effect of Coexisting Cardiovascular Disease on the Long-Term Efficacy and Safety of the Implantable Atrial Defibrillator. The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to eval- uate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervi- sion to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5 6 20.3% (lower 95% confidence interval [CI] 89.8%). As of the last follow-up, 58 (55%) patients had transition to receive nonphysician ob- served therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which they had received device therapy away from the hospital/ clinic (mean shock efficacy 90.5 6 39.7%). The presence of hy- pertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P . 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P , 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The ob- served proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation. (PACE 2002; 25:809–815) atrial fibrillation, implantable atrial defibrillator PACE, Vol. 25, No. 5 May 2002 809 Address for reprints: Chu-Pak Lau, M.D., Chief, Division of Cardiology, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China. Fax: (852)28551143; e-mail: cplau6hkucc.hku.hk Received February 13, 2001; revised May 29, 2001; June 7, 2001. Reprinted with permission from JOURNAL OF PACING AND CLINICAL ELECTROPHYSIOLOGY , Volume 25, No. 5, May 2002 Copyright © 2002 by Futura Publishing Company, Inc., Armonk, NY 10504-0418.