Increased cycle length variability during ventricular fibrillation: a novel predictor of arrhythmia recurrence

Predicting Electrical Storm Using Episodes' Parameters from ICD Recorded Data

Electrical storm (ES) is a life-threatening heart condition for patients with implantable cardioverter defibrillators (ICDs). ICD patients experienced episodes are at higher risk for ES. However, predicting ES using previous episodes' parameters recorded by ICDs have never been developed. This study aims to predict ES using machine learning models based on ICD remote monitoring-summaries during episodes in the anonymized large number of patients. Episode ICD-summaries from 16,022 patients were used to construct and evaluate two models, logistic regression and random forest, for predicting the short-term risk of ES. Episode parameters in this study included the total number of sustained episodes, shocks delivered and the cycle length parameters. The models evaluated on the data sections not used for model development. Random forest performed significantly better than logistic regression (P <; 0.01), achieving a test accuracy of 0.99 and an Area Under an ROC Curve (AUC) of 0.93 (vs. an accuracy of 0.98 and an AUC of 0.90). The total number of previous sustained episodes was the most relevant variables in the both models.

Tachyarrhythmia Cycle Length in Appropriate versus Inappropriate Defibrillator Shocks in Brugada Syndrome, Early Repolarization Syndrome, or Idiopathic Ventricular Fibrillation

Background and Objectives

Implantable cardioverter–defibrillators (ICDs) are indicated in patients with Brugada syndrome (BS), early repolarization syndrome (ERS), or idiopathic ventricular fibrillation (IVF) who are at high risk for sudden cardiac death. The optimal ICD programming for reducing inappropriate shocks in these patients remains to be determined. We investigated the difference in the mean cycle length of tachyarrhythmias that activated either appropriate or inappropriate ICD shocks in these three patient groups to determine the optimal ventricular fibrillation (VF) zone for minimizing inappropriate ICD shocks.

Subjects and Methods

We selected 41 patients (35 men) (mean age±standard deviation=42.6±13.0 year) who received ICD shocks between April 1996 and April 2014 to treat BS (n=24), ERS (n=9), or IVF (n=8). Clinical and ICD interrogation data were retrospectively collected and analyzed for all events with ICD shocks.

Results

Of the 244 episodes, 180 (73.8%) shocks were appropriate and 64 (26.2%) were inappropriate. The mean cycle lengths of the tachyarrhythmias that activated appropriate and inappropriate shocks were 178.9±28.7 ms and 284.8±24.4 ms, respectively (p<0.001). The cutoff value with the highest sensitivity and specificity for discriminating between appropriate and inappropriate shocks was 235 ms (sensitivity, 98.4%; specificity, 95.6%). When we programmed a single VF zone of ≤270 ms, inappropriate ICD shocks were reduced by 70.5% and appropriate shocks were missed in 1.7% of these patients.

Conclusion

Programming of a single VF zone of ≤270 ms in patients with BS, ERS, or IVF could reduce inappropriate ICD shocks, with a low risk of missing appropriate shocks.

Differences in the characteristics of induced and spontaneous episodes of ventricular fibrillation

AIMS

The degree of organization of ventricular fibrillation (VF) can be examined in terms of the regularity of the electrical activity within the ventricle. Using electrograms (EGMs) stored within implanted cardioverter defibrillators (ICDs), we examined the hypothesis that the degree of organization, or regularity, was different if the VF was induced by electrical stimulation as opposed to occurring clinically due to ischemia or scar.

METHODS AND RESULTS

We compared the statistical characteristics of EGMs recorded by ICDs during spontaneous episodes with those induced during device testing in the laboratory in nine subjects. Regularity of the VF EGM signals was quantified using autocorrelation, Shannon entropy (derived from cycle to cycle activation complexes), and Kolmogorov entropy (derived from eight second long episodes of VF). All three measurements showed a statistically greater degree of regularity for induced VF than in spontaneous episodes.

CONCLUSION

Analysis of VF EGMs using these techniques is novel and robust, providing a new way for assessing electrical organization during VF. The clinical significance and utility of differences in VF waveform regularity is unclear at this stage.

The impact of catecholamines in patients with or without beta-blockers on the ventricular fibrillation cycle length and ventricular fibrillation cycle length variability

OBJECTIVES

To evaluate the impact of epinephrine, norepinephrine, or placebo on the ventricular fibrillation cycle length (VFCL) and the variability of VFCL (cvVFCL) measurements in implantable cardioverter defibrillator (ICD) patients with or without beta-blockers.

METHODS

Forty-three patients scheduled for their 6-week post-ICD placement noninvasive electrophysiologic study were included in the study at the Arrhythmia Procedure Laboratory at Hartford Hospital, Hartford, CT. This randomized, double-blind, placebo-controlled evaluation was approved by the Hartford Hospital Institutional Review Board.

RESULTS

After 2 seconds of continuous VF, 7 consecutive VFCLs were measured from the ICD device recording printout using a 0.5 mm scale ruler under magnification at baseline and after the infusion of catecholamines (epinephrine or norepinephrine at 2 mcg/min) or matching placebo at steady state. The average VFCL and the cvVFCL were determined for each study phase. Subgroup analysis based on chronic beta-blocker use was performed. No between-group differences were noted for epinephrine, norepinephrine, or placebo group for baseline (P=0.538) or postinfusion VFCL (P=0.749) or for baseline (P=0.561) or postinfusion cvVFCL (P=0.623) Regardless of catecholamine group randomization, longer pre- and postinfusion VFCL were noted in those receiving beta-blockers (P=0.157, P=0.019) but no differences in cvVFCL were noted (P=0.216, P=0.474) versus those without beta-blockers, respectively.

CONCLUSION

Moderately dosed epinephrine or norepinephrine does not affect either VFCL or the variability of VFCL after short duration of ventricular fibrillation. Chronic cardioselective beta-blockade prolongs VFCL without any impact on coefficient of variation of VFCL.