Intra-thoracic Impedance and the Onset of Atrial and Ventricular Tachyarrhythmias: A Meta-analysis

A combined impedance compensation strategy applied to external automatic defibrillators

Transthoracic impedance is one of the key factors affecting the success of defibrillation. Impedance compensation technique is used to adjust defibrillation parameters according to the transthoracic impedance of the defibrillator. In this paper, a combined impedance compensation strategy is proposed to address the shortcomings of existing compensation strategies. In order to evaluate the performance of the combined compensation strategy, this paper uses the prototype as the experimental machine, and uses two AED with representative impedance compensation strategies as the control machine, and the simulated defibrillation method is used for comparative testing. The results show that the combined impedance compensation has a more steadier distribution over the defibrillation energy and current: compared with the energy-based impedance compensation strategy, this strategy can significantly reduce the peak current (25 Ω: 27.8 vs. 54.7 A; 50 Ω: 20.7 vs. 32.3 A) and average current (25 Ω: 24.8 vs. 37.5 A) of defibrillation at low impedance, and compared with the current impedance compensation strategy, it can significantly reduce the defibrillation energy (150 Ω: 8.6 vs. 1.7 %, 175 Ω: 15.6 vs. 4.9 %, 200 Ω: 21.9 vs. 8.5 %) at high impedance. Impedance compensation is more precise and the current passing during defibrillation is steadier.

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.

Atrial signal amplitude predicts atrial high-rate episodes in implantable cardioverter defibrillator patients: Insights from a large database of remote monitoring transmissions

BACKGROUND

Parameters measured during implantable cardioverter defibrillator (ICD) implant also depend on bioelectrical properties of the myocardium. We aimed to explore their potential association with clinical outcomes in patients with single/dual-chamber ICD and cardiac resynchronization therapy defibrillator (CRT-D).

METHODS

In the framework of the Home Monitoring Expert Alliance, baseline electrical parameters for all implanted leads were compared by the occurrence of all-cause mortality, adjudicated ventricular arrhythmia (VA), and atrial high-rate episode lasting ≥24 hours (24 h AHRE).

RESULTS

In a cohort of 2976 patients (58.1% ICD) with a median follow-up of 25 months, event rates were 3.1/100 patient-years for all-cause mortality, 18.1/100 patient-years for VA, and 9.3/100 patient-years for 24 h AHRE. At univariate analysis, baseline shock impedance was consistently lower in groups with events than without, with a 40 Ω cutoff that better identified high-risk patients. However, at multivariable analysis, the adjusted-hazard ratios (HRs) lost statistical significance for any endpoint. Baseline atrial sensing amplitude during sinus rhythm was lower in patients with 24 h AHRE than in those without (2.45 [IQR: 1.65-3.85] vs 3.51 [IQR: 2.37-4.67] mV, P < .01). The adjusted HR for 24 h AHRE in patients with atrial sensing >1.5 mV vs those with values ≤1.5 mV was 0.52 (95% CI: 0.33-0.83), P = .006.

CONCLUSIONS

Although lower baseline shock impedance was observed in patients with events, the association lost statistical significance at multivariable analysis. Conversely, low sinus rhythm atrial sensing (≤1.5 mV) measured with standard transvenous leads could identify subjects at high risk of atrial arrhythmia.

Relationship between Atrial Tachyarrhythmias and Intrathoracic Impedance in Patients with a Pacemaker and Preserved Ejection Fraction

Atrial fibrillation (AF) is responsible for significant morbidity and mortality in patients with heart failure (HF). Modern pacemakers provide an index of intrathoracic fluid status (OptiVol fluid index-OVFI) by measuring daily intrathoracic impedance. This study aimed to determine whether OVFI is associated with increased atrial tachycardia/fibrillation (AT/AF) events in patients with a preserved ejection fraction (EF). We retrospectively reviewed data from patients with Medtronic Advisa pacemakers between 2012 and 2014 in our hospital. The association and temporal relationship between OVFI and AT/AF events were determined. A total of 150 patients with 211 follow-up visits (mean 1.4 visits per patient) were evaluated. The device-detected AT/AF prevalence was 47%. Device-measured OVFI ≥ 20 Ω-days was significantly associated with the onset of AT/AF ≥ 4 h. OVFI threshold crossing preceded AT/AF events in 55.1% of cases, followed by AT/AF events in only 18.7%. Fluid overload represented by OVFI may trigger AT/AF episodes in patients with a preserved EF more often than that previously reported in patients with a reduced EF. Our findings support the view that worsening pulmonary congestion is associated with increased AT/AF frequency and suggests that fluid overload could trigger and perpetuate AT/AF events in patients with a preserved EF.

Association between changes in the intrathoracic impedance and ventricular arrhythmias in patients with heart failure

BACKGROUND

Ventricular arrhythmias (VAs) are independently related to mortality risk in patients with heart failure (HF). The wide availability of implantable cardioverter defibrillators and cardiac resynchronization therapy devices now offers an opportunity to clinically correlate the two disease processes. We hypothesized that there is an association between changes in the intrathoracic impedance and episodes of VA.

METHODS

Nonconcurrent prospective study of adults (age >20 years) with known HF with reduced ejection fraction (<35%). The OptiVol threshold was categorized as follows: 0-30 Ω-days, 31-60 Ω-days, 61-90 Ω-days, 91-120 Ω-days, and >120 Ω-days. Patients with OptiVol values at 0-30 Ω-days were used as the reference group. Receiver operating characteristic analysis was used to estimate the sensitivity and specificity at each threshold.

RESULTS

Of the 87 eligible patients, 65.5% were males. The mean age of the sample was 73.3 years (±12.7). Compared to patients in the 0-30 Ω-days category, those in the 31-60, 61-90, 91-120, and >120 Ω-days groups had, on average, 1.48, 1.64, 2.24, and 1.6 more VAs, respectively (P = 0.002, 0.009, 0.010 and 0.009, respectively). The sensitivity and specificity of each threshold were as follows: 82.6% and 61.7% at 31-60 Ω-days, 43.5% and 78.3% at 61-90 Ω-days, 30.4% and 85.0% at 91-120 Ω-days, and 21.7% and 88.3% at >121 Ω-days.

CONCLUSION

Our study found a significant positive relationship between changes in intrathoracic impedance and episodes of VAs in patients with HF.