Value of Heart Rate Variability to Predict Ventricular Arrhythmias in Recipients of Prophylactic Defibrillators with Idiopathic Dilated Cardiomyopathy

GRIMM, W., et al. : Value of Heart Rate Variability to Predict Ventricular Arrhythmias in Recipients of Prophylactic Defibrillators with Idiopathic Dilated Cardiomyopathy. This study investigated the relation between heart rate variability (HRV) measured as standard deviation of normal to normal RR intervals (SDNN) on baseline 24-hour ambulatory electrocardiogram (ECG) and subsequent appropriate implantable cardioverter defibrillator (ICD) interventions in 70 patients with idiopathic dilated cardiomyopathy (IDC) in whom ICDs were implanted prophylactically in the presence of a low left ventricular ejection fraction (LVEF). During   43 ± 26   months of follow-up, 26 of 70 (37%) study patients with IDC received one or more appropriate ICD interventions for sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) documented by electrograms stored in the ICD. Mean SDNN at ICD implant was   94 ± 33 ms   . No difference was found between patients with   (90 ± 25 ms)   versus without   (96 ± 37 ms)   appropriate ICD interventions for VT or VF during follow-up. Multivariate Cox regression analysis of baseline clinical characteristics including age, gender, LVEF, NYHA functional class, nonsustained VT on Holter, history of syncope, left bundle branch block, baseline medication and HRV revealed LVEF as the only significant predictor of arrhythmia. These findings do not support the use of HRV measured as SDNN on 24-hour ambulatory ECG to select patients with IDC for prophylactic ICD therapy. (PACE 2003; 26[Pt. II]:411–415)     

Intrinsic Conduction Maximizes Cardiopulmonary Performance in Patients with Dual Chamber Pacemakers

Dual chamber pacemaker programmability allows the possibility of atriallytracked ventricular pacing in patients who would otherwise have intrinsic atrioventricular (AV) conduction. Thirteen patients with permanent AV sequential pacemakers (ages 50–79) were evaluated with paired exercise tests to determine the Cardiopulmonary effects of pacemaker induced right ventricular activation compared with normal AV and intraventricular conduction. Peak oxygen uptake (VO₂), oxygen pulse (O₂P), respiratory rate (RR), and respiratory exchange ratio (RER) were determined using breath by-breath analysis of expired gases. Patients exercised to fatigue and exercise tests were performed in random sequence. For patients with intrinsic AV conduction (group I, n = 8) the AV delay was programmed to preserve intrinsic conduction during one study; the alternate test used AV delay programming to produce ventricular pacing. Five patients with chronic AV block (group II) acted as a control for the effects of a rate adaptive AV delay compared to a fixed AV delay. Paired t-testing showed a significantly lower peak VO₂ (P < 0.015) and O₂P (P < 0.01) in patients with atrially-tracked ventricular pacing compared to intrinsic conduction. In contrast, group II showed a significant improvement in peak VO₂ with rate adaptive AV delay compared to fixed AV delay programming (P < 0.05). In conclusion, intrinsic conduction should be preserved in patients with dual chamber pacemakers whenever possible.