Combining shock reduction strategies to enhance ICD therapy: a role for computer modeling.

OBJECTIVES: To develop a computer model to test shock reduction strategies such as antitachycardia pacing and shock withholding for supraventricular rhythms, oversensing, and nonsustained ventricular tachycardia. BACKGROUND: While the implantable cardioverter defibrillator (ICD) can reduce mortality, inappropriate ICD shocks remain a limitation. Randomized trials provide evidence of efficacy, but they are not always practical. Computer models provide an alternative approach, and are particularly useful when evaluating multiple interventions. METHODS: A computer model was developed using clinical data and validated in a large ICD data set (EMPIRIC). After validation, the model was applied to 736 adjudicated clinical episodes from the ICD arm of Sudden Cardiac Death Heart Failure Trial (SCD-HeFT). RESULTS: The shock reduction strategies hypothetically reduced the number of VT/VF shocked episodes in SCD-HeFT by an estimated 59% (from 952 observed to 395 modeled shocks, probability of >0.999) at detection duration settings (18 of 24 intervals). The percentage of patients experiencing inappropriate shocks over 5 years was decreased by 15% (23.5-8.4%), and the number of shocks for non-VT/VF episodes was decreased from 423 to 77 (82% reduction). The percentage of patients receiving shocks for VT/VF was reduced from 30.7% (SCD-HeFT) to 26.1% with the addition of ATP. Extended detection (24 of 32 or 30 of 40 intervals) showed modest additional improvement compared to 18 of 24 intervals. CONCLUSION: Computer modeling is able to predict the results of a known clinical trial and demonstrate that shock reduction strategies have the potential to significantly reduce inappropriate and unnecessary ICD shocks versus the mandated programming used in SCD-HeFT.

The effects of stochastic monopolar galvanic vestibular stimulation on human postural sway.

Galvanic vestibular stimulation (GVS) is a technique in which small currents are delivered transcutaneously to the afferent nerve endings of the vestibular system through electrodes placed over the mastoid bones. The applied current alters the firing rates of the peripheral vestibular afferents, causing a shift in a standing subject's vestibular perception and a corresponding postural sway. Previously, we showed that in subjects who are facing forward, stochastic bipolar binaural GVS leads to coherent stochastic mediolateral postural sway. The goal of this pilot study was to extend that work and to test the hypothesis that in subjects who are facing forward, stochastic monopolar binaural GVS leads to coherent stochastic anteroposterior postural sway. Stochastic monopolar binaural GVS was applied to ten healthy young subjects. Twenty-four trials, each containing a different galvanic input stimulus from among eight different frequency ranges, were conducted on each subject. Postural sway was evaluated through analysis of the center-of-pressure (COP) displacements under each subject's feet. Spectral analysis was performed on the galvanic stimuli and the COP displacement time series to calculate the coherence spectra. Significant coherence was found between the galvanic input signal and the anteroposterior COP displacement in some of the trials (i.e., at least one) in nine of the ten subjects. In general, the coherence values were highest for the mid-range frequencies that were tested, and lowest for the low- and high-range frequencies. However, the coherence values we obtained were lower than those we previously reported for stochastic bipolar binaural GVS and mediolateral sway. These differences may be due to fundamental characteristics of the vestibular system such as lower sensitivity to symmetric changes in afferent firing dynamics, and/or differences between the biomechanics of anteroposterior and mediolateral sway.