Temporal association between drops in thoracic impedance and malignant ventricular arrhythmia: A longitudinal analysis of remote monitoring trends.

INTRODUCTION: Thoracic impedance (TI) drops measured by implantable cardioverter-defibrillators (ICDs) have been reported to correlate with ventricular tachycardia/fibrillation (VT/VF). The aim of our study was to assess the temporal association of decreasing TI trends with VT/VF episodes through a longitudinal analysis of daily remote monitoring data from ICDs and cardiac resynchronization therapy defibrillators (CRT-Ds). METHODS AND RESULTS: Retrospective data from 2384 patients were randomized 1:1 into a derivation or validation cohort. The TI decrease rate was defined as the percentage of rolling weeks with a continuously decreasing TI trend. The derivation cohort was used to determine a TI decrease rate threshold for a ≥99% specificity of arrhythmia prediction. The associated risk of VT/VF episodes was estimated in the validation cohort by dividing the available follow-up into 60-day assessment intervals. Analyses were performed separately for 1354 ICD and 1030 CRT-D patients. During a median follow-up of 2.0 years, 727 patients (30.4%) experienced 3298 confirmed VT/VF episodes. In the ICD group, a TI decrease rate of >60% was associated with a higher risk of VT/VF episode in a 60-day assessment interval (stratified hazard ratio, 1.42; 95% confidence interval (CI), 1.05-1.92; p = .023). The TI decrease preceded (40.8%) or followed (59.2%) the VT/VF episodes. In the CRT-D group, no association between TI decrease and VT/VF episodes was observed (p = .84). CONCLUSION: In our longitudinal analysis, TI decrease was associated with VT/VF episodes only in ICD patients. Preventive interventions may be difficult since episodes can occur before or after TI decrease.

Circadian periodicity affects the type of ventricular arrhythmias and efficacy of implantable defibrillator therapies.

INTRODUCTION: Factors influencing malignant arrhythmia onset are not fully understood. We explored the circadian periodicity of ventricular arrhythmias (VAs) in patients with implantable cardioverter and cardiac resynchronization defibrillators (ICD/CRT-D). METHODS: Time, morphology (monomorphic/polymorphic), and mode of termination (anti-tachycardia pacing [ATP] or shock) of VAs stored in a database of remote monitoring data were adjudicated. Episodes were grouped in six 4-h timeslots from 00:00 to 24:00. Circadian distributions and adjusted marginal odds ratios (ORs), with 95% confidence interval (CI), were analyzed using mixed-effect models and logit generalized estimating equations, respectively, to account for within-subject correlation of multiple episodes. RESULTS: Among 1303 VA episodes from 446 patients (63% ICD and 37% CRT-D), 120 (9%) self-extinguished, and 842 (65%) were terminated by ATP, 343 (26%) by shock. VAs clustered from 08:00 to 16:00 with 44% of episodes, as compared with 22% from 00:00 to 08:00 (p < .001) and 34% from 16:00 to 24:00 (p = .005). Episodes were more likely to be polymorphic at night with an adjusted marginal OR of 1.66 (CI, 1.15-2.40; p = .007) at 00:00-04:00 versus other timeslots. Episodes were less likely to be terminated by ATP in the 00:00-04:00 (success-to-failure ratio, 0.67; CI, 0.46-0.98; p = .039) and 08:00-12:00 (0.70; CI, 0.51-0.96; p = .02) timeslots, and most likely to be terminated by ATP between 12:00 and 16:00 (success-to-failure ratio 1.42; CI, 1.06-1.91; p = .02). CONCLUSION: VAs did not distribute uniformly over the 24 h, with a majority of episodes occurring from 08:00 to 16:00. Nocturnal episodes were more likely to be polymorphic. The efficacy of ATP depended on the time of delivery.

Atrioventricular Interval Extension Is Highly Efficient in Preventing Unnecessary Right Ventricular Pacing in Sinus Node Disease: A Randomized Cross-Over Study Versus Dual- to Atrial Single-Chamber Mode Switch.

OBJECTIVES: This study sought to compare the Intrinsic Rhythm Support (IRSplus) and Ventricular Pace Suppress (VpS) in terms of right ventricular pacing percentage (VP %), mean atrioventricular interval (MAVI), atrial fibrillation, and cardiac volumes. BACKGROUND: Modern pacemakers are provided with algorithms for reducing unnecessary ventricular pacing. These may be classified as: periodic search for intrinsic atrioventricular (AV) conduction prolonging the AV delay accordingly; or DDD-ADI mode switch. The IRSplus and VpS algorithms belong to the former and latter classes, respectively. METHODS: Patients with sick sinus dysfunction without evidence of II/III degree AV block were 1:1 randomized to 6-month periods of either IRSplus or VpS, and then crossed over. Subsequent follow-ups were at the 12th month after randomization for device data retrieving, and at the 18th month with the same device programming for echocardiographic assessment. RESULTS: A total of 230 patients (62% males, median age 75 years [interquartile range: 69 to 79 years]) were enrolled. At a linear mixed-model analysis with order of treatment and investigational sites as nested random effects, differences in VP% and MAVI reached statistical significance: VP% was 1% (0% to 11%) during IRSplus and 3% (0% to 26%) during VpS (p = 0.029); MAVI was 225 ms (198 to 253 ms) during IRSplus and 214 ms (188 to 240 ms) during VpS (p = 0.014). No differences were observed in atrial fibrillation burden and incidence, ejection fraction, and cardiac volumes. CONCLUSIONS: Both IRSplus and VpS algorithms ensured VP% ≤3% in most patients with sinus node dysfunction and preserved AV conduction. The IRSplus was slightly more efficient in reducing VP% at the expense of a small MAVI increase, with statistical but clinically insignificant differences. (Ventricular Pace Suppression Versus Intrinsic Rhythm Support Study; NCT01528657).